Research Project 2: Summary
Tobacco use is the single most preventable cause of disease, disability, and death in the United States. Clinical studies have demonstrated that heritability is ~50% for various smoking behaviors. However, most of the genetic factors determining smoking behavior remain unknown. Genetic studies using rodent models have greatly improved our understanding of the cause of human genetic diseases and discovered many targets for therapeutic drugs. We recently established a rat model in which social cue is an important determinant of nicotine intake. This model is particularly pertinent to smoking because it incorporates the critical effect of social environment and the aversive effect of nicotine. Both of these effects are well recognized in clinical investigations, but are largely ignored in preclinical studies. The heterogenous stock (HS) rats are the result of more than 60 generations of intercrossing of 8 inbred rat strains and are particularly suitable for fine genetic mapping studies. Therefore, the primary goal of Research Project 2 is to phenotype 1,600 HS rats on socially-acquired nicotine self-administration. We will use adolescent HS rats bred locally to capture the role of this critical brain development stage on smoking initiation. We will also test these HS rats on contextual-cue induced reinstatement of drug seeking. Data on several social and emotional traits will be obtained before self-administration starts. Multiple regression will be used to analyze the relationship between these traits with nicotine intake and reinstatement. DNA sample from each rat will be sent to the Sequencing Core (Core C) for genotyping. The quantitative behavioral measures will be sent to Research Project 4 to perform a genome-wide association study on nicotine intake and reinstatement of nicotine seeking. Sex difference will be examined. Another goal of this Research Project is to use laser capture microdissection (LCM) to precisely collect tissue from 72 HS brains. Five brain regions that are critical for the behaviors investigated by Research Projects 1-3 will be targeted: nucleus accumbens core, lateral habenula, orbitofrontal cortex, infralimbic cortex, and prelimbic cortex. We select to conduct this project at UTHSC because Dr. Chen is the director of the LCM facility that operates a state-of-the-art ArcturusXT instrument. His expertise on using LCM to collect brain samples for transcriptome sequencing will ensure the success of this project. RNA extracted from these samples will be provided to the Sequencing Core. Research Project 4 will analyze these gene expression data and integrate the results with the behavioral and genomic findings.