Progressive ratio and fixed ratio schedules of cocaine-maintained responding in baboons

Roland R. Griffiths, L. Di Anne Bradford, Joseph V. Brady

Research output: Contribution to journalArticlepeer-review

94 Scopus citations


Responding maintained under progressive ratio (PR) and fixed ratio (FR 160) schedules of IV saline or cocaine (0.01-4.0 mg/kg) injections was studied in baboons. Each injection was followed by a time-out period which was 3-h with the PR schedule and was either 3 or 12 h with the FR schedule. On the PR schedule the ratio requirement was systematically increased each day until reaching the 'breaking point' at which self-injection performance fell below a criterion level (one or zero injections per day). Overall response rates on the PR schedule increased with progressive increases in the ratio until a maximum at which an abrupt reduction in responding occurred. With the 3-h time-out the dose-breaking point function on the PR schedule was similar to the dose-response rate function on the FR schedule. These dose-effect functions were inverted U-shaped curves characterized by a graded ascending limb (0.01-0.32 mg/kg) and a downturn at the highest doses (3.0-4.0 mg/kg). On the FR schedule the downturn in the dose-response rate function was attributable to a cumulative drug effect as revealed by manipulation of time-out duration and analysis of sequential interresponse time distributions and cumulative response records. PR and FR schedules provide similar information about the relative reinforcing efficacy of different cocaine doses.

Original languageEnglish (US)
Pages (from-to)125-136
Number of pages12
Issue number2
StatePublished - Oct 1 1979


  • Baboons
  • Cocaine
  • Drug self-administration
  • Fixed ratio schedule
  • Interresponse times
  • Lever press
  • Progressive ratio schedule
  • Reinforcing efficacy

ASJC Scopus subject areas

  • Pharmacology


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