Discriminative stimulus properties of d-amphetamine in pigeons

Two out of four pigeons were successfully trained in an operant procedure to discriminate between the presence and absence of the effects induced by d-amphetamine (final dose: 1.6 mg/kg). The solvent (saline) or d-amphetamine was administered intramuscularly (IM) 30 min prior to training. Tests with other drugs and dosages indicated that l-amphetamine (ED50 = 0.55 mg/kg) and cocaine (ED50 = 1.05 mg/kg) fully generalized to d-amphetamine (ED50 = 0.35 mg/kg), whereas drugs such as p-hydroxy-amphetamine (1.6 and 3.2 mg/kg), morphine (1.5, 3.0 and, 6.0 mg/kg), and delta 9-THC (0.125, 0.25, and 0.50 mg/kg) failed to do so at the doses tested. Apomorphine (0.25 and 0.50 mg/kg) and LSD-25 (0.04 and 0.08 mg/kg) produced intermediate results. Pretreatment with haloperidol (dose range: 0.04 to 1.28 mg/kg), but not propranolol (10 and 20 mg/kg), attenuated significantly the d-amphetamine (1.6 mg/kg) stimulus effects. The two pigeons emitted predominantly d-amphetamine appropriate responses when the training dose (1.6 mg/kg) of d-amphetamine was tested on different occasions 15, 60, and 120 min after the administrations. One bird emitted mostly vehicle appropriate responses when tested 240 min after the d-amphetamine injection whereas the other bird performed d-amphetamine appropriate responses. Selection of the non-drug associated key occurred in the two birds when testing was carried out 480 min (8 hrs) after the administration of d-amphetamine.