Effect of the estrous cycle on conditioned avoidance in mice

In two experiments, degraded one-way shock avoidance was found to correlate with estrus in female mice. In the first experiment, mice were trained in one session, either in estrus or nonestrus, and were tested 3 weeks later in extinction, either in estrus or nonestrus. Those tested in estrus made fewer avoidance responses than those in nonestrus, regardless of the stage in which they had been originally trained. In a second experiment, mice which were overtrained in the task had longer response latencies during estrus than nonestrus in daily training sessions. These results are discussed in terms of the hypothesis that fear motivation is reduced in estrus.