European Journal of Pharmacology, 113 (1985) 465 466 465 Elsevier Rapid communication PHENCYCLIDINE AND o OPIATE RECEPTORS IN BRAIN: BIOCHEMICAL AND AUTORADIOGRAPHICAL DIFFERENTIATION ANDREW L. GUNDLACH, BRIAN L. LARGENT and SOLOMON H. SNYDER * Departments of Neuroseience. Pharmacology and Experimental Therapeutics, P.~vchiatt T and Behavioral Sciences, The Johns Hopkins Unit,ersi O' School of Medicine, 725 North Wolfe Street, Baltimore. MD 21205, U.S.A. Received 24 June 1985, accepted 24 June 1985 Phencyclidine (PCP) and o opiates are psycho- tomimetic in man. Whether the psychotomimetic effects of o opiates are mediated by PCP receptors (Zukin and Zukin, 1981) or by distinct o receptors has not been established. [3H]SKF 10,047, the prototypical o agonist binds to sites in brain mem- branes with a different pharmacological specificity than those labeled by [3H]PCP (Su, 1982; Tam, 1985). These sites are similar to those labeled by ( + )[ 3H]3-(3-hydroxyphenyl)-N-(1-propyl)piperi- dine (3-PPP) (Largent et al., 1984). Our studies reveal that (+)[3H]SKF 10,047 labels two sites in brain which can be discriminated by biochemical and autoradiographic methods. The high affinity site corresponds to o receptors, while the low affinity site represents PCP receptors. Selective labeling of PCP and o receptors by (+)[3H]SKF 10,047 is achieved by including in the incubation mixture the selective o and PCP receptor drugs, haloperidol and 1-[1-(2-thienyl)cyclohexyl]piperi- dine (TCP) respectively. Brain membrane homogenates and slide- mounted brain sections (Largent et al., 1984) were incubated in 5.0 mM Tris buffer pH 8.0 contain- ing either 6-12 nM (+)[3H]SKF 10,047 (43.3 Ci/mmol) or 1-2 nM [3H]TCP (55.3 Ci/mmol) for 30 min at 25°C. Haloperidol and TCP, where included, were at a final concentration of 5 ~M and 2 /~M respectively. In assays of high or low affinity (+)[3H]SKF 10,047 binding, nonspecific binding was estimated with 2 ~M haloperidol or 10 /~M PCP respectively. Nonspecific binding of [3H]TCP was assessed with 10 /~M PCP. Radio- ligands were supplied by New England Nuclear (Boston, MA). Inhibitory potencies of drugs for (+)[-~H]SKF 10,047 binding to high and low affinity sites re- semble values at (+)[3H]3-PPP and [3H]TCP labeled sites respectively (table 1A; Largent et al., 1984). In the presence of 5 ~M haloperidol the drug specificity of (+)[3H]SKF 10,047 binding is similar to that of [3H]TCP binding, which selec- tively labels PCP sites (Vignon et al., 1983). TCP is the most potent agent, while haloperidol is inac- tive. The isomers of SKF 10,047 have similar affinity. By contrast, (+)[3H]SKF 10,047 binding in the presence of 2 /zM TCP labels sites with stereoselectivity for isomers of SKF 10,047, the ( + )isomer being more potent. Haloperidol is much more potent than at PCP sites and pentazocine is 60 times more potent than at [3H]TCP labeled sites. This drug specificity corresponds to that of o sites labeled with (+)[3H]3-PPP, a selective o ligand, and [3H]haloperidol employed under con- ditions which label only o receptors (Largent et al., 1984). Autoradiographic localizations also distinguish o and PCP receptors (table 1B). As previously reported (Largent et al., 1984) (+)[3H]3-PPP, shows highest densities over the pyramidal cells of the hippocampus, the granular layer of the dentate gyrus and motor nuclei of cranial nerves such as the oculomotor, facial and hypoglossal nuclei, but with negligible labeling in the interpenduncular nucleus and in nonpyramidal areas of the hippo- campus. In contrast, [3H]TCP does not label hip- pocampal pyramidal cells or motor nuclei of cranial nerves, but ~hows dense labeling in nonpyramidal regions of the hippocampus as well as the inter- penduncular nucleus. 0014-2999/85/$03.30 ~ 1985 ElsevierSciencePublishers B.V.