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Bellot-Saez A, Stevenson R, Kékesi O, Samokhina E, Ben-Abu Y, Morley JW, Buskila Y. Neuromodulation of Astrocytic K + Clearance. Int J Mol Sci 2021; 22:ijms22052520. [PMID: 33802343 PMCID: PMC7959145 DOI: 10.3390/ijms22052520] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2021] [Revised: 02/25/2021] [Accepted: 02/25/2021] [Indexed: 12/21/2022] Open
Abstract
Potassium homeostasis is fundamental for brain function. Therefore, effective removal of excessive K+ from the synaptic cleft during neuronal activity is paramount. Astrocytes play a key role in K+ clearance from the extracellular milieu using various mechanisms, including uptake via Kir channels and the Na+-K+ ATPase, and spatial buffering through the astrocytic gap-junction coupled network. Recently we showed that alterations in the concentrations of extracellular potassium ([K+]o) or impairments of the astrocytic clearance mechanism affect the resonance and oscillatory behavior of both the individual and networks of neurons. These results indicate that astrocytes have the potential to modulate neuronal network activity, however, the cellular effectors that may affect the astrocytic K+ clearance process are still unknown. In this study, we have investigated the impact of neuromodulators, which are known to mediate changes in network oscillatory behavior, on the astrocytic clearance process. Our results suggest that while some neuromodulators (5-HT; NA) might affect astrocytic spatial buffering via gap-junctions, others (DA; Histamine) primarily affect the uptake mechanism via Kir channels. These results suggest that neuromodulators can affect network oscillatory activity through parallel activation of both neurons and astrocytes, establishing a synergistic mechanism to maximize the synchronous network activity.
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Affiliation(s)
- Alba Bellot-Saez
- School of Medicine, Western Sydney University, Campbelltown, NSW 2560, Australia; (A.B.-S.); (R.S.); (O.K.); (E.S.); (J.W.M.)
| | - Rebecca Stevenson
- School of Medicine, Western Sydney University, Campbelltown, NSW 2560, Australia; (A.B.-S.); (R.S.); (O.K.); (E.S.); (J.W.M.)
| | - Orsolya Kékesi
- School of Medicine, Western Sydney University, Campbelltown, NSW 2560, Australia; (A.B.-S.); (R.S.); (O.K.); (E.S.); (J.W.M.)
| | - Evgeniia Samokhina
- School of Medicine, Western Sydney University, Campbelltown, NSW 2560, Australia; (A.B.-S.); (R.S.); (O.K.); (E.S.); (J.W.M.)
| | - Yuval Ben-Abu
- Projects and Physics Section, Sapir Academic College, D.N. Hof Ashkelon, Sderot 79165, Israel;
| | - John W. Morley
- School of Medicine, Western Sydney University, Campbelltown, NSW 2560, Australia; (A.B.-S.); (R.S.); (O.K.); (E.S.); (J.W.M.)
| | - Yossi Buskila
- School of Medicine, Western Sydney University, Campbelltown, NSW 2560, Australia; (A.B.-S.); (R.S.); (O.K.); (E.S.); (J.W.M.)
- International Centre for Neuromorphic Systems, The MARCS Institute, Western Sydney University, Penrith, NSW 2751, Australia
- Correspondence: ; Tel.: +61-246203853
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Abstract
Slices of neuronal tissue maintain a high degree of topographical and functional properties of neurons and glia and therefore are extensively used for measurements of neuronal activity at the molecular, cellular and network levels. However, the lifespan of slice preparations is narrow, averaging of 6-8 hours. Moreover, the average viability of brain slices varies according to animal age and region of interest, leading to the high variability and low reproducibility of recorded data. Previous techniques to increase the viability of brain slices focused on reducing cytotoxicity by chemical means, including alterations of the artificial cerebrospinal fluid (aCSF) composition to alleviate the direct damage of the slicing procedure or adding protective antioxidants to reduce cellular deterioration. In this protocol, we use a combination of hypothermia with firm control of the aCSF conditions in the recovery chamber (pH, temperature, and bacteria levels) to extend the slice viability significantly. Given the breadth of its usage, improving slice viability and longevity can considerably increase data reproducibility and reduce the cost, time, and number of animals used in neurophysiological studies.
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Affiliation(s)
- Orsolya Kékesi
- School of Medicine, Western Sydney University, Campbelltown, NSW, Australia.,Department of Physiology & Monash Biomedicine and Discovery Institute, Monash University, Melbourne, Victoria 3800, Australia
| | - Yossi Buskila
- School of Medicine, Western Sydney University, Campbelltown, NSW, Australia.,The MARCS Institute, Western Sydney University, Penrith, NSW, Australia
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Buskila Y, Kékesi O, Bellot-Saez A, Seah W, Berg T, Trpceski M, Yerbury JJ, Ooi L. Dynamic interplay between H-current and M-current controls motoneuron hyperexcitability in amyotrophic lateral sclerosis. Cell Death Dis 2019; 10:310. [PMID: 30952836 PMCID: PMC6450866 DOI: 10.1038/s41419-019-1538-9] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [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: 12/10/2018] [Revised: 03/13/2019] [Accepted: 03/19/2019] [Indexed: 12/13/2022]
Abstract
Amyotrophic lateral sclerosis (ALS) is a type of motor neuron disease (MND) in which humans lose motor functions due to progressive loss of motoneurons in the cortex, brainstem, and spinal cord. In patients and in animal models of MND it has been observed that there is a change in the properties of motoneurons, termed neuronal hyperexcitability, which is an exaggerated response of the neurons to a stimulus. Previous studies suggested neuronal excitability is one of the leading causes for neuronal loss, however the factors that instigate excitability in neurons over the course of disease onset and progression are not well understood, as these studies have looked mainly at embryonic or early postnatal stages (pre-symptomatic). As hyperexcitability is not a static phenomenon, the aim of this study was to assess the overall excitability of upper motoneurons during disease progression, specifically focusing on their oscillatory behavior and capabilities to fire repetitively. Our results suggest that increases in the intrinsic excitability of motoneurons are a global phenomenon of aging, however the cellular mechanisms that underlie this hyperexcitability are distinct in SOD1G93A ALS mice compared with wild-type controls. The ionic mechanism driving increased excitability involves alterations of the expression levels of HCN and KCNQ channel genes leading to a complex dynamic of H-current and M-current activation. Moreover, we show a negative correlation between the disease onset and disease progression, which correlates with a decrease in the expression level of HCN and KCNQ channels. These findings provide a potential explanation for the increased vulnerability of motoneurons to ALS with aging.
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Affiliation(s)
- Yossi Buskila
- Biomedical Engineering and Neuroscience research group, The MARCS Institute, Western Sydney University, Penrith, NSW, 2751, Australia. .,School of Medicine, Western Sydney University, Campbelltown, NSW, 2560, Australia.
| | - Orsolya Kékesi
- Biomedical Engineering and Neuroscience research group, The MARCS Institute, Western Sydney University, Penrith, NSW, 2751, Australia.,School of Medicine, Western Sydney University, Campbelltown, NSW, 2560, Australia.,School of Chemistry and Molecular Bioscience, University of Wollongong, Northfields Avenue, Wollongong, NSW, 2522, Australia.,Illawarra Health and Medical Research Institute, Northfields Avenue, Wollongong, NSW, 2522, Australia
| | - Alba Bellot-Saez
- Biomedical Engineering and Neuroscience research group, The MARCS Institute, Western Sydney University, Penrith, NSW, 2751, Australia.,School of Medicine, Western Sydney University, Campbelltown, NSW, 2560, Australia
| | - Winston Seah
- Biomedical Engineering and Neuroscience research group, The MARCS Institute, Western Sydney University, Penrith, NSW, 2751, Australia.,School of Medicine, Western Sydney University, Campbelltown, NSW, 2560, Australia.,School of Chemistry and Molecular Bioscience, University of Wollongong, Northfields Avenue, Wollongong, NSW, 2522, Australia.,Illawarra Health and Medical Research Institute, Northfields Avenue, Wollongong, NSW, 2522, Australia
| | - Tracey Berg
- School of Chemistry and Molecular Bioscience, University of Wollongong, Northfields Avenue, Wollongong, NSW, 2522, Australia.,Illawarra Health and Medical Research Institute, Northfields Avenue, Wollongong, NSW, 2522, Australia
| | - Michael Trpceski
- School of Chemistry and Molecular Bioscience, University of Wollongong, Northfields Avenue, Wollongong, NSW, 2522, Australia.,Illawarra Health and Medical Research Institute, Northfields Avenue, Wollongong, NSW, 2522, Australia
| | - Justin J Yerbury
- School of Chemistry and Molecular Bioscience, University of Wollongong, Northfields Avenue, Wollongong, NSW, 2522, Australia.,Illawarra Health and Medical Research Institute, Northfields Avenue, Wollongong, NSW, 2522, Australia
| | - Lezanne Ooi
- School of Chemistry and Molecular Bioscience, University of Wollongong, Northfields Avenue, Wollongong, NSW, 2522, Australia. .,Illawarra Health and Medical Research Institute, Northfields Avenue, Wollongong, NSW, 2522, Australia.
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4
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Szabó Z, Héja L, Szalay G, Kékesi O, Füredi A, Szebényi K, Dobolyi Á, Orbán TI, Kolacsek O, Tompa T, Miskolczy Z, Biczók L, Rózsa B, Sarkadi B, Kardos J. Extensive astrocyte synchronization advances neuronal coupling in slow wave activity in vivo. Sci Rep 2017; 7:6018. [PMID: 28729692 PMCID: PMC5519671 DOI: 10.1038/s41598-017-06073-7] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [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: 01/12/2017] [Accepted: 05/26/2017] [Indexed: 01/19/2023] Open
Abstract
Slow wave activity (SWA) is a characteristic brain oscillation in sleep and quiet wakefulness. Although the cell types contributing to SWA genesis are not yet identified, the principal role of neurons in the emergence of this essential cognitive mechanism has not been questioned. To address the possibility of astrocytic involvement in SWA, we used a transgenic rat line expressing a calcium sensitive fluorescent protein in both astrocytes and interneurons and simultaneously imaged astrocytic and neuronal activity in vivo. Here we demonstrate, for the first time, that the astrocyte network display synchronized recurrent activity in vivo coupled to UP states measured by field recording and neuronal calcium imaging. Furthermore, we present evidence that extensive synchronization of the astrocytic network precedes the spatial build-up of neuronal synchronization. The earlier extensive recruitment of astrocytes in the synchronized activity is reinforced by the observation that neurons surrounded by active astrocytes are more likely to join SWA, suggesting causality. Further supporting this notion, we demonstrate that blockade of astrocytic gap junctional communication or inhibition of astrocytic Ca2+ transients reduces the ratio of both astrocytes and neurons involved in SWA. These in vivo findings conclusively suggest a causal role of the astrocytic syncytium in SWA generation.
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Affiliation(s)
- Zsolt Szabó
- Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudósok körútja 2, 1117, Budapest, Hungary
| | - László Héja
- Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudósok körútja 2, 1117, Budapest, Hungary.
| | - Gergely Szalay
- Institute of Experimental Medicine, Hungarian Academy of Sciences, Szigony 43, 1083, Budapest, Hungary
| | - Orsolya Kékesi
- Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudósok körútja 2, 1117, Budapest, Hungary
| | - András Füredi
- Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudósok körútja 2, 1117, Budapest, Hungary.,Institute of Cancer Research, Medical University Wien, Borschkegasse 8a, 1090, Wien, Austria
| | - Kornélia Szebényi
- Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudósok körútja 2, 1117, Budapest, Hungary.,Institute of Cancer Research, Medical University Wien, Borschkegasse 8a, 1090, Wien, Austria
| | - Árpád Dobolyi
- MTA-ELTE Laboratory of Molecular and Systems Neurobiology, Department of Physiology and Neurobiology, Eötvös Loránd University, Pázmány Péter sétány 1C, 1117, Budapest, Hungary
| | - Tamás I Orbán
- Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudósok körútja 2, 1117, Budapest, Hungary
| | - Orsolya Kolacsek
- Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudósok körútja 2, 1117, Budapest, Hungary
| | - Tamás Tompa
- Institute of Experimental Medicine, Hungarian Academy of Sciences, Szigony 43, 1083, Budapest, Hungary
| | - Zsombor Miskolczy
- Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudósok körútja 2, 1117, Budapest, Hungary
| | - László Biczók
- Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudósok körútja 2, 1117, Budapest, Hungary
| | - Balázs Rózsa
- Institute of Experimental Medicine, Hungarian Academy of Sciences, Szigony 43, 1083, Budapest, Hungary
| | - Balázs Sarkadi
- Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudósok körútja 2, 1117, Budapest, Hungary
| | - Julianna Kardos
- Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Magyar tudósok körútja 2, 1117, Budapest, Hungary
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Cameron M, Kékesi O, Morley JW, Tapson J, Breen PP, van Schaik A, Buskila Y. Calcium Imaging of AM Dyes Following Prolonged Incubation in Acute Neuronal Tissue. PLoS One 2016; 11:e0155468. [PMID: 27183102 PMCID: PMC4868260 DOI: 10.1371/journal.pone.0155468] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [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: 12/18/2015] [Accepted: 04/30/2016] [Indexed: 12/12/2022] Open
Abstract
Calcium-imaging is a sensitive method for monitoring calcium dynamics during neuronal activity. As intracellular calcium concentration is correlated to physiological and pathophysiological activity of neurons, calcium imaging with fluorescent indicators is one of the most commonly used techniques in neuroscience today. Current methodologies for loading calcium dyes into the tissue require prolonged incubation time (45-150 min), in addition to dissection and recovery time after the slicing procedure. This prolonged incubation curtails experimental time, as tissue is typically maintained for 6-8 hours after slicing. Using a recently introduced recovery chamber that extends the viability of acute brain slices to more than 24 hours, we tested the effectiveness of calcium AM staining following long incubation periods post cell loading and its impact on the functional properties of calcium signals in acute brain slices and wholemount retinae. We show that calcium dyes remain within cells and are fully functional >24 hours after loading. Moreover, the calcium dynamics recorded >24 hrs were similar to the calcium signals recorded in fresh tissue that was incubated for <4 hrs. These results indicate that long exposure of calcium AM dyes to the intracellular cytoplasm did not alter the intracellular calcium concentration, the functional range of the dye or viability of the neurons. This data extends our previous work showing that a custom recovery chamber can extend the viability of neuronal tissue, and reliable data for both electrophysiology and imaging can be obtained >24hrs after dissection. These methods will not only extend experimental time for those using acute neuronal tissue, but also may reduce the number of animals required to complete experimental goals.
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Affiliation(s)
- Morven Cameron
- Biomedical Engineering and Neuroscience group, The MARCS Institute, Western Sydney University, Penrith, NSW, Australia
| | - Orsolya Kékesi
- School of Medicine, Western Sydney University, Penrith, NSW, Australia
- Biomedical Engineering and Neuroscience group, The MARCS Institute, Western Sydney University, Penrith, NSW, Australia
| | - John W. Morley
- School of Medicine, Western Sydney University, Penrith, NSW, Australia
- Biomedical Engineering and Neuroscience group, The MARCS Institute, Western Sydney University, Penrith, NSW, Australia
| | - Jonathan Tapson
- School of Medicine, Western Sydney University, Penrith, NSW, Australia
| | - Paul P. Breen
- School of Medicine, Western Sydney University, Penrith, NSW, Australia
| | - André van Schaik
- School of Medicine, Western Sydney University, Penrith, NSW, Australia
| | - Yossi Buskila
- School of Medicine, Western Sydney University, Penrith, NSW, Australia
- Biomedical Engineering and Neuroscience group, The MARCS Institute, Western Sydney University, Penrith, NSW, Australia
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6
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Ma X, Lubin H, Ioja E, Kékesi O, Simon Á, Apáti Á, Orbán TI, Héja L, Kardos J, Markó IE. Straightforward and effective synthesis of γ-aminobutyric acid transporter subtype 2-selective acyl-substituted azaspiro[4.5]decanes. Bioorg Med Chem Lett 2015; 26:417-423. [PMID: 26706177 DOI: 10.1016/j.bmcl.2015.11.100] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2015] [Revised: 11/26/2015] [Accepted: 11/27/2015] [Indexed: 10/22/2022]
Abstract
Supply of major metabolites such as γ-aminobutyric acid (GABA), β-alanine and taurine is an essential instrument that shapes signalling, proper cell functioning and survival in the brain and peripheral organs. This background motivates the synthesis of novel classes of compounds regulating their selective transport through various fluid-organ barriers via the low-affinity γ-aminobutyric acid (GABA) transporter subtype 2 (GAT2). Natural and synthetic spirocyclic compounds or therapeutics with a range of structures and biological activity are increasingly recognised in this regard. Based on pre-validated GABA transport activity, straightforward and efficient synthesis method was developed to provide an azaspiro[4.5]decane scaffold, holding a variety of charge, substituent and 3D constrain of spirocyclic amine. Investigation of the azaspiro[4.5]decane scaffold in cell lines expressing the four GABA transporter subtypes led to the discovery of a subclass of a GAT2-selective compounds with acyl-substituted azaspiro[4.5]decane core.
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Affiliation(s)
- Xiaofeng Ma
- Organic and Medicinal Chemistry Laboratories, Université catholique de Louvain, B-1348 Louvain-la-Neuve, Belgium
| | - Hodney Lubin
- Organic and Medicinal Chemistry Laboratories, Université catholique de Louvain, B-1348 Louvain-la-Neuve, Belgium
| | - Enikő Ioja
- Functional Pharmacology Research Group, Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, H-1117 Budapest, Hungary
| | - Orsolya Kékesi
- Functional Pharmacology Research Group, Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, H-1117 Budapest, Hungary
| | - Ágnes Simon
- Functional Pharmacology Research Group, Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, H-1117 Budapest, Hungary
| | - Ágota Apáti
- Laboratory of Molecular Cell Biology, Institute of Enzimology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, H-1117 Budapest, Hungary
| | - Tamás I Orbán
- Biomembrane Research Group, Institute of Enzimology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, H-1117 Budapest, Hungary
| | - László Héja
- Functional Pharmacology Research Group, Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, H-1117 Budapest, Hungary
| | - Julianna Kardos
- Functional Pharmacology Research Group, Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, H-1117 Budapest, Hungary.
| | - István E Markó
- Organic and Medicinal Chemistry Laboratories, Université catholique de Louvain, B-1348 Louvain-la-Neuve, Belgium.
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Kékesi O, Ioja E, Szabó Z, Kardos J, Héja L. Recurrent seizure-like events are associated with coupled astroglial synchronization. Front Cell Neurosci 2015; 9:215. [PMID: 26150770 PMCID: PMC4471369 DOI: 10.3389/fncel.2015.00215] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2014] [Accepted: 05/20/2015] [Indexed: 01/22/2023] Open
Abstract
Increasing evidence suggest that astrocytes significantly modulate neuronal function at the level of the tripartite synapse both in physiological and pathophysiological conditions. The global control of the astrocytic syncytium over neuronal networks, however, is still less recognized. Here we examined astrocytic signaling during epileptiform activity which is generally attributed to large-scale neuronal synchronization. We show that seizure-like events in the low-[Mg(2+)] in vitro epilepsy model initiate massive, long-range astrocytic synchronization which is spatiotemporally coupled to the synchronized neuronal activity reaching its maximum at the electrographic tonic/clonic transition. Cross-correlation analysis of neuronal and astrocytic Ca(2+) signaling demonstrates that high degree of synchronization arises not only among astrocytes, but also between neuronal and astrocyte populations, manifesting in astrocytic seizure-like events. We further show that astrocytic gap junction proteins contribute to astrocytic synchronization since their inhibition by carbenoxolone (CBX) or Cx43 antibody increased the interictal interval and in 41% of slices completely prevented recurrent seizure-like activity. In addition, CBX also induced unsynchronized Ca(2+) transients associated with decreasing incidence of epileptiform discharges afterwards. We propose therefore that local, unsynchronized astrocytic Ca(2+) transients inhibit, while long-range, synchronized Ca(2+) signaling contributes to the propagation of recurrent seizure-like events.
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Affiliation(s)
- Orsolya Kékesi
- Research Centre for Natural Sciences, Hungarian Academy of Sciences, Institute of Organic Chemistry, Functional Pharmacology Group Budapest, Hungary
| | - Enikö Ioja
- Research Centre for Natural Sciences, Hungarian Academy of Sciences, Institute of Organic Chemistry, Functional Pharmacology Group Budapest, Hungary
| | - Zsolt Szabó
- Research Centre for Natural Sciences, Hungarian Academy of Sciences, Institute of Organic Chemistry, Functional Pharmacology Group Budapest, Hungary
| | - Julianna Kardos
- Research Centre for Natural Sciences, Hungarian Academy of Sciences, Institute of Organic Chemistry, Functional Pharmacology Group Budapest, Hungary
| | - László Héja
- Research Centre for Natural Sciences, Hungarian Academy of Sciences, Institute of Organic Chemistry, Functional Pharmacology Group Budapest, Hungary
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Cinar R, Kékesi O, Birkás E, Fábián G, Schmidhammer H, Szücs M. Lack of regulatory changes of µ-opioid receptors by 14-methoxymetopon treatment in rat brain. Further evidence for functional selectivity. Curr Pharm Des 2014; 19:7348-54. [PMID: 23448478 DOI: 10.2174/138161281942140105161245] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2013] [Accepted: 02/18/2013] [Indexed: 11/22/2022]
Abstract
Here we have studied regulatory changes of µ-opioid receptors accompanying in vivo 14-methoxymetopon treatments of rats. Previously, this ligand has been shown to be an extremely potent, centrally acting µ-opioid specific analgesic with low physical dependence, tolerance, respiratory depression, constipation and other side effects. Our work shows that it is a highly potent full agonist of µ-opioid receptor coupled G-protein signaling in vitro, alike the well-known opioid agonist, etorphine. However, unlike etorphine, which desensitized and down-regulated the endogenous µ-opioid receptors, 14-methoxymetopon, given to rats intraperitoneally (i.p.) either acutely or chronically, did not change the binding or G-protein signaling of µ-opioid receptors in rat brain subcellular membranes. Thereby, these data provide further evidence that there is no direct relationship between the efficacy of the ligand in signaling and its ability to internalize or desensitize the receptor. Viewed collectively with published work, it is discussed that µ-opioid receptors display functional selectivity, also called 'biased agonism'. This concept implies that each ligand may induce unique, ligand-specific receptor conformation that can result in distinct agonist- directed trafficking and/or signal transduction pathways associated with the receptor. Ligand-specific signaling may open up new directions for designing potent analgesics that do not interact with unwanted signaling pathways, which mediate undesired side-effects, such as tolerance and dependence.
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Affiliation(s)
| | | | | | | | | | - Mária Szücs
- Institute of Biochemistry, Biological Research Center, Hungarian Academy of Sciences, H-6701 Szeged, P.O. Box 521, Hungary.
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Héja L, Nyitrai G, Kékesi O, Dobolyi A, Szabó P, Fiáth R, Ulbert I, Pál-Szenthe B, Palkovits M, Kardos J. Astrocytes convert network excitation to tonic inhibition of neurons. BMC Biol 2012; 10:26. [PMID: 22420899 PMCID: PMC3342137 DOI: 10.1186/1741-7007-10-26] [Citation(s) in RCA: 124] [Impact Index Per Article: 10.3] [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: 12/20/2011] [Accepted: 03/15/2012] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Glutamate and γ-aminobutyric acid (GABA) transporters play important roles in balancing excitatory and inhibitory signals in the brain. Increasing evidence suggest that they may act concertedly to regulate extracellular levels of the neurotransmitters. RESULTS Here we present evidence that glutamate uptake-induced release of GABA from astrocytes has a direct impact on the excitability of pyramidal neurons in the hippocampus. We demonstrate that GABA, synthesized from the polyamine putrescine, is released from astrocytes by the reverse action of glial GABA transporter (GAT) subtypes GAT-2 or GAT-3. GABA release can be prevented by blocking glutamate uptake with the non-transportable inhibitor DHK, confirming that it is the glutamate transporter activity that triggers the reversal of GABA transporters, conceivably by elevating the intracellular Na+ concentration in astrocytes. The released GABA significantly contributes to the tonic inhibition of neurons in a network activity-dependent manner. Blockade of the Glu/GABA exchange mechanism increases the duration of seizure-like events in the low-[Mg2+] in vitro model of epilepsy. Under in vivo conditions the increased GABA release modulates the power of gamma range oscillation in the CA1 region, suggesting that the Glu/GABA exchange mechanism is also functioning in the intact hippocampus under physiological conditions. CONCLUSIONS The results suggest the existence of a novel molecular mechanism by which astrocytes transform glutamatergic excitation into GABAergic inhibition providing an adjustable, in situ negative feedback on the excitability of neurons.
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Affiliation(s)
- László Héja
- Department of Functional Pharmacology, Institute of Molecular Pharmacology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Pusztaszeri 59-67, 1025 Budapest, Hungary.
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Nyitrai G, Kékesi O, Pál I, Keglevich P, Csíki Z, Fügedi P, Simon Á, Fitos I, Németh K, Visy J, Tárkányi G, Kardos J. Assessing toxicity of polyamidoamine dendrimers by neuronal signaling functions. Nanotoxicology 2011; 6:576-86. [DOI: 10.3109/17435390.2011.591511] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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11
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Kékesi O, Rakonczai G, Holland R. [Hypernephroma perforating into the colon]. Orv Hetil 1967; 108:312-3. [PMID: 6045842] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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