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 enc odes a galanin receptor based on homology, pharmacology, and anatomica l criteria. This cDNA was isolated from a rat brain cDNA library. The nucleotide sequence of the cloned receptor revealed an open reading fr ame 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-galani n 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 t he 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, a nd >1 mu M, respectively. The rank order potency of these ligands is c onsistent with that reported for the native galanin receptor. The dist ribution of the mRNA corresponding to Me galanin receptor encoded by G ALR1-rat was determined by in situ hybridization to rat brain sections . High levels of galanin receptor mRNA were detected in the ventral hi ppocampal formation, thalamic, amygdala, and medulla oblongata nuclei, and in the dorsal horn of the spinal cord.