ACUTE CORTICOSTERONE REPLACEMENT REINSTATES PERFORMANCE ON SPATIAL AND NONSPATIAL MEMORY TASKS 3 MONTHS AFTER ADRENALECTOMY DESPITE DEGENERATION IN THE DENTATE GYRUS

Long-term adrenalectomy (ADX) causes loss of spatial memory and of den tate gyrus cells. These effects are prevented by chronic replacement o f corticosterone (CORT). The effects of. acute replacement 3 months af ter ADX in rats classified as ADX or incomplete ADX (INC) on the basis of saline intake, weight, and plasma CORT levels were investigated. A DX rats swam longer and farther to find a platform in a spatial water- maze task (Exp. 1) and were impaired on a nonspatial object-recognitio n task (Exp. 2) compared with INC and SHAM rats. In both experiments, ADX decreased the size of the dentate gyrus, and replacement with CORT either 5 or 10 days prior to and during testing restored the performa nce of ADX rats without affecting the size of the dentate. CORT did no t affect INC and SHAM rats. Thus, the adverse effects of ADX on memory may not be due to damage in the dentate, and the effects of CORT repl acement may operate outside the hippocampus.