Investigation of the impact of preconditioning with lipopolysaccharide on inflammation-induced gene expression in the brain and depression-like behavior in male mice

Although several recent studies have suggested that neuroinflammation plays a role in depression, both medication and neuroinflammatory preventive strategies have been poorly investigated. Recent studies have indicated that preconditioning with lipopolysaccharide (LPS) reduces the damage that occurs following ischemic stroke and brain trauma. However, to date, the effects of LPS preconditioning on psychiatric symptoms have not been reported. Thus, we assessed gene expression and behavioral changes affected by preconditioning with low-dose (LD) LPS in male mice with systemic inflammation induced by administration of high-dose (HD) LPS. mRNA expression analyses of cytokine-, glial-, and oxidative stress-associated genes revealed that majority of these genes responded to HD LPS. Differential gene expression in the presence and absence of LD LPS preconditioning, identified a subset of genes that may contribute to the mechanism of LPS preconditioning in the brain. Notably, LPS preconditioning attenuated an increase in expression of the astrocyte marker Gfap caused by systemic inflammation, suggesting that astrocytes have a key role in endotoxin tolerance in the brain induced by LPS preconditioning. As increased astrocyte in the brain of patients with depression is suggested to contribute to the pathophysiology of major depression, LPS preconditioning might be applicable to the prevention and treatment of depression. Unfortunately, in this study, LPS preconditioning did not show a reversal effect on behavior decline due to high-dose LPS-induced systemic inflammation. Alternative aspects of behavioral changes should be assessed to identify behavioral components that are affected by LPS preconditioning. Nonetheless, the findings in the present study indicate the possibility of the mechanism of endotoxin tolerance induction in the brain via astrocyte regulation by LPS preconditioning. Since there has been reported pharmacological significance of astrocytes in psychiatric disorders, regulation of endotoxin tolerance might be a key method to control psychiatric symptoms.