Immunohistochemical study of neuropeptides in vagal and glossopharyngeal afferent neurons in the rat.

The presence and distribution of multiple neuropeptides in vagal and glossopharyngeal afferent ganglia of the rat were studied using immunohistochemistry. Substance P-, calcitonin-gene related peptide-, cholecystokinin-, neurokinin A-, vasoactive intestinal polypeptide-, and somatostatin-immunoreactive neurons were detected in each visceral afferent ganglion. Neurotensin-immunoreactive cells were not observed. In the nodose ganglion (inferior ganglion of the vagus nerve) occasional immunoreactive cells were scattered throughout the main (caudal) portion of the ganglion with small clusters of cells seen in the rostral portion. The pattern of distribution of the various peptides in the nodose ganglion was similar, with the exception of vasoactive intestinal polypeptide-immunoreactive neurons which exhibited a more caudal distribution. The relative numbers of immunoreactive cells varied, with the greatest numbers being immunoreactive for substance P or vasoactive intestinal polypeptide, and the lowest numbers being immunoreactive for neurokinin A and somatostatin. A build-up of immunoreactivity for each of the peptides, except somatostatin and neurotensin, was detected in vagal nerve fibers of colchicine-injected ganglia. Numerous peptide-immunoreactive cells were also found in the petrosal (inferior ganglion of the glossopharyngeal nerve) and jugular (superior ganglion of the vagus nerve) ganglia. No specific intraganglionic distribution was noted although the relative numbers of cells which were immunoreactive for the different peptides varied considerably. Substance P and calcitonin-gene related peptide were found in large numbers of cells, cholecystokinin was seen in moderate numbers of cells, and neurokinin A, vasoactive intestinal polypeptide and somatostatin were seen in fewer cells. These data provide evidence for the presence and non-uniform distribution of multiple peptide neurotransmitters in vagal and glossopharyngeal afferent neurons. In general, relatively greater numbers of immunoreactive cells were located in the rostral compared with caudal nodose ganglion, and in the petrosal and jugular ganglia compared with the nodose ganglion. Thus, multiple neuropeptides may be involved as afferent neurotransmitters in the reflexes mediated by vagal and glossopharyngeal sensory nerves.