The Role of Nicotinic Receptors in Nicotine Withdrawal

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DESCRIPTION (provided by applicant): Nicotine addiction is one of the primary causes of preventable mortality in the world. Withdrawal symptoms that occur after nicotine cessation account for the high incidence of relapse in people attempting to quit smoking. Thus, insight into the mechanism of nicotine withdrawal could lead to better targeted pharmacotherapy to aid in successful smoking cessation. Nicotine targets and activates neuronal nicotinic acetylcholine receptors (nAChRs), ligand gated cation channels that are normally activated by the endogenous neurotransmitter, acetylcholine. Rodent models of nicotine dependence and withdrawal have lead to a better understanding of nicotine addiction; however the specific nAChR subtypes involved in withdrawal symptoms are not fully elucidated. As in human smokers, rodents exposed to chronic nicotine exhibit somatic (physical) and affective withdrawal symptoms after drug cessation. While somatic symptoms have a peripheral component, affective symptoms are centrally mediated and associated with hypoactivity of dopaminergic neurons in midbrain reward and locomotor circuits. Recently, there is evidence that somatic and affective nicotine withdrawal symptoms may be dependent on chronic activation of distinct and separate nAChR subtypes. Previous work indicates that a4 subunit-containing (a4*) nAChRs are both necessary and sufficient for nicotine reward and tolerance, but the role they play in withdrawal is unknown. The hypothesis being tested in this application is that activation of a4* nAChRs is necessary and sufficient for affective, but not somatic nicotine withdrawal symptoms. To determine if a4* nAChR expression is necessary for somatic and/or affective withdrawal symptoms, knockout mice that do not express a4* nAChRs will be chronically treated with nicotine and both affective and somatic withdrawal symptoms will be measured upon drug cessation and compared to nicotine withdrawn wild-type (WT) animals. In Aim 2, mice expressing hypersensitive a4* nAChRs will be chronically exposed to small doses of nicotine that selectively activate the mutant receptor. Affective and somatic withdrawal symptoms will be measured upon cessation and compared to WT mice. Together, the results from this study should yield valuable insight into the molecular underpinnings of nicotine withdrawal. PUBLIC HEALTH RELEVANCE: Withdrawal symptoms that occur after nicotine cessation account for the high incidence of relapse in people attempting to quit smoking. The goal of the proposed project is to determine if a neuronal nicotinic acetylcholine receptor subtype previously linked to the acute, addictive properties of nicotine is also involved in withdrawal symptoms associated with smoking cessation. The results of this study should yield valuable insight into the molecular underpinnings of nicotine withdrawal.