RATIO SIZE AND COCAINE CONCENTRATION EFFECTS ON ORAL COCAINE-REINFORCED BEHAVIOR

Monkeys were given a choice between cocaine solutions and water under concurrent fixed-ratio reinforcement schedules. The operant response w as spout contact. Six rhesus monkeys served as subjects. The cocaine c oncentration was varied from 0.0125 to 0.8 mg/ml, and the fixed-ratio value was varied from 8 to 128. Cocaine maintained higher response rat es than did water over a wide range of conditions. Response rate and n umber of cocaine deliveries per session were inverted U-shaped functio ns of concentration. These functions were shifted to the right as the fixed ratio was increased. The number of cocaine deliveries was more p ersistent as fixed-ratio value was increased when the unit dose was la rger rather than smaller. Cocaine consumption was analyzed as a functi on of unit price (fixed-ratio value divided by cocaine concentration), and unit price accounted for between 77% and 92% of the variance in c ocaine consumption for individual monkeys. The current data support th e claim that a drug's reinforcing effects increase directly with dose and underscore the need to gather parametric data when examining the e ffects of experimental manipulations on a drug-reinforced baseline.