title: Acute and chronic effects of morphine under a progressive-ratio 25 schedule of food delivery.
abstract: The present study examined the effects of morphine in pigeons responding under a progressive-ratio 25 schedule of food delivery. Morphine initially reduced response rates and breaking points. With chronic exposure, tolerance developed to these effects. The magnitude of the observed tolerance was not obviously different from that previously reported under a PR 5 schedule of food delivery. In addition, when drug effects were compared under the fixed-ratio 25 and fixed-ratio 100 components comprised by the progressive-ratio schedule, comparable tolerance was observed. Although prior studies using other procedures have shown that ratio size modulates the development of tolerance to morphine and other drugs, the present data suggest that this relation is constrained, and is not easily observed under progressive-ratio schedules.
authors.affiliation: Department of Psychology, Western Michigan University, Kalamazoo 49008, USA.
authors.forename: K
authors.initials: K
authors.lastname: Jarema
authors.forename: C
authors.initials: C
authors.lastname: Macomber
authors.forename: M
authors.initials: M
authors.lastname: Lesage
authors.forename: A
authors.initials: A
authors.lastname: Poling
mesh_terms: D000701:Analgesics, Opioid / Q000008:administration & dosage* / Q000494:pharmacology; D000818:Animals; D010856:Columbidae; D004305:Dose-Response Relationship, Drug; D004361:Drug Tolerance; D018565:Food-Drug Interactions; D009020:Morphine / Q000008:administration & dosage* / Q000494:pharmacology