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Micheva KD, Kiraly M, Perez MM, Madison DV. Extensive Structural Remodeling of the Axonal Arbors of Parvalbumin Basket Cells during Development in Mouse Neocortex. J Neurosci 2021; 41:9326-9339. [PMID: 34583957 PMCID: PMC8580153 DOI: 10.1523/jneurosci.0871-21.2021] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2021] [Revised: 09/12/2021] [Accepted: 09/21/2021] [Indexed: 12/26/2022] Open
Abstract
Parvalbumin-containing (PV+) basket cells are specialized cortical interneurons that regulate the activity of local neuronal circuits with high temporal precision and reliability. To understand how the PV+ interneuron connectivity underlying these functional properties is established during development, we used array tomography to map pairs of synaptically connected PV+ interneurons and postsynaptic neurons from the neocortex of mice of both sexes. We focused on the axon-myelin unit of the PV+ interneuron and quantified the number of synapses onto the postsynaptic neuron, length of connecting axonal paths, and their myelination at different time points between 2 weeks and 7 months of age. We find that myelination of the proximal axon occurs very rapidly during the third and, to a lesser extent, fourth postnatal weeks. The number of synaptic contacts made by the PV+ interneuron on its postsynaptic partner meanwhile is significantly reduced to about one-third by the end of the first postnatal month. The number of autapses, the synapses that PV+ interneurons form on themselves, however, remains constant throughout the examined period. Axon reorganizations continue beyond postnatal month 2, with the postsynaptic targets of PV+ interneurons gradually shifting to more proximal locations, and the length of axonal paths and their myelin becoming conspicuously uniform per connection. These continued microcircuit refinements likely provide the structural substrate for the robust inhibitory effects and fine temporal precision of adult PV+ basket cells.SIGNIFICANCE STATEMENT The axon of adult parvalbumin-containing (PV+) interneurons is highly specialized for fast and reliable neurotransmission. It is myelinated and forms synapses mostly onto the cell bodies and proximal dendrites of postsynaptic neurons for maximal impact. In this study, we follow the development of the PV+ interneuron axon, its myelination and synapse formation, revealing a rapid sequence of axonal reorganization, myelination of the PV+ interneuron proximal axon, and pruning of almost two-thirds of the synapses in an individual connection. This is followed by a prolonged period of axon refinement and additional myelination leading to a remarkable precision of connections in the adult mouse cortex, consistent with the temporal precision and fidelity of PV+ interneuron action.
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Affiliation(s)
- Kristina D Micheva
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, California 94305
| | - Marianna Kiraly
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, California 94305
| | - Marc M Perez
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, California 94305
| | - Daniel V Madison
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, California 94305
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Kuljis DA, Micheva KD, Ray A, Wegner W, Bowman R, Madison DV, Willig KI, Barth AL. Gephyrin-Lacking PV Synapses on Neocortical Pyramidal Neurons. Int J Mol Sci 2021; 22:ijms221810032. [PMID: 34576197 PMCID: PMC8467468 DOI: 10.3390/ijms221810032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Revised: 09/01/2021] [Accepted: 09/07/2021] [Indexed: 11/26/2022] Open
Abstract
Gephyrin has long been thought of as a master regulator for inhibitory synapses, acting as a scaffold to organize γ-aminobutyric acid type A receptors (GABAARs) at the post-synaptic density. Accordingly, gephyrin immunostaining has been used as an indicator of inhibitory synapses; despite this, the pan-synaptic localization of gephyrin to specific classes of inhibitory synapses has not been demonstrated. Genetically encoded fibronectin intrabodies generated with mRNA display (FingRs) against gephyrin (Gephyrin.FingR) reliably label endogenous gephyrin, and can be tagged with fluorophores for comprehensive synaptic quantitation and monitoring. Here we investigated input- and target-specific localization of gephyrin at a defined class of inhibitory synapse, using Gephyrin.FingR proteins tagged with EGFP in brain tissue from transgenic mice. Parvalbumin-expressing (PV) neuron presynaptic boutons labeled using Cre- dependent synaptophysin-tdTomato were aligned with postsynaptic Gephyrin.FingR puncta. We discovered that more than one-third of PV boutons adjacent to neocortical pyramidal (Pyr) cell somas lack postsynaptic gephyrin labeling. This finding was confirmed using correlative fluorescence and electron microscopy. Our findings suggest some inhibitory synapses may lack gephyrin. Gephyrin-lacking synapses may play an important role in dynamically regulating cell activity under different physiological conditions.
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Affiliation(s)
- Dika A. Kuljis
- Center for the Neural Basis of Cognition, Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213, USA; (D.A.K.); (A.R.); (R.B.)
| | - Kristina D. Micheva
- Department of Molecular and Cellular Physiology, Stanford University, Palo Alto, CA 94304, USA; (K.D.M.); (D.V.M.)
| | - Ajit Ray
- Center for the Neural Basis of Cognition, Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213, USA; (D.A.K.); (A.R.); (R.B.)
| | - Waja Wegner
- Optical Nanoscopy in Neuroscience, Center for Nanoscale Microscopy and Molecular Physiology of the Brain, University Medical Center Göttingen, 37075 Göttingen, Germany; (W.W.); (K.I.W.)
- Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Ryan Bowman
- Center for the Neural Basis of Cognition, Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213, USA; (D.A.K.); (A.R.); (R.B.)
| | - Daniel V. Madison
- Department of Molecular and Cellular Physiology, Stanford University, Palo Alto, CA 94304, USA; (K.D.M.); (D.V.M.)
| | - Katrin I. Willig
- Optical Nanoscopy in Neuroscience, Center for Nanoscale Microscopy and Molecular Physiology of the Brain, University Medical Center Göttingen, 37075 Göttingen, Germany; (W.W.); (K.I.W.)
- Max Planck Institute of Experimental Medicine, 37075 Göttingen, Germany
| | - Alison L. Barth
- Center for the Neural Basis of Cognition, Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213, USA; (D.A.K.); (A.R.); (R.B.)
- Correspondence: ; Tel.: +1-412-268-1198
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Prieto ML, Firouzi K, Khuri-Yakub BT, Madison DV, Maduke M. Spike frequency-dependent inhibition and excitation of neural activity by high-frequency ultrasound. J Gen Physiol 2021; 152:182190. [PMID: 33074301 PMCID: PMC7534904 DOI: 10.1085/jgp.202012672] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2020] [Accepted: 09/14/2020] [Indexed: 01/09/2023] Open
Abstract
Ultrasound can modulate action potential firing in vivo and in vitro, but the mechanistic basis of this phenomenon is not well understood. To address this problem, we used patch-clamp recording to quantify the effects of focused, high-frequency (43 MHz) ultrasound on evoked action potential firing in CA1 pyramidal neurons in acute rodent hippocampal brain slices. We find that ultrasound can either inhibit or potentiate firing in a spike frequency–dependent manner: at low (near-threshold) input currents and low firing frequencies, ultrasound inhibits firing, while at higher input currents and higher firing frequencies, ultrasound potentiates firing. The net result of these two competing effects is that ultrasound increases the threshold current for action potential firing, the slope of frequency-input curves, and the maximum firing frequency. In addition, ultrasound slightly hyperpolarizes the resting membrane potential, decreases action potential width, and increases the depth of the after-hyperpolarization. All of these results can be explained by the hypothesis that ultrasound activates a sustained potassium conductance. According to this hypothesis, increased outward potassium currents hyperpolarize the resting membrane potential and inhibit firing at near-threshold input currents but potentiate firing in response to higher-input currents by limiting inactivation of voltage-dependent sodium channels during the action potential. This latter effect is a consequence of faster action potential repolarization, which limits inactivation of voltage-dependent sodium channels, and deeper (more negative) after-hyperpolarization, which increases the rate of recovery from inactivation. Based on these results, we propose that ultrasound activates thermosensitive and mechanosensitive two-pore-domain potassium (K2P) channels through heating or mechanical effects of acoustic radiation force. Finite-element modeling of the effects of ultrasound on brain tissue suggests that the effects of ultrasound on firing frequency are caused by a small (<2°C) increase in temperature, with possible additional contributions from mechanical effects.
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Affiliation(s)
- Martin Loynaz Prieto
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA
| | - Kamyar Firouzi
- E.L. Ginzton Laboratory, Stanford University, Stanford, CA
| | | | - Daniel V Madison
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA
| | - Merritt Maduke
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA
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Micheva KD, Kiraly M, Perez MM, Madison DV. Conduction Velocity Along the Local Axons of Parvalbumin Interneurons Correlates With the Degree of Axonal Myelination. Cereb Cortex 2021; 31:3374-3392. [PMID: 33704414 DOI: 10.1093/cercor/bhab018] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2020] [Revised: 12/18/2020] [Accepted: 01/18/2021] [Indexed: 02/06/2023] Open
Abstract
Parvalbumin-containing (PV+) basket cells in mammalian neocortex are fast-spiking interneurons that regulate the activity of local neuronal circuits in multiple ways. Even though PV+ basket cells are locally projecting interneurons, their axons are myelinated. Can this myelination contribute in any significant way to the speed of action potential propagation along such short axons? We used dual whole cell recordings of synaptically connected PV+ interneurons and their postsynaptic target in acutely prepared neocortical slices from adult mice to measure the amplitude and latency of single presynaptic action potential-evoked inhibitory postsynaptic currents. These same neurons were then imaged with immunofluorescent array tomography, the synapses between them identified and a precise map of the connections was generated, with the exact axonal length and extent of myelin coverage. Our results support that myelination of PV+ basket cells significantly increases conduction velocity, and does so to a degree that can be physiologically relevant.
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Affiliation(s)
- Kristina D Micheva
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA, USA
| | - Marianna Kiraly
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA, USA
| | - Marc M Perez
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA, USA
| | - Daniel V Madison
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA, USA
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McMartin L, Kiraly M, Heller HC, Madison DV, Ruby NF. Disruption of circadian timing increases synaptic inhibition and reduces cholinergic responsiveness in the dentate gyrus. Hippocampus 2021; 31:422-434. [PMID: 33439521 PMCID: PMC8048473 DOI: 10.1002/hipo.23301] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2020] [Revised: 12/28/2020] [Accepted: 01/02/2021] [Indexed: 12/11/2022]
Abstract
We investigated synaptic mechanisms in the hippocampus that could explain how loss of circadian timing leads to impairments in spatial and recognition memory. Experiments were performed in hippocampal slices from Siberian hamsters (Phodopus sungorus) because, unlike mice and rats, their circadian rhythms are easily eliminated without modifications to their genome and without surgical manipulations, thereby leaving neuronal circuits intact. Recordings of excitatory postsynaptic field potentials and population spikes in area CA1 and dentate gyrus granule cells revealed no effect of circadian arrhythmia on basic functions of synaptic circuitry, including long-term potentiation. However, dentate granule cells from circadian-arrhythmic animals maintained a more depolarized resting membrane potential than cells from circadian-intact animals; a significantly greater proportion of these cells depolarized in response to the cholinergic agonist carbachol (10 μM), and did so by increasing their membrane potential three-fold greater than cells from the control (entrained) group. Dentate granule cells from arrhythmic animals also exhibited higher levels of tonic inhibition, as measured by the frequency of spontaneous inhibitory postsynaptic potentials. Carbachol also decreased stimulus-evoked synaptic excitation in dentate granule cells from both intact and arrhythmic animals as expected, but reduced stimulus-evoked synaptic inhibition only in cells from control hamsters. These findings show that loss of circadian timing is accompanied by greater tonic inhibition, and increased synaptic inhibition in response to muscarinic receptor activation in dentate granule cells. Increased inhibition would likely attenuate excitation in dentate-CA3 microcircuits, which in turn might explain the spatial memory deficits previously observed in circadian-arrhythmic hamsters.
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Affiliation(s)
- Laura McMartin
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, California, USA
| | - Marianna Kiraly
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, California, USA
| | - H Craig Heller
- Biology Department, Stanford University, Stanford, California, USA
| | - Daniel V Madison
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, California, USA
| | - Norman F Ruby
- Biology Department, Stanford University, Stanford, California, USA
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Prieto ML, Madison DV, Khuri-Yakub BT, Maduke M. Focused Ultrasound Activates Task Potassium Channels, Increases Membrane Capacitance, and Modulates Action Potential Waveform and Firing Properties in Hippocampal Brain Slices. Biophys J 2018. [DOI: 10.1016/j.bpj.2017.11.3609] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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Sun Y, Paşca SP, Portmann T, Goold C, Worringer KA, Guan W, Chan KC, Gai H, Vogt D, Chen YJJ, Mao R, Chan K, Rubenstein JL, Madison DV, Hallmayer J, Froehlich-Santino WM, Bernstein JA, Dolmetsch RE. A deleterious Nav1.1 mutation selectively impairs telencephalic inhibitory neurons derived from Dravet Syndrome patients. eLife 2016; 5. [PMID: 27458797 PMCID: PMC4961470 DOI: 10.7554/elife.13073] [Citation(s) in RCA: 83] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2015] [Accepted: 06/30/2016] [Indexed: 12/12/2022] Open
Abstract
Dravet Syndrome is an intractable form of childhood epilepsy associated with deleterious mutations in SCN1A, the gene encoding neuronal sodium channel Nav1.1. Earlier studies using human induced pluripotent stem cells (iPSCs) have produced mixed results regarding the importance of Nav1.1 in human inhibitory versus excitatory neurons. We studied a Nav1.1 mutation (p.S1328P) identified in a pair of twins with Dravet Syndrome and generated iPSC-derived neurons from these patients. Characterization of the mutant channel revealed a decrease in current amplitude and hypersensitivity to steady-state inactivation. We then differentiated Dravet-Syndrome and control iPSCs into telencephalic excitatory neurons or medial ganglionic eminence (MGE)-like inhibitory neurons. Dravet inhibitory neurons showed deficits in sodium currents and action potential firing, which were rescued by a Nav1.1 transgene, whereas Dravet excitatory neurons were normal. Our study identifies biophysical impairments underlying a deleterious Nav1.1 mutation and supports the hypothesis that Dravet Syndrome arises from defective inhibitory neurons. DOI:http://dx.doi.org/10.7554/eLife.13073.001
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Affiliation(s)
- Yishan Sun
- Novartis Institutes for BioMedical Research, Cambridge, United States.,Department of Neurobiology, Stanford University School of Medicine, Stanford, United States
| | - Sergiu P Paşca
- Department of Neurobiology, Stanford University School of Medicine, Stanford, United States.,Department of Psychiatry and Behavioral Sciences, Stanford University School of Medicine, Stanford, United States
| | - Thomas Portmann
- Department of Neurobiology, Stanford University School of Medicine, Stanford, United States
| | - Carleton Goold
- Novartis Institutes for BioMedical Research, Cambridge, United States.,Department of Neurobiology, Stanford University School of Medicine, Stanford, United States
| | | | - Wendy Guan
- Novartis Institutes for BioMedical Research, Cambridge, United States
| | - Karen C Chan
- Department of Neurobiology, Stanford University School of Medicine, Stanford, United States
| | - Hui Gai
- Department of Neurobiology, Stanford University School of Medicine, Stanford, United States
| | - Daniel Vogt
- Department of Psychiatry, University of California, San Francisco, San Francisco, United States
| | - Ying-Jiun J Chen
- Department of Psychiatry, University of California, San Francisco, San Francisco, United States
| | - Rong Mao
- Department of Neurobiology, Stanford University School of Medicine, Stanford, United States
| | - Karrie Chan
- Novartis Institutes for BioMedical Research, Cambridge, United States
| | - John Lr Rubenstein
- Department of Psychiatry, University of California, San Francisco, San Francisco, United States
| | - Daniel V Madison
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, United States
| | - Joachim Hallmayer
- Department of Psychiatry and Behavioral Sciences, Stanford University School of Medicine, Stanford, United States
| | - Wendy M Froehlich-Santino
- Department of Psychiatry and Behavioral Sciences, Stanford University School of Medicine, Stanford, United States
| | - Jonathan A Bernstein
- Department of Pediatrics, Division of Genetics, Stanford University School of Medicine, Stanford, United States
| | - Ricardo E Dolmetsch
- Novartis Institutes for BioMedical Research, Cambridge, United States.,Department of Neurobiology, Stanford University School of Medicine, Stanford, United States
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Valenzuela RA, Micheva KD, Kiraly M, Li D, Madison DV. Array tomography of physiologically-characterized CNS synapses. J Neurosci Methods 2016; 268:43-52. [PMID: 27141856 DOI: 10.1016/j.jneumeth.2016.04.017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2015] [Revised: 04/15/2016] [Accepted: 04/22/2016] [Indexed: 01/11/2023]
Abstract
BACKGROUND The ability to correlate plastic changes in synaptic physiology with changes in synaptic anatomy has been very limited in the central nervous system because of shortcomings in existing methods for recording the activity of specific CNS synapses and then identifying and studying the same individual synapses on an anatomical level. NEW METHOD We introduce here a novel approach that combines two existing methods: paired neuron electrophysiological recording and array tomography, allowing for the detailed molecular and anatomical study of synapses with known physiological properties. RESULTS The complete mapping of a neuronal pair allows determining the exact number of synapses in the pair and their location. We have found that the majority of close appositions between the presynaptic axon and the postsynaptic dendrite in the pair contain synaptic specializations. The average release probability of the synapses between the two neurons in the pair is low, below 0.2, consistent with previous studies of these connections. Other questions, such as receptor distribution within synapses, can be addressed more efficiently by identifying only a subset of synapses using targeted partial reconstructions. In addition, time sensitive events can be captured with fast chemical fixation. COMPARISON WITH EXISTING METHODS Compared to existing methods, the present approach is the only one that can provide detailed molecular and anatomical information of electrophysiologically-characterized individual synapses. CONCLUSIONS This method will allow for addressing specific questions about the properties of identified CNS synapses, even when they are buried within a cloud of millions of other brain circuit elements.
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Affiliation(s)
- Ricardo A Valenzuela
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305-5345, USA
| | - Kristina D Micheva
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305-5345, USA
| | - Marianna Kiraly
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305-5345, USA
| | - Dong Li
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305-5345, USA
| | - Daniel V Madison
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305-5345, USA.
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Chang AJ, Ortega FE, Riegler J, Madison DV, Krasnow MA. Oxygen regulation of breathing through an olfactory receptor activated by lactate. Nature 2015; 527:240-4. [PMID: 26560302 PMCID: PMC4765808 DOI: 10.1038/nature15721] [Citation(s) in RCA: 200] [Impact Index Per Article: 22.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2015] [Accepted: 08/28/2015] [Indexed: 12/25/2022]
Abstract
Animals have evolved homeostatic responses to changes in oxygen availability that act on different time scales. Although the hypoxia-inducible factor (HIF) transcriptional pathway that controls long term responses to low oxygen (hypoxia) has been established1, the pathway that mediates acute responses to hypoxia in mammals is not well understood. Here we show that the olfactory receptor Olfr78 is highly and selectively expressed in oxygen-sensitive glomus cells of the carotid body, a chemosensory organ at the carotid artery bifurcation that monitors blood oxygen and stimulates breathing within seconds when oxygen declines2. Olfr78 mutants fail to increase ventilation in hypoxia but respond normally to hypercapnia. Glomus cells are present in normal numbers and appear structurally intact, but hypoxia-induced carotid body activity is diminished. Lactate, a metabolite that rapidly accumulates in hypoxia and induces hyperventilation3–6, activates Olfr78 in heterologous expression experiments, induces calcium transients in glomus cells, and stimulates carotid sinus nerve activity through Olfr78. We propose that in addition to its role in olfaction, Olfr78 acts as a hypoxia sensor in the breathing circuit by sensing lactate produced when oxygen levels decline.
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Affiliation(s)
- Andy J Chang
- Department of Biochemistry, Stanford University School of Medicine and Howard Hughes Medical Institute, Stanford, California 94305-5307, USA
| | - Fabian E Ortega
- Department of Biochemistry, Stanford University School of Medicine and Howard Hughes Medical Institute, Stanford, California 94305-5307, USA
| | - Johannes Riegler
- Department of Medicine, Stanford University School of Medicine, Stanford, California 94305, USA
| | - Daniel V Madison
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California 94305, USA
| | - Mark A Krasnow
- Department of Biochemistry, Stanford University School of Medicine and Howard Hughes Medical Institute, Stanford, California 94305-5307, USA
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Abstract
Pair recordings involve simultaneous whole cell patch clamp recordings from two synaptically connected neurons, enabling not only direct electrophysiological characterization of the synaptic connections between individual neurons, but also pharmacological manipulation of either the presynaptic or the postsynaptic neuron. When carried out in organotypic hippocampal slice cultures, the probability that two neurons are synaptically connected is significantly increased. This preparation readily enables identification of cell types, and the neurons maintain their morphology and properties of synaptic function similar to that in native brain tissue. A major advantage of paired whole cell recordings is the highly precise information it can provide on the properties of synaptic transmission and plasticity that are not possible with other more crude techniques utilizing extracellular axonal stimulation. Paired whole cell recordings are often perceived as too challenging to perform. While there are challenging aspects to this technique, paired recordings can be performed by anyone trained in whole cell patch clamping provided specific hardware and methodological criteria are followed. The probability of attaining synaptically connected paired recordings significantly increases with healthy organotypic slices and stable micromanipulation allowing independent attainment of pre- and postsynaptic whole cell recordings. While CA3-CA3 pyramidal cell pairs are most widely used in the organotypic slice hippocampal preparation, this technique has also been successful in CA3-CA1 pairs and can be adapted to any neurons that are synaptically connected in the same slice preparation. In this manuscript we provide the detailed methodology and requirements for establishing this technique in any laboratory equipped for electrophysiology.
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Affiliation(s)
- Chantelle Fourie
- Department of Physiology and Centre for Brain Research, University of Auckland
| | - Marianna Kiraly
- Department of Molecular and Cellular Physiology, Stanford University
| | - Daniel V Madison
- Department of Molecular and Cellular Physiology, Stanford University
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Salih DAM, Rashid AJ, Colas D, de la Torre-Ubieta L, Zhu RP, Morgan AA, Santo EE, Ucar D, Devarajan K, Cole CJ, Madison DV, Shamloo M, Butte AJ, Bonni A, Josselyn SA, Brunet A. FoxO6 regulates memory consolidation and synaptic function. Genes Dev 2012; 26:2780-801. [PMID: 23222102 DOI: 10.1101/gad.208926.112] [Citation(s) in RCA: 99] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The FoxO family of transcription factors is known to slow aging downstream from the insulin/IGF (insulin-like growth factor) signaling pathway. The most recently discovered FoxO isoform in mammals, FoxO6, is highly enriched in the adult hippocampus. However, the importance of FoxO factors in cognition is largely unknown. Here we generated mice lacking FoxO6 and found that these mice display normal learning but impaired memory consolidation in contextual fear conditioning and novel object recognition. Using stereotactic injection of viruses into the hippocampus of adult wild-type mice, we found that FoxO6 activity in the adult hippocampus is required for memory consolidation. Genome-wide approaches revealed that FoxO6 regulates a program of genes involved in synaptic function upon learning in the hippocampus. Consistently, FoxO6 deficiency results in decreased dendritic spine density in hippocampal neurons in vitro and in vivo. Thus, FoxO6 may promote memory consolidation by regulating a program coordinating neuronal connectivity in the hippocampus, which could have important implications for physiological and pathological age-dependent decline in memory.
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Affiliation(s)
- Dervis A M Salih
- Department of Genetics, Stanford University, Stanford, California 94305, USA
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Stephan AH, Madison DV, Mateos JM, Fraser D, Coutellier L, Lovelett E, Tsai HH, Huang E, Rowitch D, Kim L, Tenner A, Shamloo M, Barres BA. A role for C1q in normal brain aging. Immunobiology 2012. [DOI: 10.1016/j.imbio.2012.08.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Mitra A, Blank M, Madison DV. Developmentally altered inhibition in Ts65Dn, a mouse model of Down syndrome. Brain Res 2012; 1440:1-8. [PMID: 22284618 DOI: 10.1016/j.brainres.2011.12.034] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2011] [Revised: 12/14/2011] [Accepted: 12/16/2011] [Indexed: 12/21/2022]
Abstract
We studied the development of GABA-mediated synaptic inhibition in the CA1 region of the hippocampus in Ts65Dn mice, a model system for Down syndrome (DS). While there was no significant difference in the amplitude of stimulus-evoked monosynaptic inhibitory postsynaptic potentials (IPSPs) between acute hippocampal slices from Ts65Dn mice and diploid (2N) wild-type littermates at the end of the first and third postnatal weeks, the Ts65Dn animals showed significantly larger inhibitory responses when compared to age-matched controls at the end of the second postnatal week. This transient change in evoked inhibition was strikingly layer specific, observed only when stimulating in the strata radiatum and pyramidale but not in the stratum oriens. In addition, the frequency (but not amplitude) of spontaneous action potential independent miniature inhibitory postsynaptic currents (mIPSCs) was significantly increased in the Ts65Dn mice during the second postnatal week. Additional measurements of paired-pulse ratios showed no significant difference between the genotypes. We conclude that the excess inhibition at the end of the second postnatal week in Ts65Dn mice is not due to increases in release probability or postsynaptic quantal size. Overall these experiments indicate that there is a specific disruption of the normal developmental progression of inhibitory synaptic transmission in Ts65Dn mice at a critical time point in the development of neuronal circuitry. This raises the possibility that a transient early disruption of inhibitory function may have lasting impact on other network properties and could contribute to later neural circuit dysfunction in DS.
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Affiliation(s)
- Ananya Mitra
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA
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Selcher JC, Xu W, Hanson JE, Malenka RC, Madison DV. Glutamate receptor subunit GluA1 is necessary for long-term potentiation and synapse unsilencing, but not long-term depression in mouse hippocampus. Brain Res 2011; 1435:8-14. [PMID: 22197030 DOI: 10.1016/j.brainres.2011.11.029] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2011] [Revised: 11/10/2011] [Accepted: 11/11/2011] [Indexed: 12/01/2022]
Abstract
Receptor subunit composition is believed to play a major role in the synaptic trafficking of AMPA receptors (AMPARs), and thus in activity-dependent synaptic plasticity. To isolate a physiological role of GluA1-containing AMPARs in area CA3 of the hippocampus, pair recordings were performed in organotypic hippocampal slices taken from genetically modified mice lacking the GluA1 subunit. We report here that long-term potentiation (LTP) is impaired not only at active but also at silent synapses when the GluA1 subunit is absent. The GluA1 knockout mice also exhibited reduced AMPAR-mediated evoked currents between pairs of CA3 pyramidal neurons under baseline conditions suggesting a significant role for GluA1-containing AMPARs in regulating basal synaptic transmission. In two independent measures, however, long-term depression (LTD) was unaffected in tissue from these mice. These data provide a further demonstration of the fundamental role that GluA1-containing AMPARs play in activity-dependent increases in synaptic strength but do not support a GluA1-dependent mechanism for reductions in synaptic strength.
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Affiliation(s)
- Joel C Selcher
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA
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16
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Hanson JE, Madison DV. Imbalanced pattern completion vs. separation in cognitive disease: network simulations of synaptic pathologies predict a personalized therapeutics strategy. BMC Neurosci 2010; 11:96. [PMID: 20704756 PMCID: PMC2931521 DOI: 10.1186/1471-2202-11-96] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2010] [Accepted: 08/13/2010] [Indexed: 12/14/2022] Open
Abstract
Background Diverse Mouse genetic models of neurodevelopmental, neuropsychiatric, and neurodegenerative causes of impaired cognition exhibit at least four convergent points of synaptic malfunction: 1) Strength of long-term potentiation (LTP), 2) Strength of long-term depression (LTD), 3) Relative inhibition levels (Inhibition), and 4) Excitatory connectivity levels (Connectivity). Results To test the hypothesis that pathological increases or decreases in these synaptic properties could underlie imbalances at the level of basic neural network function, we explored each type of malfunction in a simulation of autoassociative memory. These network simulations revealed that one impact of impairments or excesses in each of these synaptic properties is to shift the trade-off between pattern separation and pattern completion performance during memory storage and recall. Each type of synaptic pathology either pushed the network balance towards intolerable error in pattern separation or intolerable error in pattern completion. Imbalances caused by pathological impairments or excesses in LTP, LTD, inhibition, or connectivity, could all be exacerbated, or rescued, by the simultaneous modulation of any of the other three synaptic properties. Conclusions Because appropriate modulation of any of the synaptic properties could help re-balance network function, regardless of the origins of the imbalance, we propose a new strategy of personalized cognitive therapeutics guided by assay of pattern completion vs. pattern separation function. Simulated examples and testable predictions of this theorized approach to cognitive therapeutics are presented.
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Affiliation(s)
- Jesse E Hanson
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA.
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Emond MR, Montgomery JM, Huggins ML, Hanson JE, Mao L, Huganir RL, Madison DV. AMPA receptor subunits define properties of state-dependent synaptic plasticity. J Physiol 2010; 588:1929-46. [PMID: 20351044 DOI: 10.1113/jphysiol.2010.187229] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Many synapses undergo immediate and persistent activity-dependent changes in strength via processes that fall under the umbrella of synaptic plasticity. It is known that this type of synaptic plasticity exhibits an underlying state dependence; that is, as synapses change in strength they move into distinct 'states' that are defined by the mechanism and ability to undergo future plasticity. In this study, we have investigated the molecular mechanisms that underlie state-dependent synaptic plasticity. Using intracellular application of peptides that mimic the C-terminal tail sequences of GluR1 and GluR2 AMPA receptor subtypes, combined with paired recordings of minimal synaptic connections, we have shown that AMPA receptor subtypes present in the membrane at a given time confer some properties of plasticity states. These data show that during synaptic plasticity, AMPA receptor subtypes are differentially stabilized by postsynaptic density proteins in or out of the postsynaptic membrane, and this differential synaptic expression of different AMPA receptor subtypes defines distinct synaptic states.
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Affiliation(s)
- Michelle R Emond
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA
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18
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Hanson JE, Orr AL, Madison DV. Altered hippocampal synaptic physiology in aged parkin-deficient mice. Neuromolecular Med 2010; 12:270-6. [PMID: 20232175 DOI: 10.1007/s12017-010-8113-y] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2009] [Accepted: 02/26/2010] [Indexed: 12/22/2022]
Abstract
We examined synaptic function in the hippocampus of aged mice deficient for the Parkinson's disease-linked protein, parkin. Surprisingly, heterozygous but not homozygous parkin-deficient mice exhibited impairments in basal excitatory synaptic strength. Similarly heterozygous mice exhibited broad deficits in paired-pulse facilitation, while homozygous parkin-deficient mice exhibited more restricted deficits. In contrast to the measurements of basal synaptic function, synaptic plasticity was not altered in aged heterozygous parkin-deficient mice, but was enhanced in aged homozygous parkin-deficient mice, due to an absence of age-related decline. These findings of differential synaptic phenotypes in heterozygous vs. homozygous parkin deficiency suggest compensatory responses to genetic abnormalities could play an important role during the development of pathology in response to parkin deficiency.
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Affiliation(s)
- Jesse E Hanson
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA.
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19
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Abstract
This unit presents a procedure for the preparation of acute mammalian hippocampal slices for electrophysiological recording. Although this protocol should not be taken as the only means of making brain slices, it is a widely-used typical procedure. It is simple and straightforward. It can be used on a variety of mammalian species, though it is discussed here for use in rats.
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Affiliation(s)
- D V Madison
- Stanford University School of Medicine, Stanford, California, USA
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20
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Abstract
Almost all female and some male fragile X syndrome (FXS) patients are mosaic for expression of the FMR1 gene, yet all research in models of FXS has been in animals uniformly lacking Fmr1 expression. Therefore, we developed a system allowing neuronal genotype to be visualized in vitro in mouse brain slices mosaic for Fmr1 expression. Whole-cell recordings from individual pairs of presynaptic and postsynaptic neurons in organotypic hippocampal slices were used to probe the cell-autonomous effects of Fmr1 genotype in mosaic networks. These recordings revealed that wild-type presynaptic neurons formed synaptic connections at a greater rate than presynaptic neurons lacking normal Fmr1 function in mosaic networks. At the same time, the postsynaptic Fmr1 genotype did not influence the probability that a neuron received synaptic connections. Asymmetric presynaptic function during development of the brain could result in a decreased participation in network function by the portion of neurons lacking FMR1 expression.
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Affiliation(s)
- Jesse E. Hanson
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California 94305
| | - Daniel V. Madison
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California 94305
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21
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Hanson JE, Blank M, Valenzuela RA, Garner CC, Madison DV. The functional nature of synaptic circuitry is altered in area CA3 of the hippocampus in a mouse model of Down's syndrome. J Physiol 2006; 579:53-67. [PMID: 17158177 PMCID: PMC2075378 DOI: 10.1113/jphysiol.2006.114868] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Down's syndrome (DS) is the most common cause of mental retardation, and memory impairments are more severe in DS than in most if not all other causes of mental retardation. The Ts65Dn mouse, a genetic model of DS, exhibits phenotypes of DS, including memory impairments indicative of hippocampal dysfunction. We examined functional synaptic connectivity in area CA3 of the hippocampus of Ts65Dn mice using organotypic slice cultures as a model. We found reductions in multiple measures of synaptic function in both excitatory and inhibitory inputs to pyramidal neurons in CA3 of the Ts65Dn hippocampus. However, associational synaptic connections between pyramidal neurons were more abundant and more likely to be active rather than silent in the Ts65Dn hippocampus. Synaptic potentiation was normal in these associational connections. Decreased overall functional synaptic input onto pyramidal neurons expressed along with the specific hyperconnectivity of associational connections between pyramidal neurons will result in predictable alterations of CA3 network function, which may contribute to the memory impairments seen in DS.
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Affiliation(s)
- Jesse E Hanson
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305-5345, USA
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22
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Affiliation(s)
- Daniel V Madison
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, CA 94305-5345, USA.
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Hanson JE, Emond MR, Madison DV. Blocking polysynaptic inhibition via opioid receptor activation isolates excitatory synaptic currents without triggering epileptiform activity in organotypic hippocampal slices. J Neurosci Methods 2005; 150:8-15. [PMID: 16081163 DOI: 10.1016/j.jneumeth.2005.04.022] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2005] [Accepted: 04/18/2005] [Indexed: 11/30/2022]
Abstract
The abundance of synaptic connectivity in the cultured hippocampal slice preparation allows measurements of the unitary excitatory connection between pairs of pyramidal neurons using simultaneous presynaptic and postsynaptic intracellular recordings. However, the useful yield of these recordings can be greatly reduced by the presence of polysynaptic inhibition that occludes the measurement of the monosynaptic excitatory postsynaptic current (EPSC). We have found that the traditional method of eliminating contaminating synaptic inhibition with GABA receptor antagonists is of limited usefulness because the recurrent excitatory connections in organotypic slices cause epileptiform bursting in the absence of inhibitory function. This bursting obscures EPSCs to an even greater extent than the normally occurring polysynaptic inhibitory transmission. Here, we report a new method for isolating monosynaptic EPSCs using the mu-opioid agonist peptide DAMGO to reduce polysynaptic inhibition during these recordings. Activation of mu-opioid receptors is known to hyperpolarize inhibitory neurons. We found that DAMGO application reduces the amplitude and frequency of polysynaptic inhibition, allowing isolation of the excitatory connection between the two neurons being recorded. Furthermore, because inhibitory function is not completely eliminated by DAMGO application, epileptiform bursting very rarely develops. Therefore, the use of DAMGO to prevent polysynaptic inhibition without causing epileptiform bursting provides a useful tool to substantially increase the yield of experiments measuring the unitary excitatory connection between pyramidal neurons in the cultured hippocampal slice preparation.
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Affiliation(s)
- Jesse E Hanson
- Stanford University School of Medicine, Department of Molecular and Cellular Physiology, Beckman Center, Rm B003, Stanford, CA 94305-5345, USA.
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24
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Montgomery JM, Selcher JC, Hanson JE, Madison DV. Dynamin-dependent NMDAR endocytosis during LTD and its dependence on synaptic state. BMC Neurosci 2005; 6:48. [PMID: 16042781 PMCID: PMC1187896 DOI: 10.1186/1471-2202-6-48] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2005] [Accepted: 07/22/2005] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The N-methyl-D-aspartate (NMDA)-type glutamate receptor expressed at excitatory glutamatergic synapses is required for learning and memory and is critical for normal brain function. At a cellular level, this receptor plays a pivotal role in triggering and controlling synaptic plasticity. While it has been long recognized that this receptor plays a regulatory role, it was considered by many to be itself immune to synaptic activity-induced plasticity. More recently, we and others have shown that NMDA receptor-mediated synaptic responses can be subject to activity-dependent depression. RESULTS Here we show that depression of synaptic transmission mediated by NMDA receptors displays a state-dependence in its plasticity; NMDA receptors are resistant to activity-induced changes at silent and recently-silent synapses. Once synapses transition to the active state however, NMDA receptors become fully 'plastic'. This state-dependence is identical to that shown by the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor. Furthermore, the down-regulation of NMDAR-mediated responses during synaptic depression is prevented by disruption of dynamin-dependent endocytosis. CONCLUSION NMDA receptor-mediated synaptic responses are plastic in a state-dependent manner. Depending on the plasticity state in which a synapse currently resides, NMDA receptors will either be available or unavailable for down-regulation. The mechanism underlying the down-regulation of NMDA receptor-mediated synaptic responses is endocytosis of the NMDA receptor. Other potential mechanisms, such as receptor diffusion along the plane of the membrane, or changes in the activity of the channel are not supported. The mechanisms of AMPA receptor and NMDA receptor endocytosis appear to be tightly coupled, as both are either available or unavailable for endocytosis in the same synaptic states. Endocytosis of NMDA receptors would serve as a potent mechanism for metaplasticity. Such state-dependent regulation of NMDAR endocytosis will provide fundamental control over downstream NMDA receptor-dependent plasticity of neuronal circuitry.
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Affiliation(s)
- Johanna M Montgomery
- Department of Molecular and Cellular Physiology, Beckman Center for Molecular and Genetic Medicine, Stanford University School of Medicine Stanford, CA, 94305 USA
- Department of Physiology, Faculty of Medical and Health Sciences, University of Auckland, New Zealand
| | - Joel C Selcher
- Department of Molecular and Cellular Physiology, Beckman Center for Molecular and Genetic Medicine, Stanford University School of Medicine Stanford, CA, 94305 USA
| | - Jesse E Hanson
- Department of Molecular and Cellular Physiology, Beckman Center for Molecular and Genetic Medicine, Stanford University School of Medicine Stanford, CA, 94305 USA
| | - Daniel V Madison
- Department of Molecular and Cellular Physiology, Beckman Center for Molecular and Genetic Medicine, Stanford University School of Medicine Stanford, CA, 94305 USA
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25
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Abstract
Synapses can change their strength in response to afferent activity, a property that might underlie a variety of neural processes such as learning, network synaptic weighting, synapse formation and pruning. Recent work has shown that synapses change their strength by jumping between discrete mechanistic states, rather than by simply moving up and down in a continuum of efficacy. Coincident with this, studies have provided a framework for understanding the potential mechanistic underpinnings of synaptic plastic states. Synaptic plasticity states not only represent a new and fundamental property of CNS synapses, but also can provide a context for understanding outstanding issues in synaptic function, plasticity and development.
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Affiliation(s)
- Johanna M Montgomery
- Department of Physiology, Faculty of Medical and Health Sciences, University of Auckland, New Zealand
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26
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Abstract
Phorbol esters, activators of protein kinase C (PKC), have been shown to enhance synaptic transmission. One potential downstream target of PKC in the presynaptic terminal is the soluble N-ethylmaleimide sensitive factor (NSF) attachment protein receptor (SNARE) SNAP-25, which has a PKC phosphorylation site in its C-terminal coil centered at serine 187 (S187/Ser187). We examined the role of S187 in hippocampal synaptic transmission. After proteolytic cleavage of native SNAP-25 by botulinum neurotoxin E (BoNT/E), synaptic transmission was restored in a subset of transfected CA3 pyramidal cells with a toxin-resistant form of SNAP-25 containing unaltered S187 (Swt), S187 mutated to alanine (SA) or S187 mutated to glutamate (SE). We observed that phorbol-12,13-diacetate (PDAc, 10 microM) induced potentiation of neurotransmission to a similar degree for both Swt and SA (2.4-fold and 3.1-fold increase, respectively). Furthermore, basal levels of transmission mediated by SE were reduced relative to that of Swt (failure rates of 72% and 41%, respectively). Together, these data suggest that phosphorylation of SNAP-25 S187 does not mediate the observed enhancement of neurotransmission by phorbol esters at hippocampal synapses.
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Affiliation(s)
- Michael F A Finley
- Howard Hughes Medical Institute, Stanford University School of Medicine, Beckman Center B003, Stanford, CA 94305, USA.
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27
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Abstract
Paired recordings between CA3 pyramidal neurons were used to study the properties of synaptic plasticity in active and silent synapses. Synaptic depression is accompanied by decreases in both AMPAR and NMDAR function. The mechanisms of synaptic depression, and the potential to undergo activity-dependent plastic changes in efficacy, differ depending on whether a synapse is active, recently silent, or potentiated. These results suggest that silent and active synapses represent distinct synaptic "states," and that once unsilenced, synapses express plasticity in a graded manner. The state in which a synapse resides, and the states recently visited, determine its potential and mechanism for undergoing subsequent plastic changes.
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Affiliation(s)
- Johanna M Montgomery
- Department of Molecular and Cellular Physiology, Beckman Center, Stanford University School of Medicine, CA 94305, USA
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28
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Finley MFA, Patel SM, Madison DV, Scheller RH. The core membrane fusion complex governs the probability of synaptic vesicle fusion but not transmitter release kinetics. J Neurosci 2002; 22:1266-72. [PMID: 11850454 PMCID: PMC6757574] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/23/2023] Open
Abstract
Synaptic vesicle fusion is driven by the formation of a four-helical bundle composed of soluble N-ethylmaleimide sensitive factor (NSF) attachment protein receptors (SNAREs). Exactly how the structural interactions that lead to the formation of this complex relate to neurotransmitter release is not well understood. To address this question, we used a strategy to "rescue" synaptic transmission after proteolytic cleavage of the synaptosome-associated protein of 25 kDa (SNAP-25) by botulinum neurotoxin E (BoNtE). Transfection of CA3 hippocampal pyramidal cells with BoNtE-resistant SNAP-25 restored synaptic transmission. Additional mutations that alter the interaction between SNAP-25 C-terminal coil and the other SNARE coils dramatically reduce transmitter release probability but leave the kinetics of synaptic responses unaltered. These data indicate that at synapses, SNARE interactions are necessary for fusion but are not the rate-limiting step of neurotransmission.
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Affiliation(s)
- Michael F A Finley
- Howard Hughes Medical Institute and Department of Molecular and Cellular Physiology, Stanford University, Stanford, California 94305, USA
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29
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Affiliation(s)
- J M Montgomery
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA
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30
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Abstract
The activation of silent synapses is a proposed mechanism to account for rapid increases in synaptic efficacy such as long-term potentiation (LTP). Using simultaneous recordings from individual pre- and postsynaptic neurons in organotypic hippocampal slices, we show that two CA3 neurons can be connected entirely by silent synapses. Increasing release probability or application of cyclothiazide does not produce responses from these silent synapses. Direct measurement of NMDAR-mediated postsynaptic responses in all-silent synaptic connections before and after LTP induction show no change in failure rate, amplitude, or area. These data do not support hypotheses that synapse silent results from presynaptic factors or that LTP results from increases in presynaptic glutamate release. LTP is also associated with an increase in postsynaptic responsiveness to exogenous AMPA. We conclude that synapse silence, activation, and expression of LTP are postsynaptic.
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Affiliation(s)
- J M Montgomery
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA
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31
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Braun JE, Madison DV. A novel SNAP25-caveolin complex correlates with the onset of persistent synaptic potentiation. J Neurosci 2000; 20:5997-6006. [PMID: 10934248 PMCID: PMC6772581] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/17/2023] Open
Abstract
We have identified synaptic protein complexes in intact rat hippocampal slices using the rapid chemical cross-linking reagent paraformaldehyde. Cellular proteins were rapidly cross-linked, solubilized, separated electrophoretically by SDS-PAGE, and then identified immunologically. Multiple complexes containing syntaxin, the synaptosomal-associated protein of 25 kDa (SNAP25), and vesicle-associated membrane protein (VAMP) were observed to coexist in a single hippocampal slice including a 100 kDa cross-linked protein complex that exhibited the same electrophoretic migration as a member of the previously identified SDS-resistant soluble N-ethylmaleimide-sensitive fusion attachment protein receptor "core" of the 20 S complex. A VAMP-synaptophysin complex, reported previously in vitro, was also observed in the hippocampal slices. This study links biochemical and physiological studies involving presynaptic proteins implicated in secretion and confirms that these proteins that have been studied extensively previously in the presence of detergent do form "bona fide" cellular complexes. Importantly, we have also detected additional novel protein complexes that do not correspond to complexes identified previously in vitro. After the induction of persistent synaptic potentiation, an abundant 40 kDa SNAP25-caveolin1 complex was observed. The SNAP25-caveolin1 complex was not abundant in control slices and, therefore, represents the first demonstration of a reorganization of protein complexes in intact hippocampal slices during the induction of synaptic potentiation. The interaction between caveolin1 and SNAP25 was confirmed biochemically by demonstration of the association of caveolin with recombinant-immobilized SNAP25 and by the coimmunoprecipitation of SNAP25 using caveolin-specific antisera. Caveolin1, like SNAP25, was observed to be abundant in isolated hippocampal nerve terminals (synaptosomes). Immunofluorescent studies demonstrated that both SNAP25 and caveolin1 are present in neurons and colocalize in axonal varicosities. These results suggest that a short-lasting SNAP25-caveolin interaction may be involved in the early phase of synaptic potentiation.
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Affiliation(s)
- J E Braun
- Department of Physiology and Biophysics, Neuroscience Research Group, The University of Calgary, Calgary, Alberta, Canada T2N 4N1
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32
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Pavlidis P, Montgomery J, Madison DV. Presynaptic protein kinase activity supports long-term potentiation at synapses between individual hippocampal neurons. J Neurosci 2000; 20:4497-505. [PMID: 10844019 PMCID: PMC6772468] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/16/2023] Open
Abstract
Simultaneous microelectrode recording from two individual synaptically connected neurons enables the direct analysis of synaptic transmission and plasticity at a minimal synaptic connection. We have recorded from pairs of CA3 pyramidal neurons in organotypic hippocampal slices to examine the properties of long-term potentiation (LTP) at such minimal connections. LTP in minimal connections was found to be identical to the NMDA-dependent LTP expressed by CA3-CA1 synapses, demonstrating this system provides a good model for the study of the mechanisms of LTP expression. The LTP at minimal synaptic connections does not behave as a simple increase in transmitter release probability, because the amplitude of unitary EPSCs can increase several-fold, unlike what is observed when release probability is increased by raising extracellular calcium. Taking advantage of the relatively short axon connecting neighboring CA3 neurons, we found it feasible to introduce pharmacological agents to the interior of presynaptic terminals by injection into the presynaptic soma and have used this technique to investigate presynaptic effects on basal transmission and LTP. Presynaptic injection of nicotinamide reduced basal transmission, but LTP in these pairs was essentially normal. In contrast, presynaptic injection of H-7 significantly depressed LTP but not basal transmission, indicating a specific role of presynaptic protein kinases in LTP. These results demonstrate that pharmacological agents can be directly introduced into the presynaptic cell and that a purely presynaptic perturbation can alter this plasticity.
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Affiliation(s)
- P Pavlidis
- Department of Molecular Physiology, Stanford University School of Medicine, Stanford, California 94305-5345, USA
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33
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McQuiston AR, Madison DV. Muscarinic receptor activity induces an afterdepolarization in a subpopulation of hippocampal CA1 interneurons. J Neurosci 1999; 19:5703-10. [PMID: 10407011 PMCID: PMC6783057] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/13/2023] Open
Abstract
Cholinergic input to the hippocampus may be involved in important behavioral functions and the pathophysiology of neurodegenerative diseases. Muscarinic receptor activity in interneurons of the hippocampus may play a role in these actions. In this study, we investigated the effects of muscarinic receptor activity on the excitability of different subtypes of interneurons in rat hippocampal CA1. Most interneurons displayed an afterhyperpolarizing potential (AHP) after depolarization by injected current or synaptic stimulation. In the presence of a muscarinic agonist, the AHP of a subset of these interneurons was replaced by an afterdepolarization (ADP), often of sufficient magnitude to evoke action potentials in the absence of further stimulation. The ADP was insensitive to cadmium and low extracellular calcium. It was blocked by low extracellular sodium but not by tetrodotoxin or low concentrations of amiloride. Muscarinic ADPs were sometimes observed in isolation but were often accompanied by depolarizing, hyperpolarizing, or biphasic changes in the membrane potential. Interneurons with muscarinic ADPs were found in all strata of CA1 and did not fall into a single morphological classification. The potential functions of the prolonged action potential output of interneurons produced by the ADP could include changes in hippocampal circuit properties and facilitation of the release of peptide cotransmitters in these interneurons.
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Affiliation(s)
- A R McQuiston
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California 94305, USA
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34
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McQuiston AR, Madison DV. Muscarinic receptor activity has multiple effects on the resting membrane potentials of CA1 hippocampal interneurons. J Neurosci 1999; 19:5693-702. [PMID: 10407010 PMCID: PMC6783075] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/13/2023] Open
Abstract
Inhibitory interneurons appear to be an important target for the muscarinic actions of cholinergic inputs to the hippocampus. We investigated the effect of muscarinic receptor activity on the membrane potential (V(m)) and currents of rat hippocampal CA1 interneurons using whole-cell recording from visually identified CA1 interneurons. The predominant response observed was a muscarinic depolarization that was detected in interneurons from all layers of CA1. This depolarization was mediated by at least two mechanisms: a reduction in a potassium current and a mechanism that depended on extracellular sodium. Other interneurons responded to muscarinic agonists with a hyperpolarization or a biphasic response (hyperpolarization followed by depolarization). Hyperpolarizations and biphasic responses were found in all layers of CA1 but more frequently in stratum radiatum and stratum lacunosum moleculare. Muscarinic hyperpolarization was caused by the activation of a barium- and cesium-sensitive inwardly rectifying potassium channel. A small number of interneurons, primarily in or bordering the stratum pyramidale, produced slow membrane potential (0.04 Hz) oscillations. Many interneurons did not respond to muscarinic activity at all; half of these were in the stratum oriens. There was no strong correlation between any changes in V(m) response to muscarine and morphology, as determined by reconstruction of the interneurons. It was not possible to predict the morphology or the layer distribution of an interneuron based on the type of muscarinic membrane potential response it had. This lack of correlation between muscarinic function and morphology implies a greater complexity of interneuron function than has been realized previously.
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Affiliation(s)
- A R McQuiston
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California 94305, USA
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35
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Abstract
We performed simultaneous whole cell recordings from pairs of monosynaptically coupled hippocampal CA3 pyramidal neurons in organotypic slices. Stimulation of an action potential in a presynaptic cell resulted in an AMPA-receptor-mediated excitatory postsynaptic current (EPSC) in the postsynaptic cell that averaged approximately 34 pA. The average size of EPSCs varied in amplitude over a 20-fold range across different pairs. Both paired-pulse facilitation and depression were observed in the synaptic current in response to two presynaptic action potentials delivered 50 ms apart, but the average usually was dominated by depression. In addition, the amplitude of the second EPSC depended on the amplitude of the first EPSC, indicating competition between successive events for a common resource that is not restored within the 50-ms interpulse interval. Variation in the synaptic strength among pairs could arise from a variety of sources. Our data from anatomic reconstruction, 1/CV2 analysis, paired-pulse analysis, and manipulations of calcium/magnesium ratio suggest that differences in quantal size and release probability do not appear to vary sufficiently to fully account for the observed differences in amplitude. Thus it seems most likely that the variability in EPSC amplitude between pairs arises primarily from differences in the number of functional synapses. Injections of the calcium chelator bis-(o-aminophenoxy)-N, N,N',N'-tetraacetic acid into the presynaptic neuron resulted in a rapid and nearly complete block of transmission, whereas injection of the slower-acting chelator EGTA resulted in a variable and partial block. In addition to demonstrating the feasibility of manipulating the intracellular presynaptic environment by injection into the presynaptic soma, these data, and the EGTA results in particular may suggest variability in the linkage between calcium entry sites an release sites in these synapses.
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Affiliation(s)
- P Pavlidis
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California, 94305-5345, USA
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36
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Abstract
Cognitive impairment is an early symptom of Huntington's disease (HD). Mice engineered to carry the HD mutation in the endogenous huntingtin gene showed a significant reduction in long-term potentiation (LTP), a measure of synaptic plasticity often thought to be involved in memory. However, LTP could be induced in mutant slices by an 'enhanced' tetanic stimulus, implying that the LTP-producing mechanism is intact in mutant mice, but that their synapses are less able to reach the threshold for LTP induction. Mutant mice showed less post-tetanic potentiation than wild-type animals, and also showed decreased paired pulse facilitation, suggesting that excitatory synapses in HD mutant mice are impaired in their ability to sustain transmission during repetitive stimulation. We show that mutants, while normal in their ability to transmit at low frequencies, released significantly less glutamate during higher frequency synaptic activation. Thus, a reduced ability of Huntington synapses to respond to repetitive synaptic demand of even moderate frequency could result not only in a functional impairment of LTP induction, but could also serve as a substrate for the cognitive symptoms that comprise the early-stage pathology of HD.
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Affiliation(s)
- M T Usdin
- Department of Genetics, B111 Beckman Center, Stanford University School of Medicine, Stanford, CA 94305, USA
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37
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McQuiston AR, Madison DV. Nicotinic receptor activation excites distinct subtypes of interneurons in the rat hippocampus. J Neurosci 1999; 19:2887-96. [PMID: 10191306 PMCID: PMC6782295] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/11/2023] Open
Abstract
We examined the function of nicotinic acetylcholine receptors (nAChRs) in interneurons of area CA1 of the rat hippocampus. CA1 interneurons could be classified into three categories based on nicotinic responses. The first class was depolarized by alpha7 nAChRs, found in all layers of CA1 and as a group, had axonal projections to all neuropil layers of CA1. The second class had both fast alpha7 and slow non-alpha7 nAChR depolarizing responses, was localized primarily to the stratum oriens, and had axonal projections to the stratum lacunosum-moleculare. The third group had no nicotinic response. This group was found in or near the stratum pyramidale and had axonal projections almost exclusively within and around this layer. Low concentrations (500 nM) of nicotine desensitized fast and slow nAChR responses. These findings demonstrate that there are distinct subsets of interneurons with regard to nicotinic receptor expression and with predictable morphological properties that suggest potential cellular actions for nicotinic receptor activation in normal CNS function and during nicotine abuse.
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Affiliation(s)
- A R McQuiston
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California 94305, USA
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38
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Abstract
Nitric oxide (NO) production has been widely reported to be required for the induction of long-term potentiation (LTP) in hippocampal CA1 cells. Of the two constitutive isoforms of NO synthase, the endothelial form (eNOS) has been implicated in the induction of LTP in these cells. The distribution of eNOS within CA1 cells is not uniform, however, being present in the cell bodies and apical dendrites but absent from the basal dendrites. Using extracellular and intracellular recording techniques, we demonstrate that LTP induction in stratum radiatum synapses (onto apical dendrites) is dependent on NO production, being attenuated by pretreatment with a NOS inhibitor. LTP induced in stratum oriens synapses (onto basal dendrites) is, however, resistant to NOS inhibitors. Both forms of LTP require the activation of N-methyl-D-aspartate (NMDA) receptors because induction of LTP in both stratum radiatum and stratum oriens is blocked by AP5. Thus, it appears that synapses onto apical and basal dendrites of CA1 cells use different cellular mechanisms of LTP induction.
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Affiliation(s)
- J E Haley
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, California 94305, USA
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39
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Bergles DE, Doze VA, Madison DV, Smith SJ. Excitatory actions of norepinephrine on multiple classes of hippocampal CA1 interneurons. J Neurosci 1996; 16:572-85. [PMID: 8551341 PMCID: PMC6578664] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Norepinephrine (NE) causes an increase in the frequency of inhibitory postsynaptic potentials in CA1 pyramidal neurons in vitro. The possibility that this increase in tonic inhibition is caused by an excitatory effect on inhibitory interneurons was investigated through whole-cell recordings from pyramidal cells and both whole-cell and cell-attached patch recordings from visualized interneurons in acute slices of rat hippocampus. Adrenergic agonists caused a large increase in the frequency and amplitude of spontaneous IPSCs recorded from pyramidal cells in the presence of ionotropic glutamate receptor blockers, but they had no effect on either the frequency or the amplitude of action potential-independent miniature IPSCs recorded in tetrodotoxin. This effect was mediated primarily by an alpha adrenoceptor, although a slight beta adrenoceptor-dependent increase in IPSCs was also observed. NE caused interneurons located in all strata to depolarize and begin firing action potentials. Many of these cells had axons that ramified throughout the stratum pyramidale, suggesting that they are responsible for the IPSCs observed in pyramidal neurons. This depolarization was also mediated by an alpha adrenoceptor and was blocked by a selective alpha 1- but not a selective alpha 2-adrenoceptor antagonist. However, a slight beta adrenoceptor-dependent depolarization was detected in those interneurons that displayed time-dependent inward rectification. In the presence of a beta antagonist, NE induced an inward current that reversed near the predicted K+ equilibrium potential and was not affected by changes in intracellular Cl- concentration. In the presence of an alpha 1 antagonist, NE induced an inwardly rectifying current at potentials negative to approximately -70 mV that did not reverse (between -130 and -60 mV), characteristics similar to the hyperpolarization-activated current (lh). However, the depolarizing action of NE is attributable primarily to the alpha 1 adrenoceptor-mediated decrease in K+ conductance and not the beta adrenoceptor-dependent increase in lh. These results provide evidence that NE increases action potential-dependent IPSCs in pyramidal neurons by depolarizing surrounding inhibitory interneurons. This potent excitatory action of NE on multiple classes of hippocampal interneurons may contribute to the NE-induced decrease in the spontaneous activity of pyramidal neurons and the antiepileptic effects of NE observed in vivo.
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Affiliation(s)
- D E Bergles
- Department of Molecular and Cellular Physiology, Beckman Center for Molecular and Genetic Medicine, Stanford University School of Medicine, California 94305-5426, USA
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40
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Doze VA, Cohen GA, Madison DV. Calcium channel involvement in GABAB receptor-mediated inhibition of GABA release in area CA1 of the rat hippocampus. J Neurophysiol 1995; 74:43-53. [PMID: 7472344 DOI: 10.1152/jn.1995.74.1.43] [Citation(s) in RCA: 112] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
1. Experiments were performed in rat hippocampal slices to examine the nature of GABAergic inhibition of inhibitory synaptic transmission. In these experiments the effects of the gamma-aminobutyric acid-B (GABAB) receptor agonist, baclofen, and of subtype-selective calcium channel blockers were tested with the use of intracellular recordings of evoked inhibitory postsynaptic potentials (IPSPs) and whole cell recordings of spontaneous GABAergic inhibitory postsynaptic currents (IPSCs). 2. Baclofen inhibited evoked and spontaneous (action-potential-dependent) monosynaptic GABAA-mediated IPSPs and IPSCs but had no effect on the frequency of tetrodotoxin-resistant (action-potential-independent) miniature IPSCs recorded in CA1 pyramidal neurons. 3. Depolarizing GABAergic synaptic terminals by raising the extracellular potassium concentration caused an increase in action-potential-independent miniature IPSC frequency that could be inhibited by either baclofen or cadmium, a blocker of voltage-dependent calcium channels. In addition, under these depolarizing conditions, cadmium occluded the baclofen inhibition of miniature IPSCs. These data suggest that baclofen reduces only depolarization-induced, not quantal, GABA release and that it does so by decreasing presynaptic voltage-dependent calcium influx. 4. Experiments with subtype-selective calcium channel blockers demonstrate that the presynaptic action of baclofen was mediated through both omega-conotoxin-GVIA-sensitive and omega-agatoxin-IVA-sensitive, but not dihydropyridine-sensitive calcium channels.
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Affiliation(s)
- V A Doze
- Department of Molecular and Cellular Physiology, Beckman Center for Molecular and Genetic Medicine, Stanford University School of Medicine, California 94305-5426, USA
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41
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Madison DV, Schuman EM. Diffusible messengers and intercellular signaling: locally distributed synaptic potentiation in the hippocampus. Curr Top Microbiol Immunol 1995; 196:5-6. [PMID: 7634824 DOI: 10.1007/978-3-642-79130-7_2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- D V Madison
- Department of Molecular and Cellular Physiology, School of Medicine, Stanford University Medical Center, CA 94305-5426, USA
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42
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Schuman EM, Meffert MK, Schulman H, Madison DV. An ADP-ribosyltransferase as a potential target for nitric oxide action in hippocampal long-term potentiation. Proc Natl Acad Sci U S A 1994; 91:11958-62. [PMID: 7991564 PMCID: PMC45355 DOI: 10.1073/pnas.91.25.11958] [Citation(s) in RCA: 115] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Recent studies of long-term potentiation (LTP) in the CA1 region of the hippocampus have demonstrated that nitric oxide (NO) may be involved in some forms of LTP and have suggested that postsynaptically generated NO is a candidate to act as a retrograde messenger. However, the molecular target(s) of NO in LTP remain to be elucidated. The present study examined whether either of two potential NO targets, a soluble guanylyl cyclase or an ADP-ribosyltransferase (ADPRT; EC 2.4.2.31) plays a role in LTP. The application of membrane-permeant analogs of cGMP did not produce any long-lasting alterations in synaptic strength. In addition, application of a cGMP-dependent protein kinase inhibitor did not prevent LTP. We found that the CA1 tissue from hippocampus possesses an ADPRT activity that is dramatically stimulated by NO and attenuated by two different inhibitors of mono-ADPRT activity, phylloquinone and nicotinamide. The extracellular application of these same inhibitors prevented LTP. Postsynaptic injection of nicotinamide failed to attenuate LTP, suggesting that the critical site of ADPRT activity resides at a nonpostsynaptic locus. These results suggest that ADP-ribosylation plays a role in LTP and are consistent with the idea that an ADPRT may be a target of NO action.
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Affiliation(s)
- E M Schuman
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, CA 94305-5426
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43
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Meffert MK, Haley JE, Schuman EM, Schulman H, Madison DV. Inhibition of hippocampal heme oxygenase, nitric oxide synthase, and long-term potentiation by metalloporphyrins. Neuron 1994; 13:1225-33. [PMID: 7524564 DOI: 10.1016/0896-6273(94)90060-4] [Citation(s) in RCA: 177] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Four potent metalloporphyrin inhibitors of heme oxygenase were used to assess whether carbon monoxide production was required for induction of LTP in the CA1 region of the hippocampus. Although the metalloporphyrins produced a similar and substantial inhibition of heme oxygenase activity in hippocampal slices, only two compounds reduced the amount of LTP elicited by tetanic stimulation (chromium mesoporphyrin IX and zinc protoporphyrin IX). Both chromium mesoporphyrin IX and zinc protoporphyrin IX inhibited nitric oxide synthase in the hippocampus; tin mesoporphyrin IX and zinc deuteroporphyrin IX bis glycol neither reduced LTP induction nor inhibited NOS activity, although they did inhibit heme oxygenase. None of these metalloporphyrins reversed established LTP. Thus, together these data do not support carbon monoxide as a mediator in either LTP induction or expression/maintenance and emphasize further the nonselectivity of some metalloporphyrins.
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Affiliation(s)
- M K Meffert
- Department of Neurobiology, Stanford University Medical Center, California 94305
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44
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Affiliation(s)
- E M Schuman
- Dept. of Molecular and Cellular Physiology, Stanford University Medical Center, California 94303
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45
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Abstract
The long-lasting increase in synaptic strength known as long-term potentiation has been advanced as a potential physiological mechanism for many forms of both developmental and adult neuronal plasticity. In many models of plasticity, intercellular communication has been proposed to account for observations in which simultaneously active neurons are strengthened together. The data presented here indicate that long-term potentiation can be communicated between synapses on neighboring neurons by means of a diffusible messenger. This distributed potentiation provides a mechanism for the cooperative strengthening of proximal synapses and may underlie a variety of plastic processes in the nervous system.
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Affiliation(s)
- E M Schuman
- Department of Molecular and Cellular Physiology, Beckman Center for Molecular and Genetic Medicine, Stanford Medical School, CA 94305
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46
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Affiliation(s)
- E M Schuman
- Division of Biology, California Institute of Technology, Pasadena 91125
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47
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Abstract
1. The effects of phorbol esters on evoked and spontaneous excitatory neurotransmission were studied in the CA1 area in the in vitro hippocampal slice preparation of the rat. Experiments were conducted using field potential recording and whole-cell voltage clamp of CA1 pyramidal neurons. 2. Pyramidal cells dialysed during whole-cell recording with EGTA-containing electrode solutions, unable to support the induction of long-term potentiation (LTP), still showed robust phorbol ester-induced potentiation of excitatory synaptic transmission. 3. Spontaneous miniature excitatory postsynaptic currents (EPSCs), recorded in whole-cell voltage clamp in the presence of tetrodotoxin and picrotoxin, had amplitudes ranging from 4 to 40 pA and occurred at an average frequency of 0.8-5 Hz. Neither the amplitude nor the frequency of spontaneous EPSCs was altered by cadmium, dihydropyridines, or omega-conotoxin GVIA. 4. The phorbol ester 4-beta-phorbol 12,13-diacetate increased the frequency of spontaneous miniature EPSCs without changing the shape of the EPSC amplitude distribution, suggesting that phorbol esters exert their potentiating effects presynaptically. 5. Blockade of voltage-dependent calcium channels with cadmium attenuated the phorbol-induced increase in spontaneous miniature EPSCs frequency. The phorbol ester-induced increase in miniature EPSC frequency was also attenuated by dihydropyridines, but not by omega-conotoxin GVIA. 6. Unlike spontaneous synaptic currents, stimulus-evoked synaptic currents were reduced by omega-conotoxin but not by nifedipine. 7. We conclude that the phorbol ester increases spontaneous release of glutamate by modulating an L-type channel that does not participate in stimulus-evoked neurotransmitter release.
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Affiliation(s)
- K D Parfitt
- Department of Molecular and Cellular Physiology, Beckman Center for Molecular and Genetic Medicine, Stanford University School of Medicine, CA 94305-5426
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48
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Affiliation(s)
- D V Madison
- Department of Molecular and Cellular Physiology, Beckman Center for Molecular and Genetic Medicine, Stanford University School of Medicine, CA 94305-5426
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49
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Abstract
Axon terminals from retinal ganglion cells in the left and right eyes initially overlap with each other in the lateral geniculate nucleus of the neonatal ferret, then segregate into eye-specific layers via an activity-dependent process. Brain slices were used to show that, during this period of reorganization, retinal terminals within the lateral geniculate nucleus evoke excitatory postsynaptic currents composed of both NMDA and non-NMDA receptor-mediated currents. The amplitude of these currents could be enhanced for several tens of minutes to more than an hour by several bursts of high frequency synaptic stimulation, and the induction of enhancement appears to depend on NMDA receptor activation. Synaptic enhancement such as this could provide one of the physiological mechanisms by which retinal terminals segregate into eye-specific layers during development.
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Affiliation(s)
- R Mooney
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, California 94305
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50
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