Electron microscopy of adrenergic, cholinergic, and "p-type" nerves in the myometrium and a special kind of synaptic contacts with smooth muscle cells.

In the cat uterus, three types of axons have been indentified by electron microscopy on the basis of the appearance of the synaptic vesicles in the axon varicosities following treatment with 5-hydroxydopamine: (1) most axons were adrenergic, with numerous small osmiophilic vesicles of a diameter of approximately 50 nm. together with large (100 to 150 nm. in diameter) granules, (2) some axons contained only empty small granules together with the large granules; these are probably cholinergic, and (3) a small number of the axon varicosities had only large-sized vesicles with a moderately electron-dense content. They are interpreted as a polypeptide type of nerves ("p-terminals"). Close appositions at a distance of 25 nm. were sometimes found between the varicosities. A specialized neuromuscular connection was found: the muscle cells at "the end" of muscle bundles extended small stout processes, containing numerous myofilaments, onto a small nerve bundle, the distance being 20 to 25 nm.