Influence of prepartum chronic ultramild stress on maternal pup care behavior in mice

Background: Stress administered to pregnant rodents has been shown to lead to biological and behavioral alterations in both mother and pups. Most of these stress procedures use noxious stressors. Chronicity is obtained by simple repetition of one or two stressors and may be more representative of moderate daily stress experienced during normal life than stress during severe life events. The effects of this procedure were assessed by observing maternal pup-care behavior and testing maternal aggression. Methods: The subjects included eight controls and eight stressed B6D2F1 females. Chronic ultramild stress was applied from mating to postpartum day (PD) 0. Pup-care behavior was observed on PD 1. Maternal aggression against a male intruder was tested on PD 8, which corresponds to the peak in the display of this behavior. Results: Prenatal stress did not affect basic pup-care behavior, but dramatically impaired defense behavior designed to protect the pups from an external attacker. Conclusions: The results suggest that gestating females subjected to chronic ultramild stress suffer from a long-lasting decline in recognition of external distress cues either from a resident intruder and/or their own litter. It is assumed these effects are due to the chronicity of the stress rather than its severity.