The Mechanism Of VTA-NAc Reward Circuit In Mediating Individual Alcohol Drinking Behaviors

Alcohol-Use Disorders(AUDs)are considered as one of the devastating health problems in the world.Interestingly,most people have more or less drinking experience,and a significant portion of individuals drinks alcohol regularly.However,only 3-5%subpopulation of these individuals develops a pathological use of alcohol and is diagnosed as AUDs.These observations indicate that there are evident individual variations in alcohol drinking behaviors.However,the mechanisms underlying these drinking variations,particularly at neural circuit level,have not been fully explored yet.Midbrain Dopamine Reward system,origins from Ventral Tegmental Area(VTA)and projects to Nucles Accumbens(NAc)is a neural circuit that plays an important role in mediating drug dependence and motivation behaviors.Dopaminergic nurons,which are the primary neurons in VTA,have two firing patterns:a low-frequency tonic firing,and a high frequency burst/phasic firing.It is known that changes of dopaminergic firing patterns may affect the downstream dopamine release in NAc,which finally leads to a behavioral altermation.On the other hand,Due to the differences in anatomy,as well as in functions,NAc at least can be divided into two subregions,the core and the shell.Interestingly,NAc core and NAc shell play similar or even opposite roles in manipulating rewarding behaviors.In this study,therefore,my research goal is to investigate whether the dopamine neuronal activity in VTA and dopamine release in the NAc differ in variable alcohol drinking individuals.Method:1.By using 8-week old wild type C57BL/6J male mice,13-day two-bottle choice(2-BC)paradigm was set up to pare out mice into high alcohol drinking mice(HAD)and low alcohol drinking mice(LAD).Blood ethanol concentration(BEC)had been measured in HAD and LAD mice.2.In vivo single-unit recordings were performed to measure the neiuronal activity of VTA dopaminergic neurons in C57BL/6J EtOH naive control,LAD and HAD mice.3.8-week old TH-BAC-Cre male mice(Cre recombinase express in neurons that contain tyrosine hydroxylase(TH)promotor)were used to go through the 13-day,2-BC paradigm to obtain LAD and HAD mice.BEC had been measured in TH-BAC-Cre HAD and LAD mice.4.In vivo optical phasic stimulation(Optogenetics)was used to increase neiuronal activity in TH-BAC-Cre HAD mice.Then alcohol drinking preference were measured to investigate whether or not the drinking behavior was alleviated by optogenetically increased burst firing of VTA-NAc dopaminergic neurons.5.In vitro electrophysiological recordings were performed to measure the firing rate of VTA-NAc dopaminergic neurons.6.FSCV(Fast Scan Cyclic Voltammetry)techniques were utilized to quantitatively measure the amount of dopamine release in NAc core and the shell.Results:1.After the 13-day 2-BC paradigm,mice were successfully split into HAD and LAD mice.HAD mice had significant higher BEC than that of LAD mice.2.In vivo single-unit recordings showed an elevated activity of dopaminergic neurons in the VTA of LAD group as compared to HAD group and EtOH naive control group.3.TH-BAC-Cre mice were successfully split into HAD and LAD mice.TH-BAC-Cre HAD mice had significant higher BEC than that of LAD mice.4.HAD mice showed an attenuated alcohol consumption in contrast with EtOH naive group after optic phasic stimulations.5.In vitro cell-attach/whole cell recordings showed an increased firing rate of VTA-NAc dopaminergic neurons in LAD mice compared to HAD mice and EtOH naive mice.6.FSCV techniques demonstrated a decrease of dopamine concentrations in NAc core of HAD mice as compared to EtOH naive control group.There was no significant difference in dopamine concentrations in the NAc shell within these three groups of mice.Conclusion:In conclusion,by utilizing various approaches and techniques,including behavioral measurements,optogenetics,electrophysiology,and FSCV,we found that:1.The firing activity of dopaminergic neurons in the VTA was increased in LAD group.2.Changes of dopamine release in NAc core and shell in alcohol drinking groups suggested a subrigional dependent of dopamine concentrations in alcohol drinking mice.