Li, M., Wessinger, W. D, & McMillan, D. E. (2005).
Effects of amphetamine-CNS depressant combinations and of other CNS stimulants
in four-choice drug discriminations.
Journal of the Experimental Analysis of Behavior, 84, 77-
97.
Three pigeons were trained to discriminate among 5 mg/kg pentobarbital, 2 mg/kg
amphetamine, a combination of these two drugs at these doses, and saline using a
four-choice procedure (amphetamine--pentobarbital group). Three other pigeons
were trained to discriminate among 5 mg/kg morphine, 2 mg/kg methamphetamine, a
combination of these two drugs at these doses, and saline (methamphetamine--
morphine group). After 10 to 13 months of training, the pigeons averaged more
than 90% of their responses on the appropriate key during training sessions. In
subsequent testing, dose-response curves were determined for the individual
drugs, for a wide range of dose combinations of the training drugs, and for two
drugs to which the pigeons had not been exposed previously (pseudoephedrine and
nicotine). After low test doses of the training drugs, pigeons responded on the
saline key. As the dose increased, responding on the key associated with that
drug during training sessions increased. When training drugs were combined at
doses that were not discriminable when given alone, responding occurred on the
saline key. When a discriminable dose of one training drug was combined with a
nondiscriminable dose of the other training drug, responding occurred on the key
associated with the discriminable dose. When both drugs were given at
discriminable doses, responding almost always occurred on the drug-combination
key. The response-rate decreasing effects of pentobarbital and amphetamine were
mutually antagonized when the drugs were combined, but the rate-decreasing
effects of morphine and methamphetamine were not. After low doses of
pseudoephedrine and nicotine, pigeons in both groups responded on the saline
key. After higher doses of pseudoephedrine and nicotine, responding in the
amphetamine--pentobarbital group occurred primarily on the amphetamine key. In
the methamphetamine--morphine group, higher doses of pseudoephedrine and
especially nicotine engendered more responding on the combination key than had
occurred in the other group. The four-choice procedure can reveal subtle
effects in the discrimination of individual drugs and drug combinations that are
not apparent with procedures offering fewer response alternatives.
Key words: four-choice drug discrimination, drug combinations, stimulants,
depressants, key peck, pigeons