Cocaine and automaintained responding in pigeons: Rate-reducing effects and tolerance thereto with different CS-US pairing probabilities

To examine whether CS-US pairing probability, hence rate (or probability) of food delivery, modulated the effects of cocaine, pigeons were exposed to an autoshaping procedure in which 6-s red, green, and white illuminations of a response key were immediately followed by response-independent food delivery with a probability of 1.0, 0.5, and 0.25, respectively. Substantial responding occurred at all probabilities. Pre- and post-chronic administrations of cocaine (1.0-17.8 mg/kg) produced dose-dependent decreases in mean percent trials (key illuminations) with a response and total responses per session at all probabilities. In general, sensitivity to the drug was lowest at the highest probability, suggesting that rate (or probability) of food delivery influenced the behavioral effects of cocaine.