Brief daily postpartum separations from the litter alter dam response to psychostimulants and to stress.

Early separation also changes the mother’s later responses

Experiments involving brief separation of newborn rats from their mothers usually focus on the offspring. This study reversed the viewpoint and asked whether the same repeated separations had lasting effects on the mothers themselves.

Following mothers beyond the separation period. One group of litters was removed from the mother for ten minutes a day during the first ten days after birth; another was left undisturbed. After weaning, the researchers assessed the mothers’ sweet-food intake, behavior in a forced-swim test and movement after a psychostimulant. They later measured leptin, a hormone related to energy stores, and corticosterone, the main stress hormone in rats, after an acute restraint challenge.

Some responses changed while others did not. Previously separated mothers showed a greater movement response to the stimulant diethylpropion and released more corticosterone after restraint. Sweet-food intake, forced-swim behavior and baseline leptin did not differ between groups.

The stronger stimulant response is consistent with increased sensitivity in systems influenced by dopamine, although it is an indirect behavioral measure. The hormone result indicates an altered response to a later stressor, persisting after the original period of separation had ended.

The study shows that an intervention in the mother–offspring relationship can affect both participants. That matters when interpreting neonatal experiments: an apparent effect of handling on pups can occur within a relationship in which the mother’s behavior and physiology are also changing. The findings provide a reason to study that relationship over time, rather than treating the maternal environment as a fixed background.