EFFECTS OF CHRONIC CORTICOSTERONE INGESTION ON SPATIAL MEMORY PERFORMANCE AND HIPPOCAMPAL SEROTONERGIC FUNCTION

The effects of chronic ingestion of corticosterone (8 weeks via the dr inking water, 400 mug/ml) on spatial memory performance and on monoami ne levels in brain areas related to memory were investigated. Corticos terone treatment was associated with a long lasting (5 weeks post trea tment) increase in 5-HT levels (44%) in the dentate gyrus of the hippo campus and decrease in 5-HT (50%) and NE (36%) levels in the frontal c ortex. No effects were found in CAI, CA3 or in nucleus basalis. Perfor mance of the rats on an 8-arm radial arm maze showed no overall effect of corticosterone treatment on trials to criterion or choice accuracy scores. However, three of the treated rats, who had consumed the most corticosterone during treatment, 12.5 +/- 0.3 mg/day, were impaired r elative to all subjects. Thus, these results suggest that hippocampal serotonergic terminals show long lasting effects from corticosterone a nd may also be an early indicator of deleterious effects of glucocorti coids on hippocampal function. However, since only a small number of c orticosterone-treated rats showed behavioral changes, future experimen ts are necessary to address the possibility that a higher level of cor ticosterone intake alters spatial memory as well as brain morphology a nd neurochemistry. Additional studies are also needed to determine whe ther such changes represent a threshold effect of the steroid or a dos e-response function.