The antidepressant- and anxiolytic-like effects of fluoxetine and clozapine in chronically isolated rats involve inhibition of hippocampal TNF-α

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Brain oxidative stress and neuroinflammation are implicated in psychiatric disorders. Thus, it is important to investigate the effects of individual psychotropic agents on antioxidative defense and proinflammatory mediators in brain regions associated with these disorders. Psychosocial stress is recognized as a threat to mental health, and the hippocampus is a primary target of stress-related damage. Chronic social isolation (CSIS) is a mild psychosocial stress used to model the pathophysiology of depression. We examined the antioxidative and anti-inflammatory potential of the antidepressant fluoxetine (FLX) and atypical antipsychotic clozapine (CLZ) in the hippocampus in the CSIS model of depression. We measured the effects of FLX and CLZ on depressive- and anxiety-like behaviors in non-stressed rats and rats exposed to 21d of CSIS. We further evaluated the content of reduced glutathione (GSH), the protein expression and activity of the GSH-related enzymes, the subcellular localization of nuclear factor-kappa B (NF-κB) and protein levels of proinflammatory mediators cyclooxygenase-2 (COX-2), interleukin-1beta (IL-1β), and tumor necrosis factor-alpha (TNF-α) in these groups of rats. CSIS resulted in an increase in depressive- and anxiety-like behaviors that corresponded with compromised glutathione peroxidase (GPx)-mediated antioxidative defense and increased TNF-α, but not with changes in NF-κB, IL-1β and COX-2 levels. FLX and CLZ, applied during CSIS, prevented the behavioral changes associated with CSIS, and inhibited the increase in TNF-α, but did not affect GPx-mediated antioxidative defense. Furthermore, both drugs decreased hippocampal GPx activity when applied to non-stressed rats. These results emphasize the significance of hippocampal TNF-α-mediated proinflammmatory signaling in the pathophysiology of depressive symptoms and the importance of the anti-inflammatory action of both FLX and CLZ in the prevention of these symptoms.Graphical abstractHighlightsChronic social isolation (CSIS) induced depressive- and anxiety-like behaviors.These behavioral changes were prevented by fluoxetine (FLX) or clozapine (CLZ).CSIS decreased hippocampal glutathione peroxidase (GPx) activity.CSIS increased hippocampal TNF-α level without affecting IL-1β or NF-kB activation.FLX and CLZ prevented changes in TNF-α level, but not in GPx activity.

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