5-HT1A Receptor Ligands Research Articles

N‐[3‐[4‐(2‐methoxyphenyl) piperaziny‐1‐yl]propyl]cyclam: synthesized as a potential 5‐HT1A receptor ligand and labelled with 99mTc‐nitrido core

AbstractThis paper reports the synthesis of new potential 5‐HT1A receptor ligand N‐[3‐[4‐(2‐methoxyphenyl)piperaziny‐1‐yl]propyl]cyclam (MPPC) and radiolabelling of it with 99mTc‐nitrido core. The novel neutral complex 99mTcN‐MPPC combines 1,4,8,11‐tetraazacyclotetradecane (cyclam) ligand as chelate moiety for 99mTc‐nitrido with a 1‐(2‐methoxyphenyl)piperazine moiety derived from WAY 100635 via a 3‐carbon alkyl chain. This provided a reliable and reproducible method for attaching the technetium to the pharmacophore moiety of WAY 100635. 99mTcN‐MPPC was prepared by a two‐step procedure and the radiochemical purity was found to be greater than 95%. It was hydrophilic and stable for at least 4 h at room temperature. In vivo stability study in normal rats showed that no degradation of 99mTcN‐MPPC was found in deproteinated blood samples at 2 h post‐injection. This effective 99mTc‐labelling strategy for obtaining neutral 99mTc nitrido complexes would be a useful tool to prepare new SPECT agents to image 5‐HT1A receptor with cyclam conjugated ligands. Copyright © 2008 John Wiley & Sons, Ltd.

Adaptations in pre- and postsynaptic 5-HT1A receptor function and cocaine supersensitivity in serotonin transporter knockout rats

While individual differences in vulnerability to psychostimulants have been largely attributed to dopaminergic neurotransmission, the role of serotonin is not fully understood. To study the rewarding and motivational properties of cocaine in the serotonin transporter knockout (SERT-/-) rat and the involvement of compensatory changes in 5-HT1A receptor function are the objectives of the study. The SERT-/- rat was tested for cocaine-induced locomotor activity, cocaine-induced conditioned place preference, and intravenous cocaine self-administration. In addition, the function and expression of 5-HT1A receptors was assessed using telemetry and autoradiography, respectively, and the effect of 5-HT1A receptor ligands on cocaine's psychomotor effects were studied. Cocaine-induced hyperactivity and conditioned place preference, as well as intravenous cocaine self-administration were enhanced in SERT-/- rats. Furthermore, SERT-/- rats displayed a reduced hypothermic response to the 5-HT1A receptor agonist 8-OHDPAT. S-15535, a selective somatodendritic 5-HT1A receptor agonist, reduced stress-induced hyperthermia (SIH) in wild-type controls (SERT+/+), while it increased SIH in SERT-/- rats. As 5-HT1A receptor binding was reduced in selective brain regions, these thermal responses may be indicative for desensitized 5-HT1A receptors. We further found that both 8-OHDPAT and S-15535 pretreatment increased low-dose cocaine-induced locomotor activity in SERT-/- rats, but not SERT+/+ rats. At a high cocaine dose, only SERT+/+ animals responded to 8-OHDPAT and S-15535. These data indicate that SERT-/- -associated 5-HT1A receptor adaptations facilitate low-dose cocaine effects and attenuate high-dose cocaine effects in cocaine supersensitive animals. The role of postsynaptic and somatodendritic 5-HT1A receptors is discussed.

Quantitative structure-affinity relationship of 5-HT1A receptor ligands by the classification tree method

The influence of molecular structure of 346 ligands on their affinity for 5-HT1A receptors was investigated. It was shown that the effectiveness of the proposed novel approach for interpretation of decision tree models compared favourably with the PLS method. In the context of the proposed approach, molecular fragments and their values of the relative influence on the affinity for 5-HT1A receptors were defined.

Mouse strain related effects of cannabinoid and serotonergic ligands on alcohol appetence

Because cannabinoid (CB) and serotonin (5-HT) systems have been proposed to play an important role in drug craving, we investigated whether CB1 and 5-HT1A receptor ligands could affect voluntary alcohol intake in two mouse strains, C57BL/6J and DBA/2J, with marked differences in native alcohol preference. When offered progressively (3% to 10% ethanol) in drinking water, in a free-choice procedure, alcohol intake was markedly lower (~70%) in DBA/2J than in C57BL/6J mice. In DBA/2J mice, chronic treatment with the CB receptor agonist WIN 55,212-2 increased alcohol intake. This effect was prevented by both chronic CB1 receptor blockade by rimonabant or chronic 5-HT1A receptor stimulation by 8-OH-DPAT, which, on their own, did not affect alcohol intake. In C57BL/6J mice, WIN 55,212-2 had no effect but CB1 receptor blockade or 5-HT1A receptor stimulation significantly decreased alcohol intake. Parallel autoradiographic investigations showed that chronic treatment with WIN55,212-2 significantly decreased 5-HT1A-mediated [35S]GTP-γ-S binding in the hippocampus of both mouse strains. Conversely, chronic rimonabant increased this binding in C57BL/6J mice.These results show that CB neurotransmission can exert a permissive control on alcohol intake, possibly through CB1-5-HT1A interactions. However, the differences between C57BL/6J and DBA/2J mice indicate that such modulations of alcohol intake are under genetic control.

Agonist and antagonist properties of antipsychotics at human dopamine D4.4 receptors: G-protein activation and K+ channel modulation in transfected cells

Interaction at dopamine D4 receptors may improve cognitive function, which is highly impaired in individuals with schizophrenia, but comparative studies of recent antipsychotics in cellular models of D4 receptor activation are lacking. Here, we report the in-vitro profile of over 30 ligands at recombinant hD4.4 receptors. In [35S]GTPgammaS binding experiments using membranes of CHO-hD4.4 cells, apomorphine, preclamol and the selective D4 agonists, ABT724, CP226269, Ro-10-5824 and PD168077, behaved as partial agonists (Emax 20-60% vs. dopamine), whereas L745870 and RBI257, displayed antagonist properties. The 'conventional' antipsychotic, haloperidol and the 'atypicals', clozapine and risperidone, exhibited antagonist properties, while 'third generation' compounds bifeprunox, SLV313 and F15063, acted as partial agonists (10-30%). Aripiprazole and SSR181507 slightly stimulated [35S]GTPgammaS binding at micromolar concentrations. In Xenopus laevis oocytes co-expressing hD4.4 receptors with G-protein-coupled inwardly rectifying potassium (GIRK) channels, apomorphine, preclamol, ABT724, CP226269, and PD168077 stimulated GIRK currents (Emax 70-80%). The 5-HT1A receptor ligands, WAY100635 and flibanserin, also exhibited partial agonist activity (30% and 15%, respectively). Haloperidol, clozapine, olanzapine and nemonapride did not stimulate GIRK currents, whereas aripiprazole, bifeprunox, SLV313 and F15063, but not SSR181507, exhibited partial agonism (Emax 20-35%). In-vitro responses depended on experimental conditions: increasing NaCl concentration (30 mm to 100 mm) reduced agonist efficacy in [35S]GTPgammaS binding, whereas decreasing the amount of hD4.4 cRNA injected into oocytes (from 2.0 to 0.5 ng/oocyte) reduced agonist efficacy of several compounds. These data indicate that, unlike conventional or 'atypical' antipsychotics, several 'third generation' agents display D4 receptor partial agonism that may be sufficient to influence physiological D4 receptor activity in vivo.

Effects of the serotonin 5-HT2A and 5-HT2C receptor ligands on the discriminative stimulus effects of nicotine in rats

The present study tested the hypothesis that serotonergic (5-HT) 5-HT2A or 5-HT2C receptors or their pharmacological stimulation modulated the discriminative stimulus effects of nicotine in male Wistar rats. To this end the selective 5-HT2A receptor antagonist R-(+)-alpha-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenyl)ethyl]-4-piperidinemethanol (M100,907; 0.5-1 mg/kg, i.p.), the functional 5-HT2A receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI; 0.1-1 mg/kg, s.c.), the selective 5-HT2C receptor antagonist 6-chloro-5-methyl-1-{[2-(2-methylpyrid-3-yloxy)pyrid-5-yl]carbamoyl}indoline (SB 242,084; 0.25-1 mg/kg, i.p.) and the 5-HT2C receptor agonists (S)-2-chloro-5-fluoro-indol-1-yl)-1-methylethylamine fumarate (Ro 60-0175; 0.3-1 mg/kg, s.c.) and (7bR, 10aR)-1,2,3,4,8,9,10,10a-octahydro-7bH-cyclopenta-[b][1,4]diazepino[6,7,1hi]indole (WAY 163,909; 0.75-1.5 mg/kg, i.p.) were used. Additionally, the effects of the selective alpha4beta2 nicotinic acetylcholine receptor subtype agonist 5-iodo-3-(2(S)-azetidinylmethoxy)pyridine (5-IA; 0.01 mg/kg, s.c.) were investigated. In rats trained to discriminate (-)-nicotine (0.4 mg/kg, s.c.) from saline in a two-lever, water-reinforced fixed ratio 10 task, substitutions were not observed with 5-HT2 receptor ligands (<32% nicotine-lever responding), conversely 5-IA induced a full substitution (100% nicotine-lever responding). In combination studies, fixed doses of M100,907 (0.5-1 mg/kg) or SB 242,084 (0.25-1 mg/kg) did not alter the dose-response curve of nicotine, while DOI (0.3 mg/kg), Ro 60-0175 (1 mg/kg) and WAY 163,909 (1 and 1.5 mg/kg) attenuated the discriminative stimulus effects of nicotine. The decrease in the expression of the discriminative stimulus effects of nicotine produced by DOI was blocked by M100,907 (1 mg/kg), but not by SB 242,084 (1 mg/kg), while that evoked by Ro 60-0175 or WAY 163,909 was blocked by SB 242,084 (1 mg/kg), but not by M100,907 (1 mg/kg). Further studies showed that DOI (0.3 mg/kg) and Ro 60-0175 (1 mg/kg), but not WAY 163,909 (1.5 mg/kg) blocked full substitution of 5-IA (0.01 mg/kg) for nicotine. Our pharmacological analyses indicate that tonic activation of 5-HT2A or 5-HT2C receptors is not required for subjective effects of nicotine, however these receptors appear to have inhibitory influence on nicotine cue, since pharmacological stimulation of either receptor attenuates the discriminative stimulus effects of nicotine.

Synthesis and in vivo evaluation of a novel 5-HT1A receptor agonist radioligand [O-methyl-11C]2-(4-(4-(2-methoxyphenyl)piperazin-1-yl)butyl)-4-methyl-1,2,4-triazine-3,5(2H,4H)dione in nonhuman primates

Serotonin1A (5-HT1A) receptors exist in high- and low-affinity states, and agonist ligands bind preferentially to the high-affinity state of the receptor and provide a measure of functional 5-HT1A receptors. Although the antagonist tracers are established PET ligands in clinical studies, a successful 5-HT1A receptor agonist radiotracer in living brain has not been reported. [11C]MPT, our first-generation agonist radiotracer, shows in vivo specificity in baboons; however, its utility is limited owing to slow washout and immeasurable plasma free fraction. Hence we performed structure-activity relationship studies of MPT to optimize a radiotracer that will permit valid quantification of 5-HT1A receptor binding. We now report the synthesis and evaluation of [11C]MMP as an agonist PET tracer for 5-HT1A receptors in baboons. In vitro binding assays were performed in bovine hippocampal membranes and membranes of CHO cells expressing 5-HT1A receptors. [11C] labeling of MMP was performed by reacting desmethyl-MMP with [11C]CH(3)OTf. In vivo studies were performed in baboons, and blocking studies were conducted by pretreatment with 5-HT1A receptor ligands WAY-100635 and (+/-)-8-OH-DPAT. MMP is a selective 5-HT1A receptor agonist (Ki 0.15 nM). Radiosynthesis of [11C]MMP was achieved in 30 +/- 5% (n = 15) yield at EOS with a specific activity of 2,600 +/- 500 Ci/mmol (n = 12). PET studies in baboons demonstrated specific binding of [11C]MMP to 5-HT1A receptor-enriched brain regions, as confirmed by blockade with WAY-100635 and (+/-)-8-OH-DPAT. We identified [11C]MMP as an optimal agonist PET tracer that shows quantifiable, specific binding in vivo to 5-HT1A receptors in baboons.

Pharmacophore Models for Metabotropic 5-HT Receptor Ligands

An overview of pharmacophore models, developed for different subtypes of serotonin receptors belonging to the GPCR family, is presented. Starting with early models for 5-HT1A and 5-HT2 receptor ligands, and ending with the latest ones for 5-HT6- and 5-HT7 receptors, as many as fifty others are briefly summarized. No models have been developed for 5-HT1F-, 5-HT2B- and 5-HT5B receptor ligands, and in the case of 5-HT1E- and 5-HT5A Rs only single pilot studies with non-selective tryptamine derivatives are reported. For all the other subtypes of 5-HTRs, various pharmacophore hypotheses--either qualitative and/or quantitative--are characterized by sets of ligands used for their generation, a templates for alignment, the computational methods applied and, eventually, interfeature distances and/or statistical results--if available.

Synthesis of conformationally constrained aryl- or heteroarylpiperazinyl derivatives of selected imides as 5-HT1A receptor ligands.

The preparation of a number of cyclic imide 5-HT(1A) receptor ligand derivatives has been described. Their structures were conformationally constrained by introducing rigid linkers containing unsaturated bonds or aromatic benzene rings. These compounds are expected to possess anxiolytic and antidepressant activity.

Arylpiperazines with N-acylated amino acids as 5-HT1A receptor ligands

A library consisting of 60 arylpiperazines modified with N-acylated amino acids was prepared on BAL linker SynPhase™ Lanterns and evaluated in vitro for 5-HT1A receptor affinity. Biological screening, followed by a simple Fujita–Ban analysis, enabled the description of structure–activity relationships and allowed the selection of some potent, high-affinity ligands for in vivo pharmacological investigations.

Cortical serotonin 5-HT2A receptor binding and social communication in adults with Asperger's syndrome: an in vivo SPECT study.

The cause of autistic spectrum disorder (i.e., autism and Asperger's syndrome) is unknown. The serotonergic (5-HT) system may be especially implicated. However, cortical 5-HT2A receptor density in adults with the disorder has not been examined, to the authors' knowledge. The authors investigated cortical 5-HT2A receptor binding in eight adults with Asperger's syndrome and in 10 healthy comparison subjects with single photon emission computed tomography and the selective 5-HT2A receptor ligand 123I iodinated 4-amino-N-[1-[3-(4-fluorophenoxy)propyl]-4-methyl-4-piperidinyl]-5-iodo-2-methoxybenzamide (123I-5-I-R91150). People with Asperger's syndrome had a significant reduction in cortical 5-HT2A receptor binding in the total, anterior, and posterior cingulate; bilaterally in the frontal and superior temporal lobes; and in the left parietal lobe. Also, reduced receptor binding was significantly related to abnormal social communication. The authors' findings suggest that adults with Asperger's syndrome have abnormalities in cortical 5-HT2A receptor density and that this deficit may underlie some clinical symptoms.

P.1.d.006 Behavioral phenotyping of sodium-myo-inositol cotransporter knockout mice with reduced brain inositol

Our previous studies in a group of arylpiperazine derivatives of 1,3-dimethyl-3,7-dihydro-purine-2,6-diones, aimed at chemical diversification of the purine-2,6-dione by introduction of hydrophobic substituent in a 7- or 8- position or elongation of the linker length between arylpiperazine and purine core, allowed a selection of potent 5-HT1A, 5-HT2A and 5-HT7 receptor ligands displaying anxiolytic and antidepressant properties. Continuing our research in this field, in the present studies we designed a new series of 8-aminoalkylamino (15–35) and 8-arylpiperazinylpropoxy (36–42) derivatives of 7-substituted 1,3-dimethyl-3,7-dihydropurine- 2,6-dione as potential 5-HT1A, 5-HT2A and 5-HT7 receptor ligands with potential psychotropic activity.Radioligand binding assays were employed for determining the affinity and the selectivity profile of the synthesized compounds for native 5-HT1A, 5-HT2A, and cloned 5-HT6 and 5-HT7 receptors. The functional activity of the selected compounds at 5-HT1A and 5-HT2A receptors was tested in the commonly used in vivo models. Antidepressant and anxiolytic properties were evaluated in the forced swim (FST) and the four-plate test (FPT) in mice, respectively.Among the evaluated series, selected 7-benzyl-8-((4-(4-(3-chlorophenyl)piperazin-1-yl)butyl)amino)-1,3-dimethyl- 1H-purine-2,6(3H,7H)-dione (21), a mixed 5-HT1A/5-HT2A/5-HT7 receptor ligand, produced an antidepressant-like effect in FST, and exerted anxiolytic-like activity in FPT. Another pharmacologically evaluated compound 42 (a mixed 5-HT1A/5-HT7 ligand) slightly, but non-significantly attenuated the immobility time of mice in FST and was devoid of activity in FPT.Study revealed advantage of mixed 5-HT1A/5-HT2A/5-HT7 receptor ligands over 5-HT1A/5-HT7 agents to display antidepressant- and anxiolytic-like activity. Modification of arylalkyl/allyl substituent in position 7 of purine-2,6-dione opens possibility for designing new 5-HT ligands with preserved π electron system and lower molecular weight.

SAR Study of 1-Aryl-4-(phenylarylmethyl)piperazines as Ligands for Both Dopamine D2 and Serotonin 5-HT1A Receptors Showing Varying Degrees of (Ant)agonism. Selection of a Potential Atypical Antipsychotic

The syntheses of several 1-aryl-4-(arylpyridylmethyl)piperazines (4) and their affinities for dopamine D(2) and serotonin 5-HT(1A) receptors are described. The compounds were evaluated both in vitro and in vivo, resulting in the identification of the drug candidate SLV313 (4e) with equipotent and full D(2) receptor antagonism and 5-HT(1A) receptor agonism. Minor structural modifications in SLV313 revealed the possibility of designing compounds possessing varying degrees of partial agonism on one or both target receptors.

Motion correction eliminates discontinuities in parametric PET images of neuroreceptor binding

Head movements during PET studies of cerebral neuroreceptors with positron emission tomography (PET), which are often recorded as dynamic studies over periods ranging from one to two hours, do not only lead to blurred images, but, by distorting pixel time-activity curves, may also seriously disturb the kinetic analysis. Here we report on the effect of head motion on parametric images of the distribution volume ratio (DVR) as well as on the elimination of artefacts, if the dynamic PET data are corrected for head movements. For this purpose we utilized six PET studies done with the 5HT2A-receptor ligand [18F]-altanserin. Prior to the tracer injection a transmission scan of 10 min was recorded for measured attenuation correction. During the PET scan, which was acquired in listmode for 1 h, the position of the head was monitored by a Polaris infrared motion tracking system. The listmode data were sorted into 42 time frames between 10 s and 2 min in duration. A time frame consists of 63 images of 128 128 voxels with a voxel size of 2 mm 2 mm 2.43 mm. The motion correction used the multiple acquisition frame (MAF) approach, which calculates individual attenuation files for each emission frame and its corresponding head position to avoid a misalignment between transmission and emission data. After reconstruction of attenuation corrected emission frames each image frame was realigned to match the head position of the first emission frame. Both the motion corrected and not corrected dynamic images were evaluated by the non-invasive Logan plot method to obtain parametric images of DVR. In addition, a dynamic [18F]-altanserin PET scan was simulated and affected by similar movements as seen in the human studies. In this way data without statistical noise could be analysed. DVR images of motion-affected [18F]-altanserin scans showed artefacts whose extent was dependent on the amount of movement. The artefacts were mainly located at the border of the cortical tissue, especially at the interior edge towards white matter. The artefacts exhibited as discontinuities and small spots, whose values exceeded the expected DVR values or were even negative. The discontinuities were found with movements of 4 mm and greater. Isolated spots were present even with movements of only 2 mm. The artefacts disappeared when the MAF based motion correction was applied. The observations obtained in human data could be confirmed in the simulated noise free [18F]-altanserin images confirming that the artefacts are due to motion and not to statistical noise. Whereas the native PET images look just blurred, if the patient has moved during the PET scan, parametric images of the Logan DVR, which are calculated by pixel-wise linear regression, contain severe discontinuities primarily at the cortical edge. At this location, the data used in the DVR calculation change between grey and white matter data because of the head motion. The MAF based head motion correction is able to avoid the described errors.

The 5-HT1A receptor and the stimulus effects of LSD in the rat.

It has been suggested that the 5-HT1A receptor plays a significant modulatory role in the stimulus effects of the indoleamine hallucinogen lysergic acid diethylamide (LSD). The present study sought to characterize the effects of several compounds with known affinity for the 5-HT1A receptor on the discriminative stimulus effects of LSD. Twelve male Fischer 344 rats were trained in a two-lever, fixed-ratio (FR) 10, and food-reinforced task with LSD (0.1 mg/kg, i.p.; 15-min pretreatment) as a discriminative stimulus. Combination and substitution tests with the 5-HT(1A) agonists, 8-OH-DPAT, buspirone, gepirone, and ipsapirone, with LSD-induced stimulus control were then performed. The effects of these 5-HT1A ligands were also tested in the presence of the selective 5-HT1A receptor antagonist, WAY-100,635 (0.3 mg/kg, s.c.; 30-min pretreatment). In combination tests, stimulus control by LSD was increased by all 5-HT1A receptor ligands with agonist properties. Similarly, in tests of antagonism, the increase in drug-appropriate responding caused by stimulation of the 5-HT1A receptor was abolished by administration of WAY-100,635. These data, obtained using a drug discrimination model of the hallucinogenic effects of LSD, provide support for the hypothesis that the 5-HT1A receptor has a significant modulatory role in the stimulus effects of LSD.

Derivatives as 5HT1A Receptor Ligands-Past and Present

Serotonin is a neuromediator, well-know for its implication in mood regulation, anxiety, depression and, insomnia as well as in normal human function such as sleep, sexual activity and appetite. In this way, serotonin (5-hydroxytryptamine, 5-HT) is one of the most attractive targets for medicinal chemists and pharmaceutical companies. Among 5-HTRs, the 5-HT1A subtype is the best studied, and it is generally accepted that it is involved in psychiatric disorders such as anxiety and depression. Several structurally different compounds are known to bind 5-HT1A receptor sites such as aminotetralins, ergolines, arylpiperazines, indolylalkylamines, aporphines and aryloxyalkyl-amines. In this review, we report an overview of the 5-HT1A receptor ligands, belonging to different chemical classes.

Experiment assessment of mass effects in the rat: implications for small animal PET imaging

In vivo imaging using positron emission tomography (PET) is important in the development of new radiopharmaceuticals in rodent animal models for use as biochemical probes, diagnostic agents, or in drug development. We have shown mathematically that, if small animal imaging studies in rodents are to have the same “quality” as human PET studies, the same number of coincidence events must be detected from a typical rodent imaging “voxel” as from the human imaging voxel. To achieve this using the same specific activity preparation, we show that roughly the same total amount of radiopharmaceutical must be given to a rodent as to a human subject. At high specific activities, the mass associated with human doses, when administered to a rodent, may not decrease the uptake of radioactivity at non saturable sites or sites where an enzyme has a high capacity for a substrate. However, in the case of binding sites of low density such as receptors, the increased mass injected could saturate the receptor and lead to physiologic effects and non-linear kinetics. Because of the importance of the mass injected for small animal PET imaging, we experimentally compared high and low mass preparations using ex vivo biodistribution and phosphorimaging of three compounds: 2-fluoro-2-deoxyglucose (FDG), 6-fluoro-L-metatyrosine (FMT) and one receptor-directed compound, the serotonin 5HT 1A receptor ligand, trans-4-fluoro-N-{2-[4-(2-methoxylphenyl) piperazino]ethyl}-N-(2-pyridyl) cyclohexane- carboxamide (FCWAY). Changes in the mass injected per rat did not affect the distribution of FDG, FMT, and FCWAY in the range of 0.6–1.9 nmol per rat. Changes in the target to nontarget ratio were observed for injected masses of FCWAY in the range of ∼5–50 nmol per rat. If the specific activity of such compounds and/or the sensitivity of small animal scanners are not increased relative to human studies, small animal PET imaging will not correctly portray the “true” tracer distribution. These difficulties will only be exacerbated in animals smaller than the rat, e.g., mice.

Cluster analysis in kinetic modelling of the brain: a noninvasive alternative to arterial sampling

In emission tomography, quantification of brain tracer uptake, metabolism or binding requires knowledge of the cerebral input function. Traditionally, this is achieved with arterial blood sampling. We propose a noninvasive alternative via the use of a blood vessel time–activity curve (TAC) extracted directly from dynamic positron emission tomography (PET) scans by cluster analysis. Five healthy subjects were injected with the 5HT 2A-receptor ligand [ 18F]-altanserin and blood samples were subsequently taken from the radial artery and cubital vein. Eight regions-of-interest (ROI) TACs were extracted from the PET data set. Hierarchical K-means cluster analysis was performed on the PET time series to extract a cerebral vasculature ROI. The number of clusters was varied from K = 1 to 10 for the second of the two-stage method. Determination of the correct number of clusters was performed by the ‘within-variance’ measure and by 3D visual inspection of the homogeneity of the determined clusters. The cluster-determined input curve was then used in Logan plot analysis and compared with the arterial and venous blood samples, and additionally with one of the currently used alternatives to arterial blood sampling, the Simplified Reference Tissue Model (SRTM) and Logan analysis with cerebellar TAC as an input. There was a good agreement ( P < 0.05) between the values of Distribution Volume (DV) obtained from the K-means-clustered input function and those from the arterial blood samples. This work acts as a proof-of-principle that the use of cluster analysis on a PET data set could obviate the requirement for arterial cannulation when determining the input function for kinetic modelling of ligand binding, and that this may be a superior approach as compared to the other noninvasive alternatives.

Ca2+ responses in Chinese hamster ovary-K1 cells demonstrate an atypical pattern of ligand-induced 5-HT1A receptor activation.

Little experimental evidence has been reported for diverse signaling via 5-hydroxytryptamine (5-HT)1A receptors despite the fact that agonists seem to be more efficacious at dorsal raphe somatodendritic 5-HT1A autoreceptors than at postsynaptic 5-HT1A receptors. The present study investigated Ca2+ responses in Chinese hamster ovary (CHO)-K1 cells expressing a human 5-HT1A receptor by 5-HT, prototypical 5-HT1A agonists, N-(3-chloro-4-fluorobenzoyl)-4-fluoro-4-[(5-methyl-6-; methylaminopyridin-2-yl)-methylaminomethyl]-piperidine (F 14679), and especially N-(3-chloro-4-fluorobenzoyl)-4-fluoro-4-[(5-methylpyridin-2-yl)-; methylaminomethyl]piperidine (F 13640) as representative ligands of a new chemical class (methylamino-pyridine) that combines both high efficacy and selectivity for 5-HT1A receptors. 5-HT (pEC50 = 6.70 +/- 0.02) induced a pertussis toxin-sensitive, transient high-magnitude Ca2+ response. High-magnitude Ca2+ responses (Emax, percentage versus 5-HT) were also found with F 13640 (107 +/- 4), 5-carboxamidotryptamine (100 +/- 3), and F 14679 (87 +/- 3). In contrast, the prototypical 5-HT1A receptor agonists buspirone, ipsapirone, and 8-(hydroxy-2-(di-n-propylamino)tetralin, and also flesinoxan and eptapirone, were virtually inactive (< or =5). This atypical pattern of 5-HT1A receptor activation contrasts with the broad spectrum of the ligands' partial agonist properties as observed by measuring guanosine 5'-O-(3-[35 S]thio)triphosphate ([35S]GTPgammaS) binding responses with membranes of either CHO-K1 or C6-glial cells stably expressing a human 5-HT1A receptor. Remarkably, differences between ligands that seem small in the [35S]GTPgammaS binding assay translate into huge differences in the magnitude of Ca2+ responses. Therefore, some of these 5-HT1A ligands (i.e., F 13640) may in a selective way induce responses that may be not at all be achieved with other ligands (i.e., buspirone). In conclusion, the pharmacology of 5-HT1A receptor ligands seems to be codetermined by the effector pathway.

Synthesis and 5-HT2A radioligand receptor binding assays of DOMCl and DOMOM, two novel 5-HT2A receptor ligands.

A synthesis of two new active substances, DOMCl (1-(4-chloromethyl-2, 5-dimethoxyphenyl)-2-propanamine; 2) and DOMOM (1-(2, 5-dimethoxy-4-methoxymethylphenyl)-2-propanamine; 3), was developed. Unexpectedly, the Blanc reaction permitted successful synthesis of 2, 5-dimethoxyphenylpropylamine derivatives having a substituted methyl group in position 4 since solvation of the reactant occurs during the reaction. Afterwards, their affinities towards the 5-HT(2A) receptor were examined in 5-HT(2A) radioligand receptor binding assays. The study of these substances is of considerable interest because they were predicted, by preliminary molecular modeling studies based on mescalin units, to be potential new hallucinogens that should be added to the list of substances prohibited by law. It was assumed that DOMCl would be 82 times more potent as a hallucinogen than mescalin, and DOMOM would be 94 times more potent. The 5-HT(2A) radioligand receptor binding studies showed that the affinities of DOMCl and DOMOM for the 5-HT(2A) receptor are less than expected but are nevertheless 1.6 and 8.7 times higher, respectively, than that of mescalin. Therefore, scheduling these substances as potential drugs of abuse might be considered.