Role for serotonin in the antidepressant-like effect of a flavonoid extract of Xiaobuxin-Tang

Xiaobuxin-Tang (XBXT), a traditional Chinese herbal decoction, has been used for the treatment of depressive disorders for centuries in China. Herein, we explored the antidepressant-like effect and its monoaminergic mechanism of the total flavonoids (XBXT-2) isolated from the extract of XBXT. In present study, single XBXT-2 (25, 50, 100 mg/kg, p.o.) administration significantly potentiated the mouse head-twitch response induced by 5-hydroxytryptophan (5-HTP, a metabolic precursor to serotonin), and also, decreased the immobility time in mouse tail suspension test, which was completely prevented by p-chlorophenylalanine (PCPA, an inhibitor of serotonin synthesis) pretreatment. However, single treatment with XBXT-2 had no effect on yohimbine toxicity and high dose of apomorphine-induced hypothermia in mice. These results indicated that acute treatment with XBXT-2 produced serotonergic, but not noradrenergic activation. In addition, chronic XBXT-2 (25, 50 mg/kg, p.o., 28 days) treatments significantly reversed the depressive-like behaviors in chronically mildly stressed (CMS) rats, including the reduced sucrose preference, deficient locomotor activity and prolonged latency to novelty-suppressed feeding. Furthermore, XBXT-2 normalized the neurotransmitter changes, including the decreased serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) levels in hippocampus and prefrontal cortex in CMS rats. These findings confirm the antidepressant-like effect of XBXT-2 in CMS model of rats, which may be primarily based on its serotonergic activation.