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Ueno T, Yamanaka M, Taniguchi W, Nishio N, Matsuyama Y, Miyake R, Kaimochi Y, Nakatsuka T, Yamada H. Methylglyoxal activates transient receptor potential A1/V1 via reactive oxygen species in the spinal dorsal horn. Mol Pain 2024; 20:17448069241233744. [PMID: 38323375 PMCID: PMC10868495 DOI: 10.1177/17448069241233744] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2023] [Revised: 12/11/2023] [Accepted: 01/12/2024] [Indexed: 02/08/2024] Open
Abstract
Methylglyoxal (MGO), a highly reactive dicarbonyl metabolite of glucose primarily formed during the glycolytic pathway, is a precursor of advanced glycation end-products (AGEs). Recently, numerous studies have shown that MGO accumulation can cause pain and hyperalgesia. However, the mechanism through which MGO induces pain in the spinal dorsal horn remains unclear. The present study investigated the effect of MGO on spontaneous excitatory postsynaptic currents (sEPSC) in rat spinal dorsal horn neurons using blind whole-cell patch-clamp recording. Perfusion of MGO increased the frequency and amplitude of sEPSC in spinal horn neurons in a concentration-dependent manner. Additionally, MGO administration increased the number of miniature EPSC (mEPSC) in the presence of tetrodotoxin, a sodium channel blocker. However, 6-cyano-7-nitroqiunocaline-2,3-dione (CNQX), an AMPA/kainate receptor antagonist, blocked the enhancement of sEPSC by MGO. HC-030031, a TRP ankyrin-1 (TRPA1) antagonist, and capsazepine, a TRP vanilloid-1 (TRPV1) antagonist, inhibited the action of MGO. Notably, the effects of MGO were completely inhibited by HC-030031 and capsazepine. MGO generates reactive oxygen species (ROS) via AGEs. ROS also potentially induce pain via TRPA1 and TRPV1 in the spinal dorsal horn. Furthermore, we examined the effect of MGO in the presence of N-tert-butyl-α-phenylnitrone (PBN), a non-selective ROS scavenger, and found that the effect of MGO was completely inhibited. These results suggest that MGO increases spontaneous glutamate release from the presynaptic terminal to spinal dorsal horn neurons through TRPA1, TRPV1, and ROS and could enhance excitatory synaptic transmission.
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Affiliation(s)
- Takeru Ueno
- Department of Orthopaedic Surgery, Wakayama Medical University, Wakayama, Japan
| | - Manabu Yamanaka
- Department of Orthopaedic Surgery, Wakayama Medical University, Wakayama, Japan
| | - Wataru Taniguchi
- Department of Orthopaedic Surgery, Wakayama Medical University, Wakayama, Japan
| | - Naoko Nishio
- Department of Orthopaedic Surgery, Wakayama Medical University, Wakayama, Japan
| | - Yuki Matsuyama
- Department of Orthopaedic Surgery, Wakayama Medical University, Wakayama, Japan
| | - Ryo Miyake
- Department of Orthopaedic Surgery, Wakayama Medical University, Wakayama, Japan
| | - Yuta Kaimochi
- Department of Orthopaedic Surgery, Wakayama Medical University, Wakayama, Japan
| | - Terumasa Nakatsuka
- Pain Research Center, Kansai University of Health Sciences, Osaka, Japan
| | - Hiroshi Yamada
- Department of Orthopaedic Surgery, Wakayama Medical University, Wakayama, Japan
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Tonomura S, Gu JG. Role of Voltage-Gated K(+) Channels and K2P Channels in Intrinsic Electrophysiological Properties and Saltatory Conduction at Nodes of Ranvier of Rat Lumbar Spinal Ventral Nerves. J Neurosci 2022; 42:4980-94. [PMID: 35606142 DOI: 10.1523/JNEUROSCI.0514-22.2022] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2022] [Revised: 05/02/2022] [Accepted: 05/17/2022] [Indexed: 12/24/2022] Open
Abstract
Ion channels at the nodes of Ranvier (NRs) are believed to play essential roles in intrinsic electrophysiological properties and saltatory conduction of action potentials (AP) at the NRs of myelinated nerves. While we have recently shown that two-pore domain potassium (K2P) channels play a key role at the NRs of Aβ-afferent nerves, K+ channels and their functions at the NRs of mammalian motor nerves remain elusive. Here we addressed this issue by using ex vivo preparations of lumbar spinal ventral nerves from both male and female rats and the pressure-patch-clamp recordings at their NRs. We found that depolarizing voltages evoked large noninactivating outward currents at NRs. The outward currents could be partially inhibited by voltage-gated K+ channel blockers, largely inhibited by K2P blockers and cooling temperatures. Inhibition of the outward currents by voltage-gated K+ channel blockers, K2P blockers, or cooling temperatures significantly altered electrophysiological properties measured at the NRs, including resting membrane potential, input resistance, AP width, AP amplitude, AP threshold, and AP rheobase. Furthermore, K2P blockers and cooling temperatures significantly reduced saltatory conduction velocity and success rates of APs in response to high-frequency stimulation. Voltage-gated K+ channel blockers reduced AP success rates at high-frequency stimulation without significantly affecting saltatory conduction velocity. Collectively, both K2P and voltage-gated K+ channels play significant roles in intrinsic electrophysiological properties and saltatory conduction at NRs of motor nerve fibers of rats. The effects of cooling temperatures on saltatory conduction are at least partially mediated by K2P channels at the NRs.SIGNIFICANCE STATEMENT Ion channels localized at the NRs are believed to be key determinants of saltatory conduction on myelinated nerves. However, ion channels and their functions at the NRs have not been fully studied in different types of mammalian myelinated nerves. Here we use the pressure-patch-clamp recordings to show that both K2P and voltage-gated K+ channels play significant roles in intrinsic electrophysiological properties and saltatory conduction at NRs of lumbar spinal ventral nerves of rats. Furthermore, cooling temperatures exert effects on saltatory conduction via inhibition of ion channels at the NRs. Our results provide new insights into saltatory conduction on myelinated nerves and may have physiological as well as pathologic implications.
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Huang YB, Ma ZG, Zheng C, Ma XKK, Taylor DH, Gao M, Lukas RJ, Wu J. Levo-tetrahydropalmatine inhibits α4β2 nicotinic receptor response to nicotine in cultured SH-EP1 cells. Acta Pharmacol Sin 2022; 43:889-896. [PMID: 34253876 PMCID: PMC8975845 DOI: 10.1038/s41401-021-00709-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2021] [Accepted: 05/30/2021] [Indexed: 02/05/2023] Open
Abstract
Nicotine, a major component of tobacco, is highly addictive and acts on nicotinic acetylcholine receptors (nAChRs) to stimulate reward-associated circuits in the brain. It is well known that nAChRs play critical roles in mediating nicotine reward and addiction. Current FDA-approved medications for smoking cessation are the antidepressant bupropion and the nicotinic partial agonist varenicline, yet both are limited by adverse side effects and moderate efficacy. Thus, development of more efficacious medications with fewer side effects for nicotine addiction and smoking cessation is urgently needed. l-Tetrahydropalmatine (l-THP) is an active ingredient of the Chinese medicinal herb Corydalis ambigua that possesses rich neuropharmacological actions on dopamine (DA) receptors in the mesocorticolimbic dopaminergic reward pathway. L-THP has been explored as anti-addiction treatments for drug abuse including nicotine. However, the targets and mechanisms of l-THP-caused anti-nicotine effects are largely unknown. In this study we address this question by elucidating the effects of l-THP on human neuronal nAChRs using patch-clamp recordings. Human neuronal α4β2-nAChRs were heterologously expressed in SH-EP1 human epithelial cells. Bath application of nicotine (0.1-100 μM) induced inward currents, co-application of l-THP (3 μM) inhibited nicotine-induced currents in the transfected cells. L-THP-caused inhibition was concentration-dependent (the EC50 values for inhibiting the peak and steady-state current were 18 and 2.1 μM, respectively) and non-competitive. Kinetic analysis of the whole-cell currents showed that l-THP slowed rising time and accelerated decay time constants. L-THP specifically modulated α4β2-nAChRs, as it did not affect α7-nAChRs or α1*-nAChRs (muscle type). Interestingly, two putative α4β2-nAChR isoforms, namely sazetidine A-activated, high-sensitive one (α42β23-nAChR) and cytisine-activated, low-sensitive one (α43β22-nAChR) were pharmacologically separated, and the low-sensitive one was more susceptible to l-THP inhibition than the high-sensitive one. In conclusion, we demonstrate that l-THP blocks neuronal α4β2-nAChR function, which may underlie its inhibition on nicotine addiction.
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Affiliation(s)
- Yuan-Bing Huang
- Department of Neurology, Yunfu People's Hospital, Yunfu, 527300, China
- Department of Neurobiology, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, AZ, 85013, USA
| | - Ze-Gang Ma
- Department of Neurobiology, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, AZ, 85013, USA
- Electrophysiology Laboratory, Wannan Medical College, Wuhu, 695011, China
| | - Chao Zheng
- Department of Neurobiology, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, AZ, 85013, USA
- Institution of Brain Sciences and Diseases, Qingdao University, Qingdao, 266071, China
| | - Xiao-Kuang K Ma
- Department of Neurobiology, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, AZ, 85013, USA
- Department of Pharmacology, Shantou University Medical College, Shantou, 515041, China
| | - Devin H Taylor
- Department of Neurobiology, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, AZ, 85013, USA
- Department of Biology, Utah Valley University, Orem, UT, 84058, USA
| | - Ming Gao
- Department of Neurobiology, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, AZ, 85013, USA
| | - Ronald J Lukas
- Department of Neurobiology, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, AZ, 85013, USA
| | - Jie Wu
- Department of Neurobiology, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, AZ, 85013, USA.
- Institution of Brain Sciences and Diseases, Qingdao University, Qingdao, 266071, China.
- Department of Pharmacology, Shantou University Medical College, Shantou, 515041, China.
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William M, Singh S, Chu XP. Commentary: Large Acid-Evoked Currents, Mediated by ASIC1a, Accompany Differentiation in Human Dopaminergic Neurons. Front Cell Neurosci 2021; 15:789354. [PMID: 34880731 PMCID: PMC8646021 DOI: 10.3389/fncel.2021.789354] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2021] [Accepted: 10/29/2021] [Indexed: 11/18/2022] Open
Affiliation(s)
- Matthew William
- Department of Biomedical Sciences, School of Medicine, University of Missouri-Kansas City, Kansas City, MO, United States
| | - Som Singh
- Department of Biomedical Sciences, School of Medicine, University of Missouri-Kansas City, Kansas City, MO, United States
| | - Xiang-Ping Chu
- Department of Biomedical Sciences, School of Medicine, University of Missouri-Kansas City, Kansas City, MO, United States
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5
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Kawatani M, deGroat W, Itoi K, Uchida K, Sakimura K, Yamanaka A, Yamashita T, Kawatani M. Downstream projection of Barrington's nucleus to the spinal cord in mice. J Neurophysiol 2021; 126:1959-1977. [PMID: 34731061 DOI: 10.1152/jn.00026.2021] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Barrington's nucleus (Bar) which controls micturition behavior through downstream projections to the spinal cord contains two types of projection neurons BarCRH and BarESR1 that have different functions and target different spinal circuitry. Both types of neurons project to the L6-S1 spinal intermediolateral (IML) nucleus while BarESR1 neurons also project to the dorsal commissural nucleus (DCN). To obtain more information about the spinal circuits targeted by Bar, we used patch-clamp recording in spinal slices from adult mice in combination with optogenetic stimulation of Bar terminals. Recording of opto-evoked excitatory post synaptic currents (oEPSCs) in DiI-labeled lumbosacral preganglionic neurons (LS-PGN) revealed that both Bar neuronal populations make strong glutamatergic monosynaptic connections with LS-PGN, while BarESR1 neurons also elicited smaller amplitude glutamatergic polysynaptic oEPSCs or polysynaptic inhibitory post synaptic currents (oIPSCs) in some LS-PGN. Optical stimulation of BarCRH and BarESR1 terminals also elicited monosynaptic oEPSCs and polysynaptic oIPSCs in sacral DCN neurons, some of which must include interneurons projecting either to the IML or ventral horn. Application of capsaicin increased opto-evoked firing during repetitive stimulation of Bar terminals through the modulation of spontaneous post synaptic currents in LS-PGN. In conclusion, our experiments have provided insights into the synaptic mechanisms underlying the integration of inputs from Bar to autonomic circuitry in the lumbosacral spinal cord that may control micturition.
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Affiliation(s)
- Masahiro Kawatani
- Department of Neurophysiology, Graduate School of Medicine, Akita University, Akita, Japan.,Department of Neuroscience II, Research Institute of Environmental Medicine, Nagoya University, Aichi, Japan.,Department of Physiology, School of Medicine, Fujita Health University, Aichi, Japan
| | - William deGroat
- Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA, United States
| | - Keiichi Itoi
- Department of Neuroendocrinology, Graduate School of Medicine, Tohoku University, Sendai, Japan
| | - Katsuya Uchida
- Department of Neuroendocrinology, Graduate School of Medicine, Tohoku University, Sendai, Japan
| | - Kenji Sakimura
- Department of Animal Model Development, Brain Research Institute, Niigata University, Niigata, Japan
| | - Akihiro Yamanaka
- Department of Neuroscience II, Research Institute of Environmental Medicine, Nagoya University, Aichi, Japan
| | - Takayuki Yamashita
- Department of Neuroscience II, Research Institute of Environmental Medicine, Nagoya University, Aichi, Japan.,Department of Physiology, School of Medicine, Fujita Health University, Aichi, Japan
| | - Masahito Kawatani
- Department of Neurophysiology, Graduate School of Medicine, Akita University, Akita, Japan
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6
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Caseley EA, Muench SP, Jiang LH. Tyrosine 288 in the extracellular domain of the human P2X7 receptor is critical for receptor function revealed by structural modeling and site-directed mutagenesis. Proteins 2021; 90:619-624. [PMID: 34622987 DOI: 10.1002/prot.26259] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2021] [Revised: 09/08/2021] [Accepted: 10/03/2021] [Indexed: 11/06/2022]
Abstract
The P2X7 receptor (P2X7R) is a calcium-permeable cation channel activated by high concentrations of extracellular ATP. It plays a role in vital physiological processes, particularly in innate immunity, and is dysregulated in pathological conditions such as inflammatory diseases, neurodegenerative diseases, mood disorders, and cancers. Structural modeling of the human P2X7R (hP2X7R) based on the recently available structures of the rat P2X7 receptor (rP2XR) in conjunction with molecular docking predicts the orientation of tyrosine at position 288 (Y288) in the extracellular domain to face ATP. In this short communication, we combined site-directed mutagenesis and whole-cell patch-clamp recording to investigate the role of this residue in the hP2X7R function. Mutation of this extracellular residue to amino acids with different properties massively impaired current responses to both ATP and BzATP, suggesting that Y288 is important for normal receptor function. Such a finding facilitates development of an in-depth understanding of the molecular basis of hP2X7R structure-function relationships.
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Affiliation(s)
- Emily A Caseley
- Leeds Institute of Rheumatic and Musculoskeletal Medicine, St James's University Hospital, Leeds, UK.,School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds, UK
| | - Stephen P Muench
- School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds, UK
| | - Lin-Hua Jiang
- School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds, UK
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7
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Shah S, Chu Y, Cegielski V, Chu XP. Acid-Sensing Ion Channel 1 Contributes to Weak Acid-Induced Migration of Human Malignant Glioma Cells. Front Physiol 2021; 12:734418. [PMID: 34557113 PMCID: PMC8452845 DOI: 10.3389/fphys.2021.734418] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2021] [Accepted: 08/16/2021] [Indexed: 12/24/2022] Open
Affiliation(s)
- Sareena Shah
- Department of Biomedical Sciences, School of Medicine, University of Missouri-Kansas City, Kansas City, MO, United States
| | - Yuyang Chu
- Feinberg School of Medicine, Northwestern University, Chicago, IL, United States
| | - Victoria Cegielski
- Department of Biomedical Sciences, School of Medicine, University of Missouri-Kansas City, Kansas City, MO, United States
| | - Xiang-Ping Chu
- Department of Biomedical Sciences, School of Medicine, University of Missouri-Kansas City, Kansas City, MO, United States
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William M, Cegielski V, Chu XP. Commentary: Slowing of the Time Course of Acidification Decreases the Acid-Sensing Ion Channel 1a Current Amplitude and Modulates Action Potential Firing in Neurons. Front Cell Neurosci 2021; 15:714204. [PMID: 34335195 PMCID: PMC8322612 DOI: 10.3389/fncel.2021.714204] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2021] [Accepted: 06/23/2021] [Indexed: 11/13/2022] Open
Affiliation(s)
- Matthew William
- Department of Biomedical Sciences, School of Medicine, University of Missouri-Kansas City, Kansas City, MO, United States
| | - Victoria Cegielski
- Department of Biomedical Sciences, School of Medicine, University of Missouri-Kansas City, Kansas City, MO, United States
| | - Xiang-Ping Chu
- Department of Biomedical Sciences, School of Medicine, University of Missouri-Kansas City, Kansas City, MO, United States
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Nishimura Y, Ikegaya Y, Sasaki T. Prefrontal synaptic activation during hippocampal memory reactivation. Cell Rep 2021; 34:108885. [PMID: 33761365 DOI: 10.1016/j.celrep.2021.108885] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2020] [Revised: 12/07/2020] [Accepted: 02/25/2021] [Indexed: 12/22/2022] Open
Abstract
Cooperative reactivation of hippocampal and prefrontal neurons is considered crucial for mnemonic processes. To directly record synaptic substances supporting the interregional interactions, we develop concurrent spike recordings of hippocampal neuronal ensembles and whole-cell patch-clamp recordings of medial prefrontal neurons in awake rats. We find that medial prefrontal neurons depolarize when hippocampal neurons synchronize. The depolarization in medial prefrontal neurons is larger when hippocampal place cells that encoded overlapping place fields and place cells that encoded a novel environment are synchronously reactivated. Our results suggest a functional circuit-synapse association that enables prefrontal neurons to read out specific memory traces from the hippocampus.
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Affiliation(s)
- Yuya Nishimura
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
| | - Yuji Ikegaya
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan; Center for Information and Neural Networks, National Institute of Information and Communications Technology, 1-4 Yamadaoka, Suita City, Osaka 565-0871, Japan; Institute for AI and Beyond, The University of Tokyo, Tokyo 113-0033, Japan
| | - Takuya Sasaki
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan; Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.
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10
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Noguchi A, Ikegaya Y, Matsumoto N. In Vivo Whole-Cell Patch-Clamp Methods: Recent Technical Progress and Future Perspectives. Sensors (Basel) 2021; 21:1448. [PMID: 33669656 PMCID: PMC7922023 DOI: 10.3390/s21041448] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/23/2020] [Revised: 02/12/2021] [Accepted: 02/16/2021] [Indexed: 02/01/2023]
Abstract
Brain functions are fundamental for the survival of organisms, and they are supported by neural circuits consisting of a variety of neurons. To investigate the function of neurons at the single-cell level, researchers often use whole-cell patch-clamp recording techniques. These techniques enable us to record membrane potentials (including action potentials) of individual neurons of not only anesthetized but also actively behaving animals. This whole-cell recording method enables us to reveal how neuronal activities support brain function at the single-cell level. In this review, we introduce previous studies using in vivo patch-clamp recording techniques and recent findings primarily regarding neuronal activities in the hippocampus for behavioral function. We further discuss how we can bridge the gap between electrophysiology and biochemistry.
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Affiliation(s)
- Asako Noguchi
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo 113-0033, Japan; (A.N.); (Y.I.)
| | - Yuji Ikegaya
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo 113-0033, Japan; (A.N.); (Y.I.)
- Institute for AI and Beyond, The University of Tokyo, Tokyo 113-0033, Japan
- Center for Information and Neural Networks, National Institute of Information and Communications Technology, Suita City, Osaka 565-0871, Japan
| | - Nobuyoshi Matsumoto
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo 113-0033, Japan; (A.N.); (Y.I.)
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Demontis GC, Pezzini F, Margari E, Bianchi M, Longoni B, Doccini S, Lalowski MM, Santorelli FM, Simonati A. Electrophysiological Profile Remodeling via Selective Suppression of Voltage-Gated Currents by CLN1/PPT1 Overexpression in Human Neuronal-Like Cells. Front Cell Neurosci 2020; 14:569598. [PMID: 33390903 PMCID: PMC7772423 DOI: 10.3389/fncel.2020.569598] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2020] [Accepted: 11/18/2020] [Indexed: 12/21/2022] Open
Abstract
CLN1 disease (OMIM #256730) is an inherited neurological disorder of early childhood with epileptic seizures and premature death. It is associated with mutations in CLN1 coding for Palmitoyl-Protein Thioesterase 1 (PPT1), a lysosomal enzyme which affects the recycling and degradation of lipid-modified (S-acylated) proteins by removing palmitate residues. Transcriptomic evidence from a neuronal-like cellular model derived from differentiated SH-SY5Y cells disclosed the potential negative roles of CLN1 overexpression, affecting the elongation of neuronal processes and the expression of selected proteins of the synaptic region. Bioinformatic inquiries of transcriptomic data pinpointed a dysregulated expression of several genes coding for proteins related to voltage-gated ion channels, including subunits of calcium and potassium channels (VGCC and VGKC). In SH-SY5Y cells overexpressing CLN1 (SH-CLN1 cells), the resting potential and the membrane conductance in the range of voltages close to the resting potential were not affected. However, patch-clamp recordings indicated a reduction of Ba2+ currents through VGCC of SH-CLN1 cells; Ca2+ imaging revealed reduced Ca2+ influx in the same cellular setting. The results of the biochemical and morphological investigations of CACNA2D2/α2δ-2, an accessory subunit of VGCC, were in accordance with the downregulation of the corresponding gene and consistent with the hypothesis that a lower number of functional channels may reach the plasma membrane. The combined use of 4-AP and NS-1643, two drugs with opposing effects on Kv11 and Kv12 subfamilies of VGKC coded by the KCNH gene family, provides evidence for reduced functional Kv12 channels in SH-CLN1 cells, consistent with transcriptomic data indicating the downregulation of KCNH4. The lack of compelling evidence supporting the palmitoylation of many ion channels subunits investigated in this study stimulates inquiries about the role of PPT1 in the trafficking of channels to the plasma membrane. Altogether, these results indicate a reduction of functional voltage-gated ion channels in response to CLN1/PPT1 overexpression in differentiated SH-SY5Y cells and provide new insights into the altered neuronal excitability which may underlie the severe epileptic phenotype of CLN1 disease. It remains to be shown if remodeling of such functional channels on plasma membrane can occur as a downstream effect of CLN1 disease.
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Affiliation(s)
| | - Francesco Pezzini
- Neurology (Child Neurology and Neuropathology), Department of Neuroscience, Biomedicine and Movement, University of Verona, Verona, Italy
| | - Elisa Margari
- Department of Pharmacy, University of Pisa, Pisa, Italy
| | - Marzia Bianchi
- Research Unit for Multi-factorial Diseases, Obesity and Diabetes, Bambino Gesù Children's Hospital Istituto di Ricerca e Cura a Carattere Scientifico, Rome, Italy
| | - Biancamaria Longoni
- Department of Translational Research and New Technology in Medicine, University of Pisa, Pisa, Italy
| | - Stefano Doccini
- Molecular Medicine for Neurodegenerative and Neuromuscular Diseases Unit, Istituto di Ricerca e Cura a Carattere Scientifico Stella Maris Foundation, Pisa, Italy
| | - Maciej Maurycy Lalowski
- Medicum, Biochemistry/Developmental Biology and HiLIFE-Helsinki Institute of Life Science, Meilahti Clinical Proteomics Core Facility, University of Helsinki, Helsinki, Finland
| | - Filippo Maria Santorelli
- Molecular Medicine for Neurodegenerative and Neuromuscular Diseases Unit, Istituto di Ricerca e Cura a Carattere Scientifico Stella Maris Foundation, Pisa, Italy
| | - Alessandro Simonati
- Neurology (Child Neurology and Neuropathology), Department of Neuroscience, Biomedicine and Movement, University of Verona, Verona, Italy
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Fernandez-Chiappe F, Hermann-Luibl C, Peteranderl A, Reinhard N, Senthilan PR, Hieke M, Selcho M, Yoshii T, Shafer OT, Muraro NI, Helfrich-Förster C. Dopamine Signaling in Wake-Promoting Clock Neurons Is Not Required for the Normal Regulation of Sleep in Drosophila. J Neurosci 2020; 40:9617-33. [PMID: 33172977 DOI: 10.1523/JNEUROSCI.1488-20.2020] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2020] [Revised: 10/15/2020] [Accepted: 10/21/2020] [Indexed: 11/21/2022] Open
Abstract
Dopamine is a wake-promoting neuromodulator in mammals and fruit flies. In Drosophila melanogaster, the network of clock neurons that drives sleep/activity cycles comprises both wake-promoting and sleep-promoting cell types. The large ventrolateral neurons (l-LNvs) and small ventrolateral neurons (s-LNvs) have been identified as wake-promoting neurons within the clock neuron network. The l-LNvs are innervated by dopaminergic neurons, and earlier work proposed that dopamine signaling raises cAMP levels in the l-LNvs and thus induces excitatory electrical activity (action potential firing), which results in wakefulness and inhibits sleep. Here, we test this hypothesis by combining cAMP imaging and patch-clamp recordings in isolated brains. We find that dopamine application indeed increases cAMP levels and depolarizes the l-LNvs, but, surprisingly, it does not result in increased firing rates. Downregulation of the excitatory D1-like dopamine receptor (Dop1R1) in the l-LNvs and s-LNvs, but not of Dop1R2, abolished the depolarization of l-LNvs in response to dopamine. This indicates that dopamine signals via Dop1R1 to the l-LNvs. Downregulation of Dop1R1 or Dop1R2 in the l-LNvs and s-LNvs does not affect sleep in males. Unexpectedly, we find a moderate decrease of daytime sleep with downregulation of Dop1R1 and of nighttime sleep with downregulation of Dop1R2. Since the l-LNvs do not use Dop1R2 receptors and the s-LNvs also respond to dopamine, we conclude that the s-LNvs are responsible for the observed decrease in nighttime sleep. In summary, dopamine signaling in the wake-promoting LNvs is not required for daytime arousal, but likely promotes nighttime sleep via the s-LNvs.SIGNIFICANCE STATEMENT In insect and mammalian brains, sleep-promoting networks are intimately linked to the circadian clock, and the mechanisms underlying sleep and circadian timekeeping are evolutionarily ancient and highly conserved. Here we show that dopamine, one important sleep modulator in flies and mammals, plays surprisingly complex roles in the regulation of sleep by clock-containing neurons. Dopamine inhibits neurons in a central brain sleep center to promote sleep and excites wake-promoting circadian clock neurons. It is therefore predicted to promote wakefulness through both of these networks. Nevertheless, our results reveal that dopamine acting on wake-promoting clock neurons promotes sleep, revealing a previously unappreciated complexity in the dopaminergic control of sleep.
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Noda S, Suzuki Y, Yamamura H, Imaizumi Y. Single Molecule Fluorescence Imaging Reveals the Stoichiometry of BKγ1 Subunit in Living HEK293 Cell Expression System. Biol Pharm Bull 2020; 43:1118-1122. [PMID: 32612074 DOI: 10.1248/bpb.b20-00125] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Large conductance Ca2+-activated K+ (BKCa) channels are ubiquitously expressed in plasma membrane of both excitable and non-excitable cells and possess significant physiological functions. A tetrameric complex of α subunit (BKα) forms a functional pore of BKCa channel. The properties of BKCa channel, such as voltage-dependence, Ca2+ sensitivity and pharmacological responses, are extensively modulated by co-expressing accessory β subunits (BKβ), which can associate with BKα in one to one manner. Although the functional significance of newly identified γ subunits (BKγ) has been revealed, the stoichiometry between BKα and BKγ1 remains unclear. In the present study, we utilized a single molecule fluorescence imaging with a total internal reflection fluorescence (TIRF) microscope to directly count the number of green fluorescent protein (GFP)-tagged BKγ1 (BKγ1-GFP) within a single BKCa channel complex in HEK293 cell expression system. BKγ1-GFP significantly enhanced the BK channel activity even when the intracellular Ca2+ concentration was kept lower, i.e., 10 nM, than the physiological resting level. BKγ1-GFP stably formed molecular complexes with BKα-mCherry in the plasma membrane. Counting of GFP bleaching steps revealed that a BKCa channel can contain up to four BKγ1 per channel at the maximum. These results suggest that BKγ1 forms a BKCa channel complex with BKα in a 1 : 1 stoichiometry in a human cell line.
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Affiliation(s)
- Sayuri Noda
- Department of Molecular & Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University
| | - Yoshiaki Suzuki
- Department of Molecular & Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University
| | - Hisao Yamamura
- Department of Molecular & Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University
| | - Yuji Imaizumi
- Department of Molecular & Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University
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Eguchi K, Velicky P, Hollergschwandtner E, Itakura M, Fukazawa Y, Danzl JG, Shigemoto R. Advantages of Acute Brain Slices Prepared at Physiological Temperature in the Characterization of Synaptic Functions. Front Cell Neurosci 2020; 14:63. [PMID: 32265664 PMCID: PMC7096554 DOI: 10.3389/fncel.2020.00063] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2019] [Accepted: 03/02/2020] [Indexed: 11/27/2022] Open
Abstract
Acute brain slice preparation is a powerful experimental model for investigating the characteristics of synaptic function in the brain. Although brain tissue is usually cut at ice-cold temperature (CT) to facilitate slicing and avoid neuronal damage, exposure to CT causes molecular and architectural changes of synapses. To address these issues, we investigated ultrastructural and electrophysiological features of synapses in mouse acute cerebellar slices prepared at ice-cold and physiological temperature (PT). In the slices prepared at CT, we found significant spine loss and reconstruction, synaptic vesicle rearrangement and decrease in synaptic proteins, all of which were not detected in slices prepared at PT. Consistent with these structural findings, slices prepared at PT showed higher release probability. Furthermore, preparation at PT allows electrophysiological recording immediately after slicing resulting in higher detectability of long-term depression (LTD) after motor learning compared with that at CT. These results indicate substantial advantages of the slice preparation at PT for investigating synaptic functions in different physiological conditions.
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Affiliation(s)
- Kohgaku Eguchi
- Institute of Science and Technology Austria (IST Austria), Klosterneuburg, Austria
| | - Philipp Velicky
- Institute of Science and Technology Austria (IST Austria), Klosterneuburg, Austria
| | | | - Makoto Itakura
- Department of Biochemistry, Kitasato University School of Medicine, Sagamihara-shi, Japan
| | - Yugo Fukazawa
- Department of Brain Structure and Function, Research Center for Child Mental Development, Faculty of Medical Sciences, University of Fukui, Fukui, Japan
| | - Johann Georg Danzl
- Institute of Science and Technology Austria (IST Austria), Klosterneuburg, Austria
| | - Ryuichi Shigemoto
- Institute of Science and Technology Austria (IST Austria), Klosterneuburg, Austria
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Hussein RA, Ahmed M, Breitinger HG, Breitinger U. Modulation of Glycine Receptor-Mediated Pain Signaling in vitro and in vivo by Glucose. Front Mol Neurosci 2019; 12:280. [PMID: 31824259 PMCID: PMC6883931 DOI: 10.3389/fnmol.2019.00280] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2019] [Accepted: 11/01/2019] [Indexed: 11/27/2022] Open
Abstract
The inhibitory glycine receptor (GlyR) plays an important role in rapid synaptic inhibition in mammalian spinal cord, brainstem, higher brain centers, and is involved in transmission of nociceptive signals. Glucose and related mono- and disaccharides potentiate currents mediated by recombinant α1, α1-β, and α3 GlyRs. Here, we confirmed the specific potentiation of α3 GlyR signaling by glucose through: (i) patch-clamp electrophysiology on recombinant receptors; and (ii) by verifying in vitro data in a mouse model in vivo. Mice were intraperitoneally (IP) injected with glucose (2 g/kg) or vehicle, and then challenged with sublethal doses of strychnine (0.2 mg/kg and 0.5 mg/kg). Pain-related behavior was assessed using two established models: (i) touch sensitivity tests using von Frey filaments; and (ii) hotplate assay. We observed a reduction of pain sensitivity in glucose-treated mice relative to vehicle-treated control mice. Injection of strychnine resulted in an increased sensitivity to tactile and heat stimuli, which was reversed in the presence of glucose. Analgesic effects of glucose were more pronounced in von Frey experiments, consistent with the established use of this model for neuropathic pain. Overall, glucose showed mild analgesic effects and was able to compensate for strychnine-induced allodynia in mice. Since the action of strychnine is specific for GlyR, these experiments show for the first time an in vivo potentiation of GlyR activity by glucose and suggest a molecular mechanism for glucose-mediated analgesia.
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Affiliation(s)
| | - Marwa Ahmed
- Department of Biochemistry, German University in Cairo, New Cairo, Egypt
| | | | - Ulrike Breitinger
- Department of Biochemistry, German University in Cairo, New Cairo, Egypt
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16
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Pressler RT, Strowbridge BW. Functional Specialization of Interneuron Dendrites: Identification of Action Potential Initiation Zone in Axonless Olfactory Bulb Granule Cells. J Neurosci 2019; 39:9674-88. [PMID: 31662426 DOI: 10.1523/JNEUROSCI.1763-19.2019] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2019] [Revised: 09/25/2019] [Accepted: 09/29/2019] [Indexed: 12/19/2022] Open
Abstract
Principal cells in the olfactory bulb (OB), mitral and tufted cells, play key roles in processing and then relaying sensory information to downstream cortical regions. How OB local circuits facilitate odor-specific responses during odor discrimination is not known but involves GABAergic inhibition mediated by axonless granule cells (GCs), the most abundant interneuron in the OB. Most previous work on GCs has focused on defining properties of distal apical dendrites where these interneurons form reciprocal dendrodendritic connections with principal cells. Less is known about the function of the proximal dendritic compartments. In the present study, we identified the likely action potentials (AP) initiation zone by comparing electrophysiological properties of rat (either sex) GCs with apical dendrites severed at different locations. We find that truncated GCs with long apical dendrites had active properties that were indistinguishable from intact GCs, generating full-height APs and short-latency low-threshold Ca2+ spikes. We then confirmed the presumed site of AP and low-threshold Ca2+ spike initiation in the proximal apical dendrite using two-photon Ca2+ photometry and focal TTX application. These results suggest that GCs incorporate two separate pathways for processing synaptic inputs: an already established dendrodendritic input to the distal apical dendrite and a novel pathway in which the cell body integrates proximal synaptic inputs, leading to spike generation in the proximal apical dendrite. Spikes generated by the proximal pathway likely enables GCs to regulate lateral inhibition by defining time windows when lateral inhibition is functional.SIGNIFICANCE STATEMENT The olfactory bulb plays a central role in processing sensory input transduced by receptor neurons. How local circuits in the bulb function to facilitate sensory processing during odor discrimination is not known but appears to involve inhibition mediated by granule cells, axonless GABAergic interneurons. Little is known about the active conductances in granule cells including where action potentials originate. Using a variety of experimental approaches, we find the Na+-based action potentials originate in the proximal apical dendrite, a region targeted by cortical feedback afferents. We also find evidence for high expression of low-voltage activated Ca2+ channels in the same region, intrinsic currents that enable GCs to spike rapidly in response to sensory input during each sniff cycle.
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Zhang H, Mu L, Wang D, Xia D, Salmon A, Liu Q, Wong‐Riley MTT. Uncovering a critical period of synaptic imbalance during postnatal development of the rat visual cortex: role of brain-derived neurotrophic factor. J Physiol 2018; 596:4511-4536. [PMID: 30055019 PMCID: PMC6138289 DOI: 10.1113/jp275814] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Accepted: 07/26/2018] [Indexed: 01/17/2023] Open
Abstract
KEY POINTS With daily electrophysiological recordings and neurochemical analysis, we uncovered a transient period of synaptic imbalance between enhanced inhibition and suppressed excitation in rat visual cortical neurons from the end of the fourth toward the end of the fifth postnatal weeks. The expression of brain-derived neurotrophic factor (BDNF), which normally enhances excitation and suppresses inhibition, was down-regulated during that time, suggesting that this may contribute to the inhibition/excitation imbalance. An agonist of the BDNF receptor tropomyosin-related kinase B (TrkB) partially reversed the imbalance, whereas a TrkB antagonist accentuated the imbalance during the transient period. Monocular lid suture during the transient period is more detrimental to the function and neurochemical properties of visual cortical neurons than before or after this period. We regard the period of synaptic imbalance as the peak critical period of vulnerability, and its existence is necessary for neurons to transition from immaturity to a more mature state of functioning. ABSTRACT The mammalian visual cortex is immature at birth and undergoes postnatal structural and functional adjustments. The exact timing of the vulnerable period in rodents remains unclear. The critical period is characterized by inhibitory GABAergic maturation reportedly dependent on brain-derived neurotrophic factor (BDNF). However, most of the studies were performed on experimental/transgenic animals, questioning the relationship in normal animals. The present study aimed to conduct in-depth analyses of the synaptic and neurochemical development of visual cortical neurons in normal and monocularly-deprived rats and to determine specific changes, if any, during the critical period. We found that (i) against a gradual increase in excitation and inhibition with age, a transient period of synaptic and neurochemical imbalance existed with suppressed excitation and enhanced inhibition at postnatal days 28 to 33/34; (ii) during this window, the expression of BDNF and tropomyosin-related kinase B (TrkB) receptors decreased, along with glutamatergic GluN1 and GluA1 receptors and the metabolic marker cytochrome oxidase, whereas that of GABAA Rα1 receptors continued to rise; (iii) monocular deprivation reduced both excitatory and inhibitory synaptic activity and neurochemicals mainly during this period; and (iv) in vivo TrkB agonist partially reversed the synaptic imbalance in normal and monocularly-deprived neurons during this time, whereas a TrkB antagonist accentuated the imbalance. Thus, our findings highlight a transitory period of synaptic imbalance with a negative relationship between BDNF and inhibitory GABA. This brief critical period may be necessary in transitioning from an immature to a more mature state of visual cortical functioning.
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Affiliation(s)
- Hanmeng Zhang
- Department of Cell Biology, Neurobiology and AnatomyMedical College of WisconsinMilwaukeeWIUSA
| | - Lianwei Mu
- Department of Cell Biology, Neurobiology and AnatomyMedical College of WisconsinMilwaukeeWIUSA
| | - Dandan Wang
- Department of Cell Biology, Neurobiology and AnatomyMedical College of WisconsinMilwaukeeWIUSA
| | - Dongdong Xia
- Department of Cell Biology, Neurobiology and AnatomyMedical College of WisconsinMilwaukeeWIUSA
| | - Alexander Salmon
- Department of Cell Biology, Neurobiology and AnatomyMedical College of WisconsinMilwaukeeWIUSA
| | - Qiuli Liu
- Department of Cell Biology, Neurobiology and AnatomyMedical College of WisconsinMilwaukeeWIUSA
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Briggs C, Hirasawa M, Semba K. Sleep Deprivation Distinctly Alters Glutamate Transporter 1 Apposition and Excitatory Transmission to Orexin and MCH Neurons. J Neurosci 2018; 38:2505-18. [PMID: 29431649 DOI: 10.1523/JNEUROSCI.2179-17.2018] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Revised: 01/23/2018] [Accepted: 01/29/2018] [Indexed: 11/21/2022] Open
Abstract
Glutamate transporter 1 (GLT1) is the main astrocytic transporter that shapes glutamatergic transmission in the brain. However, whether this transporter modulates sleep-wake regulatory neurons is unknown. Using quantitative immunohistochemical analysis, we assessed perisomatic GLT1 apposition with sleep-wake neurons in the male rat following 6 h sleep deprivation (SD) or following 6 h undisturbed conditions when animals were mostly asleep (Rest). We found that SD decreased perisomatic GLT1 apposition with wake-promoting orexin neurons in the lateral hypothalamus compared with Rest. Reduced GLT1 apposition was associated with tonic presynaptic inhibition of excitatory transmission to these neurons due to the activation of Group III metabotropic glutamate receptors, an effect mimicked by a GLT1 inhibitor in the Rest condition. In contrast, SD resulted in increased GLT1 apposition with sleep-promoting melanin-concentrating hormone (MCH) neurons in the lateral hypothalamus. Functionally, this decreased the postsynaptic response of MCH neurons to high-frequency synaptic activation without changing presynaptic glutamate release. The changes in GLT1 apposition with orexin and MCH neurons were reversed after 3 h of sleep opportunity following 6 h SD. These SD effects were specific to orexin and MCH neurons, as no change in GLT1 apposition was seen in basal forebrain cholinergic or parvalbumin-positive GABA neurons. Thus, within a single hypothalamic area, GLT1 differentially regulates excitatory transmission to wake- and sleep-promoting neurons depending on sleep history. These processes may constitute novel astrocyte-mediated homeostatic mechanisms controlling sleep-wake behavior.SIGNIFICANCE STATEMENT Sleep-wake cycles are regulated by the alternate activation of sleep- and wake-promoting neurons. Whether and how astrocytes can regulate this reciprocal neuronal activity are unclear. Here we report that, within the lateral hypothalamus, where functionally opposite wake-promoting orexin neurons and sleep-promoting melanin-concentrating hormone neurons codistribute, the glutamate transporter GLT1, mainly present on astrocytes, distinctly modulates excitatory transmission in a cell-type-specific manner and according to sleep history. Specifically, GLT1 is reduced around the somata of orexin neurons while increased around melanin-concentrating hormone neurons following sleep deprivation, resulting in different forms of synaptic plasticity. Thus, astrocytes can fine-tune the excitability of functionally discrete neurons via glutamate transport, which may represent novel regulatory mechanisms for sleep.
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Edalat L, Stegen B, Klumpp L, Haehl E, Schilbach K, Lukowski R, Kühnle M, Bernhardt G, Buschauer A, Zips D, Ruth P, Huber SM. BK K+ channel blockade inhibits radiation-induced migration/brain infiltration of glioblastoma cells. Oncotarget 2016; 7:14259-78. [PMID: 26893360 DOI: 10.18632/oncotarget.7423] [Citation(s) in RCA: 52] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2015] [Accepted: 01/29/2016] [Indexed: 12/14/2022] Open
Abstract
Infiltration of the brain by glioblastoma cells reportedly requires Ca2+ signals and BK K+ channels that program and drive glioblastoma cell migration, respectively. Ionizing radiation (IR) has been shown to induce expression of the chemokine SDF-1, to alter the Ca2+ signaling, and to stimulate cell migration of glioblastoma cells. Here, we quantified fractionated IR-induced migration/brain infiltration of human glioblastoma cells in vitro and in an orthotopic mouse model and analyzed the role of SDF-1/CXCR4 signaling and BK channels. To this end, the radiation-induced migratory phenotypes of human T98G and far-red fluorescent U-87MG-Katushka glioblastoma cells were characterized by mRNA and protein expression, fura-2 Ca2+ imaging, BK patch-clamp recording and transfilter migration assay. In addition, U-87MG-Katushka cells were grown to solid glioblastomas in the right hemispheres of immunocompromised mice, fractionated irradiated (6 MV photons) with 5 × 0 or 5 × 2 Gy, and SDF-1, CXCR4, and BK protein expression by the tumor as well as glioblastoma brain infiltration was analyzed in dependence on BK channel targeting by systemic paxilline application concomitant to IR. As a result, IR stimulated SDF-1 signaling and induced migration of glioblastoma cells in vitro and in vivo. Importantly, paxilline blocked IR-induced migration in vivo. Collectively, our data demonstrate that fractionated IR of glioblastoma stimulates and BK K+ channel targeting mitigates migration and brain infiltration of glioblastoma cells in vivo. This suggests that BK channel targeting might represent a novel approach to overcome radiation-induced spreading of malignant brain tumors during radiotherapy.
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Fukaya R, Yamada R, Kuba H. Tonotopic Variation of the T-Type Ca 2+ Current in Avian Auditory Coincidence Detector Neurons. J Neurosci 2018; 38:335-46. [PMID: 29167400 DOI: 10.1523/JNEUROSCI.2237-17.2017] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2017] [Revised: 11/13/2017] [Accepted: 11/14/2017] [Indexed: 12/29/2022] Open
Abstract
Neurons in avian nucleus laminaris (NL) are binaural coincidence detectors for sound localization and are characterized by striking structural variations in dendrites and axon initial segment (AIS) according to their acoustic tuning [characteristic frequency (CF)]. T-type Ca2+ (CaT) channels regulate synaptic integration and firing behavior at these neuronal structures. However, whether or how CaT channels contribute to the signal processing in NL neurons is not known. In this study, we addressed this issue with whole-cell recording and two-photon Ca2+ imaging in brain slices of posthatch chicks of both sexes. We found that the CaT current was prominent in low-CF neurons, whereas it was almost absent in higher-CF neurons. In addition, a large Ca2+ transient occurred at the dendrites and the AIS of low-CF neurons, indicating a localization of CaT channels at these structures in the neurons. Because low-CF neurons have long dendrites, dendritic CaT channels may compensate for the attenuation of EPSPs at dendrites. Furthermore, the short distance of AIS from the soma may accelerate activation of axonal CaT current in the neurons and help EPSPs reach spike threshold. Indeed, the CaT current was activated by EPSPs and augmented the synaptic response and spike generation of the neurons. Notably, the CaT current was inactivated during repetitive inputs, and these augmenting effects predominated at the initial phase of synaptic activity. These results suggested that dendritic and axonal CaT channels increase the sensitivity to sound at its onset, which may expand the dynamic range for binaural computation in low-CF NL neurons.SIGNIFICANCE STATEMENT Neurons in nucleus laminaris are binaural coincidence detectors for sound localization. We report that T-type Ca2+ (CaT) current was prominent at dendrites and the axonal trigger zone in neurons tuned to low-frequency sound. Because these neurons have long dendrites and a closer trigger zone compared with those tuned to higher-frequency sound, the CaT current augmented EPSPs at dendrites and accelerated spike triggers in the neurons, implying a strategic arrangement of the current within the nucleus. This effect was limited to the onset of repetitive inputs due to progressive inactivation of CaT current. The results suggested that the CaT current increases the sensitivity to sound at its onset, which may expand the dynamic range for binaural computation of low-frequency sound.
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Wu YN, Shen KZ, Johnson SW. Differential actions of AMP kinase on ATP-sensitive K + currents in ventral tegmental area and substantia nigra zona compacta neurons. Eur J Neurosci 2017; 46:2746-2753. [PMID: 29057540 DOI: 10.1111/ejn.13756] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2017] [Revised: 09/22/2017] [Accepted: 10/16/2017] [Indexed: 12/21/2022]
Abstract
ATP-sensitive K+ (K-ATP) channels play significant roles in regulating the excitability of dopamine neurons in the substantia nigra zona compacta (SNC). We showed previously that K-ATP channel function is up-regulated by AMP-activated protein kinase (AMPK). This study extended these studies to the neurons adjacent to the SNC in the ventral tegmental area (VTA). Using patch pipettes to record whole-cell currents in slices of rat midbrain, we found that the AMPK activator A769662 increased the amplitude of currents evoked by the K-ATP channel opener diazoxide in presumed dopamine-containing VTA neurons. However, current evoked by diazoxide with A769662 was significantly smaller in VTA neurons compared to SNC neurons. Moreover, a significantly lower proportion of VTA neurons responded to diazoxide with outward current. However, A769662 was able to increase the incidence of diazoxide-responsive neurons in the VTA. In contrast, A769662 did not potentiate diazoxide-evoked currents in presumed non-dopamine VTA neurons. These results show that AMPK activation augments K-ATP currents in presumed dopamine neurons in the VTA and SNC, although diazoxide-evoked currents remain less robust in the VTA. We conclude that K-ATP channels may play important physiological roles in VTA and SNC dopamine neurons.
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Affiliation(s)
- Yan-Na Wu
- Department of Neurology, Oregon Health & Science University, Portland, OR, USA
| | - Ke-Zhong Shen
- Department of Neurology, Oregon Health & Science University, Portland, OR, USA
| | - Steven W Johnson
- Department of Neurology, Oregon Health & Science University, Portland, OR, USA.,Veterans Affairs Portland Health Care System, Portland, OR, 97239, USA
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Liang M, Yin XL, Wang LY, Yin WH, Song NY, Shi HB, Li CY, Yin SK. NAD+ Attenuates Bilirubin-Induced Hyperexcitation in the Ventral Cochlear Nucleus by Inhibiting Excitatory Neurotransmission and Neuronal Excitability. Front Cell Neurosci 2017; 11:21. [PMID: 28217084 PMCID: PMC5289950 DOI: 10.3389/fncel.2017.00021] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2016] [Accepted: 01/23/2017] [Indexed: 02/05/2023] Open
Abstract
Nicotinamide adenine dinucleotide (NAD+) is an important molecule with extensive biological functions in various cellular processes, including protection against cell injuries. However, little is known regarding the roles of NAD+ in neuronal excitation and excitotoxicity associated with many neurodegenerative disorders and diseases. Using patch-clamp recordings, we studied its potential effects on principal neurons in the ventral cochlear nucleus (VCN), which is particularly vulnerable to bilirubin excitotoxicity. We found that NAD+ effectively decreased the size of evoked excitatory postsynaptic currents (eEPSCs), increased paired-pulse ratio (PPR) and reversed the effect of bilirubin on eEPSCs, implicating its inhibitory effects on the presynaptic release probability (Pr). Moreover, NAD+ not only decreased the basal frequency of miniature EPSCs (mEPSCs), but also reversed bilirubin-induced increases in the frequency of mEPSCs without affecting their amplitude under either condition. Furthermore, we found that NAD+ decreased the frequency of spontaneous firing of VCN neurons as well as bilirubin-induced increases in firing frequency. Whole-cell current-clamp recordings showed that NAD+ could directly decrease the intrinsic excitability of VCN neurons in the presence of synaptic blockers, suggesting NAD+ exerts its actions in both presynaptic and postsynaptic loci. Consistent with these observations, we found that the latency of the first postsynaptic spike triggered by high-frequency train stimulation of presynaptic afferents (i.e., the auditory nerve) was prolonged by NAD+. These results collectively indicate that NAD+ suppresses presynaptic transmitter release and postsynaptic excitability, jointly weakening excitatory neurotransmission. Our findings provide a basis for the exploration of NAD+ for the prevention and treatment of bilirubin encephalopathy and excitotoxicity associated with other neurological disorders.
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Affiliation(s)
- Min Liang
- Department of Otorhinolaryngology, The Sixth People's Hospital, Shanghai Jiao Tong University Shanghai, China
| | - Xin-Lu Yin
- Department of Otorhinolaryngology, The Sixth People's Hospital, Shanghai Jiao Tong University Shanghai, China
| | - Lu-Yang Wang
- Programs in Neurosciences and Mental Health, SickKids Research Institute and Department of Physiology, University of Toronto Toronto, ON, Canada
| | - Wei-Hai Yin
- Med-X Research Institute and School of Biomedical Engineering, Shanghai Jiao Tong University Shanghai Shanghai, China
| | - Ning-Ying Song
- Department of Otorhinolaryngology, West China Hospital, Sichuan University Chengdu, China
| | - Hai-Bo Shi
- Department of Otorhinolaryngology, The Sixth People's Hospital, Shanghai Jiao Tong University Shanghai, China
| | - Chun-Yan Li
- Department of Otorhinolaryngology, The Sixth People's Hospital, Shanghai Jiao Tong University Shanghai, China
| | - Shan-Kai Yin
- Department of Otorhinolaryngology, The Sixth People's Hospital, Shanghai Jiao Tong University Shanghai, China
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Lu TZ, Kostelecki W, Sun CLF, Dong N, Pérez Velázquez JL, Feng ZP. High sensitivity of spontaneous spike frequency to sodium leak current in a Lymnaea pacemaker neuron. Eur J Neurosci 2016; 44:3011-3022. [PMID: 27711993 DOI: 10.1111/ejn.13426] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2016] [Revised: 09/25/2016] [Accepted: 09/30/2016] [Indexed: 11/28/2022]
Abstract
The spontaneous rhythmic firing of action potentials in pacemaker neurons depends on the biophysical properties of voltage-gated ion channels and background leak currents. The background leak current includes a large K+ and a small Na+ component. We previously reported that a Na+ -leak current via U-type channels is required to generate spontaneous action potential firing in the identified respiratory pacemaker neuron, RPeD1, in the freshwater pond snail Lymnaea stagnalis. We further investigated the functional significance of the background Na+ current in rhythmic spiking of RPeD1 neurons. Whole-cell patch-clamp recording and computational modeling approaches were carried out in isolated RPeD1 neurons. The whole-cell current of the major ion channel components in RPeD1 neurons were characterized, and a conductance-based computational model of the rhythmic pacemaker activity was simulated with the experimental measurements. We found that the spiking rate is more sensitive to changes in the Na+ leak current as compared to the K+ leak current, suggesting a robust function of Na+ leak current in regulating spontaneous neuronal firing activity. Our study provides new insight into our current understanding of the role of Na+ leak current in intrinsic properties of pacemaker neurons.
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Affiliation(s)
- T Z Lu
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, ON, M5S 1A8, Canada
| | - W Kostelecki
- Institute of Medical Science, University of Toronto, Toronto, ON, Canada.,Neurosciences and Mental Health, Hospital for Sick Children, Toronto, ON, Canada
| | - C L F Sun
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, ON, M5S 1A8, Canada
| | - N Dong
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, ON, M5S 1A8, Canada
| | - J L Pérez Velázquez
- Institute of Medical Science, University of Toronto, Toronto, ON, Canada.,Neurosciences and Mental Health, Hospital for Sick Children, Toronto, ON, Canada
| | - Z-P Feng
- Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, ON, M5S 1A8, Canada
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Sonekatsu M, Taniguchi W, Yamanaka M, Nishio N, Tsutsui S, Yamada H, Yoshida M, Nakatsuka T. Interferon-gamma potentiates NMDA receptor signaling in spinal dorsal horn neurons via microglia-neuron interaction. Mol Pain 2016; 12:1744806916644927. [PMID: 27094552 PMCID: PMC4956380 DOI: 10.1177/1744806916644927] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2015] [Revised: 02/29/2016] [Accepted: 03/20/2016] [Indexed: 01/25/2023] Open
Abstract
BACKGROUND Glia-neuron interactions play an important role in the development of neuropathic pain. Expression of the pro-inflammatory cytokne →cytokine Interferon-gamma (IFNγ) is upregulated in the dorsal horn after peripheral nerve injury, and intrathecal IFNγ administration induces mechanical allodynia in rats. A growing body of evidence suggests that IFNγ might be involved in the mechanisms of neuropathic pain, but its effects on the spinal dorsal horn are unclear. We performed blind whole-cell patch-clamp recording to investigate the effect of IFNγ on postsynaptic glutamate-induced currents in the substantia gelatinosa neurons of spinal cord slices from adult male rats. RESULTS IFNγ perfusion significantly enhanced the amplitude of NMDA-induced inward currents in substantia gelatinosa neurons, but did not affect AMPA-induced currents. The facilitation of NMDA-induced current by IFNγ was inhibited by bath application of an IFNγ receptor-selective antagonist. Adding the Janus activated kinase inhibitor tofacitinib to the pipette solution did not affect the IFNγ-induced facilitation of NMDA-induced currents. However, the facilitatory effect of IFNγ on NMDA-induced currents was inhibited by perfusion of the microglial inhibitor minocycline. These results suggest that IFNγ binds the microglial IFNγ receptor and enhances NMDA receptor activity in substantia gelatinosa neurons. Next, to identify the effector of signal transmission from microglia to dorsal horn neurons, we added an inhibitor of G proteins, GDP-β-S, to the pipette solution. In a GDP-β-S-containing pipette solution, IFNγ-induced potentiation of the NMDA current was significantly suppressed after 30 min. In addition, IFNγ-induced potentiation of NMDA currents was blocked by application of a selective antagonist of CCR2, and its ligand CCL2 increased NMDA-induced currents. CONCLUSION Our findings suggest that IFNγ enhance the amplitude of NMDA-induced inward currents in substantia gelatinosa neurons via microglial IFNγ receptors and CCL2/CCR2 signaling. This mechanism might be partially responsible for the development of persistent neuropathic pain.
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Affiliation(s)
- Mayumi Sonekatsu
- Department of Orthopaedic Surgery, Wakayama Medical University, Wakayama, Japan
| | - Wataru Taniguchi
- Department of Orthopaedic Surgery, Wakayama Medical University, Wakayama, Japan
| | - Manabu Yamanaka
- Department of Orthopaedic Surgery, Wakayama Medical University, Wakayama, Japan
| | - Naoko Nishio
- Department of Orthopaedic Surgery, Wakayama Medical University, Wakayama, Japan
| | - Shunji Tsutsui
- Department of Orthopaedic Surgery, Wakayama Medical University, Wakayama, Japan
| | - Hiroshi Yamada
- Department of Orthopaedic Surgery, Wakayama Medical University, Wakayama, Japan
| | - Munehito Yoshida
- Department of Orthopaedic Surgery, Wakayama Medical University, Wakayama, Japan
| | - Terumasa Nakatsuka
- Pain Research Center, Kansai University of Health Science, Kumatori, Osaka, Japan
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Du Y, Kiyoshi CM, Wang Q, Wang W, Ma B, Alford CC, Zhong S, Wan Q, Chen H, Lloyd EE, Bryan RM, Zhou M. Genetic Deletion of TREK-1 or TWIK-1/TREK-1 Potassium Channels does not Alter the Basic Electrophysiological Properties of Mature Hippocampal Astrocytes In Situ. Front Cell Neurosci 2016; 10:13. [PMID: 26869883 PMCID: PMC4738265 DOI: 10.3389/fncel.2016.00013] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2015] [Accepted: 01/14/2016] [Indexed: 01/03/2023] Open
Abstract
We have recently shown that a linear current-to-voltage (I-V) relationship of membrane conductance (passive conductance) reflects the intrinsic property of K+ channels in mature astrocytes. While passive conductance is known to underpin a highly negative and stable membrane potential (VM) essential for the basic homeostatic function of astrocytes, a complete repertoire of the involved K+ channels remains elusive. TREK-1 two-pore domain K+ channel (K2P) is highly expressed in astrocytes, and covalent association of TREK-1 with TWIK-1, another highly expressed astrocytic K2P, has been reported as a mechanism underlying the trafficking of heterodimer TWIK-1/TREK-1 channel to the membrane and contributing to astrocyte passive conductance. To decipher the individual contribution of TREK-1 and address whether the appearance of passive conductance is conditional to the co-expression of TWIK-1/TREK-1 in astrocytes, TREK-1 single and TWIK-1/TREK-1 double gene knockout mice were used in the present study. The relative quantity of mRNA encoding other astrocyte K+ channels, such as Kir4.1, Kir5.1, and TREK-2, was not altered in these gene knockout mice. Whole-cell recording from hippocampal astrocytes in situ revealed no detectable changes in astrocyte passive conductance, VM, or membrane input resistance (Rin) in either kind of gene knockout mouse. Additionally, TREK-1 proteins were mainly located in the intracellular compartments of the hippocampus. Altogether, genetic deletion of TREK-1 alone or together with TWIK-1 produced no obvious alteration in the basic electrophysiological properties of hippocampal astrocytes. Thus, future research focusing on other K+ channels may shed light on this long-standing and important question in astrocyte physiology.
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Affiliation(s)
- Yixing Du
- Department of Neuroscience, The Ohio State University Wexner Medical CenterColumbus, OH, USA; Department of Neurology, The First Affiliated Hospital of Nanjing Medical UniversityNanjing, China
| | - Conrad M Kiyoshi
- Department of Neuroscience, The Ohio State University Wexner Medical Center Columbus, OH, USA
| | - Qi Wang
- Department of Neuroscience, The Ohio State University Wexner Medical CenterColumbus, OH, USA; Department of Neurology, Meitan General HospitalXibahe Nanli, Beijing, China
| | - Wei Wang
- Department of Physiology, Institute of Brain Research, School of Basic Medicine, Huazhong University of Science and Technology Wuhan, China
| | - Baofeng Ma
- Department of Neuroscience, The Ohio State University Wexner Medical Center Columbus, OH, USA
| | - Catherine C Alford
- Department of Neuroscience, The Ohio State University Wexner Medical Center Columbus, OH, USA
| | - Shiying Zhong
- Department of Neuroscience, The Ohio State University Wexner Medical Center Columbus, OH, USA
| | - Qi Wan
- Department of Neurology, The First Affiliated Hospital of Nanjing Medical University Nanjing, China
| | - Haijun Chen
- Department of Biological Science, University at Albany, State University of New York Albany, NY, USA
| | - Eric E Lloyd
- Department of Anesthesiology, Baylor College of Medicine Houston, TX, USA
| | - Robert M Bryan
- Department of Anesthesiology, Baylor College of Medicine Houston, TX, USA
| | - Min Zhou
- Department of Neuroscience, The Ohio State University Wexner Medical Center Columbus, OH, USA
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Tabuchi M, Dong L, Inoue S, Namiki S, Sakurai T, Nakatani K, Kanzaki R. Two types of local interneurons are distinguished by morphology, intrinsic membrane properties, and functional connectivity in the moth antennal lobe. J Neurophysiol 2015; 114:3002-13. [PMID: 26378200 DOI: 10.1152/jn.00050.2015] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2015] [Accepted: 09/15/2015] [Indexed: 11/22/2022] Open
Abstract
Neurons in the silkmoth antennal lobe (AL) are well characterized in terms of their morphology and odor-evoked firing activity. However, their intrinsic electrical properties including voltage-gated ionic currents and synaptic connectivity remain unclear. To address this, whole cell current- and voltage-clamp recordings were made from second-order projection neurons (PNs) and two morphological types of local interneurons (LNs) in the silkmoth AL. The two morphological types of LNs exhibited distinct physiological properties. One morphological type of LN showed a spiking response with a voltage-gated sodium channel gene expression, whereas the other type of LN was nonspiking without a voltage-gated sodium channel gene expression. Voltage-clamp experiments also revealed that both of two types of LNs as well as PNs possessed two types of voltage-gated potassium channels and calcium channels. In dual whole cell recordings of spiking LNs and PNs, activation of the PN elicited depolarization responses in the paired spiking LN, whereas activation of the spiking LN induced no substantial responses in the paired PN. However, simultaneous recording of a nonspiking LN and a PN showed that activation of the nonspiking LN induced hyperpolarization responses in the PN. We also observed bidirectional synaptic transmission via both chemical and electrical coupling in the pairs of spiking LNs. Thus our results indicate that there were two distinct types of LNs in the silkmoth AL, and their functional connectivity to PNs was substantially different. We propose distinct functional roles for these two different types of LNs in shaping odor-evoked firing activity in PNs.
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Affiliation(s)
- Masashi Tabuchi
- Department of Advanced Interdisciplinary Studies, Graduate School of Engineering, The University of Tokyo, Meguro-ku, Tokyo, Japan; Research Center for Advanced Science and Technology, The University of Tokyo, Meguro-ku, Tokyo, Japan
| | - Li Dong
- Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan; and
| | - Shigeki Inoue
- Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan; and
| | - Shigehiro Namiki
- Research Center for Advanced Science and Technology, The University of Tokyo, Meguro-ku, Tokyo, Japan
| | - Takeshi Sakurai
- Research Center for Advanced Science and Technology, The University of Tokyo, Meguro-ku, Tokyo, Japan
| | - Kei Nakatani
- Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan; and
| | - Ryohei Kanzaki
- Research Center for Advanced Science and Technology, The University of Tokyo, Meguro-ku, Tokyo, Japan
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27
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Youngstrom IA, Strowbridge BW. Respiratory modulation of spontaneous subthreshold synaptic activity in olfactory bulb granule cells recorded in awake, head-fixed mice. J Neurosci 2015; 35:8758-67. [PMID: 26063910 DOI: 10.1523/JNEUROSCI.0311-15.2015] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Although the firing patterns of principal neurons in the olfactory bulb are known to be modulated strongly by respiration even under basal conditions, less is known about whether inhibitory local circuit activity in the olfactory bulb (OB) is modulated phasically. The diverse phase preferences of principal neurons in the OB and olfactory cortex that innervate granule cells (GCs) may interfere and prevent robust respiratory coupling, as suggested by recent findings. Using whole-cell recording, we examined the spontaneous, subthreshold membrane potential of GCs in the OBs of awake head-fixed mice. We found that, during periods of basal respiration, the synaptic input to GCs was strongly phase modulated, leading to a phase preference in the average, cycle-normalized membrane potential. Subthreshold phase tuning was heterogeneous in both mitral and tufted cells (MTCs) and GCs but relatively constant within each GC during periods of increased respiratory frequency. The timing of individual EPSPs in GC recordings also was phase modulated with the phase preference imparted by large-amplitude EPSPs, with fast kinetics often matching the phase tuning of the average membrane potential. These results suggest that activity in a subset of excitatory afferents to GCs, presumably including cortical feedback projections and other sources of large-amplitude unitary EPSPs, function to provide a timing signal linked to respiration. The phase preference we find in the membrane potential may provide a mechanism to dynamically modulate recurrent and lateral dendrodendritic inhibition of MTCs and to selective engage a subpopulation of interneurons based on the alignment of their phase tuning relative to sensory-driven MTC discharges.
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28
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Chen W, Sheng J, Guo J, Gao F, Zhao X, Dai J, Wang G, Li K. Tumor necrosis factor-α enhances voltage-gated Na⁺ currents in primary culture of mouse cortical neurons. J Neuroinflammation 2015; 12:126. [PMID: 26112872 PMCID: PMC4510892 DOI: 10.1186/s12974-015-0349-x] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2015] [Accepted: 06/18/2015] [Indexed: 02/05/2023] Open
Abstract
BACKGROUND Previous studies showed that TNF-α could activate voltage-gated Na(+) channels (VGSCs) in the peripheral nervous system (PNS). Since TNF-α is implicated in many central nervous system (CNS) diseases, we examined potential effects of TNF-α on VGSCs in the CNS. METHODS Effects of TNF-α (1-1000 pg/mL, for 4-48 h) on VGSC currents were examined using whole-cell voltage clamp and current clamp techniques in primary culture of mouse cortical neurons. Expression of Nav1.1, Nav1.2, Nav1.3, and Nav1.6 were examined at both the mRNA and protein levels, prior to and after TNF-α exposure. RESULTS TNF-α increased Na(+) currents by accelerating the activation of VGSCs. The threshold for action potential (AP) was decreased and firing rate were increased. VGSCs were up-regulated at both the mRNA and protein levels. The observed effects of TNF-α on Na(+) currents were inhibited by pre-incubation with the NF-κB inhibitor BAY 11-7082 (1 μM) or the p38 mitogen-activated protein kinases (MAPK) inhibitor SB203580 (1 μM). CONCLUSIONS TNF-α increases Na(+) currents by accelerating the channel activation as well as increasing the expression of VGSCs in a mechanism dependent upon NF-κB and p38 MAPK signal pathways in CNS neurons.
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Affiliation(s)
- Weiqiang Chen
- Department of Microbiology and Immunology, Key Immunopathology Laboratory of Guangdong Province, Shantou University Medical College, 22 Xinling Road, Shantou, 515041, , Guangdong, China.
- Department of Neurosurgery, First Affiliated Hospital, Shantou University Medical College, 57 Changping Road, Shantou, 515041, , Guangdong, China.
| | - Jiangtao Sheng
- Department of Microbiology and Immunology, Key Immunopathology Laboratory of Guangdong Province, Shantou University Medical College, 22 Xinling Road, Shantou, 515041, , Guangdong, China.
| | - Jingfang Guo
- Department of Neurosurgery, First Affiliated Hospital, Shantou University Medical College, 57 Changping Road, Shantou, 515041, , Guangdong, China.
| | - Fenfei Gao
- Department of Pharmacology, Shantou University Medical College, 22 Xinling Road, Shantou, 515041, , Guangdong, China.
| | - Xiangfeng Zhao
- Department of Microbiology and Immunology, Key Immunopathology Laboratory of Guangdong Province, Shantou University Medical College, 22 Xinling Road, Shantou, 515041, , Guangdong, China.
| | - Jianping Dai
- Department of Microbiology and Immunology, Key Immunopathology Laboratory of Guangdong Province, Shantou University Medical College, 22 Xinling Road, Shantou, 515041, , Guangdong, China.
| | - Gefei Wang
- Department of Microbiology and Immunology, Key Immunopathology Laboratory of Guangdong Province, Shantou University Medical College, 22 Xinling Road, Shantou, 515041, , Guangdong, China.
| | - Kangsheng Li
- Department of Microbiology and Immunology, Key Immunopathology Laboratory of Guangdong Province, Shantou University Medical College, 22 Xinling Road, Shantou, 515041, , Guangdong, China.
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Haselmann H, Röpke L, Werner C, Kunze A, Geis C. Interactions of Human Autoantibodies with Hippocampal GABAergic Synaptic Transmission - Analyzing Antibody-Induced Effects ex vivo. Front Neurol 2015; 6:136. [PMID: 26124746 PMCID: PMC4463933 DOI: 10.3389/fneur.2015.00136] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2015] [Accepted: 05/28/2015] [Indexed: 02/04/2023] Open
Abstract
Autoantibodies (aAB) to the presynaptic located enzyme glutamate decarboxylase 65 (GAD65) are a characteristic attribute for a variety of autoimmune diseases of the central nervous system including subtypes of limbic encephalitis, stiff person-syndrome, cerebellar ataxia, and Batten’s disease. Clinical signs of hyperexcitability and improvement of disease symptoms upon immunotherapy in some of these disorders suggest a possible pathogenic role of associated aAB. Recent experimental studies report inconsistent results regarding a direct pathogenic influence of anti-GAD65 aAB affecting inhibitory synaptic transmission in central GABAergic pathways. We here provide a method for direct evaluation of aAB-induced pathomechanisms in the intact hippocampal network. Purified patient IgG fractions containing aAB to GAD65 together with fixable lipophilic styryl dyes (FMdyes) are stereotactically injected into the hilus and the dentate gyrus in anesthetized mice. Twenty-four hours after intrahippocampal injection, acute hippocampal slices are prepared and transferred to a patch-clamp recording setup equipped with a fluorescence light source. Intraneural incorporated FMdyes show correct injection site for patch-clamp recording. Whole-cell patch-clamp recordings are performed from granule cells in the dentate gyrus and extracellular stimulation is applied in the border area of the dentate gyrus-hilus region to stimulate GABAergic afferents arising from parvalbumin positive basket cells. GABA-A receptor mediated inhibitory postsynaptic currents (IPSC) and miniature IPSC are recorded after blocking glutamatergic transmission. This approach allows investigation of potential aAB-induced effects on GABA-A receptor signaling ex vivo in an intact neuronal network. This offers several advantages compared to experimental procedures used in previous studies by in vitro AB preincubation of primary neurons or slice preparations. Furthermore, this method requires only small amounts of patient material that are often limited in rare diseases.
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Affiliation(s)
- Holger Haselmann
- Hans Berger Department of Neurology, Jena University Hospital , Jena , Germany ; The Integrated Research and Treatment Center for Sepsis Control and Care (CSCC), Jena University Hospital , Jena , Germany
| | - Luise Röpke
- Hans Berger Department of Neurology, Jena University Hospital , Jena , Germany
| | - Christian Werner
- Hans Berger Department of Neurology, Jena University Hospital , Jena , Germany
| | - Albrecht Kunze
- Hans Berger Department of Neurology, Jena University Hospital , Jena , Germany
| | - Christian Geis
- Hans Berger Department of Neurology, Jena University Hospital , Jena , Germany ; The Integrated Research and Treatment Center for Sepsis Control and Care (CSCC), Jena University Hospital , Jena , Germany
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Du Y, Ma B, Kiyoshi CM, Alford CC, Wang W, Zhou M. Freshly dissociated mature hippocampal astrocytes exhibit passive membrane conductance and low membrane resistance similarly to syncytial coupled astrocytes. J Neurophysiol 2015; 113:3744-50. [PMID: 25810481 DOI: 10.1152/jn.00206.2015] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2015] [Accepted: 03/23/2015] [Indexed: 01/25/2023] Open
Abstract
Mature astrocytes exhibit a linear current-to-voltage K(+) membrane conductance (passive conductance) and an extremely low membrane resistance (Rm) in situ. The combination of these electrophysiological characteristics establishes a highly negative and stable membrane potential that is essential for basic functions, such as K(+) spatial buffering and neurotransmitter uptake. However, astrocytes are coupled extensively in situ. It remains to be determined whether the observed passive behavior and low Rm are attributable to the intrinsic properties of membrane ion channels or to gap junction coupling in functionally mature astrocytes. In the present study, freshly dissociated hippocampal tissues were used as a new model to examine this basic question in young adult animals. The morphologically intact single astrocytes could be reliably dissociated from animals postnatal day 21 and older. At this animal age, dissociated single astrocytes exhibit passive conductance and resting membrane potential similar to those exhibited by astrocytes in situ. To precisely measure the Rm from single astrocytes, dual-patch single-astrocyte recording was performed. We show that dissociated single astrocytes exhibit a low Rm similarly to syncytial coupled astrocytes. Functionally, the symmetric expression of high-K(+) conductance enabled rapid change in the intracellular K(+) concentrations in response to changing K(+) drive force. Altogether, we demonstrate that freshly dissociated tissue preparation is a highly useful model for study of the functional expression and regulation of ion channels, receptors, and transporters in astrocytes and that passive behavior and low Rm are the intrinsic properties of mature astrocytes.
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Affiliation(s)
- Yixing Du
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, Ohio; Department of Neurology, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China; and
| | - Baofeng Ma
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, Ohio
| | - Conrad M Kiyoshi
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, Ohio
| | - Catherine C Alford
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, Ohio
| | - Wei Wang
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, Ohio; Department of Physiology, Institute of Brain Research, School of Basic Medicine, Huazhong University of Science and Technology, Wuhan, China
| | - Min Zhou
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, Ohio;
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Wayman WN, Chen L, Napier TC, Hu XT. Cocaine self-administration enhances excitatory responses of pyramidal neurons in the rat medial prefrontal cortex to human immunodeficiency virus-1 Tat. Eur J Neurosci 2015; 41:1195-206. [PMID: 25707266 DOI: 10.1111/ejn.12853] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2014] [Revised: 01/14/2015] [Accepted: 01/16/2015] [Indexed: 11/28/2022]
Abstract
The medial prefrontal cortex (mPFC) plays a critical role in reward-motivated behaviors. Repeated cocaine exposure dysregulates the dorsal mPFC, and this is thought to contribute to cocaine-seeking and relapse of abstinent abusers. Neuropathology of the mPFC also occurs in human immunodeficiency virus (HIV)-positive individuals, and this is exaggerated in those who also abuse cocaine. The impact of the comorbid condition on mPFC neuronal function is unknown. To fill this knowledge gap, we performed a behavioral and electrophysiological study utilising adult male rats that self-administered cocaine by pressing a lever for 14 once-daily operant sessions. Saline-yoked (SAL-yoked) rats served as controls. Cue reactivity (CR) was used to indicate drug-seeking, assessed by re-exposing the rats to cocaine-paired cues wherein non-reinforced lever pressing was quantified 1 day (CR1) and 18-21 days (CR2) after the 14th operant session. Only cocaine self-administration (COC-SA) rats showed CR. One day after CR2, brain slices were prepared for electrophysiological assessment. Whole-cell patch-clamp recordings of dorsal (prelimbic) mPFC pyramidal neurons from COC-SA rats showed a significant increase in firing evoked by depolarizing currents as compared with those from SAL-yoked control rats. Bath application of the toxic HIV-1 protein transactivator of transcription (Tat) also depolarized neuronal membranes and increased evoked firing. The Tat-induced excitation was greater in the neurons from withdrawn COC-SA rats than in controls. Tat also reduced spike amplitude, and this co-varied with cocaine-seeking during CR2. Taken together, these novel findings provide support at the neuronal level for the concept that the increased excitability of mPFC pyramidal neurons following cocaine self-administration drives drug-seeking and augments the neuropathophysiology caused by HIV-1 Tat.
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Affiliation(s)
- Wesley N Wayman
- Department of Pharmacology, Rush University Medical Center, 1735 W. Harrison Street, Cohn Research Building, Rm. 463, Chicago, IL, 60612, USA; Center for Compulsive Behavior and Addiction, Rush University Medical Center, Chicago, IL, 60612, USA
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Liu Y, Harding M, Pittman A, Dore J, Striessnig J, Rajadhyaksha A, Chen X. Cav1.2 and Cav1.3 L-type calcium channels regulate dopaminergic firing activity in the mouse ventral tegmental area. J Neurophysiol 2014; 112:1119-30. [PMID: 24848473 DOI: 10.1152/jn.00757.2013] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Dopaminergic projections from the ventral tegmental area (VTA) constitute the mesolimbocortical system that underlies addiction and psychosis primarily as a result of increased dopaminergic transmission. Dopamine release is spike dependent. L-type calcium channels (LTCCs) play an important role in regulating firing activities, but the contribution of specific subtypes remains unclear. This article describes different functions of Cav1.2 and Cav1.3 subtypes in regulating firing properties with two transgenic mouse strains. For basal firing, Cav1.3-deficient (Cav1.3(-/-)) mice had a lower basal firing frequency. The dihydropyridine (DHP) channel blocker nifedipine reduced single-spike firing in mice expressing DHP-insensitive Cav1.2 channels (Cav1.2DHP(-/-) mice), confirming the significant contribution from the Cav1.3 subtype in basal firing. Moreover, the DHP channel activator (S)-(-)-Bay K8644 and the non-DHP channel activator FPL 64176 converted firing patterns from single spiking to bursting in Cav1.2DHP(-/-) mice. Nifedipine inhibited burst firing induced by both activators, suggesting that Cav1.3 also serves an essential role in burst firing. However, FPL 64176 also induced bursting in Cav1.3(-/-) mice. These results indicate that the Cav1.3 subtype is crucial to regulation of basal single-spike firing, while activation of both Cav1.2 and Cav1.3 can support burst firing of VTA neurons.
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Affiliation(s)
- Yudan Liu
- Department of Physiology, School of Life Science and Biopharmaceutics, Shenyang Pharmaceutical University, Shenyang, Liaoning, China;
| | - Meghan Harding
- Division of Biomedical Sciences, Faculty of Medicine, Memorial University of Newfoundland, St. John's, Newfoundland, Canada
| | - Andrea Pittman
- Division of Biomedical Sciences, Faculty of Medicine, Memorial University of Newfoundland, St. John's, Newfoundland, Canada
| | - Jules Dore
- Division of Biomedical Sciences, Faculty of Medicine, Memorial University of Newfoundland, St. John's, Newfoundland, Canada
| | - Jörg Striessnig
- Department of Pharmacology and Toxicology, Institute of Pharmacy and Center for Molecular Biosciences Innsbruck (CMBI), University of Innsbruck, Innsbruck, Austria; and
| | - Anjali Rajadhyaksha
- Division of Pediatric Neurology, Department of Pediatrics and Brain and Mind Research Institute, Weill Cornell Medical College of Cornell University, New York
| | - Xihua Chen
- Division of Biomedical Sciences, Faculty of Medicine, Memorial University of Newfoundland, St. John's, Newfoundland, Canada
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Raster P, Späth A, Bultakova S, Gorostiza P, König B, Bregestovski P. New GABA amides activating GABAA-receptors. Beilstein J Org Chem 2013; 9:406-10. [PMID: 23503884 PMCID: PMC3596083 DOI: 10.3762/bjoc.9.42] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2012] [Accepted: 01/25/2013] [Indexed: 11/23/2022] Open
Abstract
We have prepared a series of new and some literature-reported GABA-amides and determined their effect on the activation of GABAA-receptors expressed in CHO cells. Special attention was paid to the purification of the target compounds to remove even traces of GABA contaminations, which may arise from deprotection steps in the synthesis. GABA-amides were previously reported to be partial, full or superagonists. In our hands these compounds were not able to activate GABAA-receptor channels in whole-cell patch-clamp recordings. New GABA-amides, however, gave moderate activation responses with a clear structure–activity relationship suggesting some of these compounds as promising molecular tools for the functional analysis of GABAA-receptors.
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Affiliation(s)
- Peter Raster
- Institute of Organic Chemistry, University of Regensburg, D-93040 Regensburg, Germany
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Yamada Y, Mikoshiba K. Quantitative comparison of novel GCaMP-type genetically encoded Ca(2+) indicators in mammalian neurons. Front Cell Neurosci 2012; 6:41. [PMID: 23060748 PMCID: PMC3465963 DOI: 10.3389/fncel.2012.00041] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2012] [Accepted: 09/19/2012] [Indexed: 01/30/2023] Open
Abstract
New variants of GCaMP-type genetically encoded Ca(2+) indicators (GECIs) have been continuously developed and heavily used in many areas of biology including neuroscience. The latest subfamily called "GECOs" were developed with in vitro high-throughput screening, and shown to have novel spectral properties and/or improved fluorescent responses over their ancestor GCaMP3. The most critical parameter in evaluating performance in neurons, however, remains uncharacterized: the relationship between the GECI responses and the number of action potentials (APs). Here we analyzed the GECI responses to APs in cortical pyramidal cells of mouse acute brain slices. Unexpectedly, we found that none of the GECOs exhibited any improved performance over GCaMP3. Our results imply that careful validation is required for the accurate prediction of the actual performance of GECIs in mammalian neurons. We propose that appropriate guidelines for evaluating their efficacy should be established for the benefit of research community, given the rapidly expanding use of GECIs in neuroscience.
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Affiliation(s)
- Yoshiyuki Yamada
- Laboratory for Developmental Neurobiology, Brain Science Institute, RIKEN Wako-shi, Saitama, Japan ; Central Institute for Experimental Animals Kawasaki-shi, Kanagawa, Japan
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Abstract
Studying the physiological properties and synaptic connections of specific neurons in the intact tissue is a challenge for those cells that lack conspicuous morphological features or show a low population density. This applies particularly to retinal amacrine cells, an exceptionally multiform class of interneurons that comprise roughly 30 subtypes in mammals(1). Though being a crucial part of the visual processing by shaping the retinal output(2), most of these subtypes have not been studied up to now in a functional context because encountering these cells with a recording electrode is a rare event. Recently, a multitude of transgenic mouse lines is available that express fluorescent markers like green fluorescent protein (GFP) under the control of promoters for membrane receptors or enzymes that are specific to only a subset of neurons in a given tissue(3,4). These pre-labeled cells are therefore accessible to directed microelectrode targeting under microscopic control, permitting the systematic study of their physiological properties in situ. However, excitation of fluorescent markers is accompanied by the risk of phototoxicity for the living tissue. In the retina, this approach is additionally hampered by the problem that excitation light causes appropriate stimulation of the photoreceptors, thus inflicting photopigment bleaching and transferring the retinal circuits into a light-adapted condition. These drawbacks are overcome by using infrared excitation delivered by a mode-locked laser in short pulses of the femtosecond range. Two-photon excitation provides energy sufficient for fluorophore excitation and at the same time restricts the excitation to a small tissue volume minimizing the hazards of photodamage(5). Also, it leaves the retina responsive to visual stimuli since infrared light (>850 nm) is only poorly absorbed by photopigments(6). In this article we demonstrate the use of a transgenic mouse retina to attain electrophysiological in situ recordings from GFP-expressing cells that are visually targeted by two-photon excitation. The retina is prepared and maintained in darkness and can be subjected to optical stimuli which are projected through the condenser of the microscope (Figure 1). Patch-clamp recording of light responses can be combined with dye filling to reveal the morphology and to check for gap junction-mediated dye coupling to neighboring cells, so that the target cell can by studied on different experimental levels.
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Affiliation(s)
- Mark Pottek
- Department of Neurobiology, University of Oldenburg
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Yamada Y, Michikawa T, Hashimoto M, Horikawa K, Nagai T, Miyawaki A, Häusser M, Mikoshiba K. Quantitative comparison of genetically encoded Ca indicators in cortical pyramidal cells and cerebellar Purkinje cells. Front Cell Neurosci 2011; 5:18. [PMID: 21994490 PMCID: PMC3182323 DOI: 10.3389/fncel.2011.00018] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2011] [Accepted: 09/11/2011] [Indexed: 11/13/2022] Open
Abstract
Genetically encoded Ca2+ indicators (GECIs) are promising tools for cell type-specific and chronic recording of neuronal activity. In the mammalian central nervous system, however, GECIs have been tested almost exclusively in cortical and hippocampal pyramidal cells, and the usefulness of recently developed GECIs has not been systematically examined in other cell types. Here we expressed the latest series of GECIs, yellow cameleon (YC) 2.60, YC3.60, YC-Nano15, and GCaMP3, in mouse cortical pyramidal cells as well as cerebellar Purkinje cells using in utero injection of recombinant adenoviral vectors. We characterized the performance of the GECIs by simultaneous two-photon imaging and whole-cell patch-clamp recording in acute brain slices at 33 ± 2°C. The fluorescent responses of GECIs to action potentials (APs) evoked by somatic current injection or to synaptic stimulation were examined using rapid dendritic imaging. In cortical pyramidal cells, YC2.60 showed the largest responses to single APs, but its decay kinetics were slower than YC3.60 and GCaMP3, while GCaMP3 showed the largest responses to 20 APs evoked at 20 Hz. In cerebellar Purkinje cells, only YC2.60 and YC-Nano15 could reliably report single complex spikes (CSs), and neither showed signal saturation over the entire stimulus range tested (1–10 CSs at 10 Hz). The expression and response of YC2.60 in Purkinje cells remained detectable and comparable for at least over 100 days. These results provide useful information for selecting an optimal GECI depending on the experimental requirements: in cortical pyramidal cells, YC2.60 is suitable for detecting sparse firing of APs, whereas GCaMP3 is suitable for detecting burst firing of APs; in cerebellar Purkinje cells, YC2.60 as well as YC-Nano15 is suitable for detecting CSs.
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Affiliation(s)
- Yoshiyuki Yamada
- Japan Science and Technology Agency, International Cooperative Research Project and Solution-Oriented Research for Science and Technology, Calcium Oscillation Project, Wako-shi Saitama, Japan
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Minamisawa G, Funayama K, Matsuki N, Ikegaya Y. Intact internal dynamics of the neocortex in acutely paralyzed mice. J Physiol Sci 2011; 61:343-8. [PMID: 21633910 PMCID: PMC10717566 DOI: 10.1007/s12576-011-0155-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2011] [Accepted: 05/18/2011] [Indexed: 10/18/2022]
Abstract
Animals collect sensory information through self-generated movements. Muscle movements drive active feedback of sensory information and determine large parts of the sensory inputs the animal receives; however, little is known about how this active feedback process modulates the ongoing dynamics of the brain. We made electrophysiological recordings from layer 2/3 neurons of the mouse neocortex and compared spontaneous cortical activity in local field potentials and intracellular potential fluctuations between normal and hypomyotonic conditions. We found that pancuronium-induced paralysis did not affect the electrophysiological properties of ongoing cortical activity and its perturbation evoked by visual and tactile stimuli. Thus, internal cortical dynamics are not much affected by active muscle movements, at least, in an acute phase.
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Affiliation(s)
- Genki Minamisawa
- Laboratory of Chemical Pharmacology, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, 113-0033 Japan
| | - Kenta Funayama
- Laboratory of Chemical Pharmacology, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, 113-0033 Japan
| | - Norio Matsuki
- Laboratory of Chemical Pharmacology, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, 113-0033 Japan
| | - Yuji Ikegaya
- Laboratory of Chemical Pharmacology, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, 113-0033 Japan
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Petrovic M, Sedlacek M, Horak M, Chodounska H, Vyklický L. 20-oxo-5beta-pregnan-3alpha-yl sulfate is a use-dependent NMDA receptor inhibitor. J Neurosci 2005; 25:8439-50. [PMID: 16162926 PMCID: PMC6725663 DOI: 10.1523/jneurosci.1407-05.2005] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2005] [Revised: 07/26/2005] [Accepted: 07/28/2005] [Indexed: 11/21/2022] Open
Abstract
NMDA receptors are ligand-gated ion channels permeable to calcium and play a critical role in excitatory synaptic transmission, synaptic plasticity, and excitotoxicity. They are heteromeric complexes of NR1 combined with NR2A-D and/or NR3A-B subunits that are activated by glutamate and glycine and whose activity is modulated by allosteric modulators. In this study, patch-clamp recordings from human embryonic kidney 293 cells expressing NR1/NR2 receptors were used to study the molecular mechanism of the endogenous neurosteroid 20-oxo-5beta-pregnan-3alpha-yl sulfate (3alpha5betaS) action at NMDA receptors. 3alpha5betaS was a twofold more potent inhibitor of responses mediated by NR1/NR2C-D receptors than those mediated by NR1/NR2A-B receptors. The structure of the extracellular loop between the third and fourth transmembrane domains of the NR2 subunit was found to be critical for the neurosteroid inhibitory effect. The degree of 3alpha5betaS-induced inhibition of responses to glutamate was voltage independent, with recovery lasting several seconds. In contrast, application of 3alpha5betaS in the absence of agonist had no effect on the subsequent response to glutamate made in the absence of the neurosteroid. A kinetic model was developed to explain the use-dependent action of 3alpha5betaS at NMDA receptors. In accordance with the model, 3alpha5betaS was a less potent inhibitor of NMDA receptor-mediated EPSCs and responses induced by a short application of 1 mm glutamate than of those induced by a long application of glutamate. These results suggest that 3alpha5betaS is a use-dependent but voltage-independent inhibitor of NMDA receptors, with more potent action at tonically than at phasically activated receptors. This may be important in the treatment of excitotoxicity-induced neurodegeneration.
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Affiliation(s)
- Milos Petrovic
- Institute of Physiology, Academy of Sciences of the Czech Republic, 142 20 Prague 4, Czech Republic
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Li B, Otsu Y, Murphy TH, Raymond LA. Developmental decrease in NMDA receptor desensitization associated with shift to synapse and interaction with postsynaptic density-95. J Neurosci 2003; 23:11244-54. [PMID: 14657184 PMCID: PMC6741033] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/27/2023] Open
Abstract
NMDA receptors (NMDARs) play a crucial role in neuronal development, synaptic plasticity, and excitotoxicity; therefore, regulation of NMDAR function is important in both physiological and pathological conditions. Previous studies indicate that the NMDAR-mediated synaptic current decay rate increases during development because of a switch in receptor subunit composition, contributing to developmental changes in plasticity. To test whether NMDAR desensitization also changes during development, we recorded whole-cell NMDA-evoked currents in cultured rat hippocampal neurons. We found that glycine-independent desensitization of NMDARs decreases during development. This decrease was not dependent on a switch in subunit composition or differential receptor sensitivity to agonist-, Ca2+-, or Zn2+-induced increase in desensitization. Instead, several lines of evidence indicated that the developmental decrease in desensitization was tightly correlated with synaptic localization of the receptor, suggesting that association of NMDARs with proteins selectively expressed at synapses in mature neurons might account for developmental alterations in desensitization. Accordingly, we tested the role of interactions between PSD-95 (postsynaptic density-95) and NMDARs in regulating receptor desensitization. Overexpression of PSD-95 reduced NMDAR desensitization in immature neurons, whereas agents that interfere with synaptic targeting of PSD-95, or induce movement of NMDARs away from synapses and uncouple the receptor from PSD-95, increased NMDAR desensitization in mature neurons. We conclude that synaptic localization and association with PSD-95 increases stability of hippocampal neuronal NMDAR responses to sustained agonist exposure. Our results elucidate an additional mechanism for differentially regulating NMDAR function in neurons of different developmental stages or the response of subpopulations of NMDARs in a single neuron.
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Affiliation(s)
- Bo Li
- Kinsmen Laboratory, Department of Psychiatry, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
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40
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Gryder DS, Rogawski MA. Selective antagonism of GluR5 kainate-receptor-mediated synaptic currents by topiramate in rat basolateral amygdala neurons. J Neurosci 2003; 23:7069-74. [PMID: 12904467 PMCID: PMC6740668] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/04/2023] Open
Abstract
Topiramate is a widely used antiepileptic agent whose mechanism of action is poorly understood. The drug has been reported to interact with various ion channel types, including AMPA/kainate receptors. In whole-cell voltage-clamp recordings from principal neurons of the rat basolateral amygdala, topiramate at low concentrations (IC50, approximately 0.5 microm) selectively inhibited pharmacologically isolated excitatory synaptic currents mediated by kainate receptors containing the GluR5 subunit. Topiramate also partially depressed predominantly AMPA-receptor-mediated EPSCs, but with lower efficacy. Topiramate did not alter the degree of facilitation in paired-pulse experiments, and it reduced the amplitude of miniature EPSCs without affecting their frequency, demonstrating that the block of synaptic responses occurs postsynaptically. Inhibition of GluR5 kainate receptors could represent a key mechanism underlying the anticonvulsant activity of topiramate. Moreover, these results support the concept that GluR5 kainate receptors represent a novel target for antiepileptic drug development.
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Affiliation(s)
- Divina S Gryder
- Epilepsy Research Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-4457, USA
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41
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Gebremedhin D, Yamaura K, Zhang C, Bylund J, Koehler RC, Harder DR. Metabotropic glutamate receptor activation enhances the activities of two types of Ca2+-activated k+ channels in rat hippocampal astrocytes. J Neurosci 2003; 23:1678-87. [PMID: 12629172 PMCID: PMC6741958] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/01/2023] Open
Abstract
The influence of activation of glutamate receptor (GluR) on outward K(+) current in cultured neonate rat hippocampal astrocytes was investigated. Patch-clamp analysis of K(+) channel currents in cultured astrocytes identified the existence of 71 +/- 6 and 161 +/- 11 pS single-channel K(+) currents that were sensitive to changes in voltage and [Ca(2+)](i) and blocked by external TEA but not by charybdotoxin, iberiotoxin, apamin, or 4-aminopyridine. Reverse transcriptase (RT)-PCR and Northern blot analysis revealed transcripts of the Ca(2+)-activated K(+) channel (K(Ca)) beta(4)-subunit (beta4) (KCNMB4) in cultured astrocytes. Expression of the metabotropic glutamate receptor (mGluR) subtypes mGluR1 and mGluR5 and the ionotropic glutamate receptor (iGluR) subtypes iGluR1 and iGluR4 were detected by RT-PCR and immunofluorescence analysis in cultured astrocytes. The mGluR agonists L-glutamate and quisqualate increased the open state probability (NP(o)) of the 71 and 161 pS K(+) channel currents that were prevented by the mGluR receptor antagonists 1-aminoindan-1,5-dicarboxylic acid or L-(+)-2-amino-3-phosphonopropionic acid and not by the iGluR antagonists (+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imine maleate or CNQX. Activation of the two types of K(+) channel currents by mGluR agonists was attenuated by pertussis toxin and by inhibition of phospholipase C (PLC) or cytochrome P450 arachidonate epoxygenase. These results indicate that brain astrocytes contain the KCNMB4 transcript and express two novel types of K(Ca) channels that are gated by activation of a G-protein coupled metabotropic glutamate receptor functionally linked to PLC and cytochrome P450 arachidonate epoxygenase activity.
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Affiliation(s)
- Debebe Gebremedhin
- Department of Physiology and Cardiovascular Research Center, Medical College of Wisconsin, Milwaukee 53226, USA.
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42
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Flores-Herr N, Protti DA, Wässle H. Synaptic currents generating the inhibitory surround of ganglion cells in the mammalian retina. J Neurosci 2001; 21:4852-63. [PMID: 11425912 PMCID: PMC6762364] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/20/2023] Open
Abstract
The receptive field (RF) of retinal ganglion cells (RGCs) consists of an excitatory central region, the RF center, and an inhibitory peripheral region, the RF surround. It is still unknown in detail which inhibitory interneurons (horizontal or amacrine cells) and which inhibitory circuits (presynaptic or postsynaptic) generate the RF surround. To study surround inhibition, light-evoked whole-cell currents were recorded from RGCs of the isolated, intact rabbit retina. The RFs were stimulated with light or dark spots of increasing diameters and with annular light stimuli. Direct inhibitory currents could be isolated by voltage clamping ganglion cells close to the Na(+)/K(+) reversal potential. They mostly represent an input from GABAergic amacrine cells that contribute to the inhibitory surround of ganglion cells. This direct inhibitory input and its physiological function were also investigated by recording light-evoked action potentials of RGCs in the current-clamp mode and by changing the intracellular Cl(-) concentration. The excitatory input of the ganglion cells could be isolated by voltage clamping ganglion cells at the Cl(-) reversal potential. Large light spots and annular light stimuli caused a strong attenuation of the excitatory input. Both GABA(A) receptors and GABA(C) receptors contributed to this inhibition, and picrotoxinin was able to completely block it. Together, these results show that the RF surround of retinal ganglion cells is mediated by a combination of direct inhibitory synapses and presynaptic surround inhibition.
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Affiliation(s)
- N Flores-Herr
- Neuroanatomische Abteilung, Max-Planck-Institut für Hirnforschung, D-60528 Frankfurt am Main, Germany
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43
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Dupere JR, Dale TJ, Starkey SJ, Xie X. The anticonvulsant BW534U87 depresses epileptiform activity in rat hippocampal slices by an adenosine-dependent mechanism and through inhibition of voltage-gated Na+ channels. Br J Pharmacol 1999; 128:1011-20. [PMID: 10556938 PMCID: PMC1571724 DOI: 10.1038/sj.bjp.0702881] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/1999] [Revised: 08/11/1999] [Accepted: 08/13/1999] [Indexed: 11/08/2022] Open
Abstract
1. The cellular and molecular actions of BW534U87 were studied using intracellular and extracellular recordings from the CA1 region of rat hippocampal slices and whole-cell voltage-clamp recordings of recombinant human brain type IIA Na+ channels expressed in Chinese hamster ovary (CHO) cells. 2. Normal excitatory and inhibitory postsynaptic potentials evoked in hippocampal slices were unaffected by BW534U87 or the adenosine deaminase inhibitor EHNA. However, epileptiform activity was depressed by BW534U87 (50 micronM) and this inhibition was reversed by the adenosine receptor antagonist 8-phenyl theophylline (8-PT, 30 micronM). EHNA (10 micronM) mimicked the effects of BW534U87. Furthermore, BW534U87 enhanced the inhibitory effects of exogenous adenosine on evoked synaptic potentials. BW534U87 (50 micronM) also voltage- and use-dependently inhibited action potentials elicited by current injection, independent of the adenosine system, since it was not affected by 8-PT. 3. In CHO cells expressing the recombinant human brain Na+ channel, BW534U87 produced a concentration- and voltage-dependent inhibition of Na+ currents with a half-maximal inhibitory concentration of 10 micronM at a Vh of -60 mV. Use-dependent inhibition was evident at high-frequencies (20x20 ms pulse train at 10 Hz). 4 In conclusion, BW534U87 blocks hippocampal epileptiform activity by a dual mechanism. The first action is similar to that produced by EHNA and is dependent on endogenous adenosine probably by inhibition of adenosine deaminase. Secondly, BW534U87 directly inhibits voltage-gated Na+ channels in a voltage- and frequency-dependent manner. Both actions of BW534U87 are activity-dependent and may synergistically contribute to its overall anticonvulsant effects in animal models of epilepsy.
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Affiliation(s)
- J R Dupere
- Neuroscience Unit, GlaxoWellcome Research and Development, Medicines Research Centre, Stevenage, Hertfordshire SG1 2NY, U.K
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Meza U, Bannister R, Melliti K, Adams B. Biphasic, opposing modulation of cloned neuronal alpha1E Ca channels by distinct signaling pathways coupled to M2 muscarinic acetylcholine receptors. J Neurosci 1999; 19:6806-17. [PMID: 10436038 PMCID: PMC6782876] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/13/2023] Open
Abstract
Neuronal alpha1E subunits are thought to form R-type Ca channels. When expressed in human embryonic kidney cells with M2 muscarinic acetylcholine receptors, Ca channels encoded by rabbit alpha1E exhibit striking biphasic modulation. Receptor activation first produces rapid inhibition of current amplitude and activation rate. However, in the continued presence of agonist, alpha1E currents subsequently increase. Kinetic slowing persists during this secondary stimulation phase. After receptor deactivation, kinetic slowing is quickly relieved, and current amplitude over-recovers before returning toward control levels. These features indicate that inhibition and stimulation of alpha1E are separate processes, with stimulation superimposed on inhibition. Pertussis toxin eliminates inhibition without affecting stimulation, demonstrating that inhibition and stimulation involve distinct signaling pathways. Neither inhibition nor stimulation is altered by coexpression of Ca channel beta2a or beta3 subunits. Stimulation is abolished by staurosporine and reduced by intracellular 5'-adenylylimidodiphosphate, suggesting that phosphorylation is required. However, stimulation does not seem to involve cAMP-dependent protein kinase, protein kinase C, cGMP-dependent protein kinase, tyrosine kinases, or phosphoinositide 3-kinases. Stimulation does not require a Ca signal, because it is not specifically altered by varying intracellular Ca buffering or by substituting Ba as the charge carrier. In contrast to those formed by alpha1E, Ca channels formed by alpha1A or alpha1B display only inhibition and no stimulation during prolonged activation of M2 receptors. The dual modulation of alpha1E may confer unique physiological properties on native R-type Ca channels. As one possibility, R-type channels may continue to mediate Ca influx during steady inhibition of N-type and P/Q-type channels by muscarinic or other receptors.
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Affiliation(s)
- U Meza
- Department of Physiology and Biophysics, University of Iowa, College of Medicine, Iowa City, Iowa 52242-1109, USA
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45
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Chen N, Luo T, Raymond LA. Subtype-dependence of NMDA receptor channel open probability. J Neurosci 1999; 19:6844-54. [PMID: 10436042 PMCID: PMC6782868] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/13/2023] Open
Abstract
NMDA receptor-mediated calcium transients play a critical role in synaptogenesis, synaptic plasticity, and excitotoxicity. NMDA receptors are heteromeric complexes of NR1A combined with NR2A, NR2B, NR2C, and/or NR2D subunits. The NR2 subunits determine a variety of electrophysiological and pharmacological properties of the NMDA receptor complex. In this report, we provide evidence for the first time that there is also a significant difference in peak channel open probability (P(o)) between NMDA receptors composed of NR1A/NR2A and those of NR1A/NR2B subunits. First, whole-cell patch-clamp recordings from human embryonic kidney (HEK) 293 cells expressing NMDA receptors revealed that NR1A/NR2A-mediated peak current densities are approximately four times larger than those of NR1A/NR2B. We show that this fourfold difference is unlikely caused by differences in receptor surface expression, since these levels were similar for the two subtypes by Western blot analysis. To determine whether P(o) contributed to the difference in peak current densities, we used two different open channel antagonists, MK-801 and 9-aminoacridine, in a variety of experimental paradigms. Our results indicate that peak P(o) is significantly higher (twofold to fivefold) for NR1A/NR2A than NR1A/NR2B, with estimated values of approximately 0.35 and 0.07, respectively. These results suggest that a change in the relative expression levels of NR2A and NR2B can regulate peak amplitude of NMDA receptor-mediated excitatory postsynaptic potentials and therefore may play a role in mechanisms underlying synaptic plasticity.
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Affiliation(s)
- N Chen
- Kinsmen Laboratory of Neurological Research, Department of Psychiatry, University of British Columbia, Vancouver, British Columbia V6T 1Z3 Canada
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46
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Basiry SS, Mendoza P, Lee PD, Raymond LA. Agonist-induced changes in substituted cysteine accessibility reveal dynamic extracellular structure of M3-M4 loop of glutamate receptor GluR6. J Neurosci 1999; 19:644-52. [PMID: 9880585 PMCID: PMC6782208] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/1998] [Revised: 10/30/1998] [Accepted: 11/02/1998] [Indexed: 02/09/2023] Open
Abstract
Recent evidence suggests that the transmembrane topology of ionotropic glutamate receptors differs from other members of the ligand-gated ion channel superfamily. However, the structure of the segment linking membrane domains M3 and M4 (the M3-M4 loop) remains controversial. Although various data indicate that this loop is extracellular, other results suggest that serine residues in this segment are sites of phosphorylation and channel modulation by intracellular protein kinases. To reconcile these data, we hypothesized that the M3-M4 loop structure is dynamic and, more specifically, that the portion containing putative phosphorylation sites may be translocated across the membrane to the cytoplasmic side during agonist binding. To test this hypothesis, we mutated Ser 684, a putative cAMP-dependent protein kinase site in the kainate-type glutamate receptor GluR6, to Cys. Results of biochemical and electrophysiological experiments are consistent with Cys 684 being accessible, in the unliganded state, from the extracellular side to modification by a Cys-specific biotinylating reagent followed by streptavidin (SA). Interestingly, our data suggest that this residue becomes inaccessible to the extracellular biotinylating reagent during agonist binding. However, we find it unlikely that Cys 684 undergoes membrane translocation, because the addition of SA to Cys-biotinylated GluR6(S684C) has no effect on peak glutamate-evoked current and only a small effect on macroscopic desensitization. We conclude that residue 684 in GluR6 is extracellular in the receptor-channel's closed, unliganded state and does not cross the membrane after agonist binding. However, an agonist-induced conformational change in the receptor substantially alters accessibility of position 684 to the extracellular environment.
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Affiliation(s)
- S S Basiry
- Kinsmen Laboratory of Neurological Research, Department of Psychiatry, University of British Columbia, Vancouver, British Columbia V6T 1Z3 Canada
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Colbert CM, Johnston D. Axonal action-potential initiation and Na+ channel densities in the soma and axon initial segment of subicular pyramidal neurons. J Neurosci 1996; 16:6676-86. [PMID: 8824308 PMCID: PMC6579266] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
A long-standing hypothesis is that action potentials initiate first in the axon hillock/initial segment (AH-IS) region because of a locally high density of Na+ channels. We tested this idea in subicular pyramidal neurons by using patch-clamp recordings in hippocampal slices. Simultaneous recordings from the soma and IS confirmed that orthodromic action potentials initiated in the axon and then invaded the soma. However, blocking Na+ channels in the AH-IS with locally applied tetrodotoxin (TTX) did not raise the somatic threshold membrane potential for orthodromic spikes. TTX applied to the axon beyond the AH-IS (30-60 microm from the soma) raised the apparent somatic threshold by approximately 8 mV. We estimated the Na+ current density in the AH-IS and somatic membranes by using cell-attached patch-clamp recordings and found similar magnitudes (3-4 pA/microm2). Thus, the present results suggest that orthodromic action potentials initiate in the axon beyond the AH-IS and that the minimum threshold for spike initiation of the neuron is not determined by a high density of Na+ channels in the AH-IS region.
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Affiliation(s)
- C M Colbert
- Division of Neuroscience, Baylor College of Medicine, Houston, Texas 77030, USA
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