Maternal condition reduces fear behaviors but not the endocrine response to an emotional threat in virgin female rats

Lactating dams and maternal virgin females are less fearful in behavioral tests compared with non-maternal animals, suggesting that maternal condition per se reduces the negative value of threatening stimuli. In addition, lactating females exhibit a diminished hypothalamic-pituitary-adrenal response to potential environmental threats. Can the maternal condition, independently of the endocrine profile of lactation, promote a reduction in the behavioral as well as in the endocrine response to an emotional stressor? To answer this question, anxiety-related and fear behaviors as well as the levels of corticosterone were evaluated in response to a bright-lit open field-loud noise model in maternal and non-maternal non-ovariectomized virgin females and lactating dams in the presence of the pups. Maternal animals, both lactating and virgin, presented an increased exploration of the bright-lit open field and a significant reduction of fear behaviors, indicated by the decreased flight and immobility responses to the subsequent activation of a loud noise, in comparison to non-maternal virgins. Interestingly, maternal virgin females, as non-maternal rats, showed high corticosterone plasma levels, in contrast to the lower endocrine response exhibited by lactating dams when confronted to this threat. Present results suggest that maternal condition allows females to take risks when caring for their young, a behavioral strategy that is independent of the reduced hypothalamic-pituitary-adrenal axis response characteristic of lactation. This evidence points towards a clear dissociation in the mechanisms regulating behavioral and endocrine responses to emotional stressors during motherhood. (c) 2007 Elsevier Inc. All rights reserved.