The richness of social stimuli shapes developmental trajectories: Are laboratory mouse pups impoverished?

The early environment is crucial for brain and behavior development. In particular, social experiences involving the mother and the peers are critical in shaping the adult individual. Though animal models of psychiatric disorders have widely investigated the relevance of the mother–offspring interaction, the peer interaction has so far been rarely studied. The communal nest (CN) is an innovative experimental strategy that favors a more comprehensive investigation of the long-term effects of both components. CN is a rearing condition employed by up to 90% of mouse females in naturalistic settings and consists of a single nest where two or more mothers keep their pups together and share care-giving. In a CN, the developing pup is exposed to high levels of both maternal care and interaction with peers. At adulthood, these mice display relevant changes in bran function and behavior, including high levels of neural plasticity markers, such as BDNF, and elaborate adult social competences. Overall, on the one hand, CN is an experimental approach complementary to the ones currently used that allows to investigate how the early environment determines developmental trajectories. On the other, it may represent a strategy to improve the study of animal models of psychiatric disorders characterized by social dysfunction, such as major depression, autism and attention deficit hyperactivity disorder. Indeed, the more elaborate social competences shown by these mice at adulthood may allow to better characterize deficits in the social domain induced by genetic and/or environmental manipulations.

Research Highlights
► In rodents, communal nest (CN) rearing is an early social enrichment.
► CN rearing markedly affects brain and behavior development.
► CN is a strategy to study how the early environment affects development.
► CN allows to investigate the effects of the interaction with the mother and peers.
► Improved social competences shown by CN mice are helpful to study social deficit.