Cocaine and Food as Reinforcers: Effects of Reinforcer Magnitude and Response Requirement Under Second‐order Fixed‐ratio and Progressive‐ratio Schedules

Abstract

Reinforcer magnitude and fixed-ratio requirement were varied under two second-order schedules. Under one, the first sequence of a fixed number of responses completed after the lapse of a 10-min fixed interval produced reinforcement. Under the second, a second-order progressive-ratio schedule, the fixed number of responses increased after each reinforcement. Either cocaine (0 to 300 micrograms/kg/inj) or food (0 to 5,700 mg/delivery) reinforcers were delivered. Under some conditions, a 2-s illumination of stimulus lights occurred on completion of each ratio sequence. Under the second-order schedule, as cocaine dose or amount of food increased, rates of responding increased; at the highest values, rates of responding decreased. Increases in the ratio requirement from 10 to 170 responses minimally decreased overall response rates. Under the second-order progressive-ratio schedule, increases in dose of cocaine or amount of food increased rates of responding; at the highest amounts of food, rates of responding decreased but response rates at the highest dose of cocaine remained relatively high. The highest ratio requirement that was completed (breaking point) depended on the dose of cocaine but was less dependent on the amount of food. Removing brief-stimulus presentations had a greater effect on completion of ratio requirements with cocaine compared to food.

Stimuli produced by observing responses make rats' ethanol self-administration more resistant to price increases

“…The increased persistence of ethanol consumption in the presence of the ethanol-associated stimulus is similar to effects obtained with stimuli paired with cocaine infusions in second-order schedules of reinforcement (Spear and Katz 1991;Ranaldi and Roberts 1996). That is, cocaine-maintained responding persists at higher response requirements when these responses also intermittently produce stimuli paired with cocaine infusions.…”

Progressive-ratio schedules of drug delivery in the analysis of drug self-administration: a review

“…Further, several of the experiments that have measured such performance have observed that the vehicle often maintains a breaking point substantially greater than zero (e.g. Gerber and Stretch 1975;Hoffmeister 1979;Spear and Katz 1991). Data from other reports indicate that the vehicle maintains little or no responding (e.g.…”

Comparison of the reinforcing efficacy of cocaine and procaine in rhesus monkeys responding under a progressive-ratio schedule

“…The response requirement at which responding ceases has been called the breaking point or breakpoint (BP). A variety of PR schedules have been used to study behavior maintained by several different positive reinforcers, including food (Spear and Katz 1991), sweetened solutions (Bedford et al 1978;Hodos 1961) and electrical stimulation of the brain (Hodos 1965;Keesey and Goldstein 1968). A general conclusion of those studies has been that BP increases with reinforcer magnitude.…”