Mechanism Of Ventral Tegmental Area Anterior-interstitial Nucleus Of The Posterior Limb Of The Anterior Commissure Pathway Mediated Acquisition Of Morphine Conditioned Place Preference

Background and Objective:Drug addiction is a chronic recurrent encephalopathy,patients showed that they knew that the use of drugs would have adverse consequences,but still repeatedly forced to use drugs,it has brought great harm to the individual and society of addicts.Opioid drugs such as heroin are the third most popular drug in the world,and opioid analgesics such as morphine are widely used in clinic.The adverse reactions such as addiction and withdrawal effect have been difficult to solve in clinic.The reward effect of opioids is an important positive reinforcement mechanism,which can promote the repeated drug seeking behavior of addicts by participating in the formation of drug-associate memory,involves the interaction of multiple brain regions in the mesolimbic system.Previous studies have explored the formation mechanism of morphine reward effect from the circuit,molecular and other aspects,but the specific mechanism of its mediating addiction is still unclear.Dopaminergic neurons in ventral tegmental area(VTA)of the middle brain are considered to be the key factors for regulating the reward effects mediated by various psychoactive substances.The circuit research related to dopaminergic neurons in VTA is also a key issue in the study of opiate addiction.Recent studies have confirmed that gamma aminobutyric acid(GABAergic)neurons in VTA also play an important role in drug addiction,but the related research is relatively insufficient.Interstitial nucleus of the posterior limb of the anterior Commissure(IPAC),a sub region of the extended amygdala,the previous research on its function is relatively insufficient.Our study found that IPAC is involved in morphine mediated conditioned place preference and receives direct projections from GABAergic neurons in VTA.Therefore,further exploring how GABAergic neurons in VTA participate in the process of morphine addiction through regulating IPAC can further enrich the neurobiological mechanism of opioid addiction and provide new potential targets for the treatment of opioid addiction.Subjects and Methods:In this study,adult male Sprague Dawley rats were selected as the research object.The role of VTA-IPAC circuit in morphine mediated conditioned place preference was studied by immunofluorescence staining,pharmacogenetics,whole cell patch clamp recording and optical fiber recording.Result:1.Through immunofluorescence staining,pharmacogenetics and whole cell patch clamp,confirmed that morphine could activate Ca MKII α positive neurons in IPAC and induce conditioned place preference in rats.2.The Ca MKII α positive neurons in IPAC received direct projections from GABAergic neurons in VTA.3.Through optical fiber recording,whole cell patch clamp confirmed that morphine injection paired with white chamber enhanced the activity of Ca MKII α positive neurons in IPAC by inhibiting VTA-IPAC circuit.4.Pharmacogenetics confirmed that activation of VTA-IPAC circuit inhibited morphine mediated acquisition of conditioned place preference in rats.5.Through pharmacogenetics and sweet food intake experiments,it was confirmed that morphine mediated morphine reward effect by inhibiting VTA-IPAC circuit,and did not affect the natural reward of rats.Conclusion:It was confirmed by the appeal experiment that morphine injection matched with the white chamber enhanced the activity of Ca MKII α positive neurons in IPAC by inhibiting the inhibitory transmission of VTA-IPAC,resulting in morphine specific reward effect,which mediated the acquisition of conditioned place preference in rats.