Genetics of novelty seeking and propensity for drug abuse in outbred rats

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Substance abuse disorders (SUDs) are a major challenge to individuals and society and are caused by the interplay between genetic factors that shape vulnerability to drug addiction and environmental variables that can trigger and affect the course of these disorders. The goal of this project is to uncover the genetic and genomic mechanisms underlying the propensity for drug seeking and drug addiction.

Evidence shows that the vast inter-individual differences in vulnerability to SUDs are strongly related to temperamental traits. We therefore established a unique animal model of temperament that is highly genetic and highly predictive of drug-related behaviors. We selectively bred two lines of rats based on differences in their propensity for exploratory locomotion (EL) in a mildly stressful novel environment.

The bred High Responders (bHRs) and bred Low Responders (bLRs) show contrasting spectra of heritable behaviors. Compared to bLRs, bHRs exhibit higher sensation seeking and impulsivity, a greater propensity to sensitize to psychostimulants, and lower thresholds for drug- and cue-induced relapse, reminiscent of human “externalizing disorders”. The bLRs are more prone to anxious and depressive behaviors, more responsive to stress, which triggers drug-seeking behavior.

Thus, the two lines model sensation seeking and high reactivity to stress as two paths to SUD. Our working hypothesis is that functional DNA variants, derived from outbred Sprague Dawley founders, account for the current neural and behavioral divergence of the two lines and are relevant to drug addiction. During the past funding period, we have identified quantitative trait loci (QTL) for EL and anxiety behaviors and have uncovered several genes and genetic pathways associated with differences in temperament.

Our current goal is to increase our understanding of the genetic architecture of our two selectively bred lines and to focus on specific genes likely to shape the differential propensity for cocaine-seeking. Our Specific Aims (SA) are:

SA1: Deepen our understanding of the genomic and transcriptional neural activity of the bHR-bLR lines using new technologies to characterize structural variations, chromatin accessibility and single nuclei multiomics.

SA2: Characterize the differential impact of cocaine acquisition on the brains of bHRs vs. bLRs and relate the findings to genetic and genomic differences between them. Use chromatin accessibility/gene expression at the single cell level and spatial transcriptomics to define the neural impact of cocaine with cellular granularity.

SA3: Identify target genes that play a key role in temperamental differences and/or the response to psychostimulants using stringent convergent criteria. We will characterize their expression and regulation by cocaine in specific cell types and brain areas implicated in addiction. This will lay the groundwork for mechanistic studies that establish their causal role in addiction and will enable future pharmacological interventions.

Our discoveries will illuminate the genetic and neurobiological links between sensation seeking and psychostimulant abuse in humans and inform precision approaches to the treatment and prevention of SUDs.