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Our previous studies have shown that ginsenoside Rg1 (Rg1) exerts antidepressant-like effects in animal models of depression, accompanied by an improvement of astrocytic gap junction functions. However, whether connexin 43 (Cx43), the major connexin forming gap junctions between astrocytes, is the key regulator of Rg1-induced antidepressant-like effects is still unknown. In this study, we examine in vitro and in vivo the involvement of Cx43 in the antidepressant effects of Rg1. Corticosterone was used to establish an in vitro rat model of depression. Treatment with Rg1 1 h prior to corticosterone significantly improved the cell viability of astrocytes, which was significantly inhibited by carbenoxolone, a widely used gap junction inhibitor. Moreover, Rg1 treatment significantly ameliorated antidepressant-sensitive behaviours induced by infusion of carbenoxolone or Gap26, a selective inhibitor of Cx43, into the prefrontal cortex of the animals. Rg1 treatment increased the expression of Cx43 compared with Gap26 group. According to these results, the antidepressant-like effects of Rg1 were mainly mediated by Cx43-formed gap junctions., Competing Interests: Declaration of competing interest All the authors declare no conflicts of interest., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Increasing evidence has implicated astrocyte pathology in the etiopathology of major depressive disorder (MDD). In particular, dysfunction of gap junctions in astrocytes is a potential target for MDD treatment. However, the mechanism underlying stress-induced dysfunction of gap junctions is still unknown. We therefore studied the mechanism of stress-induced dysfunction of gap junctions in prefrontal cortical and hippocampal astrocytes. Corticosterone (CORT) was used to induce stress conditions; CORT damaged the function of gap junctions, which resulted from less distribution of connexin43 (Cx43) on membranes and the enhanced phosphorylation of Cx43 at S368. Moreover, CORT downregulated the biosynthesis of Cx43 but increased the degradation of Cx43. Interestingly, both autophagy and the proteasome system were involved in the degradation of Cx43 in prefrontal cortical astrocytes, but only the proteasome system was involved in the degradation of Cx43 in hippocampal astrocytes. CORT significantly induced the formation of annular gap junction vesicles in prefrontal cortical astrocytes; however, Cx43 mainly presented as small dots in the hippocampal astrocytes. Furthermore, CORT increased N-Cadherin expression and the interactions of Cx43 with ZO-1/drebrin in prefrontal cortical astrocytes, but these interactions were oppositely modulated in hippocampal astrocytes. In conclusion, this study clarified the alternations of the Cx43 life cycle in the prefrontal cortical and hippocampal astrocytes exposed to CORT, which may contribute to our understanding of the mechanisms underlying stress-induced dysfunction of gap junctions., (Copyright © 2017 Elsevier Ltd. All rights reserved.)