Neuropeptide Y phase shifts circadian rhythms in vivo via a Y₂ receptor

Neuropeptide Y (NPY) injected into the suprachiasmatic region 6 h before the onset of locomotor activity produces phase advances in circadian rhythms. The present study investigated whether the phase advances produced by NPY in Syrian hamsters are mediated by a Y₁- or Y₂-like NPY(3-36), following their injection into the suprachiasmatic region. Microinjection of the Y₂ agonist produced phase advances that were significantly greater than those produced by the microinjection of the Y₁ agonist. These data support the hypothesis that the phase advancing effects of NPY in the suprachiasmatic region are mediated by a Y₂-like NPY receptor, similar to results found in vitro.