Mechanisms of P2XR-Mediated Ethanol Consumption

Abstract

Alcohol use disorder (AUD) affects over 18 million people in the United States alone and can be attributed to an economic burden of over $200 billion per year. Despite considerable efforts toward developing new therapies for AUD, there are currently only three FDA-approved medications to pharmacologically treat AUD, none of which are considered to be particularly effective in reducing alcohol consumption or craving. The field of neuroscience has an abundance of research dedicated to the roles of individual receptors involved in alcohol addiction, such as gamma-aminobutyric acid (GABA) and glutamate (NMDA) receptors, although attempts to target these receptors has failed to produce promising results in the clinic. More recently, the purinergic (P2XR) family of receptors has become an emerging target for various diseases. In particular, the purinergic receptor family member P2X4 has been linked to the voluntary alcohol consumption pathway in AUD mouse models. Genetic, pharmacological and behavioral mouse studies report an inverse relationship between ethanol (EtOH) intake and P2X4R activity, although the underlying mechanism for this phenomenon is not understood. Interestingly, several members of the P2XR family have been shown to cross-regulate the activity of another receptor type (e.g. GAB_AA or AMPA receptors.) P2X4Rs are expressed in the Ventral Tegmental Area (VTA) of the brain, along with ionotropic NMDA receptors (NMDARs), a central component of addiction circuitry. The goal of this dissertation is to investigate molecular and cellular mechanisms by which P2X4Rs regulate ethanol consumption and addiction. This is accomplished using complementary techniques in electrophysiology, molecular biology, and biochemistry. Chapter 1 describes our understanding of AUD as it relates to treatment and pharmacotherapy. Chapter 2 describes a novel interaction between residues that is required for P2X4R channel function and a site for ethanol action. Chapter 3 describes an interaction between P2XRs (either P2X2R or P2X4R) and NMDARs, which provides a previously unrecognized link to addiction targets. Chapter 4 describes the role of P2X4Rs in mediating the effects of ethanol in the ventral tegmental area (VTA) of the brain, a region known to play a key role in reward and addiction. Chapter 5 summarizes the results of my findings, describes the limitations of my studies, and provides future directions of investigation. Overall, my findings 1) indicate that P2X4Rs play a previously unrecognized role in neuronal cell firing within the VTA 2) suggest a novel mechanism for the regulation of NMDARs, and 3) provide potential targets for the treatment of AUD and other neurological diseases.