Nicotine & Nodose: A Neural Basis for Peripheral Control over Nicotine Intake

摘要

ABSTRACT Nicotine addiction in the form of habitual tobacco use is the leading cause of premature death in the United States and costs at least $170 billion in healthcare-related expenses each year. In addition to its addictive qualities, nicotine triggers a plethora of respiratory, cardiovascular, gastrointestinal, and immune disorders, reflecting its actions in not only the brain, but also in the body of smokers. While it is well established that the addictive properties of nicotine are related to its direct pharmacological actions on nicotinic acetylcholine receptors located in reward and motivation brain circuits, evidence from our lab suggests that noxious effects of nicotine related to its actions on hindbrain aversion circuits (e.g. nucleus of the solitary tract (NTS), interpeduncular nucleus, and medial habenula) play a significant role in regulating nicotine intake as well. However, it is unclear if nicotine acts solely on these circuits by direct action on centrally expressed nicotinic receptors or if nicotine also acts indirectly via vagally (nodose ganglia, NG) derived sensory inputs that terminate primarily at the NTS. Preliminary data presented in this grant application strongly suggest a role for peripheral actions of nicotine in controlling nicotine intake. For instance, the peripherally-restricted, full nicotine agonist, methylnicotinium causes a conditioned place aversion beyond that generated by an equimolar dose of nicotine. Further, the peripherally-restricted cholecystokinin receptor (CCKR) agonist, CCK-8 (10 µ*kg-1) decreased volitional nicotine intake, especially at anxiogenic nicotine doses. Given these preliminary data and the observation that plasma CCK levels are dysregulated by nicotine in rodents and humans, I hypothesize that CCKRs in gut-innervating NG neurons potentiate aversive nicotine signals from the periphery to the NTS thereby regulating nicotine intake. I will test this hypothesis using a nicotine intravenous self-administration mouse model in combination with CCKR-specific lesions of the NG, FosTRAP mice, and chemogenetics. I will then define the transcriptional responsiveness of the NG to an aversive dose of nicotine using single cell RNA sequencing. Finally, I will employ an in vivo CRISPR-Cas9-mediated genomic cleavage strategy to knockdown prioritized nicotine-response genes in the NG and assess the consequences on nicotine intake. Completion of this highly innovative proposal will substantially advance my technical skills in mouse genetics, surgery, and computer programing, and provide me with entirely new training in single cell sequencing, bioinformatics, and advanced genome editing technologies. It will also contribute to the currently sparse literature about how sensory information related to nicotine actions in the periphery are transmitted via the vagus to the hindbrain. Defining such a mechanism will position me for a successful independent career in the exciting and rapidly growing field of brain-body interactions. In summation, this training plan will provide me with the conceptual, technical, and learning experiences that will serve as a springboard for my transition to an independent research investigator.