Chronic inflammatory pain suppresses alcohol intake and accumbal dopamine response

Abstract

Alcohol use disorders (AUDs) are influenced by factors that initiate, maintain, and/or induce relapse. Chronic pain is both a risk factor for and consequence of AUD, sharing neurological pathways that affect the mesolimbic dopaminergic system. This study examines how inflammatory pain impacts long-term alcohol intake and mesolimbic dopamine transmission in alcohol-naïve rats. Inflammatory pain was induced in eight-week-old Sprague Dawley rats using complete Freund adjuvant (CFA), while controls received saline. Two protocols were followed: one group had continuous access to 20 % ethanol for one month (n = 10/sex), and the second group for three months (n = 8/sex) in a two-bottle choice paradigm. Mechanical nociception was assessed weekly using the Von Frey test. Dopamine levels in the nucleus accumbens core were measured through microdialysis during the final 1.5 months of ethanol exposure in the second cohort. Due to experimental limitations animals underwent microdialysis at different time points after alcohol was firstly introduced, this was done in a balanced manner by alternating sex and group. After a month of alcohol exposure, rats showed no differences in alcohol consumption. However, from the second month until the end, rats exhibited a non-sex-dependent decrease in alcohol intake, significantly lower in CFA-animals. This reduction was accompanied by a blunted ethanol-evoked dopamine release in the nucleus accumbens. Moreover, low mechanical nociception was maintained until the end of the experiment in CFA-animal. These findings provide insights into the effect of pain on alcohol-elicited neurochemical responses and drinking behaviour, showing how pain alters dopamine response to alcohol, affecting drinking patterns and prolonging nociception from CFA.