Withdrawal convulsions in mice following nitrous oxide

Mice may be induced to convulse after (but not prior to) breathing nitrous oxide. We found that the incidence of this withdrawal phenomenon is related to the partial pressure of nitrous oxide. A minimum (threshold) value of about 0.5 atm is necessary and the majority of mice convulse following exposure to 0.9 atm or greater. Exposures of longer than 15 to 30 minutes do not significantly increase the incidence of convulsions at any given partial pressure. The mice remain susceptible to the induction of convulsions for only a brief period after removal from nitrous oxide. Although the duration of susceptibility is slightly increased after exposure to higher partial pressures, susceptibility in almost all cases is lost by 90 minutes. In mice, exposure to nitrous oxide is associated with evidence of physical dependence as evidenced by withdrawal symptoms, symptoms that be related to the appearance of excitement which sometimes follows nitrous oxide anesthesia.