Nitrous oxide generalizes to a discriminative stimulus produced by ethylketocyclazocine but not morphine.

Nitrous oxide, an analgesic and anesthetic gas, produces subjective effects in rats that resemble those of psychotomimetic drugs rather than morphine. Rats trained to discriminate ethylketocyclazocine, a psychotomimetic opioid, generalized the cue to nitrous oxide in a concentration-dependent manner, while rats trained to discriminate morphine did not generalize even at 80 percent nitrous oxide. The narcotic antagonist naltrexone did not block this generalization. These findings align with human studies and suggest that nitrous oxide, despite sharing some analgesic properties with morphine, has distinct subjective effects similar to psychotomimetic substances.

Study at a glance

Abstract

The discriminative stimulus properties of nitrous oxide, an analgesic and anesthetic gas, were evaluated in rats trained to discriminate the effects of morphine or ethylketocyclazocine. Administration of nitrous oxide in concentrations as high as 80 percent did not produce generalization to the discriminative cue produced by morphine. Nitrous oxide did, however, generalize in a concentration-dependent manner in rats trained to discriminate ethylketocyclazocine, a psychotomimetic opioid. Naltrexone, a potent narcotic antagonist, did not block the generalization of nitrous oxide to ethylketocyclazocine. These results suggest that the subjective effects of nitrous oxide are similar to those produced by psychotomimetic drugs rather than those produced by morphine. These findings are in close agreement with those generated in man. Thus, nitrous oxide exhibits some pharmacological properties similar to those of morphine, for example, naloxone reversible analgesia. Yet, it has other properties such as subjective effects that are dissimilar from morphine.