Developmental shifts in the behavioral phenotypes of inbred mice: the role of postnatal and juvenile social experiences.

The interaction between genotype and environment is an important feature of the process of development. We investigate this interaction by examining the influence of postnatal cross-fostering and post-weaning cross-housing on the behavioral development of 129S and B6 mice. Following cross-fostering, we found significant alterations in the frequency of maternal care as a function of maternal strain and pup type as well as interactions between these variables. In adulthood, we find there are sex-specific and strain-specific alterations in anxiety-like behavior as a function of rearing environment, with males exhibiting more pronounced rearing-induced effects. Mixed-strain housing of weanlings was found to lead to alterations in home-cage social and feeding behavior as well as changes in adult anxiety-like responses of 129S mice. Anxiety-like behavior in B6 mice was altered as a function of the interaction between housing condition and weaning weight. These data illustrate the complex pathways through which early and later social experiences may lead to variations in behavior.