Choosing to take cocaine in the human laboratory: Effects of cocaine dose, inter-choice interval, and magnitude of alternative reinforcement

Cocaine abuse involves a variety of behaviors including the initiation of cocaine-seeking, the self-selected patterning of cocaine administrations, and the cessation of cocaine-taking. To date, most human laboratory models of cocaine self-administration have only assessed the amount of cocaine consumed under a fixed set of conditions. This double-blind, randomized, within-subject, inpatient study evaluated a novel model of human cocaine self-administration that aimed to quantify the reinforcing value of cocaine after cocaine-taking was initiated. Cocaine-dependent volunteers (n=8) sampled cocaine (12.5, 25 or 50 mg per 70 kg i.v.) or placebo and were subsequently allowed to choose between another injection of the same dose or money over six trials during 12 experimental sessions. The value of the monetary alternative increased with each trial from $1 to 16. Each cocaine dose was assessed under three inter-choice intervals: 15 min, 30 min, and an interval selected by the volunteer. Injection choices increased dose dependently; however, there was little relationship between the value of the alternative reinforcer and the choice to take cocaine. Most volunteers exclusively chose injections when active cocaine was available and money when placebo was available. Inter-choice interval did not affect cocaine choices. These results illustrate the persistence of cocaine self-administration once cocaine-taking has been initiated.