Effects of enriched postoperative housing conditions on spatial memory deficits in rats with selective lesions of either the hippocampus, subiculum or entorhinal cortex

Long-Evans male, adult rats received selective and bilateral lesions of eit her the hippocampus, subiculum or lateral entorhinal cortex, and were then housed for 30 days in either enriched or standard conditions. Rats were the n tested in the eight-arm radial maze to assess spatial working memory and the strategies that were employed (i.e. pattern of arms visited). Lesions o f the hippocampus induced both a working-memory impairment and a loss in th e use of allocentric strategies to perform the task. Rats with lesions of t he subiculum were also impaired but less than hippocampectomized rats and s howed a similar pattern of arm visits as control rats. In contrast with oth er lesioned rats, rats with lateral entorhinal cortex lesions performed the task like control rats. Postoperative enriched housing conditions (EHC) gl obally enhanced performance of rats, but did not affect the strategies sele cted by the rats to solve the task. The beneficial effect of EHC was partic ularly obvious in rats with lesions of the subiculum. In enriched rats with such lesions, performance was not significantly different from that of con trol rats housed in standard conditions. The present results indicate that 1) the structures within the hippocampal formation are not similarly involv ed in spatial learning and memory processes and in the management of naviga tional demands of the radial maze, and 2) enriched conditions may enhance t he spared spatial abilities of some lesioned rats thus promoting functional recovery.