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Psychopharmacology

, Volume 53, Issue 2, pp 169–173 | Cite as

Differential haloperidol effect on two indices of fentanyl-saline discrimination

  • Francis C. Colpaert
  • Carlos J. E. Niemegeers
  • Paul A. J. Janssen
Original Investigations

Abstract

Using a discrete-trial, two-lever, foodreward discrimination learning paradigm, we trained rats (n=6) to discriminate 0.04 mg/kg fentanyl (s.c. t-30′) from saline. Stimulus generalization experiments with an adequate dose range (0.01–0.04 mg/kg) of fentanyl revealed that the ED50 value for drug lever selection is 0.02 mg/kg, irrespective of whether the animals were pretreated (s.c., t-60′) with either saline or 0.08 mg/kg haloperidol. With increasing doses of the haloperidol-fentanyl combination, the percentage of total responding on the selected lever progressively decreased, and reached the 50% level at the highest drug combination. It is concluded that this percentage is heavily contaminated by factors unrelated to the discrimination condition being studied; these factors seem to invalidate this percentage as a discrimination index under experimental conditions (e.g., behaviorally toxic doses of drugs) where they are likely to operate. The use of response selection as a discrimination index in drug discrimination research is further argued.

Key words

Haloperidol Fentanyl Drug discrimination Narcotic cue Discrimination index 

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Copyright information

© Springer-Verlag 1977

Authors and Affiliations

  • Francis C. Colpaert
    • 1
  • Carlos J. E. Niemegeers
    • 1
  • Paul A. J. Janssen
    • 1
  1. 1.Department of PharmacologyJanssen Pharmaceutica Research LaboratoriesBeerseBelgium

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