Neuropeptide Y does not reset the circadian clock in NPY Y2-/- mice.

Mammalian circadian rhythms are modulated by neuropeptide Y (NPY), a peptide contained in the projection from the intergeniculate leaflet to the suprachiasmatic nuclei of the circadian pacemaker. NPY resets the circadian clock during the subjective day, mediating non-photic inputs. Previous studies using receptor-selective agonists have indicated that this action of NPY is mediated by the Y2 receptor in hamsters. The present study determined if NPY applied to the suprachiasmatic nuclei in the mid-subjective day can phase-advance the rhythm of spontaneous firing rate of Y2-/- mice. We observed that NPY did reset the rhythm of control mice but did not significantly shift the phase of this rhythm in the Y2-/- mice. These results provide strong evidence for the role of the Y2 receptor mediating neuropeptide Y subjective day phase-advance shifts in mice.