Circadian rhythms, endogenously generated by the suprachiasmatic nucleus (SCN), can be synchronized to a variety of photic and non-photic environmental stimuli. Neuropeptide Y (NPY) is produced in the intergeniculate leaflet (IGL) and known to mediate both photic and non-photic influences on the SCN. We recently found that npy-/- mice were slower to shift their locomotor activity onset to the new time of light offset when photoperiod was abruptly changed from light/dark (LD) cycle 18:6 to LD 6:18. In the present study, we measured the locomotor response of npy-/- mice to gradual changes in photoperiod (4 min a day) for 141 days (LD 16:8 changing to LD 8:16), mimicking external LD cycles in nature. When the photoperiod approached LD 8:16, npy-/- mice showed a significantly delayed onset of activity compared to wild-type mice. Activity patterns disintegrated into multiple bouts and intensity of activity decreased as the photoperiod changed and these changes were more pronounced in npy-/- mice. Our results lend further support to the idea that NPY is involved in circadian entrainment responses to seasonal photoperiod changes.
Circadian rhythm, Entrainment, Intergeniculate leaflet, Neuropeptide Y, Photoperiod
Kim, Hyun Jung and Harrington, Mary E., "Neuropeptide Y-Deficient Mice Show Altered Circadian Response to Simulated Natural Photoperiod" (2008). Psychology: Faculty Publications, Smith College, Northampton, MA.