were four hours. Food training for the PR schedule was essential for increasing the number of animals that learned to lever press for cocaine and to decrease the time needed to train the animals after surgery. Complications associated with intravenous (IV) catheter patency and maintenance of head mounts, make it important to minimize the training period. The PR reinforcement schedule required animals to increase lever presses progressively for each successive reward in the following series, within a self-administration session: FR1, 2, 4, 6, 9, 12, 15, 20, 25, 32, 40, 50, 62, 77, 95, 118, 145, 178, 219, 268, 328, 402, 492, 603, 737, 901. Sessions on PR schedules were terminated if the animal stopped pressing the active lever for longer than 60 minutes. The last ratio successfully completed was registered as the BP for that session.
