Three days of novel wheel access diminishes light-induced phase delays in vivo with no effect on per1 induction by light

The mammalian circadian clock, located in the hypothalamic suprachiasmatic nuclei, synchronizes endogenous behavioral and physiological rhythms to a 24h period through responses to two types of stimuli: photic (light) and nonphotic (behaviorally induced arousal and/or increases in activity). Photic stimuli can block nonphotic effects and vice versa, although the mechanisms and levels of interactions between these two stimuli types are unknown. Here, we investigated whether 3 d of access to a novel running wheel alters the phase shift to light in vivo, and whether this effect could be seen on induction by light of the circadian gene per1. Through measurement of running wheel activity of golden hamsters, access to a new wheel for 3 d was shown to diminish photic phase delays with no effect on phase advances. As seen using in situ hybridization, however, there was no effect on levels of light-induced per1 mRNA. This study indicates a possible role for this paradigm as a model of interactions between photic and nonphotic stimuli.