EFFECTS OF CHRONIC NIMODIPINE TREATMENT ON THE RELEASE OF ACETYLCHOLINE FROM THE HIPPOCAMPUS OF CONSCIOUS RATS

A previous report indicated that chronic nimodipine treatment enhanced memory performance and increased in vivo release of acetylcholine (AC h) in the hippocampus of Fischer-344 rats. In the present investigatio n, the effects of nimodipine on hippocampal ACh release measured by in vivo microdialysis were determined in Fischer-344 and Long-Evans rats . Young male Fischer-344 rats were implanted with subcutaneous sustain ed-release pellets of nimodipine (20 mg) or placebo pellets. Young mal e Long-Evans rats were implanted with either 10 or 20 mg pellets of ni modipine or placebo pellets. Fourteen days following pellet implantati on, stereotaxic surgery was performed to place a guide cannula in the dorsal hippocampus. Microdialysis studies were conducted twenty-one da ys after pellet implantation and 7 days after guide cannula placement. Samples were collected over a 6.5-7 hr period. In Fischer-344 rats, n o effect of chronic nimodipine was found on hippocampal extracellular ACh levels. In Long-Evans rats, 20 mg nimodipine pellets significantly increased hippocampal extracellular ACh levels during the early phase (20 - 140 min) of microdialysis.