Repeated exposure to corticosterone, but not restraint, decreases the number of reelin-positive cells in the adult rat hippocampus

Stress is an important risk factor for the emergence of depression, but little is known about the neurobiological mechanisms by which stress might promote depressive symptomatology. Much of the research on this topic has focused on stress-induced changes in hippocampal plasticity, specifically the idea that decreased hippocampal plasticity could be a precipitating factor for depression. Interestingly, recent evidence has described a regulatory role for the extracellular matrix protein reelin in important aspects of neural plasticity within the hippocampus and dentate gyrus. Given this association between reelin and hippocampal plasticity, we investigated whether repeated exposure to corticosterone or physical restraint might decrease reelin expression in specific hippocampal regions. Rats were subjected to either 21 days of corticosterone injections or physical restraint and then sacrificed so that the number of reelin-positive cells throughout the hippocampus and dentate gyrus could be quantified using immunohistochemistry. Our results revealed a significant decrease in the number of reelin-positive cells in the CA1 stratum lacunosum and the subgranular zone of the dentate gyrus in rats that received corticosterone, but not in rats that received restraint. Interestingly, these results parallel our previous observation that corticosterone increases depression-like behavior but physical restraint does not. These novel findings suggest that altered reelin signaling could play a role in the expression of depressive symptomatology after exposure to high levels of glucocorticoids. (C) 2009 Elsevier Ireland Ltd. All rights reserved.