Effects of sibutramine and rimonabant in rats trained to discriminate between 22- and 2-h food deprivation

Objective: The objective of the study was to evaluate whether sibutramine and rimonabant, drugs that decrease food intake in human and non-human animals, affect the discriminative stimulus effects associated with acute food deprivation ("hunger"). Materials and methods: Rats were trained to discriminate between 22- and 2-h food deprivation in a two-lever choice procedure. After rats acquired the discrimination, subjects were food-restricted for 22 h and administered with sibutramine (0.32-10 mg/kg, p.o.) or rimonabant (0.32-10 mg/kg, s.c.) before a generalization test session. Results: Sibutramine (3.2 mg/kg) produced significant decreases in 22-h deprivation-appropriate responding, response rates (resulting in lever pressing rates similar to those following 2-h food deprivation), and food intake measured 1 h after the generalization test. A larger sibutramine dose eliminated responding and significantly reduced food intake. Rimonabant did not alter the discriminative stimulus effects of 22-h food deprivation, but rimonabant did significantly reduce both response rates and food intake. Conclusion: Sibutramine appears to decrease food intake by reducing hunger sensations associated with food deprivation. In contrast, rimonabant does not alter the discrimination of acute food deprivation. The use of food-deprivation discrimination techniques may be useful in identifying the role of specific neuroactive compounds in eating stimulated by a sense of hunger and may aid in medication development for more effective treatments for obesity and other eating-related conditions.