Periodic postpartum separation from the offspring results in long-lasting changes in anxiety-related behaviors and sensitivity to morphine in Long-Evans mother rats

According to recent studies daily, 3-h separations from the dam on postnatal days 2-14 produce long-lasting changes in responses to stressors and sensitivity to morphine in Long-Evans offspring. It has not been investigated whether daily dam-litter separations can have long-lasting effects also on the mother beyond weaning of the pups. We tested whether dams that were separated from their litter for 3 h daily (LS) on postpartum days 2-14, like their offspring, exhibit altered anxiety-like behaviors and sensitivity to morphine, compared to dams that experienced only brief (15-min) separations (BS) from the litter or that were left undisturbed (NH) during the same period. Four to six weeks after weaning, subjects were tested on the elevated plus-maze, in a novel locomotor activity arena, or were exposed to loud auditory stimuli. Sensitivity to morphine was assessed using hot-plate and tail-flick tests. LS dams spent significantly more time in the open arms of the plus-maze and in the center of the locomotor activity arena, and were more likely to emit ultrasonic vocalizations in response to auditory startle stimuli compared to NH dams. Furthermore, LS dams were less sensitive to morphine, primarily in the tail-flick test. Dams that experienced brief litter separations (BS), like LS dams, exhibited altered performance on the plus-maze and elevated ultrasonic vocalizations. However, BS dams were similar to NH controls in locomotor activity and sensitivity to morphine. Multiple postpartum separations from the offspring alter the behavior of Long-Evans dams in novel/aversive environments and affect their sensitivity to the antinociceptive effects of morphine.