Differences in the behavioral time course of effects of rate-increasing and rate-decreasing doses of cocaine in pigeons

Although past research has examined the time course of plasma levels of cocaine in a variety of species, the time course of behavioral effects of cocaine on operant behavior has not been carefully described. The purpose of the present study was to examine the time course of effects of cocaine on operant behavior of pigeons, using a method that allowed comparison of dose-response functions, in individual subjects, within a session. Five pigeons responded under a multiple Fixed Interval 10 min Fixed Ratio 30 (FI 10 min FR 30) schedule of food presentation, with each component presented 10 times per session. Following acute administration, dose-response functions remained stable for about 45 min. Effects of acute cocaine administration also revealed that behavioral effects of large doses of cocaine diminished later in sessions, but effects were evident for at least 2 h. Exposure to chronic (i.e., daily) cocaine administration of a rate-decreasing dose led to tolerance that was characterized by diminished potency. Effects of formerly rate-decreasing doses diminishing earlier in the session compared to acute administration, and formerly rate-increasing doses resulted in rates similar to those under the saline-vehicle control from the session outset.