Antidepressant-like effects and memory enhancement of a herbal formula in mice exposed to chronic mild stress.

Shen Yuan Gan (SYG) is a Chinese herbal prescription composed of total saponins of Panax ginseng and total oligosaccharide esters of Polygala tenuifolia (2:1). Our previous studies have demonstrated that SYG has antidepressant-like effects in various mouse models of behavioral depression. The present study aimed to test whether SYG affected chronic mild stress (CMS)-induced depression and cognitive impairment in mice. We found that a 5-week CMS schedule induced significant degradation of the coat state, decreased sucrose intake in the sucrose-preference test, and increased the latency to feed in the noveltysuppressed feeding test. All of these CMS-induced changes were ameliorated by SYG (100 and 200 mg/kg) and fluoxetine (10 mg/kg). In addition, SYG restored the decreased monoamine neurotransmitter concentrations (serotonin, dopamine, norepinephrine and acetylcholine) induced by CMS in the prefrontal cortex. Interestingly, SYG ameliorated CMS-induced cognitive impairment in the step-through test, and increased the acetylcholine level in the prefrontal cortex. These results suggest that SYG has an antidepressant-like action and enhances cognition by modulating the serotonin, dopamine, norepinephrine, and acetylcholine levels in the prefrontal cortex.