Alternative reinforcer response cost impacts cocaine choice in humans

Abstract

Cocaine use disorders are an unrelenting public health concern. Behavioral treatments reduce cocaine use by providing non-drug alternative reinforcers. The purpose of this human laboratory experiment was to determine how response cost for non-drug alternative reinforcers influenced cocaine choice. Seven cocaine-using, non-treatment-seeking subjects completed a crossover, double-blind protocol in which they first sampled doses of intranasal cocaine (5, 10, 20 or 30 mg) and completed a battery of subject-rated and physiological measures. Subjects then made eight discrete choices between the sampled dose and an alternative reinforcer (US$0.25). The response cost to earn a cocaine dose was always a fixed ratio (FR) of 100 responses. The response cost for the alternative reinforcer varied across sessions (FR1, FR10, FR100, FR1000). Dose-related increases were observed for cocaine choice. Subjects made fewer drug choices when the FR requirements for the alternative reinforcers were lower than that for drug relative to when the FR requirements were equal to or higher than that for drug. Intranasal cocaine also produced prototypical stimulant-like subject-rated and physiological effects (e.g., increased ratings of Like Drug; elevated blood pressure). These data demonstrate that making alternative reinforcers easier to earn reduces cocaine self-administration, which has implications for treatment efforts.

Fig. 1

Top Panel: Mean number of drug choices for 7 subjects. X-axis: cocaine dose. Symbols represent the FR values for the alternative reinforcer: FR1 (circles), FR10 (squares), FR100 (triangles), FR1000 (diamonds). Symbols for FR1 and FR10 at the 30 mg dose overlapped so they are offset for clarity. Bottom Panel: Mean subject ratings for Like Drug for 7 subjects. X-axis: cocaine dose. Data are collapsed across FR values and come from measures completed 15 min after intranasal cocaine administration. Error bars are omitted due to the repeated measures design of the study.