Relationship Between Period and Phase Angle Differences in Mus booduga Under Abrupt Versus Gradual Light-Dark Transitions

摘要

Entrainment of the circadian rhythm of locomotor activity in the field mouse Mus booduga was studied un-der light-dark (LD) cycles in which the LD transitions were either abrupt (n=18) or gradual (n = 23), mimicking "dawn" and "dusk" transitions. The phase-angle-difference (ψ) in both types of LD treatments and the free-running period (τ) in continuous darkness (DD) were computed for each individual. It was observed that the τ and ψ of these animals in LD regime with gradual light to dark or dark to light (LD) transition were significantly correlated (r=-0.803; P < 0.001). On the other hand, τ and ψ of animals in LD regime with abrupt LD transitions did not show any significant correlation (r= 0.199; P = 0.43). The results of these experiments clearly indicate that a tight relationship between τ and ψ is exhibited in the regime with gradual LD transitions, whereas there is no such relationship in the regime with abrupt LD transitions. This difference may be due to stronger after-effects on τ of the LD regime with abrupt transitions as compared to the LD regime with gradual transitions.