Physical dependence on nitrous oxide in mice: resemblance to alcohol but not to opiate withdrawal.

Mice of two strains, Crl:CD-1(1CR)Br and C57BL6, were exposed to nitrous oxide at concentrations of 50, 65 and 80 per cent for 34 or 68 hours. Cessation of nitrous oxide resulted in characteristic convulsions similar to those seen in alcohol withdrawal in all mice. These peaked in severity within 2-3 minutes after removal from nitrous oxide and declined over 6 hours. The severity and duration of these convulsions were related to the nitrous oxide concentration and duration of exposure. Naloxone or naltrexone produced no significant increase in severity of convulsions. The narcotic antagonists did not precipitate acute weight loss or characteristic jumping behaviour seen in animals dependent on opiates. These results demonstrate that chronic exposure to nitrous oxide results in development of physical dependence which resembles alcohol and not opiate dependence. Analgesia and physical dependence produced by nitrous oxide appear to be mediated through separate mechanisms.