Introduction: There are numerous pharmacologic treatments for opioid use disorder (OUD), but none that directly target the underlying addictive effects of opioids. Oxytocin, a peptide hormone produced in the paraventricular nucleus of the hypothalamus (PVN), has been investigated as a potential therapeutic for OUD. Promising preclinical and clinical results have been reported, but the brain region(s) and mechanism(s) by which oxytocin impacts reward processes remain undetermined. Methods: Here, we assess peripherally administered oxytocin’s impacts on cued reinstatement of heroin seeking following forced abstinence and its effects on neuronal activation in the PVN and key projection regions. We also examine how DREADD-mediated activation or inhibition of oxytocinergic PVN neurons alters cued heroin seeking and social interaction. Results: As predicted, peripheral oxytocin administration successfully decreased cued heroin seeking on days 1 and 30 of abstinence. Oxytocin administration also led to increased neuronal activity within the PVN and the central amygdala (CeA). Activation of oxytocinergic PVN neurons with an excitatory (Gq) DREADD did not impact cued reinstatement or social interaction. In contrast, suppression with an inhibitory (Gi) DREADD reduced heroin seeking on abstinence day 30 and decreased time spent interacting with a novel conspecific. Discussion: These findings reinforce oxytocin’s therapeutic potential for OUD, the basis for which may be driven in part by increased PVN-CeA circuit activity. Our results also suggest that oxytocin has distinct signaling and/or other mechanisms of action to produce these effects, as inhibition, but not activation, of oxytocinergic PVN neurons did not recapitulate the suppression in heroin seeking.

Relapse to drug seeking involves transient synaptic remodeling that occurs in response to drug associated cues. This remodeling includes activation of matrix metalloproteinases (MMPs) to initiate catalytic signaling in the extracellular matrix (ECM) in the nucleus accumbens core (NAcore). We hypothesized that MMP activity would be increased in the NAcore during cue-induced methamphetamine (meth) seeking in a rat model of meth use and relapse. Male and female rats had indwelling jugular catheters and bilateral intracranial cannula targeting the NAcore surgically implanted. Following recovery, rats underwent meth or saline self-administration (6hr/day for 15 days) in which active lever responding was paired with a light+tone stimulus complex, followed by home cage abstinence. Testing occurred after 7 or 30 days of abstinence. On test day, rats were microinjected with a FITC-quenched gelatin substrate that fluoresces following cleavage by MMPs, allowing for the quantification of gelatinase activity by MMP-2 and -9 during cued relapse testing. MMP-2,9 activity was significantly increased in the NAcore by meth cues presentation after 7 and 30 days of abstinence, indicating that remodeling by MMPs occurs during presentation of meth associated cues. Surprisingly, while cue-induced seeking increased between days 7 and 30, suggesting behavioral incubation, MMP-2,9 activity did not increase. These findings indicate that while MMP activation is elicited during meth cue-induced seeking, MMP activation did not parallel the behavioral incubation that occurs during extended drug abstinence.

Relapse to drug seeking involves transient synaptic remodelling that occurs in response to drug-associated cues. This remodelling includes activation of matrix metalloproteinases (MMPs) to initiate catalytic signalling in the extracellular matrix in the nucleus accumbens core (NAcore). We hypothesized that MMP activity would be increased in the NAcore during cue-induced methamphetamine (meth) seeking in a rat model of meth use and relapse. Male and female rats had indwelling jugular catheters and bilateral intracranial cannula targeting the NAcore surgically implanted.Following recovery, rats underwent meth or saline self-administration (6 h/day for 15 days) in which active lever responding was paired with a light + tone stimulus complex, followed by home cage abstinence. Testing occurred after 7 or 30 days of abstinence. On test day, rats were microinjected with a fluorescein isothiocyanate (FITC)-quenched gelatin substrate that fluoresces following cleavage by MMP-2,9, allowing for the quantification of gelatinase activity during cued-relapse testing.MMP-2,9 activity was significantly increased in the NAcore by meth cues presentation after 7 and 30 days of abstinence, indicating that remodelling by MMPs occurs during presentation of meth associated cues. Surprisingly, although cue-induced seeking increased between Days 7 and 30, MMP-2,9 activity did not increase. These findings indicate that although MMP activation is elicited during meth cue-induced seeking, MMP activation did not parallel the meth seeking that occurs during extended drug abstinence.