¹University of Kansas, Pharmacology and Toxicology, Lawrence, United States

Background: Substance use disorder (SUD), particularly opioid use disorder (OUD), is associated with social impairments that exacerbate relapse risk. The prefrontal cortex (PFC), specifically the prelimbic (PrL) region, regulates both social cognition and drug-seeking behaviors. Clinical and animal studies indicate that chronic opioid exposure disrupts PFC function, leading to heightened responses to drug cues but diminished responses to social stimuli. However, real-time neuronal dynamics in PrL excitatory neurons during these behaviors after prolonged heroin abstinence remain underexplored.

Aims & Objectives: This study aimed to investigate how PrL CaMKII-expressing excitatory neurons respond to heroin-associated cues and social stimuli following 14 days of abstinence from heroin self-administration (SA) in male and female mice. We recorded calcium activity via fiber photometry, assessed its correlation with social behaviors, and examined the underlying synaptic changes to link PFC dysfunction to social deficits and relapse vulnerability.

Method: Male and female C57BL/6J mice underwent jugular catheterization and 10 days of heroin (0.05 mg/kg/infusion) or saline SA. After 14 days of forced abstinence, drug-seeking (1-hour cue-induced test) and social interaction (10-minute test with a conspecific under a capsule) were assessed. AAV-CaMKII-GCaMP6f virus was injected into PrL for fiber photometry recording of calcium signals during home cage baseline, drug-seeking, and social interaction. Whole-cell patch-clamp electrophysiology measured excitatory postsynaptic currents (EPSCs). Data were analyzed using ANOVA, mixed-model ANOVA, and Pearson correlations.

Results: Mice acquired heroin SA, showing increased infusions and active responses versus saline controls. After abstinence, heroin groups exhibited elevated drug-seeking responses and reduced social interaction time in both sexes. PrL neurons displayed hypoactivity at baseline (reduced peak frequency/amplitude in home cage) and during social investigation (decreased z-scores and AUC), with greater reductions in females. Conversely, responses to heroin cues were enhanced (increased z-scores and AUC). Electrophysiology revealed decreased AMPAR- and NMDAR-EPSC amplitudes during abstinence. Moreover, drug-seeking negatively correlated with social time in low-responding heroin mice, and baseline hypoactivity correlated with heightened cue responses.

Discussion & Conclusions: Together, these data suggest that prolonged heroin abstinence impairs PrL excitatory neuron function, yielding opposing responses: heightened sensitivity to drug cues but blunted reactivity to social stimuli. These alterations, linked to synaptic deficits, may underlie social withdrawal and elevated relapse risk in OUD. Targeting PFC circuits could inform novel interventions to mitigate social impairments and prevent relapse.