Phencyclidine (PCP): effects of acute and chronic administration on EEG activities in the rhesus monkey

Effects of acute and chronic administration of phencyclidine (PCP) on EEG activities and gross behavior were studied in monkeys with electrodes implanted in the brain. Administration of PCP (2.0 or 4.0 mg/kg i.v.) in monkeys produced a biphasic pattern of inhibition and excitation of behavior during 6-8 h observation period. The inhibitory phase appeared 1-3 min after PCP injection, and was uniquely characterized by high-voltage slow waves with delta waves (0.6-0.8 c/sec) in the parietal lobe and by those with theta waves (4-5 c/sec) in the occipital lobe and hippocampus during behavioral stupor. This inhibitory phase lasted 1-1.5 h, and subsequently, high-voltage fast wave with enhancement of theta waves and nystagmus appeared during behavioral arousal. Upon chronic PCP administration, the intensity and duration of the inhibitory phase progressively decreased, while the effects of the excitatory phase increased. The results suggest that PCP administration in monkeys produces a biphasic pattern of inhibitory and excitatory effects and upon chronic administration a tolerance develops to the inhibitory effect while an augmentation of the excitatory effect develops.