Profiling the effects of alcohol history on cognitive performance during abstinence: an examination of proenkephalin-A-derived peptides in the medial prefrontal cortex

Cognitive impairments during abstinence may complicate recovery from alcohol use disorder, but their persistence across executive domains and accompanying cortical adaptations remain unclear. Neuropeptides are candidate mediators of persistent alcohol (ethanol; EtOH) effects, and emerging evidence implicates endogenous opioid peptides in cortical processing. Here, we examined cognitive function and medial prefrontal cortex (mPFC) enkephalin profiles in rats with a history of chronic EtOH exposure. Using a longitudinal operant-based approach, we assessed cognitive flexibility during early abstinence and delay-dependent working memory during protracted abstinence. We then quantified methionine-enkephalin (Met-ENK) and leucine-enkephalin (Leu-ENK) and profiled the proenkephalin-A (PENK)-derived peptide pool in the mPFC. EtOH history did not alter overall trials or errors to criterion during strategy set-shifting or reversal learning. During reversal, however, EtOH rats showed greater perseverative bias, with response adjustments less aligned with recent feedback and more strongly influenced by prior reinforcement. During initial testing at the longest working memory delay, EtOH rats also showed lower accuracy. Performance across these tasks was correlated in EtOH rats, suggesting individual differences in cognitive susceptibility were maintained across abstinence. Targeted analyses showed comparable levels of Met-ENK and Leu-ENK between groups. Although individual PENK-derived sequences did not differ in abundance, compositional analysis showed a greater summed relative contribution of C-terminal fragments in EtOH samples. These findings indicate that EtOH history produces lasting cognitive vulnerabilities that emerge under greater task demands, with some animals remaining more susceptible than others. C-terminal PENK profiling may reveal novel targets associated with enduring mPFC adaptations during abstinence.