Research Component 1: Limbic Glutamatergic Circuits in Ethanol Self-administration
UNC Alcohol Research Center
Molecular and Circuit Pathogenesis of Alcohol Use Disorder
Research Component 1: Limbic Glutamatergic Circuits in Ethanol Self-adminstration
Primary Investigator: Dr. Clyde Hodge
Co-Investigators: Dr. Zoe McElligott
Alcohol use disorder (AUD) is one of the most widespread neuropsychiatric conditions in the US with a lifetime prevalence of 29.1% (men 36%; women 22.7%) 1. Growing evidence indicates that the addictive properties of alcohol and other drugs derive, in part, through misappropriating glutamatergic mechanisms of neural plasticity in brain reward pathways 2-12. Accordingly, our preclinical studies show that non-dependent operant alcohol self-administration increases activity and membrane insertion of Ca2+-permeable AMPARs (CP-AMPAR) in basolateral amygdala (BLA) neurons that project to the nucleus accumbens (Acb) in mice. Moreover, we found that GluA1-containing AMPAR activity and trafficking in the BLA is required for the positive reinforcing effects of alcohol 13. It is not known if these plasticity-linked mechanisms also drive maladaptive escalations in the reinforcing effects of alcohol use that characterize AUD. To address this critical gap in knowledge, we propose three separate but integrated specific aims to evaluate the overall hypothesis: CP-AMPAR expression and activity in the BLA→Acb pathway is a target of alcohol dependence that, in turn, drives escalated alcohol self-administration in C57BL/6J mice.
Specific Aim 1. Test the hypothesis that alcohol dependence alters mechanisms of excitatory/inhibitory balance in the BLA→Acb circuit (molecular and electrophysiological approach). CP-AMPAR expression and activity are targeted by chronic alcohol 14,15; however, their role in specific reward-related neural circuits remains to be fully elucidated. To address this question, we propose complementary molecular and physiological studies in C57BL/6J mice to evaluate the impact of chronic intermittent ethanol vapor (CIE-v) as a model of dependence 16-18 on: 1) expression of excitatory (AMPAR subunits GluA1 and GluA2, CaMKII, and associated PDZ domain molecules) and inhibitory (GABA-A subunits and gephyrin) in the BLA and other Acb projecting regions; 2) electrophysiological properties of Acb projecting BLA neurons including E/I ratios (sEPSCs/sIPSCs), cell excitability, and incorporation of CP-AMPARs on BLA neurons projecting to the Acb. This work integrates with CP5 (mouse escalated drinking) and CP2 (interspecies generality) and addresses overall ARC themes. These studies will increase understanding of dependence-induced maladaptive changes in excitatory AMPAR expression and activity within a critical reward-related neural circuit.
Specific Aim 2. Test the hypothesis that GluA1-containing CP-AMPARs in the BLA→Acb circuit functionally regulate dependence-induced escalated alcohol self-administration (behavioral approach). Our prior data show that postsynaptic trafficking of GluA1-containing AMPARs in the BLA is required for the reinforcing effects of alcohol 13. Accordingly, preliminary data show that CIE-v exposure increases operant alcohol self-administration and upregulates gene expression of GluA1 and the associated PDZ domain molecule PSD-95 in the BLA. Together, these findings suggest that GluA1-containing AMPAR activity is a target of alcohol dependence that regulates pathological escalated self-administration. To address this question, we will use converging site-specific pharmacological and innovative circuit-specific CRISPR gene deletion methods to determine if GluA1-containing AMPARs in the BLA→Acb neural circuit regulate dependence-induced escalated operant alcohol self-administration in C57BL/6J mice. These groundbreaking studies will move the field forward in understanding how glutamatergic mechanisms of plasticity in the BLA→Acb circuit regulates the escalated reinforcing effects of alcohol associated with AUD.
Specific Aim 3. Test the hypothesis that alcohol dependence-induced escalated alcohol self-administration is associated with altered E/I dynamics in specific cortical and limbic brain regions (photometry and behavioral approach). AUD is associated with widespread dysfunction of excitatory and inhibitory neurotransmission; however, the specific neural circuits and mechanisms that are targeted by alcohol dependence remails to be fully elucidated. Based on strong preliminary data, we propose to use multichannel fiber photometry, with support from the Scientific Resource Core (SRC), to evaluate Ca2+ activity in genetically encoded excitatory and inhibitory neurons in the Acb and the BLA, aIC, and mPFC (Acb input regions) in C57BL/6J mice during dependence-induced escalated alcohol self-administration. Functional relevance of upregulated Ca2+ signaling to escalated self-administration will be evaluated by site-specific inhibition of CaMKII in the BLA. By elucidating the impact of alcohol dependence on E/I dynamics during operant self-administration, this innovative work will define a basic circuit mechanism underlying the heightened, or escalated, reinforcing effects of alcohol that characterize AUD.
The UNC-ARC seeks to increase understanding of molecular and cellular pathogenesis in alcohol use disorder. To address this goal, Research Component 1 (CP1) proposes a set of innovative studies designed to identify and validate novel neural targets of alcohol dependence that, in turn, drive dependence-induced escalated self-administration, which is a hallmark of AUD. This work has significant potential to guide development of novel pharmacotherapeutic approaches.