Ultrastructural study of nerve terminals in the submucous plexus and mucous membrane after extirpation of the myenteric plexus.

An attempt is made to separate in the submucous plexus and mucous membrane of the chronically isolated intestine of the cat the fibers originating from the myenteric plexus and those originating from the submucous plexus by secondary degeneration after the extirpation of the myenteric plexus. A considerable part of the nerve processes in the submucous plexus originate from the cells of the myenteric ganglia and establish direct synaptic relationships between the ganglion cells, or are very close to the blood vessels. The numerous intact synapses between the different nerve elements in the submucous plexus point to local reflex connexions within the plexus itself. The degeneration of sub-epithelial nerve elements, containing always clear and dense-core (1,000-1,200 A in diameter) vesicles besides the numerous intact nerve elements, might indicate the presence of real sensory nerve processes in this layer. The terminal fibers remaining intact after removal of the myenteric plexus contain numerous medium-sized dense-core vesicles in potassium permanganate-fixed material. This suggests that there are cells containing 5-hydroxytryptamine in the submucous plexus.