Acute corticosterone replacement reinstates performance on spatial and nonspatial memory tasks 3 months after adrenalectomy despite degeneration in the dentate gyrus.

Abstract

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.

Flattening the Glucocorticoid Rhythm causes Changes in Hippocampal Expression of Messenger RNAs Coding Structural and Functional Proteins: Implications for Aging and Depression

“…Structural changes observed include a marked loss of granule cells (Sloviter et al, 1993(Sloviter et al, , 1995Gould et al, 1990), impoverishment of granule cell dendrites, and reduction in synapses between mossy fibers and the apical dendrites of CA3 pyramidal neurons (Sousa et al, 1999). ADX also attenuates both LTP (Smriga et al, 1996;Shors et al, 1990) and spatial working memory (McCormick et al, 1997).…”

Object/context-specific memory deficits associated with loss of hippocampal granule cells after adrenalectomy in rats

“…In direct contrast to these findings, Spanswick et al (2007) report that administration of CORT after 6 wk of ADX does not alleviate spatial deficits in a moving-platform version of the Morris water task. Also in opposition to Conrad and Roy (1995) and McCormick et al (1997), studies utilizing colchicine as a method to remove granule cells report spatial deficits as a result of cell loss (Sutherland et al 1983;Xavier et al 1999;Jeltsch et al 2001).Here, we show using three versions of a novelty-preference task (novel object, novel place, and object/context mismatch) that lesions limited to the granule cell layer of the DG produce deficits that are specific to detecting an object/context mismatch. Our results support the idea that the hippocampus (specifically the DG) is critical in situations in which contextual discrimination is important.…”

“…This is likely a result of incomplete ADX permitting secretion of CORT and preventing the degeneration associated with ADX (Sloviter et al 1989). Given the lack of difference between these rats and controls, as well as evidence from previous research suggesting intact memory ability in incomplete ADX rats (McCormick et al 1997), we grouped them together.At the time of behavioral testing, our ADX rats were receiving replacement CORT. There is debate surrounding behavioral deficits as a result of chronic ADX; both removal of CORT and degeneration of the granule cells could be responsible for the observed deficits.…”

“…This is likely a result of incomplete ADX permitting secretion of CORT and preventing the degeneration associated with ADX (Sloviter et al 1989). Given the lack of difference between these rats and controls, as well as evidence from previous research suggesting intact memory ability in incomplete ADX rats (McCormick et al 1997), we grouped them together.…”

“…In direct contrast to these findings, Spanswick et al (2007) report that administration of CORT after 6 wk of ADX does not alleviate spatial deficits in a moving-platform version of the Morris water task. Also in opposition to Conrad and Roy (1995) and McCormick et al (1997), studies utilizing colchicine as a method to remove granule cells report spatial deficits as a result of cell loss (Sutherland et al 1983;Xavier et al 1999;Jeltsch et al 2001).…”