Expression of galanin and the galanin receptor in rat taste buds.

Galanin, a 29-amino-acid neuropeptide, was initially isolated from porcine intestine. It has a wide spread distribution in the central nervous system and is also present in the primary sensory neuron. Galanin has been suggested to be involved in numerous neuronal and endocrine functions as a neurotransmitter and neuromodulator. We examined the expression of galanin and galanin receptors by using a reverse transcription-polymerase chain reaction (RT-PCR), immunohistochemistry, and in situ hybridization. RT-PCR analysis showed that mRNA of galanin and GalR2 were detected in the taste bud-containing epithelium of the circumvallate papilla of rats. Immunohistochemical analyses detected galanin was detected in a subset of taste bud cells of the circumvallate papillae. Double-label studies showed that galanin colocalized with alpha-gustducin, NCAM, and PLCbeta2. Our results of double staining with galanin and taste cell markers indicate that galanin-expressing taste cells are type II and type III cells. Taken together with previous studies, these findings show that galanin may function as a taste bud neurotransmitter. Furthermore, GalR2 mRNA was expressed in some taste bud cells. This suggests that, galanin release may not only excite the peripheral afferent nerve fiber but also may act on neighboring taste receptor cells via the activation of GalR2.