Expression and distribution of galanin receptor subtypes in the rat carotid body.

Galanin is a 29 amino acid neuropeptide that is widely distributed in the nervous system and acts by binding to three G protein-coupled receptors (GalR1, GalR2 and GalR3). In the literature, the presence of galanin has been reported in nerve fibers innervating the rat carotid body; however, direct evidence of the different galanin receptor subtypes expressed in carotid body cells has yet to be provided. In the present study, we investigated the presence and location of the three galanin receptor subtypes in 12 rat carotid bodies through real-time polymerase chain reaction (PCR) and immunohistochemistry. Real-time PCR identified GalR1 and GalR2 mRNA, with GalR2 gene expression being 100 times higher than that of the GalR1 gene. GalR3 mRNA was not detected. Statistically significant differences were not observed between the mean number of GalR1- and GalR2-positive type I cells (40.5±15.5 vs. 37.1±13.2%). Anti-GalR3 immunohistochemistry did not identify positive cells in the carotid body. Type II cells were negative for the three galanin receptor subtypes. Our findings suggest that galanin may play a neuromodulator or trophic role in type I cells by binding to GalR1 and GalR2.