Microglia depletion by administration of a colony-stimulating factor 1 receptor antagonist exacerbates inflammation-induced fatigue in mice
Production of inflammatory mediators by activated microglial cells in the central nervous system is commonly considered to be responsible for the development of symptoms of depression including fatigue and lack of energy (anergia) in response to systemic inflammation. Methods: In order to directly test the validity of this hypothesis, male C57BL/6 mice were treated orally with PLX5622, a specific antagonist of colony stimulating factor receptor to eliminate microglia before administration of a
... dministration of a fatigue-inducing dose of lipopolysaccharide (LPS) according to a 2 (PLX5622 versus control diet) x 2 (LPS x control) factorial design. Fatigue was measured by decreased wheel running activity. Results: Chronic administration of PLX5622 eliminated microglia and peripheral tissue macrophages. However, it did not abrogate the inducible expression of proinflammatory cytokines in the brain in response to LPS. Instead PLX5622 increased IL-6 and abrogated IL-10 response to LPS. PLX5622 had only moderate effects on the liver inflammatory response to LPS. In accordance with these neuroimmune effects, PLX5622-treated mice responded to LPS with the same level of decreased locomotor activity in a new environment as mice given the control diet. Further, PLX5622-treated mice displayed a prolonged decrease in running wheel activity. In addition, PLX5622-treated mice were less active in running wheels than mice given the control diet even in baseline conditions. Conclusions: These findings reveal a role for microglia in the regulation of immune-to-brain signaling that is different from the one usually ascribed to it and call for a re-evaluation of the importance of microglia in the brain response to physical exercise. Tissue processing Mice were euthanized by exposure to CO 2 . Livers and brains were collected after intracardiac perfusion of PBS, snap frozen in liquid nitrogen, and stored at − 80°C until analyzed. RNA was extracted using E.Z.N.A. Total RNA Isolation kit (Omega Bio-Tek, Norcross, GA). RNA was reverse transcribed using a High Capacity cDNA Reverse Transcription Kit (Applied Biosystems, Thermo Fisher Scientific, Waltham, MA) and analyzed by real-time PCR using TaqMan Gene expression assays. GADPH was used as a house keeping gene. Primers are listed in Table 1 . 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