An enriched environment promotes synaptic plasticity and cognitive recovery after permanent middle cerebral artery occlusion in mice

Cerebral ischemia activates an endogenous repair program that induces plastic changes in neurons. In this study, we investigated the effects of environmental enrichment on spatial learning and memory as well as on synaptic remodeling in a mouse model of chronic cerebral ischemia, produced by subjecting adult male C57BL/6 mice to permanent left middle cerebral artery occlusion. Three days postoperatively, mice were randomly assigned to the environmental enrichment and standard housing groups. Mice in the standard housing group were housed and fed a standard diet. Mice in the environmental enrichment group were housed in a cage with various toys and fed a standard diet. Then, 28 days postoperatively, spatial learning and memory were tested using the Morris water maze. The expression levels of growth-associated protein 43, synaptophysin and postsynaptic density protein 95 in the hippocampus were analyzed by western blot assay. The number of synapses was evaluated by electron microscopy. In the water maze test, mice in the environmental enrichment group had a shorter escape latency, traveled markedly longer distances, spent more time in the correct quadrant (northeast zone), and had a higher frequency of crossings compared with the standard housing group. The expression levels of growth-associated protein 43, synaptophysin and postsynaptic density protein 95 were substantially upregulated in the hippocampus in the environmental enrichment group compared with the standard housing group. Furthermore, electron microscopy revealed that environmental enrichment increased the number of synapses in the hippocampal CA1 region. Collectively, these findings suggest that environmental enrichment ameliorates the spatial learning and memory impairment induced by permanent middle cerebral artery occlusion. Environmental enrichment in mice with cerebral ischemia likely promotes cognitive recovery by inducing plastic changes in synapses.