Sex- and genotype-dependent nicotine plus cue-primed reinstatement is enhanced in adolescent Sprague Dawley rats containing the human CHRNA6 3′-UTR polymorphism (rs2304297)

Rationale: Large-scale human candidate gene studies have indicated that a genetic variant (rs2304297) in the alpha(alpha)6 nicotinic acetylcholine receptor (nAChR) subunit, encoded by the CHRNA6 gene, may play a key role in adolescent nicotine addictive behavior. We hypothesized that the polymorphism selectively enhances nicotine + cue-primed reinstatement, but not nicotine- or cue-reinstatement in alpha 6(GG) (risk) vs. alpha 6(CC) (non-risk) allele carriers, without having baseline effects on natural rewards. Methods: Using CRISPR-Cas9 genomic engineering, we developed a humanized rat line with the human gene variant of the CHRNA6 3 '-UTRC123G polymorphism in Sprague-Dawley rats. Genetically modified adolescent male and female rats were food trained under a fixed-ratio (FR)1 schedule of reinforcement and progressively increased to FR5. Animals were implanted with catheters and began nicotine self-administration (15 mu g/kg/infusion) at FR5. Upon reaching stable responding, reinforced behavior was extinguished by removal of drug and cues. Reinstatement testing began for cue only, nicotine only, and nicotine + cue in a Latin Square Design. Animals were returned to extinction conditions for 2 days minimum between testing. Results: For natural food rewards, nicotine self-administration, progressive ratio, and extinction, adolescent male and female (alpha 6(GG) and alpha 6(CC)) rats exhibited equivalent behaviors. Male alpha 6(GG) rats show enhanced nicotine + cue-primed reinstatement when compared with male alpha 6(CC) rats. This genotype effect on reinstatement was not seen in female rats. Conclusion: Our findings support the in vivo functional role of the human CHRNA6 3 '-UTR SNP genetic variant in sex-dependently enhancing nicotine seeking behavior in adolescent rats. Overall, the findings support clinical and preclinical data highlighting a role of alpha 6 nAChRs mediating sex heterogeneity in substance use and related phenotypes.

Automated summary

A genetic variant (rs2304297) in the CHRNA6 gene has been found to play a key role in adolescent nicotine addiction. This variant selectively enhances nicotine + cue-primed reinstatement, without affecting baseline effects on natural rewards.