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 dentate gyrus cells. These effects are prevented by chronic replacement of corticosterone (CORT). The effects of acute replacement 3 months after ADX in rats classified as ADX or incomplete ADX (INC) on the basis of saline intake, weight, and plasma CORT levels were investigated. ADX rats swam longer and farther to find a platform in a spatial water-maze task (Exp. 1) and were impaired on a nonspatial object-recognition 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 performance of ADX rats without affecting the size of the dentate. CORT did not 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 replacement may operate outside the hippocampus.