Papel da neurogênese nos efeitos promnésicos do ambiente enriquecido sobre a memória social

Abstract

Social memory comprehends the information necessary to identify and recognize co-specifics. This kind of memory is essential in many forms of social interaction and is modulated by the environmental conditions. Previous studies from our laboratory showed that social isolation impairs the social memory persistence and that enriched environment (EE) prevents that deficit. Our working hypothesis is that the neurogenesis is the mechanism by wich EE exerts promnesic effects on social memory. To address this hypothesis we used behavioral tests to evaluate social memory, anxiety and olfaction; immunofluorescence to label BrdU/NeuN positive neurons and pharmacological blockade of neurogenesis through the administration of the anti-mitotic agent AraC. Our results showed that one week of social isolation impaired long-term social memory (S-LTM), but not social short-term memory or anxiety in SWISS mice. The EE prevented the S-LTM deficit and increased the neurogenesis in the dentate gyros (DG) of the hippocampus of social isolated mice, which partially confirm our hypothesis. Interestingly, the EE also increased the neurogenesis in the DG of group-housed mice, which probably allowed S-LTM to be more persistent and stable in those mice. We also analyzed the functionality and the neurogenesis in the olfactory bulb (OB). In the olfactory behavioral test, named buried-food finding test, the social isolated mice have a worse performance that was partially recover by the EE, though we did not find difference between groups in the neurogenesis. Interestingly, we observed more new neurons in the external granular layer of the OB in the grouped-house mice maintained in the EE. However, the EE did not change the performance of these mice in the olfactory behavioral test. The AraC decreased the cellular proliferation in both granular layers of the OB and also in the DG. Furthermore, AraC impaired S-LTM, but not the olfaction. Taken together, our results confirm our hypothesis that the EE prevents the S-LTM deifict of social isolated mice by increasing neurogenesis. In addition, we showed that the somatory of the EE and social stimulus increases neurogenesis in the DG and OB, and also improves the social memory persistence and stability. Finally, our results indicate that there are no direct relation between olfaction, at least measured in the buried food-finding test, and the neurogenesis in the OB, wich arouses the reassessment of the neurogenesis role on olfaction.