Once a mother, always a mother: maternal experience protects females from the negative effects of stress on learning.

Women experience profound hormonal fluctuations throughout their reproductive lives. They are especially susceptible to disturbances in mood and cognition during the transition from pregnancy into postpartum and motherhood (Brummelte & Galea, 2010). Their behavioral and hormonal responses to stressful stimuli are also altered during this time. These changes are not limited to humans but occur in many mammalian species. Virgin female rats express a severe learning deficit in associative eyeblink conditioning after a stressful life event (Wood, Beylin, & Shors, 2001; Wood & Shors, 1998), but lactating females or those that are caring for young learn well even after the stressor (Leuner & Short, 2006). However, we do not know whether maternal experience persistently alters learning after a stressful event. Here we hypothesized that females that had been maternal at some time in their lives would learn well even after exposure to a stressful event. To test this hypothesis, females that had at least one brood of young and expressed a normal estrous cycle were exposed to an acute stressful event that reliably impairs learning in virgin females. Animals were trained 24 hr later with classical eyeblink conditioning. Exposure to the stressor suppressed learning in virgins but not in females that had been mothers at some time in their lives. These data suggest that maternal experience induces a protective mechanism in mothers, which promotes associative learning long after the offspring have left their care.