While the concurrent use of alcohol and cocaine is common in patterns of polysubstance use, little is known about the combined effects of these substances on the brain. Proteomics approaches enable the identification of potential biomarkers and new pharmacological targets for the diagnosis and treatment of addiction and related psychiatric disorders. The main goal of this study was to explore how the combination of cocaine and alcohol affects brain peptide/protein signatures in the mesolimbic dopaminergic pathway.

To this end, we used a chronic and simultaneous intravenous administration of these substances in a Wistar rat animal model. Peptide/protein profiles in five brain regions (ventral hippocampus, dorsal hippocampus, amygdala, nucleus accumbens and prefrontal cortex) from individual animals were characterised by means of matrix-assisted laser desorption/ionisation imaging mass spectrometry (MALDI-IMS).

Our results showed that, compared to exposure to cocaine or alcohol separately, the combination of cocaine and alcohol has a synergistic effect on the number of differentially expressed peptides/proteins (DEPs) detected in all regions, particularly the amygdala. ANOVA reveals 13 DEPs, corresponding to 12 peptides/proteins, that vary significantly between all groups. Gene ontology (GO) analysis indicated that most of the DEPs found for the combined treatment are enriched in neuropeptide receptor binding, neuropeptide signalling and regulation of circadian sleep/wake process pathways.

Our findings demonstrate that the combination of cocaine and alcohol significantly exacerbates the effects of each substance separately on the expression of peptides and proteins with multiple physiological functions, including the opioid- and GABA-ergic neurotransmission systems. This study therefore provides the basis for future research on biomarkers and substance recovery therapies.

These insights underscore the importance of examining the interactions between cocaine and alcohol in terms of their effects on neurotransmitter systems in the context of polysubstance use, particularly when addressing issues related to cocaine and alcohol co-use.