Effect of light intensity on the phase and period response curves in the nocturnal field mouse Mus booduga.

The effect of light intensity on the phase response curve (PRC) and the period response curve (tauRC) of the nocturnal field mouse Mus booduga was studied. PRCs and tauRCs were constructed by exposing animals free-running in constant darkness (DD), to fluorescent light pulses (LPs) of 100 lux and 1000 lux intensities for 15 min duration. The waveform of the PRCs and tauRCs evoked by high light intensity (1000 lux) stimuli was significantly different compared to those constructed using low light intensity (100 lux). Moreover, a weak but significant correlation was observed between phase shifts and period changes when light stimuli of 1000 lux intensity were used; however, the phase shifts and period changes in the 100lux PRC and tauRC were not correlated. This suggests that the intensity of light stimuli affects both phase and period responses in the locomotor activity rhythm of the nocturnal field mouse M. booduga. These results indicate that complex mechanisms are involved in entrainment of circadian clocks, even in nocturnal rodents, in which PRC, tauRC, and dose responses play a significant role.