Absolute and intensity-difference taste thresholds in the rat: evaluation of an automated multi-channel gustometer.

An operant conditioning procedure is described for assessing taste detection and discrimination in rats. Rats were trained to lick at a 10-barrel stimulus delivery tube for a 0.005-ml sample of a positive (S+) or negative (S-) stimulus and to switch to a water delivery tube after presentation of S+. The system is computer controlled and selection of stimuli can be made interactive with performance. After preliminary training, absolute and intensity-difference thresholds can be determined in 1-2 sessions. Mean absolute thresholds in 10 rats for NaCl, sodium-saccharin, and sucrose were 0.0049%, 0.0012%, and 0.035%, respectively. Intensity-difference thresholds (not reported previously in the rat) for NaCl and saccharin were 16.1% and 12.3%, respectively. With these procedures rats also rapidly acquired 2-tastant discriminations, including those involving taste mixtures.