B]thiophenyl)cyclohexyl]piperidine Research Articles

Priming with BTCP, a dopamine reuptake blocker, reinstates cocaine-seeking and enhances cocaine cue-induced reinstatement

N-[1-(2-benzo[ b]thiophenyl)cyclohexyl]piperidine (BTCP), a potent dopamine reuptake inhibitor, substitutes for the reinforcing effects of cocaine and meets other criteria for possible agonist pharmacotherapeutic potential. The purpose of this study was to determine (1) whether BTCP modifies reinstatement of cocaine-seeking elicited by cocaine-related environmental stimuli and (2) whether this compound produces priming effects. Male Wistar rats were trained to associate discriminative stimuli (S D) with cocaine availability (0.25 mg/infusion) versus non-reward and then were subjected to repeated extinction sessions during which the reinforcer and S D were withheld. Subsequent presentation of the cocaine S D produced recovery of cocaine-seeking. BTCP (2.5–30 mg/kg; i.p.) did not attenuate the conditioned reinstatement induced by the cocaine S D but, rather, potentiated this effect at 10 mg/kg. To test whether BTCP, by itself, exerts priming effects, different groups of rats were trained to self-administer cocaine (0.25 mg/infusion) for 2 weeks. After a 2-week extinction period, BTCP (5, 10 and 20 mg/kg, i.p.) reinstated cocaine-seeking, showing that BTCP not only increases cocaine-seeking induced by cocaine-related stimuli but also produces priming effects following abstinence. The results suggest that, in cocaine abstinent rats, BTCP produces cocaine-like effects.

Involvement of the Sigma1 Receptor in Cocaine-induced Conditioned Place Preference: Possible Dependence on Dopamine Uptake Blockade

The involvement of the sigma1 receptor on the rewarding effects of cocaine was examined using the conditioned place preference (CPP) procedure in C57BL/6 mice. Acquisition or expression of cocaine (20 mg/kg i.p.)-induced CPP was significantly decreased by pre-treatment with the selective sigma1 receptor antagonists N,N-dipropyl-2-(4-methoxy-3-(2-phenylethoxy)phenyl)ethylamine (NE-100) or N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(dimethylamino)ethylamine (BD1047), 1–10 mg/kg, i.p. The sigma1 receptor agonists igmesine or 2-(4-morpholinoethyl-1-phenylcyclohexane-1-carboxylate hydrochloride (PRE-084) failed to induce CPP when injected alone. Moreover, the CPP induced by N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine (BTCP), a selective dopamine reuptake inhibitor, was blocked by treatments with the sigma1 receptor antagonists as was similarly observed with cocaine. In addition, the repetitive treatment with cocaine during conditioning increased sigma1 receptor mRNA expression in the nucleus accumbens, but not in the caudate putamen, prefrontal cortex or cerebellum. These data show that the sigma1 receptor is not only necessary for acquisition of the cocaine-induced CPP, but that it is also implicated in its expression, confirming that activation of the sigma1 receptor is induced during cocaine's early effects. The sigma1 receptor is activated consequently to dopamine reuptake blockade and is not sufficient to induce CPP by itself. The mechanism of the sigma1 receptor involvement in CPP and the selectivity toward the CPP-inducing drug remains however to be determined. These results show that strategies targeting the sigma1 receptor with selective antagonists may allow effective attenuation of cocaine's rewarding properties and, in turn, offer new treatment strategies against drug addiction.

BTCP is a potent reinforcer in rats:: Comparison of behavior maintained on fixed- and progressive-ratio schedules

N-[1-(2-Benzo[ b]thiophenyl)cyclohexyl]piperidine (BTCP) is a phencyclidine (PCP) derivative that acts as a potent dopamine (DA) reuptake inhibitor. Earlier studies have shown that BTCP can substitute for the reinforcing effects of cocaine. Therefore, the aim of the study was to further characterize the reinforcing effects of BTCP. The reinforcing actions of BTCP were compared to those of cocaine at equimolar concentrations in drug-naı̈ve rats. Two groups of animals were implanted with jugular catheters and trained to intravenously self-administer BTCP or cocaine (0.25 mg/infusion) on a fixed-ratio five schedule (FR 5) of reinforcement. Both BTCP and cocaine produced comparable inverted U-shaped dose–effect curves on this schedule over doses of 0.03, 0.06, 0.125, and 0.25 mg/infusion. Two doses (0.125 and 0.25 mg/infusion) that produced reliable self-administration in all the animals for cocaine and BTCP were then tested on a progressive-ratio schedule. At each dose, BTCP supported higher breaking points (BPs) than cocaine. The results demonstrate that rats readily acquire responding maintained by BTCP and suggest that BTCP may have greater reinforcing effects than cocaine at equimolar concentrations.

Behavioral and neurochemical effects of 3-OH-pip-BTCP, an active metabolite of BTCP in rats.

The effects of N-[1-(2-benzo[b]thiophenyl)cyclohexyl]piperidin-3-ol (3-OH-pip-BTCP), an active metabolite of N-[1-(2-benzo[b]thiophenyl)cyclohexyl]piperidine (BTCP) was examined on locomotor activity and dopamine (DA) levels in the nucleus accumbens (NAcc) in rats. To study the stimulant action of 3-OH-pip-BTCP, rats were placed into activity chambers and injected with the compound (0-40 mg/kg, i.p.). To measure the effects of 3-OH-pip-BTCP on DA levels, rats were implanted with microdialysis probes into the NAcc and the same doses as used in the locomotor activity experiment were administered i.p. 3-OH-pip-BTCP dose-dependently increased locomotor activity and DA levels in the NAcc which lasted 4-5 h at 20 and 40 mg/kg. The results suggest that 3-OH-pip-BTCP exerts long lasting stimulating effects on locomotion and extracellular DA levels in the NAcc, suggesting that 3-OH-pip-BTCP contributes importantly to the pharmacological effects of its parent compound, BTCP.

Non Reciprocal Cross-Sensitization Between Cocaine and BTCP on Locomotor Activity in the Rat

MARTIN-FARDON, R., O. BEN-SHAHAR AND F. WEISS. Non reciprocal cross-sensitization between cocaine and BTCP on locomotor activity in the rat. PHARMACOL BIOCHEM BEHAV 66(3) 631–635, 2000.—Measurement of locomotor sensitization was employed to characterize the effect of intermittent treatment with N-[1-(2-benzo[b]thiophenyl)cyclohexyl]piperidine (BTCP) and cocaine in the rat. Like cocaine, BTCP possesses high affinity for the dopamine transporter and inhibits dopamine reuptake. Although both drugs exhibit similar behavioral and neurochemical profiles with acute administration, there is tentative evidence to suggest that following chronic treatment BTCP does not induce neurochemical sensitization, and can attenuate cocaine-induced neurochemical sensitization in the striatum. Male Wistar rats were randomly divided into five groups after determining baseline locomotor activity. Three groups were treated with either saline (saline/saline), cocaine (20 mg/kg; cocaine/cocaine), or BTCP (10 mg/kg; BTCP/BTCP) for 10 days. The remaining two groups were treated with cocaine (20 mg/kg) or BTCP (10 mg/kg) for 3 days, followed by administration of BTCP (10 mg/kg; cocaine/BTCP) or cocaine (20 mg/kg; BTCP/cocaine) for 7 days. Locomotor sensitization was observed in all groups. However, although cross-sensitization on the day of substitution (day 4) was found in the BTCP/cocaine group, cross-sensitization was not observed in the cocaine/BTCP group. These results suggest that although the locomotor-activating effects of BTCP and cocaine are similar, the two drugs do not act identically, and different neural mechanisms may underlie BTCP and cocaineinduced sensitization.

The low affinity PCP sites in the rat cerebellum not only bind TCP-like but also BTCP-like structures

Congeners of the potent dopamine (DA) re-uptake inhibitor 1-[1-(2-benzo[b]thiophenyl)cyclohexyl]piperidine (BTCP) are unexpectedly able to bind in the rat cerebellum, although this structure is devoid of dopaminergic nerve endings. In line with previous studies the hypothesis that they bind to low affinity PCP sites labelled with [ 3H]TCP in the rat cerebellum, even though they do not bind to the high affinity PCP sites in the forebrain, was considered. Analogues of 1-[1-(2-thiophenyl)cyclohexyl]piperidine (TCP) and BTCP with a modified aromatic moiety and with O or S atoms substituted in the cyclohexyl ring were prepared and tested in competition experiments both in rat forebrain and cerebellum membranes labelled with [ 3H]TCP, and in rat striatum membranes labelled with [ 3H]BTCP. Results indicated that BTCP and congeners could bind to low affinity PCP sites labelled with [ 3H]TCP in the rat cerebellum with a decrease of the selectivity for the DA transporter. On the contrary, some TCP analogues displayed a very high selectivity for these low affinity sites; they might be important pharmacological tools to elucidate the nature and function at yet unknown of these sites.

Sensitivity of the PCP receptor and the dopamine transporter to ligands bearing multiple asymmetric centres

Summary Generation of one or two asymmetric carbons by means of a methyl substitution into cyclohexyl or piperidine moieties of 1-[1-(2-thienyl)cyclohexyl]piperidine (TCP) and 1-[1-(2-benzo[ b ]thiophenyl)cyclohexyl]piperidine (BTCP) structures has revealed improved affinity and/or selectivity for the PCP receptor and the dopamine (DA) transporter, respectively. Therefore, to get more information about the influence of chiral centres on affinity and selectivity, simultaneous methyl substitutions of cyclohexyl and piperidine moieties have been performed to generate three asymmetric carbons into the parent structures. Thus, cis -(Pip/Me)-1-[1-(2-thienyl)-2-methylcyclohexyl]-3-methylpiperidines and cis -(Pip/Me)-1-[1-(2-benzo[ b ]thiophenyl)-2-methylcyclohexyl]-3-methylpiperidines in homochiral forms have been prepared and their affinities for the PCP receptor ([ 3 H]TCP binding) and for the DA transporter ([ 3 H]BTCP binding) have been measured on rat brain and striatal membranes, respectively. None of the enantiomeric structures revealed affinities and/or selectivities in the same range as molecules bearing one or two asymmetric centres. In the TCP series the best compounds were in the same range as the parent compound. In the BTCP series, pure stereomers displayed lowered affinities and considerably reduced selectivities than the parent compound.

Binding domains for blockers and substrates on the dopamine transporter in rat striatal membranes studied by protection against N-ethylmaleimide-induced reduction of [3H]WIN 35,428 binding.

Binding sites for 2 beta-carbomethoxy-3 beta-(4-fluorophenyl)[3H]tropane ([3H]WIN 35,428) on rat striatal membranes were alkylated with N-ethylmaleimide (NEM), and the protective potency was measured of the blockers cocaine, N[1-(2-benzo[b]thiophenyl) cyclohexyl]piperidine (BTCP), benztropine, WIN 35,428; and nomifensine, and of the substrates dopamine, norepinephrine, S(+)-amphetamine, tyramine, and metaraminol. In general, the protective potency was lower (at least 3 times) than the potency in inhibiting [3H]WIN 35,428 binding with the compounds present under the same experimental conditions used for the NEM-induced alkylation. However, the disparity was substantially greater for all substrates tested (10- to 93-fold) than for the blockers (2- to 6-fold), especially cocaine and BTCP (3-fold). [3H]WIN 35,428 binding was best described by a l-site model under the present conditions. The results are discussed in terms of models involving blocker-induced conformational changes and overlapping nonidentical binding domains for blockers and substrates.

Binding domains for blockers and substrates on the cloned human dopamine transporter studied by protection against N-Ethylmaleimide-induced reduction of 2β-carbomethoxy-3β-(4-fluorophenyl)[ 3H]tropane ([ 3H]WIN 35,428) binding

Binding sites for 2β-carbomethoxy-3β-(4-fluorophenyl)[ 3H]tropane ([ 3H]WIN 35,428) on the human dopamine transporter expressed in C6 glioma cells were alkylated with N-ethylmaleimide (NEM), and the protective potency of the blockers cocaine, N[1-(2-benzo[b]thiophenyl)cyclohexyl]piperidine (BTCP), and benztropine, and of the substrates dopamine, d-amphetamine, and norepinephrine was measured. In general, the protective potency was lower (at least 4–5 times) than the potency in inhibiting [ 3H]WIN 35,428 binding with the compounds present under the same experimental conditions used for the NEM alkylation. However, the disparity was substantially greater for all substrates tested (23- to 44-fold) than for the blockers (4- to 11-fold), especially cocaine (5-fold) and BTCP (4-fold). Benztropine took an intermediate place (11-fold) between cocaine (5-fold) and BTCP (4-fold), on the one hand, and dopamine (23-fold), on the other hand. [ 3H]WIN 35,428 binding was best described by a one-site model under the present conditions. The results are discussed in terms of models involving blocker-induced conformational changes and overlapping nonidentical binding domains for blockers and substrates.

N-[1-(2-Benzo(tb)thiophenyl)cyclohexyl]piperidine (BTCP) and cocaine induce similar effects on striatal dopamine: a microdialysis study in freely moving rats

N-[1-(2-Benzo( b)thiophenyl)cyclohexyl]piperidine (BTCP) and cocaine inhibit dopamine (DA) uptake but bind to different sites on the transporter. Their dose-dependent effects (i.p. administration) on extracellular DA levels in the rat striatum were measured by in vivo microdialysis. Both drugs dose-dependently increased DA levels with a maximum effect 60 min post injection. BTCP (20 mg/kg) had a greater peak effect than cocaine (40 mg/kg). For doses inducing similar behavioral effects (cocaine, 20 mg/kg; BTCP, 10 mg/kg) similar DA increases were observed in the striatum and the nucleus accumbens. Although both drugs bind on the DA transporter on different sites and induce different behavioral effects when administered chronically, their acute administration increased striatal DA level in a similar way.

Effect of lowered lipophilicity on the affinity of PCP analogues for the PCP receptor and the dopamine transporter

Summary Oxygen and sulphur atoms were introduced in the cyclohcxyl and piperidinyl moieties of the basic structures 1-(1-phenyl-cyclohexyl)piperidine (PCP), 1-[1-(2-thienyl)cyclohexyl]piperidine (TCP), and 1-[1-(2-benzo[ b ]thiophenyl)cyclohexyl]piperidine (BTCP) to lower their global lipophilicity. The compounds obtained were tested comparatively for their affinity for the PCP receptor labelled with [ 3 H]TCP and for the dopamine (DA) transporter labelled with [ 3 H]BTCP. Lowering the global lipophilicity in PCP and TCP series is detrimental to the affinity and selectivity for the PCP receptor. In the BTCP series lowering of the global lipophilicity is less deleterious and may, on the contrary, be a useful way of increasing selectivity for the DA transporter in some instances.

PCP receptor and dopamine uptake sites are discriminated by chiral TCP and BTCP derivatives of opposite configuration

Summary 3-Methylpiperidine derivatives of 1-[1-(2-thienyl)cyclohexyl]piperidine (TCP) and l-[1-(2-benzo[ b ]thiophenyl)cyclohexyl] piperidine (BTCP) were obtained in their racemic and homochiral forms. They have been tested for their affinity for the PCP receptor labeled with [ 3 H]TCP and for the dopamine transporter labeled with [ 3 H]BTCP. The homochiral TCP derivative (+)- R displayed a very high affinity (5.2 nM) and selectivity for the PCP receptor. In contrast, the homochiral BTCP derivative (−)- S therefore of opposite configuration, displayed a very high affinity (3.5 nM) and selectivity for the dopamine transporter.

Dopamine uptake inhibitory activity of novel tryptamine 5‐HT1 receptor ligands

AbstractIn the search for novel serotonin receptor ligands, a series of 5‐thiazolyl‐N,N‐dimethyltryptamine derivatives was synthesized which exhibited high affinity binding to 5‐HT1A, 5‐HT1B, and 5‐HT1D receptors and the functional characteristics of receptor agonists. One member, 5‐(4‐anilnomethyl‐2‐thiazolyl)‐N,N‐dimethyltryptamine (CP‐110,330), was found also to be a potent and selective inhibitor of dopamine uptake in rat striatal synaptosomes. This activity was confirmed by its potent displacement of [3H]N(1‐[2‐benzo(b)thiophenyl]cyclohexyl piperidine (BTCP) binding to the dopamine transporter in striatal membranes. A limited structure‐activity study indicated that optimal dopamine uptake blocking activity was obtained when the thiazole C4 substituent consisted of phenyl with a 2‐atom spacer. The potent effect of these 5‐HT1 receptor ligands on dopamine uptake can be rationalized by the observation that the flexibility of these tryptamine molecules allows the superimposition of the phenyl ring and amino group of the side chain with the corresponding moieties of tametraline, a known catecholamine uptake inhibitor of fixed conformation. A related compound, 3‐(R‐N‐methyl‐2‐pyrrolidinylmethyl)‐5‐(4‐benzyl‐2‐thiazolylamino)‐1H‐indole (CP‐146,662) showed similar potent binding affinity to 5‐HT1 receptors and the dopamine transporter. Compounds with this dual serotonergic and dopaminergic activity may have utility as antidepressant agents. As potent dopamine uptake inhibitors, they may also have application in the treatment of cocaine addiction. © 1994 Wiley‐Liss, Inc.

Arylcyclohexylamines derived from BTCP are potent indirect catecholamine agonists

N-[1-(2-Benzo[ b]thiophenyl)cyclohexyl]piperidine (BTCP)-related molecules were prepared by means of chemical modulation of the 3 rings which constitute this dopamine (DA) and norepinephrine (NE) uptake inhibitor. Tested in vitro (binding to the DA uptake complex and to the PCP receptor sites, inhibition of the synaptosomal uptake of DA and NE) and in vivo (locomotor activity in mice) these molecules showed good homogeneity of action. The newly prepared structures, although formally related to the phencyclidine (PCP) structural model, no longer display significant affinity for the PCP receptor. These compounds behave like a new series of indirect potent stimulants of the dopaminergic and noradrenergic systems leading to potential antidepressive compounds.

Characterization of [3H]desmethylimipramine binding in bovine adrenal medulla: interactions with sigma- and (or) phencyclidine-receptor ligands.

High-affinity binding sites (apparent KD 2.87 nM) for [3H]desmethylimipramine ([3H]DMI), have been demonstrated and characterized in membrane preparations of bovine adrenal medulla. The binding of [3H]DMI improved upon pretreatment of the membrane with KCl and was saturable, sodium dependent, and potently inhibited by nisoxetine and imipramine. [3H]DMI binding was also inhibited by various phencyclidine (PCP)- and (or) sigma-receptor ligands, with the following order of potency: haloperidol > rimcazole > (-)-butaclamol > dextromethorphan > MK-801 > (+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine ((+)-3-PPP) > PCP > N-(2-thienyl)cyclohexyl-3,4-piperidine (TCP) > (+)-SKF-10047 > (-)-SKF-10047. The inhibition produced by sigma ligands was not attributed to stimulation of either sigma 1- or sigma 2-receptors, owing to inactivity of the selective sigma-receptor ligands (+)-pentazocine and 1,3-di(2-tolyl)guanidine (DTG). The inhibition of [3H]DMI binding by sigma- and PCP-receptor ligands was not attributed to PCP1- or PCP2-receptor stimulation, owing to the decreased potency (100-fold) of these ligands in [3H]DMI assays compared with the affinity for brain PCP1 sites, and the ineffectiveness of the PCP2-ligand N-(1-(2-benzo(b)thiophenyl)cyclohexyl)piperidine (BTCP). Scatchard analysis of the inhibition by the sigma-ligands haloperidol and (+)-3-PPP, as well as the PCP1 receptor ligand MK-801, demonstrated noncompetitive interaction with the site bound by [3H]DMI. These studies indicate that bovine adrenomedullary membranes possess a specific receptor for the noradrenaline uptake inhibitor [3H]DMI, which is sensitive to allosteric modulation produced by PCP and sigma-ligands.

Inhibition of locus coeruleus neurons by the phencyclidine analog, N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine: evidence for potent indirect adrenoceptor agonist properties

The effects of the phencyclidine derivative, N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine (BTCP), on the electrical activity of noradrenaline (NA) neurons of the locus coeruleus (LC) were studied in halothane-anesthetized rats. Systemic administration of BTCP potently inhibited LC neurons (ID 50 of 1.1 ± 0.1 mg/kg i.v.). This effect was mimicked by local microejection of BTCP into the LC. Both the systemic and local effects of BTCP were blocked by α 2-adrenoceptor antagonists and prevented by prior depletion of catecholamines with reserpine. These and other data suggest that BTCP behaves as a potent indirect NA agonist (i.e. via NA re-uptake and/or release systems).

Regional differences in the effect of N-[1-(2-benzo[b]thiophenyl)cyclohexyl]piperidine (BTCP) on extracellular dopamine levels: An in vivo microdialysis study

N-[1-(2-Benzo[b]thiophenyl)cyclohexyl]piperidine (BTCP) is a phencyclidine derivative highly selective for the dopamine (DA) uptake complex. Its effect on extracellular DA levels was studied by in vivo microdialysis on freely moving rats. In the striatum, BTCP induced a dose-dependent increase in DA levels, without affecting DA metabolites. In the nucleus accumbens, a lower increase in DA was observed, but with concomitant decreases in 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). These experiments show that the effects of BTCP on extracellular DA levels are significantly different on extrapyramidal and mesolimbic dopaminergic terminals.

3H]1‐[2‐(2‐thienyl)cyclohexyl]piperidine labels two high‐affinity binding sites in human cortex: Further evidence for phencyclidine binding sites associated with the biogenic amine reuptake complex

Previous work demonstrated two high-affinity PCP binding sites in guinea pig brain labeled by [3H]TCP (1-(1-[2-thienyl]cyclohexyl)piperidine): site 1 (N-methyl-D-aspartate [NMDA]-associated) and site 2 (dopamine-reuptake complex associated). The present study examined brain membranes prepared from various species, including human, for the presence of site 2, defined as binding in the presence of (+)-5-methyl-10,11-dihydro-5H-dibenzo [a, d]cyclohepten-5,10-imine maleate ((+)-MK801) minus binding in the presence of 10 microM TCP (nonspecific binding). Studies were conducted in absence of sodium which was found to be inhibitory to [3H]TCP binding. The results demonstrated detectable levels of site 2 in brain membranes of guinea pig, rabbit, pig, mouse, sheep, and human but not in the rat or chicken. Using human cortical membranes, site 2 was the predominant binding site. Detailed studies conducted with human cortical tissue showed that high-affinity dopamine (1-[2- [bis(4-fluorophenyl)-methoxy]ethyl]-4-(3-phenylpropyl)piperazine (GBR12909)], [1,2]benzo(b)thiophenylcyclo-hexylpiperidine (BTCP), and serotonin (fluoxetine) uptake inhibitors produced a wash-resistant inhibition of [3H]TCP binding to site 2, but not site 1. Preincubation of guinea pig brain membranes with BTCP was shown to produce an increase in the dissociation rate of [3H]TCP from PCP site 2. Structure activity studies with various uptake inhibitors showed that GBR12909, benztropine, fluoxetine, and BTCP have higher affinity for site 2 than for site 1. (+)-MK801, ketamine, and tiletamine were very selective for site 1, whereas dexoxadrol and TCP were moderately selective for site 1. These results suggest that human cortex possesses high-affinity PCP binding sites associated with biogenic reuptake binding sites, and that guinea pig brain, but not rat brain, may be an appropriate animal model for studying PCP site 2 in human brain.

Desipramine and the phencyclidine derivative BTCP differently inhibit [ 3H]TCP binding to high- and low-affinity sites

The effects of N-[1-(2-benzo(b)thiophenyl)cyclohexyl]piperidine (BTCP) and desipramine on [ 3H]N-[1-(2-thienyl)cyclohexyl]piperidine ([ 3H]TCP) binding were investigated in vivo and in vitro. In the cerebrrum, both drugs were competitive inhibitors of high-affinity [ 3H]TCP binding. Conversely, in the cerebellum, they were non-competitive inhibitors of low-affinity [ 3H]TCP binding. These results imply that the different [ 3H]TCP binding sites have distinct pharmacological properties, and show that, although chemically related to TCP, BTCP has an effect similar to that of desipramine.

In vivo labeling of phencyclidine (PCP) receptors with 3H‐TCP in the mouse brain

The phencyclidine (PCP) derivative N-[1-(2-thienyl)cyclohexyl]-piperidine (3H-TCP) was used to label in vivo the N-methyl-D-aspartate (NMDA) receptor-associated ionic channel in the mouse brain. After the injection of a tracer dose of 3H-TCP, a spread labeling throughout the brain was observed, but was the highest in the cerebellum. Preadministration of unlabeled TCP (30 mg/kg) resulted in a 90% reduction of 3H-TCP binding. PCP, TCP, MK-801, dexoxadrol, ketamine, and SKF 10,047 isomers dose-dependently prevented the in vivo 3H-TCP binding. ID50 determined in the cerebrum and the cerebellum were respectively correlated with K0.5 for 3H TCP high (rat cortex) and low affinity (rat cerebellum) sites in vitro. The pharmacological specificity of the 3H-TCP binding site in the cerebellum was significantly different from that in the cerebrum. ID50 values were generally higher than in the cerebrum and, particularly, MK-801, the most potent drug in the cerebrum, was without significant effect in the cerebellum, at any time and at doses as high as 30 mg/kg. N-[1-(2-benzo(b) thiophenyl)cyclohexyl]piperidine (BTCP), desipramine, and atropine showed a more efficient prevention of 3H-TCP binding in the cerebellum than in the cerebrum. The prevention of the binding by TCP or PCP, at doses close to their ID50 values, was rapid and then decreased slowly. The effect of MK-801 was long-lasting. This study confirm previous in vitro studies: 3H-TCP is an efficient tool for the labeling of the NMDA receptor-associated ionic channel.(ABSTRACT TRUNCATED AT 250 WORDS)