Determination of carbon dioxide detection thresholds in trained rats

Concentration-response functions for the detection of CO2 were established for six rats. The animals were tested in a wind tunnel apparatus and trained using standard operant techniques and a discrete trials, go, no-go successive discrimination paradigm. The primary conclusion to be drawn from the performance measurements is that, at least under carefully controlled conditions, rats can detect physiologic concentrations of CO2 (0-4%). Minimum detectable concentrations fell within the range of 0.04-1.7% CO2. The concentration-response function describing the detectability of CO2 for the six rats was divided into an upper and lower limb at a concentration (5%) that was approximately equal to the end expiratory CO2 levels for the rat (4.88%). High levels of performance were observed for concentrations above this point, while those below it (0.02-2.5%) represented the dynamic range of detectability. Based on a 65% performance criterion, the average threshold performance for six rats was 0.52%. Possible interpretations of these data are discussed.