EFFECTS OF POSTOPERATIVE HOUSING CONDITIONS ON FUNCTIONAL RECOVERY INRATS WITH LESIONS OF THE HIPPOCAMPUS, SUBICULUM, OR ENTORHINAL CORTEX

In order to study the effects of differential housing conditions on re covery from damage to different components of the hippocampal formatio n, 85 rats received bilateral lesions of the hippocampus, entorhinal c ortex, or subiculum or sham surgery and then were housed for 30 days i n 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 a nd reference memory in the Morris water maze, and learning in the Hebb -Williams maze. Rats with the hippocampus removed showed impairments i n most of the tasks we used (home-cage and novelty-induced locomotor a ctivity, water maze, and Hebb-Williams maze). Most of the deficits ind uced by lesions to the entorhinal cortex were similar to those induced by the removal of the hippocampus. Some differences appear to be amon g the deficits induced by the lesions of these structures when assessi ng the home-cage locomotor activity, the reactions to novelty, and one aspect of the Hebb-Williams maze learning. Lesions to the subiculum i nduced only an impairment in the probe trial of the water-maze task. C onfirming and extending previous findings in rats with various (but no nexcitotoxic) 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 fr om having been housed in the enriched environment. However, their faci litated recovery was not observed in all tasks. After damage to differ ent components of the hippocampal formation, the beneficial effects in duced by the enriched housing conditions were shown to be both lesion- locus- and task-dependent. (C) 1997 Academic Press.