Communal nesting, an early social enrichment, increases the adult anxiety-like response and shapes the role of social context in modulating the emotional behavior.

Early experiences affect brain function and behavior at adulthood. Being reared in a communal nest (CN), consisting in a single nest where three mothers keep their pups together and share care-giving behavior from birth to weaning (postnatal day 25), provides a highly stimulating social environment to the developing pup. CN characterizes the natural ecological niche of many rodent species including the mouse. Here we show that, at adulthood, compared to mice reared in standard laboratory conditions (SN), CN reared mice displayed increased anxiety-like behavior, performing more thigmotaxis in the open field and spending less time in the open arms of the plus-maze. Furthermore, we showed that social context (being alone or with a familiar conspecific in the test apparatus) affects the emotional response in both the plus-maze and open field test and that the relevance of social context changes according to the early social experiences. In particular, CN mice display higher levels of anxiety-like behavior, compared to SN mice, only when alone but not in the presence of a familiar conspecific. Overall, in line with previous findings, the present study suggests that CN mice have a more elaborate social and emotional behavior compared to SN mice and thus may be more appropriate to investigate socio-emotional impairments, in particular in the case of mouse models of neurodevelopmental disorders, such as autism, or anxiety and mood disorders.