Food deprivation and methadone effects on fixed-interval performance by pigeons.
Five adult male White Carneaux pigeons, maintained at approximately 70, 80 or 90% free-feeding weight, were administered methadone (0.5, 1.5, and 2.5 mg/kg) prior to sessions of key pecking maintained under 5-min fixed-interval schedules of food presentation. Increasing deprivation levels attenuated the rate-decreasing effects of methadone. Methadone effects on pause time were unchanged. Three pigeons, maintained at 80% free-feeding weight were then administered methadone hydrochloride (0.62, 1.25 and 2.5 mg/kg) and naloxone hydrochloride (.0001, .0003, .001, .003 or .01 mg/kg) alone and in combination while responding under these same contingencies. Naloxone had no systematic behavioral effects alone but antagonized methadone's effects on fixed-interval responding and pausing. Naloxone also altered methadone's rate-dependent effects. These results suggest the behavioral effects of methadone are differentially altered following food-deprivation and opiate antagonist manipulations.
Department of Psychology, University of Minnesota, Minneapolis 55455.
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D000818:Animals; D001835:Body Weight; D010856:Columbidae; D003216:Conditioning, Operant / Q000187:drug effects*; D005508:Food Deprivation; D008691:Methadone / Q000494:pharmacology*; D009043:Motor Activity / Q000187:drug effects; D009270:Naloxone / Q000494:pharmacology; D012055:Reinforcement Schedule
D009270:Naloxone; D008691:Methadone