Stress and sex effects on associative learning: For better or for worse

It is clear that male and female animals have distinct cognitive capacities and emotional responses. For instance, exposure to a fearful and stressful event of restraint and intermittent tail-shocks impairs instrumental learning in male rats, but has minimal consequence in female rats. Conversely, exposure to a similar stressor facilitates classical conditioning in male rats and dramatically impairs conditioning in female rats. Many such sex differences in learning and responses to stress are attributable to the effects of sex hormones on brain morphology and physiology. indeed, the stress-induced facilitation of classical conditioning in male rats is dependent on activation of the NMDA type of glutamate receptor in the amygdala, whereas the impaired conditioning in female rats is dependent on activational influences of the ovarian hormone estrogen. The role of estrogen and progesterone in the diametrically opposed effects of stress on learning are discussed, as are neuronal mechanisms that underlie sex differences in memory formation.