Quantitative characterization of multiple binding sites for phencyclidine and N-allynormetazocine in membranes from rat and guinea pig brain

Abstract

Quantitative ligand binding studies have been used to characterize binding sites for N-allylnormetazocine ((+)SKF10,047) (SKF), 1-(1-phenylcyclohexyl) piperidine (PCP), N-[1-(2-thienyl) cyclohexyl] piperidine (TCP) and haloperidol in membranes from the brain of rat and guinea pig under conditions which permitted simultaneous analysis of the binding of both PCP and SKF. Using four labelled ligands (SKF, TCP, PCP and haloperidol), each displayed by the corresponding four unlabelled ligands, four classes of binding sites were observed in membranes from the brain of the rat, corresponding to sigma (σ), two classes of PCP sites (PCP 1, PCP 2) and dopamine (D 2) sites. The σ site was suppressed by 50nM haloperidol, while the PCP 1 and PCP 2 sites were not. These results were confirmed by the studies employing a self- and cross-displacement design and dose-response surfaces for SKF and TCP, with and without blockade by haloperidol of the sigma site. Using mathematical modelling, employing the program LIGAND, it was possible to reject simpler models involving a common “PCP/sigma” site or a model involving only two classes of sites (sigma and PCP). Similar methods were used to identify two classes of σ binding sites and two classes of PCP binding sites, in membranes prepared from the brain of guinea pig. The relative potencies of 18 ligands for displacement of (+)[ 3H]SKF10,047 and [ 3H]TCP were compared: there were significant qualitative and quantitative differences in the “sigma” binding sites in the brain of rat and guinea pig, while the PCP binding sites were very similar in two the species.