Abstract

The effects of anileridine, alphaprodine and fentanyl were studied on responding by pigeons under a multiple fixed-ratio, fixed-interval schedule of food presentation. Generally, all three drugs produced dose-related decreases in responding under both components of the multiple schedule, but rate increases were observed after low doses of anileridine and alphaprodine in some birds. Naloxone (1 mg/kg) antagonized the rate-increasing and rate-decreasing effects of doses of anileridine and alphaprodine of 10 mg/kg or less, whereas the effects of higher doses were not antagonized by naloxone. Likewise, chronic methadone or morphine (120 mg/kg/day p.o.) dosing produced only a slight cross-tolerance to the rate-decreasing effects of anileridine and alphaprodine. In contrast, naloxone (0.01, 0.1 and 1 mg/kg) and chronic methadone or morphine administration shifted the dose-effect curve for fentanyl to the right, indicating narcotic antagonism and methadone and morphine-induced cross-tolerance. These data indicate that the rate-decreasing effects of anileridine and alphaprodine are related only slightly to narcotic effects, whereas the rate-decreasing effects of fentanyl are primarily narcotic effects.