Ghosts of mother's past: Previous maternal stress leads to altered maternal behavior following a subsequent pregnancy in rats

A rodent model was used to explore whether mothers that experienced a postnatal stressor in the past (i.e., daily separations from her previous litter) exhibited altered maternal behavior during a typical, subsequent rearing experience. Stress-naive female rats were bred and then separated from their pups (maternal separation) or remained with their pups (standard-rearing). After those pups were weaned, mothers were bred again with all pups from the subsequent litter being standard-reared. In the first week of life, various maternal behaviors directed towards these subsequent offspring were observed, including levels of nursing and pup retrieval. After weaning, mothers were tested for anxiety-like behavior, as well as memory on the object-recognition and object-placement tasks. The results show that previously stressed mothers retrieve their offspring significantly faster compared to mothers with no stress history, which may reflect a more overprotective mothering style. No other differences on maternal care were observed. Also, while previously stressed mothers were no more anxious than control mothers, they had impaired spatial memory on the object-placement task. This was not due to a general memory impairment as mothers performed equally on the object-recognition task, suggesting that previous maternal stress has specific effects on hippocampal-dependent tasks. That is, stress exerts lasting effects on types of behavior that are proposed to be beneficial to mothers and their offspring (i.e., efficient foraging and navigation abilities). Taken together, these results provide evidence that stress has specific and persistent effects on caregivers.