MOLECULAR-CLONING, CHARACTERIZATION, AND LOCALIZATION OF A HIGH-AFFINITY SEROTONIN RECEPTOR (5-HT(7)) ACTIVATING CAMP FORMATION

By using a strategy based on nucleotide sequence homology, we have clo ned a cDNA encoding a functional serotonin (5-HT) receptor. The deduce d amino acid sequence of the 5-HT7 receptor displays limited homology with that of other 5-HT receptors. In addition to the seven stretches of hydrophobic amino acids that characterize the superfamily of recept ors interacting with guanine nucleotide-binding proteins, the 448-aa s equence of the 5-HT7 receptor contains a hydrophobic domain located at its N-terminal end. Genomic analysis indicated the presence of intron s interrupting the coding sequence. The 5-HT7 receptor, stably express ed in transfected CHO cells, bound [H-3]5-HT with high affinity (K(d) = 1 nM), like receptors of the 5-HT1 subfamily from which, however, it was clearly distinguished by its pharmacology. 5-HT in nanomolar conc entrations stimulated cAMP accumulation in these CHO cells by almost-e qual-to 10-fold, whereas lysergic acid diethylamide displayed low intr insic agonist activity. These various properties differentiate the 5-H T7 receptor from the four other subfamilies of mammalian 5-HT receptor s (i.e., the 5-HT1-, 5-HT2-, 5-HT3-, and 5-HT4-like subfamilies) and, therefore, appear to define another receptor subfamily. Northern blot and in situ hybridization analyses showed the 5-HT7 transcripts to be expressed in discrete areas of the limbic brain (e.g., pyramidal hippo campus cells, tenia tecta, amygdaloid, or mammillary nuclei), suggesti ng that the receptor mediates serotoninergic controls in functions lik e mood, learning, or neuroendocrine and vegetative behaviors.