The Suppressive Effects of LiCl, Sucrose, and Drugs of Abuse Are Modulated by Sucrose Concentration in Food-Deprived Rats

Abstract

Suppression of intake of a gustatory conditioned stimulus (CS) occurs when paired with either an aversive or an appetitive unconditioned stimulus (US). Toxic substances, such as lithium chloride (LiCl), induce conditioned taste aversions while rewarding stimuli, such as high a concentration of sucrose, reduce intake through a comparison process referred to as anticipatory contrast. Drugs of abuse also suppress CS intake, but it is not known whether they do so via their rewarding or aversive properties. Using 0.1, 0.3, or 0.5 M sucrose solutions as the gustatory CS, we compared the suppressive effects of LiCl (5.29 mg/kg), morphine (15 mg/kg), cocaine (10 mg/kg), and a 1.0-M sucrose solution in rats that were food deprived. The doses of the three drugs have been equated in terms of their suppressive effects in water-deprived and free-feeding rats. The results showed that in food-deprived rats the sucrose US failed to suppress intake of any of the sucrose CSs, the drugs of abuse failed to suppress intake of the 0.3 and 0.5-M concentration of sucrose, and LiCl failed to suppress intake of the 0.5-M sucrose solution. When taken together, these findings reveal that the suppressive effects of all USs (aversive, appetitive, and drugs of abuse) can be offset by the use of a caloric CS when evaluated in food-deprived rats.