RELATIVE REINFORCING EFFECTS OF DIFFERENT DOSES OF ORALLY DELIVERED COCAINE

The relative reinforcing effects of different doses of oral cocaine we re investigated in two adult male rhesus monkeys. In the first experim ent, a range of cocaine doses (0.1-0.8 mg/ml) was studied with drug an d water concurrently available for 3 h each day under identical and in dependent fixed-ratio schedules. The side positions of the drug and ve hicle were alternated from session to session. Drug deliveries always exceeded vehicle deliveries, i.e., orally delivered cocaine functioned as a reinforcer. The highest rates of responding occurred at either t he lowest or next to lowest dose (0.1 or 0.2 mg/ml). In the second exp eriment, pairs of different cocaine doses were systematically presente d under identical and independent fixed-ratio schedules. The higher of two concurrently available doses usually maintained the higher respon se rate. These findings suggest that the relative reinforcing effects of orally delivered cocaine increase with dose. Absolute response rate s obtained with single cocaine doses and water concurrently available do not always reflect the magnitude of the reinforcing effects indicat ed when pairs of cocaine doses are studied together. The results of th is study are in agreement with earlier investigations in which the rel ative reinforcing effects of pairs of intravenous cocaine doses or ora l pentobarbital doses were studied. Taken together these findings indi cate that, over a range of doses and across pharmacological classes an d routes of administration, relative reinforcing effects of a drug inc rease directly as a function of increases in dose.