The nerve elements in the urinary bladder of the cat were studied by electron microscopy. According to their ultrastructure, nerve cell somata can be classified into three types: the large cells with a cytoplasm rich in organelles, several processes and numerous synaptic contacts on their surface; the cytoplasm contained 80- to 120-nm granulated vesicles. The second type is poor in cytoplasmic organelles and has very few processes and virtually no synaptic contacts on the soma. The third type contains numerous large 160- to 220-nm ‘neurosecretory’ vesicles in the cytoplasm. According to the morphology of the vesicle population, four types of nerve processes could be distinguished: Type a, with a dominant population of small (40–60 nm) agranular vesicles. These are thought to be sacral parasympathetic fibres. Type b, with small (40–60 nm) granular vesicles, which may be the noradrenergic sympathetic fibres. Type c, with 80- to 120-nm granulated vesicles, probably of local origin. Type d, with large 160- to 220-nm ‘neurosecretory’ vesicles also of local origin. Different types of nerve fibres are converging on the local nerve cells. This suggests that the local circuits can play an important role in coordinating the function of the bladder. Therefore, ganglia may be considered as an elementary functional unit.
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 Å 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.
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