Effect of post-training injections of flumazenil into the amygdala, hippocampus and septum on retention of habituation and of inhibitory avoidance in rats.

Adult rats were submitted to two different behavioral tasks using the same apparatus: the habituation of exploration of the apparatus considered as a novel environment as measured by the decrease in number of rearings and of ambulation between training and testing, and step-down inhibitory avoidance as measured by the increase in the latency to step down from a start platform onto an electrified grid between the training and the test session. The training-test interval for both tasks was 20 h. The immediate post-training injection of the benzodiazepine receptor antagonist flumazenil (10 nmol) bilaterally into the hippocampus enhanced retention of the two tasks. Application of the same drug, at the same dose to the septum or amygdala had no effect on habituation but enhanced retention of the avoidance task. The data are consistent with previous findings showing that both tasks are accompanied by the release of benzodiazepine-like immunoreactivity in the three structures and that this release is greater after the avoidance task. The present findings suggest a differential regional involvement of endogenous benzodiazepine-mediated mechanisms in memory modulation, according to the task undertaken.