The role of endogenous fluctuations of estrogen on working and reference memory across the estrous cycle of female rat

The results of many studies conducted over the past two decades suggest a role for estrogen in mammals'ability to learn and remember. In the present paper we analyzed the influence that the endogenous fluctuation of estrogen, naturally present across the different phases of the estrous cycle of female rats, can exert over the performance of tasks utilized to asses memory. In particular, we analyzed the performances in an eight arm radial maze task, dependent upon working memory, and in a water maze task, dependent upon spatial reference memory. The WM is aversively motivated by the desire to escape onto a safe platform, whereas the RAM is motivated by food reward. The difference in reinforcement may affect the speed of learning, the strategy adopted and the necessity for accurate navigation. Therefore, coherent results obtained through the two different tasks can be due to mnemonic factors. The study was conducted during a long period of time, 14 months, utilizing gonadally intact females, without pharmacological and surgical treatments. In order to evaluate the post-acquisition phase we first trained the animals to reach the criterion in performing tasks, and then we submitted them to experimental phase. Our results show that estrogen can have an effect on memory processes, and that this effect may be different in relation to different kinds of memory. In fact, in our study, estrogen selectively improved working memory, but not reference memory, during post-acquisition performance of a radial maze task with four baited and four un-baited arms. Moreover, water maze performances showed that estrogen has a negative effect on spatial reference memory.