S100B overexpression increases behavioral and neural plasticity in response to the social environment during adolescence.

Genetic variants as well as increased serum levels of the neurotrophic factor S100B are associated with different psychiatric disorders. However, elevated S100B levels are also related to a better therapeutic outcome in psychiatric patients. The functional role of elevated S100B in psychiatric disorders is still unclear. Hence, this study was designed in order to elucidate the differential effects of S100B overexpression in interaction with chronic social stress during adolescence on emotional behavior and adult neurogenesis. S100B transgenic and wild-type mice were housed either in socially stable or unstable environments during adolescence, between postnatal days 28 and 77. In adulthood, anxiety-related behavior in the open field, dark-light, and novelty-induced suppression of feeding test as well as survival of proliferating hippocampal progenitor cells were assessed. S100B transgenic mice revealed significantly reduced anxiety-related behavior in the open field compared to wild-types when reared in stable social conditions. In contrast, when transgenic mice grew up in unstable social conditions, their level of anxiety-related behavior was comparable to the levels of wild-type mice. In addition, S100B overexpressing mice from unstable housing conditions displayed higher numbers of surviving newborn cells in the adult hippocampus which developed into mature neurons. In conclusion, elevated S100B levels increase the susceptibility to environmental stimuli during adolescence resulting in more variable behavioral and neural phenotypes in adulthood. In humans, this increased plasticity might lead to both, enhanced risk for psychiatric disorders in negative environments and improved therapeutic outcome in positive environments.