|Budget Amount *help
¥3,300,000 (Direct Cost : ¥3,300,000)
Fiscal Year 1999 : ¥1,500,000 (Direct Cost : ¥1,500,000)
Fiscal Year 1998 : ¥1,800,000 (Direct Cost : ¥1,800,000)
CS strain, an inbred strain of mouse, show unique characteristics in the daily rhythms of behavior. The present study investigated the behavioral and molecular features of circadian rhythms of CS mice under continuous darkness condition (DD) in order to clarify the dual-oscillator model for circadian clock system in mammal. Following findings were obtained.
1. CS mice demonstrated two distinctive characteristics in the freerunning circadian rhythms of wheel running activity in DD. One of them is an unstable freerunning period (large inter-individual variation and large intra-individual variation). The other is a spontaneous rhythm splitting (an activity component of the rhythm separates into two different components). These features suggest that the CS mice have two different oscillators in the circadian clock system, and that the coupling relationship between the two oscillators in the CS mice might be weak.
2. Two activity components of split rhythm showed different phase-shift responses to brief light exposure (30 min) in DD. This result suggests that the two oscillators might have different phase-shift responses to light, and that the difference might regulate the photic entrainment of the clock.
3. The mRNA rhythms of three clock genes (mPer1, BMAL1, Clock) in the SCN and the cerebral cortex during the rhythm splitting in behavior were examined. The mRNA rhythms of these genes in the SCN were unimodal, while the behavioral rhythm was clearly bimodal (splitting pattern). However, the mPer1 mRNA rhythm in the cerebral cortex was bimodal in consistent with the behavioral rhythm. These results suggest that the rhythm splitting of CS mice might be unrelated to the clock genes in the SCN, rather related to the output pathway from the SCN main oscillator.