Arousal by sexual stimuli accelerates the re-entrainment of hamsters to phase advanced light-dark cycles

Summary

The arousal caused by the 3 h presentation of female socio-sexual cues to male hamsters given an 8 h advance of the light-dark cycle caused an acceleration in the rate of re-entrainment to this new light-dark cycle. This accelerating effect was seen most clearly in animals allowed to run in their wheels in response to a nearby female hamster in estrous condition. However, wheel-running was not a necessary condition for enhancement. In one experiment, males with their wheels prevented from rotating also showed an accelerated rate of re-entrainment; in another experiment, the effect was almost significant (P=0.058). Mating itself seemed to counteract this accelerating effect. Males aroused by nearby but inaccessible estrous females re-entrained quicker than males allowed to mate with an estrous female. Lastly, male hamsters placed in a novel wheel but not allowed to run showed a variable rate of re-entrainment to an 8 h light-dark cycle advance; individuals judged to be sleeping during most of the 3 h in the novel wheel took longer to re-entrain than those judged to be awake during most of the 3 h. These results suggest that there is a general arousal mechanism through which non-specific, non-photic events can enhance the phase advancing actions of a lightentrainable clock.