Abstract
Social stimuli during the neonatal and juvenile periods are known to affect various aspects of physiological and behavioral development in rodents. For example, maternal behavior and partner preference in the adulthood are determined by the social environments in which the animals are reared. These phenomena are so called "non-genomic transmissions". In this study, we investigated the long-lasting influences of earlier weaning on adulthood behavioral traits in rats and mice. Subjects were weaned from their mothers one week earlier than the normal weaning period. To assess anxiety levels at ages 8 weeks and 22 weeks, both early weaned and control mice pups were subjected to several behavioral tests, and it was found that the early-weaned animals had a sustained increase in anxiety levels compared to the control groups. Social behavioral tests performed in other sets of mice revealed that early weaned pups engaged in more fights under several conditions, including co-housing them with other mice, although neither isolation-induced aggression nor territorial aggression differed from normally weaned mice. In addition, early weaned females repressed maternal behavior. Similar results were obtained in rats as well. Concurrently, neurochemicals that are responsible for the behavioral and endocrine responses to stress were affected by the early weaning manipulations. These results suggest that the absence of mother-pup interactions during the last several days of pre-weaning period may lead to a persistent increase in anxiety and aggression during adulthood in rodents. [J Physiol Sci. 2006;56 Suppl:S61]
