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Mogg AJ, Jones FA, Pullar IA, Sharples CGV, Wonnacott S. Functional responses and subunit composition of presynaptic nicotinic receptor subtypes explored using the novel agonist 5-iodo-A-85380. Neuropharmacology 2004; 47:848-59. [PMID: 15527819 DOI: 10.1016/j.neuropharm.2004.06.013] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2004] [Revised: 05/21/2004] [Accepted: 06/18/2004] [Indexed: 11/24/2022]
Abstract
The novel compound 5-iodo-A-85380 binds with higher affinity to alpha4beta2* nicotinic acetylcholine receptors (nAChR), compared with other nAChR subtypes (Mukhin et al., 2000). In the present study, we have confirmed that in competition binding assays for three major nAChR subtypes, 5-iodo-A-85380 is 850 and 27,000-fold more potent at rat brain alpha4beta2* binding sites than at alpha3beta4 and alpha7 subtypes, respectively. In functional assays, 5-iodo-A-85380 potently activated (EC50 12-35 nM) both alpha-CTx-MII-sensitive and -insensitive components of [3H]dopamine release from rat striatal synaptosomes, corresponding to alpha6beta2* and alpha4beta2* nAChR, respectively. 5-Iodo-A-85380 was markedly less potent at eliciting [3H]ACh release from rat interpeduncular nucleus synaptosomes, [3H]noradrenaline release from rat hippocampal slices, and Ca2+ increases in a cell line expressing rat alpha3beta4 nAChR (EC50 = 5, 3.2, 1.6 microM, respectively). As predicted by ligand binding studies, 5-iodo-A-85380 is a more discriminating agonist than the parent compound epibatidine. However, it is not specific for alpha4beta2* nAChR as it also potently activates alpha6beta2* nAChR.
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Affiliation(s)
- Adrian J Mogg
- Lilly Research Centre, Eli Lilly and Company Ltd., Erl Wood Manor, Sunninghill Road, Windlesham, Surrey GU20 6PH, UK.
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152
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Zhang N, Tomizawa M, Casida JE. Drosophila nicotinic receptors: evidence for imidacloprid insecticide and α-bungarotoxin binding to distinct sites. Neurosci Lett 2004; 371:56-9. [PMID: 15500966 DOI: 10.1016/j.neulet.2004.08.040] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2004] [Revised: 07/27/2004] [Accepted: 08/17/2004] [Indexed: 11/21/2022]
Abstract
The principal mammalian brain nicotinic acetylcholine receptors (nAChRs) are the alpha-bungarotoxin (alpha-BGT)-insensitive alpha 4 beta 2 and the alpha-BGT-sensitive alpha 7 subtypes assayed with radiolabeled nicotinoids and alpha-BGT, respectively. Drosophila head membranes bind the insecticide radioligand [(3)H]imidacloprid ([(3)H]IMI) and [(3)H]alpha-BGT with K(D) 5.7 and 2.7 nM and B(max) 980 and 1400 fmol/mg protein, respectively. The hypothesis that [(3)H]IMI at 2.5 or 20 nM and [(3)H]alpha-BGT at 1 or 10 nM bind to distinct sites or subtypes is tested by using these radioligands alone and together in simultaneous dual binding experiments. These studies show no interference by one radioligand in the binding of the other one, i.e., independent binding, and that both unlabeled IMI and alpha-BGT give biphasic displacement curves. The pharmacological profiles of [(3)H]IMI and [(3)H]alpha-BGT suggest distinct binding sites for the two radioligands. These findings are consistent with those obtained with hybrid receptors assembled from Drosophila alpha subunits and a vertebrate beta subunit and with immunological and protein biochemical approaches. This study, therefore, provides direct evidence for distinct IMI- and alpha-BGT-sensitive sites or subtypes in Drosophila brain.
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Affiliation(s)
- Nanjing Zhang
- Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, 114 Wellman Hall, Berkeley, CA 94720-3112, USA
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153
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Jensen AA, Mikkelsen I, Frølund B, Frydenvang K, Brehm L, Jaroszewski JW, Bräuner-Osborne H, Falch E, Krogsgaard-Larsen P. Carbamoylcholine homologs: synthesis and pharmacology at nicotinic acetylcholine receptors. Eur J Pharmacol 2004; 497:125-37. [PMID: 15306197 DOI: 10.1016/j.ejphar.2004.06.038] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2004] [Revised: 06/17/2004] [Accepted: 06/22/2004] [Indexed: 11/18/2022]
Abstract
In a recent study, racemic 3-(N,N-dimethylamino)butyl-N,N-dimethylcarbamate (1) was shown to be a potent agonist at neuronal nicotinic acetylcholine receptors with a high selectivity for nicotinic over muscarinic acetylcholine receptors [Mol. Pharmacol. 64 (2003) 865-875]. Here we present the synthesis and pharmacological characterization of a series of analogs of, where the methyl group at C-3 has been replaced by different alkyl substituents. Ring systems have been incorporated into the carbon backbone of some of the molecules, or the amino group has been build into ring systems. Furthermore, the (+)- and (-)-enantiomers of have been separated, and X-ray crystallography has revealed that (-)-1 possesses (S)-configuration. The compounds have been characterized pharmacologically at recombinant nicotinic receptor subtypes. The structure-activity relationship study has provided valuable insight into the mode of interactions of and its analogs with neuronal nicotinic acetylcholine receptors.
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Affiliation(s)
- Anders A Jensen
- Department of Medicinal Chemistry, The Danish University of Pharmaceutical Sciences, Universitetsparken 2, DK-2100 Copenhagen, Denmark.
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154
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Placzek AN, Grassi F, Papke T, Meyer EM, Papke RL. A single point mutation confers properties of the muscle-type nicotinic acetylcholine receptor to homomeric alpha7 receptors. Mol Pharmacol 2004; 66:169-77. [PMID: 15213309 DOI: 10.1124/mol.66.1.169] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Although the muscle-type and homomeric alpha7-type nicotinic acetylcholine receptors (nAChRs) share many structural features and bind alpha-bungarotoxin with high affinity, several important functional and pharmacological properties distinguish these two major nAChR subtypes. We have shown previously that amino acid sequence in the second transmembrane (TM) domain of the beta subunit is critical for pharmacological distinction between muscle type and heteromeric neuronal (e.g., ganglionic) nAChRs. We tested the hypothesis that homologous substitution of amino acid sequence from the muscle beta1 subunit into the alpha7 subunit would confer specific properties of muscle-type receptors to mutant alpha7 nAChRs. In this study, we show that a single amino acid substitution at the alpha7 TM2 6' position makes both biophysical and pharmacological properties of the mutant receptors resemble those of wild-type muscle nAChR. This mutation produces significant changes in acetylcholine potency and response kinetics, eliminating the characteristic fast desensitization of alpha7 and dramatically reducing divalent ion permeability relative to wild-type alpha7. The TM2 T6'F mutation also produces a profound increase in activation by succinylcholine compared with either wild-type alpha7 or neuronal beta-subunit-containing receptors and the loss of potentiation by 5-hydroxyindole. Thus, the alpha7 TM2 T6'F mutant displays several features that are similar to the muscle nAChR, some of which are not typically thought to be regulated by the pore-lining domain of the receptor.
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Affiliation(s)
- Andon N Placzek
- Department of Pharmacology and Therapeutics, J. Hills Miller-Health Science Center, University of Florida, Gainesville, FL 32610-0267, USA
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155
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Wickramaratna JC, Fry BG, Loiacono RE, Aguilar MI, Alewood PF, Hodgson WC. Isolation and characterization at cholinergic nicotinic receptors of a neurotoxin from the venom of the Acanthophis sp. Seram death adder. Biochem Pharmacol 2004; 68:383-94. [PMID: 15194010 DOI: 10.1016/j.bcp.2004.03.033] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2004] [Accepted: 03/25/2004] [Indexed: 10/26/2022]
Abstract
The present study describes the isolation of the first neurotoxin (acantoxin IVa) from Acanthophis sp. Seram death adder venom and an examination of its activity at nicotinic acetylcholine receptor (nAChR) subtypes. Acantoxin IVa (MW 6815; 0.1-1.0 microM) caused concentration-dependent inhibition of indirect twitches (0.1 Hz, 0.2 ms, supramaximal V) and inhibited contractile responses to exogenous nicotinic agonists in the chick biventer cervicis nerve-muscle, confirming that this toxin is a postsynaptic neurotoxin. Acantoxin IVa (1-10 nM) caused pseudo-irreversible antagonism at skeletal muscle nAChR with an estimated pA2 of 8.36+/-0.17. Acantoxin IVa was approximately two-fold less potent than the long-chain (Type II) neurotoxin, alpha-bungarotoxin. With a pKi value of 4.48, acantoxin IVa was approximately 25,000 times less potent than alpha-bungarotoxin at alpha7-type neuronal nAChR. However, in contrast to alpha-bungarotoxin, acantoxin IVa completely inhibited specific [3H]-methyllycaconitine (MLA) binding in rat hippocampus homogenate. Acantoxin IVa had no activity at ganglionic nAChR, alpha4beta2 subtype neuronal nAChR or cytisine-resistant [3H]-epibatidine binding sites. While long-chain neurotoxin resistant [3H]-MLA binding in hippocampus homogenate requires further investigation, we have shown that a short-chain (Type I) neurotoxin is capable of fully inhibiting specific [3H]-MLA binding.
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156
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Synthesis of simple analogues of methyllycaconitine—an efficient method for the preparation of the N-substituted anthranilate pharmacophore. Tetrahedron 2004. [DOI: 10.1016/j.tet.2004.05.024] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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157
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Haberberger RV, Bernardini N, Kress M, Hartmann P, Lips KS, Kummer W. Nicotinic acetylcholine receptor subtypes in nociceptive dorsal root ganglion neurons of the adult rat. Auton Neurosci 2004; 113:32-42. [PMID: 15296793 DOI: 10.1016/j.autneu.2004.05.008] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2003] [Revised: 05/03/2004] [Accepted: 05/13/2004] [Indexed: 10/26/2022]
Abstract
Stimulation of nicotinic acetylcholine receptors (nAChR) excites peripheral sensory nerve fibres, but also exert antinociceptive effects. The differences in these nAChR-mediated effects could be related to the expression of different nAChR subtypes located on nociceptive neurons. In the present study, we focused on the recently described alpha 10-nAChR subunit, and on alpha 4 and alpha 7 subunits, which are the most abundant subunits in the central nervous system. In nociceptive neurons from thoracic and lumbar dorsal root ganglia (DRG), nAChR subunits were found at transcriptional (RT-PCR), translational (immunohistochemistry) and functional levels. Cultured DRG neurons express mRNA for the subunits alpha 2-7 and alpha 10. The alpha-subunit proteins 4, 7 and 10 were colocalised in virtually all nociceptive neurons that were identified by immunoreactivity for the vanilloid receptor TRPV-1. These findings were corroborated by current recordings and calcium measurements, which revealed excitatory inward currents and calcium responses in capsaicin sensitive neurons.
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Affiliation(s)
- Rainer Viktor Haberberger
- Institute for Anatomy and Cell Biology Justus Liebig University, Aulweg 123, D-35385 Giessen, Germany.
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158
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Jones IW, Barik J, O'Neill MJ, Wonnacott S. Alpha bungarotoxin-1.4 nm gold: a novel conjugate for visualising the precise subcellular distribution of alpha 7* nicotinic acetylcholine receptors. J Neurosci Methods 2004; 134:65-74. [PMID: 15102504 DOI: 10.1016/j.jneumeth.2003.11.001] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2003] [Revised: 11/04/2003] [Accepted: 11/05/2003] [Indexed: 11/18/2022]
Abstract
Alpha 7 subunit-containing nicotinic acetylcholine receptors (alpha7* nAChR) are involved in a variety of functions in the mammalian brain, including modulating neurotransmitter release and synaptic plasticity. Identifying the precise cellular distribution of alpha7* nAChRs with respect to the local neurochemical environment is crucial to understanding these biological roles. Current strategies for localising alpha7* nAChRs at the subcellular level have limitations. Anti-alpha7 subunit antibodies detect both assembled and unassembled subunits whereas biotinylated alphabungarotoxin (alphaBgt) only binds to assembled alpha7* nAChRs, but interpretation of labelling is marred by co-detection of endogenous tissue biotin. To overcome these problems, we have characterised a novel 1.4 nm gold alphaBgt conjugate used to directly localise alpha7* nAChR. Gold conjugation does not significantly decrease binding affinity, and gold alphaBgt specifically labels alpha7* nAChR in both unfixed and aldehyde-fixed tissue at the light and electron microscope levels, labelling being abolished in the presence of excess competing toxin. At the ultrastructural level, gold alphaBgt is associated with neuronal membranes and located at axon-dendritic synapses in the rat hippocampus CA1 stratum radiatum. These results reveal gold alphaBgt to be a valuable new tool in elucidating the functional neuroanatomy of alpha7* nAChR in the central nervous system.
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Affiliation(s)
- Ian W Jones
- Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, UK.
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159
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Bohme GA, Letchworth SR, Piot-Grosjean O, Gatto GJ, Obinu MC, Caldwell WS, Laville M, Brunel P, Pellerin R, Leconte JP, Genevois-Borella A, Dubedat P, Mazadier M, Pradier L, Bencherif M, Benavides J. In vitro and in vivo characterization of TC-1827, a novel brain?4?2 nicotinic receptor agonist with pro-cognitive activity. Drug Dev Res 2004. [DOI: 10.1002/ddr.10352] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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160
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Xiao Y, Kellar KJ. The comparative pharmacology and up-regulation of rat neuronal nicotinic receptor subtype binding sites stably expressed in transfected mammalian cells. J Pharmacol Exp Ther 2004; 310:98-107. [PMID: 15016836 DOI: 10.1124/jpet.104.066787] [Citation(s) in RCA: 130] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We stably transfected human embryonic kidney cells (HEK 293 cells) with genes encoding rat neuronal nicotinic receptor alpha2, alpha3, or alpha4 subunits in combination with the beta2 or beta4 subunit to generate six cell lines that express defined subunit combinations that represent potential subtypes of rat neuronal nicotinic acetylcholine receptors (nAChRs). These cell lines were designated KXalpha2beta2, KXalpha2beta4, KXalpha3beta2, KXalpha3beta4, KXalpha4beta2, and KXalpha4beta4. The Kd values of [3H](+/-)epibatidine ([3H]EB) binding to membranes from these six cell lines ranged from approximately 0.02 to 0.3 nM. The pharmacological profiles of the agonist binding sites of these putative nAChR subtypes were examined in competition studies in which unlabeled nicotinic ligands, including 10 agonists and two antagonists, competed against [3H]EB. Most nicotinic ligands examined had higher affinity for the receptor subtypes containing the beta2 subunit compared with those containing the beta4 subunit. An excellent correlation (r > 0.99) of the binding affinities of the 10 agonists was observed between receptors from KXalpha4beta2 cells and from rat forebrain tissue, in which [3H]EB binding represents predominantly alpha4beta2 nAChRs. More important, the affinities (Ki values) for the two tissues were nearly identical. The densities of the binding sites of all six cell lines were increased after a 5-day exposure to (-)-nicotine or the quaternary amine agonist carbachol. These data indicate that these cell lines expressing nAChR subunit combinations should be useful models for investigating pharmacological properties and regulation of the binding sites of potential nAChR subtypes, as well as for studying the properties of nicotinic compounds.
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Affiliation(s)
- Yingxian Xiao
- Department of Pharmacology, Georgetown University School of Medicine, Washington, DC 20057-2195, USA
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161
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Baker ER, Zwart R, Sher E, Millar NS. Pharmacological Properties of α9α10 Nicotinic Acetylcholine Receptors Revealed by Heterologous Expression of Subunit Chimeras. Mol Pharmacol 2004; 65:453-60. [PMID: 14742688 DOI: 10.1124/mol.65.2.453] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The nicotinic acetylcholine receptor (nAChR) alpha9 and alpha10 subunits are expressed primarily within hair cells of the inner ear and have been implicated in auditory processing. Although functional recombinant nAChRs generated by the coexpression of alpha9 and alpha10 in Xenopus laevis oocytes have been described previously, there have been no reports of the successful heterologous expression of alpha9alpha10 nAChRs in cultured cell lines. In this study, subunit chimeras (alpha9chi and alpha10chi) have been constructed that contain the extracellular, ligand binding domain of the alpha9 or alpha10 subunits fused to the C-terminal domain of the 5-hydroxytryptamine type 3A (5HT3A) subunit. Specific high-affinity binding of the nicotinic radioligand [3H]methyllycaconitine was detected in membrane preparations of mammalian cells transfected with alpha9chi or alpha10chi alone, but significantly higher levels of binding were detected when alpha9chi and alpha10chi were cotransfected, providing evidence of a requirement for coassembly of alpha9 and alpha10 for the efficient formation of a nicotinic binding site. The pharmacological profile of alpha9chialpha10chi receptors, determined by equilibrium radioligand binding studies, is broadly similar to that determined previously by electrophysiological studies conducted with native and recombinant alpha9alpha10 nAChRs. In agreement with evidence that alpha9alpha10 nAChRs exhibit an atypical pharmacological profile, we have identified specific high-affinity binding of several non-nicotinic ligands including strychnine (a glycine receptor antagonist), bicuculline (a GABAA receptor antagonist), and atropine (a muscarinic acetylcholine receptor antagonist). Results have also been compared with radioligand binding data conducted with a previously described alpha7/5HT3A (alpha7chi) subunit chimera.
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Affiliation(s)
- Elizabeth R Baker
- Department of Pharmacology, University College London, Gower Street, London, United Kingdom
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162
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Marrero MB, Papke RL, Bhatti BS, Shaw S, Bencherif M. The neuroprotective effect of 2-(3-pyridyl)-1-azabicyclo[3.2.2]nonane (TC-1698), a novel alpha7 ligand, is prevented through angiotensin II activation of a tyrosine phosphatase. J Pharmacol Exp Ther 2004; 309:16-27. [PMID: 14722323 DOI: 10.1124/jpet.103.061655] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We have recently provided evidence for nicotine-induced complex formation between the alpha7 nicotinic acetylcholine receptor (nAChR) and the tyrosine-phosphorylated enzyme Janus kinase 2 (JAK2) that results in subsequent activation of phosphatidylinositol-3-kinase (PI-3-K) and Akt. Nicotine interaction with the alpha7 nAChR inhibits Abeta (1-42) interaction with the same receptor, and the Abeta (1-42)-induced apoptosis is prevented through nicotine-induced activation of JAK2. These effects can be shown by measuring markers of cytotoxicity, including the cleavage of the nuclear protein poly(ADP-ribose) polymerase (PARP), the induction of caspase 3, or cell viability. In this study, we found that 2-(3-pyridyl)-1-azabicyclo[3.2.2]nonane (TC-1698), a novel alpha7-selective agonist, exerts neuroprotective effects via activation of the JAK2/PI-3K cascade, which can be neutralized through activation of the angiotensin II (Ang II) AT(2) receptor. Vanadate not only augmented the TC-1698-induced tyrosine phosphorylation of JAK2 but also blocked the Ang II neutralization of TC-1698-induced neuroprotection against Abeta (1-42)-induced cleavage of PARP. Furthermore, when SHP-1 was neutralized via antisense transfection, the Ang II inhibition of TC-1698-induced neuroprotection against Abeta (1-42) was prevented. These results support the main hypothesis that states that JAK2 plays a central role in the nicotinic alpha7 receptor-induced activation of the JAK2-PI-3K cascade in PC12 cells, which ultimately contribute to nAChR-mediated neuroprotection. Ang II inhibits this pathway through the AT(2) receptor activation of the protein tyrosine phosphatase SHP-1. This study supports central and opposite roles for JAK2 and SHP-1 in the control of apoptosis and alpha7-mediated neuroprotection in PC12 cells.
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Affiliation(s)
- Mario B Marrero
- Targacept Inc., 200 East First Street, Suite 300, Winston-Salem, NC 27101-4165, USA
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163
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Mulholland PJ, Self RL, Harris BR, Littleton JM, Prendergast MA. (−)-nicotine ameliorates corticosterone's potentiation of N-methyl-d-aspartate receptor-mediated cornu ammonis 1 toxicity. Neuroscience 2004; 125:671-82. [PMID: 15099681 DOI: 10.1016/j.neuroscience.2004.02.007] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/09/2004] [Indexed: 11/22/2022]
Abstract
Hypercortisolemia, long-term exposure of the brain to high concentrations of stress hormones (i.e. cortisol), may occur in patients suffering from depression, alcoholism, and other disorders. This has been suggested to produce neuropathological effects, in part, via increased function or sensitivity of N-methyl-d-aspartate (NMDA)-type glutamate receptors. Given that cigarette smoking is highly prevalent in some of these patient groups and nicotine has been shown to reduce toxic consequences of NMDA receptor function, it may be suggested that nicotine intake may attenuate the neurotoxic effects of hypercortisolemia. To investigate this possibility, organotypic hippocampal slice cultures derived from rat were pre-treated with corticosterone (0.001-1 microM) alone or in combination with selective glucocorticoid receptor antagonists for 72-h prior to a brief (1-h) NMDA exposure (5 microM). Pre-treatment with corticosterone (0.001-1 microM) alone did not cause hippocampal damage, while NMDA exposure produced significant cellular damage in the cornu ammonis (CA)1 subregion. No significant damage was observed in the dentate gyrus or CA3 regions following NMDA exposure. Pre-treatment of cultures with corticosterone (0.1-1 microM) markedly exacerbated NMDA-induced CA1 and dentate gyrus region damage. This effect in the CA1 region was prevented by co-administration of the glucocorticoid receptor antagonist RU486 (>or=1 microM), but not spironolactone (1-10 microM), a mineralocorticoid receptor antagonist. In a second series of studies, both acute and pre-exposure of cultures to (-)-nicotine (1-10 microM) significantly reduced NMDA toxicity in the CA1 region. Co-administration of cultures to (-)-nicotine (1-10 microM) with 100 nM corticosterone prevented corticosterone's exacerbation of subsequent CA1 insult. This protective effect of (-)-nicotine was not altered by co-exposure of cultures to 10 microM dihydro-beta-erythroidine but was blocked by co-exposure to 100 nM methyllycaconitine, suggesting the involvement of nicotinic acetylcholine receptors possessing the alpha7* subunit. The present studies suggest a role for hypercortisolemia in sensitizing the hippocampal NMDA receptor system to pathological activation and indicate that prolonged nicotine exposure attenuates this sensitization. Thus, it is possible that one consequence of heavy smoking in those suffering from hypercortisolemia may be a reduction of neuronal injury and sparing of cellular function.
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Affiliation(s)
- P J Mulholland
- Department of Psychology, University of Kentucky, 115 Kastle Hall, Lexington, KY 40506-0044, USA
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164
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Glennon RA. 2. Medicinal chemistry of alpha4beta2 nicotinic cholinergic receptor ligands. PROGRESS IN MEDICINAL CHEMISTRY 2004; 42:55-123. [PMID: 15003719 DOI: 10.1016/s0079-6468(04)42002-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/29/2023]
Affiliation(s)
- Richard A Glennon
- Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, Box 581 MCV Station, Richmond, VA 23298, USA
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165
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Clarke PB. Nicotinic modulation of thalamocortical neurotransmission. PROGRESS IN BRAIN RESEARCH 2003; 145:253-60. [PMID: 14650920 DOI: 10.1016/s0079-6123(03)45017-6] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
Affiliation(s)
- Paul B Clarke
- Department of Pharmacology and Therapeutics, McGill University, 3655 Promenade Sir William Osler, Montreal, QC H3G 1Y6, Canada.
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166
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Roger G, Lagnel B, Rouden J, Besret L, Valette H, Demphel S, Gopisetti J, Coulon C, Ottaviani M, Wrenn LA, Letchworth SR, Bohme GA, Benavides J, Lasne MC, Bottlaender M, Dollé F. Synthesis of a [2-Pyridinyl-18F]-labelled fluoro derivative of (−)-Cytisine as a candidate radioligand for brain nicotinic α4β2 receptor imaging with PET. Bioorg Med Chem 2003; 11:5333-43. [PMID: 14642577 DOI: 10.1016/j.bmc.2003.09.042] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In recent years, there has been considerable effort to design and synthesize radiotracers suitable for use in Positron Emission Tomography (PET) imaging of the alpha4beta2 neuronal nicotinic acetylcholine receptor (nAChR) subtype. A new fluoropyridinyl derivative of (-)-cytisine (1), namely (-)-9-(2-fluoropyridinyl)cytisine (3, K(i) values of 24 and 3462 nM for the alpha4beta2 and alpha7 nAChRs subtypes, respectively) has been synthesized in four chemical steps from (-)-cytisine and labelled with fluorine-18 (T(1/2): 119.8 min) using an efficient two-step radiochemical process [(a). nucleophilic heteroaromatic ortho-radiofluorination using the corresponding N-Boc-protected nitro-derivative, (b). TFA removal of the Boc protective group]. Typically, 20-45 mCi (0.74-1.67 GBq) of (-)-9-(2-[18F]fluoropyridinyl)cytisine ([18F]-3, 2-3 Ci/micromol or 74-111 GBq/micromol) were easily obtained in 70-75 min starting from a 100 mCi (3.7 GBq) aliquot of a cyclotron-produced [18F]fluoride production batch (20-45% non decay-corrected yield based on the starting [18F]fluoride). The in vivo pharmacological profile of (-)-9-(2-[18F]fluoropyridinyl)cytisine ([18F]-3) was evaluated in rats with biodistribution studies and brain radioactivity monitoring using intracerebral radiosensitive beta-microprobes. The observed in vivo distribution of the radiotracer in brain was rather uniform, and did not match with the known regional densities of nAChRs. It was also significantly different from that of the parent compound (-)-[3H]cytisine. Moreover, competition studies with (-)-nicotine (5 mg/kg, 5 min before the radiotracer injection) did not reduce brain uptake of the radiotracer. These experiments clearly indicate that (-)-9-(2-[18F]fluoropyridinyl)cytisine ([18F]-3) does not have the required properties for imaging nAChRs using PET.
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Affiliation(s)
- Gaëlle Roger
- Département de Recherche Médicale, CEA/DSV, 4 place du Général Leclerc, F-91401 Orsay, France
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167
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Dajas-Bailador FA, Heimala K, Wonnacott S. The Allosteric Potentiation of Nicotinic Acetylcholine Receptors by Galantamine Is Transduced into Cellular Responses in Neurons: Ca2+ Signals and Neurotransmitter Release. Mol Pharmacol 2003; 64:1217-26. [PMID: 14573772 DOI: 10.1124/mol.64.5.1217] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Neuronal nicotinic acetylcholine receptors (nAChR) modulate a variety of cellular responses, including Ca2+ signals and neurotransmitter release, which can influence neuronal processes such as synaptic efficacy and neuroprotection. In addition to receptor activation through the agonist binding site, an allosteric modulation of nAChR has also been described for a novel class of allosteric ligands. Of these, the acetylcholinesterase inhibitor and Alzheimer drug galantamine represents the prototypical allosteric ligand, based on its potentiation of nAChR-evoked single-channel and whole-cell currents. The aim of this study was to establish whether the allosteric potentiation of nAChR currents is transduced in downstream cellular responses to nAChR activation, namely increases in intracellular Ca2+ and [3H]noradrenaline release. In SH-SY5Y cells, galantamine potentiated nicotine-evoked increases in intracellular Ca2+ and [3H]noradrenaline release with a bell-shaped concentration-response profile; maximum enhancement of nicotine-evoked responses occurred at 1 muM galantamine. This potentiation was blocked by mecamylamine, whereas galantamine had no effect on these measures in the absence of nicotine. Galantamine did not compete for radioligand binding to the agonist binding sites of several nAChR subtypes, consistent with an allosteric mode of action. Unlike galantamine, the acetylcholinesterase inhibitors rivastigmine and donepezil did not potentiate nAChR-mediated responses, whereas donepezil was a reasonably potent inhibitor of nicotine- and KCl-evoked increases in Ca2+. nAChR-mediated [3H]noradrenaline release from hippocampal slices was also potentiated by galantamine, with an additional component attributable to acetylcholinesterase inhibition and subsequent increase in acetylcholine. These results indicate that the allosteric regulation of nAChR results in the potentiation of receptor-dependent cellular processes relevant to many of the physiological consequences of nAChR activation.
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168
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Jensen AA, Mikkelsen I, Frølund B, Bräuner-Osborne H, Falch E, Krogsgaard-Larsen P. Carbamoylcholine homologs: novel and potent agonists at neuronal nicotinic acetylcholine receptors. Mol Pharmacol 2003; 64:865-75. [PMID: 14500743 DOI: 10.1124/mol.64.4.865] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The classic muscarinic acetylcholine receptor (mAChR) agonist carbamoylcholine (carbachol) does not seem to be the most obvious lead for the development of selective ligands at nicotinic acetylcholine receptors (nAChRs). In the past, however, N-methylations of carbachol have provided N-methylcarbamoylcholine and N,N-dimethylcarbamoylcholine (DMCC), which predominantly display nicotinic activity. In this study, 12 homologous analogs of DMCC and its corresponding tertiary amine, N,N-dimethylcarbamoyl-N,N-dimethylaminoethanol, were synthesized and their binding affinities to native mAChR and nAChR sites estimated. One of the compounds in the series, 3-N,N-dimethylaminobutyl-N,N-dimethylcarbamate (7), displayed low nanomolar binding affinity to nAChRs and a 400-fold selectivity for nAChRs over mAChRs. Hence, a new series of compounds was synthesized in which alkyl and aryl groups and different ring systems were introduced in the carbamate moiety of 7. In a [3H]epibatidine binding assay, the Ki values of 7 and its analogs at rat alpha2beta2, alpha4beta2, alpha2beta4, alpha3beta4, and alpha4beta4 nAChRs, stably expressed in mammalian cell lines, ranged from low nanomolar to midmicromolar concentrations, whereas all of the compounds displayed weak binding to an alpha7/5-HT3 chimera and to native mAChRs. Compound 7 and its analogs were determined to be agonists at the alpha3beta4 nAChR subtype. This series includes the most potent and selective nicotinic agonists structurally derived from ACh to date. Furthermore, the compounds are tertiary amines, implying some advantages in terms of bioavailability pertinent to future in vivo pharmacological studies. Finally, observations made in the study hold promising perspectives for future development of ligands selective for specific nAChR subtypes.
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Affiliation(s)
- Anders A Jensen
- Department of Medicinal Chemistry, The Danish University of Pharmaceutical Sciences, Universitetsparken 2, DK-2100 Copenhagen, Denmark.
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169
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Azam L, Winzer-Serhan U, Leslie FM. Co-expression of alpha7 and beta2 nicotinic acetylcholine receptor subunit mRNAs within rat brain cholinergic neurons. Neuroscience 2003; 119:965-77. [PMID: 12831856 DOI: 10.1016/s0306-4522(03)00220-3] [Citation(s) in RCA: 118] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Nicotine enhances cognitive and attentional processes through stimulation of the basal forebrain cholinergic system. Although muscarinic cholinergic autoreceptors have been well characterized, pharmacological characterization of nicotinic autoreceptors has proven more difficult. The present study used double-labeling in situ hybridization to determine expression of nicotinic acetylcholine receptor (nAChR) subunit mRNAs within basal forebrain cholinergic neurons in order to gain information about possible nAChR autoreceptor properties. Cholinergic cells of the mesopontine tegmentum and striatal interneurons were also examined, as were septohippocampal GABAergic neurons that interact with cholinergic neurons to regulate hippocampal activity. alpha7 and beta2 nAChR mRNAs were found to be co-expressed in almost all cholinergic cells and in the majority of GABAergic neurons examined. alpha4 nAChR mRNA expression was restricted to cholinergic cells of the nucleus basalis magnocellularis, and to non-cholinergic cells of the medial septum and mesopontine tegmentum. These data suggest possible regional differences in the pharmacological properties of nicotinic autoreceptors on cholinergic cells. Whereas most cholinergic cells express rapidly desensitizing alpha7 homomers or alpha7beta2 heteromers, cortical projection neurons may also express a pharmacologically distinct alpha4beta2 nAChR subtype. There may also be differential nAChR regulation of cholinergic and non-cholinergic cells within the mesopontine tegmentum that are implicated in acquisition of nicotine self-administration.
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Affiliation(s)
- L Azam
- Department of Biology, University of Utah, Salt Lake City, UT 84112, USA
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170
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Grinevich VP, Crooks PA, Sumithran SP, Haubner AJ, Ayers JT, Dwoskin LP. N-n-alkylpyridinium analogs, a novel class of nicotinic receptor antagonists: selective inhibition of nicotine-evoked [3H] dopamine overflow from superfused rat striatal slices. J Pharmacol Exp Ther 2003; 306:1011-20. [PMID: 12766255 DOI: 10.1124/jpet.103.051789] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Structural simplification of N-n-alkylnicotinium analogs, antagonists at neuronal nicotinic acetylcholine receptors (nAChRs), was achieved by removal of the N-methylpyrrolidino moiety affording N-n-alkylpyridinium analogs with carbon chain lengths of C1 to C20. N-n-Alkylpyridinium analog inhibition of [3H]nicotine and [3H]methyllycaconitine binding to rat brain membranes assessed interaction with alpha4beta2* and alpha7* nAChRs, respectively, whereas inhibition of nicotine-evoked 3H overflow from [3H]dopamine ([3H]DA)-preloaded rat striatal slices assessed antagonist action at nAChR subtypes mediating nicotine-evoked DA release. No inhibition of [3H]methyllycaconitine binding was observed, although N-n-alkylpyridinium analogs had low affinity for [3H]nicotine binding sites, i.e., 1 to 3 orders of magnitude lower than that of the respective N-n-alkylnicotinium analogs. These results indicate that the N-methylpyrrolidino moiety in the N-n-alkylnicotinium analogs is a structural requirement for potent inhibition of alpha4beta2* nAChRs. Importantly, N-n-alkylpyridinium analogs with n-alkyl chains < C10 did not inhibit nicotine-evoked [3H]DA overflow, whereas analogs with n-alkyl chains ranging from C10 to C20 potently and completely inhibited nicotine-evoked [3H]DA overflow (IC50 = 0.12-0.49 microM), with the exceptions of N-n-pentadecylpyridinium bromide (C15) and N-n-eicosylpyridinium bromide (C20), which exhibited maximal inhibition of approximately 50%. The mechanism of inhibition of a representative analog of this structural series, N-n-dodecylpyridinium iodide, was determined by Schild analysis. Linear Schild regression with slope not different from unity indicated competitive antagonism at nAChRs mediating nicotine-evoked [3H]DA overflow and a KB value of 0.17 microM. Thus, the simplified N-n-alkylpyridinium analogs are potent, selective, and competitive antagonists of nAChRs mediating nicotine-evoked [3H]DA overflow, indicating that the N-methylpyrrolidino moiety is not a structural requirement for interaction with nAChR subtypes mediating nicotine-evoked DA release.
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171
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Mulholland PJ, Harris BR, Wilkins LH, Self RL, Blanchard JA, Holley RC, Littleton JM, Prendergast MA. Opposing effects of ethanol and nicotine on hippocampal calbindin-D28k expression. Alcohol 2003; 31:1-10. [PMID: 14615005 DOI: 10.1016/j.alcohol.2003.09.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Long-term ethanol exposure produces multiple neuroadaptations that likely contribute to dysregulation of Ca(2+) balance and neurotoxicity during ethanol withdrawal. Conversely, nicotine exposure may reduce the neurotoxic consequences of Ca(2+) dysregulation, putatively through up-regulation of the Ca(2+)-buffering protein calbindin-D(28k). The current studies were designed to examine the extent to which 10-day ethanol exposure and withdrawal altered calbindin-D(28k) expression in rat hippocampus. Further, in these studies, we examined the ability of nicotine, through action at alpha(7)(*)-bearing nicotinic acetylcholine receptors (nAChRs), to antagonize the effects of ethanol exposure on calbindin-D(28k) expression. Organotypic cultures of rat hippocampus were exposed to ethanol (50-100 mM) for 10 days. Additional cultures were exposed to 500 nM (-)-nicotine with or without the addition of 50 mM ethanol, 100 nM methyllycaconitine (an alpha(7)*-bearing nAChR antagonist), or both. Prolonged exposure to ethanol (>/=50 mM) produced significant reductions of calbindin-D(28k) immunolabeling in all regions of the hippocampal formation, even at nontoxic concentrations of ethanol. Calbindin-D(28k) expression levels returned to near-control levels after 72 h of withdrawal from 10-day ethanol exposure. Extended (-)-nicotine exposure produced significant elevations in calbindin-D(28k) expression levels that were prevented by methyllycaconitine co-exposure. Co-exposure of cultures to (-)-nicotine with ethanol resulted in an attenuation of ethanol-induced reductions in calbindin-D(28k) expression levels. These findings support the suggestion that long-term ethanol exposure reduces the neuronal capacity to buffer accumulated Ca(2+) in a reversible manner, an effect that likely contributes to withdrawal-induced neurotoxicity. Further, long-term exposure to (-)-nicotine enhances calbindin-D(28k) expression in an alpha(7)* nAChR-dependent manner and antagonizes the effects of ethanol on calbindin-D(28k) expression.
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Affiliation(s)
- Patrick J Mulholland
- Department of Psychology, University of Kentucky, 115 Kastle Hall, Lexington, KY 40506-0044, USA
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172
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Romanelli MN, Gualtieri F. Cholinergic nicotinic receptors: competitive ligands, allosteric modulators, and their potential applications. Med Res Rev 2003; 23:393-426. [PMID: 12710018 DOI: 10.1002/med.10037] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Discovery of the important role played by nicotinic acetylcholine receptors (nAChRs) in several CNS disorders has called attention to these membrane proteins and to ligands able to modulate their functions. The existence of different subtypes at multiple levels has complicated the understanding of this receptor's physiological role, but at the same time has increased the efforts to discover selective compounds in order to improve the pharmacological characterization of this kind of receptor and to make the possible therapeutical use of its modulators safer. This review focuses on the structure of new ligands for nAChRs, agonists, antagonists and allosteric modulators, and on their possible applications.
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Affiliation(s)
- M Novella Romanelli
- Dipartimento di Scienze Farmaceutiche, Università di Firenze, via Gino Capponi 9, 50121 Firenze, Italy.
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173
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Hahn B, Sharples CGV, Wonnacott S, Shoaib M, Stolerman IP. Attentional effects of nicotinic agonists in rats. Neuropharmacology 2003; 44:1054-67. [PMID: 12763099 DOI: 10.1016/s0028-3908(03)00099-6] [Citation(s) in RCA: 117] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Nicotine can increase stimulus detection, response rate and speed in the five-choice serial reaction time task, a rodent test of attention. In the present experiments, four other nicotinic agonists with different pharmacological profiles were compared in the same procedure. The response profile of epibatidine resembled that previously obtained with nicotine in that response accuracy was enhanced and omission errors and correct response latency decreased. ABT-418 transiently increased accuracy in the first 10 min of test sessions and reduced response latency. Isoarecolone caused a dose-related increase in accuracy, but had no effect on omissions or response latency. This absence of effects on response rate- or speed-related measures may be related to its previously reported reduced ability to release dopamine as compared with nicotine. The alpha7-agonist AR-R17779 was without effect on any measure, indicating that this receptor subtype may not mediate nicotinic effects on attention. Affinity constants of compounds, determined in competition binding assays targeting the alpha4beta2, alpha7, alpha3beta4 and alpha3beta2* nAChR subtypes, could not explain the differential behavioural effects observed. Differences in their functional efficacy at nAChR subtypes may instead be responsible. The finding that attentional performance and response rate and speed can be selectively modulated by nicotinic agonists is encouraging for the development of drugs with therapeutic properties similar to those of nicotine but with reduced unwanted effects.
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Affiliation(s)
- Britta Hahn
- Section of Behavioural Pharmacology, P049, Institute of Psychiatry, King's College London, De Crespigny Park, London, SE5 8AF, UK.
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174
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Fitch RW, Xiao Y, Kellar KJ, Daly JW. Membrane potential fluorescence: a rapid and highly sensitive assay for nicotinic receptor channel function. Proc Natl Acad Sci U S A 2003; 100:4909-14. [PMID: 12657731 PMCID: PMC153654 DOI: 10.1073/pnas.0630641100] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Seven cell lines expressing native and transfected nicotinic receptor subtypes were evaluated functionally by using fluorescent assays based on membrane potential and calcium dynamics with "no-wash" dye systems. Both assays provided the same rank orders of potency for (+/-)-epibatidine, 2S-(-)-nicotine, 7R,9S-(-)-cytisine, and 1,1-dimethyl-4-phenylpiperazinium in a cell line expressing rat alpha 3 beta 4 receptors. Nicotinic antagonists mecamylamine and dihydro-beta-erythroidine inhibited responses in both assays. Both agonist and antagonist activity were assessed within the same experiment. Agonists seemed more potent in the membrane potential assay than in the calcium assay, whereas the converse was true for antagonists. The membrane potential assay afforded robust responses in K-177 cells expressing human alpha 4 beta 2 receptors, in IMR-32 and SH-SY5Y cells expressing human ganglionic receptors, and in TE-671 cells expressing human neuromuscular receptors. These lines gave weak to modest calcium responses. Moreover, membrane potential responses were obtained in cell lines expressing rat alpha 4 beta 2 and alpha 4 beta 4 receptors, which were devoid of calcium responses. Thus, membrane potential serves as a sensitive measure of nicotinic activity, and the resulting depolarization may be as important as calcium in cell signaling.
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Affiliation(s)
- Richard W Fitch
- Section on Pharmacodynamics, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA
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175
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Lucas-Meunier E, Fossier P, Baux G, Amar M. Cholinergic modulation of the cortical neuronal network. Pflugers Arch 2003; 446:17-29. [PMID: 12690458 DOI: 10.1007/s00424-002-0999-2] [Citation(s) in RCA: 144] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/04/2002] [Indexed: 01/15/2023]
Abstract
Acetylcholine (ACh) is an important neurotransmitter of the CNS that binds both nicotinic and muscarinic receptors to exert its action. However, the mechanisms underlying the effects of cholinergic receptors have still not been completely elucidated. Central cholinergic neurons, mainly located in basal forebrain, send their projections to different structures including the cortex. The cortical innervation is diffuse and roughly topographic, which has prompted some authors to suspect a modulating role of ACh on the activity of the cortical network rather than a direct synaptic role. The cholinergic system is implicated in functional, behavioural and pathological states including cognitive function, nicotine addiction, Alzheimer's disease, Tourette's syndrome, epilepsies and schizophrenia. As these processes depend on the activation of glutamatergic and GABAergic systems, the cholinergic terminals must exert their effects via the modulation of excitatory and/or inhibitory neurotransmission. However, the understanding of cholinergic modulation is complex because it is the result of a mixture of positive and negative modulation, implying that there are various types, or even subtypes, of cholinergic receptors. In this review, we summarize the current knowledge on central cholinergic systems (projections and receptors) and then aim to focus on the implications for ACh in the modulation of cortical neuronal activity.
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Affiliation(s)
- E Lucas-Meunier
- Laboratoire de Neurobiologie Cellulaire et Moléculaire, INAF-CNRS, 1 avenue de la Terrasse, 91198 Gif-sur-Yvette cedex, France.
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176
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Uteshev VV, Meyer EM, Papke RL. Regulation of neuronal function by choline and 4OH-GTS-21 through alpha 7 nicotinic receptors. J Neurophysiol 2003; 89:1797-806. [PMID: 12611953 DOI: 10.1152/jn.00943.2002] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A unique feature of alpha7 nicotinic acetylcholine receptor physiology is that, under normal physiological conditions, alpha7 receptors are constantly perfused with their natural selective agonist, choline. Studying neurons of hypothalamic tuberomammillary (TM) nucleus, we show that choline and the selective alpha7 receptor agonist 4OH-GTS-21 can regulate neuronal functions directly, via activation of the native alpha7 receptors, and indirectly, via desensitizing those receptors or transferring them into a state "primed" for desensitization. The direct action produces depolarization and thereby increases the TM neuron spontaneous firing (SF) rate. The regulation of the spontaneous firing rate is robust in a nonphysiological range of choline concentrations >200 microM. However, modest effects persist at concentrations of choline that are likely to be attained perineuronally under some conditions (20-100 microM). At high physiological concentration levels, the indirect choline action reduces or even eliminates the responsiveness of alpha7 receptors and their availability to other strong cholinergic inputs. Similarly to choline, 4OH-GTS-21 increases the TM neuron spontaneous firing rate via activation of alpha7 receptors, and this regulation is robust in the range of clinically relevant concentrations of 4OH-GTS-21. We conclude that factors that regulate choline accumulation in the brain and in experimental slices such as choline uptake, hydrolysis of ACh, membrane phosphatidylcholine catabolism, and solution perfusion rate influence alpha7 nAChR neuronal and synaptic functions, especially under pathological conditions such as stroke, seizures, Alzheimer's disease, and head trauma, when the choline concentration in the CSF is expected to rise.
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Affiliation(s)
- Vladimir V Uteshev
- Department of Pharmacology and Therapeutics, University of Florida College of Medicine, University of Florida, Gainesville, Florida 32610-0267, USA
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177
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Chen J, Norrholm S, Dwoskin LP, Crooks PA, Bai D. N,N-disubstituted piperazines: synthesis and affinities at alpha4beta2(*) and alpha7(*) neuronal nicotinic acetylcholine receptors. Bioorg Med Chem Lett 2003; 13:97-100. [PMID: 12467625 PMCID: PMC3749776 DOI: 10.1016/s0960-894x(02)00849-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A series of N,N-disubstituted piperazines were prepared and evaluated for binding to alpha4beta2(*) and alpha7(*) neuronal nicotinic acetylcholine receptors using rat striatum and whole brain membrane preparations, respectively. This series of compounds exhibited selectivity for alpha4beta2(*) nAChRs and did not interact with the alpha7(*) nAChRs subtype. The most potent analogues were compounds 8b and 8f (K(i)=32 microM). Thus, linking together a pyridine pi-system and a cyclic amine moiety via a piperazine ring affords compounds with low affinity, but good selectivity for alpha4beta2(*) nicotinic receptors.
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Affiliation(s)
- Jianhong Chen
- Shanghai Institute of Materia Medica, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 294 Tai-yuan Road, Shanghai 200031, China
| | - Seth Norrholm
- Division of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, 800 Rose Street, Lexington, KY 40536-0082, USA
| | - Linda P. Dwoskin
- Division of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, 800 Rose Street, Lexington, KY 40536-0082, USA
| | - Peter A. Crooks
- Division of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, 800 Rose Street, Lexington, KY 40536-0082, USA
- Corresponding authors. Tel.: +86-21-64311833628; fax: +86-21-64370269; (D. Bai); Tel.: +1-859-257-1718; fax: +1-859-257-7585; (P. A. Crooks)
| | - Donglu Bai
- Shanghai Institute of Materia Medica, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 294 Tai-yuan Road, Shanghai 200031, China
- Corresponding authors. Tel.: +86-21-64311833628; fax: +86-21-64370269; (D. Bai); Tel.: +1-859-257-1718; fax: +1-859-257-7585; (P. A. Crooks)
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178
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Wilkins LH, Grinevich VP, Ayers JT, Crooks PA, Dwoskin LP. N-n-alkylnicotinium analogs, a novel class of nicotinic receptor antagonists: interaction with alpha4beta2* and alpha7* neuronal nicotinic receptors. J Pharmacol Exp Ther 2003; 304:400-10. [PMID: 12490617 DOI: 10.1124/jpet.102.043349] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The current study demonstrates that N-n-alkylnicotinium analogs with increasing n-alkyl chain lengths from 1 to 12 carbons have varying affinity (Ki = 90 nM-20 microM) for S-(-)-[3H]nicotine binding sites in rat striatal membranes. A linear relationship was observed such that increasing n-alkyl chain length provided increased affinity for the alpha4beta2* nicotinic acetylcholine receptor (nAChR) subtype, with the exception of N-n-octylnicotinium iodide (NONI). The most potent analog was N-n-decylnicotinium iodide (NDNI; Ki = 90 nM). In contrast, none of the analogs in this series exhibited high affinity for the [3H]methyllycaconitine binding site, thus indicating low affinity for the alpha7* nAChR. The C8 analog, NONI, had low affinity for S-(-)-[3H]nicotine binding sites but was a potent inhibitor of S-(-)-nicotine-evoked [3H]dopamine (DA) overflow from superfused striatal slices (IC50 = 0.62 microM), thereby demonstrating selectivity for the nAChR subtype mediating S-(-)-nicotine-evoked [3H]DA overflow (alpha3alpha6beta2* nAChRs). Importantly, the N-n-alkylnicotinium analog with highest affinity for the alpha4beta2* subtype, NDNI, lacked the ability to inhibit S-(-)-nicotine-evoked [3H]DA overflow and, thus, appears to be selective for alpha4beta2* nAChRs. Furthermore, the present study demonstrates that the interaction of these analogs with the alpha4beta2* subtype is via a competitive mechanism. Thus, selectivity for the alpha4beta2* subtype combined with competitive interaction with the S-(-)-nicotine binding site indicates that NDNI is an excellent candidate for studying the structural topography of alpha4beta2* agonist recognition binding sites, for identifying the antagonist pharmacophore on the alpha4beta2* nAChR, and for defining the role of this subtype in physiological function and pathological disease states.
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Affiliation(s)
- Lincoln H Wilkins
- College of Pharmacy, University of Kentucky, Lexington, Kentucky 40536-0082, USA.
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179
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Abbruscato TJ, Lopez SP, Mark KS, Hawkins BT, Davis TP. Nicotine and cotinine modulate cerebral microvascular permeability and protein expression of ZO-1 through nicotinic acetylcholine receptors expressed on brain endothelial cells. J Pharm Sci 2002; 91:2525-38. [PMID: 12434396 DOI: 10.1002/jps.10256] [Citation(s) in RCA: 131] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The blood-brain barrier (BBB) adapts to a variety of pathological processes. Little is known about the effects of nicotine exposure on BBB function and the ability to adapt to stroke conditions. We have demonstrated, using a well-characterized in vitro BBB model, bovine brain microvessel endothelial cells (BBMEC) model, that nicotine and its major metabolite, cotinine, modulate BBB integrity by opening the paracellular route of solute entry into the brain. Additionally, nicotine and cotinine together increase the permeability change observed after 6 h of hypoxia/aglycemia, an in vitro model of stroke. This has important implications for how the BBB initially adapts to stroke in an environment that is previously exposed to nicotine. Nicotine and cotinine exposure also resulted in reduced ZO-1 immunoreactivity (tight junctional protein) that occurred in a time-dependent manner. Interestingly, attenuation of bovine brain microvessel endothelial cell (BBMEC) ZO-1 protein expression was reversed using 10 nM BGT, an alpha7 nicotinic acetycholine receptor (nAChR) antagonist, suggesting that the effects of nicotine on BBMEC protein expression of ZO-1 protein are mediated by nAChR expressed on brain endothelial cells. In addition to alpha7, we found that BBMEC also contain positive immunoreactivity for the alpha3, alpha5, beta2, beta3 nAChR subunit. Both alpha7 and beta2 nAChR subunit protein levels decreased with prior nicotine and cotinine exposure. These data provide evidence that nicotine and cotinine alter BBB permeability and tight junctional protein expression of ZO-1, thereby altering the BBB response to stroke conditions. These changes in brain endothelial cell paracellular permeability are believed to be associated with nicotine binding to nAChRs present at the BBB.
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Affiliation(s)
- Thomas J Abbruscato
- Department of Pharmaceutical Sciences, Texas Tech University Health Sciences Center, School of Pharmacy, 1300 Coulter, Amarillo, Texas 79106, USA.
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180
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Mugnaini M, Tessari M, Tarter G, Merlo Pich E, Chiamulera C, Bunnemann B. Upregulation of [3H]methyllycaconitine binding sites following continuous infusion of nicotine, without changes of alpha7 or alpha6 subunit mRNA: an autoradiography and in situ hybridization study in rat brain. Eur J Neurosci 2002; 16:1633-46. [PMID: 12431215 DOI: 10.1046/j.1460-9568.2002.02220.x] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
It is well established that exposure of experimental animals to nicotine results in upregulation of the alpha4beta2-subtype of neuronal nicotinic acetylcholine receptors (nAChRs). The aim of this study was to determine the effect of nicotine on the levels of alpha7-nAChRs in rat brain, for which only partial information is available. Rats were infused with nicotine (3 mg/kg/day) or saline for 2 weeks and their brains processed for receptor autoradiography with [3H]methyllycaconitine (MLA), a radioligand with nanomolar affinity for alpha7-nAChRs. In control rats binding was high in hippocampus, intermediate in cerebral cortex and hypothalamus, and low in striatum, thalamus and cerebellum. There was high correlation between the distribution of [3H]MLA binding sites and alpha7 subunit mRNA (r = 0.816). With respect to saline-treated controls, nicotine-treated rats presented higher [3H]nicotine binding in 11 out of 15 brain regions analysed (average increase 46 +/- 6%). In contrast, only four regions showed greater [3H]MLA binding, among which the ventral tegmental area (VTA) and cingulate cortex (mean increase 32 +/- 3%). No changes in alpha7 mRNA levels were observed after nicotine treatment. Similarly, there was no variation of alpha6 subunit transcript in the VTA, a region which may contain MLA-sensitive (non-alpha7)-alpha6*-nAChRs (Klink et al., 2001). In conclusion, nicotine increased [3H]MLA binding, although to a smaller extent and in a more restricted regional pattern than [3H]nicotine. The enhancement of binding was not paralleled by a significant change of alpha7 and alpha6 subunit transcription. Finally, the present results provide the first anatomical description of the distribution of [3H]MLA binding sites in rat brain.
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Affiliation(s)
- Manolo Mugnaini
- Biology Department, Psychiatry-CEDD, GlaxoSmithKline S.p.A., Medicines Research Centre, Verona, Italy.
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181
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Bryant DL, Free RB, Thomasy SM, Lapinsky DJ, Ismail KA, Arason KM, Bergmeier SC, McKay DB. Effects of methyllycaconitine and related analogues on bovine adrenal alpha3beta4* nicotinic acetylcholine receptors. Ann N Y Acad Sci 2002; 971:139-41. [PMID: 12438104 DOI: 10.1111/j.1749-6632.2002.tb04448.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Adrenal secretion and binding studies were performed using ring E analogues of methyllycaconitine to assess structural determinants affecting activity on bovine adrenal alpha3beta4* nicotinic receptors. The most potent analogues are as potent as many inhibitors of adrenal secretion. Our data support the potential use of methyllycaconitine analogues to generate nicotinic receptor subtype-specific compounds.
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Affiliation(s)
- Darrell L Bryant
- Division of Pharmacology, The Ohio State University, College of Pharmacy, Columbus, Ohio 43210, USA
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182
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Miller DK, Wong EHF, Chesnut MD, Dwoskin LP. Reboxetine: functional inhibition of monoamine transporters and nicotinic acetylcholine receptors. J Pharmacol Exp Ther 2002; 302:687-95. [PMID: 12130733 DOI: 10.1124/jpet.302.2.687] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The present study determined whether repeated administration of the antidepressant and selective norepinephrine (NE) uptake inhibitor reboxetine resulted in an adaptive modification of the function of the NE transporters (NETs), serotonin (5-HT) transporters, or dopamine (DA) transporters. Because antidepressants may be effective tobacco smoking cessation agents and because antidepressants have recently been shown to interact with nicotinic acetylcholine receptors (nAChRs), the interaction of reboxetine with nAChRs was also evaluated. Repeated administration of reboxetine (10 mg/kg i.p., twice daily for 14 days) did not alter the potency or selectivity of reboxetine inhibition of [(3)H]NE, [(3)H]DA, or [(3)H]5-HT uptake into striatal or hippocampal synaptosomes (IC(50) values = 8.5 nM, 89 microM, and 6.9 microM, respectively). In a separate series of experiments, reboxetine did not inhibit (K(i) > 1 microM) [(3)H]methyllycaconitine, [(3)H]cytisine, or [(3)H]epibatidine binding to rat whole brain membranes. However, at concentrations that did not exhibit intrinsic activity, reboxetine potently inhibited (IC(50) value = 7.29 nM) nicotine-evoked [(3)H]NE overflow from superfused hippocampal slices via a noncompetitive mechanism. In the latter experiments, the involvement of NET was eliminated by inclusion of desipramine (10 microM) in the superfusion buffer. Reboxetine also inhibited (IC(50) value = 650 nM) nicotine-evoked (86)Rb(+) efflux at reboxetine concentrations that did not exhibit intrinsic activity in this assay. Thus, in addition to inhibition of NET function, reboxetine inhibits nAChR function, suggesting that it may have potential as a smoking cessation agent.
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Affiliation(s)
- Dennis K Miller
- College of Pharmacy, University of Kentucky, Lexington, KY 40536-0082, USA
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183
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Application of olefin metathesis to the synthesis of ABE ring analogues of methyllycaconitine. Tetrahedron Lett 2002. [DOI: 10.1016/s0040-4039(02)01214-5] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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184
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Mogg AJ, Whiteaker P, McIntosh JM, Marks M, Collins AC, Wonnacott S. Methyllycaconitine is a potent antagonist of alpha-conotoxin-MII-sensitive presynaptic nicotinic acetylcholine receptors in rat striatum. J Pharmacol Exp Ther 2002; 302:197-204. [PMID: 12065717 DOI: 10.1124/jpet.302.1.197] [Citation(s) in RCA: 128] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The plant alkaloid methyllycaconitine (MLA) is considered to be a selective antagonist of the alpha7 subtype of neuronal nicotinic acetylcholine receptor (nAChR). However, 50 nM MLA partially inhibited (by 16%) [(3)H]dopamine release from rat striatal synaptosomes stimulated with 10 microM nicotine. Other alpha7-selective antagonists had no effect. Similarly, MLA (50 nM) inhibited [(3)H]dopamine release evoked by the partial agonist (2-chloro-5-pyridyl)-9-azabicyclo[4.2.1]non-2-ene (UB-165) (0.2 microM) by 37%. In both cases, inhibition by MLA was surmountable with higher agonist concentrations, indicative of a competitive interaction. At least two subtypes of presynaptic nAChR can modulate dopamine release in the striatum, and these nAChR are distinguished by their differential sensitivity to alpha-conotoxin-MII (alpha-CTx-MII). MLA was not additive with a maximally effective concentration of alpha-CTx-MII (100 nM) in inhibiting [(3)H]dopamine release elicited by 10 microM nicotine or 0.2 microM UB-165, suggesting that both toxins act at the same site. This was confirmed in quantitative binding assays with (125)I-alpha-CTx-MII, which displayed saturable specific binding to rat striatum and nucleus accumbens with B(max) values of 9.8 and 16.5 fmol/mg of protein, and K(d) values of 0.63 and 0.83 nM, respectively. MLA fully inhibited (125)I-alpha-CTx-MII binding to striatum and nucleus accumbens with a K(i) value of 33 nM, consistent with the potency observed in the functional assays. We speculate that MLA and alpha-CTx-MII interact with a presynaptic nAChR of subunit composition alpha3/alpha6beta2beta3* on dopamine neurons. The use of MLA as an alpha7-selective antagonist should be exercised with caution, especially in studies of nAChR in basal ganglia.
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Affiliation(s)
- Adrian J Mogg
- Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, United Kingdom
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185
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Navarro HA, Xu H, Zhong D, Abraham P, Carroll FI. In vitro and in vivo characterization of [125I]iodomethyllycaconitine in the rat. Synapse 2002; 44:117-23. [PMID: 11954042 DOI: 10.1002/syn.10062] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The in vitro and in vivo binding characteristics of [125I]iodomethyllycaconitine ([125I]iodoMLA) were determined in the rat. [125I]iodoMLA binding to rat cerebral cortex membranes was saturable and reversible and its specific binding represented approximately 70-80% of the total binding. [125I]iodoMLA labeled a single site with Kd = 1.8 +/- 0.4 nM and Bmax = 68 +/- 3 fmol/mg protein. Kinetic analysis revealed a t1/2 for association and dissociation of 10.5 +/- 3.1 and 10.3 +/- 1.6 min, respectively. Pharmacological characterization of [125I]iodoMLA binding indicated that it was specific for the alpha7 nAChR. In vitro brain region binding studies revealed greater binding in regions known to contain high numbers of alpha7 nAChRs. The analysis of the biodistribution of intravenously administered [125I]iodoMLA indicated that it was rapidly cleared and exhibited poor brain penetration; nevertheless, the levels of [125I]iodoMLA in alpha7 nAChR-rich target regions were significantly increased compared to the nontarget region (cerebellum) 60-120 min after administration. No metabolism of MLA by human liver S9 fraction was detected. Our results suggest that [125I]iodoMLA will be a useful radioligand to study the alpha7 nAChR in vitro and in vivo.
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Affiliation(s)
- H A Navarro
- Center for Organic and Medicinal Chemistry, Chemistry and Life Sciences, Research Triangle Institute, Research Triangle Park, North Carolina 27709, USA.
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186
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Rahman S, Ali Khan R, Kumar A. Experimental study of the morphine de-addiction properties of Delphinium denudatum Wall. BMC COMPLEMENTARY AND ALTERNATIVE MEDICINE 2002; 2:6. [PMID: 12036433 PMCID: PMC116424 DOI: 10.1186/1472-6882-2-6] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/04/2001] [Accepted: 05/29/2002] [Indexed: 11/10/2022]
Abstract
BACKGROUND Our aim was to explore the de-addiction properties of Delphinium denudatum Wall. in morphine dependent rats. METHODS Charles Foster male albino rats were made morphine dependent by injecting morphine sulphate in increasing doses twice a day for 7 days. The spontaneous withdrawal signs observed 12 h after the last dose were quantified by the 'counted' and 'checked' signs. The drug (alcoholic extract of Delphinium denudatum) was administered p.o. in different regimen: a) single dose (700 mg/kg) 10 h before the first dose of morphine, b) single dose (700 mg/kg) 10 h after the last dose of morphine, c) multiple doses (350 mg/kg) along with morphine twice a day for 7 days. RESULT Administration of Delphinium denudatum extract caused significant reduction in the frequency of counted signs as well as the presence of checked signs of morphine withdrawal. The maximum reduction was observed in regimen 'b' followed by regimen 'c' and 'a'. CONCLUSION Delphinium denudatum Wall. significantly reduces the aggregate scores for all parameters in morphine withdrawal syndrome by central action and thus may prove to be an alternative remedy in morphine de-addiction.
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Affiliation(s)
- Syed Rahman
- Department of Pharmacology, Jawaharlal Nehru Medical College, Aligarh Muslim Unviversity, Aligarh-202002, India
| | - Rahat Ali Khan
- Department of Pharmacology, Jawaharlal Nehru Medical College, Aligarh Muslim Unviversity, Aligarh-202002, India
| | - Anil Kumar
- Department of Pharmacology, Jawaharlal Nehru Medical College, Aligarh Muslim Unviversity, Aligarh-202002, India
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187
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Xu R, Dwoskin LP, Grinevich V, Sumithran SP, Crooks PA. Synthesis and evaluation of conformationally restricted pyridinoN-alkylated nicotine analogs as nicotinic acetylcholine receptor antagonists. Drug Dev Res 2002. [DOI: 10.1002/ddr.10049] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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188
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Abstract
Although alpha3beta4 subunit combination is clearly prevalent in the nAChRs of autonomic ganglia neurons, the ganglia are strikingly different in the ratio of neurons containing each particular nAChR subunit, as found with immunohistochemical methods and from the analysis of the effects of nAChR subunit-specific antibodies on the ACh-induced membrane currents. In particular, the number of neurons containing alpha3, alpha4, alpha5 or alpha7 subunits is by about three times higher in sympathetic ganglia than in parasympathetic ganglia. This difference may explain why the parasympathetic and sympathetic ganglia markedly differ in their pharmacology. Still, alpha7 subunit makes the highest contribution to ACh-induced membrane current. No correlation between the physiological functions of the ganglia and subunit composition of their nAChRs has been found as yet. High permeability for Ca2+ should permit the nAChRs with alpha7 subunits to influence a variety of Ca2+-dependent events in autonomic neurons. As found with biochemical methods and site-directed mutagenesis, the ACh binding site is formed in the alpha/beta subunits interface by multiple loops containing cysteine, tyrosine and tryptophan amino residues as important for ACh binding. Likewise, both alpha and beta subunits are important for the effects of blocking agents on nAChRs. As found by electrophysiological methods, each neuron of sympathetic and parasympathetic ganglia, as a rule, possesses nAChRs of two groups, "fast" and "slow", with the mean duration of the burst of single channel openings ranging approximately from 5 to 10 and from 25 to 45 ms, respectively. These groups of channels differ from each other with their pharmacology. The burst-like activity of autonomic nAChRs channels is possible only if the disulfide bonds are left intact, otherwise only single openings of the channel are observed. The ionic channel of a nAChRs pentamer is formed by M2 transmembrane segments arranging glutamate, serine, threonine, leucine, and valine rings critical for channel conductance and ionic selectivity. In particular, the mutations V251T and E237A, and insertion of proline or alanine, convert a cation-selective channel into an anion-selective one. The open-channel blockers bind to the nAChR channel at the level where the channel diameter is nearly 12 A, both for "fast" and "slow" channel groups.
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Affiliation(s)
- Vladimir I Skok
- Department of Autonomic Nervous System and Physiology, Bogomoletz Institute of Physiology, Kiev, Ukraine.
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189
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Gündisch D, Kämpchen T, Schwarz S, Seitz G, Siegl J, Wegge T. Syntheses and evaluation of pyridazine and pyrimidine containing bioisosteres of (+/-)-pyrido[3.4-b]homotropane and pyrido-[3.4-b]tropane as novel nAChR ligands. Bioorg Med Chem 2002; 10:1-9. [PMID: 11738601 DOI: 10.1016/s0968-0896(01)00258-9] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Bioisosteric replacement of the pyridine pharmacophoric element in (+/-)-pyrido[3.4-b]homotropane (PHT) and pyrido[3.4-b]tropane with the pyridazine and pyrimidine nucleus resulted in hitherto unknown nAChR ligands such as 5-8. Inverse type Diels-Alder reactions constitute the key steps in the new routes to the pyridazine- or pyrimidine-annulated bioisosteres. The enantiopure (+)-2-tropinone (11) from the 'chiral pool' is transformed to the ring-expanded silyl enol ether 12 and to the enamine 15. Both proved to be highly dienophilic species in the inverse type [4+2] cycloaddition reactions with the 1,2,4,5-tetrazines 13 and 16a,b or with the 1,3,5-triazine 19 to provide the enantiopure target compounds 5-7. In the same way the racemic pyrimidine-annulated species 8 was obtained from 3-tropanone 21. The new ligands were tested for their in vitro affinity for (alpha4)2(beta2)3 and alpha7* nAChR subtype. In comparison to PHT, well known to exhibit affinity for agonist binding sites in rat brain approximately equivalent to that of (+)-anatoxin-a (1), replacement of the pyridine by the bioisosteric pyridazine resulted in 30-fold lower affinity at the (alpha4)2(beta2)3 subtype. The annulated diazinotropanes 6-8, ligands with ferruginine-like structures more or less retained the affinity of (-)-norferruginine (3) except of compound 7. Remarkably, all of the novel ligands are devoid of affinity at the alpha7* subtype.
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Affiliation(s)
- Daniela Gündisch
- Department of Pharmaceutical Chemistry, Rhein.Friedr.Wilh. University, Kreuzbergweg 26, D-53115, Bonn, Germany
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190
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Bryant DL, Free RB, Thomasy SM, Lapinsky DJ, Ismail KA, McKay SB, Bergmeier SC, McKay DB. Structure-activity studies with ring E analogues of methyllycaconitine on bovine adrenal alpha3beta4* nicotinic receptors. Neurosci Res 2002; 42:57-63. [PMID: 11814609 DOI: 10.1016/s0168-0102(01)00304-2] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The development of new agents that selectively interact with subtypes of neuronal nicotinic receptors (nAChRs) is of primary importance for the study of physiological processes and pathophysiological conditions involving these receptors. Our laboratory has evidence that simple ring E analogues of methyllycaconitine (MLA) act as antagonists to bovine adrenal alpha3beta4* nAChRs. The following studies were designed to characterize the concentration-response effects of several ring E analogues of MLA in order to assess structural requirements involved with their inhibitory activity on bovine adrenal alpha3beta4* nAChRs. Ring E analogues with various substitutions on the ring E nitrogen were tested for their ability to inhibit nicotinic stimulated adrenal catecholamine release and [3H]epibatidine binding to a bovine adrenal membrane preparation. Several N-alkyl derivatives inhibited secretion with IC50 values in the low micromolar range. The N-phenpropyl analogue was the most potent of the analogues tested (IC50, 11 microM) on adrenal secretion. Competition binding studies suggest a noncompetitive interaction of the analogues with bovine adrenal nAChRs. These studies identify several structural features of ring E analogues of MLA which significantly affect their inhibitory activity on bovine adrenal alpha3beta4* nAChRs.
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Affiliation(s)
- Darrell L Bryant
- Division of Pharmacology, The Ohio State University, College of Pharmacy, 500 West 12th Avenue, Columbus, OH 43210, USA
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191
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Leonard S, Adler LE, Benhammou K, Berger R, Breese CR, Drebing C, Gault J, Lee MJ, Logel J, Olincy A, Ross RG, Stevens K, Sullivan B, Vianzon R, Virnich DE, Waldo M, Walton K, Freedman R. Smoking and mental illness. Pharmacol Biochem Behav 2001; 70:561-70. [PMID: 11796154 DOI: 10.1016/s0091-3057(01)00677-3] [Citation(s) in RCA: 195] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Patients with mental illness have a higher incidence of smoking than the general population and are the major consumers of tobacco products. This population includes subjects with schizophrenia, manic depression, depression, posttraumatic stress disorder (PTSD), attention-deficit disorder (ADD), and several other less common diseases. Smoking cessation treatment in this group of patients is difficult, often leading to profound depression. Several recent findings suggest that increased smoking in the mentally ill may have an underlying biological etiology. The mental illness schizophrenia has been most thoroughly studied in this regard. Nicotine administration normalizes several sensory-processing deficits seen in this disease. Animal models of sensory deficits have been used to identify specific nicotinic receptor subunits that are involved in these brain pathways, indicating that the alpha 7 nicotinic receptor subunit may play a role. Genetic linkage in schizophrenic families also supports a role for the alpha 7 subunit with linkage at the alpha 7 locus on chromosome 15. Bipolar disorder has some phenotypes in common with schizophrenia and also exhibits genetic linkage to the alpha 7 locus, suggesting that these two disorders may share a gene defect. The alpha 7 receptor is decreased in expression in schizophrenia. [(3)H]-Nicotine binding studies in postmortem brain indicate that high-affinity nicotinic receptors may also be affected in schizophrenia.
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Affiliation(s)
- S Leonard
- Department of Psychiatry, University of Colorado Health Sciences Center, Box C-268-71, 4200 East 9th Avenue, Denver, CO 80262, USA.
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192
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Ridley DL, Rogers A, Wonnacott S. Differential effects of chronic drug treatment on alpha3* and alpha7 nicotinic receptor binding sites, in hippocampal neurones and SH-SY5Y cells. Br J Pharmacol 2001; 133:1286-95. [PMID: 11498514 PMCID: PMC1621156 DOI: 10.1038/sj.bjp.0704207] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1. The aim of this study was to compare the effects of chronic treatment (for 4 or 7 days) with nicotinic drugs and 20 mM KCl on numbers of surface alpha7 nicotinic AChR, identified by [(125)I]-alpha bungarotoxin (alpha-Bgt) binding, in primary hippocampal cultures and SH-SY5Y cells. Numbers of alpha3* nicotinic AChR were also examined in SH-SY5Y cells, using [(3)H]-epibatidine, which is predicted to label the total cellular population of predominantly alpha3beta2* nicotinic AChR under the conditions used. 2. All the nicotinic agonists examined, the antagonists d-tubocurarine and methyllycaconitine, and KCl, upregulated [(125)I]-alpha Bgt binding sites by 20 - 60% in hippocampal neurones and, where examined, SH-SY5Y cells. 3. Upregulation of [(125)I]-alpha-Bgt binding sites by KCl was prevented by co-incubation with the L-type Ca2+ channel blocker verapamil or the Ca2+-calmodulin dependent kinase II (CaM-kinase II) inhibitor KN-62. Upregulation of [(125)I]-alpha-Bgt binding sites by nicotine or 3,[(4-dimethylamino) cinnamylidene] anabaseine maleate (DMAC) was insensitive to these agents. 4. [(3)H]-Epibatidine binding sites in SH-SY5Y cells were not affected by KCl but were upregulated in a verapamil-insensitive manner by nicotine and DMAC. KN-62 itself provoked a 2 fold increase in [(3)H]-epibatidine binding. The inactive analogue KN-04 had no effect, suggesting that CaM-kinase II plays a role in regulating numbers of alpha3* nicotinic AChR. 5. These data indicate that numbers of alpha3* and alpha7 nicotinic AChR are modulated differently. Nicotinic agonists and KCl upregulate alpha7 nicotinic AChR through distinct cellular mechanisms, the latter involving L-type Ca2+ channels and CaM-kinase II. In contrast, alpha3* nicotinic AChR are not upregulated by KCl. This difference may reflect the distinct physiological roles proposed for alpha7 nicotinic AChR.
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Affiliation(s)
- Diana L Ridley
- Department of Biology and Biochemistry, University of Bath, Bath, BA2 7AY
| | - Adrian Rogers
- Department of Biology and Biochemistry, University of Bath, Bath, BA2 7AY
| | - Susan Wonnacott
- Department of Biology and Biochemistry, University of Bath, Bath, BA2 7AY
- Author for correspondence:
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193
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Xu R, Dwoskin LP, Grinevich VP, Deaciuc G, Crooks PA. Neuronal nicotinic acetylcholine receptor binding affinities of boron-containing nicotine analogues. Bioorg Med Chem Lett 2001; 11:1245-8. [PMID: 11354387 DOI: 10.1016/s0960-894x(01)00193-7] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A series of boron-containing nicotine (NIC) analogues 7-9 was synthesized and evaluated for binding to alpha4beta2 and alpha7 nicotinic receptors. Compound ACME-B inhibited [3H]methyllycaconitine binding to rat brain membranes with a similar potency compared to NIC (Ki = 2.4 and 0.77 microM, respectively), but was markedly less potent in inhibiting [3H]NIC binding when compared to NIC (Ki = 0.60 microM and 1.0 nM, respectively). Thus, tethering a two-carbon bridge between the 2-pyridyl and 3'-pyrrolidino carbons of NIC or 7 affords analogues that bind to the alpha7 receptor in a manner similar to NIC, but with a dramatic loss of affinity for the alpha4beta2 receptor.
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Affiliation(s)
- R Xu
- Division of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, Lexington 40536-0082, USA
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194
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Lind RJ, Hardick DJ, Blagbrough IS, Potter BV, Wolstenholme AJ, Davies AR, Clough MS, Earley FG, Reynolds SE, Wonnacott S. [3H]-Methyllycaconitine: a high affinity radioligand that labels invertebrate nicotinic acetylcholine receptors. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2001; 31:533-542. [PMID: 11267892 DOI: 10.1016/s0965-1748(00)00153-3] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Nicotinic acetylcholine receptors (nAChR) of insect and other invertebrates are heterogeneous and new tools are needed to dissect their multiplicity. [(3)H]-Methyllycaconitine ([(3)H]-MLA) is a novel radioligand which is a potent antagonist at vertebrate alpha7-type nAChR. Putative invertebrate nAChR of the aphid Myzus persicae, the moths Heliothis virescens and Manduca sexta, the fly Lucilia sericata, and the squid Loligo vulgaris were investigated in radioligand binding studies with [(3)H]-MLA. Saturable binding was consistent with a single class of high affinity binding sites for each of these invertebrates, characterised by a dissociation constant, K(d), of approximately 1 nM and maximal binding capacities, B(max), between 749 and 1689 fmol/mg protein for the insects and 14,111 fmol/mg protein for squid. [(3)H]-MLA binding to M. persicae membranes was characterised in more detail. Kinetic analysis demonstrated rapid association in a biphasic manner and slow, monophasic dissociation. Displacement studies demonstrate the nicotinic character of [(3)H]-MLA binding sites. Data for all nicotinic ligands, except MLA itself, are consistent with displacement from a high and a low affinity site, indicating that displacement is occurring from two or more classes of nicotinic binding site that are not distinguished by MLA itself. Autoradiographic analysis of the distribution of [(3)H]-MLA binding sites in Manduca sexta shows discrete labelling of neuropil areas of the optic and antennal lobes.
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Affiliation(s)
- R J Lind
- Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK.
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195
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Imming P, Klaperski P, Stubbs MT, Seitz G, Gündisch D. Syntheses and evaluation of halogenated cytisine derivatives and of bioisosteric thiocytisine as potent and selective nAChR ligands. Eur J Med Chem 2001; 36:375-88. [PMID: 11461763 DOI: 10.1016/s0223-5234(01)01222-3] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
We have developed one-step syntheses of halogenated derivatives of (-)-cytisine featuring a halogen substituent at positions 3, 5 or 3 and 5 of the 2-pyridone fragment, and prepared the novel bioisosteric thiocytisine by oxygen-sulphur exchange. The affinities of these pyridone-modified analogs of (-)-cytisine for (alpha 4)(2)(beta 2)(3) and alpha 7* nAChRs in rat forebrain membranes were determined by competition with (+/-)-[(3)H]epibatidine and [(3)H]MLA, respectively. The 3-halocytisines 7 possess subnanomolar affinities for (alpha 4)(2)(beta 2)(3) nAChRs, higher than those found for (-)-cytisine as well as for the 5-halocytisines 8 and 3,5-dihalocytisines 6. In contrast to the parent alkaloid the 3-halogenated species display much a higher affinity for the alpha 7* nAChR subtype. The most potent molecule was 3-bromocytisine (7b) with preferential selectivity (200-fold) for the (alpha 4)(2)(beta 2)(3) subtype [K(i)=10 pM (alpha 4 beta 2) and 2.0 nM (alpha 7*)]. Replacement of the lactam with a thiolactam pharmacophore to thiocytisine (12) resulted in a subnanomolar affinity for the (alpha 4)(2)(beta 2)(3) nAChR subtype (K(i)=0.832 nM), but in a drastic decrease of affinity for the alpha 7* subtype; thiocytisine (12) has a K(i) value of 4000 nM (alpha 7*), giving a selectivity of 4800-fold for the neuronal (alpha 4)(2)(beta 2)(3)-nAChR and thus displaying the best affinity-selectivity profile in the series under consideration.
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Affiliation(s)
- P Imming
- Department of Pharmaceutical Chemistry, Philipps-University, Marbacher Weg 6, D-35032 Marburg, Germany
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196
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Lee MJ, Breese CR, Strook ML, Leonard S. The effect of nicotine and haloperidol co-treatment on nicotinic receptor levels in the rat brain. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 2001; 86:115-24. [PMID: 11165378 DOI: 10.1016/s0169-328x(00)00274-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Genetic and biological data have suggested a role for the neuronal nicotinic acetylcholine receptors in the neuropathophysiology of schizophrenia. Studies in human postmortem brain demonstrate dose-dependent increases in nicotinic receptor binding in normal smokers. We found this upregulation to be reduced in schizophrenic smokers, many of whom had taken typical neuroleptics during their lifetime. The present study examined the hypothesis that typical antipsychotic drug treatment might modulate nicotinic receptor upregulation in a rat model. Nicotine, administered alone or in combination with haloperidol, increased both high and low affinity neuronal nicotinic receptors in a region specific manner. Haloperidol had no generalized effect on basal levels of nicotinic receptor binding or nicotine induced upregulation of nicotinic receptors. However, haloperidol attenuated high affinity nicotinic receptor upregulation in thalamus and low affinity receptor upregulation in hippocampus. These results suggest that haloperidol is not likely to affect nicotinic receptor regulation by smoking in most brain regions.
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Affiliation(s)
- M J Lee
- The Neuroscience Program, University of Colorado Health Sciences Center, Denver, CO 80262, USA
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197
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Grottick AJ, Higgins GA. Effect of subtype selective nicotinic compounds on attention as assessed by the five-choice serial reaction time task. Behav Brain Res 2000; 117:197-208. [PMID: 11099773 DOI: 10.1016/s0166-4328(00)00305-3] [Citation(s) in RCA: 200] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Nicotine can improve attentional functioning in humans, and a number of studies have recently demonstrated that under specific task conditions, nicotine can also improve attention in the rat. Neuronal nicotinic receptors comprise combinations of alpha(2-9) and beta(2-4) subunits, arranged to form a pentameric receptor, with the principal CNS subtypes currently believed to be alpha(4)beta(2) and a homomeric alpha(7) receptor. In the present studies, we attempted to delineate the particular nicotinic receptor subtype(s) contributing to the effects of nicotine on attention by assessing various nicotinic ligands on performance in the five-choice serial reaction time task (5-CSRTT). In rats performing below criterion (<80% correct, >20% omissions to a 1-s visual stimulus), subchronic dosing with nicotine (0.2 mg/kg sc) and the alpha(4)beta(2) agonist SIB 1765F (5 mg/kg sc) increased correct responding and decreased response latencies across the treatment week; whereas the alpha(7) agonist AR-R 17779 (20 mg/kg sc) was without effect. In subjects meeting the criterion, the competitive high affinity (including alpha(4)beta(2)) nicotine receptor antagonist DHbetaE (1-10 mg/kg sc) and the alpha(7) antagonist methyllycaconitine (MLA: 5-10 mg/kg i.p.) did not disrupt performance, whereas at the highest dose, the non-competitive antagonist mecamylamine (0.3-3 mg/kg sc) decreased accuracy and increased response latencies. These changes bore some similarities to those of pre-feeding and the non-competitive NMDA antagonist dizocilpine (0.03-0.06 mg/kg sc), suggesting that mecamylamine-induced performance disruption may relate to non-nicotinic receptor effects. In subjects chronically treated with nicotine, acute nicotine challenge (0.4 mg/kg sc) significantly increased accuracy whilst having no effect on any other performance measures. Finally, in these same nicotine pre-treated rats, the decrease in latency and increase in premature responses induced by nicotine (0.2 mg/kg sc) to a target stimulus of 150 ms was fully antagonised by DHbetaE (3 mg/kg sc) but not MLA (5 mg/kg i.p.). These results suggest that alpha(7) receptors do not play a role in any of the behavioural effects of nicotine observed in the 5-CSRTT, whereas a high affinity site, perhaps alpha(4)beta(2), is more likely involved.
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Affiliation(s)
- A J Grottick
- Preclinical CNS Research, Pharma Division, F. Hoffmann-La Roche Ltd., 4070, Basel, Switzerland
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198
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Martin-Ruiz CM, Piggott M, Gotti C, Lindstrom J, Mendelow AD, Siddique MS, Perry RH, Perry EK, Court JA. Alpha and beta nicotinic acetylcholine receptors subunits and synaptophysin in putamen from Parkinson's disease. Neuropharmacology 2000; 39:2830-9. [PMID: 11044753 DOI: 10.1016/s0028-3908(00)00110-6] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
It is well established that nicotinic receptors in the mammalian striatum are involved in modulation of the release of several neurotransmitters, including dopamine. In addition, nicotinic receptors with high affinity for agonists have generally been found to be reduced in the striatum in Parkinson's disease. In the present study antibodies have been used to examine which subunits contribute to the striatal nicotinic receptor loss in Parkinson's disease, and whether the reduction in [(3)H]nicotine binding correlates with synaptic loss. Autopsy tissue from the putamen of 12 Parkinson's disease cases and 12 age-matched control subjects was analysed by immunoblotting using antibodies against recombinant peptides specific for alpha3, alpha4, alpha7, beta2 and beta4 nicotinic acetylcholine receptor (nAChR) subunits and the synaptic marker synaptophysin, in conjunction with assessment of [(3)H]nicotine binding by autoradiography. The data indicate that there is no loss of alpha3, alpha4, alpha7 and beta2 immunoreactivity in the putamen in Parkinson's disease, despite a highly significant reduction in [(3)H]nicotine binding. An intense signal of beta4 immunoreactivity was found in human dorsal root ganglia, but not in temporal cortex or putamen samples. Synaptophysin immunoreactivities were also similar in Parkinson's disease and control cases. These results suggest that the loss of nicotine binding in the putamen in Parkinson's disease may involve an nAChR subunit (e.g., alpha5 and/or alpha6) other than those investigated. Alternatively, the results could reflect impaired subunit assembly at the plasma membrane.
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Affiliation(s)
- C M Martin-Ruiz
- Joint MRC Newcastle University Centre Development for Clinical Brain Aging, MRC Building, Newcastle General Hospital, Westgate Road, NE4 6BE, Newcastle upon Tyne, UK
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199
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Quik M, Polonskaya Y, Gillespie A, Jakowec M, Lloyd GK, Langston JW. Localization of nicotinic receptor subunit mRNAs in monkey brain by in situ hybridization. J Comp Neurol 2000; 425:58-69. [PMID: 10940942 DOI: 10.1002/1096-9861(20000911)425:1<58::aid-cne6>3.0.co;2-x] [Citation(s) in RCA: 136] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Nicotinic receptors are implicated in memory, learning, locomotor activity, and addiction. Identification of the specific receptor subtypes that mediate these behaviors is essential for understanding their role in central nervous system (CNS) function. Although expression of nicotinic receptor transcript has been studied in rodent brain, their localization in the monkey CNS, which may be a better model for the human brain, is not yet known. We therefore investigated the distribution of alpha4, alpha6, alpha7, beta2, beta3, and beta4 receptors subunit mRNAs in the monkey brain by using in situ hybridization. alpha4 and alpha7 mRNAs were very widely expressed, with a substantial degree of overlap in their distribution, except for the reticular nucleus of the thalamus in which alpha7 mRNA was much more prominently expressed. beta2 and beta4 mRNA were also widely distributed, although beta4 was more prominently localized in thalamic nuclei than beta2. The distribution of alpha6 and beta3 mRNA was very distinct from that of the other transcripts, being restricted to catecholaminergic nuclei, the cerebellum, and a few other areas. Although there were similarities in distribution of the nicotinic receptor subunit mRNAs in monkey and rodent brain, there were prominent differences in areas such as the caudate, putamen, locus coeruleus, medial habenula, and cerebellum. In fact, the distribution of alpha4 and alpha7 mRNAs in the monkey caudate and putamen was more similar to that reported in the human than rodent brain. These findings have implications for the development of drug therapies for neurological disorders, such as Alzheimer's and Parkinson's disease, in which nicotinic receptors are decreased.
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Affiliation(s)
- M Quik
- The Parkinson's Institute, Sunnyvale, California 94089, USA.
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200
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Wang HY, Lee DH, Davis CB, Shank RP. Amyloid peptide Abeta(1-42) binds selectively and with picomolar affinity to alpha7 nicotinic acetylcholine receptors. J Neurochem 2000; 75:1155-61. [PMID: 10936198 DOI: 10.1046/j.1471-4159.2000.0751155.x] [Citation(s) in RCA: 317] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We have recently reported evidence that a very high affinity interaction between the beta-amyloid peptide Abeta(1-42) and the alpha7 nicotinic acetylcholine receptor (alpha7nAChR) may be a precipitating event in the formation of amyloid plaques in Alzheimer's disease. In the present study, the kinetics for the binding of Abeta(1-42) to alpha7nAChR and alpha4beta2nAChR were determined using the subtype-selective nicotinic receptor ligands [(3)H]methyllycaconitine and [(3)H]cytisine. Synaptic membranes prepared from rat and guinea pig cerebral cortex and hippocampus were used as the source of receptors. Abeta(1-42) bound to the alpha7nAChR with exceptionally high affinity, as indicated by K(i) values of 4.1 and 5.0 pM for rat and guinea pig receptors, respectively. When compared with the alpha7nAChR, the affinity of Abeta(1-42) for the alpha4beta2nAChR was approximately 5,000-fold lower, as indicated by corresponding K(i) values of 30 and 23nM. The results of this study support the concept that an exceptionally high affinity interaction between Abeta(1-42) and alpha7nAChR could serve as a precipitating factor in the formation of amyloid plaques and thereby contribute to the selective degeneration of cholinergic neurons that originate in the basal forebrain and project to the cortex and hippocampus.
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Affiliation(s)
- H Y Wang
- R. W. Johnson Pharmaceutical Research Institute, Spring House, PA 19477-0776, USA.
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