Influence of narcotic antagonist drugs upon nitrous oxide analgesia in mice

Abstract

Nitrous oxide produced a concentration-related suppression of phenylquinone-induced abdominal constriction in mice. This analgesic effect was significantly reduced (but not abolished) by systemic pretreatment with (-)-naloxone or naltrexone but not (+)-naloxone. Systemic pretreament with methylnaltrexone failed to appreciably influence nitrous oxide analgesia: however, methylnaltrexone, administered centrally, significantly attenuated the drug effect. Furthermore, nitrous oxide analgesia was significantly reduced by MR-2266 (which is relatively selective for κ-opioid receptors) but notby β-funaltrexamine (which is selective for μ-opioid receptors) at the doses employed in this study. These findings suggest that nitrous oxide analgesia might involve an activation of κ-opioid receptors in the central nervous system; however, a possible involvement of μ-opioid receptors is not absolutely precluded by this study. © 1988.