Accelerated hydrolytic and ultraviolet aging studies on SI-18NB and SI-20NB silicone lenses. This report describes the results of in vitro accelerated hydrolytic and ultraviolet aging studies performed on SI-18NB and SI-20NB silicone intraocular lenses. The hydrolytic aging study simulated the effects of 20 years in vivo. The ultraviolet aging study simulated the effects of 17 years in vivo. No significant changes in the focal length and resolution of the lenses were observed. Examination of the lens surfaces using scanning electron microscopy revealed no changes in surface morphology.


Radial keratotomy in a patient with keratoconus. A 30-year-old white male with keratoconus had uneventful radial keratotomy in his right eye. Although a good initial response was obtained with total correction of myopia and astigmatism, by 18 months postoperatively the entire result had regressed and the patient demonstrated reformation of the cone and regression to high myopia. Scarring occurred in the three inferior cuts overlying the cone. Cuts on the horizontal axis, and superiorly (above the cone), had a normal appearance with normal wound healing. Because of the nature of the wound healing overlying the portion of the cornea affected by the keratoconus and because of the total regression of effect, radial keratotomy in patients with keratoconus does not appear to be an effective modality.


The binding properties of the solubilized sulfonylurea receptor from a pancreatic B-cell line are modulated by the Mg(++)-complex of ATP. Previous studies demonstrated that the Mg complex of ATP decreases glyburide- and increases diazoxide-binding to membranes from pancreatic islets. To examine further the mechanism of these effects, the sulfonylurea receptors in microsomes of the hamster B-cell line HIT-T15 were solubilized with detergents. Maximum recovery of receptors (40%) was obtained with Triton X-100. Specific binding of [3H]glyburide to the solubilized receptors (Kd = 0.35 nM, maximum number of binding sites = 170 fmol/mg of protein) corresponded well to specific binding to microsomes. In Triton X-100 extracts, MgATP (300 microM) reduced the number of high-affinity sites for [3H]glyburide by 50% and increased the dissociation constant for [3H]glyburide by 4-fold; MgATP was half-maximally effective at 20 microM. Development of MgATP-induced inhibition of [3H]glyburide binding to solubilized binding sites was not slower than dissociation of [3H]glyburide binding. Alkaline phosphatase accelerated the reversal of MgATP-induced inhibition of [3H]glyburide binding. In the presence of Mg++, not only ATP but also ADP, GTP and GDP inhibited [3H]glyburide binding to the solubilized receptor. However, MgADP did not inhibit [3H]glyburide binding when the MgATP concentration was kept low by the hexokinase reaction. MgATP significantly enhanced diazoxide-induced displacement of [3H]glyburide from the solubilized receptor. The MgATP-induced inhibition of binding was weakened by millimolar concentrations of free ATP. It is concluded that the binding sites for MgATP, glyburide and diazoxide are located at a single protein or at closely associated proteins which may include a protein kinase.


Time-dependent effects of dexamethasone administration on the suppression of plasma hydrocortisone, assessed with a pharmacokinetic model. The influence of the time of dexamethasone (DEX) administration (0.5 mg i.v.) on the suppression of plasma hydrocortisone (HC) was investigated in six healthy subjects, by comparing dosage times of 8 and 20 hr. To estimate HC production after DEX administration a pharmacokinetic model was developed and applied to the time course of plasma HC. This model was based on the assumption that HC production could be described as a continuous i.v. infusion, that stops and starts instantaneously. After DEX at 8 hr, HC production was reduced instantaneously to a minimum level and HC disappeared rapidly from plasma with an elimination half-life of 1.32 +/- 0.28 hr (mean +/- S.D.). Almost complete suppression of HC production lasted for 20 hr. The nocturnal increase in HC production at 20 hr after DEX administration was still attenuated compared to the preceding night. After DEX administration at 20 hr, plasma HC was lower than control for about 20 hr, but it was not reduced to the very low level observed after DEX dosage in the morning. Approximately 20 hr after dosage of DEX at 20 hr, HC production seemed to follow the normal diurnal variation of the control values again. To explain the difference in HC suppression by DEX at different dosage times, we constructed a curve describing the relationship between DEX concentration and suppression of the sudden increase in HC production during the night. This curve indicates that HC suppression by DEX could be completely dependent on DEX concentration, without a DEX independent circadian variation.


Kinetic-dynamic modeling of lymphocytopenia induced by the combined action of dexamethasone and hydrocortisone in humans, after inhalation and intravenous administration of dexamethasone. Ten healthy male volunteers received 5 mg of dexamethasone sodium phosphate (DEX) i.v. and, on an other occasion, by way of nebulization. Plasma DEX and hydrocortisone (HC) concentrations as well as blood lymphocyte count (BLC) were monitored over 12 hr and at 24 to 28 hr after DEX administration. Bioavailability of DEX after inhalation was about 27% of DEX i.v. DEX-induced depletion of plasma HC could be predicted with a pharmacokinetic model. The reonset rate of HC-production was dependent of DEX dose. BLCs declined after DEX administration, reaching a minimum between 4- and 8-hr postdosing. The DEX- and HC-induced depression of BLC could be described by an integrated pharmacokinetic-pharmacodynamic competitive-interaction model that assumes that both agonists act on the same receptor. With this model the potency and efficacy of DEX and HC with respect to lymphocytopenia could be estimated simultaneously. The potency of DEX was 10 times greater than the potency of HC. The estimated efficacy suggests that HC is only a partial agonist; the maximal lymphocytopenic effect (Emax) of HC was estimated at 80% (27-99%) of the efficacy of DEX. Our results indicate that DEX should be preferred instead of HC in conditions in which the lymphocytopenic effect is the primary systemic corticosteroid treatment goal.


Effects of perindopril on myocardial inotropy, lusitropy and economy, and on diaphragmatic contractility in the cardiomyopathic Syrian hamster. Over a 5-month period, 22 1-month-old cardiomyopathic Syrian hamsters were randomly treated with either angiotensin-converting enzyme inhibitor (perindopril 1 mg/kg/day) (PE, n = 11) or placebo (PL, n = 11), and 7 age-matched controls (C) were given placebo. Compared to C, mechanics of left ventricular papillary muscles from PL exhibited a lower maximum unloaded shortening velocity (Vmax) (P less than .01) and normalized peak active force (P less than .05), and a significantly less curved shape of the force-velocity (F-V) relationship (P less than .01). The curvature of the F-V relationship has been proposed as a reflection of the efficiency of muscle contraction. Compared to PL, PE had a 68% inhibition of plasma ACE activity and a greater Vmax (P less than .05), whereas active force (AF) was similar. This resulted in a lesser decrease of the curvature of the F-V relationship compared to that of C (P less than .05). Muscle strips from the ventral costal diaphragm were dissected from the muscle in situ. In both twitch and tetanus modes, intrinsic mechanical performance of diaphragm muscle was markedly decreased in PL compared to C as regards normalized positive (+dF/dtmax/mm2) and negative (-dF/dtmax/mm2) peak rate of force, and normalized peak active force (AF/mm2) (P less than .01 each). In both twitch and tetanus modes, PE had an increased +dF/dtmax/mm2 (P less than .05), -dF/dtmax/mm2 and AF/mm2 (P less than .01 each), compared to PL. These results indicate 1) that the low inotropic state observed in cardiomyopathic Syrian hamsters was associated with decreased myothermal economy of cardiac contraction and with a major impairment of diaphragm intrinsic contractility, and 2) that early therapy with angiotensin-converting enzyme inhibitor helped to preserve myocardial contractility and economy, and diaphragm contractility.


Adenosine 5'-(2-fluorodiphosphate) is not a selective P2Y purinoceptor agonist in the rabbit jugular vein. The relaxant properties of the putative selective P2Y agonist adenosine 5'-(2-fluorodiphosphate) (ADP-beta-F) and its structural analog adenosine 5'-(2-thiodiphosphate) have been investigated in the rabbit precontracted jugular vein preparation. In tissues with intact endothelium, ADP-beta-F produced a multiphasic agonist concentration/effect curve made up of two vasorelaxant components which were kinetically and pharmacologically distinct. The higher potency phase (p[A50] 5.58 +/- 0.13), characterized by slow, tonic responses, was retained after endothelial denudation and blocked by the selective P1 purinoceptor antagonist 8-sulphophenyltheophylline. The lower potency phase (p[A50] 3.98 +/- 0.07), characterized by fast, phasic responses, was abolished by endothelial denudation and is presumed to be mediated at P2Y purinoceptors. By contrast, the agonist concentration/effect curve to adenosine 5'-(2-dithiophosphate) in endothelium-intact tissues appear monophasic and was unaffected by 8-sulphophenyltheophylline (p[A50] 6.86 +/- 0.12), although endothelial denudation revealed a secondary P1-induced relaxant component (p[A50] 5.73 +/- 0.20). This study demonstrates that in the rabbit jugular vein, relaxant responses to ADP-beta-F are mediated primarily by activation of P1 purinoceptors, and it is, therefore, invalid to regard ADP-beta-F as a selective probe for P2Y purinoceptors, whereas adenosine 5'-(2-thiodiphosphate) does show some selectivity for this receptor.


The antihypertensive effect of the angiotensin II receptor antagonist DuP 753 may not be due solely to angiotensin II receptor antagonism. The angiotensin II (AII) receptor antagonist, DuP 753 (10 mg/kg intraduodenal), produced a sustained and long-lasting antihypertensive effect in conscious renin-dependent hypertensive rats. Blood pressures were still reduced markedly 24 to 72 hr after administration of a single dose of DuP 753. However, pressor responses elicited by either angiotensin I or AII were not blocked at these times despite the continued antihypertensive effect of DuP 753. In a model of orthostatic hypotension, DuP 753 and the selective alpha-1 adrenoceptor antagonist prazosin produced a marked orthostatic hypotension response in renin-dependent hypertensive rats as demonstrated by potentiation of the decrease in blood pressure induced by a 90 degrees tilt. The nonpeptide AII receptor antagonist SK&F 108566 (10 mg/kg intraduodenal) did not produce orthostatic hypotension and the angiotensin converting enzyme inhibitor enalapril produced only a slight orthostatic response to tilting. In conscious spontaneously hypertensive rats (SHR), allowed 3 to 4 days to recover from surgery, administration of either enalapril (1 mg/kg i.v.) or SK&F 108566 (10 mg/kg i.v.) did not significantly effect blood pressure. In SHR tested within 24 hr of surgery, enalapril was effective in lowering blood pressure. In contrast, in surgically recovered SHR, DuP 753 (10 mg/kg i.v.) produced an antihypertensive effect that was slow in onset, sustained and extremely long in duration. Blood pressures did not return to predrug levels until 48 hr after administration of DuP 753. Stimulation of the thoracolumbar sympathetic outflow in pithed rats produced frequency-dependent pressor responses that were significantly potentiated by continuous infusion of a subpressor dose of AII.(ABSTRACT TRUNCATED AT 250 WORDS)


Cardiovascular effects of cocaine in conscious rats: relative significance of central sympathetic stimulation and peripheral neuronal monoamine uptake and release mechanisms. Cocaine (0.03-3 mg/kg, i.v.) produced a dose-dependent increase in mean arterial blood pressure and heart rate in conscious Sprague-Dawley rats. Pretreatment with the competitive ganglionic blockers pentolinium or hexamethonium attenuated cocaine's pressor effect, whereas noncompetitive (chlorisondamine) or mixed (mecamylamine) type blockers not only abolished, but also reversed it to a depressor effect. Cocaine's tachycardiac effect was attenuated by all four ganglionic blockers. The relative effectiveness of the four ganglionic blockers in antagonizing cocaine-induced cardiovascular effects was similar to that of antagonism of phenylephrine-induced, centrally mediated reflex bradycardia. All four ganglionic blockers at all the doses tested produced similar reductions in base-line BP, thereby suggesting that these agents produced similar degrees of maximal reduction of basal sympathetic tone. The pressor responses to norepinephrine (0.2 micrograms/kg) were potentiated, whereas those to tyramine (0.3 mg/kg) were inhibited by cocaine (0.3-3 mg/kg); the former effect was not dose dependent (bell-shaped dose-response curve), whereas the latter effect was dose-dependent. The amine uptake inhibitory potency (ED50, 0.85 mg/kg) of cocaine is about 10 times less than its potency to produce pressor (ED50, 0.075 mg/kg) and tachycardiac (ED50, 0.083 mg/kg) effects. Chlorisondamine did not antagonize the pressor effects of the indirect sympathomimetic agent, tyramine. These results suggest that the blockade of cocaine's pressor and tachycardiac effects by ganglionic blockers is not related to their ability to eliminate basal sympathetic tone and, thereby, indirectly blunt cocaine's inhibitory effect on sympathetic neuronal uptake of norepinephrine. Rather, the results indicate that these effects are mainly due to their antagonistic actions on cocaine-induced central stimulation of sympathetic activity.(ABSTRACT TRUNCATED AT 250 WORDS)


Pharmacokinetics and pharmacodynamics of labetalol in the pregnant sheep. The maternal-fetal disposition of labetalol, a combined alpha-1 and beta adrenergic blocker, and its pharmacodynamics in pregnancy are not well understood. This study describes the pharmacokinetics, cardiovascular and metabolic effects of labetalol in the mother and in utero fetus after a 100-mg maternal i.v. bolus administration, in the chronically instrumented pregnant sheep. Labetalol shows a triexponential decline in the mother with a total body clearance of 30.8 +/- 3.83 ml/min/kg, an apparent steady-state volume of distribution (nonparametric) of 3.02 +/- 0.18 liters/kg and terminal elimination half-life of 2.79 +/- 0.66 hr. These estimates are similar to the reported values in pregnant women. Labetalol rapidly crosses the sheep placenta. The peak fetal plasma concentration was 33.7 +/- 5.8 ng/ml, the fetal exposure to labetalol as calculated by the fetal to maternal area under the curve ratio was 14.37 +/- 1.54% and the apparent fetal elimination half-life was 3.71 +/- 0.5 hr. Labetalol persists in the amniotic and fetal tracheal fluids up to 24 hr with concentrations reaching 2- to 4 times the fetal plasma concentration. Whereas there were no significant maternal or fetal cardiovascular effects, some very significant metabolic effects were observed, including fetal and maternal lactic acidosis and hyperglycemia. Lactic acid accumulates in the fetal blood and amniotic fluid with peak concentrations (6.0 +/- 0.31 and 5.5 +/- 0.26 mM, respectively) showing a more than 300% increase over control values. The exact mechanism by which labetalol causes these metabolic effects is not clear, but it may involve its partial beta-2 agonist activity.


Behavioral evidence for differential adaptation of the serotonergic system after acute and chronic treatment with (+/- )-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) or ketanserin. The 5-hydroxytryptamine (5-HT)2 agonist (+/- )-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and antagonist ketanserin were evaluated for acute and chronic effects on the 5-HT2 receptor-mediated head-twitch response (HTR) in mice. A single dose of DOI resulted in tolerance to the DOI-induced HTR at 24 hr but supersensitivity at 48 hr. This apparent supersensitivity persisted up to 144 hr after the first DOI injection. Chronic once daily DOI administration significantly reduced the HTR frequency (days 2-6), which then returned slowly to control levels by treatment day 13. A 48-hr withdrawal from this chronic regimen produced a similar supersensitivity to that observed after a single DOI injection upon a 48-hr challenge. This effect also persisted up to 144 hr after cessation of chronic treatment. Acute pretreatment with a single injection of ketanserin significantly reduced the DOI-induced HTR frequency when tested 24 and 48 hr, but not 120 hr, after injection of the antagonist. After withdrawal from chronic ketanserin treatment, the DOI-induced HTR was significantly reduced at 24 hr but significantly increased at 48 hr. This enhanced effect subsided when mice were tested with DOI 72 hr after cessation of chronic antagonist treatment. These data suggest that the serotonergic system adapts to chronic exposure of either agonists or antagonists in a fashion distinctly different from that exhibited by other monoamine neurotransmitter systems.


Subjective and behavioral effects of diphenhydramine, lorazepam and methocarbamol: evaluation of abuse liability. The effects of orally administered placebo, diphenhydramine, lorazepam, methocarbamol and placebo were studied in volunteers with histories of recreational substance abuse including sedative/hypnotics. Placebo, diphenhydramine (100, 200 and 400 mg), lorazepam (1 and 4 mg) and methocarbamol (2.25 and 9 g) were tested in a randomized, double-blind crossover study using 14 subjects. Psychomotor and cognitive performance and subject- and observer-rated responses were measured daily before and for 5.5 hr after drug administration. The results showed that each of the drugs exhibited a different profile of effects on the test battery. Lorazepam produced significant increases in subjects' ratings of drug effect and liking, increases in measures of sedation and impairment of psychomotor performance. Methocarbamol also produced significant increases in subjects' ratings of drug effect and liking and measures of sedation, but it produced only minor impairment of psychomotor and cognitive performance. Diphenhydramine increased subjects' and observers' ratings of drug effect and measures of sedation, but it produced less psychomotor performance impairment and liking than lorazepam. Diphenhydramine produced the most side effects. The present study clearly differentiated the behavioral and subjective profiles of diphenhydramine, lorazepam and methocarbamol. Consistent with its recognized low abuse liability, diphenhydramine produced fewer increases in measures of positive mood and more adverse effects. The considerable overlap in subjective effect measures of positive mood make further differentiation with respect to abuse liability difficult.


Influence of epithelium on the reactivity of guinea pig isolated, perfused trachea to bronchoactive drugs. The mechanisms by which the epithelium affects reactivity of guinea pig trachealis to agonists were examined using the isolated, perfused trachea preparation. Contractile agonists (acetylcholine, methacholine, carbachol or histamine) were more potent when applied to the serosal (extraluminal, EL) surface compared to the mucosal (intraluminal, IL) surface, and the IL maximum responses to these agents were smaller. In epithelium-denuded tracheae, IL reactivity to the agonists was increased to the EL level. Physostigmine (10(-7) M) increased the EL and IL potency of acetylcholine to that of carbachol (+/- epithelium), and elevated the IL acetylcholine maximum response (+ epithelium); the relative role of epithelial acetylcholinesterase could not be defined. Indomethacin (3 x 10(-6) M) increased, in an epithelium-dependent manner, the IL acetylcholine, carbachol and histamine maximum responses to the EL level. Phentolamine plus propranolol (both 10(-6) M) potentiated the IL maximum response to methacholine, Isoproterenol also was more potent extraluminally than intraluminally, and the EL and IL maximum responses were similar. IL isoproterenol reactivity was elevated to the EL level in rubbed tracheae. Corticosterone (5 x 10(-5) M) potentiated EL and IL responses to isoproterenol (+/- epithelium); the relative role of epithelial extraneuronal uptake could not be delineated. The epithelium reduces reactivity to mucosally applied drugs by acting as a diffusion barrier. In addition, responses to mucosally administered contractile agonists are inhibited by a physiological antagonism caused by modulatory prostanoids, catecholamines and, possibly, epithelium-derived relaxing factor.


Tolerance, cross-tolerance and withdrawal in rats made dependent on diazepam. Rats were trained to discriminate pentylenetetrazole (PTZ; 20 mg/kg) from midazolam (MDZ; 1 mg/kg) and from saline using a three-lever food-reinforced choice task. Using a cumulative dosing procedure, PTZ substituted for PTZ, and MDZ, chlordiazepoxide and diazepam (DZP) substituted for MDZ, in a dose-dependent manner. The animals were then treated with chronic DZP (20 mg/kg/8 hr for 7 days); 24 hr after the last dose of this regimen, the dose-effect curve of DZP was redetermined. The ED50 for the discrimination of DZP increased 4.8-fold after chronic DZP. In a second group of subjects trained on this discrimination and treated with DZP (20 mg/kg/8 hr for 7 days), the ED50 for the discrimination of MDZ was increased 2.2-fold. After 14 days of recovery, the MDZ dose-effect curve shifted back to the left and was not significantly different from the ED50 value obtained before chronic DZP treatment. When the benzodiazepine antagonist flumazenil was tested in a cumulative manner (1.0-32.0 mg/kg), the animals selected the saline lever. Analogous to the previous chronic dosing regimen, DZP (20 mg/kg/8 hr/7 days) was then administered, and a combination of three tests were then given at 1, 2, 4, 7, 10 and 14 days after the last DZP treatment. On each of these days, a saline test was given first; it was followed by a DZP (2.5 mg/kg) test; which was then followed by a flumazenil (32.0 mg/kg) test. On the 1st day of testing, tolerance was seen to DZP and precipitated withdrawal (PTZ lever selection) was seen with flumazenil.(ABSTRACT TRUNCATED AT 250 WORDS)


Biochemical and pharmacological properties of SR 46349B, a new potent and selective 5-hydroxytryptamine2 receptor antagonist. A new potent, selective and p.o. active serotonergic [5-hydroxytryptamine (5-HT2)] receptor antagonist, SR 46349B [trans, 4-([3Z)3-(2-dimethylaminoethyl)oxyimino-3(2-flurophenyl++ +)propen-1-yl]phenol hemifumarate) has been characterized by a series of "in vitro" and "in vivo" methods. Based upon binding studies with 5-HT2 receptors in rat brain cortical membranes and blockade of 5-HT-induced contractions in isolated tissues (rabbit thoracic aorta, rat jugular vein, rat caudal artery, rat uterus and guinea pig trachea), SR 46349B showed high affinity for 5-HT2 receptors. Furthermore, SR 46349B displayed moderate affinity for the 5-HT1C receptor and had no affinity for the other 5-HT1 subclass (5-HT1A, 5-HT1B or 5-HT1D), dopamine (D1 or D2), "alpha" adrenergic (alpha-1 or alpha-2), sodium and calcium channel and histamine (H1) receptors. It did not interact with histamine (H1), alpha-1 adrenergic and 5-HT3 receptors in smooth muscle preparations. No inhibition of the uptake of norepinephrine, dopamine or 5-HT was seen. Based upon blockade of pressor responses to 5-HT in pithed rats and in vivo binding studies in mice, SR 46349B was found to be a potent and p.o. active 5-HT2 receptor antagonist with a relatively long duration of action. Behavioral experiments, including mescaline- and 5-hydroxytryptophan-induced head twitches and learned helplessness, as well as sleep-waking cycle and EEG spectral parameter studies, indicated that SR 46349B has a classical 5-HT2 psychopharmacological antagonist profile.


Effect of amineptine on regional extracellular concentrations of dopamine and noradrenaline in the rat brain. The effect of amineptine (1.25-20 mg/kg i.p.), an antidepressant inhibiting dopamine uptake, on extracellular concentrations of dopamine was studied in the rat striatum and nucleus accumbens by using the microdialysis technique and two Ca++ concentrations (1.26 and 3.4 mM) in the perfusion medium. In one experiment the effect of amineptine was studied on extracellular concentrations of dopamine and noradrenaline in the frontal cortex perfused with a medium containing 1.26 mM Ca++. Basal extracellular concentrations of dopamine in the striatum and nucleus accumbens were significantly higher at 3.4 mM Ca++. At 5 to 20 mg/kg, amineptine dose-dependently increased extracellular dopamine in the striatum and nucleus accumbens. No differences were found in the effect of amineptine in the two brain regions at the two calcium concentrations. When extracellular dopamine was expressed as a percentage of basal values, amineptine (20 mg/kg) caused greater increases in rats perfused with 1.26 mM Ca++ than in rats perfused with 3.4 mM Ca++ in both brain regions. A similar effect was found when 10 microM amineptine was infused through the dialysis fiber. The effect of 10 mg/kg i.p. of amineptine on dopamine output in the two brain regions was prevented by infusing 1 microM tetrodotoxin in the dialysis fiber. In the frontal cortex, 10 and 20 mg/kg of amineptine significantly raised dopamine and noradrenaline concentrations, whereas 5 mg/kg only increased noradrenaline output significantly. At 10 mg/kg i.p., amineptine also increased extracellular noradrenaline in the dorsal hippocampus. Amineptine had no consistent effects on the concentrations of dihydroxyphenylacetic acid and homovanillic acid in the various brain regions.(ABSTRACT TRUNCATED AT 250 WORDS)


Voltage- and time-dependent block of the delayed K+ current in cardiac myocytes by dofetilide. The delayed K+ current (ik) and its change by dofetilide was studied in single myocytes from the guinea pig and rabbit heart using the two-electrode voltage clamp technique. In rabbit myocytes, ik consisted of only one component (Kr), which developed for moderate depolarizations and with a fast time course. In guinea pig myocytes, activation consisted of a rapid and a slow component, and the latter (Ks) only became manifest for depolarizations positive to 0 mV. Ks was resistant to block by dofetilide. Kr, however, was very sensitive: Kd 3.9 x 10(-9) M, Hill coefficient 2.0 (n = 5). The effect was voltage-dependent block increasing at depolarized levels. Block development was time dependent and occurred in two phases: a first fast and voltage-dependent phase was followed by a second much slower phase (time constant of 4.4 +/- 0.48 sec (n = 11). Recovery from block was slower as the membrane potential became more negative. This resulted in the absence of a steady-state frequency-dependent effect at negative membrane potentials. It is concluded that dofetilide is an efficient blocker of the fast component of ik. The block, as well as recovery, are voltage and time dependent. Block is greater at more depolarized levels, recovery is slower at more hyperpolarized levels.


Accumulation of boron-10 (10B) in cell cultures exposed to mercaptododecaborate (Na2H(11)10B12SH) used for the neutron capture therapy of brain tumors. Toxicity of mercaptoundecahydro-closo-dodecaborate (MHB, Na2H(11)10B12SH) and accumulation of MHB-derived 10B were studied in E7 neuroblastoma, C6 glioma, HeLa cells and embryonic lung LEP 19 fibroblasts in culture in exponential and stationary phases of growth (2- and 7-day-old cultures, respectively). The pilot study of acute toxicity, performed on C6 glioma cells, showed good tolerance of the drug up to 1000 micrograms/ml (4.8 x 10(-3) M), when cell growth slowed and a small part of the population was lethally damaged (8.3%, 20-h incubation interval). The changes became more extensive and appeared sooner (toward 5 h) at 2000 micrograms MHB/ml (9.5 x 10(-3) M). None of the four cell lines used was found to be affected in gross morphology or growth by 200 micrograms MHB/ml within a 5-day culture interval. When exposed to this dose for 4 h, the amount of 10B accumulated in cell lines at the exponential growth phase ranged from 0.51 to 4.4 ng/micrograms protein; in the stationary cultures of the corresponding cell phenotype, the 10B values were 3 to 10 times lower (0.12-1.2 ng/micrograms protein). Irrespective of the growth phase, the values achieved in C6 glioma cells were several times higher than in the other cell lines. Furthermore, in the glioma cells, particularly in the exponential phase of growth, accumulation of 10B proceeded against the marked concentration gradient. The data provide a new indication for the use of MHB for boron neutron capture therapy of brain tumors.


Recovery of endothelium-dependent responses by reseeding endothelial cells in culture onto the denuded coronary artery. Endothelium-denuded coronary artery was reseeded with the endothelial cells in culture, and the endothelium-dependent responses were compared with those in arteries with or without native endothelium. A23187 produced a relaxation in the arterial preparations reseeded with cultured endothelial cells in the cell suspension of 10(5) cells/ml for 17 to 19 hr, whereas no relaxation was observed in the denuded artery. Relaxing response to Ca++ ionophore A23187 was dependent on the number of endothelial cells reseeded. The A23187-induced relaxation in the cell-reseeded artery was inhibited markedly by pretreatment with 3 x 10(-4) M NG-monomethyl-L-arginine or 5 x 10(-5) M methylene blue, but not 10(-4) M aspirin. NG-monomethyl-L-arginine (3 x 10(-4) M) and methylene blue (5 x 10(-5) M) produced a contraction in the cell-reseeded artery. Contraction evoked by bradykinin in the denuded arteries was attenuated by reseeding endothelial cells. KCl-induced contraction in the endothelium-reseeded artery did not differ from that in the denuded artery. Contractile responses to norepinephrine and serotonin were attenuated by reseeding endothelial cells onto the denuded artery to a small extent. Scanning electron microscopy showed that the luminal surface of endothelium-reseeded arteries was partly covered with endothelial cells. We conclude that when the cultured endothelial cells are reseeded onto a denuded coronary artery, endothelium-derived relaxing factor release occurs, but endothelium-dependent mechanisms are not the same as those for native cells.


Effect of leukotriene D4 on gastric emptying and secretion in rhesus monkeys. Gastric function was evaluated in conscious rhesus monkeys after an i.v. infusion of saline (0.11 ml/min) or leukotriene D4 (LTD4) (0.1 or 0.2 microgram/kg/min), a s.c. injection of nordihydroguaiaretic acid (4,4'-(2,3-dimethyl-1,4-butanediyl)-bis[1,2-benzenediol]) (NDGA), a nonspecific lipoxygenase inhibitor, or an intragastric bolus of (1,1,1-trifluoro-N-[3-(2-quinolinylmethoxy)phenyl] methane sulfonamide) (Wy-48,252), a LTD4 receptor antagonist. Using a technesium diethylenetriamine-pentaacetic acid dilution technique, gastric emptying and secretion were determined in response to an 80-ml load of water. At the end of some studies, the animals were gastroscoped to obtain biopsies for histological evaluation. There were no differences in the microscopic appearance of the mucosa among the various groups. A continuous infusion of LTD4 significantly inhibited hydrogen and sodium ion secretion at doses that had no effect on systemic blood pressure or heart rate. In contrast, NDGA and Wy-48,252 had no effect on unstimulated (basal) fluid or ion secretion. Gastric emptying after the water load was unaltered by LTD4, but high doses of NDGA or Wy-48,252 decreased gastric emptying during the first 10 min. Thus, LTD4 does not appear to play a major role in gastric emptying or secretion in response to a water load, but may contribute to the changes in gastric function in response to potential gastric irritants.


Fuscoside: an anti-inflammatory marine natural product which selectively inhibits 5-lipoxygenase. Part I: Physiological and biochemical studies in murine inflammatory models. The biological and biochemical pharmacology of fuscoside, a novel anti-inflammatory marine natural product isolated from the Caribbean gorgonian Eunicea fusca, has recently been characterized using murine (part I) and human (part II) models of inflammation. Topically applied fuscoside (FSD) effectively inhibits phorbol myristate acetate (PMA)-induced edema in mouse ears at levels comparable with indomethacin over a 3.3-hr exposure period, and is significantly more efficacious than indomethacin over 24 hr in the PMA model. Histological preparations and quantification of the neutrophil-specific marker, myeloperoxidase, demonstrate that FSD inhibits neutrophil infiltration into PMA-induced regions of edema and inflammation. In systemic studies, where FSD is injected i.p. before the topical application of PMA, negligible effects on ear inflammation are observed. FSD does not inhibit bee venom or human synovial fluid phospholipase A2 up to concentrations of 500 microM. In calcium ionophore-activated cultures of mouse peritoneal macrophages, FSD selectively and irreversibly inhibits leukotriene C4 biosynthesis (IC50 = 8 microM), yet has negligible effects on prostaglandin E2 production. FSD is also without effect on the conversion of arachidonic acid to prostaglandin E2 by ram seminal vesicle cyclooxygenase. Chromatographic and spectroscopic studies suggest that FSD is not metabolized, and that drug uptake/binding by macrophages is time dependent, saturable and independent of active transport mechanisms. These studies represent the first report of an anti-inflammatory marine natural product that selectively inhibits leukotriene biosynthesis.


Sensory characteristics of monkey thalamic and motor cortex neurones. 1. Extracellular single-cell recordings were made from the cerebellar thalamus, the ventro-posterior lateralis par caudalis (VPLc) and motor cortex of three conscious monkeys. Recordings were made from the thalamus as well as the cortex in two monkeys. In all, recordings were made from the thalamus in four hemispheres and from the motor cortex in four hemispheres. The animals were trained to permit a detailed examination when relaxed. Unexpected perturbations were applied to the wrist. Seventy-seven wrist-related neurones were recorded in the cerebellar thalamus, forty-two neurones from the VPLc and eighty-four neurones in motor cortex. 2. Cerebellar nuclear stimulation was used to physiologically identify thalamic neurones receiving input from the cerebellum. The location of all neurones was verified histologically. 3. The majority of cerebellar thalamic neurones had deep sensory receptive fields related to a single muscle, a group of synergists or a single joint. There was a distinct topographical organization. These fields were similar to sensory fields in motor cortical neurones, but had higher thresholds. 4. VPLc neurones had discrete deep or cutaneous sensory fields, or a combination of these fields, which suggests convergence. VPLc neurones had fields with lower thresholds than cerebellar thalamic neurones. The somatotopically located forelimb area in the VPLc was posterior to and continuous with the forelimb area in the cerebellar thalamus. 5. VPLc neurones responded with a shorter latency to wrist perturbations than did cerebellar thalamic neurones. VPLc neurones with deep sensory fields changed firing significantly earlier than those with cutaneous fields. The VPLc is likely to be the major source of sensory input to the motor cortex, and based on the results of this study we suggest that the VPLc is the thalamic nucleus best placed to transmit short-latency afferent input from the forelimb. 6. The timing of the neuronal discharge of cerebellar thalamic and VPLc cells, which resulted from perturbations of the wrist, was best linked to the duration of movement rather than its amplitude. The cells began firing as soon as the velocity changed sign and continued firing until the sign of the velocity changed again. In subsequent corrective movements neuronal discharge in the VPLc appeared to also encode movement acceleration.


Impulses and resting membrane properties of small cultured rat hippocampal neurons. 1. The impulses and resting membrane parameters of small (soma diameter less than 10 microM) cultured hippocampal neurons from rat embryos were studied with the tight-seal whole-cell recording technique. 2. Mean resting potential was -47 mV, mean input resistance 3.3 G omega, mean capacitance 11 pF, and mean time constant 33 ms. 3. Rectangular suprathreshold current steps elicited regenerative potential responses. The amplitude and time course of the responses were clearly stimulus dependent: stronger current steps caused impulses of larger amplitude. 4. The current threshold was very low: rheobase current was less than 15 pA. 5. The potential response depended on the preceding holding potential, responses from more negative potentials showing sharper peaks than those from more positive potentials. 6. Spontaneous impulses with pre-potentials similar to synaptically induced events were recorded from several cells. The amplitude of the spontaneous impulses varied similarly to that of the stimulus-induced responses.


Membrane currents in small cultured rat hippocampal neurons: a voltage-clamp study. 1. The currents underlying the graded impulses in small cultured hippocampal neurons from rat embryos were analysed under voltage-clamp conditions with the tight-seal whole-cell recording technique. 2. The leak and capacitative currents induced by a potential step were linearly related to the potential in the range studied (-60 to -100 mV). 3. With steps to potentials more positive than -40 mV, at least two different potential-activated currents were detected: an initial transient current and a delayed sustained one. In addition, 40% of the cells studied showed a delayed transient current. 4. The initial transient current showed sigmoid activation and roughly exponential inactivation. Its reversal potential depended on the Na+ concentration and was close to the Na+ equilibrium potential. Further, it was blocked by 3.0 microM-tetrodotoxin, and was abolished when choline was substituted for Na+ in the extracellular solution. We concluded that this current was carried mainly by Na+ ions. 5. The delayed sustained current showed sigmoid activation and almost no inactivation within 40 ms. The reversal potential was close to the K+ equilibrium potential. We concluded that this current was carried mainly by K+ ions. 6. The delayed transient current was outward in the potential range studied (-50 to +120 mV) and did not depend on the pipette Cl- concentration. It was assumed that this current was carried mainly by K+ ions. 7. A quantitative description of the initial transient and the delayed sustained currents was developed on the basis of earlier descriptions of excitable membranes.


Computed potential responses of small cultured rat hippocampal neurons. 1. The potential responses of small hippocampal neurons were computed on the basis of a previous mathematical description of the currents recorded under voltage-clamp conditions. 2. The computed action potentials were graded with respect to stimulus strength, in accordance with previous experimental findings. 3. The time course of the membrane currents and of the permeabilities and permeability variables during the impulse was computed for different stimulus intensities. 4. The effect of the membrane time constant on the impulse amplitude was investigated. It was concluded that the value of the time constant used was not per se sufficient to explain the amplitude variation of the impulse. 5. The effect of the magnitudes of the different potential-dependent permeabilities on the impulse amplitude was investigated. A Na+ permeability within a certain range caused impulses of variable amplitude, and this variability was affected by the K+ permeability.


Role of protein kinase C in constrictor responses of the rat basilar artery in vivo. 1. The goal of this study was to determine the effects of activation and inhibition of protein kinase C on the rat basilar artery in vivo. 2. The diameter of the basilar artery was measured through a craniotomy in rats anaesthetized with pentobarbitone sodium (50 mg kg-1, I.P., supplemented with 20 mg kg-1 h-1). Diameters were measured under control conditions and during topical application of various agonists, both alone and in the presence of antagonists. 3. Serotonin (5-HT) produced concentration-related constriction of the basilar artery (baseline diameter = 234 +/- 9 microns, mean +/- S.E.M.), which was inhibited by the 5-HT2 receptor antagonist LY53857. 4. Sphingosine (10(-6) M), a protein kinase C inhibitor which binds to the regulatory site of protein kinase C, inhibited the response to 10(-8) M-serotonin (-19 +/- 2% before vs. -3 +/- 2% during sphingosine, P less than 0.05). In contrast, constrictor responses to prostaglandin F2 alpha to (PGF2 alpha; 10(-6) M) were not inhibited by sphingosine (-16 +/- 2% before vs. -18 +/- 2% during sphingosine, P greater than 0.05). 5. H-7 (10(-9) M), another protein kinase C inhibitor, which binds to the catalytic site of protein kinase C, also inhibited constriction of the basilar artery in response to serotonin, but not prostaglandin F2 alpha. 6. Phorbol 12,13-dibutyrate (PDBu, 10(-8) M), which activates protein kinase C, produced slowly developing constriction of the basilar artery. PDBu-induced vasoconstriction (-33 +/- 2%) was attenuated by sphingosine (-11 +/- 4% during sphingosine, P less than 0.05) and H-7 (-1.5 +/- 5% during H-7, P less than 0.05). 7. In summary, activation of protein kinase C appears to mediate vasoconstrictor responses of the basilar artery to serotonin, but not PGF2 alpha.


Spontaneous release of nitric oxide inhibits electrical, Ca2+ and mechanical transients in canine gastric smooth muscle. 1. In canine antrum, rhythmic electrical activity consists of a rapid upstroke phase followed by a plateau depolarization. In response to slow waves, cytosolic Ca2+ ([Ca2+]cyt) and tension increased. 2. Addition of sodium nitroprusside (SNP, 0.5 microM) decreased the amplitude of the plateau phase of slow waves without significant effects on the upstroke depolarization. SNP also inhibited changes in [Ca2+]cyt and tension associated with the plateau potential. SNP induced a negative chronotropic effect at concentrations above 0.1 microM. 3. Similar to the effects of SNP, illumination of muscles during slow waves with ultraviolet (UV) light caused premature repolarization. UV illumination is known to release NO in some tissues. 4. L-NG-monomethyl-arginine (L-NMMA, 300 microM), Methylene Blue (MB, 5 microM) and oxyhaemoglobin (oxy-Hb, 5 microM) increased the force of contractions. In contrast, L-arginine (L-Arg, 300 microM) decreased contractile force and antagonized the effects of L-NMMA. 5. During the upstroke phase, SNP caused a small reduction in [Ca2+]cyt and a large reduction in force, suggesting that SNP caused a decrease in Ca2+ sensitivity. 6. In muscles permeabilized by alpha-toxin, cyclic GMP (100 microM) and UV illumination inhibited Ca(2+)-induced contraction (at pCa 5.5). 7. These data suggest that NO or NO-related compounds are spontaneously released in gastric muscles. These agents have two effects on excitation-contraction coupling: (i) inhibition (directly and/or indirectly) of the voltage-dependent Ca2+ channels that participate in the plateau phase of slow waves, and (ii) reduction in the Ca2+ sensitivity of the contractile element.


The role of acetylcholinesterase in denervation supersensitivity in the frog cardiac ganglion. 1. The sensitivity of normal and denervated cardiac ganglion cells to the cholinergic agonists acetylcholine and carbamylcholine (carbachol) were compared in the frog, Rana pipiens. Acetylcholine and carbachol bind to the same acetylcholine receptors, but, unlike acetylcholine, carbachol is resistant to hydrolysis by acetylcholinesterase. 2. Sensitivity was assessed by the peak depolarization elicited in response to a sustained pulse of ligand emitted from a pipette positioned 10 microns from the ganglion cell surface. This technique allows the sensitivity of the entire cell to be recorded with a single measurement. 3. The acetylcholine sensitivity of normal cardiac ganglion cells was increased by inhibiting extracellular acetylcholinesterase with echothiophate. 4. Denervation increased the sensitivity of cardiac ganglion cells to acetylcholine but not to carbachol. 5. Following the inhibition of extracellular acetylcholinesterase with echothiophate, sensitivity to acetylcholine was similar in normal and in denervated ganglion cells. 6. The increased sensitivity to acetylcholine of cardiac ganglion cells following denervation is caused by a reduction in the hydrolysis of the transmitter by acetylcholinesterase rather than by changes in the number and/or properties of acetylcholine receptors.


The activity of monkey thalamic and motor cortical neurones in a skilled, ballistic movement. 1. Three monkeys were trained to perform a reaction-time task of the wrist and single-cell recordings were made from the motor cortex (eighty-four cells), ventro-posterior lateralis par caudalis (VPLc) (forty-two cells) and cerebellar thalamus (seventy-seven cells). 2. The majority (43/77, 56%) of cerebellar thalamic neurones fired phasically during movement, whereas in the motor cortex most neurones (53/84, 64%) had a phasic-tonic discharge pattern. Most neurones in both locations discharged in relation to the direction of movement (reciprocal pattern). 3. The cerebellar thalamus is unlike the motor cortex in that it does not usually encode a signal for force or joint position in its discharge. 4. Twenty-two per cent (17/77) of cerebellar thalamic neurones had a period of reduced discharge rate before the phasic burst of activity, and represent a pattern of discharge not seen in motor cortex or VPLc neurones. 5. The onset of phasic activity in the cerebellar thalamus was significantly later (average 94 ms) than in the motor cortex but occurred just before electromyogram (EMG) activity. The phasic activity in the cerebellar thalamus usually ended before the phasic component of motor cortex discharge was completed. 6. Phasic activity in VPLc neurones commenced after the onset of EMG discharge and on average 26 ms after the commencement of movement. Most neurones with deep sensory receptive fields fired with a reciprocal pattern, while neurones with cutaneous fields usually fixed bidirectionally in relation to the task. Almost one-third of neurones signalled force and a similar number had discharge levels that encoded characteristics of the joint position. 7. The duration of discharge of VPLc neurones during the voluntary movement was marginally less than the duration of the movement velocity peak and the VPLc may therefore be signalling the duration of the velocity. Phasic activity in cerebellar thalamic neurones fired for a duration similar to the VPLc neurones, but commenced before the movement. Therefore, if the cerebellar thalamus is carrying information about the duration of the velocity, it does so before the movement starts. 8. The phasic burst of activity in cells of the cerebellar thalamus is timed so that it can contribute to the later component of the phasic burst of motor cortical discharge. Thus we speculate that in skilled, ballistic movements, the cerebellum may provide a response which travels via the cerebellar thalamus and helps to determine the magnitude and duration of the phasic part of cortical discharge.(ABSTRACT TRUNCATED AT 400 WORDS)


Evidence that action potentials activate an internodal potassium conductance in lizard myelinated axons. 1. We have studied action potentials and after-potentials evoked in the internodal region of visualized lizard intramuscular nerve fibres by stimulation of the proximal nerve trunk. Voltage recordings were obtained using microelectrodes inserted into the axon (intra-axonal) or into the layers of myelin (peri-internodal), with the goal of studying conditions required to activate internodal K+ currents. 2. Peri-internodal recordings made using K2SO4-, KCl- or NaCl-filled electrodes exhibited a negligible resting potential (less than 2 mV), but showed action potentials with peak amplitudes of up to 78 mV and a duration less than or equal to that of the intra-axonally recorded action potential. 3. Following ionophoretic application of potassium from a peri-internodal microelectrode, the peri-internodal action potential was followed by a prolonged (hundreds of milliseconds) negative plateau. This plateau was not seen following peri-internodal ionophoresis of sodium. The prolonged negative potential (PNP) was confined to the K(+)-injected internode: it could be recorded by a second peri-internodal microelectrode inserted into the same internode, but not into an adjacent internode. 4. The peri-internodally recorded PNP was accompanied by an equally prolonged intra-axonal depolarizing after-potential, and by an increase in the conductance of the internodal axolemma. However, the K+ ionophoresis that produced the PNP had little or no detectable effect on the intra-axonally or peri-internodally recorded resting potential or action potential. These findings suggest that the PNP is generated by an inward current across the axolemma of the K(+)-injected internode, through channels opened following the action potential. 5. Following peri-internodal K+ ionophoresis a PNP could also be evoked by passage of depolarizing current pulses through an intra-axonal electrode or by passage of negative current pulses through an electrode in the K(+)-filled peri-internodal region. The threshold for evoking a PNP was less than the threshold for evoking an action potential, and the PNP persisted in 10 microM-tetrodotoxin. Thus the PNP is evoked by depolarization of the axolemma rather than by Na+ influx. 6. The PNP was reversibly blocked by tetraethylammonium (TEA, 2-10 mM), but was not blocked by 100 microM-3,4-diaminopyridine or 5 mM-4-aminopyridine.(ABSTRACT TRUNCATED AT 400 WORDS)


The field adaptation of the human rod visual system. 1. Incremental thresholds were measured in a retinal region 12 deg temporal from the fovea with a target of 200 ms in duration and 6 deg in diameter superimposed on background fields of various intensities and wavelengths. Measurements were made under rod-isolation conditions in five normal observers and in a typical, complete achromat observer who had no cone function. 2. The rise in threshold with background intensity changes with background wavelength in the normal trichromat observers. On 450, 520 and 560 nm backgrounds the average slope in logarithmic co-ordinates (0.78 +/- 0.04, S.D.) is similar to that found for the achromat--whose slope is independent of background wavelength (0.79 +/- 0.03)--but on a 640 nm background it more nearly approaches Weber's law (0.91 +/- 0.02). This indicates that the sensitivity of the rods to an incremental target is not determined by quantal absorptions in the rods alone but by quantal absorptions in both the rods and the cones. 3. Rod incremental thresholds were also measured in various colour-blind observers lacking one or more of the cone classes: a blue-cone monochromat, four deuteranopes and a protanope. For the blue-cone monochromat, like the achromat, the slope of the increment threshold curve is constant with background wavelength. For the deuteranopes and the protanope, like the normal, the slope increases with wavelength. The protanope, however, shows a smaller increase in slope, consistent with the lower sensitivity of his cones to long-wavelength light. 4. The dependence of the field adaptation of the rods on the cones was confirmed by field-mixture experiments, in which the incremental threshold was measured against bichromatic backgrounds, and in silent substitution experiments, in which backgrounds equated for their effects on either the cones or the rods but not both were instantaneously substituted for one another.


Depolarization of Ib afferent axons in the cat spinal cord during homonymous muscle contraction. 1. Intra-axonal records from the intraspinal course of Ib and Ia afferent fibres innervating the gastrocnemius medialis muscle were obtained in chloralose or Nembutal-anaesthetized cats during submaximal contractions of the muscle. 2. Afferent fibres in continuity with their muscle of origin were functionally identified by their responses to muscle stretch or contraction. 3. In six out of eight Ib afferents, primary depolarizations (PADs) were recorded during contraction. They were independent of the presence of orthodromic impulses fired by tendon organs. 4. These observations support the assumption that the reduction of Ib autogenetic inhibition in homonymous and synergic motoneurones during GM contractions is due to presynaptic inhibition of transmission in Ib pathways.


Hyperpolarization as a mechanism for endothelium-dependent relaxations in the porcine coronary artery. 1. The nature of endothelium-dependent relaxations resistant to nitro-L-arginine was investigated in porcine coronary arteries by measuring isometric force and membrane potential in the presence of indomethacin. 2. Bradykinin induced concentration- and endothelium-dependent relaxations and hyperpolarization in tissues contracted with prostaglandin F2 alpha. Nitro-L-arginine did not affect either the relaxations or the hyperpolarization induced by bradykinin. The threshold concentration of bradykinin was the same for the nitro-L-arginine-resistant relaxations and the membrane hyperpolarization. 3. Nitro-L-arginine-resistant relaxations were evoked by several agents (A23187, thrombin and UK 14304) in addition to bradykinin. The amplitude of membrane hyperpolarizations observed with all agents was proportional to that of nitro-L-arginine-resistant relaxations. 4. Thrombin caused more transient relaxations and hyperpolarizations than bradykinin in the presence of nitro-L-arginine. 5. In tissues contracted with high K+ or tetrabutylammonium (a non-selective K(+)-channel blocker), bradykinin inhibited the contractions in a concentration-dependent manner, whereas membrane hyperpolarization was not observed. The relaxations evoked by the kinin were abolished by nitro-L-arginine. 6. These results suggest that endothelium-dependent relaxations which are resistant to nitro-L-arginine are mediated by membrane hyperpolarization in the porcine coronary artery.


Synaptic behaviour in the myenteric plexus of the guinea-pig gastric antrum. 1. Intracellular recording methods were used to study the synaptic behaviour of neurones in the myenteric plexus of the guinea-pig gastric antrum. Synaptic potentials occurred spontaneously or were evoked by focal electrical stimulation of interganglionic fibre tracts. Synaptic events consisted of fast and slow excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs). 2. Fast EPSPs with durations less than 20 ms were evoked in every antral neurone in a population sample of 370 cells. Most of the ganglion cells received multiple inputs from axons entering the individual ganglia in several different interganglionic fibre tracts. Many of the neurones also received input from multiple axons projecting in individual fibre tracts. The fast EPSPs behaved like nicotinic cholinergic EPSPs. They were evoked at stimulus frequencies up to 60 Hz without evidence of the run-down characteristic of fast EPSPs in the intestine. 3. Slow EPSPs were evoked by repetitive stimulation of the interganglionic connectives. They consisted of a slowly activating depolarization which persisted for several seconds after termination of the stimulus. The depolarizing responses were associated with an increase in the input resistance, with enhanced excitability and with suppression of hyperpolarizing after-potentials in AH/type 2 neurones. They were observed in 14.4% of the neurones of which 89% were AH/type 2 neurones. AH/type 2 neurones, unlike other myenteric neurones, were identified by action potentials with long lasting after-hyperpolarization. 4. IPSPs were hyperpolarizing potentials evoked by repetitive stimulation of interganglionic fibre tracts. The hyperpolarizing responses were associated with decreased input resistance. They occurred in 1.4% of the antral neurones. 5. Application of acetylcholine (ACh) by micro-ejection mimicked the fast EPSPs in all neurones. This fast nicotinic response to ACh was followed by a slowly activating, long-lasting muscarinic depolarization in 32% of the neurones. The slow muscarinic response was associated with increased input resistance, suppression of hyperpolarizing after-potentials and enhanced excitability. 6. Fast EPSPs were not suppressed by accumulation of ACh at presynaptic transmitter release sites. Unlike the intestine, presynaptic muscarinic autoreceptors appeared to be absent from the microcircuits in the antrum. 7. Synaptic behaviour in the local circuits of the gastric antrum differed from the gastric corpus. This may be a reflection of specialization of the circuits for organization of the distinctive patterns of digestive behaviour found in this region of the stomach.


Slow and fast transient potassium currents in cultured rat hippocampal cells. 1. Potassium currents have been recorded from rat hippocampal neurons in dissociated cultures prepared at E17-E19. Currents were studied with the whole-cell version of the patch clamp method. The kinetics and pharmacological properties of two transient outward currents have been characterized. 2. Most of the recordings have been done in cells which had been in culture 10-18 days. Both a fast and a slow transient current could be elicited. A subtraction procedure was used to isolate the fast transient current. The fast transient current decayed monoexponentially with a time constant of about 10 ms. The slow transient current decayed with two time constants in the order of 500 ms and of 3.4 s. The reversal potential of the slow current shifted by 54 mV for a tenfold change in extracellular potassium concentration. 3. Studies on the removal of inactivation for the two currents revealed time constants of 29 and 107 ms for the fast and slow transient current, respectively. 4. The steady-state inactivation properties of the fast transient current were determined by studying the current with a fixed depolarizing command of -10 mV and varying pre-pulse amplitudes from a holding potential of -50 mV. The inactivation curve could be fitted with a Boltzmann equation. Half-maximal inactivation occurred at -81 mV. The steady-state activation properties of the fast transient current were determined by varying the depolarizing voltage commands following a fixed pre-pulse to -110 mV. The threshold for activation was between -70 and -60 mV. Half-maximal activation was reached at -19 mV. 5. The steady-state inactivation properties of the slow transient current were determined by studying the current elicited by varying the hyperpolarizing voltage steps from a holding potential of 0 mV. The inactivation curve could be fitted with a Boltzmann equation. Half-maximal inactivation was obtained at -61 mV. The steady-state activation properties were determined in a manner similar to the fast current. The threshold for activation was between -40 and -30 mV. 6. The slow transient current was not inactivated immediately when the conditioning pre-pulse was stopped. The rate of current decay increased with stimulus frequency. 7. Both transient currents were sensitive to 4-aminopyridine (4-AP). The fast transient current was blocked completely by 5 mM provided a pre-pulse of 1 s to -110 mV was employed. The slow transient current was already depressed by 4-AP applied in the 100 microM range but could never be blocked completely.(ABSTRACT TRUNCATED AT 400 WORDS)


The importance of competition between motoneurones in developing rat muscle; effects of partial denervation at birth. 1. The number of motor units in developing fourth deep lumbrical muscles was reduced by unilateral partial denervation of the muscle at birth, by cutting the lateral plantar nerve. A minority of the motor axons arrive via the sural nerve, and were thus not cut. Those muscles that contained one motor unit (one-unit muscles) after partial denervation developed in the absence of competition between motoneurones. Muscles with two motor units had little competition. A few four-unit muscles were studied for comparison. 2. Isometric twitch and tetanic tensions of single motor units were recorded in vitro at 60 days of age in response to stimulation of the sural nerve. On average, units in partially denervated muscles generated more tension than normal units. The isometric tension characteristics of the units in the one-unit and two-unit muscles were different from the normal units (e.g. slower contracting and more fatiguable). The units of four-unit muscles had properties similar to those of normal muscles. 3. Fibres of an individual unit were identified by glycogen depletion and S (slow) fibres were identified in cross-section that bound a polyclonal antibody to slow type I myosin. Those fibres that did not bind the antibody were designated F fibres. The units of one-unit muscles had the same total number of fibres and fibre type composition (both S and F fibres in the same unit) as estimated from previous work to exist at birth. The units of two-unit muscles contained the same total number of fibres, but apparently fewer S fibres, though this may have been as a result of incomplete glycogen depletion of some fibres. 4. It is concluded that competition between motoneurone terminals is necessary for the withdrawal of mismatched connections on muscle fibres present at birth; or, alternatively, that such withdrawal cannot take place if it would result in denervation of the muscle fibre.


Plasma proteins modify the endothelial cell glycocalyx of frog mesenteric microvessels. 1. We have investigated the interaction of plasma proteins with the endothelial cell using cationized ferritin as a marker of the cell surface glycocalyx. 2. Single microvessels of the frog mesentery were sequentially perfused using glass micropipettes with solutions containing cationized ferritin (CF, 6.7 mg ml-1) in 0.10 M-NaCl and then with either frog plasma or bovine serum albumin (BSA; 50 or 10 mg ml-1), or protein-free Ringer solution, before suffusion fixation in 2.5% glutaraldehyde. 3. A layer of CF, usually two to four molecules thick, was associated with the luminal endothelial cell surface. In vessels post-flushed with protein-free Ringer solution the CF layer was closely adherent to all regions of the luminal endothelium, including the plasma membrane, vesicle diaphragms, coated pits and the entrances to clefts. However, when plasma was present during fixation the CF layer was separated from the cell surface by up to 100 nm over all regions. In vessels post-flushed with BSA the CF layer was also separated from the membrane but the effect was less striking. 4. The association of cationized ferritin with the endothelial cell surface was assessed quantitatively using electron micrographs of transverse sections (approximately 50 nm thick) of the perfused vessels, and expressed in terms of the depth of the layer of CF associated with the endothelial cell surface, its separation from the plasma membrane of the luminal endothelium, and the concentration of CF in the layer. The mean (+/- S.D.) separation in the presence of plasma, 32.3 +/- 10.5 nm (n = 12), was significantly greater (P less than 0.01) than that with either protein-free Ringer solution, 3.0 +/- 1.4 nm (n = 9), or BSA in Ringer solution, 8.3 +/- 3.0 nm (n = 8). The separation seen with BSA in Ringer was also significantly greater than that measured with a final Ringer solution perfusion (P less than 0.01). The effects of 10 and 50 mg ml-1 BSA were not different from one another. The total glycocalyx thickness, defined as the sum of the separation layer and depth of CF layer, with plasma present, 56.2 +/- 13.7 nm, was twice the value seen with Ringer solution, 28.0 +/- 9.1 nm (P less than 0.01), while the total thickness with BSA, 30.9 +/- 5.4 nm, was not different from the Ringer solution value.(ABSTRACT TRUNCATED AT 400 WORDS)


A frequency analysis of neuronal activity in monkey thalamus, motor cortex and electromyograms in wrist oscillations. 1. Extracellular recordings were made in three monkeys while recording from neurones in the motor cortex (eighty-four cells), ventro-posterior lateralis pars caudalis (VPLc, forty-two cells) and cerebellar thalamus (seventy-seven cells). 2. This experiment was designed to produce active and reflex movements of varying velocities in order to study the relationship between amplitude of velocity and magnitude of neuronal discharge of thalamic neurones. The active movements were voluntary rapid alternating movements (RAMs) of the wrist and the reflex movements were produced by forcibly oscillating the wrist joint between frequencies of 1 and 7 Hz (forced oscillations). 3. This study was also designed to examine cerebellar influences on a reflex path, namely the transcortical reflex loop. Forced oscillations were predicted to provide circumstances where active damping was required to prevent excessive oscillations in the reflex path. Rapid alternating movements of the wrist were predicted to provide circumstances where oscillations at the natural frequency in that reflex path would support and propagate the movements. 4. Forced oscillations from 1 to 7 Hz produced movements of different velocities. VPLc and cerebellar thalamic neurones discharged in relation to the duration of movement in a particular direction, but their discharge levels were unrelated to the magnitude of the velocity. Motor cortex neurones fired in a pattern which was related to the timing but not the magnitude of the acceleration. 5. In forced oscillations of the wrist the resonant frequency was between 3 and 7 Hz. They may be controlled in part by a transcortical reflex. The cerebellar thalamic neurones did not fire before motor cortex neurones. Therefore, it is unlikely that the cerebello-thalamo-cortical pathway is necessary to damp these potentially unstable oscillations by an effect on antagonist-related cortical neurones. 6. Rapid alternating movements (RAMs) of monkeys' wrists were performed in a stereotyped fashion over a narrow range of frequencies with the greatest displacement in joint angle and peak velocity at the natural frequency of 3-5 Hz. 7. During the performance of RAMs, neuronal discharge modulated sinusoidally in the VPLc, cerebellar thalamus and motor cortex. There was no relationship between velocity and neuronal discharge of the cerebellar thalamic and motor cortical neurones but there did appear to be a relationship between velocity and VPLc neuronal discharge. 8. The onset of electromyogram (EMG) discharge changed earlier than neuronal discharge in the motor cortex and thalamus during the performance of RAMs.(ABSTRACT TRUNCATED AT 400 WORDS)


The effect of intracellular pH on ATP-dependent potassium channels of frog skeletal muscle. 1. We have used patch-clamp methods to study the effects of pH at the cytoplasmic surface of the membrane on ATP-dependent K+ channels (KATP channels) in patches excised from frog (Rana temporaria) skeletal muscle, and to study the kinetics of ATP binding. 2. In the absence of ATP, a reduction in pH led to a slight decrease in single-channel current amplitude, an increase in the number of very brief closings, an increase in the apparent mean open time, and an increase in burst duration. After correction for missed closings, the change in mean open time was slight. Despite these changes in detailed kinetics, the channel open-state probability, Popen, changed little with changes in pH in the absence of ATP. 3. In the presence of ATP, a decrease in internal pH (pHi) reduced the degree of channel inhibition by ATP, shifting the curve relating Popen and [ATP] to higher concentrations of ATP without altering its steepness. The ATP concentration for half-inhibition of channel activity (Ki) was 17 microM at pH 7.2 and 260 microM at pH 6.3. 4. The effect of pH could be modelled by assuming that one or two protons bind to the channel and prevent ATP binding to exert its effect of causing channel closure. The predicted dissociation constants for ATP and H+ respectively were 5.4 and 0.11 microM. 5. The rate constants for binding and unbinding of ATP were estimated from the dependence of the mean open time on [ATP] and from the Ki. The apparent rate constants for ATP binding were 0.6 and 0.04 mM-1 ms-1 at pH 7.2 and 6.3 respectively, while the rate constant for unbinding was 0.01 ms-1. In terms of our model the calculated true rate constant for ATP binding was 1.85 mM-1 ms-1. ATP binding also led to a reduction in burst duration. 6. The effect of pH described here differs from findings in cardiac muscle and pancreatic B-cells. The results are discussed in relation to the possible function of KATP channels in skeletal muscle during exercise.


Mechanisms by which the pregnant ewe can sustain increased salt and water supply to the fetus. 1. Nine chronically catheterized pregnant ewes were monitored before, during and after 1 week in which fetal urine was drained continuously, to determine whether they could compensate for the resulting loss of salt and water and increase net supply across the placenta to the fetus. 2. Fetal growth and urine and lung liquid production were not affected by loss of all fetal fluids. 3. When fetal urine was drained, the increase (P less than 0.05) in maternal drinking was greater than the extra amount of fluid lost. Thus, maternal plasma osmolality fell (P less than 0.01). When fetal urine again flowed into the amniotic and allantoic cavities, maternal drinking did not fall significantly and plasma osmolality remained low. Maternal urine flow rate increased (P less than 0.05) and its osmolality fell (P less than 0.02). 4. Maternal food intake increased (P less than 0.005) during fetal urine drainage. 5. Maternal plasma renin activity increased (P less than 0.05), her urinary sodium excretion fell (P less than 0.005) and the Na(+)-K+ ratio in both her urine and faeces decreased (P less than 0.01 and P less than 0.05 respectively) when fetal urine was drained. Maternal urinary and faecal sodium conservation continued after drainage ceased because of continued loss of sodium in lung liquid. 6. It is concluded that the ewe can compensate for inappropriate loss of salt and water from the conceptus.


Parvalbumin, labile heat and slowing of relaxation in mouse soleus and extensor digitorum longus muscles. 1. Parvalbumin content, heat rate and rate of relaxation were measured in two mouse muscles: the slow-twitch soleus and the fast-twitch extensor digitorum longus (EDL). 2. No trace of parvalbumin was found in the soleus; EDL contained a mean of 4.86 mg of this protein per gram of fresh muscle (S.D. = 1.25). 3. Heat rate during 7 s isometric tetani in isolated soleus muscle at 20 degrees C can be described by the sum of an exponentially decaying term and a constant term. The exponential term is reduced by 67% in a second tetanus performed 1 s after a first one; its repriming is complete after a resting period of about 1 min. The exponential term has therefore the properties of labile heat. 4. Relaxation rate measured during 15 s of isometric interrupted tetani at 20 degrees C is nearly constant in the soleus, but decreases continuously with increasing tetanus duration in the EDL. In the latter, isometric tension also decreases continuously. 5. Therefore, parvalbumin can account neither for the labile heat production in mouse soleus nor for the slowing of relaxation associated with muscle fatigue observed after a few seconds of tetanus in EDL. The role of parvalbumin in striated muscles is thus reassessed, and other possible causes of labile heat production and slowing of relaxation are discussed.


Pursuit of intermittently illuminated moving targets in the human. 1. Experiments have been conducted in order to establish the changes in oculomotor activity which take place when the human subject attempts to pursue an intermittently illuminated moving target. 2. In an initial experiment, target motion in the horizontal plane was composed of one or two sinusoids at frequencies between 0.11 and 0.2 Hz. The target was illuminated for varying durations (10-320 ms) at intervals between 40 and 960 ms. As pulse interval was increased or pulse duration was decreased there was a progressive increase in eye velocity gain for the smooth component of eye movement. Some smooth eye movement was generated even when the pulse interval was as large as 960 ms. 3. In a second experiment target motion consisted of a triangular waveform in which target presentation was timed to occur at regular intervals throughout each cycle. Overlaying and averaging the response from several cycles revealed a regular pattern of pulsatile activity associated with each target presentation. This response, which was particularly evident when the pulse interval was greater than 1 s, consisted of an initial build-up of smooth eye velocity followed by an exponential decay with a time constant of 0.5-2 s. When the pulse interval was less than 1 s there was a summation of the transient responses so that eye movement appeared quite smooth when pulse interval was reduced to 320 ms. 4. The pulsatile nature of the response was accentuated when the target was made to execute a staircase-ramp waveform in which the target was illuminated only during the ramp component. The elimination of position change between ramps and the ability to achieve higher target velocity led to clear evidence of the summation of transient oculomotor responses. 5. The summated effects, however, were not simply attributable to the addition of responses to individual target presentations as indicated by the timing of each response. The eye velocity pulse was frequently initiated 200-300 ms prior to target appearance, and well before the time (100 ms) at which visual feedback would be expected to become effective. 6. The effect of target step displacement alone was investigated by examination of the smooth eye movement initiated by varying numbers of steps in the waveform. This showed that the basic step response had a peak velocity of no more than 8-10 deg/s in most individuals.(ABSTRACT TRUNCATED AT 400 WORDS)


Tension transients during steady lengthening of tetanized muscle fibres of the frog. 1. Steady lengthenings at different velocities (0.02-1.6 microns/s per half-sarcomere, temperature 2.5-5.5 degrees C) were imposed on isolated frog muscle fibres at the plateau of the isometric tetanus (tension T0). When tension during lengthening had attained a steady value (Ti), which varied from about 1.5 to about 2 times T0 depending on lengthening velocity, tension transients were elicited by applying step length changes of different amplitudes. The change in length of a selected segment, close to the end of the fibre connected to the force transducer, was controlled by means of a striation follower. 2. The instantaneous plots of tension versus the length change during the step itself showed that at the high forces developed during steady lengthening, as at the plateau of isometric tetanus, the elasticity of the fibre was almost undamped in the whole range of lengthening velocities used. 3. The tension transient elicited by step length changes imposed in isometric conditions exhibited the characteristic four phases described previously: following the tension change simultaneous with the step (phase 1), there was a quick partial recovery (phase 2, the speed of which increased going from the largest step stretch to the largest step release), a subsequent pause or inversion in recovery (phase 3) and finally a slower approach to the tension before the step (phase 4). 4. In the region of small steps the plot of the extreme tension attained during the step (T1) versus step amplitude appeared more linear during steady lengthening than in isometric conditions and deviated progressively from linearity with increase in the size of step releases. The amount of instantaneous shortening necessary to drop tension to zero (Y0), measured by the abscissa intercept of the straight line drawn through T1 points for small steps, was about 4.1 nm per half-sarcomere in isometric conditions and 5.4 nm per half-sarcomere during lengthening at low speed (0.09 microns/s per half-sarcomere, Ti about 1.6 T0). Taken altogether this indicates, in agreement with previous work, that force enhancement during steady lengthening is due to increase in both number and extension of attached cross-bridges. During lengthening at high speed (0.8 microns/s per half-sarcomere), further enhancement in steady force (Ti about 1.9 T0) was accompanied by increase of Y0 to 6.3 nm per half-sarcomere, indicating that increase in lengthening velocity exclusively produces increase in cross-bridge extension.(ABSTRACT TRUNCATED AT 400 WORDS)


Effects of amino acids on zinc transport in rat erythrocytes. 1. A significant proportion of plasma zinc exists complexed with amino acids. The effect of amino acids on the accumulation of radioactive zinc by rat erythrocytes was studied in vitro, to investigate the hypothesis that zinc might be transported into cells as an amino acid-zinc complex. 2. L-Histidine (500 microM-10 mM) stimulated 65Zn uptake; 50 mM-L-histidine gave a slight inhibition of uptake. D-Histidine (500 microM-10 mM) inhibited uptake in a dose-dependent manner. A non-zinc-binding amino acid, L-alanine, did not affect 65Zn uptake. 3. The effect of L-histidine was sodium dependent and temperature dependent, but was DIDS insensitive. These properties suggest that zinc is being transported as a zinc-histidine complex, utilizing an amino acid carrier system. Uptake of zinc in the presence of L-histidine differed from the previously described ionic mechanism, and may represent a physiological route of uptake. 4. L-Histidine stimulated efflux of 65Zn from pre-loaded cells. 5. The relevance of transport of a zinc-histidine complex is discussed with reference to histidinaemia, and as a significant zinc transport system in the presence of the very low ionic zinc concentrations found in plasma.


Fetal breathing, sleep state and cardiovascular adaptations to anaemia in sheep. 1. In unanaesthetized fetal sheep (greater than 0.8 term) prolonged anaemia initially reduced the incidences of low-voltage electrocortical activity, rapid eye movements and breathing activity; but the incidence of each returned to normal within 4-7 h. 2. Anaemia induced a persistent rise in fetal heart rate and plasma concentrations of adrenaline, noradrenaline and cortisol. 3. After 16 h the fetal haematocrit was returned to normal. Isocapnic hypoxia induced less than 1 h later also inhibited eye and breathing activity. 4. After 1 h fetal arterial PO2 (Pa,O2) was returned to normal. This rise in O2 tension was associated with an elevation in the incidence of low-voltage electrocortical activity, eye movements and breathing. Breathing movements also occurred during high-voltage electrocortical activity. 5. It is concluded that the brain PO2 set-point for hypoxic inhibition adapts rapidly to alterations in O2-carrying capacity and is probably due to changes in the concentration and/or receptor affinity of a central neuromodulator. Secondly, a rise in brain PO2 at birth may contribute to the onset of continuous breathing.


The source of calcium for muscarinic-mediated catecholamine release from cat adrenals. 1. In view of conflicting reports on the source of Ca2+ needed to trigger the secretory response to muscarinic stimulation of chromaffin cells, we have reinvestigated this problem in the cat adrenal gland perfused with oxygenated Krebs solution at 37 degrees C. Above a basal rate of secretion of 60 ng/30 s of total catecholamines, 5 s pulses of 100 microM-methacholine evoked 10-fold increases of secretion. This response was entirely mediated by muscarinic receptors, since it was blocked by submicromolar concentrations of atropine but not by d-tubocurarine. 2. Delayed application of methacholine pulses after Ca2+ removal from the Krebs solution led to a progressive decline of the secretory response with a t1/2 of 15 s. Secretion was blocked by 85% after a 60 s period of Ca2+ deprivation; extension of the external Ca2+ (Ca2+o) wash-out period up to 5 min did not further reduce the secretory response. 3. When EGTA (1 mM) was present in the 0 Ca2+ solution, the rate of decline of methacholine responses, as a function of the time of exposure to 1 mM-EGTA, was similar to that obtained with 0 Ca2+. Again, about 15-20% of the secretory response was resistant even to prolonged periods of washing out with the 0 Ca(2+)-EGTA solution. 4. The Ca2+ ionophore ionomycin (1 microM) first decreased and then accelerated the rate of decline of methacholine responses upon Ca2+o wash-out. Particularly relevant is the complete blockade of secretion when the Ca2+o wash-out is performed in the presence of this ionophore. This suggests the existence of a small intracellular functional Ca2+ store sensitive to ionomycin. 5. After abolition of the secretory response through 60 s periods of wash-out with a 0 Ca(2+)-EGTA-ionomycin solution, followed by delayed 5 s methacholine pulses after Ca2+o reintroduction, the glands instantly recovered their normal muscarinic-mediated secretory response. This suggests that upon muscarinic stimulation, Ca2+ required by the secretory machinery to trigger such response immediately comes from extracellular sources. How Ca2+o gains the cell interior so fast upon muscarinic stimulation is unknown; we have previously suggested that the muscarinic receptor in the cat chromaffin cell could be coupled to an ionophore channel which might be chemically activated by muscarinic agonists. 6. Secretory responses to 5 s pulses with 35 or 100 mM-K+ declined faster (t1/2 of 3 and 6 s, respectively) upon Ca2+o wash-out than those of methacholine.(ABSTRACT TRUNCATED AT 400 WORDS)


Effects of 2-amino-4-phosphonobutyric acid on cells in the distal layers of the tiger salamander's retina. 1. We studied the effects of 2-amino-4-phosphonobutyric acid (APB) on the response properties of rods, horizontal cells and bipolar cells in the isolated, perfused retina of the tiger salamander, Ambystoma tigrinum. A concentration of 100 microM was found to be sufficient to elicit maximal effects. 2. Rods hyperpolarized slightly upon exposure to 100 microM-APB and their response amplitudes were slightly reduced. The amplitude of the cone-generated component of the rod's response to 700 nm light was not significantly affected by APB. 3. Horizontal cells hyperpolarized by 2-5 mV upon exposure to 100 microM-APB. The rod-driven component of the horizontal cell response increased in amplitude while the cone-driven component decreased in amplitude. APB thus causes an increase in voltage gain between rods and horizontal cells and a decrease in cone/horizontal cell gain. These findings can be explained in terms of an APB-induced reduction in transmitter release from the cones. 4. APB at a concentration of 100 microM caused an increase in the length constant of the horizontal cell syncytium. Our analysis shows this to be due primarily to a 50% reduction in the coupling impedance between the cells of the syncytium. 5. The effects of APB on off-centre bipolar cells were qualitatively similar to those on horizontal cells. APB increased the amplitudes of rod-driven responses and reduced those of cone-driven responses. The length constants, both of the receptive field centre and of the surround, were increased and the strength of the surround relative to the centre was reduced by about 20%. 6. APB abolished the depolarizing light responses of the receptive field centres of on-centre bipolar cells. A hyperpolarizing response remained whose spatial properties were similar to those of the receptive field surround. We believe this response to reflect a direct (feedforward) input to on-centre bipolar cells from horizontal cells.


Prevalence of developmental enamel defects in children with cerebral palsy. Enamel defects observed in primary anterior teeth of 123 children with congenital cerebral palsy (CP) born 1983 through 1985 in four northern California counties were categorized using an adaptation of the Developmental Defects of Enamel Index. Nineteen children (15%) had crowns or loss of tooth substance (LTS) due to attrition. Missing enamel (ME) including horizontal groove, was observed in 39 children (32%). Twenty-four children without ME (20%) had enamel pits, vertical grooves, or colored enamel opacities. Forty-one (33%) had clinically normal enamel. ME children did not differ significantly from those with normal enamel with respect to race, sex, singleton vs twin, severity or type of CP, or presence of dysmorphic features. ME children more often had shorter gestational ages than children with normal enamel. More ME children, even those who were not low in birth weight, were reported by parents to have required neonatal intensive care.


The lateral periodontal cyst: an update. Lateral periodontal cysts account for 0.8% of all jaw cysts seen in our department. Published reports have indicated that they occur most frequently in the 5th to 7th decades, that there is a male preponderance and that they are located mainly in the mandibular canine-premolar region. In our own series of 20 cases, 10 were found in the anterior maxilla. We have distinguished unicystic and multicystic (including botryoid) varieties. They were lined predominantly or exclusively by thin reduced enamel epithelium-like tissue which contained many clear cells and epithelial thickenings referred to as plaques. Glycogen was present in the epithelium of two-thirds of our cases although not exclusively in the clear cells, many of which showed no positivity. Two of our examples of the botryoid variety were different histologically, being lined predominantly by non-keratinizing stratified squamous epithelium with crowded and pyknotic nuclei and no clear cells. One case contained melanin while another showed epithelial crypt formation and superficial palisaded low columnar cells as seen in the glandular odontogenic cyst. This raised the question of whether the latter may form part of the clinicopathologic spectrum of lateral periodontal cyst. The histogenesis of lateral periodontal cysts is uncertain but we favour origin from reduced enamel epithelium.


Enhanced prostaglandin biosynthesis in human gingival fibroblasts isolated from patients treated with phenytoin. Prostaglandin E2 (PGE2) formation was studied in human gingival fibroblasts derived from three epileptic patients before and after 9 months of phenytoin (PHT) therapy. Interleukin 1 (IL-1 alpha; 0.3-6.0 ng/ml), (IL-1 beta; 10-1000 pg/ml) and tumour necrosis factor (TNF alpha; 0.01-0.1 microgram/ml) dose-dependently stimulated the formation of PGE2 in 24 h cultures. In fibroblasts, derived after 9 months of PHT therapy, IL-1 alpha, IL-1 beta and TNF alpha induced a significantly higher formation of PGE2 compared to that in fibroblasts derived before PHT therapy. IL-1 beta induced a significantly higher release also of 3H-arachidonic acid (3H-AA) from prelabelled PHT fibroblasts compared to that in prelabelled gingival fibroblasts isolated before the drug therapy. Addition of exogenous AA caused a spontaneous increase of PGE2 formation in PHT fibroblasts compared to that in fibroblasts isolated before the PHT treatment. The results indicate that PHT medication results in an upregulation of prostanoid formation in gingival fibroblasts partly due to an increased phospholipase A2 activity and partly due to an increased cyclooxygenase activity.


Distribution of fibronectin in healthy, inflamed and drug-induced gingival hyperplasia. The distribution of fibronectin (FN) in the healthy, inflamed and hyperplastic human gingiva was investigated by indirect immunofluorescence. FN appeared as a fibrillar structure in the lamina propria of the healthy gingivae. In the inflamed specimens, FN demonstrated parallel fibres, especially in the coronal areas of the tissue. In the phenytoin gingival overgrowth, tissue FN was observed as thin fibres with variable length. The thin fibres gave the appearance of penetrating the basement membrane of the epithelium. Cyclosporin A gingival enlargement could be differentiated by phenytoin lesions because of the higher length and the parallel distribution of the FN. Finally, FN was observed in the nifedipine gingival overgrowth, where a microfibrillar delicate network gave the appearance of a "cloud"-pattern of distribution. In all of the specimens, blood vessels and nerves could not be stained. These findings show that FN distribution could differentiate the structure of the gingival lesions.


Prevalence of betel quid chewing habit in Taiwan and related sociodemographic factors. The prevalence of betel quid chewing habit in Taiwan was surveyed in a group of Chinese people from Kaohsiung city and in a second group from the aboriginal inhabitants of South Taiwan. In all 1299 participants constituted Group 1 (85.2% response rate) and 827 Group 2 (70.1% response rate). People were interviewed in their homes in house-to-house survey, according to a structured questionnaire developed and evaluated by the authors. Of the Kaohsiung inhabitants covering all ages and both sexes, 6% was a current betel chewer and 4% was an ex-chewer, whereas 42% of the aborigines aged over 15 yr was a current chewer and 1% an ex-chewer. Lifetime prevalence was 10%. Betel chewing enjoys islandwide popularity among the 20 million inhabitants of Taiwan; the number of current and ex-users was estimated at 2.0 million (95% CI 1.6-2.4 million). The betel quid was prepared in two different ways. In one, used mainly by aborigines, fresh areca nut was simply wrapped with betel leaf and in another, popular mainly among Chinese, a lengthwise piece of betel fruit and lime paste was sandwiched between two halves of an areca nut. A high proportion of chewers was also a smoker and drinker, but tobacco was not found to be chewed together with betel quid. Consumption varied between 14 to 23 portions per day, with individual frequencies ranging widely from 1 to over 200 portions a day. A statistical analysis of sociodemographic factors showed that lesser educated older men, blue collar workers, smokers and drinkers were the likeliest betel chewers.


Oral-dental findings in dyskeratosis congenita. A 13-yr-old girl with dyskeratosis congenita is presented. Besides oral leukoplakia and nail dystrophies, there was evidence of pancytopenia, growth retardation, alopecia, mental retardation and microcephaly. The oral findings included caries, gingival recession, short-blunted roots, gingival bleeding, tooth mobility and severe alveolar bone loss resembling juvenile periodontitis.


Compound odontoma erupting in the mouth: 4-year follow-up of a clinical case. A case of a compound odontoma erupting in the oral cavity is presented: a follow-up study of 4 yr has been performed evaluating the possible relationship with a previous dental trauma. A discussion is presented concerning the etiologic aspects, clinical signs, diagnostic aids and therapeutic approaches to this type of lesion.


Alternative restorative approach: a clinical report. This clinical report describes a technique for restoring a maxillary right posterior segment using a combination of a conventional full-coverage retainer and adhesive resin-bonded retainer with a nonrigid connection, periodontal ridge augmentation, and a coronal-radicular amalgam alloy core. A technique has been outlined that allows for the preservation of the maximum amount of natural tooth structure while restoring a maxillary right posterior segment.


Duplication of anterior provisional fixed partial dentures for the final restoration. Using the provisional restoration as a testing ground to increase the predictability of a final restoration is well understood. With the resolution of issues through a well-developed provisional restoration comes the challenge of duplicating its contours in the final prosthesis. A method is described using elastomer impression putty and a molten wax technique by which the contours of a provisional anterior fixed partial denture can be duplicated. The described method is particularly useful when the replication of a specific irregular tooth arrangement is mandated.


Use of a scanning laser three-dimensional digitizer to evaluate dimensional accuracy of dental impression materials. A steel die was machined to represent a dental arch with teeth prepared for complete crowns. Impressions and casts were made from the die, and critical dimensions were measured by two methods--one using micrometers and the other a scanning laser three-dimensional (3-D) digitizer. The digitizer recorded measurements were more precise than the micrometer's and virtually eliminated operator error because the acquisition of data was automatic. The digitizer could also be useful for high-precision analyses of the dimensional accuracy of dental impression materials, but the cost and complexity of the instrument makes it less desirable for low-precision work.


An alternative orientation of nonrigid connectors in fixed partial dentures. Nonrigid connectors have been advocated for fixed partial dentures. However, space limitations may require overreduction of the preparation or overcontouring of the retainer to place the keyway within the retainer wall. An inverted orientation of the nonrigid connector can resolve these problems. With this design, the key is attached to the distal surface of the mesial retainer in a dual-abutment fixed partial denture, and the keyway is incorporated in the mesial surface of the pontic. This inverted orientation offers several advantages with few disadvantages.


Resin-bonded prostheses for posterior teeth. This study evaluated fixed partial dentures bonded with resin to dentin on posterior teeth with minimal tooth preparation. The patients included were missing at least one premolar or first molar. The abutment teeth next to the modification spaces were moderately restored with MOD or class II restorations on most of the teeth. A total of 20 patients with 23 fixed partial dentures were included in the study. After removal of existing restorations, the abutment teeth were prepared to eliminate undercuts on the perimeter of the preparations. Undercut areas within the preparation were not filled but were blocked out later in the laboratory. The fixed partial dentures employed inlays as retainers for a metal ceramic pontic. The metal framework was cast in a high noble gold alloy. The areas of the retainers to be bonded were treated with the Kulzer Silicoater method. Immediately before cementation, enamel was etched and exposed dentin was treated with Gluma. Kerr's resin bonded bridge cement was used for cementation. Patients were recalled after periods of 1 week, 1 month, 6 months, 1 year, 2 years, and 4 years for evaluation. None of the restorations lost retention and no major adverse effects were observed in the 4-year follow-up period.


Three-dimensional finite element stress analysis of a cantilever fixed partial denture. A three-dimensional mathematical model was generated, representing a three-unit cantilever fixed partial denture and its supporting mandibular structures. First and second premolars were used as abutments with one posterior cantilever pontic. A 5 lb vertical load was applied to the pontic. Vertical and horizontal stresses were analyzed by means of a three-dimensional finite element stress analysis technique. The results showed that a cantilever pontic creates considerable compressive stress on the abutment nearest to the pontic and produces tensile stress on the abutment farthest from the pontic.


In vitro evaluation of dynamic fluid displacement in dentinal tubules activated on pin placement. The use of cemented, friction-lock, and self-threading pins for improving retention has been essential for treatment in restorative dentistry, with the self-threading pin considered to be the most retentive. Cavity varnish has been suggested to prevent microleakage around pins. This study investigated the insertion of a self-threading pin when the pinhole was filled with a liquid dye. The results showed that pinholes filled with dye before pin placement had measurable dye displacement. Pinholes without pins displayed no measurable dye displacement through the dentin; this was also true when the dye fluid was removed before the pin placement. However, the dye in pinholes was displaced toward the path of least resistance, and fluid in a pinhole can contribute to crazing of the dentin during placement.


A drilling technique to improve the retention of self-threading pins. This study determined the effect of a modification of the drilling technique on the retention of self-threading pins. The drilling technique in two stages significantly increased the retention of self-threading pins.


Effect of bonded amalgam on the fracture resistance of teeth. The purpose of this study was to determine whether amalgam bonded to tooth structure with an adhesive resin cement can increase the fracture resistance of restored teeth. Extracted paired upper premolars were prepared for G.V. Black type mesioocclusodistal amalgam restorations. In one tooth of each pair (the experimental group), the enamel walls were etched with phosphoric acid and were painted with an adhesive resin (Panavia), and amalgam was condensed and carved. For the other tooth in each pair (the control group), amalgam was placed in the same manner but was not etched and lined with resin. The teeth were thermocycled and mounted for testing and then were loaded until fracture. A significant difference (p less than 0.05, the paired Student's t-test) was found in the force needed to fracture the bonded amalgam group (70.5 +/- 21.6 kg) compared with that needed to fracture the conventional amalgam group (60.3 +/- 16.8 kg). SEM examination of fractures at the interface occurred predominantly within the resin.


Efficient amalgam core elimination and root preservation with ultrasonic instrumentation. An efficient ultrasonic vibratory energy technique for the elimination of deeply placed amalgam core in an endodontically treated tooth is presented. Root integrity is ensured by avoiding complete reliance on rotary burs for the removal of the obstructing alloy.