INNERVATION OF THE TRACHEALIS MUSCLE IN THE GUINEA-PIG - A QUANTITATIVE ULTRASTRUCTURAL-STUDY

Abstract

The fine structure and composition of the nerve plexuses associated with the cervical and thoracic parts of the trachealis muscle were studied in 2 groups of 6 guinea-pigs. One group of animals was perfused with fixative before removal of the specimens. In the 2nd, the specimens were incubated in 5-hydroxydopamine before cold immersion fixation. In both parts of the trachea, plexuses of nerves were present within and between the fascicles of muscle cells. The number of intrafascicular nerves/1000 .mu.m2 was low, and few of the nerves contained more than 5 axons. Interfascicular nerves were more numerous and the mean number of axons/nerve was significantly higher than within the muscle. The number of efferent terminal profiles/100 axon profiles was higher in the intrafascicular than in the interfascicular nerves, but in neither case was there evidence of a very close approximation of exposed axon terminal membranes to the membranes of adjacent muscle cells. Terminals classified as those of autonomic efferent axons were much more numerous in the nerves than any other type of terminal. Examination of 5-hydroxydopamine-incubated specimens showed that less than half of these terminals were terminals of adrenergic axons. Terminals of the type considered to represent those of purinergic axons were present in much smaller numbers in the nerves than in the nerves of the submucous plexus, and the presence in the nerves of terminals with features similar to those of mechanosensitive axons was related to physiological evidence of the presence of stretch receptors in the muscle.