Differential effects of cocaine on high and low response rates maintained with and without rate requirements

Keypecking was maintained by a multiple (tandem random-interval 45-s, differential reinforcement of low rate 3-s) (tandem random-interval 45-s, differential reinforcement of high rate 0.2-s) schedule of food reinforcement in three pigeons. During non-drug sessions these schedule contingencies effectively controlled high and low response rates under approximately equal reinforcement frequencies. The behavioural effects of acute cocaine administration were assessed in the presence and absence of the response rate requirements (i.e. DRL, DRH contingencies). In the absence of response rate requirements cocaine administration consistently decreased high response rates. Low response rates tended to increase after the lower doses of cocaine, while thèy decreased consistently after the higher doses. High response rates decreased less after the lower doses of cocaine, in two of the three pigeons, when cocaine was administered in the presence of the rate requirements than when cocaine was administered in the absence of the rate requirements, while low rates increased less. Rate of reinforcement remained relatively constant across different lower doses of cocaine in the absence of high-rate requirements, but decreased in the presence of the high-rate requirements. Higher doses of cocaine consistently decreased reinforcement rate. These results support the notion that the behavioral effects of drugs may be a function of the extent to which response rates are directly controlled by schedule variables.