The effects of environmental enrichment and social isolation and their reversion on anxiety and fear conditioning.

Animal models of fear and anxiety provide important insight into anxiety-related symptoms in humans. Environmental physical conditions and social contact influence behavior and brain plasticity particularly at early developmental stages and have long lasting effects reaching even adulthood. The potential benefit that a later environmental enrichment may have on rats raised in isolation is however not fully understood. We aim to investigate the effects of housing conditions and their reversion on anxiety and fear-related behaviors in rats. In phase I, we compared the effects of different housing conditions (environmental enrichment, control and social isolation) on anxiety behaviors in the open field test, elevated plus maze and fear conditioning. We found stronger effects of housing on behavioral tests when induced at weaning (phase I), than later in development (phase II). After one month, EE rats showed lower anxiety related behaviors and more freezing in FC. In phase II, we evaluated the effects of the reversion of housing conditions on the same behavioral parameters. We observed a behavioral trend such that the groups started to behave similar to their new housing conditions in OFT mainly. These results suggest that housing conditions at weaning can have long-lasting effects on anxiety and fear-related behaviors. Because the behavioral changes observed after the housing reversal in adulthood were partial, we suggest that more time of social and physical enrichment could be necessary to promote major changes in behavior at this age.