Effects of ketazocine, ethylketazocine and phenazocine on schedule-controlled behavior: Antagonism by naloxone

Abstract

Dose-effect curves were determined for phenazocine (0.64–2.5 mg/kg), ketazocine (1.25–80 mg/kg) and ethylketazocine (1.25–80 mg/kg) in pigeons responding under a multiple fixed-ratio 30-response, fixed-interval 5-min schedule of grain presentation. All three opioid agonists decreased responding with the larger doses. The effects of phenazocine were completely antagonized by small doses of naloxone (0.01–1 mg/kg), whereas the effects of ethylketazocine required larger doses of naloxone (1–10 mg/kg) to be completely antagonized. The behavioral effects of ketazocine were partially attenuated by naloxone, but were not antagonized completely even by a 10 mg/kg dose of naloxone. These data from the pigeon are consistent with previous interpretations that the effects of phenazocine are mediated by actions at a mu opioid receptor, whereas the effects of ketazocine and ethylketazocine are mediated by actions at a kappa opioid receptor.