Tolerance to cocaine's effects on schedule-controlled behavior: role of delay between pause-ending responses and...

The schedule of reinforcement under which behavior is maintained is an important contributor to whether tolerance to the behavioral effects of cocaine develops. Schedule parameter value (for example, fixed-ratio size) has been shown to affect the development of tolerance under some schedule types but not others, but the specific procedural variables causing this effect remain to be identified. To date, schedule-parameter-related tolerance has developed when a longer pause after reinforcement does not lead to a shorter delay between the response that ends the pause and reinforcement. The current study investigated the importance of this variable in pigeons using a multiple chained Fixed-Ratio 1, Fixed-Time x schedule, in which the first key peck in a trial produced a stimulus change and initiated a delay at the end of which food was presented regardless of whether or not additional pecks were made during the delay. Dose-response curves were assessed before, during and after chronic (daily) administration of cocaine. Tolerance to the pause-increasing effects of cocaine occurred to a similar degree regardless of the scheduled time between the end of the pause and reinforcement. Therefore, the relationship between pause length and delay to reinforcement does not provide an explanation for schedule-parameter-related tolerance.