Galanin-containing nerve terminals that are involved in a dual innervation of the striated muscles of the rat esophagus.

Galanin (GAL)-immunoreactive axon terminals on motor endplates of the esophageal striated muscles were demonstrated in mice, guinea-pigs and rats. The GAL-terminals innervated 33% of AChE-reactive motor endplates in mice and 6% of those in guinea-pigs. Double immunostaining revealed that separate GAL- and CGRP-positive terminals were localized within the same motor endplates in mice and rats. The GAL and CGRP terminals had different morphologies. No CGRP-immunoreactivity was found on motor endplates of the guinea-pig esophagus. Double immunostaining in rats showed that 68% of motor endplates with CGRP-nerve terminals were also supplied by GAL-nerve terminals, suggesting that the majority of esophageal striated muscles receive a dual innervation of GAL-and CGRP/ACh-containing terminals. By immuno-electronmicroscopy in the rat esophagus. GAL-immunoreaction was found in a small type of nerve terminals that possessed many large cored vesicles (90-130 nm) with intense immunoreaction. Larger GAL-negative nerve terminals with a cluster of small clear vesicle (40-50 nm), which seemed to be ACh-containing nerve terminals, were adjacent to a depression or slight protrusion of the sarcolemma and well-developed folds in the muscle fibers. At the motor endplates, the GAL-positive terminals made a synaptic contact via basement membrane with the sarcolemma of the muscle fibers, which was characterized by post-synaptic intense electron density. In most of all situations, in which the GAL-positive terminals and GAL-negative or -positive terminals were adjacent to each other and were also apposed to the striated muscles, the terminals were separated by attenuated sheet- or tongue-like cytoplasmic processes that appeared to originate from Schwann cells. Thus, the GAL-nerve terminals seem to provide a direct innervation of the striated muscle fibers rather than innervating the ACh-containing motor nerve terminals adjacent to the GAL-terminals.