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Fessel J. Supplemental thiamine as a practical, potential way to prevent Alzheimer's disease from commencing. ALZHEIMER'S & DEMENTIA (NEW YORK, N. Y.) 2021; 7:e12199. [PMID: 34337137 PMCID: PMC8319660 DOI: 10.1002/trc2.12199] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Received: 12/11/2020] [Revised: 06/06/2021] [Accepted: 06/18/2021] [Indexed: 11/23/2022]
Abstract
It is better to attempt stopping Alzheimer's disease (AD) before it starts than trying to cure it after it has developed. A cerebral scan showing deposition of either amyloid or tau identifies those elderly persons whose cognition is currently normal but who are at risk of subsequent cognitive loss that may develop into AD. Synaptic hypometabolism is usually present in such at-risk persons. Although inadequate adenosine triphosphate (ATP) may cause synaptic hypometabolism, that may not be the entire cause because, in fact, measurements in some of the at-risk persons have shown normal ATP levels. Thiamine deficiency is often seen in elderly, ambulatory persons in whom thiamine levels correlate with Mini-Mental State Examination scores. Thiamine deficiency has many consequences including hypometabolism, mitochondrial depression, oxidative stress, lactic acidosis and cerebral acidosis, amyloid deposition, tau deposition, synaptic dysfunction and abnormal neuro-transmission, astrocyte function, and blood brain barrier integrity, all of which are features of AD. Although the clinical benefits of administering supplementary thiamine to patients with AD or mild cognitive impairment have been mixed, it is more likely to succeed at preventing the onset of cognitive loss if administered at an earlier time, when the number of aberrant biochemical pathways is far fewer. Providing a thiamine supplement to elderly persons who still have normal cognition but who have deposition of either amyloid or tau, may prevent subsequent cognitive loss and eventual dementia. A clinical trial is needed to validate that possibility.
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Affiliation(s)
- Jeffrey Fessel
- Professor of Clinical Medicine, EmeritusDepartment of MedicineUniversity of California, San FranciscoSan FranciscoCaliforniaUSA
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Bürge M, Kratzer S, Mattusch C, Hofmann C, Kreuzer M, Parsons CG, Rammes G. The anaesthetic xenon partially restores an amyloid beta-induced impairment in murine hippocampal synaptic plasticity. Neuropharmacology 2019; 151:21-32. [PMID: 30940537 DOI: 10.1016/j.neuropharm.2019.03.031] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2018] [Revised: 03/15/2019] [Accepted: 03/26/2019] [Indexed: 02/08/2023]
Abstract
BACKGROUND It is controversially discussed whether general anaesthesia increases the risk of Alzheimer's disease (AD) or accelerates its progression. One important factor in AD pathogenesis is the accumulation of soluble amyloid beta (Aβ) oligomers which affect N-methyl-d-aspartate (NMDA) receptor function and abolish hippocampal long-term potentiation (LTP). NMDA receptor antagonists, at concentrations allowing physiological activation, can prevent Aβ-induced deficits in LTP. The anaesthetics xenon and S-ketamine both act as NMDA receptor antagonists and have been reported to be neuroprotective. In this study, we investigated the effects of subanaesthetic concentrations of these drugs on LTP deficits induced by different Aβ oligomers and compared them to the effects of radiprodil, a NMDA subunit 2B (GluN2B)-selective antagonist. METHODS We applied different Aβ oligomers to murine brain slices and recorded excitatory postsynaptic field potentials before and after high-frequency stimulation in the CA1 region of hippocampus. Radiprodil, xenon and S-ketamine were added and recordings evoked from a second input were measured. RESULTS Xenon and radiprodil, applied at low concentrations, partially restored the LTP deficit induced by pre-incubated Aβ1-42. S-ketamine showed no effect. None of the drugs tested were able to ameliorate Aβ1-40-induced LTP-deficits. CONCLUSIONS Xenon administered at subanaesthetic concentrations partially restored Aβ1-42-induced impairment of LTP, presumably via its weak NMDA receptor antagonism. The effects were in a similar range than those obtained with the NMDA-GluN2B antagonist radiprodil. Our results point to protective properties of xenon in the context of pathological distorted synaptic physiology which might be a meaningful alternative for anaesthesia in AD patients.
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Affiliation(s)
- Martina Bürge
- Department of Anaesthesiology and Intensive Care Medicine, Klinikum rechts der Isar, Technische Universität München, Ismaninger Str. 22, 81675 Munich, Germany; Department of Perioperative Medicine, Barts Heart Centre, St Bartholomew's Hospital, West Smithfield, London EC1A 7BE, United Kingdom.
| | - Stephan Kratzer
- Department of Anaesthesiology and Intensive Care Medicine, Klinikum rechts der Isar, Technische Universität München, Ismaninger Str. 22, 81675 Munich, Germany
| | - Corinna Mattusch
- Department of Anaesthesiology and Intensive Care Medicine, Klinikum rechts der Isar, Technische Universität München, Ismaninger Str. 22, 81675 Munich, Germany; Hexal AG, Industriestr. 25, 83607 Holzkirchen, Germany
| | - Carolin Hofmann
- Department of Anaesthesiology and Intensive Care Medicine, Klinikum rechts der Isar, Technische Universität München, Ismaninger Str. 22, 81675 Munich, Germany
| | - Matthias Kreuzer
- Department of Anaesthesiology and Intensive Care Medicine, Klinikum rechts der Isar, Technische Universität München, Ismaninger Str. 22, 81675 Munich, Germany
| | | | - Gerhard Rammes
- Department of Anaesthesiology and Intensive Care Medicine, Klinikum rechts der Isar, Technische Universität München, Ismaninger Str. 22, 81675 Munich, Germany
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Metabolic regulation of synaptic activity. Rev Neurosci 2018; 29:825-835. [DOI: 10.1515/revneuro-2017-0090] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2017] [Accepted: 03/16/2018] [Indexed: 12/20/2022]
Abstract
Abstract
Brain tissue is bioenergetically expensive. In humans, it composes approximately 2% of body weight and accounts for approximately 20% of calorie consumption. The brain consumes energy mostly for ion and neurotransmitter transport, a process that occurs primarily in synapses. Therefore, synapses are expensive for any living creature who has brain. In many brain diseases, synapses are damaged earlier than neurons start dying. Synapses may be considered as vulnerable sites on a neuron. Ischemic stroke, an acute disturbance of blood flow in the brain, is an example of a metabolic disease that affects synapses. The associated excessive glutamate release, called excitotoxicity, is involved in neuronal death in brain ischemia. Another example of a metabolic disease is hypoglycemia, a complication of diabetes mellitus, which leads to neuronal death and brain dysfunction. However, synapse function can be corrected with “bioenergetic medicine”. In this review, a ketogenic diet is discussed as a curative option. In support of a ketogenic diet, whereby carbohydrates are replaced for fats in daily meals, epileptic seizures can be terminated. In this review, we discuss possible metabolic sensors in synapses. These may include molecules that perceive changes in composition of extracellular space, for instance, ketone body and lactate receptors, or molecules reacting to changes in cytosol, for instance, KATP channels or AMP kinase. Inhibition of endocytosis is believed to be a universal synaptic mechanism of adaptation to metabolic changes.
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Intracellular pH Regulation in iPSCs-derived Astrocytes from Subjects with Chronic Mountain Sickness. Neuroscience 2018; 375:25-33. [PMID: 29438800 DOI: 10.1016/j.neuroscience.2018.02.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2017] [Revised: 02/01/2018] [Accepted: 02/02/2018] [Indexed: 11/22/2022]
Abstract
Chronic Mountain Sickness (CMS) occurs in high-altitude residents with major neurological symptoms such as migraine headaches, dizziness and cognitive deficits. Recent work demonstrated that highlanders have increased intracellular pH (pHi) in their brain cells, perhaps for the sake of adaptation to hypoxemia and help to facilitate glycolysis, DNA synthesis, and cell cycle progression. Since there are well adapted (non-CMS) and maladapted (CMS) high-altitude dwellers, it is not clear whether pHi is differently regulated in these two high-altitude populations. In this work, we obtained induced pluripotent stem cell (iPSC)-derived astrocytes from both CMS and non-CMS highlanders who live in the Peruvian Andes (>14,000 ft) and studied pHi regulation in these astrocytes using pH-sensitive dye BCECF. Our results show that the steady-state pHi (ss pHi) is lower in CMS astrocytes compared with non-CMS astrocytes. In addition, the acid extrusion following an acid loading is faster and the pHi dependence of H+ flux rate becomes steeper in CMS astrocytes. Furthermore, the Na+ dependency of ss pHi is stronger in CMS astrocytes and the Na+/H+ exchanger (NHE) inhibitors blunted the acid extrusion in both CMS and non-CMS astrocytes. We conclude that (a) NHE contributes to the ss pHi stabilization and mediates active acid extrusion during the cytosolic acidosis in highlanders; (b) acid extrusion becomes less pHi sensitive in non-CMS (versus CMS) astrocytes which may prevent NHE from over-activated in the hypoxia-induced intracellular acidosis and render the non-CMS astrocytes more resistant to hypoxemia challenges.
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Diering GH, Numata M. Endosomal pH in neuronal signaling and synaptic transmission: role of Na(+)/H(+) exchanger NHE5. Front Physiol 2014; 4:412. [PMID: 24454292 PMCID: PMC3888932 DOI: 10.3389/fphys.2013.00412] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2013] [Accepted: 12/27/2013] [Indexed: 12/27/2022] Open
Abstract
Neuronal precursor cells extend multiple neurites during development, one of which extends to form an axon whereas others develop into dendrites. Chemical stimulation of N-methyl D-aspartate (NMDA) receptor in fully-differentiated neurons induces projection of dendritic spines, small spikes protruding from dendrites, thereby establishing another layer of polarity within the dendrite. Neuron-enriched Na+/H+ exchanger NHE5 contributes to both neurite growth and dendritic spine formation. In resting neurons and neuro-endocrine cells, neuron-enriched NHE5 is predominantly associated with recycling endosomes where it colocalizes with nerve growth factor (NGF) receptor TrkA. NHE5 potently acidifies the lumen of TrkA-positive recycling endosomes and regulates cell-surface targeting of TrkA, whereas chemical stimulation of NMDA receptors rapidly recruits NHE5 to dendritic spines, alkalinizes dendrites and down-regulates the dendritic spine formation. Possible roles of NHE5 in neuronal signaling via proton movement in subcellular compartments are discussed.
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Affiliation(s)
- Graham H Diering
- Department of Neuroscience, Johns Hopkins University School of Medicine Baltimore, MD, USA
| | - Masayuki Numata
- Department of Biochemistry and Molecular Biology, University of British Columbia Vancouver, BC, Canada
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Lukashova V, Jinadasa T, Ilie A, Verbich D, Cooper E, Orlowski J. The Na(+)/H (+) exchanger NHE5 is sorted to discrete intracellular vesicles in the central and peripheral nervous systems. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2013; 961:397-410. [PMID: 23224898 DOI: 10.1007/978-1-4614-4756-6_34] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The pH milieu of the central and peripheral nervous systems is an important determinant of neuronal excitability, function, and survival. In mammals, neural acid-base homeostasis is coordinately regulated by ion transporters belonging to the Na(+)/H(+) exchanger (NHE) and bicarbonate transporter gene families. However, the relative contributions of individual isoforms within the respective families are not fully understood. This report focuses on the NHE family, specifically the plasma membrane-type NHE5 which is preferentially transcribed in brain, but the distribution of the native protein has not been extensively characterized. To this end, we generated a rabbit polyclonal antibody that specifically recognizes NHE5. In both central (cortex, hippocampus) and peripheral (superior cervical ganglia, SCG) nervous tissue of mice, NHE5 immunostaining was punctate and highly concentrated in the somas and to lesser amounts in the dendrites of neurons. Very little signal was detected in axons. Similarly, in primary cultures of differentiated SCG neurons, NHE5 localized predominantly to vesicles in the somatodendritic compartment, though some immunostaining was also evident in punctate vesicles along the axons. NHE5 was also detected predominantly in intracellular vesicles of cultured SCG glial cells. Dual immunolabeling of SCG neurons showed that NHE5 did not colocalize with markers for early endosomes (EEA1) or synaptic vesicles (synaptophysin), but did partially colocalize with the transferrin receptor, a marker of recycling endosomes. Collectively, these data suggest that NHE5 partitions into a unique vesicular pool in neurons that shares some characteristics of recycling endosomes where it may serve as an important regulated store of functional transporters required to maintain cytoplasmic pH homeostasis.
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Pekun TG, Lemeshchenko VV, Lyskova TI, Waseem TV, Fedorovich SV. Influence of intra- and extracellular acidification on free radical formation and mitochondria membrane potential in rat brain synaptosomes. J Mol Neurosci 2012; 49:211-22. [PMID: 23124485 DOI: 10.1007/s12031-012-9913-3] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2012] [Accepted: 10/21/2012] [Indexed: 11/25/2022]
Abstract
Brain ischemia is accompanied by lowering of intra- and extracellular pH. Stroke often leads to irreversible damage of synaptic transmission by unknown mechanism. We investigated an influence of lowering of pH(i) and pH(o) on free radical formation in synaptosomes. Three models of acidosis were used: (1) pH(o) 6.0 corresponding to pH(i) decrease down to 6.04; (2) pH(o) 7.0 corresponding to the lowering of pH(i) down to 6.92: (3) 1 mM amiloride corresponding to pH(i) decrease down to 6.65. We have shown that both types of extracellular acidification, but not intracellular acidification, increase 2',7'-dichlorodihydrofluorescein diacetate fluorescence that reflects free radical formation. These three treatments induce the rise of the dihydroethidium fluorescence that reports synthesis of superoxide anion. However, the impact of amiloride on superoxide anion synthesis was less than that induced by moderate extracellular acidification. Superoxide anion synthesis at pH(o) 7.0 was almost completely eliminated by mitochondrial uncoupler carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone. Furthermore, using fluorescent dyes JC-1 and rhodamine-123, we confirmed that pH(o) lowering, but not intracellular acidification, led to depolarization of intrasynaptosomal mitochondria. We have shown that pH(o) but not pH(i) lowering led to oxidative stress in neuronal presynaptic endings that might underlie the long-term irreversible changing in synaptic transmission.
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Affiliation(s)
- Tatyana G Pekun
- Laboratory of Biophysics and Engineering of Cell, Institute of Biophysics and Cell Engineering, Akademicheskaya St., 27, Minsk 220072, Belarus
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Cammalleri M, Martini D, Ristori C, Timperio AM, Bagnoli P. Vascular endothelial growth factor up-regulation in the mouse hippocampus and its role in the control of epileptiform activity. Eur J Neurosci 2010; 33:482-98. [DOI: 10.1111/j.1460-9568.2010.07529.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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9
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The hypoxia-induced facilitation of augmented breaths is suppressed by the common effect of carbonic anhydrase inhibition. Respir Physiol Neurobiol 2010; 171:201-11. [PMID: 20382275 DOI: 10.1016/j.resp.2010.04.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2009] [Revised: 04/01/2010] [Accepted: 04/02/2010] [Indexed: 11/20/2022]
Abstract
The typical respiratory response to hypoxia includes a dramatic facilitation of augmented breaths (ABs) or 'sighs' in the breathing rhythm. We recently found that when acetazolamide treatment is used to promote CO(2) retention and counteract alkalosis during exposure to hypoxia, then the hypoxia-induced facilitation of ABs is effectively prevented. These results indicate that hyperventilation-induced hypocapnia/alkalosis is an essential factor involved in the hypoxia-induced facilitation of augmented breaths. However, acetazolamide is also known to decrease the sensitivity of the arterial chemoreceptors. Therefore, the question remains as to whether acetazolamide prevents the facilitation of ABs during hypoxia by offsetting the effects of respiratory alkalosis, or alternatively by suppressing carotid body afferent activity. In the present study, we addressed this question by studying the effects of treatment with an alternative carbonic anhydrase inhibitor, methazolamide, which has been reported to leave carotid body responsiveness to hypoxia intact. Respiratory variables were monitored before, during and after 2 days of methazolamide treatment (10 mg kg(-1) IP, bid) in unsedated and unrestrained adult male rats. Pre-treatment, the number of ABs observed in a 5 min observation window was 1.2 + or - 0.8 and 17.4 + or - 3.8 in room air and hypoxia, respectively. During methazolamide treatment, the facilitation of ABs in hypoxia was rapidly and reversibly suppressed such that ABs we no longer significantly more frequent than they were in room air. The present results demonstrate that the hypoxia-induced facilitation of ABs can be suppressed via the general effects of carbonic anhydrase inhibition, which are common to both acetazolamide and methazolamide. We discuss these results as they pertain to the mechanisms regulating augmented breath production, and the possible association between hypocapnia/alkalosis and sleep disordered breathing.
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10
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Rönicke R, Schröder UH, Böhm K, Reymann KG. The Na+/H+ exchanger modulates long-term potentiation in rat hippocampal slices. Naunyn Schmiedebergs Arch Pharmacol 2008; 379:233-9. [PMID: 18972102 DOI: 10.1007/s00210-008-0364-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2008] [Accepted: 10/07/2008] [Indexed: 11/30/2022]
Abstract
Although present in great variety in the brain, the role of Na(+)/H(+) exchangers (NHEs) in hippocampal plasticity is still unknown and the effect of NHE inhibition on long-term potentiation (LTP) has not been studied yet. As it is conceivable that NHE inhibitors may severely affect mechanisms that are considered to underlie learning and memory we investigated whether the broad-spectrum NHE inhibitor 5'-(N-ethyl-N-isopropyl)-amiloride (EIPA, 10 microM) influences LTP induced by different stimuli based on a theta burst in interface hippocampus slices from 7-8-week-old Wistar and 30-month-old Fischer 344/Brown-Norway F1 hybrid (F344/BN) rats. EIPA did not affect basal synaptic transmission, paired pulse inhibition, or LTP induced by a weak stimulus, but improved the maintenance of the LTP of the population spike induced by a strong tetanus. Our data suggest that NHE activity serves as a negative feedback mechanism to control neuronal excitability and plasticity in both young and senescent animals.
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Affiliation(s)
- Raik Rönicke
- Project Group Neuropharmacology, Leibniz Institute for Neurobiology, Brenneckestrasse 6., 39118, Magdeburg, Germany.
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11
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Rickmann M, Orlowski B, Heupel K, Roussa E. Distinct expression and subcellular localization patterns of Na+/HCO3− cotransporter (SLC 4A4) variants NBCe1-A and NBCe1-B in mouse brain. Neuroscience 2007; 146:1220-31. [PMID: 17433553 DOI: 10.1016/j.neuroscience.2007.02.061] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2007] [Revised: 02/14/2007] [Accepted: 02/21/2007] [Indexed: 11/29/2022]
Abstract
The electrogenic Na+/HCO3- cotransporter (NBCe1) has been identified as a key player for regulation of intracellular pH in several cell types. The present study was undertaken to determine expression and subcellular localization of the NH2-terminal solute carrier (SLC) 4A4 variants NBCe1-A and NBCe1-B in mouse brain using variant-specific antibodies by immunohistochemistry and immunoelectron microscopy. In addition, distribution of NBCe1 variants and activity-dependent regulation was investigated in mouse embryonic day 17.5 (E17.5) hippocampal primary cultures in vitro. The results showed NBCe1-A and NBCe1-B transcript expression in the mouse olfactory bulb, cerebral cortex, hippocampus and cerebellum. NBCe1-A was predominantly expressed in Purkinje cells, granule cells of the dentate gyrus, non-pyramidal cell bodies in cerebral cortex, and in periglomerular and mitral cells in the olfactory bulb. Pyramidal neurons in cerebral cortex and apical cell dendrites in the hippocampus were stained for both NBCe1-A and NBCe1-B. Moreover, NBCe1-B was present in Bergmann glia. At the ultrastructural level, NBCe1-B was preferentially expressed in perivascular astroglial lamellae, whereas both NBCe1 NH2-terminal variants were localized in pre- and postsynaptic compartments. Except for the olfactory bulb, NBCe1-A was always colocalized with calbindin. Treatment of E17.5 primary hippocampal cultures with KCl, showed dramatic downregulation of NBCe1-B mRNA and protein after 60 min, whereas NBCe1-A expression remained unchanged. These data demonstrate for the first time distinct cellular distribution of NBCe1 NH2-terminal variants in mouse brain. NBCe1 may be involved in neuronal modulation, and pH regulation during neuronal activity.
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Affiliation(s)
- M Rickmann
- Center for Anatomy, Department of Neuroanatomy, Georg-August-University Goettingen, Kreuzbergring 36, D-37075 Goettingen, Germany
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12
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Yang L, Ling DSF. Carbenoxolone modifies spontaneous inhibitory and excitatory synaptic transmission in rat somatosensory cortex. Neurosci Lett 2007; 416:221-6. [PMID: 17382470 PMCID: PMC1934620 DOI: 10.1016/j.neulet.2007.01.042] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2006] [Revised: 10/30/2006] [Accepted: 01/22/2007] [Indexed: 11/16/2022]
Abstract
Gap junction (GJ) coupling between neocortical GABAergic interneurons plays a critical role in the synchronization of activity in cortical networks in physiological and pathophysiological states, e.g., seizures. Past studies have shown that GJ blockers exert anticonvulsant actions in both in vivo and in vitro models of epilepsy. However, the precise mechanisms underlying these antiepileptic effects have not been fully elucidated. This is due, in part, to a lack of information of the influence of GJ blockade on network activity in the absence of convulsant agents or enhanced neuronal excitation. One key question is whether GJ blockers act on excitatory or inhibitory systems, or both. To address this issue, we examined the effects of the GJ blocker carbenoxolone (CarbX, 150 microM) on spontaneous inhibitory postsynaptic currents (sIPSCs) and excitatory postsynaptic currents (sEPSCs) in acute slices of rat somatosensory cortex. Results showed that CarbX decreased the amplitude and frequency of sIPSCs by 30.2% and 25.7%, respectively. CarbX increased the mean frequency of sEPSCs by 24.1%, but had no effect on sEPSC amplitude. During blockade of GABAA-mediated events with picrotoxin (20 microM), CarbX induced only a small increase in sEPSC frequency that was not statistically different from control, indicating CarbX enhancement of sEPECs was secondary to the depression of synaptic inhibition. These findings suggest that in neocortex, blockade of GJs leads to an increase in spontaneous excitation by uncoupling GABAergic interneurons, and that electronic communication between inhibitory cells plays a significant role in regulating tonic synaptic excitation.
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Affiliation(s)
- Lie Yang
- Department of Physiology and The Robert F. Furchgott Center for Neural and Behavioral Science, State University of New York, Downstate Medical Center, Brooklyn, NY 11203, USA.
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Kim JH, Kim JH, Kwon TH, Park YK, Chung HS. DPCPX-resistant hypoxic synaptic depression in the CA1 region of hippocampal slices: Possible role of intracellular accumulation of monocarboxylates. Neurosci Lett 2006; 403:141-6. [PMID: 16714083 DOI: 10.1016/j.neulet.2006.04.032] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2006] [Revised: 04/17/2006] [Accepted: 04/21/2006] [Indexed: 10/24/2022]
Abstract
Adenosine plays the principal role in synaptic depression during various energy-depleted conditions. However, additional inhibitory factors not associated with A1 adenosine receptors appear to be involved in hypoxic insults. Monocarboxylate accumulation and consequent acidic changes during hypoxia may be responsible for this remaining depression in synaptic activity. Field evoked potentials were recorded in the CA1 region of rat hippocampal slices. Preincubation with 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) disclosed 43% of DPCPX-resistant synaptic depression (DRSD) during oxygen deprivation (OD). In contrast, no DRSD was detected in various conditions with limited glucose utilization, such as glucose deprivation and oxygen-glucose deprivation. Inhibition of anaerobic glycolysis (iodoacetate, sodium fluoride) abolished DRSD during OD, whereas blockade of monocarboxylate utilization with alpha-cyano-4-hydroxycinnamic acid (4-CIN) provoked DRSD in normoxic medium. These observations suggest that an intracellular accumulation of monocarboxylates is responsible for DRSD during hypoxia.
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Affiliation(s)
- Jong-Hyun Kim
- Department of Neurosurgery, Korea University Guro Hospital, 80 Guro-dong, Seoul 152-703, Republic of Korea
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Otsuguro KI, Yamaji Y, Ban M, Ohta T, Ito S. Involvement of adenosine in depression of synaptic transmission during hypercapnia in isolated spinal cord of neonatal rats. J Physiol 2006; 574:835-47. [PMID: 16740614 PMCID: PMC1817731 DOI: 10.1113/jphysiol.2006.109660] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Adenosine is one of the most important neuromodulators in the CNS, both under physiological and pathological conditions. In the isolated spinal cord of the neonatal rat in vitro, acute hypercapnic acidosis (20% CO2, pH 6.7) reversibly depressed electrically evoked spinal reflex potentials. This depression was partially reversed by 8-cyclopentlyl-1,3-dimethylxanthine (CPT), a selective A1 adenosine receptor antagonist. Isohydric hypercapnia (20% CO2, pH 7.3), but not isocapnic acidosis (5% CO2, pH 6.7), depressed the reflex potentials, which were also reversed by CPT. An ecto-5'-nucleotidase inhibitor did not affect the hypercapnic acidosis-evoked depression. An inhibitor of adenosine kinase, but not deaminase, mimicked the inhibitory effect of hypercapnic acidosis on the spinal reflex potentials. Accumulation of extracellular adenosine and inhibition of adenosine kinase activity were caused by hypercapnic acidosis and isohydric hypercapnia, but not isohydric acidosis. These results indicate that the activation of adenosine A1 receptors is involved in the hypercapnia-evoked depression of reflex potentials in the isolated spinal cord of the neonatal rat. The inhibition of adenosine kinase activity is suggested to cause the accumulation of extracellular adenosine during hypercapnia.
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Affiliation(s)
- Ken-ichi Otsuguro
- Laboratory of Pharmacology, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan.
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Sajikumar S, Navakkode S, Frey JU. Protein synthesis-dependent long-term functional plasticity: methods and techniques. Curr Opin Neurobiol 2005; 15:607-13. [PMID: 16150586 DOI: 10.1016/j.conb.2005.08.009] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2005] [Accepted: 08/25/2005] [Indexed: 11/16/2022]
Abstract
There is growing interest in late-LTP and late-LTD, that is, distinct forms of functional plasticity that require somatic functions such as protein synthesis in addition to the transient synaptic processes that are required for short lasting forms. Interestingly, to date only these forms of lasting plastic events could be detected in healthy, freely moving animals and thus, they are considered as physiological cellular models of learning and memory formation. Late-LTP and -LTD are characterized by 'synaptic tagging' or 'capture' and 'synaptic cross-tagging', but there are only a few laboratories that can currently perform experiments studying these properties. In brain slice work, there are many different approaches to investigate these processes using different methodological variations: some allow slices to rest for long periods before the experiment starts, others do not; some run their experiments at near to physiological temperatures, others at lower temperatures; some stimulate frequently, others do not.
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Affiliation(s)
- Sreedharan Sajikumar
- Department of Neurophysiology, Leibniz Institute for Neurobiology, Brenneckestrasse 6, 39118 Magdeburg, Germany
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Abstract
Axonal damage has recently been recognized to be a key predictor of outcome in a number of diverse human CNS diseases, including head and spinal cord trauma, metabolic encephalopathies, multiple sclerosis and other white-matter diseases (acute haemorrhagic leucoencephalitis, leucodystrophies and central pontine myelinolysis), infections [malaria, acquired immunodeficiency syndrome (AIDS) and infection with human lymphotropic virus type 1 (HTLV-I) causing HTLV-I-associated myelopathy (HAM)/tropical spastic paraparesis (TSP)] and subcortical ischaemic damage. The evidence for axonal damage and, where available, its correlation with neurological outcome in each of these conditions is reviewed. We consider the possible pathogenetic mechanisms involved and how increasing understanding of these may lead to more effective therapeutic or preventive interventions.
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Affiliation(s)
- I M Medana
- Department of Clinical Laboratory Sciences, University of Oxford, UK
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17
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Abstract
Although recent evidence demonstrates considerable neuroplasticity in the respiratory control system, a comprehensive conceptual framework is lacking. Our goals in this review are to define plasticity (and related neural properties) as it pertains to respiratory control and to discuss potential sites, mechanisms, and known categories of respiratory plasticity. Respiratory plasticity is defined as a persistent change in the neural control system based on prior experience. Plasticity may involve structural and/or functional alterations (most commonly both) and can arise from multiple cellular/synaptic mechanisms at different sites in the respiratory control system. Respiratory neuroplasticity is critically dependent on the establishment of necessary preconditions, the stimulus paradigm, the balance between opposing modulatory systems, age, gender, and genetics. Respiratory plasticity can be induced by hypoxia, hypercapnia, exercise, injury, stress, and pharmacological interventions or conditioning and occurs during development as well as in adults. Developmental plasticity is induced by experiences (e.g., altered respiratory gases) during sensitive developmental periods, thereby altering mature respiratory control. The same experience later in life has little or no effect. In adults, neuromodulation plays a prominent role in several forms of respiratory plasticity. For example, serotonergic modulation is thought to initiate and/or maintain respiratory plasticity following intermittent hypoxia, repeated hypercapnic exercise, spinal sensory denervation, spinal cord injury, and at least some conditioned reflexes. Considerable work is necessary before we fully appreciate the biological significance of respiratory plasticity, its underlying cellular/molecular and network mechanisms, and the potential to harness respiratory plasticity as a therapeutic tool.
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Affiliation(s)
- Gordon S Mitchell
- Department of Comparative Biosciences, University of Wisconsin, Madison 53706, USA.
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18
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Abstract
The expression of mRNA for acid sensing ion channels (ASIC) subunits ASIC1a, ASIC2a and ASIC2b has been reported in hippocampal neurons, but the presence of functional hippocampal ASIC channels was never assessed. We report here the first characterization of ASIC-like currents in rat hippocampal neurons in primary culture. An extracellular pH drop induces a transient Na(+) current followed by a sustained non-selective cation current. This current is highly sensitive to pH with an activation threshold around pH 6.9 and a pH(0.5) of 6.2. About half of the total peak current is inhibited by the spider toxin PcTX1, which is specific for homomeric ASIC1a channels. The remaining PcTX1-resistant ASIC-like current is increased by 300 microM Zn(2+) and, whereas not fully activated at pH 5, it shows a pH(0.5) of 6.0 between pH 7.4 and 5. We have previously shown that Zn(2+) is a co-activator of ASIC2a-containing channels. Thus, the hippocampal transient ASIC-like current appears to be generated by a mixture of homomeric ASIC1a channels and ASIC2a-containing channels, probably heteromeric ASIC1a+2a channels. The sustained non-selective current suggests the involvement of ASIC2b-containing heteromeric channels. Activation of the hippocampal ASIC-like current by a pH drop to 6.9 or 6.6 induces a transient depolarization which itself triggers an initial action potential (AP) followed by a sustained depolarization and trains of APs. Zn(2+) increases the acid sensitivity of ASIC channels, and consequently neuronal excitability. It is probably an important co-activator of ASIC channels in the central nervous system.
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Affiliation(s)
- Anne Baron
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS-UMR 6097, 660 route des Lucioles, Sophia Antipolis, 06560 Valbonne, France
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