The effects of single and repeated phencyclidine administration on [¹²⁵I] iomazenil binding in the rat brain

We measured [¹²⁵I] iomazenil binding, labeling the central-type benzodiazepine receptor in 37 discrete rat brain areas following single (7.5 mg/kg, i.p.) and repeated (7.5 mg/kg/day x 14 days, i.p.) treatment with phencyclidine (PCP), a non-competitive antagonist of the N-methyl-D-aspartate (NMDA)type glutamate receptor, using in vitro quantitative autoradiographic receptor binding assay. Both single and repeated PCP treatment produced heterogeneous changes in the rat brain in a similar manner, the magnitude of change in [¹²⁵I] iomazenil binding being generally greater in the repeated treatment group than in the single treatment group. A significant increase in [¹²⁵I] iomazenil binding was observed in the superficial layer (layer I-IV) of the parietal cortex in both of the PCP treatment groups and the CA1 of the hippocampus of the repeated PCP-treated group. There was a significant decrease in [¹²⁵I] iomazenil binding in the piriform cortex of the repeated PCP-treated group. These results suggest that the blockade of NMDA receptor-mediated glutamatergic neurotransmission by PCP produces the compensational alterations in the central-type benzodiazepine receptor antagonist binding, and that the observed diversity may be due to dissimilar modes of organizations between glutamatergic and the GABA(γ-aminobutyric acid)-benzodiazepine receptor complex.