An intravenous self-administration procedure for assessing the reinforcing effects of hallucinogens in nonhuman primates.
Self-administration procedures are the gold standard for investigating the reinforcing effects of drugs. The notable exception to good correspondence between laboratory self-administration studies and human drug taking behavior has historically been the classic hallucinogens. The present study used a well-established daily access procedure, followed by a novel intermittent access procedure, to investigate the reinforcing effects of LSD in baboons. Rates of self-injection in the daily access procedure were minimal. One baboon self-administered 0.001mgkg and a second baboon self-administered 0.0032mgkg above vehicle levels, though rates of self-injection were clearly low and neither of the two remaining baboons self-administered any LSD dose tested in the daily access procedure. Rates of self-injection using an intermittent access procedure with discriminative stimuli resulted in two doses of LSD being self-administered above vehicle levels in two of three baboons tested (0.01 and 0.032mgkg in one baboon 0.0032 and 0.01mgkg in a second). In addition, the number of self-injections at these doses was higher (range3-6 injections) in the intermittent access procedure than in the daily access procedure (range1-2 injections). The present study is the first to demonstrate LSD self-administration in a laboratory animal, and though the results are limited, they indicate intermittent access procedures with discriminative stimuli may provide a reliable and valid method for investigating the reinforcing effects of IV self-administered hallucinogens in laboratory animals. The usefulness of such procedures should be further evaluated in a larger number of subjects.