Chronic alcohol drinking modulates synchrony between midbrain gene transcription and long-lasting changes in dopamine terminal and opioid function in macaques
Alcohol use disorder is marked by disrupted behavioral and emotional states which can persist into abstinence. The enduring synaptic alterations that remain despite the absence of alcohol are of interest for interventions to prevent relapse. 28 male rhesus macaques underwent over 20 months of alcohol drinking interspersed with three 30-day forced abstinence periods. After the last abstinence period, we paired ex vivo voltammetry in nucleus accumbens slices with RNA-sequencing of the ventral tegmental area. We found persistent augmentation of dopamine transporter function, kappa opioid receptor sensitivity, and dynorphin release – all inhibitory regulators which act to decrease extracellular dopamine. Surprisingly, though transcript expression was not altered, the relationship between gene expression and functional readouts of these encoded proteins was highly dynamic and altered by drinking history. Therefore, the long-lasting synaptic impact of alcohol use suggests that assessment of transcript-function relationships may provide avenues for precision therapeutics targeted to specific synaptic pathophysiologies. Overall design: We paired a model of chronic voluntary alcohol (ethanol) drinking and protracted abstinence with within-subject measures of dopamine terminal function and assessment of gene transcription. In an effort to maximize translational relevance and implications of gene expression quantification, rhesus macaque (macaca mulatta) subjects were used, because of the genetic and behavioral diversity in the model that mirrors individual differences in human drinkers(Grant et al., 2008), as well as the homology to humans in genetic sequence(Gibbs et al., 2007) and neural circuit architecture(Balsters et al., 2020; Haber & Knutson, 2010). Following an induction protocol, subjects were allowed to self-administer alcohol under continuous access conditions for 12 months, followed by three one-month abstinence periods interspersed with three-month periods of re-access to alcohol. At the end of the third and final abstinence period, real-time dopamine release kinetics and inhibitory regulation by axonal KORs were measured directly via ex vivo fast-scan cyclic voltammetry in the NAc of 28 rhesus macaques (17 alcohol drinkers, 11 calorically-yoked or housing controls). Bulk RNA-sequencing of the VTA taken from the same subjects was used to measure gene expression upstream of dopamine terminals.