Effects of excitotoxic lesions of the CA1 region of the hippocampus on acquisition of a place and cue water maze task.

The aim of the present study was to investigate the effects of excitotoxic lesions of the dorsal CA1 region of the hippocampus on acquisition of a place and cue water maze task. The ibotenic acid injections into CA1 produced removal of the pyramidal cells in CA1, while saving most of the pyramidal cells in CA3 and granule cells in DG intact. In conditions of visible platform training trials, differences in the platform reaching latency between the animals of different groups, were not found. When testing was performed in conditions of submerged platform, the latency of the platform finding was significantly increased (P<0.05). This fact certifies for deficit of the place learning strategy in the CA1-lesioned rats. Decreased place-bias in CA1-lesioned rats in hidden platform training trials compared to the sham-operated rats was significant, but in testing trials when required to choose between the spatial location they had learned and the visible platform in a new location majority of them swam first to the old spatial location. Decreased place-bias in CA1-lesioned rats compared to the sham-operated rats was not significant. We suggest that spatial learning deficits observed after dorsal hippocampal lesions cannot be accounted solely to the loss of dorsal hippocampal CA1 region cells.