Estrous Cycles in the Mouse: Relative Influence of Continuous Light and the Presence of a Male1

Abstract

Individually housed female mice were exposed to a continuous light environment (LL), in the presence or absence of a male, in an attempt to assess the comparative influence of photoperiod and male pheromones in the control of the mouse estrous cycle. As expected, mice housed with males in LD (light/dark) 14:10 showed regular 4 day estrous cycles, while mice housed alone in this environment showed both 4 and 5 day cycles. Both groups of mice in LL showed a lengthening of their vaginal cycles, although in mice housed alone, the effect was more dramatic. Rats housed in the same chamber as the LL mice developed the state of anovulatory persistent vaginal estrus after 85 days. Only 4 of 16 mice developed anovulatory states after 120 days in constant light. There was little evidence, either direct or indirect, of increased rates of estradiol secretion in the LL mice, although the pattern of steroid secretion was markedly disrupted by comparison to LD animals. The presence of the male did not prevent this disruption of the steroid pattern in LL mice, although it did contribute a minor protective effect on cycle length. These results suggest that mouse cycles are comparatively more resistant than rat cycles to total disruption by constant light, in spite of the fact that their steroid patterns are altered.