HISTOLOGICAL OBSERVATIONS ON THE RELATIONSHIPS BETWEEN THE INTRINSIC INNERVATION AND THE EXCITABILITY OF THE SMOOTH MUSCLE IN THE STOMACH
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The intrinsic innervation of the gastric musculature of the amphibia and mammals has been studied using histochemical techniques for the localization of both cate-cholamines and acetylcholinesterases (AchE), and by electron microscopical technique. 1) In both species, myenteric (Auerbach's) plexuses contain mostly cholinergic ganglion cells and fibers, together with fluorescent nerve fibers. The catecholamine-containing nerve fiber running in musculature appears to be associated with cholinergic ganglion cells in Auerbach's plexus or blood vessels. No catecholamine-containing ganglion cells were found in Auerbach's plexus. 2) In frog's stomach, very rarely, fluorescent nerve fibers are present in Auerbach's plexus. In toad's gastric musculature sometimes cholinergic axon containing both large (1000-1500 A) and small (350-600 A) granular vesicles was observed, electron microscopically. These kinds of granulated vesicle were not depleted by reserpine. 3) The distribution and density of cholinergic nerve elements vary in the three anatomical regions of toad's stomach. The muscle coat in Pars cardiaca is the most richly innervated part of the stomach and the musculature in Pars mpylorica receives denser innervation than in Corpus ventriculi. The smooth muscle in small curvature also has plenty of cholinergic innervation more than in large curvature. The regional differences in the richness of the cholinergic innervation are closely concerned with the distribution of the membrane resting potential values. 3) Ultrastructural finding also shows that circular muscle coat in toad's stomach especially receives an extensive and heavy cholinergic innervation by close neuromuscular junctions, but not in mammals. Functional myo-myo contact was richly present in mammalian stomach musculature, but not in frog's stomach. It is conceivable that smooth muscle in toad's stomach may belong to multiunit or neurogenic type, while mammalian gastric muscle exhibits a tendency to visceral or myogenic muscle type.