Neuropeptide participation in canine laryngeal sensory innervation. Immunohistochemistry and retrograde labeling

We investigated the quantitative participation of calcitonin gene-related peptide (CGRP), substance P (SP), and leu-enkephalin (ENK) in canine laryngeal sensory innervation by immunohistochemistry in combination with retrograde labeling using the recently introduced retrograde tracer cholera toxin subunit B-conjugated gold (CTBG). In the nodose ganglion, neurons labeled from the internal branch of the superior laryngeal nerve with CTBG were investigated immunohistochemically by means of antisera against CGRP, SP, and ENK. The percentages of neurons immunoreactive to each neuropeptide were as follows: CGRP 81.5%, SP 24.5%, and ENK 7.0%. These results suggest that CGRP is the main sensory neurotransmitter in canine laryngeal sensory innervation.