Comparison of morphine, meperidine, anileridine, and alphaprodine on schedule-controlled responding and analgesia.

The effects of morphine, meperidine, alphaprodine, and anileridine were studied alone and in the presence of 1 mg/kg of naloxone in rats on level pressing under a fixed-ratio 20-response schedule of food presentation and on tail-withdrawal latency from warm water (55 degrees C) as a measure of analgesia. All four narcotics decreased rates of lever pressing and increased tail-withdrawal latencies. Naloxone antagonized the effects of all four narcotics on tail-withdrawal, but did not antagonize the rate-decreasing effect of meperidine on lever pressing. Naloxone shifted the morphine dose-effect for lever-pressing by a factor of 4-8; the alphaprodine dose-effect curve by a factor of 4-8; and the anileridine dose-effect curve by a factor of 2. These results strengthen the interpretation that meperidine's effect on schedule-controlled responding is not mediated by a narcotic action whereas the analgesic effect is. The results also suggest that anileridine has significant non-narcotic actions like meperidine.