Radial maze performance after hippocampal lesions: beneficial effects of nimodipine

Rats trained in an 8-arm radial maze were given electrolytic lesions of the dorsal hippocampus or sham operations. Within 24 h of surgery, approximately half of the rats in each groups began 14 daily oral treatments with the central calcium channel blocker, nimodipine. Retention testing began seven days after surgery. The untreated rats that received the larger hippocampal lesions did not relearn the maze within one month (2.5 times the preoperative mean number of days). The untreated rats that received the smaller lesions relearned within the allotted time but still showed clear deficits. Nimodipine improved the maze scores of the animals with the smaller lesions, but not those of the animals with the larger lesions. It was unclear whether nimodipine led to the sparing of more cells in the hippocampal region, or whether spared-but-affected cells were returning to normal modes of functioning more rapidly in the group with the smaller lesions. These findings suggest that spared hippocampus was mediating behavior, and extend previous findings from this laboratory showing that nimodipine can enhance recovery of function on higher cognitive tasks after hippocampal lesions.