Enhanced photic phase shifting after treatment with antiserum to neuropeptide Y

Previous work has shown that antiserum to neuropeptide Y blocks phase shifts to certain non-photic stimuli at circadian time 4. To examine the role of NPY in photic phase shifts, antiserum to neuropeptide Y was administered just prior to a light pulse at circadian time 18. Hamsters were implanted with guide cannulae aimed at the suprachiasmatic nucleus, and housed in constant darkness. Animals were injected at circadian time 18 under a dim red safe light with 200 nl of either antiserum to neuropeptide Y or normal serum. They were then either exposed to light (approximately 100 lux) for 15 min or returned to constant darkness. Hamsters shifted more to the light pulse when pretreated with antiserum to neuropeptide Y (mean normal serum + light = 1.18 h: mean antiserum to neuropeptide Y + light = 1.92 h; P < 0.01 on a two-tailed paired t-test). Therefore, antiserum to neuropeptide Y enhanced photic advances at circadian time 18.