Uncovering phenotypic diversity and cell-type-specific prefrontal cortex calcium dynamics in rat fentanyl self-administration

BACKGROUNDThe proliferation of the potent synthetic opioid fentanyl has exacerbated the ongoing crisis of substance use disorder and associated overdose deaths, yet the neurobiological mechanisms that underlie individual vulnerability to addiction and relapse remain poorly understood, particularly in the context of fentanyl use. The prefrontal cortex (PFC) has been identified as a key brain structure important for cognitive functions impacted in addiction, including inhibitory control of behavior and association of drug experience with specific cues, contexts, or actions. Although the heterogenous neuronal composition of the PFC complicates attribution of addiction-related behavioral regulation to specific cortical cell types and circuits, application of cell-type-specific methods in translationally relevant rodent models have begun to elucidate the key neural substrates of opioid addiction. METHODSWe used an intermittent access fentanyl self-administration (IntA SA) model to characterize individual variation and sex differences in addiction vulnerability in male and female rats. Longitudinal wireless fiber photometry recording was used to track calcium activity patterns in intratelencephalic (IT) neurons of the prelimbic cortex across acquisition of self-administration, escalation of fentanyl intake, extinction training, and cue-induced reinstatement of fentanyl seeking. RESULTSWe found that our fentanyl IntA SA paradigm produces distinct low- and high-risk addiction severity phenotypes and that female rats exhibited a greater propensity for high-risk classification, which was characterized by abundant and consistent fentanyl intake, robust responsiveness to conditioned and discriminative fentanyl-associated cues, and high levels of fentanyl-seeking during periods of drug unavailability, extinction training, and a cue-induced reinstatement test. Fiber photometry recordings revealed dynamic encoding of fentanyl-associated stimuli by prelimbic IT neurons across the IntA SA paradigm with event-related calcium transients observed in association with lever presses, fentanyl infusions, and presentation of conditioned and discriminative cues. CONCLUSIONSOur data indicate that fentanyl IntA SA is a translationally relevant paradigm that enables investigation of phenotypic diversity and the role of sex in fentanyl addiction. Longitudinal cell-type-selective calcium recordings revealed dynamic representation of fentanyl-associated stimuli by IT neurons of the prelimbic cortex consistent with a role for this cortical subpopulation in addiction-related behaviors.