An evaluation of the effect of partial hippocampal kindling on place navigation by rats in the Morris water task

Abstract

We report the results of two experiments that examine the effects of partial kindling on acquisition and retention of place navigation in the Morris water task. Rats were implanted bilaterally in sub-field CA1 of the hippocampus with electrodes for electrical stimulation and EEG recording. Half of the rats in each experiment received 20 afterdischarges (ADs) on 4 consecutive days; the other half received low-frequency stimulation that did not induce ADs. The rats in the first experiment were trained beginning the day after the last AD to navigate to a platform hidden in a fixed location in the pool. No differences in performance were detected between groups. The rats in the second experiment had received extensive training before ADs with a hidden platform that changed its location within the pool between days. Beginning either 1 day, 1 week, or 1 month after the last AD, these rats were tested in the moving-platform task both in a new room and in the original training room. The rats receiving ADs performed significantly worse in both rooms than did control rats 1 day and 1 week, but not 1 month, after the last AD. These results extend the generality of earlier findings of impaired radial-arm maze performance after partial hippocampal kindling in rats and support the idea that some consequence of hippocampal ADs disrupts normal functioning of these networks in spatial learning.