Sex and estrous cycle influence diazepam effects on anxiety and memory: Possible role of progesterone.

Studies with rodents and humans show the relationship between female sex hormones and cognitive/emotional tasks. However, despite the greater incidence of anxiety disorders in women, the data are still inconclusive regarding the mechanisms related to this phenomenon. We evaluated the effects of a classical anxiolytic/amnestic drug (diazepam; DZP) on female (at different estrous cycle phases) and male rats tested in the plus-maze discriminative avoidance task (PMDAT), that allows the concomitant evaluation of memory and anxiety-like behavior. Further, in order to investigate the role of progesterone and its metabolites in the effects of DZP in the PMDAT, female rats were pre-treated with the progesterone receptor antagonist mifepristone or the 5-alpha-reductase inhibitor finasteride. The main findings were: (1) DZP caused memory impairment and anxiolysis in both sexes, but only the highest dose induced the anxiolytic effect in females; (2) females in proestrus did not present the amnestic and anxiolytic effects of DZP (at 2.0 and 4.0mg/kg, respectively) and (3) the co-administration of mifepristone reestablished both amnestic and anxiolytic effects of DZP, while finasteride reinstated the amnestic effect in proestrus female rats. These results suggest that changes in the endogenous levels of progesterone and its metabolites are important in the modulation of emotional/cognitive behavior in female rats. Based on the influence on different aspects of DZP action, the mechanisms related to this modulation are probably linked to GABAergic transmission, but this point remains to be investigated. Further, the variation in therapeutic and adverse effects of DZP depending on sex and hormonal state is of great relevance considering the higher prevalence of anxiety disorders in women.

Estrogen levels modify scopolamine-induced amnesia in gonadally intact rats.

Previous studies suggested that estrogen plays a role in cognitive function by modulating the cholinergic transmission. However, most of the studies dealing with this subject have been conducted using ovariectomized rats. In the present study we evaluated the effects of physiological and supra-physiological variation of estrogen levels on scopolamine-induced amnesia in gonadally intact female rats. We used the plus-maze discriminative avoidance task (PMDAT) in order to evaluate anxiety levels and motor activity concomitantly to the memory performance. In experiment 1, female Wistar rats in each estrous cycle phase received scopolamine (1 mg/kg) or saline i.p. 20 min before the training session in the PMDAT. In experiment 2, rats in diestrus received estradiol valerate (1 mg/kg) or sesame oil i.m., and scopolamine (1 mg/kg) or saline i.p., 45 min and 20 min before the training, respectively. In experiment 3, rats in diestrus received scopolamine (1 mg/kg) or saline i.p. 20 min before the training, and estradiol valerate (1 mg/kg) or sesame oil i.m. immediately after the training session. In all experiments, a test session was performed 24 h later. The main results showed that: (1) scopolamine impaired retrieval and induced anxiolytic and hyperlocomotor effects in all experiments; (2) this cholinergic antagonist impaired acquisition only in animals in diestrus; (3) acute administration of estradiol valerate prevented the learning impairment induced by scopolamine and (4) interfered with memory consolidation process. The results suggest that endogenous variations in estrogen levels across the estrous cycle modulate some aspects of memory mediated by the cholinergic system. Indeed, specifically in diestrus, a stage with low estrogen levels, the impairment produced by scopolamine on the acquisition was counteracted by exogenous administration of the hormone, whereas the posttraining treatment potentiated the negative effects of scopolamine during the consolidation phase of memory.