Dietary additives and the acquisition of cocaine self-administration in rats

The effects of dietary caffeine and the amount and palatability of food on the acquisition of cocaine (0.2 mg/kg) self-administration were examined. Using an autoshaping procedure, seven groups of 13 rats each were trained to press a lever resulting in a cocaine (0.2 mg/kg infusion under a fixed-ratio 1 (FR 1) schedule. One group had ad libitum access to caffeine- (0.2% w/w) admixed food. Three groups had access to 10 g, 20 g or ad lib food each day. Another three groups had the same three amounts of ground food with powdered saccharin (0.2% w/w) added. During daily 6-h autoshaping sessions, ten infusions were delivered each hour under a random-time 90-s schedule after a brief (15 s) extension of a retractable lever. These were followed by 6-h self-administration sessions, when the lever remained extended and cocaine infusions were available under an FR 1 schedule. The acquisition criterion was self-administration of a mean of 100 infusions over 5 days. Cocaine self-administration was accelerated in the caffeine group compared to the regular chow group. However, by 30 days nearly the same percentage of rats in the caffeine and regular food groups met the acquisition criterion. In the other six groups, as the amount of food increased, the rate of acquisition and percentage of rats per group meeting the acquisition criterion decreased. In the ad lib group, acquisition was further reduced when saccharin was added to food. In summary, dietary caffeine accelerated acquisition and a greater amount and increased palatability of food independently interfered with acquisition of cocaine self-administration in rats.