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An Experimental Inquiry Into the Possible Role of Neurotrophic Mechanisms in Skeletal Development Following Removal of Neural Crest Precursor Cells of Dorsal Root Ganglia and Sympathetic Ganglia in the Chick Embryo.

This study was carried out in order to elucidate the influence of neurotrophic (GSA, GVA, or GVE) mechanisms on the developing tibiafibula in the chick embryo. In chick embryos at stage 17 (Hamburger and Hamilton, 1951), the neural crest and portions of the alar plate were removed at the leg level. Behavioral parameters, along with gross, ionic, histochemical, and neuro-skeletal parameters were studied in control and experimental embryos from 6 through 12 days of incubation. Also, an assessment of vascular flow parameters and vascular innervation was accomplished over the same embryonic period. Following incubation, control and experimental embryos were sacrificed for gross and histological studies or utilized for in vivo vascular flow studies. Analysis of tibial length, width, wet weight, and dry weight showed no statistical differences (p j< 0.05) between experimental and control embryos. Assessment of ionic concentrations (Ca++, Mg++, lPO^) showed absence of any significant differences (p _< 0.05) between control and experimental embryos. Histochemical analysis showed no observable differences between calcification and collagen parameters in the experi­ mental and control groups, however, marked changes in acid mucopoly­ saccharides were noted at every age. Vessel reactivity to exogenous catecholamines and a-blockers commenced at 7 days of incubation, and increased to maximum values at 9 days. Neurotransmitter was not found in the nerves of the vascular system until 1 day post-hatch. No synaptic xx relationships were found between neural and skeletal elements, although nerve fibers came into close association with periosteal cells. These findings indicate that the removal of afferent and visceral efferent innervation does not influence the gross development, calcification, or collagenous deposition but does effect acid mucopoly­ saccharide distribution in skeletal elements of long bones. The results also seem to show that vascular parameters are not influenced by neural crest removal, however, differences in this area of the experiment may have been masked due to the use of homeostatic controls. Since Dawes (1974) and McCuskey (1969) have shown that stressful situations can cause drastic changes in the blood levels of metabolites and in the vascular reactivity of fetal vessels, further studies are indicated to delineate the possible relationship of neural crest removal to the alterations in skeletal constituents (acid mucopolysaccharides) that have been noted in this experiment.