Phencyclidine-analogue self-injection by the baboon

Self-injection of phencyclidine HCl (PCP) and four of its analogues was examined in baboons. IV injections of drug were dependent upon completion of 160 lever presses (a 160-response fixed-ratio schedule). A 3-h time-out period followed each injection, permitting a maximum of eight injections per day. Self-injection performance was first established with cocaine and, once stable, test doses of each drug were substituted for 15 days. All five compounds maintained maximal self-injection performance, differing only in their relative potencies. The order of potency was approximately PCP>NMPCA=TCPY>NNBPCA>ketamine. Analysis of the distribution of injections throughout the day indicate that lower doses (and vehicle) were injected mainly during the daylight hours (i.e., 9 AM-6 PM), but as the dose was increased the injections became more uniformly distributed. Only the highest doses of these compounds affected food intake, though the degree of suppression was modest. No differences between these compounds with respect to their abuse potential could be found.