NPY OPPOSES PACAP PHASE-SHIFTS VIA RECEPTORS DIFFERENT FROM THOSE INVOLVED IN NPY PHASE-SHIFTS

The suprachiasmatic nuclei (SCN) of the hamster can be maintained for several days in vitro, allowing electrophysiological investigation of the mammalian circadian clock. Application of pituitary adenylate cycl ase activating peptide (PACAP) at Zeitgeber time (ZT) 6 on the first d ay in vitro can phase shift the rhythm of firing rate expressed by SCN neurons on a subsequent day in vitro. Here we report that co-applicat ion of neuropeptide Y (NPY) will block the phase-shifting action of PA CAP. This blocking action is mimicked by [Leu(31),Pro(34)]NPY and [D-T rp(32)]NPY but not by NPY22-36 or avian pancreatic polypeptide. The re sults indicate that NPY has actions in the SCN via receptors distinct from the Y2 receptor, which mediates the phase-shifting action of NPY.