Effects of postoperative housing conditions on functional recovery in rats with lesions of the hippocampus, subiculum, or entorhinal cortex.

In order to study the effects of differential housing conditions on recovery from damage to different components of the hippocampal formation, 85 rats received bilateral lesions of the hippocampus, entorhinal cortex, or subiculum or sham surgery and then were housed for 30 days in either an enriched environment or an impoverished environment. Rats were subsequently tested on a battery of tasks for assessing locomotor activity in their home cage, reactivity to novelty, spatial working and reference memory in the Morris water maze, and learning in the Hebb-Williams maze. Rats with the hippocampus removed showed impairments in most of the tasks we used (home-cage and novelty-induced locomotor activity, water maze, and Hebb-Williams maze). Most of the deficits induced by lesions to the entorhinal cortex were similar to those induced by the removal of the hippocampus. Some differences appear to be among the deficits induced by the lesions of these structures when assessing the home-cage locomotor activity, the reactions to novelty, and one aspect of the Hebb-Williams maze learning. Lesions to the subiculum induced only an impairment in the probe trial of the water-maze task. Confirming and extending previous findings in rats with various (but nonexcitotoxic) lesions of the hippocampus, an enriched environment had a beneficial effect on several of the deficits observed in the tasks we used. Further, only the rats with hippocampal lesions benefitted from having been housed in the enriched environment. However, their facilitated recovery was not observed in all tasks. After damage to different components of the hippocampal formation, the beneficial effects induced by the enriched housing conditions were shown to be both lesion-locus- and task-dependent.