Less stimulating environmental conditions decrease spatial learning ability and reduce GAP-43 and synaptophysin immunostaining in the hippocampal formation in adult male mice

Environmental conditions affect learning ability and cause neuroanatomical alterations of neurons and synapses in the hippocampal formation. We reared male mice in standard, enriched and wheel-running environments (n = 7 in each group) as well as in an impoverished environment (n = 9) for 102 days and compared their spatial learning ability and histochemical expression of growth-associated phosphoprotein (GAP-43) and synaptophysin. Spatial learning ability, as measured by the Morris water maze, decreased significantly in the impoverished environment group and increased significantly in the enriched environment group. The optical density of GAP-43 immunostaining in the stratum lacunosum-moleculare and mossy fiber layer was significantly lower in the impoverished environment group than in the other 3 groups. GAP-43 immunostaining in the mossy fiber layer was significantly more intense in the enriched environment group. Synaptophysin immunostaining in the mossy fiber layer was significantly less intense in the impoverished environment group than in the enriched and wheel-running groups. These findings suggest that non-social and less stimulating environments can reduce spatial learning ability and impair function of the hippocampal formation.