Abstract: Objective To observe the effect of melatonin (MLT) on oxidative damage and neuroendocrine derived from chronic social stress (CSS). Methods Rats were classified into 3 groups: control group、CSS group and MLT group. CSS was induced by rats housed with aggressive male rats and female rats in a crowded cage for 8 days. MLT solution was administered 3 days before accepting CSS stimulation. Results SG and MG exhibited dramatic loss of body weight. Increased plasma corticosterone (CORT) and decreased serum tT3 (total triiodothyronine), tT4 (total thyroxine), fT3 (free triiodothyronine), fT4 (free thyroxine) and TSH (thyroid stimulating hormone) levels were evident in SG. The activity of glutathione peroxidase (GSH-PX) and content of reduced glutathione (GSH) in stress group (SG) decreased significantly, Melatonin group (MG) showed a marked increase in the activity of GSH-PX and decrease in the content of MDA. In addition, in open field test, scores of horizontal activity in central region in SG were significantly fewer than those in CG and MG. Conclusion The present study indicated that CSS could induce oxidative stress and impact on neuroendocrine, e.g. thyroid functions. But these changes could be partly reversed or attenuated by MLT.

Key words: Keywords: Chronic social stress, Melatonin , Neuroendorine, Behavior