Abstract
Opioids use has been limited due to tolerance and dependence as major unwanted effects. Previous evidence has shown that targeting endocannabinoid signaling can prevent the development of opioid tolerance and dependence. This study was designed to evaluate the effect of phenylmethylsulfonyl fluoride (PMSF), an inhibitor of fatty acid amide hydrolase (FAAH), on morphine antinociceptive tolerance and physical dependence in mice. The antinociceptive effects of PMSF at the doses 60, 120, and 300 mg/kg were investigated. Results showed that PMSF has a notable antinociceptive effect at doses 120 and 300 mg/kg. The dose of (60 mg/kg, i.p.) PMSF was considered as a sub-antinociceptive dose. Morphine tolerance and dependence were induced by twice-daily injection of morphine (10 mg/kg, s.c.) for 10 consecutive days and the last dose on day 11. Tolerance was assessed by the hot-plate test and dependence by naloxone-precipitated morphine withdrawal signs. In the brain, oxidative stress markers include activities of glutathione peroxidase, catalase, superoxide dismutase, and levels of malondialdehyde and glutathione were determined. A sub-antinociceptive dose (60 mg/kg) of PMSF could reduce tolerance in both acute and chronic methods of administration. However, alleviation of dependence and suppression of oxidative stress markers occurred in the chronic administration of PMSF. In conclusion, it seems that PMSF can suppress morphine tolerance and dependence. However, more studies are needed to clarify its mechanism.