Figure 1: The estrous cycle in rodents is characterized by the fluctuation of reproductive hormones.  A) Estrous cycle stages are classified by the relative composition of different cell types within a vaginal smear. These vaginal smears correspond to elevated estradiol levels as measured by estradiol ELISA from blood serum. B) When tested on an object location memory task, mice who were stressed during their high estradiol stage (proestrus) had memory impairments. Conversely, those stressed during the low estradiol stage (estrus) had no impairments.