Neuropeptide Y (NPY) is an important central and peripheral modulator of neural and endocrine functions. This neuropeptide interacts with at least two pharmacologically distinct receptors, termed Y1 and Y2. At Y1 receptors, the NPY analog [Leu31,Pro34] NPY, but not the carboxyl-terminal fragment NPY-(18-36), displaces radiolabeled NPY and the sequence-related peptide YY, whereas Y2 receptors exhibit the opposite selectivity. We have used cultured mammalian 293 cells for the high level transient expression of a previously cloned putative neuropeptide receptor of rat brain. We report that this receptor displays the ligand binding properties and selectivity of a Y1 receptor, with a single high affinity site for 125I-NPY (Kd, 0.7 +/- 0.2 nM). The functionality of the recombinantly expressed receptor was demonstrated by an inhibition of adenylyl cyclase and a concomitant mobilization of intracellular Ca2+.