Suprachiasmatic circadian pacemaker of rat shows two windows of sensitivity to neuropeptide Y in vitro.

The geniculohypothalamic tract carries visual information from the intergeniculate leaflet to the suprachiasmatic circadian pacemaker. NPY, found in this projection, has been shown to affect the phase of behavioral rhythms and influence photic entrainment. We now demonstrate that NPY, when briefly applied to the geniculate projection sites of rat SCN in vitro, induces permanent phase-shifts in the rhythm of neuronal electrical activity at two separate phases of the circadian cycle.