Food intake, aggression, and fear behavior in the mother rat: control by neural systems concerned with milk ejection and maternal behavior.

Mother rats eat more, are more aggressive, and show less fear behavior (freezing) than during other stages of the reproductive cycle. Electrolytic lesions in the peripeduncular area of the lateral midbrain made nursing mother rats eat less and interact peacefully with male intruders. This midbrain area forms part of the ascending milk-ejection pathway, so it seems plausible that the suckling stimulus maintains hyperphagia and aggression in mother rats. Because no alteration in fear behavior was observed in mothers with lesions, it was predicted that the reduction in freezing was related primarily to maternal responsiveness to pup cues other than suckling. In line with this hypothesis, it was found that the experimental induction of maternal behavior in ovariectomized, hormone-treated females was associated with a significant decrease in fear behavior, with no concomitant changes in food intake or aggression.