Early weaning induces anxiety and aggression in adult mice

Early environmental stimuli have been shown to affect many aspects of physiological and behavioral development in humans and other mammals. In this study, we investigated the effects of early weaning on behavioral traits in adulthood. Male and female Balb/c mice were divided into two groups, one weaned from the dam at 14 days of age (early-weaned group) and the other weaned at 21 days of age (normally weaned group), as a control. At 8 and 22 weeks of age, animals of both groups were subjected to the plus maze test to assess their anxiety levels. The early-weaned mice showed lower frequency of entry into the open arms of the maze. Although a subsequent isolation-induced aggression test revealed no clear differences between the two groups, when males from each of the two weaning groups were regrouped after 1 month of isolation, the early-weaned animals showed a great number of wounds on their tails and hindquarters. These results suggest that the deprivation of mother-pup interaction from 14 through 21 postnatal days augments anxiety and aggressiveness.