Abstract
Opioid use disorder occurs alongside impaired risk-related decision-making, but the underlying neural correlates are unclear. We developed an approach-avoidance conflict task using a modified conditioned place preference procedure to study neural signals of risky opioid seeking in the prefrontal cortex, a region implicated in executive decision-making. Following morphine conditioned place preference, rats underwent a conflict test in which fear-inducing cat odor was introduced in the previously drug-paired side of the apparatus. While the saline-exposed control group avoided cat odor, the morphine group included two subsets of rats that either maintained a preference for the paired side despite the presence of cat odor (Risk-Takers) or exhibited increased avoidance (Risk-Avoiders), as revealed by K-means clustering. Single-unit recordings from the prelimbic cortex (PL) demonstrated decreased neuronal activity upon acute morphine exposure in both Risk-Takers and Risk-Avoiders, but this firing rate suppression was absent after repeated morphine administration. Risk-Avoiders also displayed distinct post-morphine excitation in PL which persisted across conditioning. During the preference test, subpopulations of PL neurons in all groups were either excited or inhibited when rats entered the paired side. Interestingly, the inhibition in PL activity was lost during the subsequent conflict test in both saline and Risk-Avoider groups, but persisted in Risk-Takers. Additionally, Risk-Takers showed an increase in the proportion of PL neurons displaying location-specific firing in the drug-paired side from the preference to the conflict test. Together, our results suggest that persistent PL inhibitory signaling in the drug-associated context during motivational conflict may underlie increased risk-taking behavior following opioid exposure.
Significance statement Risky opioid use is well established in opioid use disorder, but the underlying neural correlates are poorly understood. In this study, we present findings from a novel behavioral task in which rats face a motivational conflict between contextual opioid reward memory and a naturalistic predator threat. Performing neuronal recordings in the prelimbic prefrontal cortex (PL), a brain region critical for executive decision-making, we demonstrate enhanced representation of drug-associated context and persistent inhibitory signaling by PL neurons that occur alongside opioid-induced risk-taking behavior. Our findings refine a preclinical model for studying addiction, establish PL as a prime region for investigating drug-environment interactions, and positions the prefrontal cortex as a candidate region for translational studies targeting risky opioid use.
Footnotes
The authors declare no competing interests.
We would like to thank our colleagues who provided valuable feedback on earlier versions of this manuscript, including Christian Bravo-Rivera, Freddyson Martinez-Rivera, James Otis, and Leandro Vendruscolo. We thank Nikita Watson and Sharon Gordon for their technical and administrative assistance.
↵#These authors contributed equally to this work.
