Attenuated aversiveness of electric shock during nitrous oxide exposure

The analgesic properties of nitrous oxide (N2O) were evaluated with a fractional escape procedure ("shock titration" schedule). Shock intensity rose by a small step every few seconds. Each designated response by a rat or squirrel monkey subject reduced the amplitude of the shock by one step. Both species maintained stable tolerated levels of shock when exposed to pure oxygen or to air. Exposure to N2O yielded an elevation in maintained shock level whose magnitude depended on concentration. Statistically significant rises generally were apparent at N2O concentrations of 30 to 70%, which also tended to reduce shock level fluctuations. Since the raised shock levels were not accompanied by changes in overall response rate, they can be attributed to the analgesic properties of N2O.