High Affinity For 5-HT1A Receptors Research Articles

Deep Brain Stimulation of the dorsal raphe abolishes serotonin 1A facilitation of AMPA receptor-mediated synaptic currents in the ventral hippocampus

In a previous study we showed that Deep Brain Stimulation (DBS) of the rat dorsal subregion of the dorsal raphe (DRD), which sends serotonergic projections to forebrain areas, such as the ventral hippocampus, induces anxiolytic-like effects. The purpose of the present study was to investigate neurobiological alterations which might underline these behavioral effects. For that, we tested the influence of DBS upon the neuromodulatory action of serotonin on excitatory post-synaptic currents (EPSCs) in the ventral hippocampus. Male Wistar rats were submitted to high-frequency stimulation (100 μA, 100 Hz) of the DRD for 1 h during three consecutive days. On the third day, immediately after the DBS procedure, animals were euthanized. Slices of the ventral hippocampus were processed for whole cell patch clamp recordings of AMPA-receptor (AMPAR) mediated EPSCs in the CA1 area. As reported by others, we confirmed that in pre-weaning rats a high affinity 5-HT1A receptor agonist (8-OH-PIPAT, 0.5−5nM) inhibits EPSCs. However, in adult rats (non-operated or sham-operated), 8-OH-PIPAT (0.5−5 nM) increased EPSC amplitude, an effect blocked by the 5-HT1A antagonist WAY-100,635 (200 nM). Importantly, in adult rats exposed to DBS, the 5-HT1A agonist was devoid of effect. Taken together these results show that: 1) changes in 5-HT1A receptor-mediated hippocampal synaptic transmission occur with age; 2) these changes lead to a facilitatory effect of 5-HT1A receptors; 3) DBS blocks this serotonergic facilitatory action. These observations suggest that an alteration in serotonin modulation of limbic areas may underlie the psychotherapeutic effects of DBS.

Synthesis and biological evaluation of new multi-target 3-(1H-indol-3-yl)pyrrolidine-2,5-dione derivatives with potential antidepressant effect

A series of novel 3-(1H-indol-3-yl)pyrrolidine-2,5-dione derivatives were synthesised and evaluated for their 5-HT1A/D2/5-HT2A/5-HT6/5-HT7 receptor affinity and serotonin reuptake inhibition. Most of the evaluated compounds displayed high affinities for 5-HT1A receptors (e.g., 4cKi = 2.3 nM, 4lKi = 3.2 nM). The antidepressant activity of the selected compounds was screened in vivo using the forced swim test (FST). The results indicate that compound MW005 (agonist of the pre- and postsynaptic 5-HT1A receptor) exhibited promising affinities for the 5-HT1A/SERT/D2/5-HT6/5-HT7 receptors and showed an antidepressant-like activity in the FST model.

Synthesis, radiolabeling and biological evaluation of [125I]-1-[2-(benzylthio)ethyl]-4-(5-iodo-2-methoxyphenyl)piperazine as a new 5-HT1A receptor ligand

Abstract 5-HT1A receptors have been implicated in the pathogenesis of a wide variety of disorders related to the serotonin receptors. WAY100635 is a well-known high affinity 5-HT1A receptor antagonist. Many 11C and 18F radiolabeled derivatives and its radioiodinated analogues have been reported as imaging agents for 5-HT1A receptors. In this regard, the synthesis, radiolabeling and biological evaluation of a new 5-HT1A receptor radioligand, [125I]-1-(2-(benzylthio)ethyl)-4-(5-iodo-2-methoxyphenyl)piperazine ([125I]-BTE-IMPP), are described. Radioiodination of this newly synthesized compound was done by the direct aromatic electrophilic substitution via Iodo-Gen method. Radiochemical yield and radiochemical purity determined by TLC and RTLC were >70% and >95%, respectively. Biodistribution studies of [125I]-BTE-IMPP in rats displayed relatively high uptake in hippocampus (Hip) and low uptake in cerebellum (Cer). The level of the radiotracer uptake was over threefold higher in hippocampus than in cerebellum at 30 min post-injection. Moreover, the brain to blood uptake ratio and the blocking studies results indicated prolonged retention of the radiotracer and relatively good specific binding to 5-HT1A receptor. These findings strongly suggest that [125I]-BTE-IMPP could be a good candidate as an in vivo marker for pharmacological study of 5-HT1A receptors in animal models.

N-(4-[18F]-fluoropyridin-2-yl)-N-{2-[4-(2-methoxyphenyl)piperazin-1-yl]ethyl}carboxamides as analogs of WAY100635. New PET tracers of serotonin 5-HT1A receptors

N-(4-[18F]-Fluoropyridin-2-yl)-N-{2-[4-(2-methoxyphenyl)piperazin-1-yl]ethyl}-carboxamides were prepared by labeling their 4-nitropyridin-2-yl precursors through nitro substitution by the 18F anion. In vitro and in vivo tests showed that the cyclohexanecarboxamide derivative is a reversible, selective and high affinity 5-HT1A receptor antagonist (IC50 = 0.29 nM, ki = 0.18 nM) with high brain uptake, slow brain clearance and stability to defluorination when compared with conventional standards. This PET radioligand is a promising candidate for an improved in vivo quantification of 5-HT1A receptors in neuropsychiatric disorders.

Central activity of novel LCAP derivative with a very high affinity for 5-HT1A receptors

Central activity of novel LCAP derivative with a very high affinity for 5-HT1A receptors

SMILES-based QSAR model for arylpiperazines as high-affinity 5-HT1A receptor ligands using CORAL

A predictive quantitative structure – activity relationships model of arylpiperazines as high-affinity 5-HT1A receptor ligands was developed using CORAL software (http://www.insilico.eu/CORAL). Simplified molecular input-line entry system (SMILES) was used as representation of the molecular structure of the arylpiperazines. The balance of correlations was used in the Monte Carlo optimization aimed to build up optimal descriptors for one-variable models. The robustness of this model has been tested in four random splits into the sub-training, calibration, and test set. The obtained results reveal good predictive potential of the applied approach: correlation coefficients (r2) for the test sets of the four random splits are 0.9459, 0.9249, 0.9473 and 0.9362.

The 5-HT1A Agonism Potential of Substituted Piperazine-Ethyl-Amide Derivatives Is Conserved in the Hexyl Homologues: Molecular Modeling and Pharmacological Evaluation

In a series of carboxamide and sulphonamide alkyl (ethyl to hexyl) piperazine analogues, although the size of the linker is very different, ethyl and hexyl derivatives possess a high affinity for 5-HT(1A) receptors. Docking studies clearly show that hexyl and ethyl compounds favorably interact with the binding site of the active conformation of 5-HT(1A) receptors, thus confirming a possible agonist profile. This activity is effectively detected in electrophysiological experiments in which all four compounds inhibit the activity of rat dorsal raphe serotonergic neurons.

ChemInform Abstract: Pd(0) Amination of Benzimidazoles as an Efficient Method Towards New (Benzimidazolyl)piperazines with High Affinity for the 5-HT1A Receptor.

Abstract New (benzimidazolyl)amines have been synthesized from 4- and 6-bromobenzimidazole derivatives via palladium-mediated amination reactions. Among them, (benzimidazol-4(7)-yl)piperazine derivatives have been shown to be a new family of high affinity 5-HT1A receptor ligands.

Rectal antinociceptive properties of alverine citrate are linked to antagonism at the 5-HT1A receptor subtype.

Serotonin (5-HT) is considered as a major mediator causing hyperalgesia and is involved in inflammatory reactions and irritable bowel syndrome. Alverine citrate may possess visceral antinociceptive properties in a rat model of rectal distension-induced abdominal contractions. This study was designed to evaluate the pharmacological properties of alverine citrate in a rat model of rectal hyperalgesia induced by 5-HTP (5-HT precursor) and by a selective 5-HT1A agonist (8-OH-DPAT) and to compare this activity with a reference 5-HT1A antagonist (WAY 100635). At 4 h after their administration, 5-HTP and 8-OH-DPAT increased the number of abdominal contractions in response to rectal distension at the lowest volume of distension (0.4 mL). When injected intraperitoneally before 8-OH-DPAT and 5-HTP, WAY 100635 (1 mg kg(-1)) blocked their nociceptive effect, but also reduced the response to the highest volume of distension (1.6 mL). Similarly, when injected intraperitoneally, alverine citrate (20 mg kg(-1)) suppressed the effect of 5-HTP, but not that of 8-OH-DPAT. However, when injected intracerebroventricularly (75 microg/rat) alverine citrate reduced 8-OH-DPAT-induced enhancement of rectal distension-induced abdominal contractions. In-vitro binding studies revealed that alverine citrate had a high affinity for 5-HT1A receptors and a weak affinity for 5-HT3 and 5-HT4 subtypes. These results suggest that 5-HTP-induced rectal hypersensitivity involves 5-TH1A receptors and that alverine citrate acts as a selective antagonist at the 5-HT1A receptor subtype to block both 5-HTP and 8-OH-DPAT-induced rectal hypersensitivity.

P.4.d.004 A comparison of the anxiolytic-like efficacy of mechanistically-distinct compounds in animal behavioural models

Rats were trained with either 8-OH-DPAT (0.2 mg/kg) or ipsapirone (10 mg/kg) versus saline in a 2-lever discrimination task. Tests of generalization were then conducted with yohimbine. All drugs were administered IP 15 min before testing. In 8-OH-DPAT-trained subjects, 85% of the responses following yohimbine (3 mg/kg) were on the drug-appropriate lever. Likewise, yohimbine (6 mg/kg) yielded 86% drug-appropriate responses in ipsapirone-trained rats. Previous studies have provided evidence that both 8-OH-DPAT and ipsapirone have high affinity for 5-HT1A receptors and the anxiolytic-like activity of the latter drug has been attributed to its activity at those receptors. In contrast, yohimbine is an alpha2 adrenergic antagonist, has negligible affinity for the 5-HT1A receptor, and is generally regarded as being anxiogenic. The present data, which indicate a high degree of similarity between the stimuli induced by yohimbine, 8-OH-DPAT, and ipsapirone, suggest that a re-evaluation of the presumed mechanisms of actions of these drugs is in order.

Perospirone hydrochloride: the novel atypical antipsychotic agent with high affinities for 5-HT2, D2 and 5-HT1A receptors

We reviewed the pharmacological properties of perospirone hydrochloride (perospirone), a novel atypical antipsychotic agent, and discussed the potential role of 5-HT2 and 5-HT1A receptors in its action for the treatment of schizophrenia. Perospirone shows potent 5-HT2 and D2 receptor blocking activities in various animal models in vivo. Unlike other serotonin and dopamine antagonists (SDA), such as risperidone and olanzapine, perospirone exhibits a high affinity for 5-HT1A receptors, and acts as a partial agonist. Perospirone has efficacies not only for classical animal models for schizophrenia, but also in the models of negative symptoms and mood disorders, where the typical antipsychotics were inactive. In addition, perospirone has a weaker propensity to induce extrapyramidal side effects, such as catalepsy and bradykinesia in rodents, compared with haloperidol and risperidone. Depressant actions of the central nervous system (e.g. potentiation of anesthesia and inhibition of motor coordination) and a lower propensity to induce orthostatic hypotension seemed to be low. Our studies revealed that serotonergic mechanisms of perospirone (i.e. 5-HT2 receptor and 5-HT1A receptor action) are involved in its atypical properties such as weaker propensities to induce extrapyramidal side-effects or improvement of mood disturbance. These findings suggest that perospirone is a new type of antipsychotic agent with a broad therapeutic spectrum and fewer side effects.

Biochemical profile of anseculin (KA‐672) at different brain receptors

AbstractAnseculin (KA‐672) is a multifunctional antidementia agent under development that may be of therapeutic value in the treatment of progressive neuronal and cognitive decline, which are common in Alzheimer disease. In vitro and ex vivo experiments have characterized anseculin as a potent functional antagonist of central α1‐adrenoceptors. In comparison to prazosin, the in vitro potency of anseculin for α1‐adrenoceptors is about 8 times less. Like prazosin, anseculin shows an inhibition of phenylephrine‐ (norepinephrine‐) induced accumulation of inositol phosphates. Oral treatment with 1 mg/kg anseculin or 1 mg/kg prazosin show similar effects on α1‐adrenergic receptor binding ex vivo, indicating a greater ex vivo potency of anseculin on central α1‐adrenergic receptors. Anseculin has only weak affinity for central muscarinic cholinergic receptors. Anseculin inhibited adenylate cyclase and reduced intracelluar cAMP levels of about 30%, similar to the 5‐HT1A agonist, 8‐OH‐DPAT. Together with its high affinity for 5‐HT1A receptors (IC50 for 3H‐8‐OH‐DPAT binding is about 8 nM), these data suggest that anseculin also exhibits 5‐HT1A agonistic properties. Drug Dev. Res. 55:187–196, 2002. © 2002 Wiley‐Liss, Inc.

Increased expression of glyceraldehyde-3-phosphate dehydrogenase in cultured astrocytes following exposure to manganese

The effect of chronic administration (0.4% for 30 days) of lithium carbonate (Li2CO3) on 5-HT1 receptor-linked second messenger system was studied in regions of rat brain. We observed that chronic treatment of Li2CO3, significantly decreased the density of [3H]5-HT binding sites in cortex (62%), hippocampus (64%) and striatum (65%), compared to the control levels. The affinity of [3H]5-HT to 5-HT1 binding sites was significantly decreased in all the regions. A significant decrease in the density of high affinity 5-HT1A receptor sites was observed in cortex (81%) and hippocampus (42%), without change in the affinity of [3H]8-OH-DPAT for 5-HT1A sites in these regions. 5-HT-stimulated, but not basal, adenylyl cyclase activity was significantly increased in all the regions after Li treatment. The present study concludes that the increase in the 5-HT-stimulated adenylyl cyclase activity might be attributed to the functional downregulation of 5-HT1 receptors, as these are negatively coupled to adenylyl cyclase, suggesting the involvement of 5-HT1 receptor mediated response in the therapeutic efficacy of lithium.

Pharmacological characterization of LB50016, N-(4-amino)butyl 3-phenylpyrrolidine derivative, as a new 5-HT1A receptor agonist.

LB50016 was characterized as a selective and potent 5-HT1A receptor agonist and evaluate its anxiolytic and antidepressant activities. It shows high affinity for 5-HT1A receptor, moderate affinity for alpha 2 adrenergic and 5-HT2A receptors and no significant affinity for other receptors tested. Hypothermia and increased serum corticosterone level were observed in LB50016-treated rats, which are mediated mostly by post synaptic 5-HT1A receptor activation. In the mouse forced swim model for depression, LB50016-elicited dose-dependent reductions in immobility time, showing ED50 of approximately 3 mg/kg i.p., which was blocked by pretreatment of NAN-190, 5-HT1A antagonist. In face-to-face test for anxiolytic activity in mice, estimated ED50 was 2 mg/kg, i.p. In isolation-induced aggression test with mice, fifty-fold increases in latency to attack were observed at 30 min and last up to 4 h after LB50016 treatment (3 mg/kg, i.p.). Taken together, LB50016-induced pharmacological activities are mediated by activation of 5-HT1A receptors, offering an effective therapeutic candidate in the management of anxiety and depression in humans.

Enhancement of cortical and hippocampal cholinergic neurotransmission through 5-HT1A receptor-mediated pathways by BAY×3702 in freely moving rats

Involvement of serotonin (5-HT) in the regulation of cholinergic neuronal activity by modulation of acetylcholine (ACh) release has been reported for various regions of the brain. Cortical and hippocampal cholinergic neurotransmission is of particular importance in the mechanisms of attention as well as learning and memory. In the present study, we investigated the effect of R-(-)-2-{4-[(chroman-2-ylmethyl)-amino-butyl}-1,1-dioxo-benzo[d]isothiazolone hydrochloride (BAYx3702), a novel, high-affinity 5-HT1A receptor agonist, on ACh release in the cerebral cortex and hippocampus of freely moving rats using an in vivo microdialysis technique. Acetylcholine efflux from the cortex and hippocampus was measured every 30 m using a sensitive and specific radioimmunoassay and was stable for at least 5 h. The ACh efflux from the cortex and hippocampus was increased significantly by BAY×3702 (0.3 mg/kg, i.p.) compared with saline administration. WAY-100635 (0.6 mg/kg, s.c.), a selective 5-HT1A receptor antagonist, eliminated the augmentation of ACh efflux induced by BAY×3702 in both brain regions. These results demonstrate that stimulation by BAY×3702 enhanced ACh release in both the cortex and hippocampus through 5-HT1A receptor-mediated pathways.

Design and synthesis of a series of 6-substituted-2-pyridinylmethylamine derivatives as novel, high-affinity, selective agonists at 5-HT1A receptors.

A search for novel, selective agonists with high intrinsic activity at the 5-HT1A subtype of serotonin (5-HT) receptors was undertaken. Mechanistic and thermodynamic considerations led to the design of 6-substituted-2-pyridinylmethylamine as a potential 5-HT1A pharmacophore. Various adducts derived from the 6-substituted-2-pyridinylmethylamine moiety were tested for their affinity at 5-HT1A, alpha1-adrenergic, and D2-dopaminergic receptors. Compounds with high affinity for 5-HT1A receptors (pKi >/= 8) were examined for agonist properties by measuring their ability to inhibit forskolin-stimulated cAMP production in HA7 cells (i.e., HeLa cells permanently transfected with the h5-HT1A receptor gene and expressing the h5-HT1A receptor protein). Several compounds of the type aryl¿4-[(6-substituted-pyridin-2-ylmethylamino)methyl]piperidin -1-yl¿ methanone had nanomolar affinity for 5-HT1A binding sites and were more than 500-fold selective with respect to alpha1 and D2 sites. Importantly, their 5-HT1A agonist properties were demonstrated in HA7 cells where they behaved as potent inhibitors of cAMP accumulation. In particular, (3, 4-dichlorophenyl)¿4-[(6-oxazol-5-ylpyridin-2-ylmethylamin o)methyl]pip eridin-1-yl¿methanone (70) and (3, 4-dichlorophenyl)¿4-[(6-azetidinopyridin-2-ylmethylamino)met hyl]piper idin-1-yl¿methanone (36) appeared to be more potent than, and at least as efficacious as, the prototypical 5-HT1A agonist (+/-)-8-OH-DPAT. SAR studies revealed that the pyridine nitrogen atom and the nature and the position of the substituents on the pyridine ring were critically involved in the ability of the compounds to recognize and activate 5-HT1A receptors. Structural modifications of the nonpharmacophoric part of the molecule showed, however, that the entire structure was required for affinity at 5-HT1A binding sites.

3-amino-3,4-dihydro-2H-1-benzopyran derivatives as 5-HT1A receptor ligands and potential anxiolytic agents. 2. Synthesis and quantitative structure-activity relationship studies of spiro[pyrrolidine- and piperidine-2,3'(2'H)-benzopyrans

In continuation of our work on 3-amino-3,4-dihydro-2H-1-benzopyran derivatives with high affinity for 5-HT1A receptors, we have prepared rigid spirobenzopyran analogues designed from the pharmacophore models of Mellin and selected via a quantitative structure-activity relationship approach mainly based on similarity indices. A series of spiro[pyrrolidine- and piperidine-2,3'(2'H)-benzopyrans] with various substitutions on the aromatic ring as well as on the extracyclic spiranic nitrogen atom were then synthesized and evaluated for their serotonergic and dopaminergic activities. Good correlation between the predicted and the experimental binding values was observed with an average difference of 0.2 unit on log(IC50). Affinities for the 5-HT1A receptors were in the nanomolar range for the best compounds ((+)-11a,23) with a high selectivity versus other 5-HT (5-HT1B, 5-HT2, 5-HT3) or dopamine (D1, D2) receptor subtypes. As for the 3-amino-3,4-dihydro-2H-1-benzopyran series, the dextrorotatory enantiomer (+)-11a showed better affinity and selectivity for 5-HT1A receptors than its levorotatory analogue (-)-11a. Compound (+)-11a proved in vitro to be a full agonist and in vivo to be active in various comportmental tests predictive of psychotropic activity, such as the forced swim test and the tail suspension test, and is currently under complementary investigations.

1-aryl-4-[(1-tetralinyl)alkyl]piperazines: alkylamido and alkylamino derivatives. Synthesis, 5-HT1A receptor affinity, and selectivity. 3.

The synthesis and binding profile on 5-HT1A, 5-HT2, D-1, D-2, alpha 1, and alpha 2 receptors of the N-4 long-chain arylpiperazines 22-40 are reported, where an amino or amido function is inserted into the intermediate chain linked to the alpha position of the tetralin nucleus. Unlike the buspirone analogues, for the amido derivatives studied in this paper, the terminal amide function of long-chain piperazines is not important for 5-HT1A receptor affinity binding, and its removal yields high-affinity 5-HT1A receptor agents.

Adrenocorticotropic hormone activation of adenylate cyclase in raphe neurons: Multiple regulatory pathways control serotonergic neuronal differentiation

The RN46A cell line was derived from embryonic day 13 rat medullary raphe cells by infection with a retrovirus encoding the temperature-sensitive mutant of SV40 large T antigen (tsT-ag). The RN46A cell line is neuronally restricted and constitutively differentiates following a shift to nonpermissive temperature. Differentiated RN46A cells express low levels of tryptophan hydroxylase (TPH) but no detectable levels of serotonin (5-HT). Treatment of cultures with the adrenocorticotropic hormone peptide ACTH4-10 up-regulates the expression of TPH immunoreactivity in differentiated RN46A cells, but 5-HT synthesis requires initial treatment with ACTH4-10, followed by partial membrane depolarizing conditions. Up-regulation of TPH by ACTH4-10 is apparently due to activation of adenylate cyclase, whereas the increased 5-HT synthesis with membrane depolarization can be blocked with the voltage-sensitive Ca(2+)-channel blockers nifedipine and omega-conotoxin. ACTH4-10 treatment also markedly up-regulates the expression of the 5-HT reuptake transporter, as do dibutyryl cyclic AMP and forskolin; chronic membrane depolarization has no effect on 5-HT reuptake. The expression of the high-affinity 5-HT1A receptor is increased threefold by ACTH4-10 treatment during differentiation and fivefold by differentiation under partial membrane depolarizing conditions. Combining ACTH4-10 treatment and membrane depolarization does not increase expression of the 5-HT1A receptor further. 5-HT release is constitutive in ACTH-treated RN46A cells and linked to spontaneous synaptic vesicle fusion in RN46A cells. Considered with previous results, these data indicate that multiple effectors, ACTH, brain-derived neurotrophic factor, and membrane depolarization, have both distinct and overlapping effects that regulate specific elements of the serotonergic neuronal phenotype during differentiation and maturation.

Developmental Regulation of Early Serotonergic Neuronal Differentiation: The Role of Brain-Derived Neurotrophic Factor and Membrane Depolarization

The RN46A cell line was derived from Embryonic Day 13 rat medullary raphe cells by infection with a retrovirus encoding the temperature-sensitive mutant of SV40 large T antigen. This cell line is neuronally restricted and constitutively differentiates following a shift to nonpermissive temperature. Undifferentiated RN46A cells express low levels of tryptophan hydroxylase (TPH), low-affinity neurotrophin receptor (p75 NTR), and trkB immunoreactivities, but no detectable levels of serotonin (5HT) immunoreactivity. TrkB, p75 NTR, and TPH, but not 5HT, expressions increase with differentiation and treatment with brain-derived neurotrophic factor (BDNF). 5HT synthesis in RN46A cells requires initial treatment with BDNF, followed by growth under partial membrane depolarizing conditions. Embryonic raphe cultures treated similarly with BDNF and partial depolarizing conditions also demonstrate increased 5HT synthesis. The sodium-dependent transporter for 5HT reuptake is present in undifferentiated RN46A cells, and the apparent K m and B max are unchanged by differentiation or BDNF treatment and membrane depolarization. The high-affinity 5HT 1A receptor is present in both undifferentiated and differentiated RN46A cells, and while the K d is unaffected by differentiation or BDNF/membrane depolarization, the B max increases 20-fold after differentiation and 3.5-fold further with BDNF under depolarizing conditions. The expression of the synaptic vesicular monoamine transporter, as determined by the binding of [ 125I]iodovinyltetrabenazine, also increases in RN46A cells with differentiation. However, 5HT release is constitutive and is independent of acute membrane depolarization. Collectively these data indicate that distinct aspects of serotonin metabolism are differentially regulated during development and suggest that 5HT may function as a developmental signal in an autocrine loop during early serotonergic differentiation.