EFFECTS OF UNILATERAL ENTORHINAL CORTEX LESION AND GANGLIOSIDE GM1 TREATMENT ON PERFORMANCE IN A NOVEL WATER MAZE TASK

Transient deficits have been reported after unilateral entorhinal cort ex (EC) lesion. To determine whether there is a more persistent defici t, adult male Sprague-Dawley rats with electrolytic or sham lesions of the left entorhinal cortex were examined on acquisition of a modified working memory task. in the Morris water maze. This delayed matching- to-sample task, with a 1-h intertrial interval, reveals a significant deficit in total distance to platform in both presentation (Trial 1) a nd matching (Trial 2) in the rats with entorhinal lesions. We have als o found that this test can be used to assess significant deficits in p erseveration (repeated nonproductive movement) in rats with entorhinal lesions. The deficits can be seen up to 16 days postinjury. Administr ation of ganglioside GM1 resulted in a moderate improvement in perform ance in both water maze measures analyzed. All groups (sham operated, lesion with saline treatment, and lesion with ganglioside GM1 treatmen t) were given three other tests, which were used to evaluate possible contributing factors to deficient water maze performance. A one-trial test for exploration of novel objects revealed no significant, simple working memory deficit in any group. Plus maze testing, to assess poss ible differences in levels of anxiety or increased activity as a compo nent of water maze performance, also revealed no differences in the th ree groups. All groups were also similar in motor activity, shown by m onitoring of activity levels. The worsened water maze performance obse rved in rats with EC lesion may be related to deficits in working memo ry ability within the framework. of acquisition of a more complex spat ial learning task. (C) 1995 Academic Press, Inc.