NIMODIPINE ENHANCES NEW LEARNING AFTER HIPPOCAMPAL DAMAGE

Rats were trained to lever press and then were given either bilateral lesions of the hippocampus or control operations. Half of the rats in each group received oral nimodipine, a calcium entry blocker, while the remaining rats received vehicle, over a 14-day period that began the evening of surgery. The rats were studied on a DRL 20-s schedule of reinforcement (differential reinforcement of low rates of responding) that required them to withhold a response for at least 20 s after their last lever press in order to earn a reward. Rats with lesions that did not receive the drug performed poorly on the DRL 20-s schedule. In contrast, rats sustaining the same hippocampal lesions but given the drug showed scores that were virtually equivalent to those of the sham-operated control animals. Similar trends were observed when the rats were then tested on a DRL 40-s schedule of reinforcement. These findings suggest that nimodipine may attenuate the effects of acute, focal brain lesions on new learning of even difficult behavioral and cognitive tasks. © 1990 Academic Press, Inc. All rights reserved.