The antidepressant-like effects of the water extract of Panax ginseng and Polygala tenuifolia are mediated via the BDNF-TrkB signaling pathway and neurogenesis in the hippocampus

Abstract

Ethnopharmacology relevance: The water extract of Panax ginseng (GT) and Polygala tenuifolia (YT), the main constituents of the commonly used kai-xin-san formula of traditional Chinese medicine, represents SY. It possesses strong neuroprotective effects. Using behavioural tests, we have previously established that the SY formulation exerts superior antidepressant activity than that of GT or YT.

Aim: To elucidate the impact of SY treatment on chronic unpredictable mild stress (CUMS)-induced depressive-like behaviours and the prospective mechanism related to hippocampal neurogenesis and the BDNF signaling pathway.

Methods: We exposed Sprague-Dawley rats (male; 180-200 g) to CUMS for 35 days. The rats in the experimental treatment groups were daily treated with either fluoxetine (10 mg kg^-1d^-1) or SY (67.5, 135, or 270 mg kg^-1d^-1) orally until the behavioural tests (tail suspension test [TST], novelty-suppressed feeding test [NSFT], sucrose preference test [SPT], and forced swim test [FST]) were completed. We assessed the modifications in the hippocampal neurogenesis and the BDNF signaling pathway post-treatment with CUMS and SY. Additionally, K252a, a tyrosine protein kinase inhibitor, was utilized to evaluate the antidepressant mechanisms of SY.

Result: s: The results of SPT, NSFT, FST, and TST in CUMS-exposed rats confirmed the antidepressant actions of SY. Additionally, SY treatment induced the BDNF signaling pathway and reversed the hippocampal neurogenesis caused by CUMS. Moreover, we found that the TrkB antagonist K252a blocked SY effects on behavioural improvement, inhibited the incremental effects of SY on hippocampal neurogenesis, and eliminated the impact of SY on BDNF-TrkB signaling activation. Thus, the impact of SY treatment on BDNF signaling molecules (pAkt, pERK1/2, and pCREB) were significantly inhibited by K252a.

Conclusions: This study showed that SY acted as an antidepressant in rats exhibiting CUMS-induced depressive-like behaviours, and was facilitated by promoting hippocampal neurogenesis and the BDNF signaling pathway activation. Thus, SY could act as a potential novel supplement or adjuvant to prevent or treat clinical depressive disorders.

Keywords: BDNF; CUMS; Depression; Neurogenesis; SY.