Assessment of individual differences in the rat nucleus accumbens transcriptome following taste-heroin extended access.

Heroin addiction is a disease of chronic relapse that harms the individual through devaluation of personal responsibilities in favor of finding and using drugs. Only some recreational heroin users devolve into addiction but the basis of these individual differences is not known. We have shown in rats that avoidance of a heroin-paired taste cue reliably identifies individual animals with greater addiction-like behavior for heroin. Here rats received 5min access to a 0.15% saccharin solution followed by the opportunity to self-administer either saline or heroin for 6h. Large Suppressors of the heroin-paired taste cue displayed increased drug escalation, motivation for drug, and drug loading behavior compared with Small Suppressors. Little is known about the molecular mechanisms of these individual differences in addiction-like behavior. We examined the individual differences in mRNA expression in the nucleus accumbens (NAc) of rats that were behaviorally stratified by addiction-like behavior using next-generation sequencing. We hypothesized that based on the avoidance of the drug-paired cue there will be a unique mRNA profile in the NAc. Analysis of strand-specific whole genome RNA-Seq data revealed a number of genes differentially regulated in NAc based on the suppression of the natural saccharine reward. Large Suppressors exhibited a unique mRNA prolife compared to Saline controls and Small Suppressors. Genes related to immunity, neuronal activity, and behavior were differentially expressed among the 3 groups. In total, individual differences in avoidance of a heroin-paired taste cue are associated with addiction-like behavior along with differential NAc gene expression.