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Related Experiment Videos

Opioid drugs and timeout from avoidance.

M. Galizio1, E.G. Robinson, C. Ordronneau

  • 1Department of Psychology, University of North Carolina at Wilmington, Wilmington, NC 28403, USA.

Behavioural Pharmacology
|April 1, 1994
PubMed
Summary

µ agonists like fentanyl, methadone, and morphine selectively reduce timeout behavior. Kappa agonists do not selectively reduce this behavior, differentiating their effects from µ agonists.

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Variable-ratio schedules of timeout from avoidance: effects of anxiolytic drugs.

Behavioural pharmacology·1993
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Area of Science:

  • Pharmacology
  • Neuroscience
  • Behavioral Science

Background:

  • Opioid receptors, specifically mu (µ) and kappa (κ) receptors, modulate pain and reward pathways.
  • Negative reinforcement, where behavior increases to avoid an aversive stimulus, is influenced by opioid agonists.
  • Understanding differential effects of opioid receptor agonists is crucial for pain management and addiction research.

Purpose of the Study:

  • To investigate the differential effects of µ and kappa opioid agonists on behavior maintained by negative reinforcement.
  • To determine if µ agonists selectively decrease responding during timeout from avoidance, as previously reported for morphine.
  • To compare the effects of fentanyl, methadone, morphine (µ agonists), and U50,488 (kappa agonist) on avoidance and timeout behaviors.

Main Methods:

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  • Rats were trained on concurrent schedules of negative reinforcement.
  • One lever press postponed shock (Sidman avoidance schedule).
  • The other lever produced signaled timeout periods from avoidance (variable-ratio schedules).
  • Behavioral effects of µ agonists (fentanyl, methadone, morphine) and kappa agonist (U50,488) were assessed.

Main Results:

  • All µ agonists (fentanyl, methadone, morphine) decreased responding maintained by timeout from avoidance.
  • These µ agonist effects occurred at doses that did not decrease or even increased avoidance rates.
  • The kappa agonist U50,488 produced variable effects, decreasing responding in some rats and increasing it in others, without selective reduction of timeout responding.
  • No kappa agonist U50,488 effect was selective for the timeout lever.

Conclusions:

  • µ agonists, including fentanyl, methadone, and morphine, selectively decrease behavior maintained by negative reinforcement (timeout from avoidance).
  • Kappa agonists, exemplified by U50,488, do not exhibit this selective effect on timeout responding.
  • These findings highlight distinct roles of µ and kappa opioid receptors in modulating behavior under negative reinforcement conditions.