Effect of behavioural feedback on circadian clocks of the nocturnal field mouse Mus booduga

Abstract

The effect of 'novel running wheels' on circadian clocks of the nocturnal field mouse Mus booduga was investigated during free-running and entrained conditions. In order to find out whether daily access to novel running wheels can entrain the locomotor activity rhythms experimental animals (n = 6) were provided with 'novel running wheels' at a fixed time of the day. The control animals (n = 5) were handled similar to the experimental animals but were not given access to novel running wheels. The results show that daily access to novel running wheels entrained the free-running locomotor activity rhythm of these mice. The post-entrainment free-running period (τ) of the experimental animals was significantly shorter than the pre-entrainment τ, whereas the pre- and post-treatment τ of the control animals did not differ significantly. In separate set of experiments, the effect of access to novel running wheels on the rate of re-entrainment was studied after a 6 h phase advance/delay in 24 h (12:12 h) light/dark (LD) cycles. Experimental animals were given access to novel running wheels for 3-h, 1 h after the 'lights-off' only on the first day of the 'new LD cycles'. Experimental animals took fewer cycles to re-entrain to 6-h phase advanced LD cycles compared to the control animals. After a phase delay in the LD cycles by 6h, the experimental animals took more number of cycles to re-entrain compared to the control animals. These results thus suggest that access to novel running wheel can act as a Zeitgeber for the circadian clocks of the nocturnal mouse M. booduga, and can also modify the rates of re-entrainment to phase shifted LD cycles, in a time-dependent manner.