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Beaudeau JL, Blais V, Holleran BJ, Bergeron A, Piñeyro G, Guérin B, Gendron L, Dory YL. N-Guanidyl and C-Tetrazole Leu-Enkephalin Derivatives: Efficient Mu and Delta Opioid Receptor Agonists with Improved Pharmacological Properties. ACS Chem Neurosci 2019; 10:1615-1626. [PMID: 30614675 DOI: 10.1021/acschemneuro.8b00550] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Leu-enkephalin and d-Ala2-Leu-enkephalin were modified at their N- and C-termini with guanidyl and tetrazole groups. The resulting molecules were prepared in solution or by solid phase peptide synthesis. The affinity of the different analogues at mu (MOP) and delta opioid receptors (DOP) was then assessed by competitive binding in stably transfected DOP and MOP HEK293 cells. Inhibition of cAMP production and recruitment of β-arrestin were also investigated. Finally, lipophilicity (logD7.4) and plasma stability of each compound were measured. Compared to the native ligands, we found that the replacement of the terminal carboxylate by a tetrazole slightly decreased both the affinity at mu and delta opioid receptors as well as the half-life. By contrast, replacing the ammonium at the N-terminus with a guanidyl significantly improved the affinity, the potency, as well as the lipophilicity and the stability of the resulting peptides. Replacing the glycine residue with a d-alanine in position 2 consistently improved the potency as well as the stability of the analogues. The best peptidomimetic of the whole series, guanidyl-Tyr-d-Ala-Gly-Phe-Leu-tetrazole, displayed sub-nanomolar affinity and an increased lipophilicity. Moreover, it proved to be stable in plasma for up to 24 h, suggesting that the modifications are protecting the compound against protease degradation.
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Affiliation(s)
| | | | | | | | - Graciela Piñeyro
- Département de Psychiatrie, Centre de Recherche du CHU Ste-Justine, Université de Montréal, Montréal, Québec H3T 1J4, Canada
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2
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Namkung Y, LeGouill C, Kumar S, Cao Y, Teixeira LB, Lukasheva V, Giubilaro J, Simões SC, Longpré JM, Devost D, Hébert TE, Piñeyro G, Leduc R, Costa-Neto CM, Bouvier M, Laporte SA. Functional selectivity profiling of the angiotensin II type 1 receptor using pathway-wide BRET signaling sensors. Sci Signal 2018; 11:11/559/eaat1631. [PMID: 30514808 DOI: 10.1126/scisignal.aat1631] [Citation(s) in RCA: 85] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
G protein-coupled receptors (GPCRs) are important therapeutic targets that exhibit functional selectivity (biased signaling), in which different ligands or receptor variants elicit distinct downstream signaling. Understanding all the signaling events and biases that contribute to both the beneficial and adverse effects of GPCR stimulation by given ligands is important for drug discovery. Here, we report the design, validation, and use of pathway-selective bioluminescence resonance energy transfer (BRET) biosensors that monitor the engagement and activation of signaling effectors downstream of G proteins, including protein kinase C (PKC), phospholipase C (PLC), p63RhoGEF, and Rho. Combined with G protein and β-arrestin BRET biosensors, our sensors enabled real-time monitoring of GPCR signaling at different levels in downstream pathways in both native and engineered cells. Profiling of the responses to 14 angiotensin II (AngII) type 1 receptor (AT1R) ligands enabled the clustering of compounds into different subfamilies of biased ligands and showed that, in addition to the previously reported functional selectivity between Gαq and β-arrestin, there are also biases among G protein subtypes. We also demonstrated that biases observed at the receptor and G protein levels propagated to downstream signaling pathways and that these biases could occur through the engagement of different G proteins to activate a common effector. We also used these tools to determine how naturally occurring AT1R variants affected signaling bias. This suite of BRET biosensors provides a useful resource for fingerprinting biased ligands and mutant receptors and for dissecting functional selectivity at various levels of GPCR signaling.
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Affiliation(s)
- Yoon Namkung
- Department of Medicine, Research Institute of the McGill University Health Center (RI-MUHC), McGill University, Montréal, QC H4A 3J1, Canada
| | - Christian LeGouill
- Department of Biochemistry and Molecular Medicine, Institute for Research in Immunology and Cancer (IRIC), Université de Montréal, Montréal, QC H3T 1J4, Canada
| | - Sahil Kumar
- Department of Medicine, Research Institute of the McGill University Health Center (RI-MUHC), McGill University, Montréal, QC H4A 3J1, Canada
| | - Yubo Cao
- Department of Pharmacology and Therapeutics, McGill University, Montréal, QC H3G 1Y6, Canada
| | - Larissa B Teixeira
- Department of Biochemistry and Molecular Medicine, Institute for Research in Immunology and Cancer (IRIC), Université de Montréal, Montréal, QC H3T 1J4, Canada.,Departamento de Bioquímica e Imunologia, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, São Paulo 14049-900, Brazil
| | - Viktoriya Lukasheva
- Department of Biochemistry and Molecular Medicine, Institute for Research in Immunology and Cancer (IRIC), Université de Montréal, Montréal, QC H3T 1J4, Canada
| | - Jenna Giubilaro
- Department of Pharmacology and Therapeutics, McGill University, Montréal, QC H3G 1Y6, Canada
| | - Sarah C Simões
- Departamento de Bioquímica e Imunologia, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, São Paulo 14049-900, Brazil
| | - Jean-Michel Longpré
- Institut de Pharmacologie de Sherbrooke and Department of Pharmacology-Physiology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, QC J1H 5N4, Canada
| | - Dominic Devost
- Department of Pharmacology and Therapeutics, McGill University, Montréal, QC H3G 1Y6, Canada
| | - Terence E Hébert
- Department of Pharmacology and Therapeutics, McGill University, Montréal, QC H3G 1Y6, Canada
| | - Graciela Piñeyro
- Centre de Recherche de l'Hôpital Sainte-Justine, Montréal, QC H3T 1C5, Canada
| | - Richard Leduc
- Institut de Pharmacologie de Sherbrooke and Department of Pharmacology-Physiology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, QC J1H 5N4, Canada
| | - Claudio M Costa-Neto
- Departamento de Bioquímica e Imunologia, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, São Paulo 14049-900, Brazil
| | - Michel Bouvier
- Department of Biochemistry and Molecular Medicine, Institute for Research in Immunology and Cancer (IRIC), Université de Montréal, Montréal, QC H3T 1J4, Canada.
| | - Stéphane A Laporte
- Department of Medicine, Research Institute of the McGill University Health Center (RI-MUHC), McGill University, Montréal, QC H4A 3J1, Canada. .,Department of Pharmacology and Therapeutics, McGill University, Montréal, QC H3G 1Y6, Canada.,Department of Anatomy and Cell Biology, McGill University, Montréal, QC H3A 0C7, Canada
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3
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Bella Ndong D, Blais V, Holleran BJ, Proteau-Gagné A, Cantin-Savoie I, Robert W, Nadon JF, Beauchemin S, Leduc R, Piñeyro G, Guérin B, Gendron L, Dory YL. Exploration of the fifth position of leu-enkephalin and its role in binding and activating delta (DOP) and mu (MOP) opioid receptors. Pept Sci (Hoboken) 2018. [DOI: 10.1002/pep2.24070] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
- Dominique Bella Ndong
- Institut de Pharmacologie, Université de Sherbrooke, 3001 12 av. Nord; Sherbrooke Québec J1H 5N4 Canada
- Département de Biochimie, Faculté de Médecine et des Sciences de la Santé; Université de Sherbrooke; Sherbrooke Québec Canada
| | - Véronique Blais
- Institut de Pharmacologie, Université de Sherbrooke, 3001 12 av. Nord; Sherbrooke Québec J1H 5N4 Canada
- Département de Pharmacologie-Physiologie, Faculté de Médecine et des Sciences de la Santé; Université de Sherbrooke; Sherbrooke Québec Canada
| | - Brian J. Holleran
- Institut de Pharmacologie, Université de Sherbrooke, 3001 12 av. Nord; Sherbrooke Québec J1H 5N4 Canada
- Département de Pharmacologie-Physiologie, Faculté de Médecine et des Sciences de la Santé; Université de Sherbrooke; Sherbrooke Québec Canada
| | - Arnaud Proteau-Gagné
- Institut de Pharmacologie, Université de Sherbrooke, 3001 12 av. Nord; Sherbrooke Québec J1H 5N4 Canada
- Département de Chimie, Facult des Sciences; Université de Sherbrooke; Sherbrooke Québec Canada
| | - Isabelle Cantin-Savoie
- Institut de Pharmacologie, Université de Sherbrooke, 3001 12 av. Nord; Sherbrooke Québec J1H 5N4 Canada
- Département de Chimie, Facult des Sciences; Université de Sherbrooke; Sherbrooke Québec Canada
| | - William Robert
- Institut de Pharmacologie, Université de Sherbrooke, 3001 12 av. Nord; Sherbrooke Québec J1H 5N4 Canada
- Département de Pharmacologie-Physiologie, Faculté de Médecine et des Sciences de la Santé; Université de Sherbrooke; Sherbrooke Québec Canada
| | - Jean-François Nadon
- Institut de Pharmacologie, Université de Sherbrooke, 3001 12 av. Nord; Sherbrooke Québec J1H 5N4 Canada
- Département de Chimie, Facult des Sciences; Université de Sherbrooke; Sherbrooke Québec Canada
| | - Sophie Beauchemin
- Institut de Pharmacologie, Université de Sherbrooke, 3001 12 av. Nord; Sherbrooke Québec J1H 5N4 Canada
- Département de Chimie, Facult des Sciences; Université de Sherbrooke; Sherbrooke Québec Canada
| | - Richard Leduc
- Institut de Pharmacologie, Université de Sherbrooke, 3001 12 av. Nord; Sherbrooke Québec J1H 5N4 Canada
- Département de Pharmacologie-Physiologie, Faculté de Médecine et des Sciences de la Santé; Université de Sherbrooke; Sherbrooke Québec Canada
- Centre de recherche du CHU de Sherbrooke; Sherbrooke Québec Canada
| | - Graciela Piñeyro
- Département de Psychiatrie, Centre de Recherche du CHU Ste-Justine; Université de Montréal; Montreal Québec Canada
| | - Brigitte Guérin
- Institut de Pharmacologie, Université de Sherbrooke, 3001 12 av. Nord; Sherbrooke Québec J1H 5N4 Canada
- Centre de recherche du CHU de Sherbrooke; Sherbrooke Québec Canada
- Département de Médecine Nucléaire et de Radiobiologie, Faculté de Médecine et des Sciences de la Santé; Université de Sherbrooke; Sherbrooke Québec Canada
| | - Louis Gendron
- Institut de Pharmacologie, Université de Sherbrooke, 3001 12 av. Nord; Sherbrooke Québec J1H 5N4 Canada
- Département de Pharmacologie-Physiologie, Faculté de Médecine et des Sciences de la Santé; Université de Sherbrooke; Sherbrooke Québec Canada
- Centre de recherche du CHU de Sherbrooke; Sherbrooke Québec Canada
| | - Yves L. Dory
- Institut de Pharmacologie, Université de Sherbrooke, 3001 12 av. Nord; Sherbrooke Québec J1H 5N4 Canada
- Département de Chimie, Facult des Sciences; Université de Sherbrooke; Sherbrooke Québec Canada
- Centre de recherche du CHU de Sherbrooke; Sherbrooke Québec Canada
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4
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Nagi K, Piñeyro G. Regulation of opioid receptor signalling: implications for the development of analgesic tolerance. Mol Brain 2011; 4:25. [PMID: 21663702 PMCID: PMC3138391 DOI: 10.1186/1756-6606-4-25] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2011] [Accepted: 06/13/2011] [Indexed: 11/10/2022] Open
Abstract
Opiate drugs are the most effective analgesics available but their clinical use is restricted by severe side effects. Some of these undesired actions appear after repeated administration and are related to adaptive changes directed at counteracting the consequences of sustained opioid receptor activation. Here we will discuss adaptations that contribute to the development of tolerance. The focus of the first part of the review is set on molecular mechanisms involved in the regulation of opioid receptor signalling in heterologous expression systems and neurons. In the second part we assess how adaptations that take place in vivo may contribute to analgesic tolerance developed during repeated opioid administration.
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Affiliation(s)
- Karim Nagi
- Département de Pharmacologie, Faculté de Médecine, Université de Montréal, Canada
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Abstract
Bioluminescence energy transfer (BRET) has become a powerful tool to study protein-protein interactions and conformational changes among interacting proteins. In particular, BRET assays performed in living cells have revealed that heptahelical receptors (7TMRs), heterotrimeric G proteins and their proximal effectors form constitutive signalling complexes. BRET technology has also allowed us to demonstrate that these multimeric protein arrays remain intact throughout initial stages of receptor signalling, thus providing a platform for direct transmission of conformational information from activated receptors to downstream signalling partners. A clear example of the latter are the distinct intermolecular re-arrangements undergone by 7TMRs and G protein subunits following activation of the receptor by different ligands. Here we present protocols describing the type of BRET assay that has been used to reveal the existence of constitutive signalling arrays formed by 7TMRs and proximal signalling partners as well as the ability of complex components to undergo ligand-specific conformational changes.
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Affiliation(s)
- Nicolas Audet
- Department of Pharmacology, Faculty of Medicine, University of Montreal, Montreal, QC, Canada
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6
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Mnie-Filali O, Amraei MG, Benmbarek S, Archer-Lahlou E, Peñas-Cazorla R, Vilaró MT, Boye SM, Piñeyro G. Serotonin 4 receptor (5-HT4R) internalization is isoform-specific: effects of 5-HT and RS67333 on isoforms A and B. Cell Signal 2010; 22:501-9. [PMID: 19922792 DOI: 10.1016/j.cellsig.2009.11.004] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2009] [Revised: 10/25/2009] [Accepted: 11/09/2009] [Indexed: 11/25/2022]
Abstract
Serotonin 4 receptors (5-HT4Rs) are particularly abundant within the limbic system, where they constitute potential targets for the development of novel, rapid acting antidepressants. However, the population of limbic 5-HT4Rs is not homogenous, comprising various isoforms of which 5-HT4(a) and 5-HT4(b) are among the most abundant variants. Sequence divergence at their C-termini is predictive of specificity in isoform signalling and regulation, but the differences, if any, remain ill-defined. The present study compared isoforms 5-HT4(a) and 5-HT4(b) in their ability to undergo endocytic regulation following exposure to 5-HT and to the putatively fast acting antidepressant RS67333. Both ligands differed in their ability to induce internalization of either isoform, 5-HT being more effective than RS67333 in HEK293 cells and in neurons. In contrast, trafficking induced by 5-HT was isoform-specific. In particular, while PKC, GRK2 and betaarrestin were necessary for 5-HT4(a)R internalization, sequestration of 5-HT4(b)Rs required PKC but not GRK2 and relied significantly less on betaarrestin. After endocytosis, isoform (b) appeared scattered throughout the intracellular compartment and efficiently recycled to the membrane upon agonist removal. Isoform (a) accumulated in the perinuclear compartment and displayed little recycling. Isoform-specific subcellular distribution was present in HEK293 cells and in neurons. In neurons, where internalization by RS67333 was more pronounced than in HEK293 cells, receptors internalized by this ligand followed the same distribution pattern as observed with 5-HT. These results point to isoform-related differences in the way that 5-HTRs respond to different ligands. Such diversity should be taken into account when developing therapeutic agents that target 5-HT4Rs.
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Affiliation(s)
- O Mnie-Filali
- Department of Pharmacology, Faculty of Medicine, University of Montreal, and Centre de Recherche de l'Hôpital Ste Justine, Montreal, Quebec, Canada
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7
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Lucas G, Du J, Romeas T, Mnie-Filali O, Haddjeri N, Piñeyro G, Debonnel G. Selective serotonin reuptake inhibitors potentiate the rapid antidepressant-like effects of serotonin4 receptor agonists in the rat. PLoS One 2010; 5:e9253. [PMID: 20169084 PMCID: PMC2821932 DOI: 10.1371/journal.pone.0009253] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2009] [Accepted: 01/09/2010] [Indexed: 01/22/2023] Open
Abstract
BACKGROUND We have recently reported that serotonin(4) (5-HT(4)) receptor agonists have a promising potential as fast-acting antidepressants. Here, we assess the extent to which this property may be optimized by the concomitant use of conventional antidepressants. METHODOLOGY/PRINCIPAL FINDINGS We found that, in acute conditions, the 5-HT(4) agonist prucalopride was able to counteract the inhibitory effect of the selective serotonin reuptake inhibitors (SSRI) fluvoxamine and citalopram on 5-HT neuron impulse flow, in Dorsal Raphé Nucleus (DRN) cells selected for their high (>1.8 Hz) basal discharge. The co-administration of both prucalopride and RS 67333 with citalopram for 3 days elicited an enhancement of DRN 5-HT neuron average firing rate, very similar to what was observed with either 5-HT(4) agonist alone. At the postsynaptic level, this translated into the manifestation of a tonus on hippocampal postsynaptic 5-HT(1A) receptors, that was two to three times stronger when the 5-HT(4) agonist was combined with citalopram. Similarly, co-administration of citalopram synergistically potentiated the enhancing effect of RS 67333 on CREB protein phosphorylation within the hippocampus. Finally, in the Forced Swimming Test, the combination of RS 67333 with various SSRIs (fluvoxamine, citalopram and fluoxetine) was more effective to reduce time of immobility than the separate administration of each compound. CONCLUSIONS/SIGNIFICANCE These findings strongly suggest that the adjunction of an SSRI to a 5-HT(4) agonist may help to optimize the fast-acting antidepressant efficacy of the latter.
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Affiliation(s)
- Guillaume Lucas
- Department of Psychiatry, Centre de Recherche Fernand Seguin, Université de Montréal, Montréal, Québec, Canada.
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8
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Lucas G, Rymar VV, Du J, Mnie-Filali O, Bisgaard C, Manta S, Lambas-Senas L, Wiborg O, Haddjeri N, Piñeyro G, Sadikot AF, Debonnel G. Serotonin(4) (5-HT(4)) receptor agonists are putative antidepressants with a rapid onset of action. Neuron 2007; 55:712-25. [PMID: 17785179 DOI: 10.1016/j.neuron.2007.07.041] [Citation(s) in RCA: 202] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2005] [Revised: 07/24/2006] [Accepted: 07/29/2007] [Indexed: 10/22/2022]
Abstract
Current antidepressants are clinically effective only after several weeks of administration. Here, we show that serotonin(4) (5-HT(4)) agonists reduce immobility in the forced swimming test, displaying an antidepressant potential. Moreover, a 3 day regimen with such compounds modifies rat brain parameters considered to be key markers of antidepressant action, but that are observed only after 2-3 week treatments with classical molecules: desensitization of 5-HT(1A) autoreceptors, increased tonus on hippocampal postsynaptic 5-HT(1A) receptors, and enhanced phosphorylation of the CREB protein and neurogenesis in the hippocampus. In contrast, a 3 day treatment with the SSRI citalopram remains devoid of any effect on these parameters. Finally, a 3 day regimen with the 5-HT(4) agonist RS 67333 was sufficient to reduce both the hyperlocomotion induced by olfactory bulbectomy and the diminution of sucrose intake consecutive to a chronic mild stress. These findings point out 5-HT(4) receptor agonists as a putative class of antidepressants with a rapid onset of action.
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Affiliation(s)
- Guillaume Lucas
- Université McGill, Département de Psychiatrie, Bâtiment de Recherche et de Formation, Bureau 207, 1033 Avenue des Pins Ouest, Montréal, QC, H3A 1A1 Canada.
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9
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Piñeyro G, Archer-Lahlou E. Ligand-specific receptor states: Implications for opiate receptor signalling and regulation. Cell Signal 2007; 19:8-19. [PMID: 16842969 DOI: 10.1016/j.cellsig.2006.05.026] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2006] [Accepted: 05/29/2006] [Indexed: 10/24/2022]
Abstract
Opiate drugs produce their effects by acting upon G protein coupled receptors (GPCRs) and although they are among the most effective analgesics available, their clinical use is restricted by unwanted side effects such as tolerance, physical dependence, respiratory depression, nausea and constipation. As a class, opiates share a common profile of unwanted effects but there are also significant differences in ligand liability for producing these actions. A growing number of studies show that GPCRs may exist in multiple active states that differ in their signalling and regulatory properties and which may distinctively bind different agonists. In this review we summarize evidence supporting the existence of multiple active conformations for MORs and DORs, analyze information favouring the existence of ligand-specific receptor states and assess how ligand-selective efficacy may contribute to the production of longer lasting, better tolerated opiate analgesics.
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Affiliation(s)
- Graciela Piñeyro
- Département de Pharmacologie, Faculté de Médecine, Université de Montréal, Canada.
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10
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Audet N, Paquin-Gobeil M, Landry-Paquet O, Schiller PW, Piñeyro G. Internalization and Src activity regulate the time course of ERK activation by delta opioid receptor ligands. J Biol Chem 2005; 280:7808-16. [PMID: 15632168 DOI: 10.1074/jbc.m411695200] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The present study showed that delta opioid receptor (deltaOR) ligands Tyr-Ticpsi [CH(2)-NH]Cha-Phe-OH (TICP) and ICI174864 behaved as inverse agonists in the cyclase pathway but induced agonist responses in the ERK cascade. Unlike ligands that behaved as agonists in both pathways, and whose stimulation of ERK was marked but transient (10 min), ERK activation by ICI174864 and TICP was moderate and sustained, lasting for more than 1 h in the case of TICP. Biochemical experiments showed that duration of ERK activation by agonists and "dual efficacy ligands" was inversely correlated with their ability to trigger receptor phosphorylation and degradation. Thus, although TICP stabilized deltaORs in a conformation that did not incorporate (32)P, was not a substrate for tyrosine kinase Src, and was not down-regulated following prolonged exposure to the drug, the conformation stabilized by D-Pen-2,5-enkephalin (DPDPE) incorporated (32)P, was phosphorylated by Src, and suffered degradation within the first 2 h of treatment. Inhibition of endocytosis by sucrose prolonged ERK activation by DPDPE increasing the decay half-life of the response to values that resembled those of dual efficacy ligands (from a 2-min decay t((1/2)) increased to 12 min). Src inhibitor PP2 also prolonged ERK stimulation by DPDPE. It did so by maintaining a sustained activation of the kinase at approximately 20% of maximum following an initial rapid reduction in the response. These results show that specific kinetics of ERK activation by agonists and dual efficacy ligands are determined, at least in part, by the differential ability of the two types of drugs to trigger mechanisms regulating deltaOR responsiveness.
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Affiliation(s)
- Nicolas Audet
- Département de Pharmacologie, Université de Montréal, Quebec, Canada
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11
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Piñeyro G, Azzi M, deLéan A, Schiller PW, Bouvier M. Reciprocal regulation of agonist and inverse agonist signaling efficacy upon short-term treatment of the human delta-opioid receptor with an inverse agonist. Mol Pharmacol 2004; 67:336-48. [PMID: 15496503 DOI: 10.1124/mol.104.004549] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Rapid regulation of receptor signaling by agonist ligands is widely accepted, whereas short-term adaptation to inverse agonists has been little documented. In the present study, guanosine 5'-O-(3-[(35)S]thio)triphosphate ([(35)S]GTPgammaS) binding and cAMP accumulation assays were used to assess the consequences of 30-min exposure to the inverse agonist N,N-diallyl-Tyr-Aib-Aib-Phe-Leu-OH (ICI174864) (1 microM) on delta-opioid receptor signaling efficacy. ICI174864 pretreatment increased maximal effect (E(max)) for the partial agonist Tyr-1,2,3,4-tetrahydroisoquinoline-Phe-Phe-OH (TIPP) at the two levels of the signaling cascade, whereas E(max) values for more efficacious agonists like (+)-4-[(alphaR)-alpha-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide (SNC-80) and bremazocine were increased in [(35)S]GTPgammaS binding but not in cAMP accumulation assays. Pre-exposure to ICI174864 also induced a shift to the left in dose-response curves for bremazocine and TIPP. On the other hand, E(max) for the inverse agonist H-Tyr-TicPsi[CH(2)NH]Cha-Phe-OH was reduced in both assays, but no changes in potency were observed. For the weaker inverse agonist naloxone, E(max) in [(35)S]GTPgammaS binding was drastically modified because the drug turned from inverse agonist to agonist after ICI174864 pretreatment. Likewise, ICI174864 turned from inverse agonist to agonist when tested in cAMP accumulation assays. In both cases, inversion of efficacy was concomitant with marked increase in potency for agonist effects. Together with functional changes, short-term treatment with ICI174864 reduced basal receptor phosphorylation and increased immunoreactivity for Galpha(i3) in membrane preparations. Functional consequences of ICI174864 pretreatment were simulated in the cubic ternary complex model by increasing receptor/G protein coupling or G protein amount available for interaction with the receptor. Taken together, these data show that inverse agonists may induce rapid regulation in receptor signaling efficacy.
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Affiliation(s)
- Graciela Piñeyro
- Centre de Recherche Fernand Séguin, 7331 Rue Hochelaga, Montréal, Québec, H1N 3V2 Canada.
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Azzi M, Charest PG, Angers S, Rousseau G, Kohout T, Bouvier M, Piñeyro G. Beta-arrestin-mediated activation of MAPK by inverse agonists reveals distinct active conformations for G protein-coupled receptors. Proc Natl Acad Sci U S A 2003; 100:11406-11. [PMID: 13679574 PMCID: PMC208770 DOI: 10.1073/pnas.1936664100] [Citation(s) in RCA: 390] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
It is becoming increasingly clear that signaling via G protein-coupled receptors is a diverse phenomenon involving receptor interaction with a variety of signaling partners. Despite this diversity, receptor ligands are commonly classified only according to their ability to modify G protein-dependent signaling. Here we show that beta2AR ligands like ICI118551 and propranolol, which are inverse agonists for Gs-stimulated adenylyl cyclase, induce partial agonist responses for the mitogen-activated protein kinases extracellular signal-regulated kinase (ERK) 1/2 thus behaving as dual efficacy ligands. ERK1/2 activation by dual efficacy ligands was not affected by ADP-ribosylation of Galphai and could be observed in S49-cyc- cells lacking Galphas indicating that, unlike the conventional agonist isoproterenol, these drugs induce ERK1/2 activation in a Gs/i-independent manner. In contrast, this activation was inhibited by a dominant negative mutant of beta-arrestin and was abolished in mouse embryonic fibroblasts lacking beta-arrestin 1 and 2. The role of beta-arrestin was further confirmed by showing that transfection of beta-arrestin 2 in these knockout cells restored ICI118551 promoted ERK1/2 activation. ICI118551 and propranolol also promoted beta-arrestin recruitment to the receptor. Taken together, these observations suggest that beta-arrestin recruitment is not an exclusive property of agonists, and that ligands classically classified as inverse agonists rely exclusively on beta-arrestin for their positive signaling activity. This phenomenon is not unique to beta2-adrenergic ligands because SR121463B, an inverse agonist on the V2 vasopressin receptor-stimulated adenylyl cyclase, recruited beta-arrestin and stimulated ERK1/2. These results point to a multistate model of receptor activation in which ligand-specific conformations are capable of differentially activating distinct signaling partners.
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Affiliation(s)
- Mounia Azzi
- Department of Biochemistry, Université de Montréal, Montréal, QC, Canada H3C 3J7
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Azzi M, Piñeyro G, Pontier S, Parent S, Ansanay H, Bouvier M. Allosteric effects of G protein overexpression on the binding of beta-adrenergic ligands with distinct inverse efficacies. Mol Pharmacol 2001; 60:999-1007. [PMID: 11641428 DOI: 10.1124/mol.60.5.999] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Allosteric models of G protein-coupled receptors predict that G protein influences the spontaneous isomerization between inactive (R) and active (R*) conformations. Since inverse agonists have been proposed to preferentially bind to the inactive and uncoupled form(s), changes in the G protein content should influence the binding properties of these ligands. To test this hypothesis, we systematically assessed the effect of G proteins on the binding of beta(2)-adrenergic ligands with distinct levels of inverse efficacy. Recombinant baculoviruses encoding the human beta(2)-adrenoreceptor (beta(2)AR) were expressed alone or in combination with G protein subunits in Sf9 cells. Coexpression with the G protein alpha s beta 1 gamma 2 did not influence the relative efficacy of the ligands to inhibit the adenylyl cyclase but induced considerable decrease in number of sites detected by [(3)H]ICI 118551, [(3)H]propranolol, and (125)I-cyanopindolol. This loss was proportional to the inverse efficacy of the ligand used as the radiotracer in the assay. The addition of Gpp(NH)p inhibited the effects of G protein overexpression indicating that the G proteins acted allosterically. Consistent with this notion, Western blot analysis revealed that coexpression with the G proteins was not accompanied by a loss of immunoreactive beta(2)AR. Such allosteric effects of the G proteins were also observed in mammalian cells expressing endogenous level of G proteins indicating that the phenomenon is not unique to overexpression systems. Taken together, these results demonstrate that the apparent receptor number detected by radiolabeled inverse agonists is affected by the content in G proteins as a result of their influence on R/R* isomerization.
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Affiliation(s)
- M Azzi
- Département de Biochimie and le Groupe de Recherches sur le Système Nerveux Autonome, Université de Montréal, Montréal, Québec, Canada
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Piñeyro G, Azzi M, De Léan A, Schiller P, Bouvier M. Short-term inverse-agonist treatment induces reciprocal changes in delta-opioid agonist and inverse-agonist binding capacity. Mol Pharmacol 2001; 60:816-27. [PMID: 11562445] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/21/2023] Open
Abstract
This study assessed the effects of short-term treatment (30-min) with inverse agonists on receptor protein levels and on the ability of agonists, inverse agonists, and neutral antagonists to bind to the human delta-opioid receptor (h delta OR). Incubation of human embryonic kidney 293s cells stably expressing h delta OR with the inverse agonist ICI174864 (1 microM) induced reciprocal changes in agonist and inverse-agonist binding. The total number of binding sites recognized by the agonists [(3)H]bremazocine and [(3)H][D-Pen(2),D-Pen(5)]-enkephalin was reduced by 33 and 57%, respectively, whereas binding capacity for the radiolabeled inverse-agonist [(3)H]Tyr-TicY[CH(2)NH]Cha-Phe-OH increased by 44%. In contrast, total receptor protein and sites labeled by neutral antagonists [(3)H]naltrindole and [(3)H]Tyr-D-Tic-Phe-Phe-OH remained unchanged. Pertussis toxin (PTX) and 5-guanylylimidodiphosphate (GppNHp) mimicked the outcome of ICI174864 pretreatment in promoting the loss of agonist binding sites. The lack of an additive effect on [(3)H]bremazocine binding when these three agents were combined indicates that inverse agonists may, in part, share the mechanism by which GppNHp and PTX reduce agonist binding capacity. Spontaneous recovery of maximal agonist binding capacity after inverse-agonist treatment was slow, suggesting a decrease in the isomerization rate between agonist- and inverse agonist-preferring conformations. Overall, the data presented are consistent with the idea that h delta ORs exist in multiple states capable of discriminating among ligands of different levels of efficacy and show that, after short-term treatment with an inverse agonist, the receptor ability to adopt conformations preferentially induced by agonist ligands is reduced.
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Affiliation(s)
- G Piñeyro
- Département de Biochimie, Université de Montréal, Montréal, Canada
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Piñeyro G, Blier P. Autoregulation of serotonin neurons: role in antidepressant drug action. Pharmacol Rev 1999; 51:533-91. [PMID: 10471417] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/13/2023] Open
Affiliation(s)
- G Piñeyro
- Department of Psychiatry, Neurobiological Psychiatry Unit, McGill University, Montreal, Quebec, Canada
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Abstract
A very important element controlling serotonin (5-HT) release throughout the brain is the 5-HT1A autoreceptor present on the soma and dendrites of 5-HT neurons since it exerts a negative feedback influence on their firing activity. This 5-HT1A autoreceptor receives an increased activation by endogenous 5-HT at the beginning of a treatment with a selective 5-HT reuptake inhibitor (SSRI) and, consequently, a decreased 5-HT neuronal firing activity is obtained. As the SSRI treatment is prolonged, the 5-HT1A autoreceptor desensitizes and firing activity is restored in the presence of the SSRI. That this adaptive change underlies, at least in part, the delayed therapeutic effect of SSRI in major depression is supported by the acceleration of the antidepressant response by the concomitant administration of the 5-HT1A autoreceptor antagonist pindolol with SSRIs.
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Affiliation(s)
- P Blier
- Neurobiological Psychiatry Unit, McGill University, Montréal, Québec, Canada
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Piñeyro G, Blier P. Regulation of 5-hydroxytryptamine release from rat midbrain raphe nuclei by 5-hydroxytryptamine1D receptors: effect of tetrodotoxin, G protein inactivation and long-term antidepressant administration. J Pharmacol Exp Ther 1996; 276:697-707. [PMID: 8632339] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Our study was undertaken to characterize the functional properties of 5-hydroxytryptamine (5-HT)1D receptors in the rat midbrain raphe nuclei. In a first series of experiments, designed to assess whether 5-HT1D receptors are coupled to Gi/o proteins, the intracerebral injection of pertussis toxin into the dorsal raphe as well as incubation of midbrain raphe slices with the alkylating agent N-ethyl-maleimide (NEM) reduced the efficacy of the 5-HT1B/1D agonist sumatriptan to inhibit the electrically evoked overflow of [3H]5-HT from preloaded slices. Furthermore, preincubation with NEM also reduced the efficacy with which the 5-HT1B/1D antagonist GR 127935 enhanced evoked overflow of [3H]5-HT. These results indicate that, in rat midbrain raphe nuclei, 5-HT1D receptors are linked to Gi/o proteins. In an attempt to determine whether 5-HT1D receptors are located on 5-HT neurons, the inhibitory effect of sumatriptan and of the nonselective 5-HT agonist 5-carboxyamidotryptamine on K(+)-evoked overflow of [3H]5-HT was assessed in the presence of the Na+ channel blocker tetrodotoxin. Neither the inhibitory effect of sumatriptan nor that of 5-carboxyamidotryptamine were reduced by the addition of tetrodotoxin to the superfusion medium, suggesting that these 5-HT1D receptors are located on 5-HT neurons and may be considered autoreceptors. In a third series of experiments, rats were treated for 21 days either with the selective 5-HT reuptake inhibitor paroxetine (10 mg/kg/day, s.c.) or the reversible type A monoamine oxidase inhibitor befloxatone (0.75 mg/kg/day, s.c.) and superfusion experiments were performed after a 48-hr washout period. 5-HT1D receptors, similarly to 5-HT1A autoreceptors, desensitize after long-term treatment with a selective 5-HT reuptake inhibitor or a reversible type A monoamine oxidase inhibitor because the efficacy of sumatriptan and of 8-OH-DPAT to inhibit the electrically evoked overflow of [3H]5-HT was reduced after the administration of either drug.
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Affiliation(s)
- G Piñeyro
- Department of Psychiatry, McGill University, Montreal, Quebec, Canada
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Abstract
In the present study, the hypothesis that somatodendritic availability of 5-hydroxytryptamine (5-HT) could be regulated independently of the firing activity of dorsal raphe 5-HT neurons was tested. The 5-HT pathway was electrically stimulated at the level of the ventromedial tegmentum and the ensuing action potentials, recorded in the dorsal raphe, met all criteria for antidromic invasion of 5-HT neurons. The latency of antidromic spikes was current-dependent and the changes in latency were of quantal nature. This observation suggests an electrotonic coupling between 5-HT neurons. Stimulation of the ventromedial tegmentum also induced a decrease in the probability of firing of 5-HT neurons. This reduction in 5-HT neuron firing activity is a 5-HT-mediated response, due to an increased bioavailability of the neurotransmitter in the biophase of somatodendritic 5-HT1A autoreceptors. The intravenous administration of the 5-HT1 agonists TFMPP and RU 24969 reduced the duration of suppression of firing induced by the 5-HT-pathway stimulation, without altering the spontaneous firing rate of 5-HT neurons. The effect of TFMPP and RU 24969 on duration of suppression was blocked by (+-)mianserin, a drug with high affinity for the rat 5-HT1D, but not 5-HT1B, receptors. On the other hand, (-)propranolol, a mixed 5-HT antagonist also blocked the effect of TFMPP. However, the selective 5-HT1A antagonist (+)WAY 100135 did not alter the effect of TFMPP. These results, in keeping with previous anatomical studies, suggest the existence of electrotonic coupling of 5-HT neurons and indicate that 5-HT release in the rat dorsal raphe nucleus may be controlled independently of firing-regulating 5-HT1A autoreceptors. They also suggest that 5-HT1D receptors may play a role in this regulatory function of 5-HT neurons.
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Affiliation(s)
- G Piñeyro
- Department of Psychiatry, McGill University, Montreal, Quebec, Canada
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Piñeyro G, Castanon N, Hen R, Blier P. Regulation of [3H]5-HT release in raphe, frontal cortex and hippocampus of 5-HT1B knock-out mice. Neuroreport 1995; 7:353-9. [PMID: 8742487] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Regulation of the electrically evoked release of [3H]5-HT was examined in midbrain, frontal cortex and hippocampus preloaded slices obtained from wild-type and 5-HT1B knock-out mice. In the absence of any drug [3H]5-HT released was increased in midbrain and hippocampus but not in frontal cortex slices of [3H]5-HT1B knock out mice. The selective 5-HT1B agonist CP 93129 and the 5-HT1B/1D agonist sumatriptan, inhibited [3H]5-HT release in hippocampus and cortical slices obtained from control mice but had no effect in mutants. In the two projection areas studied, the non-selective 5-HT agonist 5-carboxyamidotryptamine (5-CT) inhibited [3H]5-HT release in both groups of mice, indicating that additional 5-HT receptors, other than 5-HT1B, might be involved in the regulation of [3H]5-HT release from 5-HT terminals. In slices containing midbrain raphe nuclei, CP 93129 had no effect in either group. In contrast, sumatriptan inhibited [3H]5-HT release in controls and mutants. The latter effect was blocked by the 5-HT1D antagonist GR 127935, but not the 5-HT1A antagonist (+)WAY 100135, thus suggesting that a 5-HT1D-like receptor, possibly 5-HT1D alpha, negatively regulates 5-HT release in mouse midbrain raphe nuclei.
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Affiliation(s)
- G Piñeyro
- Neurobiological Psychiatry Unit, McGill University, Montreal, Quebec, Canada
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Abstract
The aim of the present study was to characterize the pharmacological profile of 5-hydroxytryptamine (5-HT) receptors modulating 5-HT release in the mesencephalic raphe region. In a first series of experiments, differential normal pulse voltammetry and nafion-coated electrodes were used to measure extracellular 5-HT in the dorsal raphe of anesthesized rats. The intravenous administration of the selective 5-HT1A agonist 8-OH-DPAT (30 micrograms/kg) and the 5-HT1 agonist TFMPP (0.5 mg/kg) reduced the 5-hydroxyindole signal by 23% and 18%, respectively. Pretreatment with the 5-HT1A antagonist (+)WAY100135 (0.5 mg/kg IV) 30 minutes before the injection of the agonists, blocked the effect of 8-OH-DPAT but not that of TFMPP. The effect of TFMPP was blocked by (+/-)mianserin, a drug with high affinity for the rat 5-HT1D receptor, suggesting a role of this receptor subtype in the modulation of 5-HT release at the cell body level of 5-HT neurons. This was confirmed by in vitro superfusion experiments using mesencephalic raphe slices. The prototypical 5-HT1 agonist 5-carboxy-amiditryptamine (5-CT) and the 5-HT1B/1D agonist sumatriptan (1-1,000 nM) induced a concentration-dependent inhibition of the electrically evoked release of [3H]5-HT from preloaded raphe slices. 8-OH-DPAT (100 nM) produced an inhibitory effect similar to that of sumatriptan (100 nM). The selective 5-HT1B agonist CP 93129 (10-10,000 nM), had no effect in raphe slices, but it dose dependently inhibited [3H]5-HT release from hippocampal slices where autoreceptors are of the 5-HT1B subtype. The inhibitory effect of 5-CT was blocked by the 5-HT1/2 antagonist methiothepin (1 microM), the 5-HT1A antagonist S-UH-301 (1 microM), and the 5-HT1B/1D antagonist GR 127935 (1 microM). That of 8-OH-DPAT was blocked by S-UH-301 (1 microM) but not by GR 127935 (1 microM), and that of sumatriptan was blocked by GR 127935 (1 microM) but not by S-UH-301 (1 microM). These results show that, together with 5-HT1A autoreceptors, 5-HT1D receptors negatively modulate the somatodendritic release of 5-HT.
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Affiliation(s)
- G Piñeyro
- Department of Psychiatry, McGill University, Montreal, Canada
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Piñeyro G, Deveault L, de Montigny C, Blier P. Effect of prolonged administration of tianeptine on 5-HT neurotransmission: an electrophysiological study in the rat hippocampus and dorsal raphe. Naunyn Schmiedebergs Arch Pharmacol 1995; 351:119-25. [PMID: 7770094 DOI: 10.1007/bf00169325] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Extracellular unitary recordings of dorsal hippocampus CA3 pyramidal neurons and of dorsal raphe 5-hydroxytryptamine (5-HT) neurons were used to assess the effect of tianeptine, a putative antidepressant, on the efficacy of 5-HT neurotransmission. Sustained tianeptine administration (20 mg/kg/day, s.c. x 14 days) did not modify the firing activity of 5-HT neurons in the dorsal raphe. Their responsiveness to the intravenous injection of LSD, an agonist of the somatodendritic 5-HT autoreceptor, and of 8-OH-DPAT, a selective 5-HT1A agonist, was also unaffected by this treatment. The responsiveness of CA3 pyramidal neurons to microiontophoretic application of 5-HT remained unchanged after sustained tianeptine administration, but it was markedly enhanced in rats treated with repeated electroconvulsive shocks. Finally, the duration of suppression of firing activity of CA3 pyramidal neurons produced by electrical stimulation of the ascending 5-HT pathway, delivered at 1 Hz and 5 Hz, was not modified in rats treated with tianeptine. Methiothepin, an antagonist of the terminal autoreceptor enhanced the effectiveness of 5-HT pathway stimulation to the same extent in control and tianeptine-treated rats. The present results indicate that, administered at a dose known to stimulate 5-HT reuptake (20 mg/kg/day, s.c.; by minipump), and for a period of time (14 days) for which other antidepressant treatments have been shown to enhance 5-HT function, tianeptine does not modify the efficacy of 5-HT synaptic transmission in the rat hippocampus.
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Affiliation(s)
- G Piñeyro
- Department of Psychiatry, McGill University, Montréal, Québec, Canada
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Piñeyro G, Deveault L, Blier P, Dennis T, de Montigny C. Effect of acute and prolonged tianeptine administration on the 5-HT transporter: electrophysiological, biochemical and radioligand binding studies in the rat brain. Naunyn Schmiedebergs Arch Pharmacol 1995; 351:111-8. [PMID: 7770093 DOI: 10.1007/bf00169324] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
In the present study, in vivo extracellular unitary recordings, in vitro [3H]5-HT uptake and [3H]cyanoimipramine binding assays were used to assess the effect of acute and prolonged administration of the putative antidepressant tianeptine, on the 5-hydroxytryptamine (5-HT) transporter. Microiontophoretic application of tianeptine onto dorsal hippocampus CA3 pyramidal neurons, as well as its intravenous administration (2 mg/kg), increased their firing frequency. Following intracerebroventricular administration of 5,7-dihydroxytryptamine, the activation induced by the microiontophoretic application of tianeptine remained unchanged, thus suggesting that the 5-HT carrier is not involved in this effect. Furthermore, in spite of its activating effect on CA3 pyramidal neuron firing frequency, the intravenous administration of tianeptine did not alter the time of recovery of these neurons from microiontophoretic applications of 5-HT, an index of 5-HT uptake activity. In keeping with this observation, the acute administration of tianeptine did not change the effectiveness of the 5-HT reuptake blocker paroxetine (1 mg/kg, i.v.) in prolonging the suppressant effect of microiontophoretically-applied 5-HT. However, in rats that had received tianeptine for 14 days (20 mg/kg/day, s.c.), the recovery time from the suppressant effect of microiontophoretic applications of 5-HT was reduced by 40% and the effectiveness of paroxetine (1 mg/kg, i.v.) was decreased. These effects were no longer observed following a 48 h washout period. In a second series of experiments, the ability of tianeptine to interfere with the uptake blocking capacity of paroxetine was assessed in vitro, using hippocampal slices obtained from rats that had been treated with tianeptine for 14 days (20 mg/kg/day, s.c.; by minipump).(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- G Piñeyro
- Department of Psychiatry, McGill University, Montréal, Québec, Canada
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Piñeyro G, Blier P, Dennis T, de Montigny C. Desensitization of the neuronal 5-HT carrier following its long-term blockade. J Neurosci 1994; 14:3036-47. [PMID: 8182457 PMCID: PMC6577511] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
In vivo extracellular unitary recordings, in vitro 3H-5-hydroxy-tryptamine (5-HT) uptake, and 3H-paroxetine binding assays were used to assess the effect of acute and long-term administration of the 5-HT reuptake inhibitor paroxetine on the neuronal 5-HT transporter in the rat dorsal hippocampus. Recovery time of the firing activity of CA3 hippocampus pyramidal neurons following microiontophoretic application of 5-HT was used as an index of in vivo reuptake activity. In a first series of experiments, the acute intravenous administration of paroxetine and 5-HT denervation with the neurotoxin 5,7-dihydroxytryptamine produced a marked prolongation of the suppressant effect of 5-HT, indicating that reuptake into 5-HT terminals plays a significant role in terminating the action of microiontophoretically applied 5-HT. In a second series of experiments, rats were treated with paroxetine (10 mg/kg/d, s.c.) for 2 or 21 d. In both treatment groups, there was a marked prolongation of the effect of microiontophoretically applied 5-HT; however, in rats treated for 2 d, the prolongation was significantly greater than that observed in rats treated for 21 d. After the 21 d treatment with paroxetine and a 48 hr washout, the prolongation of the effect of microiontophoretically applied 5-HT by acute intravenous paroxetine was significantly reduced, suggesting a decrease in the number of 5-HT carriers. In keeping with this interpretation, following the same treatment regimen, there was a 50% and 60% reduction of the in vitro 3H-5-HT uptake in hippocampal and dorsal raphe slices, respectively, and a reduced effectiveness of paroxetine in blocking 3H-5-HT uptake in both regions. The determination of the binding parameters of 3H-paroxetine revealed that, in rats treated for 21 d with paroxetine (10 mg/kg/d, s.c.), following a 48 hr washout Kd values were unchanged but Bmax values were reduced by 70% and 60% in hippocampal and cortical membranes, respectively.
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Affiliation(s)
- G Piñeyro
- McGill University, Department of Psychiatry, Montréal, Québec, Canada
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Piñeyro G, Monti J, Orellana C, Boussard M, Jantos H, Labraga P, Olivera S, Alvariño F. 5-HT receptor agonists 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and 8-OH-DPAT increase wakefulness in the rat. Eur J Pharmacol 1990. [DOI: 10.1016/0014-2999(90)94513-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Abstract
A study was carried out on the effects of midazolam 15 mg in conjunction with ethanol 0.5 g/kg on objective and subjective sleep parameters and psychomotor performance in normal subjects. Midazolam significantly decreased total wake time. Total sleep time (TST) increase was related to larger amounts of stage 2 NREM sleep. Ethanol showed similar effects on sleep, although TST increase was associated with nonsignificant increments of NREM sleep and REM sleep. Ethanol slightly potentiated midazolam effects on sleep. Accordingly, total wake time, REM sleep time and number of wakes showed further depression than with midazolam alone. Subjective evaluations showed relatively good correlation with sleep laboratory findings. In addition, the different treatments did not impair subject's psychomotor performance the morning after their administration.
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Affiliation(s)
- J M Monti
- Department of Pharmacology and Therapeutics, School of Medicine, Hospital de Clínicas PI, Montevideo, Uruguay
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