CHOICE BETWEEN COCAINE AND FOOD IN A DISCRETE-TRIALS PROCEDURE IN MONKEYS - A UNIT PRICE ANALYSIS

In behavioral economics, the unit price (UP) model of drug consumption defines UP as the ratio of the response requirement to the dose of dr ug. This model makes two predictions: increasing UP will decrease cons umption, and consumption at a given UP will be constant regardless of the response requirement and dose that make up the UP. The present exp eriment was designed to test the UP model in rhesus monkeys allowed to choose between an IV injection of cocaine and food in a discrete-tria ls choice procedure. Both response requirement/injection and dose of c ocaine were varied in such a way as to yield UPs from 40 to 10,000 res ponses per mg/kg. The response requirement for food was always 30 and there was a 30-min time-out between trials to allow the direct effects of cocaine on responding to dissipate. Consistent with the UP model, cocaine consumption decreased as UP increased. However, at a given UP, cocaine consumption was usually higher at the higher dose. Thus, unde r the conditions of the present experiment an important component of t he UP model of drug consumption was not supported. It may be that UP i s not a reliable predictor of consumption under conditions in which th e direct effects of a drug on responding are minimized.