Behavioral tolerance is a hallmark of exposure to most drugs of abuse. It is characterized by reduced drug effects over time, either via altered metabolism of the drug, or functionally, whereby the effects of the drug decrease in spite of unaltered concentration. Indeed, the presence of enhanced acute behavioral tolerance in humans can serve as a marker for the likelihood of a future development of alcoholism. The large conductance potassium ion channel (BK) has become increasingly recognized as an important target of alcohol action, both in the intoxicating actions of the drug, as well as in adaptation to the drug (tolerance). This proposal is based upon exciting new data which identifies the BK channel beta4 subunit as an important mediator of alcohol tolerance and consumption, and provides an animal model to examine the relationship between molecular and behavioral tolerance, and consumption. We will make use of genetically engineered mice, in which the beta4 subunit is either present or "knocked out".
In Aim 1, we test the hypothesis that BK beta4 influences acute tolerance via a mechanism involving kinases and associated signaling pathways. Electrophysiological experiments will probe the role of kinases in BK acute tolerance in expression systems and in neurons of the striatum, which is important in drug reward and addiction.
In Aim 2, we test the hypothesis (based upon preliminary data) that beta4's influence on rapid tolerance will not be as pronounced as in acute tolerance. These studies will utilize electrophysiological, molecular biology, and imaging techniques, and will probe at the molecular, cellular, and behavioral levels.
Aim 2 will include studies on the role of beta4 in the finding, described in our preliminary data that in striatal neurons, there is a "switch" which is activated after 3 to 6 hrs of alcohol exposure, which radically changes the duration of tolerance after alcohol withdrawal. This has implications for the development of alcohol dependency as a function of drinking habits. Finally, in Aim 3, we test the hypothesis that beta4's influence on alcohol consumption will reflect influences on behavioral parameters such as alcohol preference and reward, both known to influence consumption. A two bottle choice variant of the "drinking in the dark" (DID) paradigm will be utilized to measure ethanol vs. water preference in beta4 KO and WT mice. In addition, we will measure the rewarding properties of ethanol in WT and beta4 KO mice using a conditioned place preference (CPP) assay. Together, these experiments will help identify the role of the beta4 subunit and acute tolerance in motivational behaviors underlying alcohol consumption.
Alcoholism represents one of the most important problems in the public health arena. Tolerance, which develops with alcohol use, may be related to the development of drug dependency and addiction. In this proposal, we pursue exciting new data which indicates a role for the BK channel beta4 subunit protein in the control of alcohol tolerance and consumption.
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