Chronic Mild Stress Increases the Expression of Genes Encoding Proinflammatory Cytokines in the Rat Brain

Alterations in the expression of genes encoding interleukins IL-1α, IL-1β, IL-6, and tumor necrosis factor-α (TNF-α) were studied in the rat brain in a model of a depressive disorder. We found that the signs of a depressionlike condition in rats, subjected to eight weeks of chronic mild unpredictable stress, were accompanied by increased IL-1α and IL-1β mRNAs levels in the neocortex, hippocampus, and brainstem and a decreased IL-6 mRNA level in the brainstem as compared to those observed in the control animals. We did not find any changes in the level of TNF-α mRNA. We suggest that region-specific alterations in the expression of cytokine genes, specifically, the most prominent increase in IL-1β expression, reflects greater vulnerability of chronically stressed animals to neuroinflammatory processes.