1
|
Kinoshita M, Okamoto H. Acetylcholine potentiates glutamate transmission from the habenula to the interpeduncular nucleus in losers of social conflict. Curr Biol 2023:S0960-9822(23)00445-1. [PMID: 37105168 DOI: 10.1016/j.cub.2023.03.087] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2022] [Revised: 03/02/2023] [Accepted: 03/31/2023] [Indexed: 04/29/2023]
Abstract
Switching behaviors from aggression to submission in losers at the end of conspecific social fighting is essential to avoid serious injury or death. We have previously shown that the experience of defeat induces a loser-specific potentiation in the habenula (Hb)-interpeduncular nucleus (IPN) and show here that this is induced by acetylcholine. Calcium imaging and electrophysiological recording using acute brain slices from winners and losers of fighting behavior in zebrafish revealed that the ventral IPN (vIPN) dominates over the dorsal IPN in the neural response to Hb stimulation in losers. We also show that GluA1 α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunits on the postsynaptic membrane increased in the vIPN of losers. Furthermore, these loser-specific neural properties disappeared in the presence of an α7 nicotinic acetylcholine receptor (nAChR) antagonist and, conversely, were induced in brain slices of winners treated with α7 nAChR agonists. These data suggest that acetylcholine released from Hb terminals in the vIPN induces activation of α7 nAChR followed by an increase in postsynaptic membrane GluA1. This results in an increase in active synapses on postsynaptic neurons, resulting in the potentiation of neurotransmissions to the vIPN. This acetylcholine-induced neuromodulation could be the neural foundation for behavioral switching in losers. Our results could increase our understanding of the mechanisms of various mood disorders such as social anxiety disorder and social withdrawal.
Collapse
Affiliation(s)
- Masae Kinoshita
- Laboratory for Neural Circuit Dynamics of Decision Making, RIKEN Center for Brain Science, Saitama 351-0198, Japan
| | - Hitoshi Okamoto
- Laboratory for Neural Circuit Dynamics of Decision Making, RIKEN Center for Brain Science, Saitama 351-0198, Japan; RIKEN CBS-Kao Collaboration Center, Saitama 351-0198, Japan.
| |
Collapse
|
2
|
Koene LM, Niggl E, Wallaard I, Proietti-Onori M, Rotaru DC, Elgersma Y. Identifying the temporal electrophysiological and molecular changes that contribute to TSC-associated epileptogenesis. JCI Insight 2021; 6:e150120. [PMID: 34877936 PMCID: PMC8675202 DOI: 10.1172/jci.insight.150120] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2021] [Accepted: 10/27/2021] [Indexed: 11/17/2022] Open
Abstract
Tuberous sclerosis complex (TSC), caused by heterozygous mutations in TSC1 or TSC2, frequently results in intractable epilepsy. Here, we made use of an inducible Tsc1-knockout mouse model, allowing us to study electrophysiological and molecular changes of Tsc1-induced epileptogenesis over time. We recorded from pyramidal neurons in the hippocampus and somatosensory cortex (L2/L3) and combined this with an analysis of transcriptome changes during epileptogenesis. Deletion of Tsc1 resulted in hippocampus-specific changes in excitability and adaptation, which emerged before seizure onset and progressed over time. All phenotypes were rescued after early treatment with rapamycin, an mTOR inhibitor. Later in epileptogenesis, we observed a hippocampal increase of excitation-to-inhibition ratio. These cellular changes were accompanied by dramatic transcriptional changes, especially after seizure onset. Most of these changes were rescued upon rapamycin treatment. Of the genes encoding ion channels or belonging to the Gene Ontology term action potential, 27 were differentially expressed just before seizure onset, suggesting a potential driving role in epileptogenesis. Our data highlight the complex changes driving epileptogenesis in TSC, including the changed expression of multiple ion channels. Our study emphasizes inhibition of the TSC/mTOR signaling pathway as a promising therapeutic approach to target epilepsy in patients with TSC.
Collapse
|
3
|
Varga AG, Maletz SN, Bateman JT, Reid BT, Levitt ES. Neurochemistry of the Kölliker-Fuse nucleus from a respiratory perspective. J Neurochem 2020; 156:16-37. [PMID: 32396650 DOI: 10.1111/jnc.15041] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2020] [Revised: 04/27/2020] [Accepted: 05/04/2020] [Indexed: 12/11/2022]
Abstract
The Kölliker-Fuse nucleus (KF) is a functionally distinct component of the parabrachial complex, located in the dorsolateral pons of mammals. The KF has a major role in respiration and upper airway control. A comprehensive understanding of the KF and its contributions to respiratory function and dysfunction requires an appreciation for its neurochemical characteristics. The goal of this review is to summarize the diverse neurochemical composition of the KF, focusing on the neurotransmitters, neuromodulators, and neuropeptides present. We also include a description of the receptors expressed on KF neurons and transporters involved in each system, as well as their putative roles in respiratory physiology. Finally, we provide a short section reviewing the literature regarding neurochemical changes in the KF in the context of respiratory dysfunction observed in SIDS and Rett syndrome. By over-viewing the current literature on the neurochemical composition of the KF, this review will serve to aid a wide range of topics in the future research into the neural control of respiration in health and disease.
Collapse
Affiliation(s)
- Adrienn G Varga
- Department of Pharmacology and Therapeutics, University of Florida, Gainesville, FL, USA.,Department of Physical Therapy, Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, FL, USA
| | - Sebastian N Maletz
- Department of Pharmacology and Therapeutics, University of Florida, Gainesville, FL, USA
| | - Jordan T Bateman
- Department of Pharmacology and Therapeutics, University of Florida, Gainesville, FL, USA.,Department of Physical Therapy, Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, FL, USA
| | - Brandon T Reid
- Department of Pharmacology and Therapeutics, University of Florida, Gainesville, FL, USA
| | - Erica S Levitt
- Department of Pharmacology and Therapeutics, University of Florida, Gainesville, FL, USA.,Department of Physical Therapy, Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, FL, USA
| |
Collapse
|
4
|
Mechanisms of zinc modulation of olfactory bulb AMPA receptors. Neuroscience 2019; 410:160-175. [PMID: 31082537 DOI: 10.1016/j.neuroscience.2019.05.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2019] [Revised: 05/01/2019] [Accepted: 05/03/2019] [Indexed: 12/31/2022]
Abstract
The alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) subtype of ionotropic glutamate receptors mediates most fast excitatory transmission. Glutamate binding to AMPA receptors (AMPARs) causes most AMPARs to rapidly and completely desensitize, and their desensitization kinetics influence synaptic timing. Thus, factors that alter AMPAR desensitization influence synaptic transmission. Synaptically released zinc is such a factor. Zinc is a neuromodulator with effects on amino acid receptors and synaptic transmission in many brain regions, including the olfactory bulb (OB). We have previously shown in the OB that zinc potentiates AMPAR-mediated currents at low concentrations (30 μM, 100 μM) and inhibits them at a higher concentration (1 mM). It has been hypothesized that zinc potentiates AMPARs by decreasing receptor desensitization. Here, we used cyclothiazide (CTZ), a drug that blocks AMPAR desensitization, to determine whether zinc-mediated potentiation and/or inhibition of AMPA-evoked currents reflect(s) changes in AMPAR desensitization. Zinc largely had biphasic concentration-dependent effects at OB AMPARs. CTZ completely blocked potentiation by zinc but had no significant effect on inhibition. There was a significant negative correlation between the degree of potentiation of AMPAR-mediated currents by 100 μM zinc and a quantitative measure of the degree of AMPAR desensitization (the steady-state to peak [S:P] ratio of AMPA-evoked currents), but no correlation between the degree of current inhibition by 1 mM zinc and the S:P ratio. Together, these findings suggest that low zinc concentrations potentiate rat OB AMPARs by decreasing receptor desensitization, but that the inhibitory effects of higher zinc concentrations are mediated by a separate mechanism.
Collapse
|
5
|
Zhang M, Stern JE. Altered NMDA receptor-evoked intracellular Ca 2+ dynamics in magnocellular neurosecretory neurons of hypertensive rats. J Physiol 2017; 595:7399-7411. [PMID: 29034474 DOI: 10.1113/jp275169] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2017] [Accepted: 10/03/2017] [Indexed: 01/03/2023] Open
Abstract
KEY POINTS NMDA receptor (NMDAR)-mediated Ca2+ signalling plays a critical role in modulating hypothalamic neurosecretory function. However, whether an altered NMDAR-evoked changes in Ca2+ (NMDAR-ΔCa2+ ) signalling in magnocellular neurosecretory cells (MNCs) may contribute to neurohumoral activation during disease states is unknown. We show that activation of NMDARs evoked similar inward currents in MNCs of sham and renovascular hypertensive (RVH) rats. Despite this, a prolonged and larger NMDAR-ΔCa2+ response was observed in the latter. The exacerbated NMDAR-ΔCa2+ responses in MNCs of RVH rats affected both somatic and dendritic compartments. Inhibition of the endoplasmic reticulum sarcoendoplasmic reticulum calcium trasport ATPase (SERCA) pump prolonged NMDAR-ΔCa2+ responses in sham rats, but not in RVH rats. Our study supports an altered spatiotemporal dynamic of NMDAR-ΔCa2+ signalling in MNCs from RVH rats, partly due to blunted endoplasmic reticulum Ca2+ buffering capacity. ABSTRACT A growing body of evidence supports an elevated NMDA receptor (NMDAR)-mediated glutamate excitatory function in the supraoptic nucleus and paraventricular nucleus of hypertensive rats that contributes to neurohumoral activation in this disease. However, the precise mechanisms underlying altered NMDAR signalling in hypertension remain to be elucidated. In this study, we performed simultaneous electrophysiology and fast confocal Ca2+ imaging to determine whether altered NMDAR-mediated changes in intracellular Ca2+ levels (NMDAR-ΔCa2+ ) occurred in hypothalamic magnocellular neurosecretory cells (MNCs) in renovascular hypertensive (RVH) rats. We found that despite evoking a similar excitatory inward current, activation of NMDARs resulted in a larger and prolonged ΔCa2+ in MNCs from RVH rats. Changes in NMDAR-ΔCa2+ dynamics were observed both in somatic and dendritic compartments. Inhibition of the sarcoendoplasmic reticulum calcium trasport ATPase (SERCA) pump activity with thapsigargin prolonged NMDAR-ΔCa2+ responses in MNCs of sham rats, but this effect was occluded in RVH rats, thus equalizing the magnitude and time course of the NMDA-ΔCa2+ responses between the two experimental groups. Taken together, our results support (1) an exacerbated NMDAR-ΔCa2+ response in somatodendritic compartments of MNCs of RVH rats, and (2) that a blunted ER Ca2+ buffering capacity contributes to the altered NMDAR-ΔCa2+ dynamics in this condition. Thus, altered spatiotemporal dynamics of the NMDAR-ΔCa2+ response stands as an underlying mechanism contributing to neurohumoral activation in neurogenic hypertension.
Collapse
Affiliation(s)
- Meng Zhang
- Department of Physiology, Medical College of Georgia, Augusta University, 1120 15th Street, Augusta, GA 30912, USA
| | - Javier E Stern
- Department of Physiology, Medical College of Georgia, Augusta University, 1120 15th Street, Augusta, GA 30912, USA
| |
Collapse
|
6
|
Passlick S, Ellis-Davies GCR. Comparative one- and two-photon uncaging of MNI-glutamate and MNI-kainate on hippocampal CA1 neurons. J Neurosci Methods 2017; 293:321-328. [PMID: 29051090 DOI: 10.1016/j.jneumeth.2017.10.013] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2017] [Revised: 10/13/2017] [Accepted: 10/16/2017] [Indexed: 11/25/2022]
Abstract
BACKGROUND The light-induced release of neurotransmitters from caging chromophores provides a powerful means to study the underlying receptors in a physiologically relevant context. Surprisingly, most caged neurotransmitters, including the widely used 4-methoxy-7-nitroindolinyl (MNI)-glutamate, show strong antagonism against GABA-A receptors. Kainate has been shown to exhibit a higher efficacy at glutamate receptors compared to glutamate itself. Thus, uncaging of kainate might allow the application of the caged compound at lower, less antagonistic concentrations. NEW METHODS This study provides a detailed comparison of MNI-glutamate and MNI-kainate uncaging by different modes of one- and two-photon irradiation on hippocampal CA1 pyramidal neurons in acute brain slices. RESULTS/COMPARISON WITH EXISTING METHODS Unexpectedly, the data revealed that currents in response to MNI-glutamate uncaging were larger compared to MNI-kainate with local one-photon laser uncaging at the soma and two-photon uncaging at the same spines. Furthermore, the direct comparison demonstrates the influence of type of caged agonist and light delivery conditions used for uncaging on the amplitude and kinetic properties of the current response. CONCLUSION These findings highlight the importance of experimental design for uncaging experiments and provide a basis for future studies employing one- and two-photon uncaging to understand glutamate-dependent processes. It further provides the first example of two-photon uncaging of kainate at single spines in acute brain slices.
Collapse
Affiliation(s)
- Stefan Passlick
- Department of Neuroscience, Mount Sinai School of Medicine, New York, NY 10029, USA.
| | | |
Collapse
|
7
|
Bettler B, Fakler B. Ionotropic AMPA-type glutamate and metabotropic GABAB receptors: determining cellular physiology by proteomes. Curr Opin Neurobiol 2017; 45:16-23. [DOI: 10.1016/j.conb.2017.02.011] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2016] [Accepted: 02/15/2017] [Indexed: 02/07/2023]
|
8
|
Brechet A, Buchert R, Schwenk J, Boudkkazi S, Zolles G, Siquier-Pernet K, Schaber I, Bildl W, Saadi A, Bole-Feysot C, Nitschke P, Reis A, Sticht H, Al-Sanna'a N, Rolfs A, Kulik A, Schulte U, Colleaux L, Abou Jamra R, Fakler B. AMPA-receptor specific biogenesis complexes control synaptic transmission and intellectual ability. Nat Commun 2017; 8:15910. [PMID: 28675162 PMCID: PMC5500892 DOI: 10.1038/ncomms15910] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2016] [Accepted: 05/11/2017] [Indexed: 11/25/2022] Open
Abstract
AMPA-type glutamate receptors (AMPARs), key elements in excitatory neurotransmission in the brain, are macromolecular complexes whose properties and cellular functions are determined by the co-assembled constituents of their proteome. Here we identify AMPAR complexes that transiently form in the endoplasmic reticulum (ER) and lack the core-subunits typical for AMPARs in the plasma membrane. Central components of these ER AMPARs are the proteome constituents FRRS1l (C9orf4) and CPT1c that specifically and cooperatively bind to the pore-forming GluA1-4 proteins of AMPARs. Bi-allelic mutations in the human FRRS1L gene are shown to cause severe intellectual disability with cognitive impairment, speech delay and epileptic activity. Virus-directed deletion or overexpression of FRRS1l strongly impact synaptic transmission in adult rat brain by decreasing or increasing the number of AMPARs in synapses and extra-synaptic sites. Our results provide insight into the early biogenesis of AMPARs and demonstrate its pronounced impact on synaptic transmission and brain function. The biogenesis of AMPA-type glutamate receptor (AMPAR) complexes is only partially understood. Here the authors identify transient assemblies of GluA1-4 proteins and proteins FRRS1l/CPT1c that drive formation of mature AMPAR complexes in the ER. Mutations in FRRS1l are associated with intellectual disability and epilepsy in three families.
Collapse
Affiliation(s)
- Aline Brechet
- Institute of Physiology, Faculty of Medicine, University of Freiburg, Hermann-Herder-Str. 7, Freiburg 79104, Germany
| | - Rebecca Buchert
- Institute of Human Genetics, University of Erlangen, Schwabachanlage 10, Erlangen 91054, Germany
| | - Jochen Schwenk
- Institute of Physiology, Faculty of Medicine, University of Freiburg, Hermann-Herder-Str. 7, Freiburg 79104, Germany.,Center for Biological Signaling Studies (BIOSS), Schänzlestr. 18, Freiburg 79104, Germany
| | - Sami Boudkkazi
- Institute of Physiology, Faculty of Medicine, University of Freiburg, Hermann-Herder-Str. 7, Freiburg 79104, Germany
| | - Gerd Zolles
- Institute of Physiology, Faculty of Medicine, University of Freiburg, Hermann-Herder-Str. 7, Freiburg 79104, Germany
| | - Karine Siquier-Pernet
- INSERM UMR 1163, Paris-Descartes-Sorbonne Paris Cité University, Institut IMAGINE, Necker-Enfants Malades Hospital, Paris 75015, France
| | - Irene Schaber
- Institute of Physiology, Faculty of Medicine, University of Freiburg, Hermann-Herder-Str. 7, Freiburg 79104, Germany
| | - Wolfgang Bildl
- Institute of Physiology, Faculty of Medicine, University of Freiburg, Hermann-Herder-Str. 7, Freiburg 79104, Germany
| | - Abdelkrim Saadi
- Department de Neurologie, Etablissement Hospitalier Specialisé de Benaknoun, Algers, Algeria
| | - Christine Bole-Feysot
- INSERM UMR 1163, Paris-Descartes-Sorbonne Paris Cité University, Institut IMAGINE, Necker-Enfants Malades Hospital, Paris 75015, France
| | - Patrick Nitschke
- INSERM UMR 1163, Paris-Descartes-Sorbonne Paris Cité University, Institut IMAGINE, Necker-Enfants Malades Hospital, Paris 75015, France
| | - Andre Reis
- Institute of Human Genetics, University of Erlangen, Schwabachanlage 10, Erlangen 91054, Germany
| | - Heinrich Sticht
- Institute of Biochemistry, Emil-Fischer Center, Fahrstraße 17, Erlangen 91054, Germany
| | - Nouriya Al-Sanna'a
- Dharan Health Center, 8131 Medical Access Rd 1, Gharb al Dharan, Dharan 34465, Saudi Arabia
| | - Arndt Rolfs
- Center for Biological Signaling Studies (BIOSS), Schänzlestr. 18, Freiburg 79104, Germany.,Albrecht-Kossel-Institute for Neuroregeneration, Medical University Rostock, Gehlsheimerstr. 20, Rostock 18147, Germany
| | - Akos Kulik
- Institute of Physiology, Faculty of Medicine, University of Freiburg, Hermann-Herder-Str. 7, Freiburg 79104, Germany.,Center for Biological Signaling Studies (BIOSS), Schänzlestr. 18, Freiburg 79104, Germany
| | - Uwe Schulte
- Institute of Physiology, Faculty of Medicine, University of Freiburg, Hermann-Herder-Str. 7, Freiburg 79104, Germany.,Center for Biological Signaling Studies (BIOSS), Schänzlestr. 18, Freiburg 79104, Germany.,Logopharm GmbH, Schlossstr. 14, March-Buchheim 79232, Germany
| | - Laurence Colleaux
- INSERM UMR 1163, Paris-Descartes-Sorbonne Paris Cité University, Institut IMAGINE, Necker-Enfants Malades Hospital, Paris 75015, France
| | - Rami Abou Jamra
- Institute of Human Genetics, University of Erlangen, Schwabachanlage 10, Erlangen 91054, Germany.,Institute of Human Genetics, University of Leipzig Hospitals and Clinics, Philipp-Rosenthal-Str. 55, 04103 Leipzig, Germany
| | - Bernd Fakler
- Institute of Physiology, Faculty of Medicine, University of Freiburg, Hermann-Herder-Str. 7, Freiburg 79104, Germany.,Center for Biological Signaling Studies (BIOSS), Schänzlestr. 18, Freiburg 79104, Germany
| |
Collapse
|
9
|
Tovar KR, Westbrook GL. Modulating synaptic NMDA receptors. Neuropharmacology 2016; 112:29-33. [PMID: 27565459 DOI: 10.1016/j.neuropharm.2016.08.023] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2016] [Accepted: 08/17/2016] [Indexed: 12/14/2022]
Abstract
Recent structural information on ligand-gated glutamate receptors and newly-discovered clinical uses for NMDA receptor antagonists has renewed interest in understanding the mechanisms of drug action at these receptors. Although the voltage-dependence and calcium permeability of NMDA receptors are well-studied, the mechanisms affecting the time course of synaptic NMDA receptor activation may be of more therapeutic value by serving as a rheostat for the total synaptic response. The NMDA receptor-mediated EPSC time course has been thought of as a fixed parameter based simply on receptor subunit composition as variably constrained by anatomical and developmental expression patterns, albeit subject to modification by kinetic behaviors such as modal gating. However, the EPSC time course also can be manipulated by endogenous and exogenous ligands. In this commentary we discuss insights into the in situ composition and kinetic behavior of synaptic NMDA receptors and propose new opportunities to target modulatory sites on NMDA receptors and to develop useful therapeutics. The emerging data on the atomic structure of NMDA receptors and knowledge of the kinetics of native receptors in neurons provide a roadmap in this regard. This article is part of the Special Issue entitled 'Ionotropic glutamate receptors'.
Collapse
Affiliation(s)
- Kenneth R Tovar
- Vollum Institute, Oregon Health & Science University, Portland, OR 97239, United States.
| | - Gary L Westbrook
- Vollum Institute, Oregon Health & Science University, Portland, OR 97239, United States.
| |
Collapse
|
10
|
Stincic TL, Frerking ME. Different AMPA receptor subtypes mediate the distinct kinetic components of a biphasic EPSC in hippocampal interneurons. Front Synaptic Neurosci 2015; 7:7. [PMID: 26042027 PMCID: PMC4434957 DOI: 10.3389/fnsyn.2015.00007] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2015] [Accepted: 04/27/2015] [Indexed: 11/13/2022] Open
Abstract
CA1 hippocampal interneurons at the border between stratum radiatum (SR) and stratum lacunosum-moleculare (SLM) have AMPA receptor (AMPAR)-mediated excitatory postsynaptic currents (EPSCs) that consist of two distinct phases: a typical fast component (FC), and a highly unusual slow component (SC) that persists for hundreds of milliseconds. To determine whether these kinetically distinct components of the EPSC are mediated by distinct AMPAR subpopulations, we examined the relative contributions of GluA2-containing and—lacking AMPARs to the SC. GluA2-containing AMPARs mediated the majority of the FC whereas GluA2-lacking AMPARs preferentially generated the SC. When glutamate uptake through the glial glutamate transporter excitatory amino acid transporter (EAAT1) was inhibited, spill over-mediated AMPAR activation recruited an even slower third kinetic component that persisted for several seconds; however, this spillover-mediated current was mediated predominantly by GluA2-containing AMPARs and therefore was clearly distinct from the SC when uptake is intact. Thus, different AMPAR subpopulations that vary in GluA2 content mediate the distinct components of the AMPAR EPSC. The SC is developmentally downregulated in mice, declining after the second postnatal week. This downregulation affects both GluA2-containing and GluA2-lacking AMPARs mediating the SC, and is not accompanied by developmental changes in the GluA2 content of AMPARs underlying the FC. Thus, the downregulation of the SC appears to be independent of synaptic GluA2 expression, suggesting the involvement of another AMPAR subunit or an auxiliary protein. Our results therefore identify GluA2-dependent and GluA2-independent determinants of the SC: GluA2-lacking AMPARs preferentially contribute to the SC, while the developmental downregulation of the SC is independent of GluA2 content.
Collapse
Affiliation(s)
- Todd L Stincic
- Casey Eye Institute, Oregon Health and Science University Portland, OR, USA
| | - Matthew E Frerking
- Department of Behavioral Neuroscience, Oregon Health and Science University Portland, OR, USA
| |
Collapse
|
11
|
Random dispersion in excitatory synapse response. Cogn Neurodyn 2014; 8:327-34. [PMID: 25009674 DOI: 10.1007/s11571-014-9285-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2013] [Revised: 03/07/2014] [Accepted: 03/12/2014] [Indexed: 10/25/2022] Open
Abstract
The excitatory synaptic function is subject to a huge amount of researches and fairly all the structural elements of the synapse are investigated to determine their specific contribution to the response. A model of an excitatory (hippocampal) synapse, based on time discretized Langevin equations (time-step = 40 fs), was introduced to describe the Brownian motion of Glutamate molecules (GLUTs) within the synaptic cleft and their binding to postsynaptic receptors. The binding has been computed by the introduction of a binding probability related to the hits of GLUTs on receptor binding sites. This model has been utilized in computer simulations aimed to describe the random dispersion of the synaptic response, evaluated from the dispersion of the peak amplitude of the excitatory post-synaptic current. The results of the simulation, presented here, have been used to find a reliable numerical quantity for the unknown value of the binding probability. Moreover, the same results have shown that the coefficient of variation decreases when the number of postsynaptic receptors increases, all the other parameters of the process being unchanged. Due to its possible relationships with the learning and memory, this last finding seems to furnish an important clue for understanding the basic mechanisms of the brain activity.
Collapse
|
12
|
The reduction of EPSC amplitude in CA1 pyramidal neurons by the peroxynitrite donor SIN-1 requires Ca2+ influx via postsynaptic non-L-type voltage gated calcium channels. Neurochem Res 2014; 39:361-71. [PMID: 24375019 DOI: 10.1007/s11064-013-1233-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2013] [Revised: 11/28/2013] [Accepted: 12/16/2013] [Indexed: 10/25/2022]
Abstract
The peroxynitrite free radical (ONOO(-)) modulation of miniature excitatory postsynaptic currents (mEPSCs) and spontaneous excitatory postsynaptic currents (sEPSCs) was investigated in rat CA1 pyramidal neurons using the whole-cell patch clamp technique. SIN-1(3-morpholino-sydnonimine), which can lead the simultaneous generation of superoxide anion and nitric oxide, and then form the highly reactive species ONOO(-), induced dose-dependent inhibition in amplitudes of both mEPSCs and sEPSCs. The SIN-1 action on mEPSC amplitude was completely blocked by U0126, a selective MEK inhibitor, suggesting that MEK contributed to the action of ONOO(-) on mEPSCs. The effect of SIN-1 was completely occluded either in the presence of the calcium chelator EGTA or the non-selective calcium channel antagonist Cd(2+). Furthermore, the application of nifedipine (20 μM), the L-type calcium channel blocker, had no effect on the ONOO(-)-induced decrease in mEPSC amplitude, excluding a role for L-type voltage-gated Ca(2+) channels in this process. SIN-1 inhibited the frequency of sEPSCs but had no effect on mEPSC frequency, which suggested a presynaptic action potential-dependent the action of ONOO(-) at CA1 pyramidal neuron synapses. The best-known glutamatergic input to CA1 pyramidal neurons is via Schaffer collaterals from CA3 area. However, no changes were observed in slices treated with SIN-1 on the spontaneous firing rates of CA3 pyramidal neurons. These findings suggested that SIN-1 inhibited glutamatergic synaptic transmission of CA1 pyramidal neurons by a postsynaptic non-L-type voltage gated calcium channel-dependent mechanism.
Collapse
|
13
|
Maheshwari A, Noebels JL. Monogenic models of absence epilepsy: windows into the complex balance between inhibition and excitation in thalamocortical microcircuits. PROGRESS IN BRAIN RESEARCH 2014; 213:223-52. [PMID: 25194492 DOI: 10.1016/b978-0-444-63326-2.00012-0] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Absence epilepsy is a common disorder that arises in childhood and can be refractory to medical treatment. Single genetic mutations in mice, at times found in patients with absence epilepsy, provide the unique opportunity to bridge the gap between dysfunction at the genetic level and pathological oscillations within the thalamocortical circuit. Interestingly, unlike other forms of epilepsy, only genes related to ion channels have so far been linked to absence phenotypes. Here, we delineate a paradigm which attempts to unify the various monogenic models based on decades of research. While reviewing the particular impact of these individual mutations, we posit a framework involving fast feedforward disinhibition as one common mechanism that can lead to increased tonic inhibition in the cortex and/or thalamus. Enhanced tonic inhibition hyperpolarizes principal cells, deinactivates T-type calcium channels, and leads to reciprocal burst firing within the thalamocortical loop. We also review data from pharmacologic and polygenic models in light of this paradigm. Ultimately, many questions remain unanswered regarding the pathogenesis of absence epilepsy.
Collapse
Affiliation(s)
- Atul Maheshwari
- Department of Neurology, Developmental Neurogenetics Laboratory, Baylor College of Medicine Houston, TX, USA.
| | - Jeffrey L Noebels
- Department of Neurology, Developmental Neurogenetics Laboratory, Baylor College of Medicine Houston, TX, USA; Department of Neuroscience, Baylor College of Medicine, Houston, TX, USA; Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA.
| |
Collapse
|
14
|
Rothman JS, Silver RA. Data-driven modeling of synaptic transmission and integration. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2014; 123:305-50. [PMID: 24560150 PMCID: PMC4748401 DOI: 10.1016/b978-0-12-397897-4.00004-8] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
In this chapter, we describe how to create mathematical models of synaptic transmission and integration. We start with a brief synopsis of the experimental evidence underlying our current understanding of synaptic transmission. We then describe synaptic transmission at a particular glutamatergic synapse in the mammalian cerebellum, the mossy fiber to granule cell synapse, since data from this well-characterized synapse can provide a benchmark comparison for how well synaptic properties are captured by different mathematical models. This chapter is structured by first presenting the simplest mathematical description of an average synaptic conductance waveform and then introducing methods for incorporating more complex synaptic properties such as nonlinear voltage dependence of ionotropic receptors, short-term plasticity, and stochastic fluctuations. We restrict our focus to excitatory synaptic transmission, but most of the modeling approaches discussed here can be equally applied to inhibitory synapses. Our data-driven approach will be of interest to those wishing to model synaptic transmission and network behavior in health and disease.
Collapse
Affiliation(s)
- Jason S Rothman
- Department of Neuroscience, Physiology & Pharmacology, University College London, London, UK
| | - R Angus Silver
- Department of Neuroscience, Physiology & Pharmacology, University College London, London, UK
| |
Collapse
|
15
|
Tang M, Song Q, Li N, Jiang Z, Huang R, Cheng G. Enhancement of electrical signaling in neural networks on graphene films. Biomaterials 2013; 34:6402-11. [DOI: 10.1016/j.biomaterials.2013.05.024] [Citation(s) in RCA: 147] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2013] [Accepted: 05/16/2013] [Indexed: 10/26/2022]
|
16
|
Yan D, Yamasaki M, Straub C, Watanabe M, Tomita S. Homeostatic control of synaptic transmission by distinct glutamate receptors. Neuron 2013; 78:687-99. [PMID: 23719165 DOI: 10.1016/j.neuron.2013.02.031] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/15/2013] [Indexed: 01/27/2023]
Abstract
Glutamate is the most abundant excitatory neurotransmitter in the brain, and distinct classes of glutamate receptors coordinate synaptic transmission and spike generation upon various levels of neuronal activity. However, the mechanisms remain unclear. Here, we found that loss of synaptic AMPA receptors increased kainate receptor activity in cerebellar granule cells without changing NMDA receptors. The augmentation of kainate receptor-mediated currents in the absence of AMPA receptor activity is required for spike generation and is mediated by the increased expression of the GluK5 high-affinity kainate receptor subunit. Increase in GluK5 expression is sufficient to enhance kainate receptor activity by modulating receptor channel properties, but not localization. Furthermore, we demonstrate that the combined loss of the AMPA receptor auxiliary TARPγ-2 subunit and the GluK5 subunit leads to early mouse lethality. Our findings reveal mechanisms mediated by distinct classes of postsynaptic glutamate receptors for the homeostatic maintenance of the neuronal activity.
Collapse
Affiliation(s)
- Dan Yan
- Program in Cellular Neuroscience, Neurodegeneration and Repair, Yale University School of Medicine, New Haven, CT 06520, USA
| | | | | | | | | |
Collapse
|
17
|
Glutamate-AMPAR interaction in a model of synaptic transmission. Brain Res 2013; 1536:168-76. [PMID: 23648359 DOI: 10.1016/j.brainres.2013.04.051] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2013] [Revised: 04/24/2013] [Accepted: 04/26/2013] [Indexed: 11/20/2022]
Abstract
Over the last several years we have investigated the excitatory synaptic response by means of a mathematical model based on a detailed description of the synapse geometry, the Brownian motion of Glutamate molecules and their binding to postsynaptic receptors. Recently, the basic model has been modified for the numbers, the size and the 3D structure of receptors according to new data from the literature. Some results of simulations performed with the updated model are shown here. They were aimed to study the synaptic response in relation to the binding probability, to the probable height of the receptors in the synaptic cleft, and to the space-time distribution of Glutamate/Receptor collisions. A first series of simulations permitted to determine a possible range of values for the binding probability of Glutamate to receptors. Other simulations, investigating the changes induced on the synaptic response by the variations of the height of AMPA receptors in synaptic cleft, allowed to identify the height producing the higher amplitude peak of the mEPSCs. Finally, two new statistical descriptors for analyzing the synaptic response were presented. The first is based on the study of the space distribution of the number of Glutamate/Receptor collisions. Simulations investigating the effects of an increasing eccentricity of the releasing vesicle allowed assessing this method. The second one considers the inter-collision times between Glutamate molecules and binding sites. The results of some of the last simulations demonstrated its capacity to highlight the subtleties and the randomness underlying the activation of the receptors. This article is part of a Special Issue entitled Neural Coding 2012.
Collapse
|
18
|
Ventriglia F, Di Maio V. Effects of AMPARs trafficking and glutamate-receptors binding probability on stochastic variability of EPSC. Biosystems 2013; 112:298-304. [PMID: 23416752 DOI: 10.1016/j.biosystems.2013.01.010] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2012] [Revised: 01/24/2013] [Accepted: 01/30/2013] [Indexed: 10/27/2022]
Abstract
Mathematical models of the excitatory synapse are providing valuable information about the synaptic response. The effects of several synaptic components on EPSC variability have been tested by computer simulation. Our model, based on Brownian diffusion of glutamate in the synaptic cleft, is basically the same we have used in previous papers but parameters have been upgraded according to the new experimental findings. The presence of filaments into the synaptic cleft and the number and the ratio of AMPA and NMDA receptors have been the main parameters upgraded. A different way of computing the binding probability of glutamate molecules to receptors by means of geometrical considerations has been also used. The obtained results were more precise and they suggested that the new elements can play a significant role in the stochastic variability of the synaptic response. Nevertheless, new problems arise concerning the value of the lower limit of the binding probability.
Collapse
|
19
|
Schwenk J, Harmel N, Brechet A, Zolles G, Berkefeld H, Müller C, Bildl W, Baehrens D, Hüber B, Kulik A, Klöcker N, Schulte U, Fakler B. High-Resolution Proteomics Unravel Architecture and Molecular Diversity of Native AMPA Receptor Complexes. Neuron 2012; 74:621-33. [DOI: 10.1016/j.neuron.2012.03.034] [Citation(s) in RCA: 269] [Impact Index Per Article: 22.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/13/2012] [Indexed: 10/28/2022]
|
20
|
Jackson AC, Nicoll RA. The expanding social network of ionotropic glutamate receptors: TARPs and other transmembrane auxiliary subunits. Neuron 2011; 70:178-99. [PMID: 21521608 DOI: 10.1016/j.neuron.2011.04.007] [Citation(s) in RCA: 288] [Impact Index Per Article: 22.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/13/2011] [Indexed: 12/25/2022]
Abstract
Ionotropic glutamate receptors (iGluRs) underlie rapid, excitatory synaptic signaling throughout the CNS. After years of intense research, our picture of iGluRs has evolved from them being companionless in the postsynaptic membrane to them being the hub of dynamic supramolecular signaling complexes, interacting with an ever-expanding litany of other proteins that regulate their trafficking, scaffolding, stability, signaling, and turnover. In particular, the discovery that transmembrane AMPA receptor regulatory proteins (TARPs) are AMPA receptor auxiliary subunits that are critical determinants of their trafficking, gating, and pharmacology has changed the way we think about iGluR function. Recently, a number of novel transmembrane proteins have been uncovered that may also serve as iGluR auxiliary proteins. Here we review pivotal developments in our understanding of the role of TARPs in AMPA receptor trafficking and gating, and provide an overview of how newly discovered transmembrane proteins expand our view of iGluR function in the CNS.
Collapse
Affiliation(s)
- Alexander C Jackson
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, CA 94143, USA.
| | | |
Collapse
|
21
|
Potapenko ES, Biancardi VC, Florschutz RM, Ryu PD, Stern JE. Inhibitory-excitatory synaptic balance is shifted toward increased excitation in magnocellular neurosecretory cells of heart failure rats. J Neurophysiol 2011; 106:1545-57. [PMID: 21697450 DOI: 10.1152/jn.00218.2011] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Despite the well-established contribution of neurohumoral activation to morbidity and mortality in heart failure (HF) patients, relatively little is known about the underlying central nervous system mechanisms. In this study, we aimed to determine whether changes in GABAergic inhibitory and glutamatergic excitatory synaptic function contribute to altered hypothalamic magnocellular neurosecretory cell (MNC) activity in HF rats. Patch-clamp recordings were obtained from MNCs in brain slices from sham and HF rats. Glutamate excitatory (EPSCs) and GABAergic inhibitory postsynaptic currents (IPSCs) were simultaneously recorded, and changes in their strengths, as well as their interactions, were evaluated. We found a diminished GABAergic synaptic strength in MNCs of HF rats, reflected as faster decaying IPSCs and diminished mean IPSC charge transfer. Opposite changes were observed in glutamate EPSC synaptic strength, resulting in a shift in the GABA-glutamate balance toward a relatively stronger glutamate influence in HF rats. The prolongation of glutamate EPSCs during HF was mediated, at least in part, by an enhanced contribution of AMPA receptor desensitization to the EPSC decay time course. EPSC prolongation, and consequently increased unitary strength, resulted in a stronger AMPA receptor-mediated excitatory drive to firing discharge in MNCs of HF rats. Blockade of GABA(A) synaptic activity diminished the EPSC waveform variability observed among events in sham rats, an effect that was blunted in HF rats. Together, our results suggest that opposing changes in postsynaptic properties of GABAergic and glutamatergic synaptic function contribute to enhanced magnocellular neurosecretory activity in HF rats.
Collapse
Affiliation(s)
- Evgeniy S Potapenko
- Department of Physiology, Medical College of Georgia, 1120 15th St., Augusta, GA 30912, USA
| | | | | | | | | |
Collapse
|
22
|
Schulte U, Müller CS, Fakler B. Ion channels and their molecular environments – Glimpses and insights from functional proteomics. Semin Cell Dev Biol 2011; 22:132-44. [DOI: 10.1016/j.semcdb.2010.09.015] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2010] [Revised: 09/29/2010] [Accepted: 09/30/2010] [Indexed: 01/09/2023]
|
23
|
Ventriglia F. Effect of filaments within the synaptic cleft on the response of excitatory synapses simulated by computer experiments. Biosystems 2010; 104:14-22. [PMID: 21195740 DOI: 10.1016/j.biosystems.2010.12.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2010] [Revised: 12/15/2010] [Accepted: 12/22/2010] [Indexed: 11/15/2022]
Abstract
Mathematical models of the excitatory synapse are furnishing valuable information about the synaptic response. Based on Brownian-diffusion of glutamate molecules, a synapse model was utilized to investigate the synaptic response on a femto-second time scale by the use of a parallel computer. In particular, the presence of fibrils crossing the synaptic cleft was simulated, which could have a role in shaping the brain activity. To this aim the model of synapse was modified by considering trans-synaptic filaments with diameters ranging from 7 nm to 3 nm, disposed on a grid with spacing of 14 nm or 8 nm. The simulation demonstrated that the presence of filaments induced an increase in the synaptic response, most likely linked to an increment in the probability of encounter between glutamate molecules and receptors. The increase was small--from 5 to 20%, but metabolic and functional considerations provide substantive hints about the importance of these small changes for brain activity. Moreover, it was shown that the presence of filaments made more stable the response of the synapse to random variations of pre-synaptic elements. Originated by these computational results, some inferences about the biological bases of mind diseases such as autism, mental retardation and schizophrenia, are reported in the Discussion.
Collapse
Affiliation(s)
- Francesco Ventriglia
- Istituto di Cibernetica E.Caianiello del CNR, Via Campi Flegrei 34, Pozzuoli (NA), Italy.
| |
Collapse
|
24
|
Alberto CO, Hirasawa M. AMPA receptor-mediated miniature EPSCs have heterogeneous time courses in orexin neurons. Biochem Biophys Res Commun 2010; 400:707-12. [DOI: 10.1016/j.bbrc.2010.08.132] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2010] [Accepted: 08/29/2010] [Indexed: 02/07/2023]
|
25
|
Schwarcz R, Guidetti P, Sathyasaikumar KV, Muchowski PJ. Of mice, rats and men: Revisiting the quinolinic acid hypothesis of Huntington's disease. Prog Neurobiol 2010; 90:230-45. [PMID: 19394403 PMCID: PMC2829333 DOI: 10.1016/j.pneurobio.2009.04.005] [Citation(s) in RCA: 127] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2009] [Accepted: 04/17/2009] [Indexed: 12/31/2022]
Abstract
The neurodegenerative disease Huntington's disease (HD) is caused by an expanded polyglutamine (polyQ) tract in the protein huntingtin (htt). Although the gene encoding htt was identified and cloned more than 15 years ago, and in spite of impressive efforts to unravel the mechanism(s) by which mutant htt induces nerve cell death, these studies have so far not led to a good understanding of pathophysiology or an effective therapy. Set against a historical background, we review data supporting the idea that metabolites of the kynurenine pathway (KP) of tryptophan degradation provide a critical link between mutant htt and the pathophysiology of HD. New studies in HD brain and genetic model organisms suggest that the disease may in fact be causally related to early abnormalities in KP metabolism, favoring the formation of two neurotoxic metabolites, 3-hydroxykynurenine and quinolinic acid, over the related neuroprotective agent kynurenic acid. These findings not only link the excitotoxic hypothesis of HD pathology to an impairment of the KP but also define new drug targets and therefore have direct therapeutic implications. Thus, pharmacological normalization of the imbalance in brain KP metabolism may provide clinical benefits, which could be especially effective in early stages of the disease.
Collapse
Affiliation(s)
- Robert Schwarcz
- Maryland Psychiatric Research Center, University of Maryland School of Medicine, Baltimore, MD, USA.
| | | | | | | |
Collapse
|
26
|
Fenwick MK, Oswald RE. On the mechanisms of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor binding to glutamate and kainate. J Biol Chem 2010; 285:12334-43. [PMID: 20110361 DOI: 10.1074/jbc.m109.086371] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) subtype of ionotropic glutamate receptors mediates much of the fast excitatory neurotransmission in the central nervous system. The ability of these receptors to shape such responses appears to be due in part to dynamic processes induced by agonists in the ligand-binding domain. Previous studies employing fluorescence spectroscopy and whole cell recording suggest that agonist binding is followed by sequential transitions to one or more distinct conformational states. Here, we used hydrogen-deuterium exchange to determine the mechanisms of binding of glutamate and kainate (full and partial agonists, respectively) to a soluble ligand-binding domain of GluR2. Our results provide a structural basis for sequential state models of agonist binding and the free energy changes of the associated state-to-state transitions. For glutamate, a multi-equilibrium binding reaction was discerned involving distinct ligand docking, domain isomerization, and lobe-locking steps. In contrast, kainate binding involves a simpler dock-isomerization process in which the isomerization equilibrium is shifted dramatically toward open domain conformations. In light of increasing evidence that the stability, in addition to the extent, of domain closure is a critical component of the channel activation mechanism, the differences in domain opening and closing equilibria detected for glutamate and kainate should be useful structural measures for interpreting the markedly different current responses evoked by these agonists.
Collapse
Affiliation(s)
- Michael K Fenwick
- Department of Molecular Medicine, Cornell University, Ithaca, New York 14853, USA
| | | |
Collapse
|
27
|
|
28
|
Walker CS, Jensen S, Ellison M, Matta JA, Lee WY, Imperial JS, Duclos N, Brockie PJ, Madsen DM, Isaac JTR, Olivera B, Maricq AV. A novel Conus snail polypeptide causes excitotoxicity by blocking desensitization of AMPA receptors. Curr Biol 2009; 19:900-8. [PMID: 19481459 DOI: 10.1016/j.cub.2009.05.017] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2009] [Revised: 04/26/2009] [Accepted: 05/05/2009] [Indexed: 11/28/2022]
Abstract
BACKGROUND Ionotropic glutamate receptors (iGluRs) are glutamate-gated ion channels that mediate excitatory neurotransmission in the central nervous system. Based on both molecular and pharmacological criteria, iGluRs have been divided into two major classes, the non-NMDA class, which includes both AMPA and kainate subtypes of receptors, and the NMDA class. One evolutionarily conserved feature of iGluRs is their desensitization in the continued presence of glutamate. Thus, when in a desensitized state, iGluRs can be bound to glutamate, yet the channel remains closed. However, the relevance of desensitization to nervous system function has remained enigmatic. RESULTS Here, we report the identification and characterization of a novel polypeptide (con-ikot-ikot) from the venom of a predatory marine snail Conus striatus that specifically disrupts the desensitization of AMPA receptors (AMPARs). The stoichiometry of con-ikot-ikot appears reminiscent of the proposed subunit organization of AMPARs, i.e., a dimer of dimers, suggesting that it acts as a molecular four-legged clamp that holds the AMPAR channel open. Application of con-ikot-ikot to hippocampal slices caused a large and rapid increase in resting AMPAR-mediated current leading to neuronal death. CONCLUSIONS Our findings provide insight into the mechanisms that regulate receptor desensitization and demonstrate that in the arms race between prey and predators, evolution has selected for a toxin that blocks AMPAR desensitization, thus revealing the fundamental importance of desensitization for regulating neural function.
Collapse
Affiliation(s)
- Craig S Walker
- Department of Biology, University of Utah, Salt Lake City, UT 84112-0840, USA
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
29
|
Schwenk J, Harmel N, Zolles G, Bildl W, Kulik A, Heimrich B, Chisaka O, Jonas P, Schulte U, Fakler B, Klocker N. Functional Proteomics Identify Cornichon Proteins as Auxiliary Subunits of AMPA Receptors. Science 2009; 323:1313-9. [DOI: 10.1126/science.1167852] [Citation(s) in RCA: 304] [Impact Index Per Article: 20.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
|
30
|
Sakai M, Chimoto S, Qin L, Sato Y. Neural mechanisms of interstimulus interval-dependent responses in the primary auditory cortex of awake cats. BMC Neurosci 2009; 10:10. [PMID: 19208233 PMCID: PMC2679037 DOI: 10.1186/1471-2202-10-10] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2008] [Accepted: 02/10/2009] [Indexed: 11/27/2022] Open
Abstract
Background Primary auditory cortex (AI) neurons show qualitatively distinct response features to successive acoustic signals depending on the inter-stimulus intervals (ISI). Such ISI-dependent AI responses are believed to underlie, at least partially, categorical perception of click trains (elemental vs. fused quality) and stop consonant-vowel syllables (eg.,/da/-/ta/continuum). Methods Single unit recordings were conducted on 116 AI neurons in awake cats. Rectangular clicks were presented either alone (single click paradigm) or in a train fashion with variable ISI (2–480 ms) (click-train paradigm). Response features of AI neurons were quantified as a function of ISI: one measure was related to the degree of stimulus locking (temporal modulation transfer function [tMTF]) and another measure was based on firing rate (rate modulation transfer function [rMTF]). An additional modeling study was performed to gain insight into neurophysiological bases of the observed responses. Results In the click-train paradigm, the majority of the AI neurons ("synchronization type"; n = 72) showed stimulus-locking responses at long ISIs. The shorter cutoff ISI for stimulus-locking responses was on average ~30 ms and was level tolerant in accordance with the perceptual boundary of click trains and of consonant-vowel syllables. The shape of tMTF of those neurons was either band-pass or low-pass. The single click paradigm revealed, at maximum, four response periods in the following order: 1st excitation, 1st suppression, 2nd excitation then 2nd suppression. The 1st excitation and 1st suppression was found exclusively in the synchronization type, implying that the temporal interplay between excitation and suppression underlies stimulus-locking responses. Among these neurons, those showing the 2nd suppression had band-pass tMTF whereas those with low-pass tMTF never showed the 2nd suppression, implying that tMTF shape is mediated through the 2nd suppression. The recovery time course of excitability suggested the involvement of short-term plasticity. The observed phenomena were well captured by a single cell model which incorporated AMPA, GABAA, NMDA and GABAB receptors as well as short-term plasticity of thalamocortical synaptic connections. Conclusion Overall, it was suggested that ISI-dependent responses of the majority of AI neurons are configured through the temporal interplay of excitation and suppression (inhibition) along with short-term plasticity.
Collapse
Affiliation(s)
- Masashi Sakai
- Department of Physiology, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Yamanashi, Japan.
| | | | | | | |
Collapse
|
31
|
Morimoto-Tomita M, Zhang W, Straub C, Cho CH, Kim KS, Howe JR, Tomita S. Autoinactivation of neuronal AMPA receptors via glutamate-regulated TARP interaction. Neuron 2009; 61:101-12. [PMID: 19146816 DOI: 10.1016/j.neuron.2008.11.009] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2008] [Revised: 11/10/2008] [Accepted: 11/12/2008] [Indexed: 10/21/2022]
Abstract
Neuronal AMPA receptors autoinactivate at high concentrations of glutamate, i.e., the current declines at glutamate concentrations above 10-100 microM. The mechanisms underlying this phenomenon are unclear. Stargazin-like TARPs are AMPA receptor auxiliary subunits that modulate receptor trafficking and channel properties. Here, we found that neuronal AMPA receptors and recombinant AMPA receptors coexpressed with stargazin autoinactivate at high concentrations of glutamate, whereas recombinant AMPA receptors expressed alone do not. The reduction of currents at high glutamate concentrations is not associated with a reduction of AMPA receptor number, but rather with the loss of stargazin-associated allosteric modulation of channel gating. We show that receptor desensitization promotes the dissociation of TARP-AMPA receptor complexes in a few milliseconds. This dissociation mechanism contributes to synaptic short-term modulation. The results demonstrate a mechanism for dynamic regulation of AMPA receptor activity to tune synaptic strength.
Collapse
Affiliation(s)
- Megumi Morimoto-Tomita
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT 06520, USA
| | | | | | | | | | | | | |
Collapse
|
32
|
Cho CH, St-Gelais F, Zhang W, Tomita S, Howe JR. Two families of TARP isoforms that have distinct effects on the kinetic properties of AMPA receptors and synaptic currents. Neuron 2007; 55:890-904. [PMID: 17880893 DOI: 10.1016/j.neuron.2007.08.024] [Citation(s) in RCA: 142] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2007] [Revised: 08/06/2007] [Accepted: 08/31/2007] [Indexed: 10/22/2022]
Abstract
Transmembrane AMPA receptor regulatory proteins (TARPs) are auxiliary AMPA receptor subunits that regulate both the trafficking and gating properties of AMPA receptors, and different TARP isoforms display distinct expression patterns in brain. Here, we compared the effects of four TARP isoforms on the kinetics of AMPA receptor currents. Each isoform slowed the deactivation of GluR1 currents, but the slowing was greatest with gamma-4 and gamma-8. Isoform-specific differences in desensitization were also observed that correlated with effects on deactivation. TARP isoforms also differentially modulated responses to trains of glutamate applications designed to mimic high-frequency presynaptic firing. Importantly, whereas both stargazin and gamma-4 rescued excitatory synaptic transmission in cerebellar granule cells from stargazer mice, the decay of miniature EPSCs was 2-fold slower in neurons expressing gamma-4. The results show that heterogeneity in the composition of AMPA receptor/TARP complexes contributes to synapse-specific differences in EPSC decays and frequency-dependent modulation of neurotransmission.
Collapse
Affiliation(s)
- Chang-Hoon Cho
- Department of Pharmacology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520-8066, USA
| | | | | | | | | |
Collapse
|
33
|
Schoppa NE. AMPA/kainate receptors drive rapid output and precise synchrony in olfactory bulb granule cells. J Neurosci 2007; 26:12996-3006. [PMID: 17167089 PMCID: PMC6674955 DOI: 10.1523/jneurosci.3503-06.2006] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Gamma frequency (30-70 Hz) synchronized oscillatory activity in the olfactory bulb is widely believed to be important for odor detection and discrimination. As in other circuits with "gamma activity," the activity in the bulb is driven by GABAergic interneurons, specifically a class of axonless cells called granule cells. However, bulb granule cells appear to lack some key mechanistic features that promote rapid synchrony in other circuits, including direct electrical interconnections and dominant actions for fast neurotransmitter receptors. At least under "static" stimulus conditions, granule cells are driven by kinetically slow NMDA receptors. Here, I used patch-clamp recordings in rat olfactory bulb slices to better understand mechanisms that shape granule cell activity under "dynamic" stimulus conditions that mimic a natural odor stimulus. During a 4 Hz patterned stimulation of olfactory nerve afferents, activation of single granule cells was primarily controlled by two classes of AMPA/kainate receptor-mediated synaptic inputs derived from output mitral cells. The rapid kinetics of these receptors, together with inactivation of A-type potassium channels, ensured that granule cells had short spike-response times. Studies in cell pairs, moreover, indicated that excitatory inputs could synchronize granule cells on a rapid time scale (2-5 ms), in turn resulting in phase-locked GABA release onto mitral cells. The precision of granule cell synchrony was controlled by the same biophysical mechanisms that promoted rapid single-cell spiking. These studies demonstrate the mechanistic underpinnings that transform a circuit with slow, uncoupled activity under static conditions into a fast, dynamic circuit operating with high precision under physiological conditions.
Collapse
Affiliation(s)
- Nathan E Schoppa
- Department of Physiology and Biophysics, University of Colorado at Denver Health Sciences Center at Fitzsimons, Aurora, Colorado 80045, USA.
| |
Collapse
|
34
|
Thompson SM, Kao JPY, Kramer RH, Poskanzer KE, Silver RA, Digregorio D, Wang SSH. Flashy science: controlling neural function with light. J Neurosci 2006; 25:10358-65. [PMID: 16280572 PMCID: PMC6725808 DOI: 10.1523/jneurosci.3515-05.2005] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Affiliation(s)
- Scott M Thompson
- Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland, 21201, USA.
| | | | | | | | | | | | | |
Collapse
|
35
|
Xia YF, Arai AC. AMPA receptor modulators have different impact on hippocampal pyramidal cells and interneurons. Neuroscience 2006; 135:555-67. [PMID: 16125852 DOI: 10.1016/j.neuroscience.2005.06.031] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2005] [Revised: 06/03/2005] [Accepted: 06/15/2005] [Indexed: 11/20/2022]
Abstract
Positive modulators of AMPA receptors enhance synaptic plasticity and memory encoding. Facilitation of AMPA receptor currents not only results in enhanced activation of excitatory neurons but also increases the activity of inhibitory interneurons by up-modulating their excitatory input. However, little is known about the effects of these modulators on cells other than pyramidal neurons and about their impact on local microcircuits. This study examined the effects of members from three subfamilies of modulators (mainly CX516, CX546 and cyclothiazide) on excitatory synaptic responses in four classes of hippocampal CA1 neurons and on excitatory and disynaptically induced inhibitory field potentials in hippocampal slices. Effects on excitatory postsynaptic currents (EPSCs) were examined in pyramidal cells, in two types of inhibitory interneurons located in stratum radiatum and oriens, and in stratum radiatum giant cells, a novel type of excitatory neuron. With CX516, increases in EPSC amplitude in pyramidal cells were two to three times larger than in interneurons and six times larger than in radiatum giant cells. The effects of CX546 on response duration similarly were largest in pyramidal cells. However, this drug also strongly differentiated between stratum oriens and radiatum interneurons with increases being four times larger in the latter. In contrast, cyclothiazide had similar effects on response duration in all cell types. In field recordings, CX516 was several times more potent in enhancing excitatory postsynaptic potentials (EPSPs) than feedback or feedforward circuits, as expected from its larger influence on pyramidal cells. In contrast, BDP-20, a CX546 analog, was more potent in enhancing feedforward inhibition than either EPSPs or feedback inhibition. This preference for feedforward over feedback circuits is probably related to its higher potency in stratum radiatum versus oriens interneurons. Taken together, AMPA receptor modulators differ substantially in their potency and/or efficacy across major classes of neurons which is likely to have consequences with regard to their impact on circuits and behavior.
Collapse
Affiliation(s)
- Y-F Xia
- Department of Pharmacology, Southern Illinois University, School of Medicine, PO Box 19629, Springfield, IL 62794-9629, USA
| | | |
Collapse
|
36
|
Castro-Alamancos MA. Dynamics of sensory thalamocortical synaptic networks during information processing states. Prog Neurobiol 2005; 74:213-47. [PMID: 15556288 DOI: 10.1016/j.pneurobio.2004.09.002] [Citation(s) in RCA: 138] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2004] [Accepted: 09/08/2004] [Indexed: 10/26/2022]
Abstract
The thalamocortical network consists of the pathways that interconnect the thalamus and neocortex, including thalamic sensory afferents, corticothalamic and thalamocortical pathways. These pathways are essential to acquire, analyze, store and retrieve sensory information. However, sensory information processing mostly occurs during behavioral arousal, when activity in thalamus and neocortex consists of an electrographic sign of low amplitude fast activity, known as activation, which is caused by several neuromodulator systems that project to the thalamocortical network. Logically, in order to understand how the thalamocortical network processes sensory information it is essential to study its response properties during states of activation. This paper reviews the temporal and spatial response properties of synaptic pathways in the whisker thalamocortical network of rodents during activated states as compared to quiescent (non-activated) states. The evidence shows that these pathways are differentially regulated via the effects of neuromodulators as behavioral contingencies demand. Thus, during activated states, the temporal and spatial response properties of pathways in the thalamocortical network are transformed to allow the processing of sensory information.
Collapse
Affiliation(s)
- Manuel A Castro-Alamancos
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, 2900 Queen Lane, Philadelphia, PA 19129, USA.
| |
Collapse
|
37
|
Abstract
We have used Monte Carlo simulations to understand the generation of quantal responses at the single active zones of CA1 synapses. We constructed a model of AMPA channel activation that accounts for the responses to controlled glutamate application and a model of glutamate diffusion in the synaptic cleft. With no further adjustments to these models, we simulated the response to the release of glutamate from a single vesicle. The predicted response closely matches the rise time of observed responses, which recent measurements show is much faster (<100 μs) than previously thought. The simulations show that initial channel opening is driven by a brief (<100 μs) glutamate spike near the site of vesicle fusion, producing a hotspot of channel activation (diameter: ∼250 nm) smaller than many synapses. Quantal size therefore depends more strongly on the density of channels than their number, a finding that has important implications for measuring synaptic strength. Recent measurements allow estimation of AMPA receptor density at CA1 synapses. Using this value, our simulations correctly predicts a quantal amplitude of ∼10 pA. We have also analyzed the properties of excitatory postsynaptic currents (EPSCs) generated by the multivesicular release that can occur during evoked responses. We find that summation is nearly linear and that the existence of multiple narrow peaks in amplitude histograms can be accounted for. It has been unclear how to reconcile the existence of these narrow peaks, which indicate that the variation of quantal amplitude is small (CV < 0.2) with the highly variable amplitude of miniature EPSCs (mEPSCs; CV ∼ 0.6). According to one theory, mEPSC variability arises from variation in vesicle glutamate content. However, both our modeling results and recent experimental results indicate that this view cannot account for the observed rise time/amplitude correlation of mEPSCs. In contrast, this correlation and the high mEPSC variability can be accounted for if some mEPSCs are generated by two or more vesicles released with small temporal jitter. We conclude that a broad range of results can be accounted for by simple principles: quantal amplitude (∼10 pA) is stereotyped, some mEPSCs are multivesicular at moderate and large synapses, and evoked responses are generated by quasi-linear summation of multiple quanta.
Collapse
Affiliation(s)
- Sridhar Raghavachari
- Dept. of Biology and Volen Center for Complex Systems, Brandeis University MS 008, 415 South S., Waltham, MA 02454, USA
| | | |
Collapse
|
38
|
Blitz DM, Foster KA, Regehr WG. Short-term synaptic plasticity: a comparison of two synapses. Nat Rev Neurosci 2004; 5:630-40. [PMID: 15263893 DOI: 10.1038/nrn1475] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Dawn M Blitz
- Department of Neurobiology, Harvard Medical School, 220 Longwood Avenue, Boston, Massachusetts 02115, USA
| | | | | |
Collapse
|
39
|
Aristizabal F, Glavinovic MI. Wavelet analysis of nonstationary fluctuations of Monte Carlo-simulated excitatory postsynaptic currents. Biophys J 2004; 85:2170-85. [PMID: 14507683 PMCID: PMC1303444 DOI: 10.1016/s0006-3495(03)74643-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
Tracking spectral changes of rapidly varying signals is a demanding task. In this study, we explore on Monte Carlo-simulated glutamate-activated AMPA patch and synaptic currents whether a wavelet analysis offers such a possibility. Unlike Fourier methods that determine only the frequency content of a signal, the wavelet analysis determines both the frequency and the time. This is owing to the nature of the basis functions, which are infinite for Fourier transforms (sines and cosines are infinite), but are finite for wavelet analysis (wavelets are localized waves). In agreement with previous reports, the frequency of the stationary patch current fluctuations is higher for larger currents, whereas the mean-variance plots are parabolic. The spectra of the current fluctuations and mean-variance plots are close to the theoretically predicted values. The median frequency of the synaptic and nonstationary patch currents is, however, time dependent, though at the peak of synaptic currents, the median frequency is insensitive to the number of glutamate molecules released. Such time dependence demonstrates that the "composite spectra" of the current fluctuations gathered over the whole duration of synaptic currents cannot be used to assess the mean open time or effective mean open time of AMPA channels. The current (patch or synaptic) versus median frequency plots show hysteresis. The median frequency is thus not a simple reflection of the overall receptor saturation levels and is greater during the rise phase for the same saturation level. The hysteresis is due to the higher occupancy of the doubly bound state during the rise phase and not due to the spatial spread of the saturation disk, which remains remarkably constant. Albeit time dependent, the variance of the synaptic and nonstationary patch currents can be accurately determined. Nevertheless the evaluation of the number of AMPA channels and their single current from the mean-variance plots of patch or synaptic currents is not highly accurate owing to the varying number of the activatable AMPA channels caused by desensitization. The spatial nonuniformity of open, bound, and desensitized AMPA channels, and the time dependence and spatial nonuniformity of the glutamate concentration in the synaptic cleft, further reduce the accuracy of estimates of the number of AMPA channels from synaptic currents. In conclusion, wavelet analysis of nonstationary fluctuations of patch and synaptic currents expands our ability to determine accurately the variance and frequency of current fluctuations, demonstrates the limits of applicability of techniques currently used to evaluate the single channel current and number of AMPA channels, and offers new insights into the mechanisms involved in the generation of unitary quantal events at excitatory central synapses.
Collapse
Affiliation(s)
- F Aristizabal
- Departments of Chemical Engineering and Physiology, McGill University, Montreal, Canada
| | | |
Collapse
|
40
|
Schlesinger F, Meywirth J, Krampfl K, Grosskreutz J, Petri S, Mauth C, Just L, Bader A, Bufler J. Ligand-gated channels in early mesencephalic neuronal precursors: immunocytochemical and electrophysiological analysis. Eur J Neurosci 2004; 19:2371-6. [PMID: 15128391 DOI: 10.1111/j.0953-816x.2004.03343.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Neuronal precursors play an important role in potential regenerative therapeutic strategies in different neurodegenerative diseases, e.g. Parkinson's disease. To understand proliferation and differentiation of these cells in vitro and in vivo, it is important to characterize functional properties of neuronal precursors in detail. The aim of the present study was to analyse the electrophysiological characteristics of ligand-gated channels of neuronal precursors prepared from the rat ventral mesencephalon (VM) of embryonic stage 12.5 during their in vitro differentiation. For the experiments we used the patch-clamp technique in combination with a system for ultrafast solution exchange and immunocytochemistry. It could be shown that functional active AMPA-type glutamate as well as GABA(A) receptor channels are expressed at an early stage of neuronal development. In culture we observed excitatory as well as inhibitory postsynaptic currents (defined by their different kinetics) which correspond to the activation of AMPAergic and GABAergic receptor channels. Two populations of glutamate-activated currents could be differentiated by their different time course of desensitization whereas the time course of resensitization and deactivation was normally distributed in all cells. GABAergic currents could be blocked by bicuculline and their kinetics correspond to that of GABA(A) receptor channel currents. Summarizing the results, in the present study it was shown for the first time that neuronal embryonic precursors of the rat VM express both functional AMPA-type glutamate and functional GABA(A) receptor channels in vitro.
Collapse
Affiliation(s)
- F Schlesinger
- Department of Neurology, Medizinische Hochschule Hannover, 30623 Hannover, Germany
| | | | | | | | | | | | | | | | | |
Collapse
|
41
|
Ventriglia F. Saturation in excitatory synapses of hippocampus investigated by computer simulations. BIOLOGICAL CYBERNETICS 2004; 90:349-359. [PMID: 15221395 DOI: 10.1007/s00422-004-0476-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/14/2003] [Accepted: 03/03/2004] [Indexed: 05/24/2023]
Abstract
The standard view of the synaptic function in excitatory synapses has been deeply questioned by recent experimental data on hippocampal glutamate synapses both for possible receptor nonsaturation and for larger and non-Gaussian peak amplitude fluctuations. Our previous investigations of the mechanisms involved in the variability of the response of hippocampal glutamatergic synapses, carried out by computer simulation of simple Brownian models of glutamate diffusion, furnished initial evidence about their presynaptic character. A new, refined model, reported here, assumes a collision volume for the glutamate molecule and a more realistic description of receptors and their binding dynamics. Based on this model, conditions for AMPA and NMDA receptor saturation have been investigated and new miniature (or quantal) EPSC parameters have been computed. The results corroborate the hypothesis that the lack of AMPA and NMDA receptor saturation and the EPSC stochastic variability are attributable to the small volume of glutamatergic synaptic vesicles and hence to the small number of glutamate molecules diffusing in the cleft after a vesicle release. The investigations better characterize some not well-known elements of the synaptic structure, such as the fusion pore, and provide useful information on AMPA receptor dynamics. Indeed, a nice fit between computed EPSCs and some miniature EPSCs in recent experimental literature allowed for the computation of new transition time values among the different AMPA receptor states through a trial-and-error optimization procedure. Moreover, the model has been used to evaluate two hypotheses on the genesis of the long-term potentiation phenomenon.
Collapse
Affiliation(s)
- Francesco Ventriglia
- Istituto di Cibernetica, E. Caianiello del CNR, Via Campi Flegrei 34, 80078, Pozzuoli (NA), Italy.
| |
Collapse
|
42
|
Losi G, Puia G, Braghiroli D, Baraldi M. IDRA-21, a positive AMPA receptor modulator, inhibits synaptic and extrasynaptic NMDA receptor mediated events in cultured cerebellar granule cells. Neuropharmacology 2004; 46:1105-1113. [PMID: 15111017 DOI: 10.1016/j.neuropharm.2004.02.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2003] [Accepted: 02/03/2004] [Indexed: 11/20/2022]
Abstract
IDRA-21 (7-chloro-3-methyl-3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxide) reduces alpha-amino-3-hydroxy-5-methylisoxazolepropionic acid (AMPA) receptors desensitisation in vitro and restores learning and cognitive impairment in vivo. In this study, we show that in cerebellar granule cells (CGCs) in culture IDRA-21 reduces N-methyl-d-aspartate receptor (NMDAR) whole-cell currents. The effect is neither competitive nor voltage-dependent. The reduction of NMDA currents is stronger at low glycine concentrations suggesting an interaction with this site. IDRA-21 shortens miniature excitatory postsynaptic currents mediated by NMDARs (NMDA-mEPSCs) in CGCs grown in low potassium with no effect on peak amplitudes. By using fast glutamate application onto CGCs nucleated patches, we found that IDRA-21 decreases both decay time constant and amplitude of the current. Experiments performed on recombinant NMDAR expressed in HEK 293 cells showed that IDRA-21 was more effective on NR1a-NR2B than NR1a-NR2A receptors highlighting a subunit selectivity of the drug. Our findings make light on a novel target for IDRA-21: NMDA receptors function is negatively modulated and the different action at the level of extrasynaptic and synaptic receptors could be ascribed to a partial selectivity for NR2B subunits.
Collapse
Affiliation(s)
- Gabriele Losi
- Dipartimento di Scienze Farmaceutiche, Università di Modena e Reggio Emilia, Via Campi, 183, 41100 Modena, Italy
| | | | | | | |
Collapse
|
43
|
Sergeeva OA, Amberger BT, Vorobjev VS, Eriksson KS, Haas HL. AMPA receptor properties and coexpression with sodium-calcium exchangers in rat hypothalamic neurons. Eur J Neurosci 2004; 19:957-65. [PMID: 15009143 DOI: 10.1111/j.1460-9568.2004.03208.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The histaminergic tuberomamillary (TM) nucleus, a center for the regulation of wakefulness, is excited by glutamatergic, aminergic and peptidergic inputs. AMPA receptor properties in relation to their expression were investigated in acutely isolated TM neurons with the help of whole-cell patch-clamp recordings combined with single-cell RT-PCR. The mRNAs encoding for the AMPA receptor GluR2 (100% of the neurons) and GluR1 (75%) were the most frequently detected, followed by the mRNA for GluR4 (56%), whereas GluR3 cDNA amplification did not yield a PCR product in any neuron. Flip splice variants prevailed over flop, in keeping with a strong glutamate-response potentiation by cyclothiazide. The expression pattern of AMPA subunits in their two splice variants was correlated with the different subtypes of Na+/Ca2+ (NCX) and Na+/Ca2+/K+ (NCKX) exchangers: glutamate receptor subunits GluR1-4 displayed no coordinated pattern with NCX. However, NCKX2 mRNA occurred only in TM cells with a fast desensitizing glutamate response, where it was coexpressed with the GluR4 subunit in the flop splice variant. NCKX3 mRNA was detected in neurons with fast or slow desensitization of glutamate responses. AMPA receptors in TM neurons were Ca2+-impermeable. As reverse Na+/Ca2+ exchange contributes to the immediate rise in intracellular calcium resulting from glutamate receptor activation, we suggest that the coordinated expression of NCKX2 with the fast desensitizing AMPA receptor-type reflects either a receptor-exchanger coupling or separate mechanisms for maintaining calcium homeostasis in neurons with fast or slow glutamate responses.
Collapse
Affiliation(s)
- O A Sergeeva
- Department of Neurophysiology, Heinrich-Heine-Universität, POB 101007, D-40001 Düsseldorf, Germany
| | | | | | | | | |
Collapse
|
44
|
Lawrence JJ, Grinspan ZM, McBain CJ. Quantal transmission at mossy fibre targets in the CA3 region of the rat hippocampus. J Physiol 2004; 554:175-93. [PMID: 14678500 PMCID: PMC1664753 DOI: 10.1113/jphysiol.2003.049551] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Recent anatomical evidence that inhibitory interneurones receive approximately 10 times more synapses from mossy fibres than do principal neurones (Acsády et al. 1998) has led to the re-examination of the extent to which interneurones are involved in CA3 network excitability. Although many of the anatomical and physiological properties of mossy fibre-CA3 interneurone synapses have been previously described (Acsády et al. 1998; Tóth et al. 2000), an investigation into the quantal nature of transmission at this synapse has not yet been conducted. Here, we employed variance-mean (VM) analysis to compare the release probability, quantal size (q) and number of release sites (n) at mossy fibre target neurones in CA3. At six of seven interneurone synapses in which a high concentration of Ca2+ was experimentally imposed, the variance-mean relationship could be approximated by a parabola. Estimates of n were 1-2, and the weighted release probability in normal Ca2+ conditions ranged from 0.34 to 0.51. At pyramidal cell synapses, the variance-mean relationship approximated a linear relationship, suggesting that release probability was significantly lower. The weighted quantal amplitude was similar at interneurone synapses and pyramidal cell synapses, although the variability in quantal amplitude was larger at interneurone synapses. Mossy fibre transmission at CA3 interneurone synapses can be explained by a lower number of release sites, a broader range of release probabilities, and larger range of quantal amplitudes than at CA3 pyramidal synapses. Finally, quantal events on to interneurones elicited spike transmission, owing in part to the more depolarized membrane potential than pyramidal cells. These results suggest that although mossy fibre synapses on to pyramidal cells are associated with a larger number of release sites per synapse, the higher connectivity, higher initial release probability, and larger relative impact per quantum on to CA3 interneurones generate strong feedforward inhibition at physiological firing frequencies of dentate granule cells. Given the central role of CA3 interneurones in mossy fibre synaptic transmission, these details of mossy fibre synaptic transmission should provide insight into CA3 network dynamics under both physiological and pathophysiological circumstances.
Collapse
Affiliation(s)
- J Josh Lawrence
- Laboratory of Cellular and Synaptic Neurophysiology, NICHD, NIH, Bethesda, MD 20892-4495, USA.
| | | | | |
Collapse
|
45
|
Abstract
The timing of action potentials is an important determinant of information coding in the brain. The shape of the EPSP has a key influence on the temporal precision of spike generation. Here we use dynamic clamp recording and passive neuronal models to study how developmental changes in synaptic conductance waveform and intrinsic membrane properties combine to affect the EPSP and action potential generation in cerebellar granule cells. We recorded EPSCs at newly formed and mature mossy fiber-granule cell synapses. Both quantal and evoked currents showed a marked speeding of the AMPA receptor-mediated component. We also found evidence for age- and activity-dependent changes in the involvement of NMDA receptors. Although AMPA and NMDA receptors contributed to quantal EPSCs at immature synapses, multiquantal release was required to activate NMDA receptors at mature synapses, suggesting a developmental redistribution of NMDA receptors. These changes in the synaptic conductance waveform result in a faster rising EPSP and reduced spike latency in mature granule cells. Mature granule cells also have a significantly decreased input resistance, contributing to a faster decaying EPSP and a reduced spike jitter. We suggest that these concurrent developmental changes, which increase the temporal precision of EPSP-spike coupling, will increase the fidelity with which sensory information is processed within the input layer of the cerebellar cortex.
Collapse
|
46
|
Grosskreutz J, Zoerner A, Schlesinger F, Krampfl K, Dengler R, Bufler J. Kinetic properties of human AMPA-type glutamate receptors expressed in HEK293 cells. Eur J Neurosci 2003; 17:1173-8. [PMID: 12670305 DOI: 10.1046/j.1460-9568.2003.02531.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
AMPA-type glutamate receptors (AMPAR) display a high variability in functional properties, which determine the time course of excitatory postsynaptic potentials. They are assembled as tetramers of GluR subunits 1-4 of different splice variants and nuclear edited isoforms. Presently, the kinetics of activation, desensitization and recovery from desensitization of human AMPARs (GluR1, 3 and 4 flip and flop, and GluR2 flip and flop in R and G edited forms, respectively) transiently expressed in HEK293 cells were studied with patch-clamp techniques and ultra fast agonist application. Activation time constants were identical for all receptors (0.13 ms). The GluR2 flip G variant showed the slowest desensitization (10.8 ms), GluR4 flip the fastest (1.6 ms). Recovery from desensitization varied between 3.1 ms (GluR4 flip) and 178 ms (GluR1 flip). To determine functional interactions between subunits in heteromeric receptors the GluR1 flip and the GluR2 flip R were coexpressed. The time constant of desensitization increased linearly from 2.5 ms (GluR1 flip homomers) to 6.8 ms (GluR2 flip R homomers) with the amount of GluR2 flip R cDNA transfected. Recovery followed a monoexponential time course and had a time constant of 178 ms in GluR1 flip homomeric expression. In all GluR1 flip/GluR2 flip heteromers and in GluR2 flip R homomers desensitization recovered with a time constant of approximately 50 ms. Thus, subunit interaction seems likely during recovery but not desensitization. Both parameters might influence the ability of AMPA receptors to mediate glutamate induced chronic excitotoxicity in neurodegenerative diseases.
Collapse
Affiliation(s)
- Julian Grosskreutz
- Department of Neurology, Medizinische Hochschule Hannover, 30625 Hannover.
| | | | | | | | | | | |
Collapse
|
47
|
Lim R, Oleskevich S, Few AP, Leao RN, Walmsley B. Glycinergic mIPSCs in mouse and rat brainstem auditory nuclei: modulation by ruthenium red and the role of calcium stores. J Physiol 2003; 546:691-9. [PMID: 12562997 PMCID: PMC2342600 DOI: 10.1113/jphysiol.2002.035071] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Spontaneous miniature inhibitory postsynaptic currents (mIPSCs) recorded in central neurons are usually highly variable in amplitude due to many factors such as intrinsic postsynaptic channel fluctuations at each release site, site-to-site variability between release sites, electrotonic attenuation due to variable dendritic locations of synapses, and the possibility of synchronous multivesicular release. A detailed knowledge of these factors is essential for the interpretation of mIPSC amplitude distributions and mean quantal size. We have studied glycinergic mIPSCs in two auditory brainstem nuclei, the rat anteroventral cochlear nucleus (AVCN) and the mouse medial nucleus of the trapezoid body (MNTB). Our previous results have demonstrated the location of glycinergic synapses on these neurons to be somatic, thus avoiding electrotonic complications. Spontaneous glycinergic mIPSCs were recorded from AVCN and MNTB neurons in brainstem slices, in the presence of TTX to block action potentials, and 6-cyano-7-nitroquinoxaline-2, 3-dione, (+/-)-2-amino-5-phosphonopentanoic acid and bicuculline to block glutamatergic and GABAergic synaptic currents. Ruthenium red (RuR), which was used to increase the frequency of mIPSCs, significantly changed the shape of most (90 %) mIPSC amplitude distributions by increasing the proportion of large-amplitude mIPSCs. The possibility was investigated (following previous evidence at GABAergic synapses) that large-amplitude glycinergic mIPSCs are due to synchronous multivesicular release initiated by presynaptic calcium sparks from ryanodine-sensitive calcium stores. Interval analysis of mIPSCs indicated that the number of potentially undetected (asynchrony < 0.5 ms) multivesicular mIPSCs was low in comparison with the number of large-amplitude mIPSCs. Ryanodine, thapsigargin and calcium-free perfusate did not reduce the frequency of large-amplitude mIPSCs (> 150 pA), arguing against a significant role for presynaptic calcium stores. Our results support previous evidence suggesting that RuR increases miniature postsynaptic current (mSC) frequency by a mechanism that does not involve presynaptic calcium stores. Our results also indicate that at glycinergic synapses in the AVCN and MNTB, site-to-site variability in mIPSC amplitude, rather than multivesicular release, is a major factor underlying the large range of amplitudes of glycinergic mIPSCs.
Collapse
Affiliation(s)
- Rebecca Lim
- Synaptic Structure and Function Group, Division of Neuroscience, John Curtin School of Medical Research, Australian National University, Canberra ACT 0200, Australia
| | | | | | | | | |
Collapse
|
48
|
Walker HC, Lawrence JJ, McBain CJ. Activation of kinetically distinct synaptic conductances on inhibitory interneurons by electrotonically overlapping afferents. Neuron 2002; 35:161-71. [PMID: 12123616 DOI: 10.1016/s0896-6273(02)00734-1] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Mossy fiber (MF) and CA3 collateral (CL) axons activate common interneurons via synapses comprised of different AMPA receptors to provide feedforward and feedback inhibitory control of the CA3 hippocampal network. Because synapses potentially occur over variable electrotonic distances that distort somatically recorded synaptic currents, it is not known whether the underlying afferent-specific synaptic conductances are associated with different time courses. Using a somatic voltage jump technique to alter the driving force at the site of the synapse, we demonstrate that MF and CL synapses overlap in electrotonic location yet differ in conductance time course. Thus, afferent-specific conductance time courses allow single interneurons to differentially integrate feedforward and feedback information without the need to segregate distinct AMPA receptor subunits to different electrotonic domains.
Collapse
Affiliation(s)
- Harrison C Walker
- Laboratory of Cellular and Synaptic Neurophysiology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
| | | | | |
Collapse
|
49
|
Warre RCH, McNaughton NCL, Randall AD. Differential discrimination of fast and slow synaptic waveforms by two low-voltage-activated calcium channels. Neuroscience 2002; 110:375-88. [PMID: 11958878 DOI: 10.1016/s0306-4522(01)00576-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Electrophysiological analysis of human embryonic kidney 293 cells stably expressing recombinant channels was used to compare how the biophysical properties of the low-voltage-activated Ca(2+) channels encoded by the alpha(1G) (Ca(V)3.1) or alpha(1I) (Ca(V)3.3) subunits shape their responses to excitatory synaptic potentials. In medium containing 2 mM extracellular Ca(2+) standard current-voltage relationships demonstrated both channel types to be clearly low-voltage activated with significant slowly activating current responses being observed at -66 mV. At all test potentials examined, activation of Ca(V)3.3 was substantially slower than that of Ca(V)3.1. To probe how these different T-type channels might respond to excitatory postsynaptic potentials (EPSPs), mock EPSPs with different kinetic profiles were created from the sum of exponentials. These waveforms were then used as command templates in voltage-clamp experiments. Ca(V)3.1-mediated channels responded effectively to both rapidly decaying mock EPSPs and slowly decaying EPSPs. In contrast, Ca(V)3.3-mediated channels were poorly gated by rapidly decaying EPSPs but were effectively activated by the more prolonged synaptic response. When activated with mock EPSPs Ca(V)3.3-mediated currents were more resistant to steady-state depolarisation of the pre-stimulus holding potential. Ca(V)3.3 currents were also more resistant to repetitive application of prolonged EPSPs, which caused substantial inactivation of Ca(V)3.1-mediated currents. The addition of a single mock action potential to the peak of a rapidly decaying EPSP voltage-clamp template greatly enhanced the currents produced by either Ca(V)3.1 or Ca(V)3.3-expressing cells. This facilitatory effect was considerably greater for Ca(V)3.3-mediated channels. From these data we suggest that the slow activation kinetics of Ca(V)3.3-mediated T-type channels enable them to respond selectively to either slow or suprathreshold synaptic potentials.
Collapse
Affiliation(s)
- R C H Warre
- Neurology CEDD, Glaxo SmithKline, New Frontiers Science Park, Harlow, Essex CM19 5AW, UK
| | | | | |
Collapse
|
50
|
Wirkner K, Köles L, Thümmler S, Luthardt J, Poelchen W, Franke H, Fürst S, Illes P. Interaction between P2Y and NMDA receptors in layer V pyramidal neurons of the rat prefrontal cortex. Neuropharmacology 2002; 42:476-88. [PMID: 11955519 DOI: 10.1016/s0028-3908(01)00199-x] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
In the first part of this study, monosynaptic excitatory postsynaptic potentials (EPSPs) in layer V of the rat prefrontal cortex were evoked by electrical stimulation of layer I. Recordings by intracellular sharp microelectrodes showed that EPSPs were concentration-dependently facilitated by the P2 receptor antagonistic ATP analogue 2-methylthio ATP (2-MeSATP), while ATP itself depressed the synaptic potentials. The inhibitory effect of ATP turned into facilitation in the presence of the adenosine A(1) receptor antagonist DPCPX. The 2-MeSATP-induced potentiation of EPSP amplitudes were prevented by the P2 receptor antagonists PPADS and Suramin. The EPSP was almost abolished by coapplication of the NMDA receptor antagonist AP-5 and the AMPA/kainate receptor antagonist CNQX. After blockade of the NMDA receptor-mediated part of the EPSP by AP-5, the stimulatory effect of 2-MeSATP disappeared. When NMDA or AMPA were pressure-applied onto pyramidal cells, only the NMDA-induced depolarization was potentiated by 2-MeSATP. In the second part of the study, NMDA-induced currents were measured by whole-cell patch-clamp pipettes. ATP, 2-MeSATP, UDP and UTP potentiated the response to NMDA, while ADP-beta-S was inactive. PPADS antagonized the effect of ATP. Synaptic isolation of pyramidal neurons by a Ca(2+)-free medium or tetrodotoxin did not alter the effect of ATP which, however, was markedly depressed when GTP in the micropipette was replaced by GDP-beta-S. These observations suggest that in layer V pyramidal neurons of the prefrontal cortex postsynaptically localized P2Y receptors interact with NMDA receptor-channels.
Collapse
Affiliation(s)
- Kerstin Wirkner
- Rudolf-Boehm-Institute of Pharmacology and Toxicology, University of Leipzig, Härtelstr. 16-18, D-04107, Leipzig, Germany.
| | | | | | | | | | | | | | | |
Collapse
|