Mouse Breathalyzer

Background:  The development of a relatively simple, noninvasive method for estimating blood ethanol concentrations in mice will be useful in behavioral studies related to alcoholism. This study validated such a method. Methods:  The apparatus consists of a body chamber fitted with a head stock through which the mouse head protrudes. This was fitted against a water‐jacketed head‐space chamber surrounding the mouse’s head. Rebreathed air maintained at 37°C in the head‐space chamber was removed using a peristaltic pump and loaded into a 1‐ml injection loop. Ethanol in the sample was quantified using gas chromatography. To validate this method, ethanol levels in breath samples were compared against those in tail blood samples collected immediately after the breath samples. Breath samples were collected at 5, 10, 20, 40, 80, 120, and 160 minutes after ethanol (0.4, 0.8, 1.2, 1.6, 2.4, and 3.2 g/kg) was administered to male C57BL/6J mice. Results:  Breath and blood ethanol levels were well correlated ( r 2  = 0.96) across time points on the descending ethanol–time curve at doses below 2.4 g/kg. Correlation for these doses on the ascending portion of the curve had greater variance, but was still well correlated ( r 2  = 0.92). Conclusions:  The mouse breathalyzer is an accurate, convenient, noninvasive and well‐tolerated method for estimating blood ethanol concentrations in mice across a range of behaviorally relevant concentrations below 2.4 g/kg, especially on the descending limb of the ethanol–time curve. Although this procedure requires a gas chromatograph in the animal facility, the ability to estimate ethanol concentrations quickly and easily will be especially useful in behavioral studies where repeated blood sampling is not feasible.