Presence of calcitonin gene-related peptide in intraepithelial nerve fibers and motor end-plates of the cat esophagus: a light and electron microscopic study.

The morphology and distribution of the motor end-plates in the striated muscle and the terminal nerve fibers in the epithelium of the wall of the esophagus, which contain calcitonin gene-related peptide, were studied by light and electron microscopic immunocytochemistry, Varicose immunoreactive nerve fibers arising from the subepithelial plexus were seen to penetrate into the epithelium where they ended in terminal boutons. These nerve fibers lost their Schwann cells just at the point of penetration into the epithelium. Characteristically, the epithelial cells of the spinous layer showed prominent tonofilaments in the part of the cytoplasm in contact with the immunoreactive nerve varicosities, but membrane specializations between these structures were not observed. In the striated muscle of the esophageal wall there were small, elliptical, immunoreactive motor end-plates, which contained a small number of axonal clear vesicles and mitochondria. They were associated with relatively short and rarely branched junctional folds, reduced postjunctional surfaces and few organelles in the underlying sarcoplasm, features characteristic of the neuromuscular junctions of slow-fatiguing red muscle fibers. The two types of immunoreactive nerve endings, epithelial and muscular, presumably participate in afferent and efferent limbs respectively of the neural control of esophageal motility. The relationship between immunoreactive nerve terminals and epithelial cells in the spinous layer exhibiting prominent tonofilaments allowed us to speculate about the existence of two different patterns of reception to sensory stimuli. The intraepithelial fibers that end in the middle layer of the epithelium could be related to mechanoreceptor reflexes, while those that end in the upper layer may be related to thermoreceptor reflexes or facilitate information about the chemical and other characteristics of foods.