Attenuating the rate-decreasing effects of phenylpiperidine analgesics by pentobarbital

The ability of pentobarbital, diazepam, and chlorpromazine to attenuate the rate-decreasing effects of a high dose (10 or 30 mg/kg) of meperidine was tested in pigeons responding under a multiple fixed-ratio, fixed-interval schedule of food presentation. Pentobarbital (10 mg/kg) attenuated the meperidine-induced rate decreases, whereas diazepam (0.3--3 mg/kg) or chlorpromazine (3--30 mg/kg) did not reliably attenuate the response rate decreases. The combination of 10 mg/kg of pentobarbital and meperidine resulted in a marked disruption of the pattern of responding in the fixed-interval component of the multiple schedule. Pentobarbital (1, 3, 10, and 17.5 mg/kg) was also tested in combination with rate-decreasing doses of normeperidine (17.5 mg/kg), anileridine (10 mg/kg), alphaprodine (10 mg/kg), and fentanyl (0.3 mg/kg). Pentobarbital reliably attenuated the rate-decreasing effects of normeperidine, anileridine, and alphaprodine, but not the rate decreases induced by fentanyl.