Cocaine and automaintained responding in pigeons: Rate-reducing effects and tolerance thereto with different durations of food delivery

Pigeons were exposed to an automaintenance procedure in which 6-s key illuminations in one color (red or white) were immediately followed by 3-s food deliveries and key illuminations in the other color were followed by 9-s food deliveries. Both conditions engendered consistent responding. With both durations of food delivery, acute and chronic cocaine administrations (1.0–17.8 mg/kg) produced dose-dependent decreases in mean percent trials (key illuminations) with a response and mean total response per session. Tolerance developed to the disruptive effects of cocaine on both response measures. Food duration did not significantly affect either response measure or significantly interact with cocaine dose or drug regimen. The orderliness of the present findings, like those of a related study examining whether probability of food delivery modulated the effects of cocaine on automaintained responding [Porritt, M., Arnold, M., Poling, A., Cocaine and automaintained responding in pigeons: rate-reducing effects and tolerance thereto with different CS–US pairing probabilities. Pharmacol Biochem Behav 2007; 87:405–411.], suggests that the automaintenance procedure is a useful assay for examining tolerance to drug effects on classically-conditioned responding. Unlike the results of that study, however, the present findings are inconsistent with a behavioral momentum analysis of drug effects on such responding.