Repeated testing within drug discrimination learning: time course studies with cocaine, amphetamine, and 3-PPP

Pigeons were trained to discriminate between 3 mg/kg cocaine and saline. Tests with cocaine and amphetamine were conducted at different intervals after administration to compare the time course of the discriminative stimulus (DS) effects. Tests were of two kinds: a) separate, that is, only one dose and interval were examined on each separate test day; and b) repeated, that is, all three intervals were assessed after a single administration of the drug dose during 1 test day. Separate and repeated determinations of the time course yielded similar estimates. The duration of the DS effects of amphetamine were longer than those of cocaine. No apparent difference, either with regard to duration of effect or potency, existed between (+)- and (-)-amphetamine. The potency of cocaine was similar to that of the amphetamine isomers. The dopamine autoreceptor blockers (+)- and (-)-3-(hydroxyphenyl)-N-n-propylpiperidine (3-PPP) (1-10 mg/kg) engendered less than 44% cocaine-associated responding for the repeatedly examined intervals (15, 60, and 120 min after administration). The results of this study encourage the use of repeated testing methodology to assess the duration of action of the DS effects of drugs.