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

Pharmacological and behavioral characterization of D-473, an orally active triple reuptake inhibitor targeting dopamine, serotonin and norepinephrine transporters

Major depressive disorder (MDD) is a debilitating disease affecting a wide cross section of people around the world. The current therapy for depression is less than adequate and there is a considerable unmet need for more efficacious treatment. Dopamine has been shown to play a significant role in depression including production of anhedonia which has been one of the untreated symptoms in MDD. It has been hypothesized that drugs acting at all three monoamine transporters including dopamine transporter should provide more efficacious antidepressants activity. This has led to the development of triple reuptake inhibitor D-473 which is a novel pyran based molecule and interacts with all three monoamine transporters. The monoamine uptake inhibition activity in the cloned human transporters expressed in HEK-293 cells (70.4, 9.18 and 39.7 for DAT, SERT and NET, respectively) indicates a serotonin preferring triple reuptake inhibition profile for this drug. The drug D-473 exhibited good brain penetration and produced efficacious activity in rat forced swim test under oral administration. The optimal efficacy dose did not produce any locomotor activation. Microdialysis experiment demonstrated that systemic administration of D-473 elevated extracellular level of the three monoamines DA, 5-HT, and NE efficaciously in the dorsal lateral striatum (DLS) and the medial prefrontal cortex (mPFC) area, indicating in vivo blockade of all three monoamine transporters by D-473. Thus, the current biological data from D-473 indicate potent antidepressant activity of the molecule.

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.

3-OH-pip-BTCP, a metabolite of the potent DA uptake blocker BTCP, exerts cocaine-like action in rats

A previous study showed that N-[1-(2-benzo[b]thiophenyl)cyclohexyl]piperidin-3-ol (3-OH-pip-BTCP), an active metabolite of the potent dopamine reuptake inhibitor N-[1-(2-benzo[b]thiophenyl)cyclohexyl]piperidine (BTCP), exhibits stimulant effects in rats (i.e. increases dopamine levels in the nucleus accumbens and increases locomotion). The present study sought to further characterize the behavioral profile of 3-OH-pip-BTCP, specifically, its interaction with cocaine-maintained behavior. Cocaine self-administration was examined in 3-OH-pip-BTCP pretreated rats. 3-OH-pip-BTCP (0-20 mg/kg, i.p.) dose-dependently decreased cocaine self-administration. Additionally, 3-OH-pip-BTCP (10 mg/kg) shifted the cocaine dose-response to the left. Together, these results suggest that 3-OH-pip-BTCP shares similar reinforcing effects with cocaine and therefore may serve as a substitutive drug and possible agonist therapy for cocaine 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-naïve 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

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.

Alterations in striatal dopamine overflow during rotational behavior induced by amphetamine, phencyclidine, and MK-801

Rats lesioned unilaterally in the medial forebrain bundle with 6-OHDA rotated ipsilateral to the lesion following injections of amphetamine, phencyclidine (PCP), and MK-801. Concurrent measurement of striatal dopamine (DA) in the intact striatum with in vivo microdialysis revealed a dissociation between rotational behavior and alterations in DA overflow induced by the three drugs. Amphetamine produced robust ipsilateral rotational behavior and a substantial elevation in striatal DA (approximately 130% increase at asymptote). PCP produced comparable increases in rotational behavior, but only approximately 30% increase in striatal DA. MK-801 also had a comparable behavioral effect but failed to alter DA overflow in the intact striatum. Since MK-801, a noncompetitive NMDA antagonist which does not enhance extracellular dopamine in the striatum, is able to produce ipsilateral rotational behavior in rats with unilateral nigrostriatal lesions, it is likely that the effects of PCP may also be determined predominantly through NMDA blockade in this model.

N-[1-(2-Benzo(b)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, 20mg/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.

RTI-4793-14, a new ligand with high affinity and selectivity for the (+)-MK801-insensitive [3H]1-]1-(2-thienyl)cyclohexyl]piperidine binding site (PCP site 2) of guinea pig brain

[3H]TCP, an analog of the dissociative anesthetic phencyclidine (PCP), binds with high affinity to two sites in guinea pig brain membranes, one that is MK-801 sensitive and one that is not. The MK-801-sensitive site (PCP site 1) is associated with NMDA receptors, whereas the MK-801-insensitive site (PCP site 2) may be associated with biogenic amine transporters (BAT). Although several "BAT ligands" are known that bind selectively to PCP site 2 and not to PCP site 1 (such as indatraline), these compounds have low affinity for site 2 (Ki values > 1 microM). Here we demonstrate that the novel pyrrole RTI-4793-14 is a selective, high affinity ligand for PCP site 2. We determined the IC50 values of RTI-4793-14 and several reference compounds [PCP, (+)-MK801 and indatraline] for PCP site 1 (assayed with [3H](+)-MK801), PCP site 2 (assayed with [3H]TCP in the presence of 500 nM (+)-MK801) and a variety of BAT-related measures ([3H]CFT binding to the DA transporter, [3H]nisoxetine binding to the norepinephrine transporter, [3H]dopamine uptake, [3H]serotonin uptake). In addition, we determined the ability of RTI-4793-14 to block NMDA responses in cultured hippocampal neurons under voltage clamp. (+)-MK801 had high affinity for PCP site 1 (4.6 nM) and potently inhibited NMDA-induced responses, but was much less potent in the BAT-related measures (IC50 s > 10 microM). PCP had high affinity at PCP site 1 (IC50 = 92 nM) and PCP site 2 (IC50 = 117 nM), and was moderately potent in all BAT-related measures except [3H]nisoxetine binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for mutually exclusive binding of cocaine, BTCP, GBR 12935, and dopamine to the dopamine transporter

The present study addressed the possibility that there are distinct but allosterically interacting populations of binding sites for dopamine/cocaine and BTCP/GBR (N-[1-(2-benzo[b]thiophenyl)cyclohexyl]piperidine/1-(2-diphenylmethox y) - ethyl]-4-(3-phenylpropyl)piperazine) (selective dopamine uptake blockers) on the dopamine transporter in the rat striatum. Dopamine uptake sites were labeled in vitro with the cocaine analog [3H]CFT (2 beta-carbomethoxy-3 beta-(4-fluorophenyl)-tropane), and the inhibition of binding by CFT or cocaine was measured. A graphic method was adopted for studying shifts in inhibitory potency resulting from the addition of a second compound. Under the conditions used, the co-presence of dopamine, GBR 12935, or BTCP decreased the inhibitory potency of CFT or cocaine to the extent predicted by a model in which all compounds bind to the same site or the binding of all compounds is mutually exclusive. No evidence for negative allosteric interactions between CFT and BTCP was found in experiments comparing inhibition of [3H]CFT binding by BTCP at a low and high concentration of [3H]CFT.