Differences in morphine and cocaine reinforcement under fixed and progressive ratio schedules; effects of extinction, reacquisition and schedule design

Abstract

Opiate reinforcement was evaluated under a progressive ratio (PR) schedule often used for psychostimulant self-administration (termed 'PR 3-4' because the third response requirement was four lever presses) and three additional schedules that were modified to provide successively lower levels of difficulty by decreasing the steepness of response requirement progression (termed 'PR 9-4', 'PR 14-4', and 'PR 26-4' because a response requirement of four was reached with step numbers of 9, 14 and 26, respectively). With the exception of the PR 3-4 schedule, all of the schedules supported morphine self-administration, and morphine self-administration during initial exposure and reacquisition did not differ by more than 10%. In contrast to morphine, cocaine was self-administered under the PR 3-4 schedule, with responding clearly exceeding levels during extinction. The PR 9-4 schedule was most suitable for morphine self-administration because it provided an intermediate level of difficulty, which supported levels of self-administration that exceeded values obtained under extinction but were less than those observed under FR-1. Under the PR 9-4 schedule, the number of self-administered injections of morphine was 61.5% of the number of injections obtained under a simple FR-1 schedule. This compares with a value of 21.0% for cocaine self-administration under the PR 3-4 schedule compared to an FR-1 schedule. These results show important differences in self-administration behavior supported by morphine and cocaine, which are consistent with a lower reinforcing efficacy for opiates relative to psychostimulants.

Enduring effects of tacrine on cocaine-reinforced behavior: Analysis by conditioned-place preference, temporal separation from drug reward, and reinstatement

“…Two additional 20-minute sessions were conducted in which food pellets were made available under a progressive-ratio schedule, to expose animals to an increased response requirement. A PR 9-4 progressive ratio schedule was utilized in these sessions with a time-out of five seconds (Li et al, 2003), which incremented response requirement in the following pattern: 1, 1, 1, 2, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 9, 9, 10, 11, 11, 12, 13, …,.…”

A theory of behaviour on progressive ratio schedules, with applications in behavioural pharmacology

“…In progressive ratio (PR) schedules, the required number of responses is systematically increased, typically from one reinforcer to the next (Hodos 1961), but sometimes between sessions (Czachowski and Samson 1999) or according to some other schedule (e.g. Li et al 2003;Richardson and Roberts 1996;. Responding on PR schedules is generally found to be well maintained under lower ratios; however, the rate of responding declines with progressive increases in the ratio The order of authorship is alphabetical.…”

Monoamine Oxidase Inhibitors Allow Locomotor and Rewarding Responses to Nicotine

“…The same drugs induce locomotor hyperactivity, behavioral sensitization, conditioned place preference, and self-administration in rodents (Vezina et al, 1994;Pontieri et al, 1995;Biala and Langwinski, 1996;Carboni et al, 2003;Li et al, 2003). Tobacco is a potent reinforcing agent in humans, and nicotine is generally considered to be the major compound responsible for its addictive properties (Dani and Heinemann, 1996;Balfour et al, 2000;Di Chiara, 2000).…”