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[Relationship between neuronal activities of the guinea-pig inferior mesenteric ganglion neurons and muscular contraction of the colon in vitro].

A perfused inferior mesenteric ganglion (IMG)-colon preparation was prepared from the guinea-pig for intracellular recording of IMG neurons and for simultaneously recording the muscular contraction. It was found that: (1) At zero preloaded tension of colon, the spontaneous fast excitatory post-synaptic potentials (f-EPSPs) could be recorded in about 50% sampled neurons. These f-EPSPs were abolished by either severing the colonic nerve or superfusing IMG with d-tubocurarine (d-TC, 50 mumol/L). (2) The contraction of circular but not longitudinal muscle was augmented and slowed down by superfusing IMG with d-TC or low Ca/high Mg solution. (3) A train stimulation of the preganglionic nerves initiated a volley of f-EPSPs or orthodromic discharges, in the IMG neurons and a quick relaxation of the longitudinal muscle with a latency of between 0.1 s and 0.2 s. The responses of the neuron and the muscle could be eliminated by superfusing IMG with d-TC. Multiple irregular responses of the circular muscle of the colon to the train stimulation could also be found. The results suggest that the IMG neurons participate in the cholinergic afferents and colo-colonic reflex mediated by cholinoceptors. The output of the reflex mainly inhibited the circular muscle contraction of the colon.