CONDITIONED SUPPRESSION AS A METHOD OF DETECTING TASTE THRESHOLDS IN THE RAT

Taste thresholds of seven male Sprague-Dawley rats (mean age 10 weeks, mean weight 250 g) were determined for four basic taste qualities: sweet, sour, salty and bitter. The method of conditioned suppression as employed. An apparatus capable of presenting any one of eight separate drinking tubes during a testing session was designed. Animals were reduced to 80-85% ad lib. body weight. They were then trained to lick a sipper tube through a slot in the back of an experimental chamber for pellet reinforcements. Animals progressed through a series of reinforcement schedules starting wit a fixed ratio (FR) schedule of five licks for each reinforcement. They advanced to a variable ratio (VR) schedule of reinforcement and finally a variable interval (VI) schedule with a mean of 17.5 s was used. While on the VI schedule animals were trained to suppress licking when any tastant other than water was presented. The first lick on any tastant was followed 10 s later by a mild electric shock if a rat made more than 20 licks on the tube in the 10-s period. Less than 20 licks on a tastant tube resulted in no shock and a 5-s time out before proceeding to the next tube. Threshold was determined using a suppression ratio formula. Threshold was defined as the 0.33 suppression ratio. Results from this experiment reveal mean threshold for the seven animals as:sucrose = 2.3 mM, NaCl = 0.63 mM, quinine HCl = 0.005 mM and citric acid = 0,085 mM.