Nicotine is one of the most heavily used addictive drugs and accounts for 90% of lung cancer cases in the U.S. Recent studies have implicated a specialized receptor class binding to nicotine, the CHRNA5 gene, which encodes the a5 subunit of the nicotinic receptor, as a contributing factor in the risk towards nicotine dependence. This, along with animal studies on the CHRNA5 indicates its potential as a therapeutic development strategy for smoking cessation. One strategy for smoking cessation therapies is to break the reward cycle between the act of smoking with the pleasurable outcome of nicotine ingestion. This is often attempted by blocking the activity of dopaminergic neurons involved in eliciting the reward signal in the brain, or by interfering with receptors, such as dopaminergic or nicotinic receptors expressed in the dopaminergic pathway. This proposal addresses the aversive aspects of nicotine and/or tobacco consumption as an alternate means of breaking the reward cycle. Recent studies have implicated the habenula in providing aversive signals in response to nicotine, and may provide a counterbalance to dopaminergic function mediating reward. In vivo animal studies have implicated the a5 nicotinic receptor subtype in the habenula, as reducing nicotine consumption through inducing aversion to nicotine. The aims of this proposal are to generate tools for developing an a5 nicotinic receptor drug development program through the creation of stable cell lines that recapitulate the functionality of a5-containing receptors in the brain. The cell lines can then be adapted for use in the high- throughput screening format suitable for drug discovery program. In addition, we will undertake animal studies to validate the CHRNA5 gene as a useful therapeutic target. In the absence of a selective pharmacological agent to a5 nicotinic receptors, we will generate a hypersensitive variant of a5 nicotinic receptors to genetically amplify a5 nicotinic receptor signaling. We will stereotactically deliver hypersensitive variants of the CHRNA5 gene into the habenula of nicotine-conditioned animal, to determine whether selective activation of a5 nicotinic receptors can be disruptive to nicotine dependence. The tools developed under this award will provide a good basis for the development of a smoking cessation program based on the CHRNA5 gene.
Public Health Relevance: Nicotine is a serious health problem that is resistant to treatment for millions of people. In the United States, tobacco use is responsible for about about 443,000 deaths per year, and an estimated 49,000 of these tobacco-related deaths are the result of secondhand smoke exposure. Cigarette smoking costs more than $193 billion (i.e., $97 billion in lost productivity plus $96 billion in health care expenditures) Nicotine is one of the most heavily used addictive drugs and accounts for 90% of lung cancer cases in the U.S. Recent studies have implicated a specialized receptor class binding to nicotine, the CHRNA5 gene as a contributing factor in the risk towards nicotine dependence, and indicates its potential as a therapeutic development strategy for smoking cessation.
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