Galanin receptor 1 is expressed in a subpopulation of glutamatergic interneurons in the dorsal horn of the rat spinal cord

The 29/30 amino acid neuropeptide galanin has been implicated in pain processing at the spinal level and local dorsal horn neurons expressing the Gal 1 receptor may play a critical role. In order to determine the transmitter identity of these neurons, we used immunohistochemistry and antibodies against the Gal 1 receptor and the three vesicular glutamate transporters (VGLUTs), as well as in situ hybridization, to explore a possible glutamatergic phenotype. Gal 1 protein, which could not be demonstrated in Gal 1 knockout mice, colocalized with VGLUT2 protein, but not with glutamate decarboxylase, in many nerve endings in lamina II. Moreover, Gal 1 and VGLUT2 transcripts were often found in the same cell bodies in laminae I–IV. Gal 1 ‐protein and galanin‐peptide showed an overlapping distribution but were not colocalized. Gal 1 staining did not appear to be affected by dorsal rhizotomy. Taken together, these findings provide strong evidence that Gal 1 is a heteroreceptor expressed on excitatory glutamatergic dorsal horn interneurons. Activation of such Gal 1 receptors may thus decrease the inhibitory tone in the superficial dorsal horn, and possibly cause antinociception. J. Comp. Neurol. 499:391–403, 2006. © 2006 Wiley‐Liss, Inc.