The vagus nerve mediates the suppressing effects of peripherally administered oxytocin on methamphetamine self-administration and seeking in rats

BackgroundThe neuropeptide oxytocin has emerged as a promising pharmacotherapy for methamphetamine (METH) addiction, and clinical trials of intranasal oxytocin are underway. However, there is debate as to how peripherally administered oxytocin alters brain signaling to modulate addiction processes. Interestingly, there is evidence for functional interactions between peripheral oxytocin administration and the vagus nerve. Therefore, this study investigated whether the effects of peripherally administered oxytocin require vagal signaling to reduce METH self-administration and reinstatement of METH-seeking behaviours. MethodsMale and female Sprague-Dawley rats underwent surgery for jugular catheterization and either subdiaphragmatic vagotomy (SDV) or a sham operation. Rats were trained to self-administer METH, and the effect of peripherally administered oxytocin on METH intake was assessed. Rats then underwent extinction, and effects of oxytocin were assessed on cue- and METH-induced reinstatement of METH-seeking. ResultsOxytocin treatment robustly attenuated METH intake in both sexes. Strikingly, SDV entirely prevented the suppressant effect of oxytocin (0.3 mg/kg) on METH intake, and partially prevented the effects of 1 mg/kg oxytocin in both sexes. After extinction, SDV impaired the suppressing effects of oxytocin on cue- and METH-primed reinstatement in males, but not females. SDV was functionally confirmed by measuring food intake following administration of the vagal dependent peptide, cholecyostokin-8. ConclusionOur data suggest that vagus nerve signaling is required for the anti-addiction effects of peripherally administered oxytocin, and that this vagal dependency is partially mediated by sex and drug withdrawal. This study has considerable implications for the applicability of oxytocin as a therapy for METH use disorder for both sexes.