Neuropeptide Y applied in vitro can block the phase shifts induced by light in vivo

The mammalian suprachiasmatic nuclei (SCN) can be synchronized by light. wi th direct glutamatergic input from the retina. Input to the SCN from the in tergeniculate leaflet contains neuropeptide Y (NPY) and can modulate photic responses. NPY can reduce the phase-resetting effect of light or glutamate . We investigated the effect of NPY applied in vitro on light-induced phase shifts of the SCN neural activity rhythm. Light pulses delivered in vivo i nduced phase shifts in brain slice preparations similar to those as measure d by behavioral activity rhythms. NPY applied after the light pulse blocked the phase shifts during both the early and late subjective night. NPY appl ied 30 min after the light pulse could block the phase delay induced by lig ht. Our results show that NPY can inhibit photic resetting of the clock dur ing the subjective night. The time course of this inhibitory effect suggest s a mechanism downstream of the glutamate receptor. NeuroReport 11:1587-159 1 (C) 2000 Lippincott Williams & Wilkins.