Effects of ethylketazocine and morphine alone and in combination with naloxone on schedule-controlled behavior in pigeons.

The behavioral effects of morphine and ethylketazocine were compared in pigeons responding under multiple fixed-interval, fixed-ratio schedules of food presentation. Both morphine and ethylketazocine produced dose-related decreases in rates of responding maintained under either schedule. Maximal effects of morphine were observed about 15-45 min after injection and typically lasted the entire session (about 60 min). Effects of ethylketazocine had a faster onset (maximal effects were observed within 15 min after injection), and shorter duration (effects diminished within the session). Ethylketazocine and morphine had similar potencies. Dose-effect curves for both drugs were shifted to a similar degree by naloxone.