Challenging early life environments: Impact on behavioral inhibition and (pro-)social behavior in rats

Individuals that have experienced profound stress during childhood can develop deficits in behavioral inhibition and social behavior, two core features of several stress related psychiatric disorders. However, not all children who grew up in challenging environments carry on to develop psychopathology and the mechanism behind this is largely unknown. As part of a Dutch collaborative effort (NWO Consortium on Individual Development) to answer the question ‘Why some children thrive and others don’t’ the research described in this thesis aims to shed light on the factors that contribute to these individual differences. More specifically, I try to answer the question of how challenging early life environments impact behavioral inhibition and (pro-)social behavior. To this end, a rodent model, the rat, was used to study how early life stress, through 24h deprivation of maternal care on the third day after birth, affects adult behavior. I also tested two adolescent interventions to examine if potential negative effects of maternal deprivation could be normalized; i) pharmacological treatment with the GR-antagonist mifepristone and ii) complex housing, in which animals are reared in socially and physically enriched housing that provides a challenging and stimulating environment from early adolescence onwards. Taken together, I show that early life stress has a negative impact on behavioral inhibition and social behavior, but the effects are modest. Because of this, interpretation of results of the two tested interventions is difficult and further research is needed to draw more solid conclusions. Finally, the two final chapters describe two new behavioral tests aimed to study pro-social behavior in rats.