Behavioural thermoregulation in mice: effects of low doses of general anaesthetics of different potency

Chloroform, monochlorodifluoromethane and nitrous oxide produced dose-related decreases in the rectal temperatures of mice allowed to choose between a warm and a cool environment. The doses used were subanaesthetic, respectively 0.0013-0.004, 0.028-0.085 and 0.25-0.5 atm. The hypothermia (up to 3.6 degrees C) was usually associated with significant reductions in time spent in the warm. The log dose-hypothermic response plots were approximately parallel and there was a marked correlation between anaesthetic potency, as measured by the abolition of the righting response, and hypothermic potency.