ArticlesDose–Effect Functions for Cocaine Self-Administration: Effects of Schedule and Dosing Procedure
Section snippets
Subjects
Twenty-seven male Fischer rats, approximately 90–120 days old at the beginning of the experiments, served as subjects. Each subject was individually housed and had access to water ad lib. Subjects were typically meal-deprived during training (see Procedure) but were given access to food ad lib after responding was well established.
Apparatus
Although some specific characteristics of the operant chambers used in each experiment were slightly different, the chambers were all roughly the same size and did
Results
Fig. 1 shows response rate (left panel) and rate of drug intake (right panel) as a function of dose for Experiments 1, 2, and 4 (free-operant FRs and VI) averaged across subjects. Over the range of doses tested, response rate was an inverse function of dose under both free-operant FR procedures and was a bitonic function under the VI schedule. Dose was a statistically significant variable (one-way repeated-measures ANOVA) within each procedure type: VI [F(4, 126) = 37.186, p < 0.0001],
Discussion
Cocaine self-administration was examined by using a variety of procedures that generated dose–effect functions that differed in certain respects. The most striking difference among the dose–effect functions concerned the dose at which the highest rate of responding (or largest number of trials with infusions, in the discrete-trial procedure) occurred. In the probe portion of Experiment 5, this dose was, for four of five rats, 0.083 mg/infusion (Fig. 5). Under the VI schedule, however, the peak
Acknowledgements
This research was supported by National Institute on Drug Abuse grants DA 07246, DA 06634, and DA 03628.
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