Social enrichment reverses the isolation-induced deficits of neuronal plasticity in the hippocampus of male rats

Environmental enrichment is known to improve brain plasticity and protect synaptic function from negative insults. In the present study we used the exposure to social enrichment to ameliorate the negative effect observed in post weaning isolated male rats in which neurotrophic factors, neurogenesis, neuronal dendritic trees and spines were altered markedly in the hippocampus. After the 4 weeks of post-weaning social isolation followed by 4 weeks of reunion, different neuronal growth markers as well as neuronal morphology were evaluated using different experimental approaches. Social enrichment restored the reduction of BDNF, NGF and Arc gene expression in the whole hippocampus of social isolated rats. This effect was paralleled by an increase in density and morphology of dendritic spines, as well as in neuronal tree arborisation in granule cells of the dentate gyrus. These changes were associated with a marked increase in neuronal proliferation and neurogenesis in the same hippocampal subregion that were reduced by social isolation stress. These results further suggest that the exposure to social enrichment, by abolishing the negative effect of social isolation stress on hippocampal plasticity, may improve neuronal resilience with a beneficial effect on cognitive function. •Social enrichment has a profound positive impact on recovery from long-lasting impairments induced by social isolation.•Resocialization restores the decrease in hippocampal neurotrophic factors observed in isolated rats.•Rearing in group after isolation enhances the hippocampal newly divided cell proliferation.•Reversal effect of resocialization on decrease of dendrites and spines morphology induced by social isolation.