Antidepressant-like effects and mechanism of action of SYG in depression model in rats

OBJECTIVES: The present study aimed to evaluate whether SYG, a Chinese herbal formula, could produce antidepressant-like effects in learned helplessness (LH) model and chronic mild stress (CMS) model in rats. The mechanism underlying the antidepressant-like action was investigated by exploring BDNF signaling way in the hippocampus. MATERIAL AND METHODS: SYG was administrated for 5 consecutive days (100 and 200 mg/kg/day, intragastrically) in the learned helplessness model; SYG was administered daily by gastric gavages during both the 5-week stress session and behavior tests periods in the chronic mild stress model (100 and 200 mg/kg). The serum corticosterone level was measured in the learned helplessness model. Levels of BDNF and Tyrosine-related kinase B (TrkB), were evaluated in the hippocampus of chronic mild stress model. RESULTS: A deficit in avoidance learning and higher corticosterone level were observed in learned helplessness rats. SYG significantly reduced this deficit and reversed the corticosterone alteration. CMS induced significant reduction of sucrose intake in the sucrose preference test, an increased latency to feed in the novelty-suppressed feeding test and an increased immobility time in the forced swim test as compared to the control. It was also found that BDNF and TrkB levels were decreased in CMS model. Chronic treatment of SYG significantly suppressed the behavioral changes and up-regulated the BDNF signal pathway in the hippocampus. CONCLUSION: Our results suggest that SYG alleviates depression induced by LH and CMS model. The antidepressant-like activity of SYG is likely mediated by activation the BDNF signal pathway in the hippocampus.