Protracted opioid withdrawal behaviors are reduced by nitric oxide inhibition in mice

Abstract

Following opioid cessation, patients with opioid use disorder experience physical and psychological withdrawal symptoms. Prolonged negative affect, including anxiety and heightened stress reactivity, continues after physical withdrawal symptoms subside, contributing to the high relapse rates. The nitric oxide system plays a role in synaptic plasticity downstream of the mu opioid receptor pathway, and nitric oxide synthase inhibitors attenuate physical opioid withdrawal signs. We hypothesized that N(gamma)-nitro-l-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, would reduce negative affect after protracted opioid withdrawal. Therefore, we first modeled withdrawal in male and female mice using 5 days of morphine injections followed by behavioral tests after one week of forced abstinence from morphine. One week of morphine withdrawal caused altered responses to tests of affective behavior in both male and female mice. There were, however, both subtle and significant sex differences among many of the behavioral measures of negative affect. Males and females had differences in immobility during the tail suspension test during morphine withdrawal, while only females had altered grooming in the sucrose splash test. Forced l-NAME in the animals’ drinking water during withdrawal attenuated all physical and affective measures of withdrawal in males and females but there were subtle differences. Together, these results suggest that the nitric oxide system may be a target to ameliorate the different behavioral manifestations of negative affect in males and females.