Oral caffeine pretreatment produced modest increases in smoked cocaine self-administration in rhesus monkeys

Abstract

Several recent studies have shown that caffeine potentiates the reinforcing, discriminative stimulus, and motor activating effects of cocaine in rats. The present study was designed to determine whether oral caffeine pretreatment would enhance the reinforcing effects of cocaine in rhesus monkeys trained to self-administer smoked cocaine base. The effects of oral caffeine pretreatment (0, 100, or 200 mg) and fixed-ratio (FR) value on cocaine-base smoking were evaluated in four male rhesus monkeys. Monkeys responded on a lever under a fixed-ratio (FR) schedule (FR 128, 256, 512, 1024, 2048, or 4096) and then made five inhalations on a smoking spout to gain access to volatilized cocaine base (0.25 or 1.0 mg/kg per delivery) during daily experimental sessions. Twenty pellets [20 non-caffeinated (0 mg caffeine), ten non-caffeinated+ten caffeinated (100 mg caffeine), or 20 caffeinated (200 mg caffeine) pellets] were administered 30 min prior to experimental sessions. The lever FR value was held constant within each experimental session, but was increased after 3 consecutive days of stable responding. Although the number of smoke deliveries that was self-administered significantly decreased from FR 128 to FR 4096, it did not change as a function of cocaine dose across the range of FR values tested. However, the interaction between cocaine dose and caffeine pretreatment was statistically significant. Compared to 0 mg caffeine, three of four monkeys pretreated with 200 mg caffeine responded for a greater number of smoke deliveries when they were maintained on a cocaine dose of 1.0 mg/kg per delivery, but not 0.25 mg/kg per delivery. Thus, caffeine pretreatment can produce small, but statistically significant increases in smoked cocaine self-administration in rhesus monkeys.