Alcohol abuse and alcoholism affect 4.5% of the United States population causing an economic burden of approximately 184 billion dollars/year. The ability to develop new pharmacotherapies to help fight the descent into alcohol dependence and recidivism requires an understanding of mechanisms of alcohol actions on the nervous system. It is particularly important to define the targets of ethanol binding as these may bring about the most complete therapeutic effect. Although alcohol is known to have distinct and profound effects on presynaptic function, the mechanisms underlying this large impact are essentially unknown. The long-term goal of this proposal is to define the molecular mechanism by which alcohol exerts its action on presynaptic function. The objective of this exploratory application is to examine the physiological and behavioral interactions between Munc13.1 protein and ethanol. Munc13.1 is a presynaptic active zone protein essential for neurotransmitter release in brain. In Caenorhabditis elegans, the homologous Unc13 protein is responsible for the sensitivity to volatile anesthetics. The C1 or diacylglycerol binding domain of the Munc13 family of proteins is structurally similar to that of protein kinase C (PKC) which regulates behavioral effects of alcohol and has alcohol binding site(s). Preliminary data demonstrate that ethanol will also bind to this C1 domain in Munc13.1. The central hypothesis to be tested is that a significant effect of ethanol on nervous system function is due to the binding of ethanol to the Munc13.1 C1 domain.
The first aim of this proposal will examine the hypothesis that ethanol binding to the C1 domain of the Munc13.1 modifies the activity of this presynaptic protein. This will be accomplished by photolabeling and mass spectrometry to identify alcohol binding residues, and by elucidating the effects of this binding on Munc13.1 activity in membrane translocation assays.
The second aim i s to determine how a reduction in Dunc13 activity changes the behavioral and physiological responses to ethanol in Drosophila melanogaster. This invertebrate model system was chosen for its ability to rapidly and economically alter Dunc13 levels and to monitor the functional consequences. These consequences of the ethanol-Dunc13 interaction will be revealed by measuring ethanol preference, stimulation, and sedation in wild type and Dunc13 reduction of function animals. Moreover, the effect of the interaction will be examined using the synapto-pHluorin sensor to image vesicle release from a specific subset of GABAergic neurons in intoxicated and sober flies. These GABAergic neurons are critical modulators of the stimulatory and sedative effects of ethanol in Drosophila. The approach is innovative as it applies the strengths of ultrasensitive biochemistry and powerful neurogenetic techniques for the first time to dissect the function of an ethanol-receptor interaction. This proposal is significant as it is expected to uncover a novel primary mechanism for an effect of ethanol on presynaptic function. Ultimately, this understanding may lead to new drugs designed to disrupt the ethanol-unc13.1 interaction providing a valuable weapon in the fight for sobriety.
Despite the huge number of alcohol related deaths (annually ~75,000-100,000 in the US) and cost to society ($184 billion/yr in the US) very few medications are available for treating alcohol abuse and addiction. To develop new medications and effective intervention it is necessary to define the target and mechanism of alcohol action at the molecular level. The goal of the present study is to establish the role of a presynaptic protein in regulating alcohol actions within the brain and the significance of this study is that it may allow the development of new therapeutics based on this target protein to combat alcohol addiction.