Early weaning deprives mouse pups of maternal care and decreases their maternal behavior in adulthood.

Weaning is one of the most important events in the early stage of life, and recently we have found that precocious weaning augments anxiety and aggressiveness in mice. Maternal behavior has been reported to be transmitted from one generation to the next; that is, female pups that received intensive maternal care showed higher maternal behavior in their adulthood. In the present study, the following three experiments were conducted to understand maternal behavior transmission in early-weaned mice that were separated from the dam on postnatal day 14. First, the maternal behavior observed from the postpartum day 15 to 21, which was deprived in the early-weaned mice, were analyzed. Mothers spent 3% of their time on licking/grooming and arched-back nursing of their pups on postpartum day 15, and the time spent on these behaviors was gradually decreased until postpartum day 21; however, they spent 50% of their time attending to their pups through postpartum days 15-21. Simultaneously, the behavior of the pups was monitored, and it was found that the early-weaned mice had higher activity and lower resting behavior over the period from postnatal day 15 to 21. Secondly, the early- and normally weaned female mice were subjected to an elevated plus maze test at the age of 8 weeks to assess their anxiety level. The early-weaned mice showed a lower frequency of entering the open arms, and a shorter duration of time spent within them, as compared to the normally weaned mice, suggesting that early-weaned females had a higher anxiety level. In the third experiment, the two groups of female mice were paired with adult male mice for 2 weeks, and the mother's maternal behavior was analyzed. The early-weaned female mice showed lower frequency of licking/grooming and arched-back nursing of their pups as compared to the normally weaned mice, whereas the time of mother-off pups and attending to pups were not different between groups. These results suggest that early-weaning manipulation deprives offspring of a certain level of maternal care, and as a consequence, the offspring show higher anxiety levels and lower maternal behavior in their own adulthood.