Environmental enrichment promotes neurogenesis and changes the extracellular concentrations of glutamate and GABA in the hippocampus of aged rats.

The aim of the present study was to investigate the effects of environmental enrichment on the neurogenesis and the extracellular concentrations of glutamate and GABA in the hippocampus of freely moving young and aged rats. Male Wistar rats of 2 (young) and 25 (old) months of age were housed during 8 weeks in an enriched environment; control rats were kept in individual plastic cages during that same period of time. Rats were injected intraperitoneally with bromodeoxyuridine (BrdU; 40 mg/kg; 7 days) during the fourth week of the housing period to detect neurogenesis in the dentate gyrus (DG) of the hippocampus. Rats were sacrified 6 weeks after the last injection of BrdU. During the last week of housing, rats were tested in the water maze for the evaluation of spatial learning. After the housing period, rats were stereotaxically implanted with guide-cannulas to accommodate microdialysis probes in the CA3 area of the hippocampus and the extracellular concentrations of glutamate and GABA were determined. Aged rats showed a decrease in the number of BrdU positive cells in the dentate gyrus compared to young rats. However, neurogenesis in the dentate gyrus of both young and old rats was increased in animals housed in an enriched environment. Microdialysis experiments in the CA3 area of the hippocampus showed that enriched housing conditions increased basal extracellular concentrations of glutamate in aged rats. Perfusion of KCl 100 mM produced a higher increase of extracellular glutamate and GABA in aged rats but not in young rats housed in an enriched environment compared to control rats. These results suggest that enriched housing conditions change both neurogenesis in the dentate gyrus and glutamate and GABA levels in the CA3 area of the hippocampus of aged rats.