Long-term effects of postnatal manipulation on emotionality are prevented by maternal anxiolytic treatment in mice.

This study investigated the role of maternal behavior on the long-term effects of postnatal manipulation (15 min of daily separation from the dam and exposure to clean bedding from Day 1 to Day 14 of postnatal life) on emotionality in the mouse. Mothers were treated with an antianxiety agent (Chlordiazepoxide: 5 mg/kg), daily upon removal of the litter from the nest. Emotionality in adult offspring was tested in the elevated plus maze. Mice manipulated during postnatal development were more explorative and less anxious than unhandled mice, but this effect was not observable in the offspring of Chlordiazepoxide-treated dams. No effect of maternal Chlordiazepoxide was observed in unhandled offspring. The pharmacological treatment of the mother did not affect either pups' ultrasonic calling during separation, or maternal behavior far apart from the daily manipulation sessions. By contrast, Chlordiazepoxide-treated dams were less responsive toward pups upon reunion following daily separation. This alteration of dams' behavior was not related to alterations in the amount of ultrasonic calls emitted by pups during reunion. Finally, when dams were daily injected with Chlordiazepoxide far apart from pups' removal, the pharmacological treatment was devoid of effects. These results support the view that the mother-infant interaction which follows separation plays a major role in determining the effects of postnatal manipulations on adult emotionality.