Discriminative stimulus effects on enadoline in pigeons

Area of Science:

• Pharmacology
• Neuroscience
• Behavioral Science

Background:

• Enadoline is a kappa opioid receptor agonist.
• Understanding drug stimulus effects is crucial for pharmacology and neuroscience.
• Pigeons are a common model organism for behavioral pharmacology studies.

Purpose of the Study:

• To characterize the discriminative stimulus effects of enadoline in pigeons.
• To investigate the receptor mechanisms underlying enadoline's effects.
• To assess the antagonist properties of other opioid compounds.

Main Methods:

• Pigeons were trained to discriminate enadoline from saline under a fixed-ratio schedule.
• Cumulative doses of enadoline were administered to assess dose-dependency.
• Substitution tests with other kappa agonists and antagonist studies were performed.
• Naltrexone, nalorphine, dynorphin A(1-13) amide (DYN), nalbuphine, butorphanol, morphine, and ketamine were used.

Main Results:

• Enadoline dose-dependently produced a discriminative stimulus in pigeons.
• Naltrexone antagonized both the discriminative and rate-decreasing effects of enadoline.
• Other kappa agonists (U-50,488, spiradoline, U-69,593, ethylketocyclazocine) partially substituted for enadoline.
• Nalbuphine and butorphanol antagonized enadoline's effects, while DYN did not.

Conclusions:

• Enadoline establishes stimulus control in pigeons, mediated by kappa opioid receptors.
• Nalbuphine and butorphanol possess kappa antagonist properties in pigeons.
• The findings support the role of kappa opioid receptors in enadoline's discriminative effects and highlight potential non-opioid roles in DYN's effects.