Effects of Dim Phase Light Intensity Modulation on Circadian Rhythms in Syrian Hamsters.

Abstract

Nonphotic stimulation induces arousal in animals and resets circadian clocks. It is known that maximal phase advances in circadian locomotor activity in Mesocricetus auratus are produced by stimuli at Zeitgeber time (ZT) 4.5. Previous studies have shown that dim illumination during the activity phase (BD) produces larger phase shifts than complete darkness during the activity phase (LD) when animals are subsequently transferred to complete darkness during the middle of the light phase (ZT 4.5). The purpose of this study is to examine whether level of dim illumination during the activity phase modulates nonphotic phase shifts and other circadian related behaviors such as overall activity levels and the time of nightly activity onset relative to the time of bright-to-dim transition.