Phencyclidine (PCP): effects on limbic afterdischarges in the rhesus monkey

Effects of phencyclidine (PCP) on eliciting afterdischarges (AD) by electrical stimulation of the hippocampus (HIPP), amygdala (AMY), thalamus (CM) and midbrain reticular formation (MRF) were studied in rhesus monkeys with permanently implanted encephalic electrodes. Prior to drug administration, the minimal amount of electrical stimulation for eliciting AD, i.e., minimal AD's stimulation (MADS), was determined for each stimulation site and employed as a parameter for evaluating the effects of PCP on AD. Following PCP administration (0.5 mg/kg IM), marked increases (130 to 240% above the control level) in MADS of the HIPP, AMY and MRF were demonstrated, while only slight increase (+40%) in MADS of the CM was found. These results suggest that PCP causes a marked decrement in the ability of electrical stimulation to elicit AD in the HIPP, AMY and MRF, along with only little similar stimulation effects in the CM. This selective increase in MADS in structures of the limbic system and the midbrain reticular formation tends to implicate these systems rather than the thalamocortical system in the modulation of PCP's effects on central nervous system activities.