Neuroprotective effect of melatonin against lipopolysaccharide-induced depressive-like behavior in mice.

Accumulating evidence indicates an interaction between inflammation and depression since increased levels of pro-inflammatory cytokines are associated with depression-related symptoms. Melatonin is a hormone synthesized and secreted by the pineal gland with antioxidant, anti-inflammatory and antidepressant-like effects. In this way, it would be interesting to evaluate the putative antidepressant-like effect of melatonin treatment in an acute inflammation mice model of depression. The present study aimed to investigate the effect of melatonin treatment on lipopolysaccharide (LPS) induced depressive-like behavior, neuroinflammation, oxidative stress and alteration on brain-derived neurotrophic fator (BDNF) levels. Mice were treated with melatonin (10 mg/kg, i.p.) 30 min before LPS (0.5 mg/kg, i.p.) injection. Twenty-four hours after LPS infusion, mice were submitted to the behavioral tests and, thereafter, biochemical determinations were performed. Melatonin treatment prevented LPS-induced depressive-like behavior in the forced swim and tail suspension tests with no alterations in locomotor activity evaluated in the open field test. Melatonin attenuated LPS-induced increase in tumor necrosis factor-α (TNF-α) and reduction of BDNF levels in the hippocampus. Treatment with melatonin also prevented LPS-induced increase in lipid peroxidation and the reduction of glutathione levels in the hippocampus. In conclusion, the present study suggests that melatonin treatment exerted neuroprotective effects against LPS-induced depressive-like behavior which may be related to reduction of TNF-α release, oxidative stress and modulation of BDNF expression.