The Role And Mechanism Of Orexin Regulating VTA In The Development Of Depression

Background and objective:Previous studies have found that the pathogenesis of depression is closely related to the dysfunction of monoamine neurotransmitters in the central nervous system.The ventral tegmental area(VTA),which is dominated by dopaminergic neurons,plays an important role in depression.Latest study indicated that abnormal firing patterns of dopamine neurons in the VTA based on projecting heterogeneity was considered to be closely related to the susceptibility of depression inducing by chronic social defeated stress.Meanwhile,studies have found that orexin played an important role in the development of depression.Orexin is an important upstream of dopaminergic neurons in the VTA,and its abnormal function can lead to sleep disorders,appetite disorders and mood disorders that could be seen in depression,so it is considered to be one of the potential targets for antidepression.Orexin regulated dopaminergic neurons in the VTA in terms of reward,addiction and energy metabolism.However,there is lack study on the effect of orexin on depression by regulating the VTA.Therefore,the purpose of this paper is to investigate the effect and mechanism of orexin on the development of depression by regulating the VTA.Methods:1.Chronic unpredictable mild stress(CUMS)was used to treat the C57 mice,and depression-related behavior was analyzed to determine whether the mice suffer from depression.Then c-Fos immunofluorescence staining combined with retro tracing virus staining was used to observe the activity changes of orexin neurons that projecting to the VTA in CUMS mice.2.Optogenetic,chemogenetic and pharmacological methods were used to regulate the levels of orexin transmitters in the VTA to observe the effect on the depression-related behavior in CUMS mice.3.The in vitro electrophysiological whole-cell patch clamp was used to observe the changes of the VTA dopaminergic neurons of CUMS mice compared with control mice.Then,the effects of up-regulation of orexin afferents and transmitters in the VTA on the electrophysiological characteristics of the VTA dopaminergic neurons of CUMS mice were observed.Results:1.The total distance travelled of CUMS mice significantly reduced in open field test compared with control mice.The immobile time of CUMS mice significantly increased in tail suspension test compared with control mice.In the sucrose preference test,the sucrose consumption ratio of CUMS mice significantly reduced compared with control mice.Among the total orexin neurons,there were 46.97 ±10.05% of orexin neurons projecting to the VTA.Following CUMS treatment,the c-Fos expression of the VTA projecting orexin neurons was significantly decreased compared with control.2.Optogenetic stimulation of orexin afferents in the VTA in CUMS mice increased the total distance travelled in open field test,significantly reduced the immobile time of in tail suspension test,and increased the sucrose consumption ratio of in the sucrose preference test.Chemogenetic activation of orexin afferents in the VTA increased the total distance travelled of CUMS mice in open field test,significantly reduced the immobile time of CUMS mice in tail suspension test and increased the sucrose consumption ratio of CUMS mice in the sucrose preference test.Microinjection of Orexin-A(100pmol)into the VTA increased the total distance travelled of CUMS mice in open field test,reduced the immobile time of CUMS mice in tail suspension test,and increased the sucrose consumption ratio of CUMS mice in the sucrose preference test.Microinjection of SB334867(10 μg)or TCSOX2-29(10 μg)into the VTA significantly reduced the total travelled distance of C57 mice in the open field test.Microinjection of SB334867(10 μg)and TCS-OX2-29(10 μg)into the VTA significantly increased the immobile time in the tail suspension test in C57 mice.Microinjection of SB334867(10 μg)and TCS-OX2-29(10 μg)into the VTA had no significant effect on sucrose consumption ratio in C57 mice.3.The membrane potential of dopaminergic neurons in the VTA of CUMS mice did not significantly change compared with control mice,but the Phasic firing increased.Optogenetically excited orexin afferent terminals in the VTA increased the firing frequency of dopaminergic neurons in the VTA in CUMS mice.Chemogenetic stimulation of orexin afferent terminals in the VTA increased the firing frequency of dopaminergic neurons in the VTA in CUMS mice.Conclusion:1.The activity of the VTA-projecting orexin neurons decreased in depression.2.Up-regulating the level of orexin neurotransmitters in the VTA distribute antidepressant effect.3.The antidepressant effect of orexin neurons is due to the release of Orexin-A on Orexin-1 and Orexin-2 receptor on the VTA dopaminergic neurons,which increases the Tonic firing and decreases the Phasic firing of the VTA dopaminergic neurons.This paper provides experimental evidence for revealing the antidepressant neural mechanism of orexin regulating the VTA.