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

Phencyclidine in the social interaction test: an animal model of schizophrenia with face and predictive validity

Phencyclidine (PCP) is a hallucinogenic drug that can mimic several aspects of the schizophrenic symptomatology in healthy volunteers. In a series of studies PCP was administered to rats to determine whether it was possible to develop an animal model of the positive and negative symptoms of schizophrenia. The rats were tested in the social interaction test and it was found that PCP dose-dependently induces stereotyped behaviour and social withdrawal, which may correspond to certain aspects of the positive and negative symptoms, respectively. The effects of PCP could be reduced selectively by antipsychotic drug treatment, whereas drugs lacking antipsychotic effects did not alleviate the PCP-induced behaviours. Together these findings indicate that PCP effects in the rat social interaction test may be a model of the positive and negative symptoms of schizophrenia with face and predictive validity and that it may be useful for the evaluation of novel antipsychotic compounds.

Binding of [3H]desglycinyl remacemide to rat brain membranes: association with the benzomorphan attachment site of the N-methyl-D-aspartic acid receptor channel

Desglycinyl remacemide (DGR), a biologically active metabolite of remacemide, was radiolabeled in an attempt to develop a ligand binding assay to identify its site of action. Incubation of the radioligand with membranes obtained from P2 fractions of whole rat brain revealed a single population of specific [3H]-DGR binding sites having a Kd of 290 nM and a Bmax of 1.3 pmole/mg protein. The specific binding of [3H]-DGR is most enriched in the P2 subcellular fraction and is heterogeneously distributed throughout the brain. The binding of [3H]-DGR to rat brain membranes was inhibited most potently by MK-801 and SKF-10,047. In contrast, haloperidol, and other sigma receptor-active agents, were relatively inactive at this site. These data suggest that DGR interacts with a channel blocking site on the NMDA receptor.

The involvement of sigma receptors in the choice reaction performance deficits induced by phencyclidine

The present study investigated the effects of phencyclidine (PCP) on choice reaction in a 3-choice serial reaction time task for studying attentional function. PCP (3.2 mg/kg) significantly delayed choice reaction time and reduced choice accuracy. A novel sigma receptor antagonist N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]-ethylamine monohydrochloride (NE-100) at 3.2 mg/kg, and 1-(cyclopropylmethyl)-4-[2'-4"-fluorophenyl)-2'-oxoethyl]piperidin e HBr (DuP734) at 1.0-3.2 mg/kg, but not 4-[2'-(4"-cyanophenyl)-2'-oxoethyl]-1-(cyclopropylmethyl)pip eridine (XJ448), antagonized both the delayed choice reaction time and the decreased choice accuracy elicited by PCP administration. The antagonism induced by NE-100 was blocked by the sigma receptor agonist (+)-N-allylnormetazocine HCl [(+)-SKF10,047]. These findings indicated that PCP (3.2 mg/kg) significantly induced attention deficit in a 3-choice serial reaction time task, and that this process may be mediated by sigma receptors.

Sigma binding in a human neuroblastoma cell line

Behaviorally, sigma1 agents modulate opioid analgesia. To examine possible mechanisms responsible for these interactions, we have identified a cell line containing both sigma1 and opioid receptors. [3H](+)-pentazocine binding in BE(2)-C human neuroblastoma cells is high affinity (KD 3.4 +/- 0.7 nM) and high density (Bmax 2.98 +/- 0.14 pmol/mg protein). Competition studies reveal a selectivity profile similar to that of sigma1 sites in guinea pig brain. (+)-Pentazocine has no effect upon either basal or forskolin-stimulated cyclase in the BE(2)-C cells, but cAMP accumulation is inhibited by the morphine, DPDPE and naloxone benzoylhydrazone. (+)-Pentazocine at concentrations as high as 10 microM does not affect this opioid effect, implying that sigma1/opioid interactions are not mediated at the level of the cell. This suggest that their behavioral interactions result from interacting neural circuits. Although (+)-pentazocine is without effect in the cyclase system, it does block carbachol-stimulated phosphoinositol turnover (IC50 6.5 +/- 1.14 microM). The specificity of the effect is confirmed by the ability of haloperidol (1 microM) to shift the IC50 value of (+)-pentazocine 2-fold to the right.

Autoradiographic study on the pharmacological characteristics of [3H]3-OH-PCP binding sites in rat brain

The pharmacological characteristics and the regional distribution of [3H]3-OH-PCP (1-[1(3-hydroxyphenyl)-cyclohexyl]piperidine) binding were investigated in rat brain by quantitative autoradiography. Kinetic analysis of [3H]3-OH-PCP binding revealed fast and slow components, in the association and dissociation studies. The regional distribution of binding closely corresponded to those of binding sites labeled by [3H]N-[l-(2-thienyl)-cyclohexyl]3,4-piperidine (TCP) and [3H](+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imi ne maleate (MK 801). High densities of [3H]3-OH-PCP binding sites were found in the stratum radiatum and orients of field CA1 in the hippocampus and in the outer layers of cerebral cortices. In contrast, low levels of binding were seen in the brain stem and the granular cell layer of the cerebellum. [3H]3-OH-PCP binding was strongly inhibited by MK 801 and 3-OH-PCP, while the potency of (+)-SKF 10047 in inhibiting [3H]3-OH-PCP binding was less in the cerebral cortex and hippocampus. The antagonists for the glutamate, glycine and polyamine recognition sites at the NMDA/PCP receptor complex displaced [3H]3-OH-PCP binding sites with a potency similar to that of [3H]MK 801. These findings suggest that the [3H]3-OH-PCP binding site is similar or identical to the PCP binding site labeled by [3H]TCP and [3H]MK 801.

Altered N-methyl-D-aspartate (NMDA) activity in the mouse spinal cord following morphine is mediated by sigma activity

The present study was designed to determine whether the increase in N-methyl-D-aspartate (NMDA) activity in the mouse spinal cord, unmasked by naloxone in morphine-pretreated mice, is mediated by sigma receptor activity. Behavioral responses to intrathecal injections of NMDA were inhibited by pretreatment (2 h) with morphine (10 mg/kg i.p.) except when NMDA was injected together with 0.1 micrograms of naloxone. This excitatory effect of morphine on NMDA-induced behaviors, unmasked in the presence of naloxone was prevented but not reversed by haloperidol, a sigma ligand and dopamine antagonist, but not by an equivalent dose of spiperone, a dopamine antagonist. Sigma activity also appeared to contribute to morphine withdrawal jumping in mice as haloperidol inhibited naloxone-induced jumping while spiperone did not. Together these data indicate that naloxone unmasks an action of morphine on NMDA and during acute withdrawal, and these effects are each brought about by mechanisms involving sigma receptor activity.

Quantitative autoradiographic localization of [3H]3-OH-PCP (1-(1(3-hydroxyphenyl)cyclohexyl)piperidine) binding sites in rat brain

Binding of a novel radioligand, [3H]3-OH-PCP (1(1(3-hydroxyphenyl) cyclohexyl)piperidine), to N-methyl-D-aspartate (NMDA) receptor-coupled and -uncoupled PCP sites was investigated in the rat brain. The highest densities of [3H]3-OH-PCP binding were observed in the hippocampal formation, notably in the stratum radiatum and oriens of CA1 region, and dentate gyrus. There were relatively high levels of binding in the olfactory system, superficial layer of cortices, the amygdala and the thalamus. In contrast, lower levels of binding were found in the globus pallidus, cerebellum, and brain stem, except for the superior colliculus. These findings demonstrate that [3H]3-OH-PCP binds to discrete regions within the rat brain. Its distribution is consistent with autoradiographic localization of [3H]TCP and [3H]MK-801 binding sites in the rat brain, suggesting that [3H]3-OH-PCP binds to NMDA/PCP ion-channel complexes in preference to sigma sites.