Immunohistochemical localization of neuron-specific enolase and calcitonin gene-related peptide in rat taste papillae.

Calcitonin gene-related peptide-like and neuron-specific enolase-like immunoreactivity (CGRP-IR and NSE-IR) were surveyed immunohistochemically in the fungi-form, foliate and circumvallate papillae in rats. A dense CGRP-IR network (subgemmal and extragemmal) in the taste papillae is linked to the presence of taste buds, even though CGRP-IR fibers are rarely present in the taste buds. Three typical fiber populations were detected with these two markers. (a) A population of coarse NSE-IR intragemmal fibers characterized by thick neural swellings, never expressing CGRP-immunoreactivity. (b) A population of thin varicose intragemmal NSE/CGRP-IR fibers. (c) A population of subgemmal and extragemmal NSE-/CGRP-IR fibers that partly penetrated the epithelium. The common distribution of CGRP-IR and NSE-IR fibers at the base of taste buds, their differential distribution and morphology within taste buds, added to their restricted nature (gustatory or somatosensory) suggest that a population of CGRP-IR fibers undergoes a target-induced inhibition of its CGRP phenotype while entering the taste buds. The combined use of NSE and CGRP allowed a better characterization of nerve fibers within and between all three types of taste papillae. NSE was also a very good marker for a subtype of taste bud cells in the foliate and in the circumvallate papillae, but no such cells could be observed in the fungiform papillae.