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Identifying genetic variants associated with nicotine-motivated behavioral traits is an important strategy to understand the fundamental mechanisms underpinning smoking and tobacco abuse. For suitable emulation of behavioral phenotype with the full advantage of this invertebrate model, we newly established a worm model of nicotine seeking by Conditioned Cue Preference (CCP). We demonstrated that C. elegans also exhibited pivotal features of nicotine-motivated behaviors as in mammals. First, we identified the nicotine-elicited cue preference is mediated by nicotinic acetylcholine receptors in worms. Additionally, we exhibited dopamine is also required for the development of CCP. Subsequently, we identified the nAChRs subunits associated with the facilitation of nicotine preference. Accordingly, we validated human GWAS candidates associated with nicotine dependence involved in the role of those nAChR subunits. we addressed the cross-species functional validation to determine the GWAS candidate genes have authentic roles in nicotine seeking associated with tobacco abuse. The loss of function strain of CACNA2D3 orthologue, calcium voltage-gated channel auxiliary subunit alpha2delta 3, was tested for CCP. We also tested the knock-out (KO) strain of the CACNA2D2 orthologue, calcium voltage-gated channel auxiliary subunit alpha2delta 2, which is closely related to CACNA2D3 in the same family and shared the human smoking phenotypes. Our orthogonal test suggests the functional conservation of the α2δ subunit of calcium channel in nicotine motivated behavior.

An improved understanding of the molecular basis of alcohol seeking despite the catastrophic consequences of alcohol abuse is likely to enrich our treatments for Alcohol Use Disorders (AUD) and comorbidities. The compulsive seeking is characterized by an imbalance between the superior drive to substance and disruption in control of substance use. To model the development of compulsive engagement of alcohol seeking, we exploit two distinct behavioral programs of C. elegans in conflict, ethanol preference and avoidance of aversive stimulus, simultaneously. We demonstrate that C. elegans exhibited the recapitulation of the pivotal features of compulsive alcohol seeking in mammals, which are repeated attempts, endurance, and finally aversion-resistant ethanol seeking. We find that the neuropeptide signaling via SEB-3, CRF receptor-like GPCR, facilitates the development of ethanol preference and compels animals to seek ethanol compulsively. Furthermore, our functional genomic approach and behavioral elucidation suggest the interaction between neuropeptidergic signaling, SEB-3 and TKR-1, Neurokinin receptor orthologue, to progress compulsive ethanol seeking behavior.