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Raimondo JV, Burman RJ, Katz AA, Akerman CJ. Ion dynamics during seizures. Front Cell Neurosci 2015; 9:419. [PMID: 26539081 PMCID: PMC4612498 DOI: 10.3389/fncel.2015.00419] [Citation(s) in RCA: 101] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2015] [Accepted: 10/04/2015] [Indexed: 12/14/2022] Open
Abstract
Changes in membrane voltage brought about by ion fluxes through voltage and transmitter-gated channels represent the basis of neural activity. As such, electrochemical gradients across the membrane determine the direction and driving force for the flow of ions and are therefore crucial in setting the properties of synaptic transmission and signal propagation. Ion concentration gradients are established by a variety of mechanisms, including specialized transporter proteins. However, transmembrane gradients can be affected by ionic fluxes through channels during periods of elevated neural activity, which in turn are predicted to influence the properties of on-going synaptic transmission. Such activity-induced changes to ion concentration gradients are a feature of both physiological and pathological neural processes. An epileptic seizure is an example of severely perturbed neural activity, which is accompanied by pronounced changes in intracellular and extracellular ion concentrations. Appreciating the factors that contribute to these ion dynamics is critical if we are to understand how a seizure event evolves and is sustained and terminated by neural tissue. Indeed, this issue is of significant clinical importance as status epilepticus—a type of seizure that does not stop of its own accord—is a life-threatening medical emergency. In this review we explore how the transmembrane concentration gradient of the six major ions (K+, Na+, Cl−, Ca2+, H+and HCO3−) is altered during an epileptic seizure. We will first examine each ion individually, before describing how multiple interacting mechanisms between ions might contribute to concentration changes and whether these act to prolong or terminate epileptic activity. In doing so, we will consider how the availability of experimental techniques has both advanced and restricted our ability to study these phenomena.
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Affiliation(s)
- Joseph V Raimondo
- Department of Human Biology, Faculty of Health Sciences, University of Cape Town Cape Town, South Africa ; UCT/MRC Receptor Biology Unit, Department of Integrative Biomedical Sciences and Institute of Infectious Disease and Molecular Medicine, Faculty of Health Sciences, University of Cape Town Cape Town, South Africa
| | - Richard J Burman
- UCT/MRC Receptor Biology Unit, Department of Integrative Biomedical Sciences and Institute of Infectious Disease and Molecular Medicine, Faculty of Health Sciences, University of Cape Town Cape Town, South Africa
| | - Arieh A Katz
- UCT/MRC Receptor Biology Unit, Department of Integrative Biomedical Sciences and Institute of Infectious Disease and Molecular Medicine, Faculty of Health Sciences, University of Cape Town Cape Town, South Africa
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52
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Activity-triggered tetrapartite neuron-glial interactions following peripheral injury. Curr Opin Pharmacol 2015; 26:16-25. [PMID: 26431645 DOI: 10.1016/j.coph.2015.09.006] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2015] [Revised: 09/14/2015] [Accepted: 09/16/2015] [Indexed: 12/11/2022]
Abstract
Recent studies continue to support the proposition that non-neuronal components of the nervous system, mainly glial cells and associated chemical mediators, contribute to the development of neuronal hyperexcitability that underlies persistent pain conditions. In the event of peripheral injury, enhanced or abnormal nerve input is likely the most efficient way to activate simultaneously central neurons and glia. Injury induces phenotypic changes in glia and triggers signaling cascades that engage reciprocal interactions between presynaptic terminals, postsynaptic neurons, microglia and astrocytes. While some responses to peripheral injury may help the nervous system to adapt positively to counter the disastrous effect of injury, the net effect often leads to long-lasting sensitization of pain transmission pathways and chronic pain.
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53
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Kadala A, Verdier D, Morquette P, Kolta A. Ion Homeostasis in Rhythmogenesis: The Interplay Between Neurons and Astroglia. Physiology (Bethesda) 2015; 30:371-88. [DOI: 10.1152/physiol.00023.2014] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Proper function of all excitable cells depends on ion homeostasis. Nowhere is this more critical than in the brain where the extracellular concentration of some ions determines neurons' firing pattern and ability to encode information. Several neuronal functions depend on the ability of neurons to change their firing pattern to a rhythmic bursting pattern, whereas, in some circuits, rhythmic firing is, on the contrary, associated to pathologies like epilepsy or Parkinson's disease. In this review, we focus on the four main ions known to fluctuate during rhythmic firing: calcium, potassium, sodium, and chloride. We discuss the synergistic interactions between these elements to promote an oscillatory activity. We also review evidence supporting an important role for astrocytes in the homeostasis of each of these ions and describe mechanisms by which astrocytes may regulate neuronal firing by altering their extracellular concentrations. A particular emphasis is put on the mechanisms underlying rhythmogenesis in the circuit forming the central pattern generator (CPG) for mastication and other CPG systems. Finally, we discuss how an impairment in the ability of glial cells to maintain such homeostasis may result in pathologies like epilepsy and Parkinson's disease.
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Affiliation(s)
- Aklesso Kadala
- Département de Neurosciences and Groupe de Recherche sur le Système Nerveux Central, Université de Montréal, Montréal, Québec, Canada; and
| | - Dorly Verdier
- Département de Neurosciences and Groupe de Recherche sur le Système Nerveux Central, Université de Montréal, Montréal, Québec, Canada; and
| | - Philippe Morquette
- Département de Neurosciences and Groupe de Recherche sur le Système Nerveux Central, Université de Montréal, Montréal, Québec, Canada; and
| | - Arlette Kolta
- Département de Neurosciences and Groupe de Recherche sur le Système Nerveux Central, Université de Montréal, Montréal, Québec, Canada; and
- Faculté de Médecine Dentaire and Réseau de Recherche en Santé Bucco-dentaire et Osseuse du Fonds de Recherche Québec-Santé, Université de Montréal, Montréal, Québec, Canada
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54
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Zimmer ER, Torrez VR, Kalinine E, Augustin MC, Zenki KC, Almeida RF, Hansel G, Muller AP, Souza DO, Machado-Vieira R, Portela LV. Long-term NMDAR antagonism correlates reduced astrocytic glutamate uptake with anxiety-like phenotype. Front Cell Neurosci 2015; 9:219. [PMID: 26089779 PMCID: PMC4452887 DOI: 10.3389/fncel.2015.00219] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2015] [Accepted: 05/22/2015] [Indexed: 12/17/2022] Open
Abstract
The role of glutamate N-methyl-D-aspartate receptor (NMDAR) hypofunction has been extensively studied in schizophrenia; however, less is known about its role in anxiety disorders. Recently, it was demonstrated that astrocytic GLT-1 blockade leads to an anxiety-like phenotype. Although astrocytes are capable of modulating NMDAR activity through glutamate uptake transporters, the relationship between astrocytic glutamate uptake and the development of an anxiety phenotype remains poorly explored. Here, we aimed to investigative whether long-term antagonism of NMDAR impacts anxiety-related behaviors and astrocytic glutamate uptake. Memantine, an NMDAR antagonist, was administered daily for 24 days to healthy adult CF-1 mice by oral gavage at doses of 5, 10, or 20 mg/kg. The mice were submitted to a sequential battery of behavioral tests (open field, light–dark box and elevated plus-maze tests). We then evaluated glutamate uptake activity and the immunocontents of glutamate transporters in the frontoparietal cortex and hippocampus. Our results demonstrated that long-term administration of memantine induces anxiety-like behavior in mice in the light–dark box and elevated plus-maze paradigms. Additionally, the administration of memantine decreased glutamate uptake activity in both the frontoparietal cortex and hippocampus without altering the immunocontent of either GLT-1 or GLAST. Remarkably, the memantine-induced reduction in glutamate uptake was correlated with enhancement of an anxiety-like phenotype. In conclusion, long-term NMDAR antagonism with memantine induces anxiety-like behavior that is associated with reduced glutamate uptake activity but that is not dependent on GLT-1 or GLAST protein expression. Our study suggests that NMDAR and glutamate uptake hypofunction may contribute to the development of conditions that fall within the category of anxiety disorders.
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Affiliation(s)
- Eduardo R Zimmer
- Department of Biochemistry, Universidade Federal do Rio Grande do Sul Porto Alegre, Brazil
| | - Vitor R Torrez
- Department of Biochemistry, Universidade Federal do Rio Grande do Sul Porto Alegre, Brazil
| | - Eduardo Kalinine
- Department of Biochemistry, Universidade Federal do Rio Grande do Sul Porto Alegre, Brazil ; Department of Physiology, Universidade Federal de Sergipe São Cristovão, Brazil
| | - Marina C Augustin
- Department of Biochemistry, Universidade Federal do Rio Grande do Sul Porto Alegre, Brazil
| | - Kamila C Zenki
- Department of Biochemistry, Universidade Federal do Rio Grande do Sul Porto Alegre, Brazil
| | - Roberto F Almeida
- Department of Biochemistry, Universidade Federal do Rio Grande do Sul Porto Alegre, Brazil
| | - Gisele Hansel
- Department of Biochemistry, Universidade Federal do Rio Grande do Sul Porto Alegre, Brazil
| | - Alexandre P Muller
- Department of Biochemistry, Universidade Federal do Rio Grande do Sul Porto Alegre, Brazil ; Laboratory of Exercise, Biochemistry and Physiology, Universidade do Extremo Sul Catarinense Criciúma, Brazil
| | - Diogo O Souza
- Department of Biochemistry, Universidade Federal do Rio Grande do Sul Porto Alegre, Brazil
| | - Rodrigo Machado-Vieira
- Laboratory of Neuroscience, LIM-27, Institute and Department of Psychiatry, Universidade de São Paulo São Paulo, Brazil ; Center for Interdisciplinary Research on Applied Neurosciences (NAPNA), Universidade de São Paulo São Paulo, Brazil ; Experimental Therapeutics and Pathophysiology Branch, National Institute of Mental Health, National Institutes of Health Bethesda, MD, USA
| | - Luis V Portela
- Department of Biochemistry, Universidade Federal do Rio Grande do Sul Porto Alegre, Brazil
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55
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Karus C, Ziemens D, Rose CR. Lactate rescues neuronal sodium homeostasis during impaired energy metabolism. Channels (Austin) 2015; 9:200-8. [PMID: 26039160 PMCID: PMC4594511 DOI: 10.1080/19336950.2015.1050163] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Recently, we established that recurrent activity evokes network sodium oscillations in neurons and astrocytes in hippocampal tissue slices. Interestingly, metabolic integrity of astrocytes was essential for the neurons' capacity to maintain low sodium and to recover from sodium loads, indicating an intimate metabolic coupling between the 2 cell types. Here, we studied if lactate can support neuronal sodium homeostasis during impaired energy metabolism by analyzing whether glucose removal, pharmacological inhibition of glycolysis and/or addition of lactate affect cellular sodium regulation. Furthermore, we studied the effect of lactate on sodium regulation during recurrent network activity and upon inhibition of the glial Krebs cycle by sodium-fluoroacetate. Our results indicate that lactate is preferentially used by neurons. They demonstrate that lactate supports neuronal sodium homeostasis and rescues the effects of glial poisoning by sodium-fluoroacetate. Altogether, they are in line with the proposed transfer of lactate from astrocytes to neurons, the so-called astrocyte-neuron-lactate shuttle.
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Affiliation(s)
- Claudia Karus
- a Institute of Neurobiology; Faculty of Mathematics and Natural Sciences; Heinrich Heine University Düsseldorf ; Düsseldorf , Germany
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56
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Hanson E, Armbruster M, Cantu D, Andresen L, Taylor A, Danbolt NC, Dulla CG. Astrocytic glutamate uptake is slow and does not limit neuronal NMDA receptor activation in the neonatal neocortex. Glia 2015; 63:1784-96. [PMID: 25914127 DOI: 10.1002/glia.22844] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2014] [Revised: 03/30/2015] [Accepted: 04/07/2015] [Indexed: 01/20/2023]
Abstract
Glutamate uptake by astrocytes controls the time course of glutamate in the extracellular space and affects neurotransmission, synaptogenesis, and circuit development. Astrocytic glutamate uptake has been shown to undergo post-natal maturation in the hippocampus, but has been largely unexplored in other brain regions. Notably, glutamate uptake has never been examined in the developing neocortex. In these studies, we investigated the development of astrocytic glutamate transport, intrinsic membrane properties, and control of neuronal NMDA receptor activation in the developing neocortex. Using astrocytic and neuronal electrophysiology, immunofluorescence, and Western blot analysis we show that: (1) glutamate uptake in the neonatal neocortex is slow relative to neonatal hippocampus; (2) astrocytes in the neonatal neocortex undergo a significant maturation of intrinsic membrane properties; (3) slow glutamate uptake is accompanied by lower expression of both GLT-1 and GLAST; (4) glutamate uptake is less dependent on GLT-1 in neonatal neocortex than in neonatal hippocampus; and (5) the slow glutamate uptake we report in the neonatal neocortex corresponds to minimal astrocytic control of neuronal NMDA receptor activation. Taken together, our results clearly show fundamental differences between astrocytic maturation in the developing neocortex and hippocampus, and corresponding changes in how astrocytes control glutamate signaling.
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Affiliation(s)
- Elizabeth Hanson
- Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts.,Neuroscience Program, Tufts Sackler School of Biomedical Sciences, Boston, Massachusetts
| | - Moritz Armbruster
- Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts
| | - David Cantu
- Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts
| | - Lauren Andresen
- Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts.,Neuroscience Program, Tufts Sackler School of Biomedical Sciences, Boston, Massachusetts
| | - Amaro Taylor
- Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts
| | - Niels Christian Danbolt
- Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
| | - Chris G Dulla
- Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts.,Neuroscience Program, Tufts Sackler School of Biomedical Sciences, Boston, Massachusetts
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