Estrus-associated decrements in a water maze task are limited to acquisition

To ascertain whether gonadal hormones have activational influences on spatial ability, the relationship between estrous cycle, sex differences and water maze performance was examined in two studies. In the first study, the performance of females at different cycle phases was compared within females and to that of males. All animals were naive to the task. Similar to other studies, females had longer latencies and distances to reach the water maze platform than males. This sex difference was statistically significant only in comparisons of estrous females and males, not in comparisons of diestrous females and males. To determine whether estrus-associated decrements in acquisition of the water maze task extended to postacquisition performance, a second study assesessed performance of ovariectomized rats--trained to criterion in the task--whose cycle phases were mimicked by exogenous hormones. In the initial trial, "estrous" animals had longer latencies to reach the platform than "diestrous" and ovariectomized animals. In subsequent trials, no hormone-dependent differences in performance were observed. Taken together, the results indicate a modest association between phase of estrous cycle, acquisition, and postacquisition performance when the task is novel. These findings suggest estrus-associated decrements in acquisition may account for previous discrepancies among studies of sex differences in spatial ability.