Calcitonin gene-related peptide-immunoreactive nerves in the tongue, epiglottis and pharynx of the rat: occurrence, distribution and origin.

The occurrence, distribution and nature of calcitonin gene-related peptide (CGRP) in the tongue, epiglottis and pharynx of the rat was investigated by immunocytochemistry and radioimmunoassay. Numerous CGRP-containing nerves were found to innervate and terminate freely within the epithelium of the tongue, epiglottis and pharynx. Immunoreactive fibres were also found in the muscle layer and around blood vessels in the tongue, and in motor end plates in the muscle of the epiglottis and pharynx. Section of the trigeminal nerve induced a marked reduction in the number of immunoreactive nerves in the anterior portion of the tongue, whereas glossopharyngeal denervation results in a depletion of CGRP immunoreactivity in the posterior portion of the tongue. Immunoreactive nerves of the epiglottis and pharynx were depleted only after superior laryngeal nerve section. A subpopulation of labelled primary sensory neurones were observed in trigeminal and glossopharyngeal ganglia following injection of True blue retrograde tracer in the tongue. Most of the labelled cells were also immunoreactive for CGRP. Following systemic treatment with capsaicin, a loss of intra- and subepithelial CGRP-immunoreactive nerves was observed in all investigated tissues, while immunoreactive motor end plates remained unchanged.