EGb761 Attenuates Depressive-like Behaviors Of Mice Induced By Long-term Light Deprivation Through InhibitingNF-κB-IL-6 Signaling Pathway

Introduction Depression or depression disorder is a complex mood disorder accompanied by adistinct long-term low mood status. Depression is the third leading cause of global burden of disease in 2004 and will move into first place by 2030, affecting about 20% of the population people world wide.The pathogenesis of depression is complex. Besides the geneticabnormality, environmental factors are believed to contribute to depression.Seasonal affective disorder is a specific form of recurrent depressive disorder that canbe induced by shortened light period. Recently it has been reported that long-term exposure to constant darkness could induce depressive-like behavior and change the expression of inflammatory cytokines in rodent animals.Over the past two decades, new developments in depression research have led to the "cytokine hypothesis" that inflammatory processes and nervous system-immune system interactions are involved in depression development. Several papers reported that some cytokines are supposed to be important contributors to the pathogenesis of depression. Research has shown that immune system activation and the production of inflammatory cytokines are common in patients with depression; conversely inflammatory cytokine injection or overexpression induced the changes of mood and behaviors in individual. The activities of pro-inflammatory cytokines and anti-inflammatory cytokines coexist in depression. The pro-inflammatory cytokines, such as IL-1、IL-6、IL-17 and TNF-α, involved in immune activation and inflammatory processes, while anti-inflammatory cytokines, such as IL-10 and IL-13, resist immune response through inhibiting of immunologicalcell activation and inflammatory modulators production.EGb761 has showed anti-inflammatory, anti-oxidative, anti-arteriosclerosis and neuro-protective activities. It was proved that EGb761 treatment can release the depression-like behaviors which may involve the anti-oxidization and anti-cell death function of EGb761 and EGb761 can affect the release of depression disorder associated neuro transmitters.Previous investigation in our lab found that Ginkgo extract EGb761 could attenuate the depressive-likebehaviors induced by a single injection of lipopolysaccharide in mice. However, it has not been investigated whether EGb761 is effective on depressive-like behaviors induced by long-term light deprivation and whether its effects are associated with the inhibition of NF-κB-IL-6 signaling pathway.Method In this study, we systematically analyzed the effect of EGb761 to depressive-like behaviors induced by long-term light deprivation and checked the expression levels of associated inflammatory factors of NF-κB-IL-6 signaling pathway.In the experiment, three groups(vehicle group, EGb761 low-dose group and EGb761 high-dose group) of C57BL/6J male mice were exposed to constant darkness for 4 weeks. The control mice remained on a 12:12 light-dark cycle. Depressive-likebehaviors were evaluated by tail suspension test (TST), forced swim test (FST) and sucrose preference test(SPT). Spontaneous locomotor activity was evaluated by open field test (OFT). Besides, the expression levels of various inflammatory factors involved in NF-κB-IL-6 signaling pathway were checked. Levels of IL-6, IL-6 mRNA,NF-KB p65, phospho-NF-KB p65, IκBa and phospho-IκBa were measured using Elisa, western blotting orPCR assays. NF-κB p65 DNA binding activity was evaluated using Chemi Transcription Factor Assay Kit.Results Results showed that in FST mice of the vehicle group performed poorly in the cylinder with more immobility time and shorterlatency to immobility than the mice of the control group (both P<0.05). Compared to the vehicle group, both the low-dose group and the high-dose group spent lessimmobility time and had longer latency to immobility in the cylinder (all P<0.05);and the high-dose group showed even less immobility time and longer latency toimmobility than the low-dose group (both In TST mice of thevehicle group spent more immobility time than the mice of the control group (P<0.05).Both the low-dose group and the high-dose group spent less immobility time than the vehicle group (both P<0.05); the immobility time of the high-dose group was even shorter than that of the low-dose group (P<0.05).Elisa or western assays showed that the vehicle group had higher levels ofNF-κB p65,phospho-NF-KB p65 and phospho-IκBa than the control group, the low-dose groupand the high-dose group (all P<0.05). The high-dose group had lower levels of thoseparameters than the low-dose group (all P<0.05). All the groups had comparable level of IκBα (P>0.05).Light deprivation increased the NF-κB p65 DNA binding activity of the vehicle groupif compared to the control group (P<0.05). The low-dose group and the high-dosegroup had lower NF-κB p65 DNA binding activity than the vehicle group (bothP<0.05). The activity of the high-dose group was even lower than the low-dose group(P<0.05).Levels of IL-6 and IL-6 mRNA of the vehicle group were higher than the controlgroup, the low-dose group and the high-dose group (all P<0.05). Their levels of thehigh-dose group were lower than the low-dose group (both P<0.05).Conclusion We conclude that long term light deprivation could increase the expression of IL-6 in mice hippocampus as described before. EGb761 can decrease the protein level of IL-6 in mice hippocampus in a dose-dependent pattern which may attenuate the depressive-like behaviors.It is supposed that EGb761 attanuate animal depression like behaviors via inhibiting the NF-κB-IL-6 signaling pathway.