1
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Furukawa K, Inoshita T, Kawaguchi SY. Graded control of Purkinje cell outputs by cAMP through opposing actions on axonal action potential and transmitter release. J Physiol 2024. [PMID: 39052311 DOI: 10.1113/jp286668] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2024] [Accepted: 07/05/2024] [Indexed: 07/27/2024] Open
Abstract
All-or-none signalling by action potentials (APs) in neuronal axons is pivotal for the precisely timed and identical size of outputs to multiple distant targets. However, technical limitations with respect to measuring the signalling in small intact axons have hindered the evaluation of high-fidelity signal propagation. Here, using direct recordings from axonal trunks and/or terminals of cerebellar Purkinje cells in slice and culture, we demonstrate that the timing and amplitude of axonal outputs are gradually modulated by cAMP depending on the length of axon. During the propagation in long axon, APs were attenuated and slowed in conduction by cAMP via specifically decreasing axonal Na+ currents. Consequently, the Ca2+ influx and transmitter release at distal boutons are reduced by cAMP, counteracting its direct facilitating effect on release machinery as observed at various CNS synapses. Together, our tour de force functional dissection has unveiled the axonal distance-dependent graded control of output timing and strength by intracellular signalling. KEY POINTS: The information processing in the nervous system has been classically thought to rely on the axonal faithful and high-speed conduction of action potentials (APs). We demonstrate that the strength and timing of axonal outputs are weakened and delayed, respectively, by cytoplasmic cAMP depending on the axonal length in cerebellar Purkinje cells (PCs). Direct axonal patch clamp recordings uncovered axon-specific attenuation of APs by cAMP through reduction of axonal Na+ currents. cAMP directly augments transmitter release at PC terminals without changing presynaptic Ca2+ influx or readily releasable pool of vesicles, although the extent is weaker compared to other CNS synapses. Two opposite actions of cAMP on PC axons, AP attenuation and release augmentation, together give rise to graded control of synaptic outputs in a manner dependent on the axonal length.
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Affiliation(s)
- Kei Furukawa
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto, Japan
| | - Takuma Inoshita
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto, Japan
| | - Shin-Ya Kawaguchi
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto, Japan
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2
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Montaño Romero A, Bonin C, Twomey EC. C-SPAM: an open-source time-resolved specimen vitrification device with light-activated molecules. IUCRJ 2024; 11:16-22. [PMID: 38096039 PMCID: PMC10833387 DOI: 10.1107/s2052252523010308] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2023] [Accepted: 11/29/2023] [Indexed: 01/10/2024]
Abstract
Molecular structures can be determined in vitro and in situ with cryo-electron microscopy (cryo-EM). Specimen preparation is a major obstacle in cryo-EM. Typical sample preparation is orders of magnitude slower than biological processes. Time-resolved cryo-EM (TR-cryo-EM) can capture short-lived states. Here, Cryo-EM sample preparation with light-activated molecules (C-SPAM) is presented, an open-source, photochemistry-coupled device for TR-cryo-EM that enables millisecond resolution and tunable timescales across broad biological applications.
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Affiliation(s)
- Alejandra Montaño Romero
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD USA
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore MD, USA
| | - Calli Bonin
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD USA
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore MD, USA
| | - Edward C. Twomey
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD USA
- The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore MD, USA
- The Beckman Center for Cryo-EM at Johns Hopkins, Johns Hopkins University School of Medicine, Baltimore, MD USA
- Diana Helis Henry Medical Research Foundation, New Orleans, LA USA
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3
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Trigo F, Kawaguchi SY. Analogue signaling of somatodendritic synaptic activity to axon enhances GABA release in young cerebellar molecular layer interneurons. eLife 2023; 12:e85971. [PMID: 37565643 PMCID: PMC10421593 DOI: 10.7554/elife.85971] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2023] [Accepted: 06/21/2023] [Indexed: 08/12/2023] Open
Abstract
Axons are equipped with the digital signaling capacity by which they generate and faithfully propagate action potentials (APs), and also with the analogue signaling capacity by which subthreshold activity in dendrites and soma is transmitted down the axon. Despite intense work, the extent and physiological role for subthreshold synaptic activity reaching the presynaptic boutons has remained elusive because of the technical limitation to record from them. To address this issue, we made simultaneous patch-clamp recordings from the presynaptic varicosities of cerebellar GABAergic interneurons together with their parent soma or postsynaptic target cells in young rat slices and/or primary cultures. Our tour-de-force direct functional dissection indicates that the somatodendritic spontaneous excitatory synaptic potentials are transmitted down the axon for significant distances, depolarizing presynaptic boutons. These analogously transmitted excitatory synaptic potentials augment presynaptic Ca++ influx upon arrival of an immediately following AP through a mechanism that involves a voltage-dependent priming of the Ca++ channels, leading to an increase in GABA release, without any modification in the presynaptic AP waveform or residual Ca++. Our work highlights the role of the axon in synaptic integration.
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Affiliation(s)
- Federico Trigo
- Departamento de Neurofisiología Celular y Molecular, Instituto de Investigaciones Biológicas Clemente EstableMontevideoUruguay
| | - Shin-ya Kawaguchi
- Department of Biophysics, Graduate School of Science, Kyoto University Oiwake-choKyotoJapan
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4
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Nahar R, Iwata S, Morita D, Tahara Y, Sugimoto Y, Miyata M, Maruta S. Multimerization of Small G-protein H-Ras Induced by Chemical Modification at Hyper Variable Region with Caged Compound. J Biochem 2021; 171:215-225. [PMID: 34738101 DOI: 10.1093/jb/mvab120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2021] [Accepted: 10/29/2021] [Indexed: 11/15/2022] Open
Abstract
The lipid-anchored small G protein Ras is a central regulator of cellular signal transduction processes, thereby functioning as a molecular switch. Ras forms a nanocluster on the plasma membrane by modifying lipids in the hypervariable region (HVR) at the C-terminus to exhibit physiological functions. In this study, we demonstrated that chemical modification of cysteine residues in HVR with caged compounds (instead of lipidation) induces multimerization of H-Ras. The sulfhydryl-reactive caged compound, 2-nitrobenzyl bromide (NBB), was stoichiometrically incorporated into the cysteine residue of HVR and induced the formation of the Ras multimer. Light irradiation induced the elimination of the 2-nitrobenzyl group, resulting in the conversion of the multimer to a monomer. SEC-HPLC and small-angle X-ray scattering (SAXS) analysis revealed that H-Ras forms a pentamer. Electron microscopic observation of the multimer showed a circular ring shape, which is consistent with the structure estimated from X-ray scattering. The shape of the multimer may reflect the physiological state of Ras. It was suggested that the multimerization and monomerization of H-Ras were controlled by modification with a caged compound in HVR under light irradiation.
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Affiliation(s)
- Rufiat Nahar
- Department of Bioinformatics, Graduate School of Engineering, Soka University, Hachioji, Tokyo 192-8577, Japan
| | - Seigo Iwata
- Department of Bioinformatics, Graduate School of Engineering, Soka University, Hachioji, Tokyo 192-8577, Japan
| | - Daiki Morita
- Department of Biomolecular Engineering, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603
| | - Yuhei Tahara
- Department of Biology, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585, Japan
| | - Yasunobu Sugimoto
- Department of Biomolecular Engineering, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603.,Nagoya University Synchrotron Radiation Research Center, Furo-cho Chikusa-ku, Nagoya 464-8603, Japan
| | - Makoto Miyata
- Department of Biology, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585, Japan
| | - Shinsaku Maruta
- Department of Bioinformatics, Graduate School of Engineering, Soka University, Hachioji, Tokyo 192-8577, Japan
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5
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Wan Y, Feng B, You Y, Yu J, Xu C, Dai H, Trapp BD, Shi P, Chen Z, Hu W. Microglial Displacement of GABAergic Synapses Is a Protective Event during Complex Febrile Seizures. Cell Rep 2021; 33:108346. [PMID: 33147450 DOI: 10.1016/j.celrep.2020.108346] [Citation(s) in RCA: 31] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2019] [Revised: 06/08/2020] [Accepted: 10/13/2020] [Indexed: 11/26/2022] Open
Abstract
Complex febrile seizures (FSs) lead to a high risk of intractable temporal lobe epilepsy during adulthood, yet the pathological process of complex FSs is largely unknown. Here, we demonstrate that activated microglia extensively associated with glutamatergic neuronal soma displace surrounding GABAergic presynapses in complex FSs. Patch-clamp electrophysiology establishes that the microglial displacement of GABAergic presynapses abrogates a complex-FS-induced increase in GABAergic neurotransmission and neuronal excitability, whereas GABA exerts an excitatory action in this immature stage. Pharmacological inhibition of microglial displacement of GABAergic presynapses or selective ablation of microglia in CD11bDTR mice promotes the generation of complex FSs. Blocking or deleting the P2Y12 receptor (P2Y12R) reduces microglial displacement of GABAergic presynapses and shortens the latency of complex FSs. Together, microglial displacement of GABAergic presynapses, regulated by P2Y12R, reduces neuronal excitability to mitigate the generation of complex FSs. Microglial displacement is a protective event during the pathological process of complex FSs.
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Affiliation(s)
- Yushan Wan
- Department of Pharmacology and Department of Pharmacy of Second Affiliated Hospital, NHC and CAMS Key Laboratory of Medical Neurobiology, Zhejiang University School of Medicine, Hangzhou, Zhejiang 310058, People's Republic of China
| | - Bo Feng
- Department of Pharmacology and Department of Pharmacy of Second Affiliated Hospital, NHC and CAMS Key Laboratory of Medical Neurobiology, Zhejiang University School of Medicine, Hangzhou, Zhejiang 310058, People's Republic of China
| | - Yi You
- Department of Pharmacology and Department of Pharmacy of Second Affiliated Hospital, NHC and CAMS Key Laboratory of Medical Neurobiology, Zhejiang University School of Medicine, Hangzhou, Zhejiang 310058, People's Republic of China
| | - Jie Yu
- Laboratory of Brain Function and Disease in Chinese Medicine, College of Basic Medical Science, Zhejiang Chinese Medical University, Hangzhou, Zhejiang, China
| | - Cenglin Xu
- Department of Pharmacology and Department of Pharmacy of Second Affiliated Hospital, NHC and CAMS Key Laboratory of Medical Neurobiology, Zhejiang University School of Medicine, Hangzhou, Zhejiang 310058, People's Republic of China
| | - Haibin Dai
- Department of Pharmacology and Department of Pharmacy of Second Affiliated Hospital, NHC and CAMS Key Laboratory of Medical Neurobiology, Zhejiang University School of Medicine, Hangzhou, Zhejiang 310058, People's Republic of China
| | - Bruce D Trapp
- Department of Neurosciences, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, USA
| | - Peng Shi
- Department of Pharmacology and Department of Pharmacy of Second Affiliated Hospital, NHC and CAMS Key Laboratory of Medical Neurobiology, Zhejiang University School of Medicine, Hangzhou, Zhejiang 310058, People's Republic of China
| | - Zhong Chen
- Department of Pharmacology and Department of Pharmacy of Second Affiliated Hospital, NHC and CAMS Key Laboratory of Medical Neurobiology, Zhejiang University School of Medicine, Hangzhou, Zhejiang 310058, People's Republic of China; Laboratory of Brain Function and Disease in Chinese Medicine, College of Basic Medical Science, Zhejiang Chinese Medical University, Hangzhou, Zhejiang, China; Epilepsy Center, Department of Neurology, Second Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, China.
| | - Weiwei Hu
- Department of Pharmacology and Department of Pharmacy of Second Affiliated Hospital, NHC and CAMS Key Laboratory of Medical Neurobiology, Zhejiang University School of Medicine, Hangzhou, Zhejiang 310058, People's Republic of China.
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6
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Zmorzyński S, Styk W, Klinkosz W, Iskra J, Filip AA. Personality traits and polymorphisms of genes coding neurotransmitter receptors or transporters: review of single gene and genome-wide association studies. Ann Gen Psychiatry 2021; 20:7. [PMID: 33482861 PMCID: PMC7825153 DOI: 10.1186/s12991-021-00328-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/04/2019] [Accepted: 01/10/2021] [Indexed: 01/11/2023] Open
Abstract
BACKGROUND The most popular tool used for measuring personality traits is the Five-Factor Model (FFM). It includes neuroticism, extraversion, openness, agreeableness and conscientiousness. Many studies indicated the association of genes encoding neurotransmitter receptors/transporters with personality traits. The relationship connecting polymorphic DNA sequences and FFM features has been described in the case of genes encoding receptors of cannabinoid and dopaminergic systems. Moreover, dopaminergic system receives inputs from other neurotransmitters, like GABAergic or serotoninergic systems. METHODS We searched PubMed Central (PMC), Science Direct, Scopus, Cochrane Library, Web of Science and EBSCO databases from their inception to November 19, 2020, to identify original studies, as well as peer-reviewed studies examining the FFM and its association with gene polymorphisms affecting the neurotransmitter functions in central nervous system. RESULTS Serotonin neurons modulate dopamine function. In gene encoding serotonin transporter protein, SLC6A4, was found polymorphism, which was correlated with openness to experience (in Sweden population), and high scores of neuroticism and low levels of agreeableness (in Caucasian population). The genome-wide association studies (GWASs) found an association of 5q34-q35, 3p24, 3q13 regions with higher scores of neuroticism, extraversion and agreeableness. However, the results for chromosome 3 regions are inconsistent, which was shown in our review paper. CONCLUSIONS GWASs on polymorphisms are being continued in order to determine and further understand the relationship between the changes in DNA and personality traits.
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Affiliation(s)
- Szymon Zmorzyński
- Department of Cancer Genetics With Cytogenetic Laboratory, Medical University of Lublin, Lublin, Poland
| | - Wojciech Styk
- Institute of Psychology, The John Paul II Catholic University of Lublin, Lublin, Poland.
| | - Waldemar Klinkosz
- Institute of Psychology, Cardinal Stefan Wyszynski University, Warsaw, Poland
| | - Justyna Iskra
- Institute of Psychology, The John Paul II Catholic University of Lublin, Lublin, Poland
| | - Agata Anna Filip
- Department of Cancer Genetics With Cytogenetic Laboratory, Medical University of Lublin, Lublin, Poland
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7
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Buceta I, Elezgarai I, Rico‐Barrio I, Gerrikagoitia I, Puente N, Grandes P. Deletion of the cannabinoid CB
1
receptor impacts on the ultrastructure of the cerebellar parallel fiber‐Purkinje cell synapses. J Comp Neurol 2019; 528:1041-1052. [DOI: 10.1002/cne.24808] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2019] [Revised: 10/09/2019] [Accepted: 10/31/2019] [Indexed: 12/15/2022]
Affiliation(s)
- Ianire Buceta
- Department of Neurosciences, Faculty of Medicine and Nursing University of the Basque Country UPV/EHU Leioa Spain
- Achucarro Basque Center for Neuroscience Science Park of the University of the Basque Country UPV/EHU Leioa Spain
| | - Izaskun Elezgarai
- Department of Neurosciences, Faculty of Medicine and Nursing University of the Basque Country UPV/EHU Leioa Spain
- Achucarro Basque Center for Neuroscience Science Park of the University of the Basque Country UPV/EHU Leioa Spain
| | - Irantzu Rico‐Barrio
- Department of Neurosciences, Faculty of Medicine and Nursing University of the Basque Country UPV/EHU Leioa Spain
- Achucarro Basque Center for Neuroscience Science Park of the University of the Basque Country UPV/EHU Leioa Spain
| | - Inmaculada Gerrikagoitia
- Department of Neurosciences, Faculty of Medicine and Nursing University of the Basque Country UPV/EHU Leioa Spain
- Achucarro Basque Center for Neuroscience Science Park of the University of the Basque Country UPV/EHU Leioa Spain
| | - Nagore Puente
- Department of Neurosciences, Faculty of Medicine and Nursing University of the Basque Country UPV/EHU Leioa Spain
- Achucarro Basque Center for Neuroscience Science Park of the University of the Basque Country UPV/EHU Leioa Spain
| | - Pedro Grandes
- Department of Neurosciences, Faculty of Medicine and Nursing University of the Basque Country UPV/EHU Leioa Spain
- Achucarro Basque Center for Neuroscience Science Park of the University of the Basque Country UPV/EHU Leioa Spain
- Division of Medical Sciences University of Victoria Victoria British Columbia Canada
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8
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Abstract
Axons functionally link the somato-dendritic compartment to synaptic terminals. Structurally and functionally diverse, they accomplish a central role in determining the delays and reliability with which neuronal ensembles communicate. By combining their active and passive biophysical properties, they ensure a plethora of physiological computations. In this review, we revisit the biophysics of generation and propagation of electrical signals in the axon and their dynamics. We further place the computational abilities of axons in the context of intracellular and intercellular coupling. We discuss how, by means of sophisticated biophysical mechanisms, axons expand the repertoire of axonal computation, and thereby, of neural computation.
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Affiliation(s)
- Pepe Alcami
- Division of Neurobiology, Department of Biology II, Ludwig-Maximilians-Universitaet Muenchen, Martinsried, Germany
- Department of Behavioural Neurobiology, Max Planck Institute for Ornithology, Seewiesen, Germany
| | - Ahmed El Hady
- Princeton Neuroscience Institute, Princeton University, Princeton, NJ, United States
- Howard Hughes Medical Institute, Princeton University, Princeton, NJ, United States
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9
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Kawaguchi SY. Dynamic Factors for Transmitter Release at Small Presynaptic Boutons Revealed by Direct Patch-Clamp Recordings. Front Cell Neurosci 2019; 13:269. [PMID: 31249514 PMCID: PMC6582627 DOI: 10.3389/fncel.2019.00269] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2019] [Accepted: 05/29/2019] [Indexed: 12/29/2022] Open
Abstract
Small size of an axon and presynaptic structures have hindered direct functional analysis of axonal signaling and transmitter release at presynaptic boutons in the central nervous system. However, recent technical advances in subcellular patch-clamp recordings and in fluorescent imagings are shedding light on the dynamic nature of axonal and presynaptic mechanisms. Here I summarize the functional design of an axon and presynaptic boutons, such as diversity and activity-dependent changes of action potential (AP) waveforms, Ca2+ influx, and kinetics of transmitter release, revealed by the technical tour de force of direct patch-clamp recordings and the leading-edge fluorescent imagings. I highlight the critical factors for dynamic modulation of transmitter release and presynaptic short-term plasticity.
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Affiliation(s)
- Shin-Ya Kawaguchi
- Society-Academia Collaboration for Innovation, Kyoto University, Kyoto, Japan.,Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto, Japan.,Institute for Advanced Study, Kyoto University, Kyoto, Japan
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10
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Zorrilla de San Martin J, Trigo FF, Kawaguchi SY. Axonal GABA A receptors depolarize presynaptic terminals and facilitate transmitter release in cerebellar Purkinje cells. J Physiol 2017; 595:7477-7493. [PMID: 29072780 DOI: 10.1113/jp275369] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2017] [Accepted: 10/20/2017] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS GABAA receptors have been described in the axonal compartment of neurons; contrary to dendritic GABAA receptors, axonal GABAA receptors usually induce depolarizing responses. In this study we describe the presence of functional axonal GABAA receptors in cerebellar Purkinje cells by using a combination of direct patch-clamp recordings from the axon terminals and laser GABA photolysis. In Purkinje cells, axonal GABAA receptors are depolarizing and induce an increase in neurotransmitter release that results in a change of short-term synaptic plasticity. These results contribute to our understanding of the cellular mechanisms of action of axonal GABAA receptors and highlight the importance of the presynaptic compartment in neuronal computation. ABSTRACT In neurons of the adult brain, somatodendritic GABAA receptors (GABAA Rs) mediate fast synaptic inhibition and play a crucial role in synaptic integration. GABAA Rs are not only present in the somatodendritic compartment, but also in the axonal compartment where they modulate action potential (AP) propagation and transmitter release. Although presynaptic GABAA Rs have been reported in various brain regions, their mechanisms of action and physiological roles remain obscure, particularly at GABAergic boutons. Here, using a combination of direct whole-bouton or perforated patch-clamp recordings and local GABA photolysis in single axonal varicosities of cerebellar Purkinje cells, we investigate the subcellular localization and functional role of axonal GABAA Rs both in primary cultures and acute slices. Our results indicate that presynaptic terminals of PCs carry GABAA Rs that behave as auto-receptors; their activation leads to a depolarization of the terminal membrane after an AP due to the relatively high cytoplasmic Cl- concentration in the axon, but they do not modulate the AP itself. Paired recordings from different terminals of the same axon show that the GABAA R-mediated local depolarizations propagate substantially to neighbouring varicosities. Finally, the depolarization mediated by presynaptic GABAA R activation augmented Ca2+ influx and transmitter release, resulting in a marked effect on short-term plasticity. Altogether, our results reveal a mechanism by which presynaptic GABAA Rs influence neuronal computation.
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Affiliation(s)
- Javier Zorrilla de San Martin
- Laboratoire de Physiologie Cérébrale, Université Paris Descartes and Centre National de la Recherche Scientifique, CNRS UMR8118, Paris, France.,Current affiliation: INSERM U1127, CNRS UMR 7225, Sorbonne Universités, UPMC Université Paris 06 UMRS 1127, Institut du Cerveau et de la Moelle épinière, ICM, Paris, France
| | - Federico F Trigo
- Laboratoire de Physiologie Cérébrale, Université Paris Descartes and Centre National de la Recherche Scientifique, CNRS UMR8118, Paris, France
| | - Shin-Ya Kawaguchi
- Graduate School of Brain Science, Doshisha University, Kyotanabe, Kyoto, Japan.,Society-Academia Collaboration for Innovation, Kyoto University, Sakyo-ku, Kyoto, 606-8501, Japan.,Department of Biophysics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto, 606-8502, Japan
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11
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Neuroligins Are Selectively Essential for NMDAR Signaling in Cerebellar Stellate Interneurons. J Neurosci 2017; 36:9070-83. [PMID: 27581450 DOI: 10.1523/jneurosci.1356-16.2016] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2016] [Accepted: 07/16/2016] [Indexed: 12/19/2022] Open
Abstract
UNLABELLED Neuroligins are postsynaptic cell-adhesion molecules that contribute to synapse specification. However, many other postsynaptic cell-adhesion molecules are known and the relative contributions of neuroligins versus other such molecules in different types of synapses and neurons remains largely unknown. Here, we have studied the role of neuroligins in cerebellar stellate interneurons that participate in a well defined circuit that converges on Purkinje cells as the major output neurons of cerebellar cortex. By crossing triple conditional knock-out (cKO) mice targeting all three major neuroligins [neuroligin-1 to neuroligin-3 (NL123)] with parvalbumin-Cre (PV-Cre) transgenic mice, we deleted neuroligins from inhibitory cerebellar interneurons and Purkinje cells, allowing us to study the effects of neuroligin deletions on cerebellar stellate cell synapses by electrophysiology in acute slices. PV-Cre/NL123 cKO mice did not exhibit gross alterations of cerebellar structure or cerebellar interneuron morphology. Strikingly, electrophysiological recordings in stellate cells from these PV-Cre/NL123 cKO mice revealed a large decrease in NMDAR-mediated excitatory synaptic responses, which, in stellate cells, are largely extrasynaptic, without a change in AMPA-receptor-mediated responses. Parallel analyses in PV-Cre/NL1 mice that are single NL1 cKO mice uncovered the same phenotype, demonstrating that NL1 is responsible for recruiting extrasynaptic NMDARs. Moreover, we observed only a modest impairment in inhibitory synaptic responses in stellate cells lacking NL123 despite a nearly complete suppression of inhibitory synaptic transmission in Purkinje cells by the same genetic manipulation. Our results suggest that, unlike other types of neurons investigated, neuroligins are selectively essential in cerebellar stellate interneurons for enabling the function of extrasynaptic NMDARs. SIGNIFICANCE STATEMENT Neuroligins are postsynaptic cell-adhesion molecules genetically linked to autism. However, the contributions of neuroligins to interneuron functions remain largely unknown. Here, we analyzed the role of neuroligins in cerebellar stellate interneurons. We deleted neuroligin-1, neuroligin-2, and neuroligin-3, the major cerebellar neuroligin isoforms, from stellate cells in triple NL123 conditional knock-out mice and analyzed synaptic responses by acute slice electrophysiology. We find that neuroligins are selectively essential for extrasynaptic NMDAR-mediated signaling, but dispensable for both AMPAR-mediated and inhibitory synaptic transmission. Our results reveal a critical and selective role for neuroligins in the regulation of NMDAR responses in cerebellar stellate interneurons.
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12
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Liu P, Chen B, Mailler R, Wang ZW. Antidromic-rectifying gap junctions amplify chemical transmission at functionally mixed electrical-chemical synapses. Nat Commun 2017; 8:14818. [PMID: 28317880 PMCID: PMC5364397 DOI: 10.1038/ncomms14818] [Citation(s) in RCA: 62] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2016] [Accepted: 02/06/2017] [Indexed: 11/09/2022] Open
Abstract
Neurons communicate through chemical synapses and electrical synapses (gap junctions). Although these two types of synapses often coexist between neurons, little is known about whether they interact, and whether any interactions between them are important to controlling synaptic strength and circuit functions. By studying chemical and electrical synapses between premotor interneurons (AVA) and downstream motor neurons (A-MNs) in the Caenorhabditis elegans escape circuit, we found that disrupting either the chemical or electrical synapses causes defective escape response. Gap junctions between AVA and A-MNs only allow antidromic current, but, curiously, disrupting them inhibits chemical transmission. In contrast, disrupting chemical synapses has no effect on the electrical coupling. These results demonstrate that gap junctions may serve as an amplifier of chemical transmission between neurons with both electrical and chemical synapses. The use of antidromic-rectifying gap junctions to amplify chemical transmission is potentially a conserved mechanism in circuit functions.
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Affiliation(s)
- Ping Liu
- Department of Neuroscience, University of Connecticut Health Center, Farmington, Connecticut 06030, USA
| | - Bojun Chen
- Department of Neuroscience, University of Connecticut Health Center, Farmington, Connecticut 06030, USA
| | - Roger Mailler
- Department of Computer Science, University of Tulsa, Tulsa, Oklahoma 74104, USA
| | - Zhao-Wen Wang
- Department of Neuroscience, University of Connecticut Health Center, Farmington, Connecticut 06030, USA
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13
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Ljungberg L, Lang-Ouellette D, Yang A, Jayabal S, Quilez S, Watt AJ. Transient Developmental Purkinje Cell Axonal Torpedoes in Healthy and Ataxic Mouse Cerebellum. Front Cell Neurosci 2016; 10:248. [PMID: 27853421 PMCID: PMC5089982 DOI: 10.3389/fncel.2016.00248] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2016] [Accepted: 10/10/2016] [Indexed: 12/13/2022] Open
Abstract
Information is carried out of the cerebellar cortical microcircuit via action potentials propagated along Purkinje cell axons. In several human neurodegenerative diseases, focal axonal swellings on Purkinje cells – known as torpedoes – have been associated with Purkinje cell loss. Interestingly, torpedoes are also reported to appear transiently during development in rat cerebellum. The function of Purkinje cell axonal torpedoes in health as well as in disease is poorly understood. We investigated the properties of developmental torpedoes in the postnatal mouse cerebellum of wild-type and transgenic mice. We found that Purkinje cell axonal torpedoes transiently appeared on axons of Purkinje neurons, with the largest number of torpedoes observed at postnatal day 11 (P11). This was after peak developmental apoptosis had occurred, when Purkinje cell counts in a lobule were static, suggesting that most developmental torpedoes appear on axons of neurons that persist into adulthood. We found that developmental torpedoes were not associated with a presynaptic GABAergic marker, indicating that they are not synapses. They were seldom found at axonal collateral branch points, and lacked microglia enrichment, suggesting that they are unlikely to be involved in axonal refinement. Interestingly, we found several differences between developmental torpedoes and disease-related torpedoes: developmental torpedoes occurred largely on myelinated axons, and were not associated with changes in basket cell innervation on their parent soma. Disease-related torpedoes are typically reported to contain neurofilament; while the majority of developmental torpedoes did as well, a fraction of smaller developmental torpedoes did not. These differences indicate that developmental torpedoes may not be functionally identical to disease-related torpedoes. To study this further, we used a mouse model of spinocerebellar ataxia type 6 (SCA6), and found elevated disease-related torpedo number at 2 years. However, we found normal levels of developmental torpedoes in these mice. Our findings suggest that the transient emergence of Purkinje cell axonal torpedoes during the second postnatal week in mice represents a normal morphological feature in the developing cerebellar microcircuit.
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Affiliation(s)
| | | | - Angela Yang
- Department of Biology, McGill University, Montreal QC, Canada
| | - Sriram Jayabal
- Department of Biology, McGill University, Montreal QC, Canada
| | - Sabrina Quilez
- Department of Biology, McGill University, Montreal QC, Canada
| | - Alanna J Watt
- Department of Biology, McGill University, Montreal QC, Canada
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14
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Abstract
Synapses from neurons of the medial nucleus of the trapezoid body (MNTB) onto neurons of the lateral superior olive (LSO) in the auditory brainstem are glycinergic in maturity, but also GABAergic and glutamatergic in development. The role for this neurotransmitter cotransmission is poorly understood. Here we use electrophysiological recordings in brainstem slices from P3-P21 mice to demonstrate that GABA release evoked from MNTB axons can spill over to neighboring MNTB axons and cause excitation by activating GABAAR. This spillover excitation generates patterns of staggered neurotransmitter release from different MNTB axons resulting in characteristic "doublet" postsynaptic currents in LSO neurons. Postembedding immunogold labeling and electron microscopy provide evidence that GABAARs are localized at MNTB axon terminals. Photolytic uncaging of p-hydroxyphenacyl (pHP) GABA demonstrates backpropagation of GABAAR-mediated depolarizations from MNTB axon terminals to the soma, some hundreds of microns away. These somatic depolarizations enhanced somatic excitability by increasing the probability of action potential generation. GABA spillover excitation between MNTB axon terminals may entrain neighboring MNTB neurons, which may play a role in the developmental refinement of the MNTB-LSO pathway. Axonal spillover excitation persisted beyond the second postnatal week, suggesting that this mechanism may play a role in sound localization, by providing new avenues of communication between MNTB neurons via their distal axonal projections. Significance statement: In this study, a new mechanism of neuronal communication between auditory synapses in the mammalian sound localization pathway is described. Evidence is provided that the inhibitory neurotransmitter GABA can spill over between axon terminals to cause excitation of nearby synapses to further stimulate neurotransmitter release. Excitatory GABA spillover between inhibitory axon terminals may have important implications for the development and refinement of this auditory circuit and may play a role in the ability to precisely localize sound sources.
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15
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Kantevari S, Passlick S, Kwon HB, Richers MT, Sabatini BL, Ellis-Davies GC. Development of Anionically Decorated Caged Neurotransmitters: In Vitro Comparison of 7-Nitroindolinyl- and 2-(p-Phenyl-o-nitrophenyl)propyl-Based Photochemical Probes. Chembiochem 2016; 17:953-61. [PMID: 26929152 PMCID: PMC4870097 DOI: 10.1002/cbic.201600019] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2016] [Indexed: 01/26/2023]
Abstract
Neurotransmitter uncaging, especially that of glutamate, has been used to study synaptic function for over 30 years. One limitation of caged glutamate probes is the blockade of γ-aminobutyric acid (GABA)-A receptor function. This problem comes to the fore when the probes are applied at the high concentrations required for effective two-photon photolysis. To mitigate such problems one could improve the photochemical properties of caging chromophores and/or remove receptor blockade. We show that addition of a dicarboxylate unit to the widely used 4-methoxy-7-nitroindolinyl-Glu (MNI-Glu) system reduced the off-target effects by about 50-70 %. When the same strategy was applied to an electron-rich 2-(p-Phenyl-o-nitrophenyl)propyl (PNPP) caging group, the pharmacological improvements were not as significant as in the MNI case. Finally, we used very extensive biological testing of the PNPP-caged Glu (more than 250 uncaging currents at single dendritic spines) to show that nitro-biphenyl caging chromophores have two-photon uncaging efficacies similar to that of MNI-Glu.
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Affiliation(s)
- Srinivas Kantevari
- Department of Neuroscience, Mount Sinai School of Medicine, New York, NY 10029, USA
| | - Stefan Passlick
- Department of Neuroscience, Mount Sinai School of Medicine, New York, NY 10029, USA
| | - Hyung-Bae Kwon
- Department of Neurobiology, Howard Hughes Medical Institute, Harvard Medical School, Cambridge, MA 02115, USA
| | - Matthew T. Richers
- Department of Neuroscience, Mount Sinai School of Medicine, New York, NY 10029, USA
| | - Bernardo L. Sabatini
- Department of Neurobiology, Howard Hughes Medical Institute, Harvard Medical School, Cambridge, MA 02115, USA
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16
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de San Martin JZ, Jalil A, Trigo FF. Impact of single-site axonal GABAergic synaptic events on cerebellar interneuron activity. J Gen Physiol 2015; 146:477-93. [PMID: 26621773 PMCID: PMC4664828 DOI: 10.1085/jgp.201511506] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2015] [Accepted: 10/13/2015] [Indexed: 11/29/2022] Open
Abstract
Axonal ionotropic receptors are present in a variety of neuronal types, and their function has largely been associated with the modulation of axonal activity and synaptic release. It is usually assumed that activation of axonal GABA(A)Rs comes from spillover, but in cerebellar molecular layer interneurons (MLIs) the GABA source is different: in these cells, GABA release activates presynaptic GABA(A) autoreceptors (autoRs) together with postsynaptic targets, producing an autoR-mediated synaptic event. The frequency of presynaptic, autoR-mediated miniature currents is twice that of their somatodendritic counterparts, suggesting that autoR-mediated responses have an important effect on interneuron activity. Here, we used local Ca(2+) photolysis in MLI axons of juvenile rats to evoke GABA release from individual varicosities to study the activation of axonal autoRs in single release sites. Our data show that single-site autoR conductances are similar to postsynaptic dendritic conductances. In conditions of high [Cl(-)](i), autoR-mediated conductances range from 1 to 5 nS; this corresponds to ∼30-150 GABA(A) channels per presynaptic varicosity, a value close to the number of channels in postsynaptic densities. Voltage responses produced by the activation of autoRs in single varicosities are amplified by a Na(v)-dependent mechanism and propagate along the axon with a length constant of 91 µm. Immunolabeling determination of synapse location shows that on average, one third of the synapses produce autoR-mediated signals that are large enough to reach the axon initial segment. Finally, we show that single-site activation of presynaptic GABA(A) autoRs leads to an increase in MLI excitability and thus conveys a strong feedback signal that contributes to spiking activity.
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Affiliation(s)
- Javier Zorrilla de San Martin
- Laboratoire de Physiologie Cérébrale, Université Paris Descartes and Centre National de la Recherche Scientifique, CNRS UMR8118, 75794 Paris, France
| | - Abdelali Jalil
- Laboratoire de Physiologie Cérébrale, Université Paris Descartes and Centre National de la Recherche Scientifique, CNRS UMR8118, 75794 Paris, France
| | - Federico F Trigo
- Laboratoire de Physiologie Cérébrale, Université Paris Descartes and Centre National de la Recherche Scientifique, CNRS UMR8118, 75794 Paris, France
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17
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Transmembrane AMPAR regulatory protein γ-2 is required for the modulation of GABA release by presynaptic AMPARs. J Neurosci 2015; 35:4203-14. [PMID: 25762667 DOI: 10.1523/jneurosci.4075-14.2015] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Presynaptic ionotropic glutamate receptors (iGluRs) play important roles in the control of synaptogenesis and neurotransmitter release, yet their regulation is poorly understood. In particular, the contribution of transmembrane auxiliary proteins, which profoundly shape the trafficking and gating of somatodendritic iGluRs, is unknown. Here we examined the influence of transmembrane AMPAR regulatory proteins (TARPs) on presynaptic AMPARs in cerebellar molecular layer interneurons (MLIs). 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a partial agonist at TARP-associated AMPARs, enhanced spontaneous GABA release in wild-type mice but not in stargazer mice that lack the prototypical TARP stargazin (γ-2). These findings were replicated in mechanically dissociated Purkinje cells with functional adherent synaptic boutons, demonstrating the presynaptic locus of modulation. In dissociated Purkinje cells from stargazer mice, AMPA was able to enhance mIPSC frequency, but only in the presence of the positive allosteric modulator cyclothiazide. Thus, ordinarily, presynaptic AMPARs are unable to enhance spontaneous release without γ-2, which is required predominantly for its effects on channel gating. Presynaptic AMPARs are known to reduce action potential-driven GABA release from MLIs. Although a G-protein-dependent non-ionotropic mechanism has been suggested to underlie this inhibition, paradoxically we found that γ-2, and thus AMPAR gating, was required. Following glutamate spillover from climbing fibers or application of CNQX, evoked GABA release was reduced; in stargazer mice such effects were markedly attenuated in acute slices and abolished in the dissociated Purkinje cell-nerve bouton preparation. We suggest that γ-2 association, by increasing charge transfer, allows presynaptic AMPARs to depolarize the bouton membrane sufficiently to modulate both phasic and spontaneous release.
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18
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Hogg DW, Pamenter ME, Dukoff DJ, Buck LT. Decreases in mitochondrial reactive oxygen species initiate GABA(A) receptor-mediated electrical suppression in anoxia-tolerant turtle neurons. J Physiol 2015; 593:2311-26. [PMID: 25781154 DOI: 10.1113/jp270474] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2014] [Accepted: 03/12/2015] [Indexed: 12/16/2022] Open
Abstract
Anoxia induces hyper-excitability and cell death in mammalian brain but in the anoxia-tolerant western painted turtle (Chrysemys picta bellii) neuronal electrical activity is suppressed (i.e. spike arrest), adenosine triphosphate (ATP) consumption is reduced, and cell death does not occur. Electrical suppression is primarily the result of enhanced γ-aminobutyric acid (GABA) transmission; however, the underlying mechanism responsible for initiating oxygen-sensitive GABAergic spike arrest is unknown. In turtle cortical pyramidal neurons there are three types of GABA(A) receptor-mediated currents: spontaneous inhibitory postsynaptic currents (IPSCs), giant IPSCs and tonic currents. The aim of this study was to assess the effects of reactive oxygen species (ROS) scavenging on these three currents since ROS levels naturally decrease with anoxia and may serve as a redox signal to initiate spike arrest. We found that anoxia, pharmacological ROS scavenging, or inhibition of mitochondrial ROS generation enhanced all three types of GABA currents, with tonic currents comprising ∼50% of the total current. Application of hydrogen peroxide inhibited all three GABA currents, demonstrating a reversible redox-sensitive signalling mechanism. We conclude that anoxia-mediated decreases in mitochondrial ROS production are sufficient to initiate a redox-sensitive inhibitory GABA signalling cascade that suppresses electrical activity when oxygen is limited. This unique strategy for reducing neuronal ATP consumption during anoxia represents a natural mechanism in which to explore therapies to protect mammalian brain from low-oxygen insults.
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Affiliation(s)
- David W Hogg
- Cell and Systems Biology, University of Toronto, Toronto, Ontario, Canada, M5S 3G5
| | - Matthew E Pamenter
- Department of Zoology, University of British Columbia, Vancouver, BC, Canada, V6T 1Z4
| | - David J Dukoff
- Cell and Systems Biology, University of Toronto, Toronto, Ontario, Canada, M5S 3G5
| | - Leslie T Buck
- Cell and Systems Biology, University of Toronto, Toronto, Ontario, Canada, M5S 3G5.,Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada, M5S 3G5
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19
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Abstract
Fast synaptic communication in the brain requires synchronous vesicle fusion that is evoked by action potential-induced Ca(2+) influx. However, synaptic terminals also release neurotransmitters by spontaneous vesicle fusion, which is independent of presynaptic action potentials. A functional role for spontaneous neurotransmitter release events in the regulation of synaptic plasticity and homeostasis, as well as the regulation of certain behaviours, has been reported. In addition, there is evidence that the presynaptic mechanisms underlying spontaneous release of neurotransmitters and their postsynaptic targets are segregated from those of evoked neurotransmission. These findings challenge current assumptions about neuronal signalling and neurotransmission, as they indicate that spontaneous neurotransmission has an autonomous role in interneuronal communication that is distinct from that of evoked release.
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20
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Puskarjov M, Ahmad F, Khirug S, Sivakumaran S, Kaila K, Blaesse P. BDNF is required for seizure-induced but not developmental up-regulation of KCC2 in the neonatal hippocampus. Neuropharmacology 2015; 88:103-9. [PMID: 25229715 DOI: 10.1016/j.neuropharm.2014.09.005] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2014] [Revised: 09/01/2014] [Accepted: 09/04/2014] [Indexed: 01/21/2023]
Abstract
A robust increase in the functional expression of the neuronal K-Cl cotransporter KCC2 during CNS development is necessary for the emergence of hyperpolarizing ionotropic GABAergic transmission. BDNF-TrkB signaling has been implicated in the developmental up-regulation of KCC2 and, in mature animals, in fast activity-dependent down-regulation of KCC2 function following seizures and trauma. In contrast to the decrease in KCC2 expression observed in the adult hippocampus following trauma, seizures in the neonate trigger a TrkB-dependent up-regulation of neuronal Cl(-) extrusion capacity associated with enhanced surface expression of KCC2. Here, we show that this effect is transient, and impaired in the hippocampus of Bdnf(-/-) mice. Notably, however, a complete absence of BDNF does not compromise the increase in KCC2 protein or K-Cl transport functionality during neuronal development. Furthermore, we present data indicating that the functional up-regulation of KCC2 by neonatal seizures is temporally limited by calpain activity.
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Affiliation(s)
- Martin Puskarjov
- Department of Biosciences and Neuroscience Center, University of Helsinki, FI-00014 Helsinki, Finland
| | - Faraz Ahmad
- Department of Biosciences and Neuroscience Center, University of Helsinki, FI-00014 Helsinki, Finland
| | - Stanislav Khirug
- Department of Biosciences and Neuroscience Center, University of Helsinki, FI-00014 Helsinki, Finland
| | - Sudhir Sivakumaran
- Department of Biosciences and Neuroscience Center, University of Helsinki, FI-00014 Helsinki, Finland
| | - Kai Kaila
- Department of Biosciences and Neuroscience Center, University of Helsinki, FI-00014 Helsinki, Finland
| | - Peter Blaesse
- Department of Biosciences and Neuroscience Center, University of Helsinki, FI-00014 Helsinki, Finland.
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21
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Trojanova J, Kulik A, Janacek J, Kralikova M, Syka J, Turecek R. Distribution of glycine receptors on the surface of the mature calyx of Held nerve terminal. Front Neural Circuits 2014; 8:120. [PMID: 25339867 PMCID: PMC4186306 DOI: 10.3389/fncir.2014.00120] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2014] [Accepted: 09/12/2014] [Indexed: 11/13/2022] Open
Abstract
The physiological functions of glycine receptors (GlyRs) depend on their subcellular locations. In axonal terminals of the central neurons, GlyRs trigger a slow facilitation of presynaptic transmitter release; however, their spatial relationship to the release sites is not known. In this study, we examined the distribution of GlyRs in the rat glutamatergic calyx of Held nerve terminal using high-resolution pre-embedding immunoelectron microscopy. We performed a quantitative analysis of GlyR-associated immunogold (IG) labeling in 3D reconstructed calyceal segments. A variable density of IG particles and their putative accumulations, inferred from the frequency distribution of inter-IG distances, indicated a non-uniform distribution of the receptors in the calyx. Subsequently, increased densities of IG particles were found in calyceal swellings, structures characterized by extensive exocytosis of glutamate. In swellings as well as in larger calyceal stalks, IG particles did not tend to accumulate near the glutamate releasing zones. On the other hand, GlyRs in swellings (but not in stalks) preferentially occupied membrane regions, unconnected to postsynaptic cells and presumably accessible by ambient glycine. Furthermore, the sites with increased GlyR concentrations were found in swellings tightly juxtaposed with GABA/glycinergic nerve endings. Thus, the results support the concept of an indirect mechanism underlying the modulatory effects of calyceal GlyRs, activated by glycine spillover. We also suggest the existence of an activity-dependent mechanism regulating the surface distribution of α homomeric GlyRs in axonal terminals of central neurons.
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Affiliation(s)
- Johana Trojanova
- Department of Auditory Neuroscience, Laboratory of Synaptic Transmission, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic Prague, Czech Republic
| | - Akos Kulik
- Department of Physiology II, University of Freiburg Freiburg, Germany ; BIOSS Centre for Biological Signalling Studies, University of Freiburg Freiburg, Germany
| | - Jiri Janacek
- Department of Biomathematics, Institute of Physiology, Academy of Sciences of the Czech Republic Prague, Czech Republic
| | - Michaela Kralikova
- Department of Auditory Neuroscience, Laboratory of Synaptic Transmission, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic Prague, Czech Republic
| | - Josef Syka
- Department of Auditory Neuroscience, Laboratory of Synaptic Transmission, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic Prague, Czech Republic
| | - Rostislav Turecek
- Department of Auditory Neuroscience, Laboratory of Synaptic Transmission, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic Prague, Czech Republic
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22
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Abstract
Axons can be depolarized by ionotropic receptors and transmit subthreshold depolarizations to the soma by passive electrical spread. This raises the possibility that axons and axonal receptors can participate in integration and firing in neurons. Previously, we have shown that exogenous GABA depolarizes cerebellar granule cell axons through local activation of GABA(A) receptors (GABA(A)Rs) and the soma through electrotonic spread of the axonal potential resulting in increased firing. We show here that excitability of granule cells is also increased by release of endogenous GABA from molecular layer interneurons (MLIs) and spillover activation of parallel fiber GABA(A)Rs in mice and rats. Changes in granule cell excitability were assessed by excitability testing after activation of MLIs with channelrhodopsin or electrical stimulation in the molecular layer. In granule cells lacking an axon, excitability was not changed, suggesting that axonal receptors are required. To determine the distance over which subthreshold potentials may spread, we estimated the effective axonal electrical length constant (520 μm) by excitability testing and focal uncaging of RuBi-GABA on the axon at varying distances from the soma. These data suggest that GABA(A)R-mediated axonal potentials can participate in integration and firing of cerebellar granule cells.
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23
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Estimating functional connectivity in an electrically coupled interneuron network. Proc Natl Acad Sci U S A 2013; 110:E4798-807. [PMID: 24248377 DOI: 10.1073/pnas.1310983110] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Even though it has been known for some time that in many mammalian brain areas interneurons are electrically coupled, a quantitative description of the network electrical connectivity and its impact on cellular passive properties is still lacking. Approaches used so far to solve this problem are limited because they do not readily distinguish junctions among direct neighbors from indirect junctions involving intermediary, multiply connected cells. In the cerebellar cortex, anatomical and functional evidence indicates electrical coupling between molecular layer interneurons (basket and stellate cells). An analysis of the capacitive currents obtained under voltage clamp in molecular layer interneurons of juvenile rats or mice reveals an exponential component with a time constant of ~20 ms, which represents capacitive loading of neighboring cells through gap junctions. These results, taken together with dual cell recording of electrical synapses, have led us to estimate the number of direct neighbors to be ~4 for rat basket cells and ~1 for rat stellate cells. The weighted number of neighbors (number of neighbors, both direct and indirect, weighted with the percentage of voltage deflection at steady state) was 1.69 in basket cells and 0.23 in stellate cells. The last numbers indicate the spread of potential changes in the network and serve to estimate the contribution of gap junctions to cellular input conductance. In conclusion the present work offers effective tools to analyze the connectivity of electrically connected interneuron networks, and it indicates that in juvenile rodents, electrical communication is stronger among basket cells than among stellate cells.
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Paul J, Zeilhofer HU, Fritschy JM. Selective distribution of GABA(A) receptor subtypes in mouse spinal dorsal horn neurons and primary afferents. J Comp Neurol 2013; 520:3895-911. [PMID: 22522945 DOI: 10.1002/cne.23129] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
In the spinal cord dorsal horn, presynaptic GABA(A) receptors (GABA(A)Rs) in the terminals of nociceptors as well as postsynaptic receptors in spinal neurons regulate the transmission of nociceptive and somatosensory signals from the periphery. GABA(A)Rs are heterogeneous and distinguished functionally and pharmacologically by the type of α subunit variant they contain. This heterogeneity raises the possibility that GABA(A)R subtypes differentially regulate specific pain modalities. Here, we characterized the subcellular distribution of GABA(A)R subtypes in nociceptive circuits by using immunohistochemistry with subunit-specific antibodies combined with markers of primary afferents and dorsal horn neurons. Confocal laser scanning microscopy analysis revealed a distinct, partially overlapping laminar distribution of α1-3 and α5 subunit immunoreactivity in laminae I-V. Likewise, a layer-specific pattern was evident for their distribution among glutamatergic, γ-aminobutyric acid (GABA)ergic, and glycinergic neurons (detected in transgenic mice expressing vesicular glutamate transporter 2-enhanced green fluorescent protein [vGluT2-eGFP], glutamic acid decarboxylase [GAD]67-eGFP, and glycine transporter 2 (GlyT2)-eGFP, respectively). Finally, all four subunits could be detected within primary afferent terminals. C-fibers predominantly contained either α2 or α3 subunit immunoreactivity; terminals from myelinated (Aβ/Aδ) fibers were colabeled in roughly equal proportion with each subunit. The presence of axoaxonic GABAergic synapses was determined by costaining with gephyrin and vesicular inhibitory amino acid transporter to label GABAergic postsynaptic densities and terminals, respectively. Colocalization of the α2 or α3 subunit with these markers was observed in a subset of C-fiber synapses. Furthermore, gephyrin mRNA and protein expression was detected in dorsal root ganglia. Collectively, these results show that differential GABA(A)R distribution in primary afferent terminals and dorsal horn neurons allows for multiple, circuit-specific modes of regulation of nociceptive circuits.
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Affiliation(s)
- Jolly Paul
- Institute of Pharmacology and Toxicology, University of Zurich, CH-8057 Zurich, Switzerland
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25
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Frola E, Patrizi A, Goetz T, Medrihan L, Petrini EM, Barberis A, Wulff P, Wisden W, Sassoè-Pognetto M. Synaptic competition sculpts the development of GABAergic axo-dendritic but not perisomatic synapses. PLoS One 2013; 8:e56311. [PMID: 23457547 PMCID: PMC3572971 DOI: 10.1371/journal.pone.0056311] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2012] [Accepted: 01/11/2013] [Indexed: 11/24/2022] Open
Abstract
The neurotransmitter GABA regulates many aspects of inhibitory synapse development. We tested the hypothesis that GABAA receptors (GABAARs) work together with the synaptic adhesion molecule neuroligin 2 (NL2) to regulate synapse formation in different subcellular compartments. We investigated mice (“γ2 knockdown mice”) with an engineered allele of the GABAAR γ2 subunit gene which produced a mosaic expression of synaptic GABAARs in neighboring neurons, causing a strong imbalance in synaptic inhibition. Deletion of the γ2 subunit did not abolish synapse formation or the targeting of NL2 to distinct types of perisomatic and axo-dendritic contacts. Thus synaptic localization of NL2 does not require synaptic GABAARs. However, loss of the γ2 subunit caused a selective decrease in the number of axo-dendritic synapses on cerebellar Purkinje cells and cortical pyramidal neurons, whereas perisomatic synapses were not significantly affected. Notably, γ2-positive cells had increased axo-dendritic innervation compared with both γ2-negative and wild-type counterparts. Moreover heterologous synapses on spines, that are found after total deletion of GABAARs from all Purkinje cells, were rare in cerebella of γ2 knockdown mice. These findings reveal a selective role of γ2 subunit-containing GABAARs in regulating synapse development in distinct subcellular compartments, and support the hypothesis that the refinement of axo-dendritic synapses is regulated by activity-dependent competition between neighboring neurons.
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Affiliation(s)
- Elena Frola
- Department of Neurosciences, University of Turin, and National Institute of Neuroscience-Italy, Torino, Italy
| | - Annarita Patrizi
- Department of Neurosciences, University of Turin, and National Institute of Neuroscience-Italy, Torino, Italy
| | - Thomas Goetz
- Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, United Kingdom
| | - Lucian Medrihan
- Department of Neuroscience and Brain Technologies, The Italian Institute of Technology, Genova, Italy
| | - Enrica Maria Petrini
- Department of Neuroscience and Brain Technologies, The Italian Institute of Technology, Genova, Italy
| | - Andrea Barberis
- Department of Neuroscience and Brain Technologies, The Italian Institute of Technology, Genova, Italy
| | - Peer Wulff
- Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, United Kingdom
| | - William Wisden
- Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, United Kingdom
- * E-mail: (WW); (MSP)
| | - Marco Sassoè-Pognetto
- Department of Neurosciences, University of Turin, and National Institute of Neuroscience-Italy, Torino, Italy
- * E-mail: (WW); (MSP)
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26
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Klán P, Šolomek T, Bochet CG, Blanc A, Givens R, Rubina M, Popik V, Kostikov A, Wirz J. Photoremovable protecting groups in chemistry and biology: reaction mechanisms and efficacy. Chem Rev 2013; 113:119-91. [PMID: 23256727 PMCID: PMC3557858 DOI: 10.1021/cr300177k] [Citation(s) in RCA: 1242] [Impact Index Per Article: 112.9] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2012] [Indexed: 02/06/2023]
Affiliation(s)
- Petr Klán
- Department of Chemistry, Faculty of Science, Masaryk University, Kamenice 5, 625 00 Brno, Czech Republic.
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Rossi B, Ogden D, Llano I, Tan YP, Marty A, Collin T. Current and calcium responses to local activation of axonal NMDA receptors in developing cerebellar molecular layer interneurons. PLoS One 2012; 7:e39983. [PMID: 22761940 PMCID: PMC3384623 DOI: 10.1371/journal.pone.0039983] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2012] [Accepted: 05/30/2012] [Indexed: 11/19/2022] Open
Abstract
In developing cerebellar molecular layer interneurons (MLIs), NMDA increases spontaneous GABA release. This effect had been attributed to either direct activation of presynaptic NMDA receptors (preNMDARs) or an indirect pathway involving activation of somato-dendritic NMDARs followed by passive spread of somatic depolarization along the axon and activation of axonal voltage dependent Ca(2+) channels (VDCCs). Using Ca(2+) imaging and electrophysiology, we searched for preNMDARs by uncaging NMDAR agonists either broadly throughout the whole field or locally at specific axonal locations. Releasing either NMDA or glutamate in the presence of NBQX using short laser pulses elicited current transients that were highly sensitive to the location of the spot and restricted to a small number of varicosities. The signal was abolished in the presence of high Mg(2+) or by the addition of APV. Similar paradigms yielded restricted Ca(2+) transients in interneurons loaded with a Ca(2+) indicator. We found that the synaptic effects of NMDA were not inhibited by blocking VDCCs but were impaired in the presence of the ryanodine receptor antagonist dantrolene. Furthermore, in voltage clamped cells, bath applied NMDA triggers Ca(2+) elevations and induces neurotransmitter release in the axonal compartment. Our results suggest the existence of preNMDARs in developing MLIs and propose their involvement in the NMDA-evoked increase in GABA release by triggering a Ca(2+)-induced Ca(2+) release process mediated by presynaptic Ca(2+) stores. Such a mechanism is likely to exert a crucial role in various forms of Ca(2+)-mediated synaptic plasticity.
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Affiliation(s)
- Bénédicte Rossi
- Laboratoire de Physiologie Cérébrale, CNRS-UMR 8118, Université Paris Descartes, Université Paris Diderot, Paris, France
| | - David Ogden
- Laboratoire de Physiologie Cérébrale, CNRS-UMR 8118, Université Paris Descartes, Université Paris Diderot, Paris, France
| | - Isabel Llano
- Laboratoire de Physiologie Cérébrale, CNRS-UMR 8118, Université Paris Descartes, Université Paris Diderot, Paris, France
| | - Yusuf P. Tan
- Laboratoire de Physiologie Cérébrale, CNRS-UMR 8118, Université Paris Descartes, Université Paris Diderot, Paris, France
| | - Alain Marty
- Laboratoire de Physiologie Cérébrale, CNRS-UMR 8118, Université Paris Descartes, Université Paris Diderot, Paris, France
| | - Thibault Collin
- Laboratoire de Physiologie Cérébrale, CNRS-UMR 8118, Université Paris Descartes, Université Paris Diderot, Paris, France
- * E-mail:
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28
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Antflick JE, Hampson DR. Modulation of glutamate release from parallel fibers by mGlu4 and pre-synaptic GABA(A) receptors. J Neurochem 2012; 120:552-63. [PMID: 22145864 DOI: 10.1111/j.1471-4159.2011.07611.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The regulation of pre-synaptic glutamate release is important in the maintenance and fidelity of excitatory transmission in the nervous system. In this study, we report a novel interaction between a ligand-gated ion channel and a G-protein coupled receptor which regulates glutamate release from parallel fiber axon terminals. Immunocytochemical analysis revealed that GABA(A) receptors and the high affinity group III metabotropic glutamate receptor subtype 4 (mGlu4) are co-localized on glutamatergic parallel fiber axon terminals in the cerebellum. GABA(A) and mGlu4 receptors were also found to co-immunoprecipitate from cerebellar membranes. Independently, these two receptors have opposing roles on glutamate release: pre-synaptic GABA(A) receptors promote, while mGlu4 receptors inhibit, glutamate release. However, coincident activation of GABA(A) receptors with muscimol and mGlu4 with the agonist (2S)-S-2-amino-4-phosphonobutanoic acid , increased glutamate release from [(3) H]glutamate-loaded cerebellar synaptosomes above that observed with muscimol alone. Further support for an interaction between GABA(A) and mGlu4 receptors was obtained in the mGlu4 knockout mouse which displayed reduced binding of the GABA(A) ligand [(35) S]tert-butylbicyclophosphorothionate, and decreased expression of the α1, α6, β2 GABA(A) receptor subunits in the cerebellum. Taken together, our data suggest a new role for mGlu4 whereby simultaneous activation with GABA(A) receptors acts to amplify glutamate release at parallel fiber-Purkinje cell synapses.
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Affiliation(s)
- Jordan E Antflick
- Department of Pharmaceutical Sciences, Leslie Dan Faculty of Pharmacy, Toronto, Ontario, Canada
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29
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Combining membrane potential imaging with L-glutamate or GABA photorelease. PLoS One 2011; 6:e24911. [PMID: 22022367 PMCID: PMC3191132 DOI: 10.1371/journal.pone.0024911] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2011] [Accepted: 08/23/2011] [Indexed: 12/18/2022] Open
Abstract
Combining membrane potential imaging using voltage sensitive dyes with photolysis of l-glutamate or GABA allows the monitoring of electrical activity elicited by the neurotransmitter at different sub-cellular sites. Here we describe a simple system and some basic experimental protocols to achieve these measurements. We show how to apply the neurotransmitter and how to vary the dimension of the area of photolysis. We assess the localisation of photolysis and of the recorded membrane potential changes by depolarising the dendrites of cerebellar Purkinje neurons with l-glutamate photorelease using different experimental protocols. We further show in the apical dendrites of CA1 hippocampal pyramidal neurons how l-glutamate photorelease can be used to calibrate fluorescence changes from voltage sensitive dyes in terms of membrane potential changes (in mV) and how GABA photorelease can be used to investigate the phenomenon of shunting inhibition. We also show how GABA photorelease can be used to measure chloride-mediated changes of membrane potential under physiological conditions originating from different regions of a neuron, providing important information on the local intracellular chloride concentrations. The method and the proof of principle reported here open the gateway to a variety of important applications where the advantages of this approach are necessary.
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30
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Synthesis and photolytic evaluation of a nitroindoline-caged glycine with a side chain of high negative charge for use in neuroscience. Tetrahedron 2011. [DOI: 10.1016/j.tet.2011.05.045] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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31
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Kavalali ET, Chung C, Khvotchev M, Leitz J, Nosyreva E, Raingo J, Ramirez DMO. Spontaneous neurotransmission: an independent pathway for neuronal signaling? Physiology (Bethesda) 2011; 26:45-53. [PMID: 21357902 DOI: 10.1152/physiol.00040.2010] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Recent findings suggest that spontaneous neurotransmission is a bona fide pathway for interneuronal signaling that operates independent of evoked transmission via distinct presynaptic as well as postsynaptic substrates. This article will examine the role of spontaneous release events in neuronal signaling by focusing on aspects that distinguish this process from evoked neurotransmission, and evaluate the mechanisms that may underlie this segregation.
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Affiliation(s)
- Ege T Kavalali
- Department of Neuroscience, UT Southwestern Medical Center, Dallas, Texas, USA.
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32
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Somatic depolarization enhances GABA release in cerebellar interneurons via a calcium/protein kinase C pathway. J Neurosci 2011; 31:5804-15. [PMID: 21490222 DOI: 10.1523/jneurosci.5127-10.2011] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
In cortical and hippocampal neurons, tonic somatic depolarization is partially transmitted to synaptic terminals, where it enhances transmitter release. It is not known to what extent such "analog signaling" applies to other mammalian neurons, and available evidence concerning underlying mechanisms is fragmentary and partially controversial. In this work, we investigate the presence of analog signaling in molecular layer interneurons of the rat cerebellum. GABA release was estimated by measuring autoreceptor currents in single recordings, or postsynaptic currents in paired recordings of synaptically connected neurons. We find with both assays that moderate subthreshold somatic depolarization results in enhanced GABA release. In addition, changes in the calcium concentration were investigated in the axon compartment using the calcium-sensitive dye OGB-1 (Oregon Green BAPTA-1). After a step somatic depolarization, the axonal calcium concentration and the GABA release probability rise with a common slow time course. However, the amount of calcium entry that is associated to one action potential is not affected. The slow increase in calcium concentration is inhibited by the P/Q calcium channel blocker ω-agatoxin-IVA. The protein kinase C inhibitor Ro 31-8220 (3-[3-[2,5-dihydro-4-(1-methyl-1H-indol-3-yl)-2,5-dioxo-1H-pyrrol-3-yl]-1H-indol-1-yl]propyl carbamimidothioic acid ester mesylate) did not affect the calcium concentration changes but it blocked the increase in GABA release. EGTA was a weak blocker of analog signaling, implicating a close association of protein kinase C to the site of calcium entry. We conclude that analog signaling is prominent in cerebellar interneurons and that it is triggered by a pathway involving activation of axonal P/Q channels, followed by calcium entry and local activation of protein kinase C.
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33
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Abstract
Axons are generally considered as reliable transmission cables in which stable propagation occurs once an action potential is generated. Axon dysfunction occupies a central position in many inherited and acquired neurological disorders that affect both peripheral and central neurons. Recent findings suggest that the functional and computational repertoire of the axon is much richer than traditionally thought. Beyond classical axonal propagation, intrinsic voltage-gated ionic currents together with the geometrical properties of the axon determine several complex operations that not only control signal processing in brain circuits but also neuronal timing and synaptic efficacy. Recent evidence for the implication of these forms of axonal computation in the short-term dynamics of neuronal communication is discussed. Finally, we review how neuronal activity regulates both axon morphology and axonal function on a long-term time scale during development and adulthood.
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Affiliation(s)
- Dominique Debanne
- Institut National de la Santé et de la Recherche Médicale U.641 and Université de la Méditerranée, Faculté de Médecine Secteur Nord, Marseille, France
| | - Emilie Campanac
- Institut National de la Santé et de la Recherche Médicale U.641 and Université de la Méditerranée, Faculté de Médecine Secteur Nord, Marseille, France
| | - Andrzej Bialowas
- Institut National de la Santé et de la Recherche Médicale U.641 and Université de la Méditerranée, Faculté de Médecine Secteur Nord, Marseille, France
| | - Edmond Carlier
- Institut National de la Santé et de la Recherche Médicale U.641 and Université de la Méditerranée, Faculté de Médecine Secteur Nord, Marseille, France
| | - Gisèle Alcaraz
- Institut National de la Santé et de la Recherche Médicale U.641 and Université de la Méditerranée, Faculté de Médecine Secteur Nord, Marseille, France
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van Welie I, Smith IT, Watt AJ. The metamorphosis of the developing cerebellar microcircuit. Curr Opin Neurobiol 2011; 21:245-53. [PMID: 21353528 PMCID: PMC3096781 DOI: 10.1016/j.conb.2011.01.009] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2011] [Accepted: 01/29/2011] [Indexed: 10/29/2022]
Abstract
The cerebellar cortical circuit with its organized and repetitive structure provides an excellent model system for studying how brain circuits are formed during development. The emergence of the mature brain requires that appropriate synaptic connections are formed and refined, which in the rodent cerebellum occurs primarily during the first three postnatal weeks. Developing circuits typically differ substantially from their mature counterparts, which suggests that development may not simply involve synaptic refinement, but rather involves restructuring of key synaptic components and network connections, in a manner reminiscent of metamorphosis. Here, we discuss recent evidence that, taken together, suggests that transient features of developing cerebellar synapses may act to coordinate network activity, and thereby shape the development of the cerebellar microcircuit.
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Affiliation(s)
- Ingrid van Welie
- Wolfson Institute for Biomedical Research, University College London, London, WC1E 6BT, United Kingdom
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35
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Axonal GABAA receptors increase cerebellar granule cell excitability and synaptic activity. J Neurosci 2011; 31:565-74. [PMID: 21228165 DOI: 10.1523/jneurosci.4506-10.2011] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
We report that activation of GABA(A) receptors on cerebellar granule cell axons modulates both transmitter release and the excitability of the axon and soma. Axonal GABA(A) receptors depolarize the axon, increasing its excitability and causing calcium influx at axonal varicosities. GABA-mediated subthreshold depolarizations in the axon spread electrotonically to the soma, promoting orthodromic action potential initiation. When chloride concentrations are unperturbed, GABA iontophoresis elicits spikes and increases excitability of parallel fibers, indicating that GABA(A) receptor-mediated responses are normally depolarizing. GABA release from molecular layer interneurons activates parallel fiber GABA(A) receptors, and this, in turn, increases release probability at synapses between parallel fibers and molecular layer interneurons. These results describe a positive feedback mechanism whereby transmission from granule cells to Purkinje cells and molecular layer interneurons will be strengthened during granule cell spike bursts evoked by sensory stimulation.
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36
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Yang K, Buhlman L, Khan GM, Nichols RA, Jin G, McIntosh JM, Whiteaker P, Lukas RJ, Wu J. Functional nicotinic acetylcholine receptors containing α6 subunits are on GABAergic neuronal boutons adherent to ventral tegmental area dopamine neurons. J Neurosci 2011; 31:2537-48. [PMID: 21325521 PMCID: PMC3081713 DOI: 10.1523/jneurosci.3003-10.2011] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2010] [Revised: 11/30/2010] [Accepted: 12/13/2010] [Indexed: 01/30/2023] Open
Abstract
Diverse nicotinic acetylcholine receptor (nAChR) subtypes containing different subunit combinations can be placed on nerve terminals or soma/dendrites in the ventral tegmental area (VTA). nAChR α6 subunit message is abundant in the VTA, but α6*-nAChR cellular localization, function, pharmacology, and roles in cholinergic modulation of dopaminergic (DA) neurons within the VTA are not well understood. Here, we report evidence for α6β2*-nAChR expression on GABA neuronal boutons terminating on VTA DA neurons. α-Conotoxin (α-Ctx) MII labeling coupled with immunocytochemical staining localizes putative α6*-nAChRs to presynaptic GABAergic boutons on acutely dissociated, rat VTA DA neurons. Functionally, acetylcholine (ACh) induces increases in the frequency of bicuculline-, picrotoxin-, and 4-aminopyridine-sensitive miniature IPSCs (mIPSCs) mediated by GABA(A) receptors. These increases are abolished by α6*-nAChR-selective α-Ctx MII or α-Ctx PIA (1 nm) but not by α7 (10 nm methyllycaconitine) or α4* (1 μm dihydro-β-erythroidine)-nAChR-selective antagonists. ACh also fails to increase mIPSC frequency in VTA DA neurons prepared from nAChR β2 knock-out mice. Moreover, ACh induces an α-Ctx PIA-sensitive elevation in intraterminal Ca(2+) in synaptosomes prepared from the rat VTA. Subchronic exposure to 500 nm nicotine reduces ACh-induced GABA release onto the VTA DA neurons, as does 10 d of systemic nicotine exposure. Collectively, these results indicate that α6β2*-nAChRs are located on presynaptic GABAergic boutons within the VTA and modulate GABA release onto DA neurons. These presynaptic α6β2*-nAChRs likely play important roles in nicotinic modulation of DA neuronal activity.
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Affiliation(s)
- Kechun Yang
- Divisions of Neurology and
- Department of Pharmacology, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China, and
| | - Lori Buhlman
- Neurobiology, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, Arizona 85013-4496
| | - Ghous M. Khan
- Department of Physiology and Pharmacology, John A. Burns School of Medicine, University of Hawaii at Manoa, Honolulu, Hawaii 96813
| | - Robert A. Nichols
- Department of Physiology and Pharmacology, John A. Burns School of Medicine, University of Hawaii at Manoa, Honolulu, Hawaii 96813
| | - Guozhang Jin
- Department of Pharmacology, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China, and
| | - J. Michael McIntosh
- Departments of Biology and Psychiatry, University of Utah, Salt Lake City, Utah 84112
| | - Paul Whiteaker
- Neurobiology, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, Arizona 85013-4496
| | - Ronald J. Lukas
- Neurobiology, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, Arizona 85013-4496
| | - Jie Wu
- Divisions of Neurology and
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37
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Ca(2+)-dependent enhancement of release by subthreshold somatic depolarization. Nat Neurosci 2010; 14:62-8. [PMID: 21170054 PMCID: PMC3130502 DOI: 10.1038/nn.2718] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2010] [Accepted: 11/09/2010] [Indexed: 11/09/2022]
Abstract
In many neurons, subthreshold somatic depolarization can spread electrotonically into the axon and modulate subsequent spike-evoked transmission. Although release probability is regulated by intracellular Ca(2+), the Ca(2+) dependence of this modulatory mechanism has been debated. Using paired recordings from synaptically connected molecular layer interneurons (MLIs) of the rat cerebellum, we observed Ca(2+)-mediated strengthening of release following brief subthreshold depolarization of the soma. Two-photon microscopy revealed that, at the axon, somatic depolarization evoked Ca(2+) influx through voltage-sensitive Ca(2+) channels and facilitated spike-evoked Ca(2+) entry. Exogenous Ca(2+) buffering diminished these Ca(2+) transients and eliminated the strengthening of release. Axonal Ca(2+) entry elicited by subthreshold somatic depolarization also triggered asynchronous transmission that may deplete vesicle availability and thereby temper release strengthening. In this cerebellar circuit, activity-dependent presynaptic plasticity depends on Ca(2+) elevations resulting from both sub- and suprathreshold electrical activity initiated at the soma.
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38
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Cossart R. The maturation of cortical interneuron diversity: how multiple developmental journeys shape the emergence of proper network function. Curr Opin Neurobiol 2010; 21:160-8. [PMID: 21074988 DOI: 10.1016/j.conb.2010.10.003] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2010] [Revised: 10/04/2010] [Accepted: 10/21/2010] [Indexed: 12/31/2022]
Abstract
If the classical functional attribute of cortical GABAergic interneurons is to mediate synaptic inhibition in the adult cortex, it is becoming evident that their major task is instead to shape the spatio-temporal dynamics of the network oscillations that support most brain functions. This complex function involves a division of labour between morpho-physiologically diverse interneuron subtypes. Both the central network function and the bewildering heterogeneity of the interneuron population are especially emphasized during cortical development: at early postnatal stages, a single GABAergic neuron can efficiently pace the activity of hundreds of other cells, whereas some interneuron subtypes are still poorly developed. Given the role of coherent activity in brain development, this confers to GABAergic interneurons a major role in the proper maturation of cortical networks.
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Affiliation(s)
- Rosa Cossart
- INMED, INSERM U901, Université de la Méditerranée, Parc Scientifique de Luminy, BP.13, 13273 Marseille Cedex 9, France.
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39
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Lindsly C, Frazier CJ. Two distinct and activity-dependent mechanisms contribute to autoreceptor-mediated inhibition of GABAergic afferents to hilar mossy cells. J Physiol 2010; 588:2801-22. [PMID: 20547680 DOI: 10.1113/jphysiol.2009.184648] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
We report that bath application of 3 mum carbachol (CCh), a muscarinic acetylcholine receptor agonist, reduces evoked IPSC amplitude recorded from hilar mossy cells in the rat dentate gyrus through a presynaptic mechanism. While CCh has been shown to inhibit evoked IPSCs in other systems, this effect is intriguing in that it does not require inhibitory action of either presynaptic muscarinic receptors or presynaptic cannabinoid receptors. Previous work from our lab has shown that identical application of CCh produces an action potential-dependent increase in ambient GABA in this system; however, inhibition of evoked IPSCs produced by both 3 and 10 mum CCh is insensitive to the GABA(B) antagonist CGP52432. Therefore we hypothesized that CCh-mediated inhibition of evoked IPSCs might be produced by activity-dependent increases in ambient GABA and subsequent activation of presynaptic GABA(A) receptors. Consistent with that hypothesis, we report that CCh-mediated inhibition of evoked IPSCs appears to be well correlated with CCh-mediated facilitation of spontaneous IPSCs and that CCh does not affect GABA(B)-mediated IPSCs recorded in the presence of the GABA(A) receptor antagonist picrotoxin. Intriguingly, however, we found that bath application of the GAT-1 transport blocker NO-711 (1 mum) produces inhibition of evoked IPSCs that is reversed by CGP52432, and that lower doses of CCh produce inhibition with greater CGP52432 sensitivity. These observations, combined with subsequent work on multiple pulse depression, reveal that feedback inhibition of GABAergic afferents to hilar mossy cells is governed by a complex relationship between two distinct and activity-dependent mechanisms.
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Affiliation(s)
- Casie Lindsly
- Department of Neuroscience, College of Medicine, University of Florida,1600 S.W. Archer Road, Gainesville, FL 32610, USA
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Abstract
Miniature synaptic events, resulting from spontaneous presynaptic release of neurotransmitter in the absence of an action potential, are often used to assay neural connectivity and are thought to play a pivotal role in the development and maintenance of neuronal circuits. In this issue of Neuron, Trigo et al. identify a new class of miniature synaptic event, called "preminis," that originate from and are subsequently detected by the presynaptic terminals of GABAergic neurons in the molecular layer of cerebellum. Remarkably, these events easily outnumber conventional minis. Their restriction to a relatively narrow time window (<15 days after birth) is a clue that they may play a critical role in wiring up interneurons within the developing cerebellar circuitry.
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