Prepartal chronic stress increases anxiety and decreases aggression in lactating female mice.

The effects of two types of prepartal chronic stress on maternal behavior, anxiety, and maternal aggression during lactation were assessed in female outbred Swiss mice. Two groups (n = 18 each) were subjected to 10 consecutive daily sessions of restraint stress (RS) or novel environment stress (NES) from Day 4 to Day 14 of pregnancy. A third group (n = 18) was left undisturbed during pregnancy (controls, C group). All females underwent a maternal behavior test (10-min observation after separation and reunion with the pups) on Postpartum Day (PD) 1, an anxiety test (a light-dark conflict test) on PD 6, and a maternal aggression test (5-min exposure to an unfamiliar adult male) on PD 7. NES and RS groups tended to show higher amounts of maternal care. Anxiety increased in the stressed females compared with controls, whereas the opposite was true for maternal aggression. In the RS group, anxiety was negatively correlated with maternal aggression. These results suggest that chronic stress may have produced neuronal and endocrine alterations in the dams, which may have led to increased avoidance of aversive stimuli. The results also support the hypothesis that, in lactating mice, anxiety is inversely related to the probability of displaying intense forms of aggression.