CLONING, PHARMACOLOGICAL CHARACTERIZATION, AND ANATOMICAL DISTRIBUTION OF A RAT CDNA-ENCODING FOR A GALANIN RECEPTOR

We have cloned and expressed a rat cDNA, designated GALR1-rat that encodes a galanin receptor based on homology, pharmacology, and anatomical criteria. This cDNA was isolated from a rat brain cDNA library. The nucleotide sequence of the cloned receptor revealed an open reading frame encoding a 346-amino-acid protein, showing 90.8% identity with the previously cloned human galanin receptor. Membranes prepared from COS cells transiently expressing GALR1-rat specifically bind I-125-galanin with high affinity (K-d = 0.12 +/- 0.01 nM). Rat, porcine, and human galanin were able to displace I-125-galanin with nanomolar Ki (0.08 +/- 0.03, 0.10 +/- 0.01, and 0.14 +/- 0.03 nM, respectively), whereas the Ki values for the porcine galanin fragments galanin-(1-16), galanin-(2-29), and galanin-(3-29) were 0.95 +/- 0.21 nM, 7.14 +/- 0.51 nM, and >1 mu M, respectively. The rank order potency of these ligands is consistent with that reported for the native galanin receptor. The distribution of the mRNA corresponding to Me galanin receptor encoded by GALR1-rat was determined by in situ hybridization to rat brain sections. High levels of galanin receptor mRNA were detected in the ventral hippocampal formation, thalamic, amygdala, and medulla oblongata nuclei, and in the dorsal horn of the spinal cord.