Action of phencyclidine on synaptic transmission in the hippocampus

A neurophysiological investigation of the effects of phencyclidine (PCP) and ketamine on synaptic transmission was carried out at the level of two excitatory connections of the hippocampal formation: the interhippocampal projections from contralateral CA3 (cCA3) to CA1 and the entorhino-dentate pathway.In urethane-anesthetized rats PCP i.v. produced a moderate depression of the population EPSP elicited in the stratum radiatum of CA1 by cCA3 stimulations (16–40%) and a large decrease (up to 97%) of the amplitude of the corresponding population spike recorded at the level of the CA1 pyramidal cell bodies (ED₅₀:1.83 mg/kg).Single-unit analysis of CA1 pyramidal cell activation triggered by cCA3 stimulations indicated that i.v. PCP did not decrease the amplitude of individual action potentials suggesting that the decrease in the size of the population spike was due to a decrease in the number of CA1 pyramidal cells activated by the stimulus. Moreover, PCP administered i.v. in the same dose range (0.6-4.0 mg/kg) reduced the maintained activity of CA1 pyramidal cells and their excitation by iontophoretically applied glutamate or ACh.Similar effects on both field potentials and single-unit activity in the CA1 area were also observed following the administration of larger i.v. doses of ketamine (ED₅₀: 7.2 mg/kg), but the effects of the latter drug were of considerably shorter duration than those of PCP.