Social enrichment affects and reverses changes of emotional state and HPA sensitivity induced by early postweaning social isolation

BIGGIO, FRANCESCA;Pisu MG;Garau A;BOERO, GIORGIA;Locci V;PIBIRI, VALERIA;Mostallino MC;Serra M.

2014-01-01

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Abstract

Adverse stress events during the adolescence period may have long-term effects on developing and emotional/behavioral state inducing deep, and sometimes irreversible, changes in the adulthood. It is well known that environmental enrichment has an heavy impact in the development brain networks as well as neuroendocrine system in the lifespan. Long-lasting stress experiences such as social isolation lead to profound neuronal and behavioral changes, increasing anxiety state, reduction in neurogenesis and dendritic arborization as well as an alteration of HPA axis function related to an abnormal hormones pattern fluctuation. We used a mild chronic stress model in rats in order to study the long-lasting effect of environmental enrichment in the future outcomes in the offspring previously socially isolated (SI). We evaluated the potential role of environmental conditions in rats deprived of social contact experience for long time (4-8 weeks) starting from weaning (21PND). Socially isolated rats usually show biochemical and behavioral alterations that persist into adult life if they live in this condition. Moreover, this kind of stress condition changes both hormones pattern and also the responsiveness to novel acute stress stimuli suggesting a greater HPA axis sensitivity. Environmental enrichment is able to revert some neuronal and behavior deficits switching the rearing social isolation. Here, we focused our attention on the effects of rat reintegration in group after 4 weeks of social isolation on different stress-related parameters such as anxiety, HPA hormones pattern and responsiveness to acute stress. We found that eight weeks of social isolation induced a decrease of plasmatic corticosterone and allopregnanolone content that in socially isolated-joined group (SI-J) were subsequently restored to levels observed in group housed animals. Similar effect was found in foot-shock-induced changes in corticosterone content and in several behavioral test such as Vogel, elevated plus maze and motility test. Our results further support that, in rats, the positive impact of environmental conditions reverts the plastic neuronal and behavioral responses to long-lasting stress.