We determined MAC, the Minimum Alveolar Concentration of anesthetic required to abolish movement in response to a tail pinch in 50% of mice [45]. The investigators assessing movement/non-movement were blinded to the identity of the mouse. Each mouse supplied a single value for the MAC of one or more of the study anesthetics. A period of 45–55 minutes was used to provide equilibration with an initial anesthetic concentration, a concentration that equaled 60%–70% of the concentration ultimately required to suppress movement. Thus all mice initially moved in response to stimulation. The concentration was then increased in steps with equilibration times of 25 to 45 minutes depending on the solubility of the anesthetic (longer times for more soluble anesthetics). At the bracketing concentrations [highest concentration(s) permitting and lowest concentration(s) preventing movement in response to stimulation], the step size equaled 10% to 15% of the preceding value. Rectal temperature was measured to maintain core temperature between 36°C and 39°C with a heating pad.
