Specific Binding of [³H] phencyclidine in rat central nervous tissue: further characterization and technical considerations

The interaction of phencyclidine (PCP) with its specific receptor sites in the central nervous system has been further characterized. Kinetic association and dissociation rate constants of 2.9 × 10⁶ M^-1 and 4.8 × 10^-1 were determined, yielding a kinetic K_D of 1.6 × 10^-7 M, in agreement with the K_D previously determined at equilibrium. Permissible separation time of 13 s was calculated from the kinetic data, well above the actual separation time of less than 10 s in the rapid filtration assay. Presoaking of filters in 0.01% poly-l-lysine eliminated displacable [³H]PCP adsorption to filter material. Binding data obtained via centrifigation assays was identical to that obtained with the rapid filtration method. Stereospecificity of the PCP receptor was demonstrated by the finding that (+)-ketamine is four-fold more potent than (-)-ketamine in displacing specifically bound [³H]PCP. Several proteolytic enzymes including trypsin, papain and thermolysin potently inactivated PCP receptors. Detailed regional distribution studies showed highest density of PCP receptors in subicular cortex and hippocampus, intermediate levels in hypothalamus, striatum, frontal cortex and cerebellum, lower levels in brainstem and spinal cord, and negligible levels in corpus callosum, a white- matter control area. Benzomorphan opiates with PCP-like behavioral effects interact with the PCP receptor. These data support the pharmacological relevance of the PCP receptor site as demonstrated by the rapid filtration method.