Effects of pharmacological manipulations on "demand" for food by baboons

In a study examining the effects of pharmacological manipulations on "demand" for food, responding of six adult male baboons (Papio c. anubis) was maintained under a fixed-ratio schedule of food reinforcement during daily 22h experimental sessions. Increasing the response requirement decreased daily food intake. Administration of anorectic drugs (amphetamine, fenfluramine, diethylpropion, phenmetrazine, phenylpropanolamine and mazindol) produced parallel dose-dependent downward shifts in responding at all response costs. In contrast, administration of the anxiolytic, diazepam, produced parallel dose-dependent upward shifts in responding at all response costs. Oral phencyclidine decreased intake during the first 8h of the session, but compensatory feeding later in the day eliminated this effect. Changes in pellet intake were fitted to a theoretical equation derived by Hursh et al. (1988) to describe changes in demand for a commodity. When responding increases as a result of increasing cost, demand is said to be inelastic, but when responding decreases as a result of increasing cost, demand is said to be elastic. Administration of anorectic drugs, while decreasing maximal intake at minimal cost, had no effect on the elasticity of demand for food. Similarly, diazepam increased maximal intake at minimal cost without affecting the elasticity of demand for food. The effect of anorectic drugs differs from the previously reported effects of caloric substitutes which increase the elasticity of demand for food. Thus, anorectic drugs do not function as caloric substitutes, in an economic sense, for food.