The Role Of The VlPAG/DRN Dopaminergic System In Depression And Thermal Pain In Mice

Objective:This study investigated the effects of dopaminergic（DA）neurons in the ventrolateral periaqueductal gray（vl PAG）and the function of dopamine D2 receptors（D2R）in dorsal raphe nucleus（DRN）on depression-like behaviors and thermal pain in chronic unpredictable mild stress（CUMS）mice,and clarified the role of vl PAG/DRN dopaminergic system in depression and thermal pain in mice.Methods:（1）Mice were randomly divided into Control group and CUMS group（n=16 per group）.Sucrose preference test（SPT）,tail suspension test（TST）,forced swim test（FST）,open field test（OFT）and thermal withdrawal latency（TWL）were used to determine depression-like behaviors and TWL changes in CUMS mice after 28 days.（2）Mice were randomly divided into Control group,CUMS group,CUMS+normal saline（NS）group,CUMS+Quinpirole group and CUMS+JNJ-37822681 group（n=10 per group）.NS,D2R-selective agonist Quinpirole and antagonist JNJ-37822681 were injected into DRN respectively in the latter three groups for 5 consecutive days.SPT,TST,OFT and TWL were used to detect the depression-like behaviors and pain changes in mice.The expression levels of D2R in DRN was detected by immunohistochemistry and western blot.（3）Dopamine transporter（DAT）-Cre mice were randomly divided into m Cherry^NS group,m Cherry^CNO group,h M3Dq^NS group,h M3Dq^CNO group,h M4Di^NS group and h M4Di^CNOgroup.（n=10 per group）The different chemogenetic virus（m Cherry group:r AAv-Ef1α-DIO-m Cherry-WPRE-h GH-p A;h M3Dq group:r AAv-Ef1α-DIO-h M3D（Gq）-m Cherry-WPREs;h M4Di group:r AAv-Ef1α-DIO-h M4D（Gi）-m Cherry-WPREs-p A）were injected into the vl PAG of mice,and CUMS intervention was performed 7 days post-surgery.After28 days,the mice were intraperitoneally injected with clozapine N-oxide（CNO）or NS,and the changes of SPT,TST,OFT and TWL were recorded.Results:（1）CUMS modeling induced depression-like behaviors and hyperalgesiaCompared with Control group,the rate of sugar preference decreased significantly（P<0.001）,the immobility time of FST and TST prolonged markedly（P<0.001）,the total distance of open field decreased significantly（P<0.001）,and the TWL decreased（P<0.001）in CUMS group of mice.（2）Quinpirole activated DRN dopamine D2 receptors to reduce depressive behaviors and thermal hyperalgesia in CUMS mice,while JNJ-37822681 antagonized DRN dopamine D2 receptors to aggravate depressive behaviors and heat hyperalgesia in CUMS miceCompared with CUMS+NS group,multiple injections of Quinpirole into DRN significantly increased the sugar water preference rate（P<0.01）,shortened the immobility time of TST（P<0.05）,increased the total distance of open field（P<0.05）,improved the TWL（P<0.001）,increased the numbers of DRN D2R positive cells（P<0.01）and up-regulated the expression level of DRN D2R protein（P<0.001）in CUMS+Quinpirole group.While multiple injections of JNJ-37822681 into DRN obviously reduced the sugar water preference rate（P<0.001）,prolonged the immobility time of TST（P<0.05）,reduced the total distance of open field（P<0.05）,decreased the TWL（P<0.05）,reduced the numbers of DRN D2R positive cells（P<0.05）and down-regulated the expression level of DRN D2R protein（P<0.001）in CUMS+JNJ-37822681 group.（3）Specific activation of vl PAG dopaminergic neurons alleviated depressive behavior and heat hyperalgesia in CUMS mice,while specific inhibition of vl PAG dopaminergic neurons aggravated depressive behavior and heat hyperalgesia in CUMS miceThe results of chemical genetics showed that compared with m Cherry^CNO group,the preference rate of sugar water was significantly reduced（P<0.01）,TST immobility time was markedly increased（P<0.01）,the total distance of OFT was distinctly decreased（P<0.05）,and the TWL was significantly decreased（P<0.001）in h M4Di ^CNO group of mice.However,the preference rate of sugar water was significantly increased（P<0.001）,TST immobility time was obviously shortened（P<0.001）,the total distance of OFT was markedly increased（P<0.001）,and the TWL was significantly increased（P<0.001）in h M3Dq^CNO group of mice.Conclusion:CUMS modelling induce depression-like behaviors and thermal pain in mice.Activation or antagonism of DRN D2R can alleviate or aggravate depression-like behaviors and thermal hyperalgesia in mice,respectively.Specific activation or inhibition dopaminergic neurons of vl PAG can alleviate or deteriorate depression-like behaviors and thermal hyperalgesia.Vl PAG/DRN dopaminergic system may be involved in the regulatory mechanisms of pain in depression.