Methadone-induced attenuation of the effects of delta 9-tetrahydrocannabinol on temporal discrimination in pigeons.
Pigeons responded under a discrete trial procedure in which they were required to peck one of two keys  depending on the duration of a conditional stimulus (general illumination of the experimental chamber). Correct choices (red key after a 4-sec stimulus; green key after an 8-sec stimulus) resulted in the intermittent presentation of food; incorrect choices resulted in a darkened chamber. Intermediate durations (probe stimuli) were also presented occasionally. The effects of tetrahydrocannabinol (THC; 0.06-0.50 mg/kg) and repeated methadone injections (2-20 mg/kg/day) were assessed alone and in combination. THC resulted in a dose-dependent decrease in accuracy with the greater effect on long-duration trials. Repeated methadone alone resulted in a decrease in accuracy only when the methadone dose was changed. High doses of methadone (6 and 20 mg/kg/day) resulted in either a complete (0.25 mg/kg of THC) or partial (0.50 mg/kg of THC) attenuation of effects of THC on temporal discrimination accuracy as compared to a low methadone dose (2 mg/kg/day) or THC alone. The results suggest the possibility of cross-tolerance or antagonism between methadone and THC.
D000818:Animals; D010856:Columbidae; D003216:Conditioning, Operant / Q000187:drug effects; D013759:Dronabinol / Q000008:administration & dosage / Q000037:antagonists & inhibitors*; D005795:Generalization, Stimulus / Q000187:drug effects; D008297:Male; D008691:Methadone / Q000008:administration & dosage / Q000494:pharmacology*; D011287:Prejudice / Q000187:drug effects; D013997:Time Factors; D013998:Time Perception / Q000187:drug effects*
D013759:Dronabinol; D008691:Methadone