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Yamada A, Ling J, Yamada AI, Furue H, Gu JG. ASICs mediate fast excitatory synaptic transmission for tactile discrimination. Neuron 2024; 112:1286-1301.e8. [PMID: 38359825 PMCID: PMC11031316 DOI: 10.1016/j.neuron.2024.01.018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2023] [Revised: 12/05/2023] [Accepted: 01/16/2024] [Indexed: 02/17/2024]
Abstract
Tactile discrimination, the ability to differentiate objects' physical properties such as texture, shape, and edges, is essential for environmental exploration, social interaction, and early childhood development. This ability heavily relies on Merkel cell-neurite complexes (MNCs), the tactile end-organs enriched in the fingertips of humans and the whisker hair follicles of non-primate mammals. Although recent studies have advanced our knowledge on mechanical transduction in MNCs, it remains unknown how tactile signals are encoded at MNCs. Here, using rodent whisker hair follicles, we show that tactile signals are encoded at MNCs as fast excitatory synaptic transmission. This synaptic transmission is mediated by acid-sensing ion channels (ASICs) located on the neurites of MNCs, with protons as the principal transmitters. Pharmacological inhibition or genetic deletion of ASICs diminishes the tactile encoding at MNCs and impairs tactile discrimination in animals. Together, ASICs are required for tactile encoding at MNCs to enable tactile discrimination in mammals.
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Affiliation(s)
- Akihiro Yamada
- Department of Anesthesiology and Perioperative Medicine, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Jennifer Ling
- Department of Anesthesiology and Perioperative Medicine, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Ayaka I Yamada
- Department of Anesthesiology and Perioperative Medicine, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Hidemasa Furue
- Department of Neurophysiology, Hyogo Medical University, Nishinomiya 663-8501, Japan
| | - Jianguo G Gu
- Department of Anesthesiology and Perioperative Medicine, University of Alabama at Birmingham, Birmingham, AL, USA; Department of Neurobiology, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
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2
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Logan DR, Hall J, Bianchi L. A helping hand: roles for accessory cells in the sense of touch across species. Front Cell Neurosci 2024; 18:1367476. [PMID: 38433863 PMCID: PMC10904576 DOI: 10.3389/fncel.2024.1367476] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2024] [Accepted: 02/05/2024] [Indexed: 03/05/2024] Open
Abstract
During touch, mechanical forces are converted into electrochemical signals by tactile organs made of neurons, accessory cells, and their shared extracellular spaces. Accessory cells, including Merkel cells, keratinocytes, lamellar cells, and glia, play an important role in the sensation of touch. In some cases, these cells are intrinsically mechanosensitive; however, other roles include the release of chemical messengers, the chemical modification of spaces that are shared with neurons, and the tuning of neural sensitivity by direct physical contact. Despite great progress in the last decade, the precise roles of these cells in the sense of touch remains unclear. Here we review the known and hypothesized contributions of several accessory cells to touch by incorporating research from multiple organisms including C. elegans, D. melanogaster, mammals, avian models, and plants. Several broad parallels are identified including the regulation of extracellular ions and the release of neuromodulators by accessory cells, as well as the emerging potential physical contact between accessory cells and sensory neurons via tethers. Our broader perspective incorporates the importance of accessory cells to the understanding of human touch and pain, as well as to animal touch and its molecular underpinnings, which are underrepresented among the animal welfare literature. A greater understanding of touch, which must include a role for accessory cells, is also relevant to emergent technical applications including prosthetics, virtual reality, and robotics.
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Affiliation(s)
| | | | - Laura Bianchi
- Department of Physiology and Biophysics, University of Miami, Miami, FL, United States
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3
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Bataille-Savattier A, Le Gall-Ianotto C, Lebonvallet N, Misery L, Talagas M. Do Merkel complexes initiate mechanical itch? Exp Dermatol 2023; 32:226-234. [PMID: 36208286 DOI: 10.1111/exd.14685] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2022] [Revised: 08/12/2022] [Accepted: 10/05/2022] [Indexed: 11/30/2022]
Abstract
Itch is a common sensation which is amenable to disabling patients' life under pathological and chronic conditions. Shared assertion easily limits itch to chemical itch, without considering mechanical itch and alloknesis, its pathological counterpart. However, in recent years, our understanding of the mechanical itch pathway, particularly in the central nervous system, has been enhanced. In addition, Merkel complexes, conventionally considered as tactile end organs only responsible for light touch perception due to Piezo2 expressed by both Merkel cells and SA1 Aβ-fibres - low threshold mechanical receptors (LTMRs) -, have recently been identified as modulators of mechanical itch. However, the tactile end organs responsible for initiating mechanical itch remain unexplored. The consensus is that some LTMRs, either SA1 Aβ- or A∂- and C-, are cutaneous initiators of mechanical itch, even though they are not self-sufficient to finely detect and encode light mechanical stimuli into sensory perceptions, which depend on the entire hosting tactile end organ. Consequently, to enlighten our understanding of mechanical itch initiation, this article discusses the opportunity to consider Merkel complexes as potential tactile end organs responsible for initiating mechanical itch, under both healthy and pathological conditions. Their unsuspected modulatory abilities indeed show that they are tuned to detect and encode light mechanical stimuli leading to mechanical itch, especially as they host not only SA1 Aβ-LTMRs but also A∂- and C-fibres.
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Affiliation(s)
| | | | | | - Laurent Misery
- University of Brest, LIEN, Brest, France.,CHU Brest, Department of Dermatology, Brest, France
| | - Matthieu Talagas
- University of Brest, LIEN, Brest, France.,CHU Brest, Department of Dermatology, Brest, France
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4
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Bataille A, Le Gall C, Misery L, Talagas M. Merkel Cells Are Multimodal Sensory Cells: A Review of Study Methods. Cells 2022; 11:cells11233827. [PMID: 36497085 PMCID: PMC9737130 DOI: 10.3390/cells11233827] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2022] [Revised: 11/23/2022] [Accepted: 11/24/2022] [Indexed: 12/05/2022] Open
Abstract
Merkel cells (MCs) are rare multimodal epidermal sensory cells. Due to their interactions with slowly adapting type 1 (SA1) Aβ low-threshold mechanoreceptor (Aβ-LTMRs) afferents neurons to form Merkel complexes, they are considered to be part of the main tactile terminal organ involved in the light touch sensation. This function has been explored over time by ex vivo, in vivo, in vitro, and in silico approaches. Ex vivo studies have made it possible to characterize the topography, morphology, and cellular environment of these cells. The interactions of MCs with surrounding cells continue to be studied by ex vivo but also in vitro approaches. Indeed, in vitro models have improved the understanding of communication of MCs with other cells present in the skin at the cellular and molecular levels. As for in vivo methods, the sensory role of MC complexes can be demonstrated by observing physiological or pathological behavior after genetic modification in mouse models. In silico models are emerging and aim to elucidate the sensory coding mechanisms of these complexes. The different methods to study MC complexes presented in this review may allow the investigation of their involvement in other physiological and pathophysiological mechanisms, despite the difficulties in exploring these cells, in particular due to their rarity.
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Affiliation(s)
- Adeline Bataille
- LIEN—Laboratoire Interactions Epithélium Neurones, Brest University, F-29200 Brest, France
- Correspondence:
| | - Christelle Le Gall
- LIEN—Laboratoire Interactions Epithélium Neurones, Brest University, F-29200 Brest, France
- Department of Dermatology, Brest University Hospital, F-29200 Brest, France
| | - Laurent Misery
- LIEN—Laboratoire Interactions Epithélium Neurones, Brest University, F-29200 Brest, France
- Department of Dermatology, Brest University Hospital, F-29200 Brest, France
| | - Matthieu Talagas
- LIEN—Laboratoire Interactions Epithélium Neurones, Brest University, F-29200 Brest, France
- Department of Dermatology, Brest University Hospital, F-29200 Brest, France
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5
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Sonekatsu M, Yamada H, Nishio N, Gu JG. Effects on low threshold mechanoreceptors in whisker hair follicles by 5-HT, Cd 2+, tetraethylammonium, 4-aminopyridine, and Ba 2. Mol Pain 2022; 18:17448069221076606. [PMID: 35189758 PMCID: PMC8873973 DOI: 10.1177/17448069221076606] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Low threshold mechanoreceptors (LTMRs) are important for environmental exploration, social interaction, and tactile discrimination. Whisker hair follicles are mechanical sensory organs in non-primate mammals that are functionally equivalent to human fingertips. Several functional types of LTMRs have been identified in rodent whisker hair follicles, including rapidly adapting (RA), slow adapting type 1 (SA1), and slowly adapting type 2 (SA2) LTMRs. Properties of these LTMRs have not been fully characterized. In the present study, we have used pressure-clamped single-fiber recording technique to record impulses of RA, SA1, and SA2 LTMRs in mouse whisker hair follicles, and tested effects of 5-HT, Cd2+, tetraethylammonium (TEA), 4-aminopyridine (4-AP), and Ba2+ on the LTMR impulses. We show that 5-HT at 2 mM suppresses SA1 impulses but has no effects on RA and SA2 impulses. Cd2+ at 100 μM suppresses both SA1 and SA2 impulses but has no effects on RA impulses. TEA at 10 mM has no effects on RA and SA1 impulses but increased SA2 impulses. However, TEA at 1 mM and 200 μM decreases SA2 impulses. 4-AP at 1 mM suppresses both SA1 and SA2 impulses but has no effects on RA impulses. Ba2+ at 5 mM increases both RA and SA1 impulses but suppresses SA2 impulses. Collectively, RA, SA1, and SA2 LTMRs show distinct pharmacological properties, suggesting that these LTMRs may use different mechanisms to tune their mechanical signaling.
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Affiliation(s)
- Mayumi Sonekatsu
- Department of Anesthesiology and Perioperative Medicine, School of Medicine, University of Alabama at Birmingham, Birmingham, AL, USA.,Department of Orthopaedic Surgery, 13145Wakayama Medical University, Wakayama, Japan
| | - Hiroshi Yamada
- Department of Orthopaedic Surgery, 13145Wakayama Medical University, Wakayama, Japan
| | - Naoko Nishio
- Department of Orthopaedic Surgery, 13145Wakayama Medical University, Wakayama, Japan
| | - Jianguo G Gu
- Department of Anesthesiology and Perioperative Medicine, School of Medicine, University of Alabama at Birmingham, Birmingham, AL, USA
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6
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Cárcaba L, García-Piqueras J, García-Mesa Y, Cobo R, García-Suárez O, Feito J, Vega JA. Human digital merkel cells display pannexin1 immunoreactivity. Ann Anat 2021; 239:151813. [PMID: 34384856 DOI: 10.1016/j.aanat.2021.151813] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2021] [Revised: 07/22/2021] [Accepted: 07/26/2021] [Indexed: 10/20/2022]
Abstract
Pannexins are channel proteins displaying functional similarities to gap junctions in vertebrates and are regarded as transmembrane ATP-releasing channels. A member of this family, denominate pannexin1, has been detected in the epidermis and cutaneous adnexal structures. Here we used immunohistochemistry to investigate whether human digital Merkel cells express this protein since ATP is postulated as a neurotransmitter in the Merkel cell-axon complexes low-threshold mecahoreceptors. Pannexin1 immunoreactivity was found in cytokeratine 20-, chromogranin A- and synaptophysin-positive cells placed at the basal layer of the epidermis. Cell displaying pannexin1 immunoreactivities were thus identified as Merkel cells and showed close contact with nerve profiles. Light pannexin1 immunoreactivity in dermal blood vessels was also verified. Present results demonstrate for the first time the expression of pannexin1 in human digital Merkel cells supporting the idea that ATP can be involved directly or indirectly in the mechanotransductional process at Merkel-axon complexes.
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Affiliation(s)
- Lucia Cárcaba
- Departamento de Morfología y Biología Celular, Grupo SINPOS, Universidad de Oviedo, Spain
| | - Jorge García-Piqueras
- Departamento de Morfología y Biología Celular, Grupo SINPOS, Universidad de Oviedo, Spain
| | - Yolanda García-Mesa
- Departamento de Morfología y Biología Celular, Grupo SINPOS, Universidad de Oviedo, Spain
| | - Ramón Cobo
- Departamento de Morfología y Biología Celular, Grupo SINPOS, Universidad de Oviedo, Spain
| | - Olivia García-Suárez
- Departamento de Morfología y Biología Celular, Grupo SINPOS, Universidad de Oviedo, Spain
| | - Jorge Feito
- Departamento de Morfología y Biología Celular, Grupo SINPOS, Universidad de Oviedo, Spain; Servicio de Anatomía Patológica, Complejo Hospitalario Universitario de Salamanca, Salamanca, Spain; Departamento de Anatomía e Histología Humanas, Universidad de Salamanca, Salamanca, Spain
| | - José A Vega
- Departamento de Morfología y Biología Celular, Grupo SINPOS, Universidad de Oviedo, Spain; Facultad de Ciencias de la Salud, Universidad Autónoma de Chile, Santiago de Chile, Chile.
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7
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Chang W, Gu JG. Effects on tactile transmission by serotonin transporter inhibitors at Merkel discs of mouse whisker hair follicles. Mol Pain 2021; 16:1744806920938237. [PMID: 32600103 PMCID: PMC7328215 DOI: 10.1177/1744806920938237] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The Merkel disc is a main type of tactile end organs formed by Merkel cells and
Aβ-afferent endings as first tactile sensory synapses. They are highly abundant in
fingertips, touch domes, and whisker hair follicles of mammals and are essential for
sensory tasks including social interaction, environmental exploration, and tactile
discrimination. We have recently shown that Merkel discs use serotonin to transmit tactile
signals from Merkel cells to Aβ-afferent endings to drive slowly adapting type 1 impulses
on the Aβ-afferent nerves. This raises a question as whether the serotoninergic
transmission at Merkel discs may be regulated by serotonin transporters and whether
serotonin transporter inhibitors may affect the tactile transmission. Here, we made
recordings from whisker afferent nerves of mouse whisker hair follicles and tested the
effects of monoamine transporter inhibitors on slowly adapting type 1 impulses. We show
that methamphetamine, a monoamine releasing facilitator and reuptake inhibitor, elicited
spontaneous impulses as well as increased the numbers of slowly adapting type 1 impulses
elicited by whisker hair deflections. S-duloxetine, a potent inhibitor of transporters of
serotonin and norepinephrine, and fluoxetine, a selective inhibitor of serotonin
transporters, both also increased the numbers of slowly adapting type 1 impulses.
Prolonged treatment of whisker hair follicles with methamphetamine abolished most of
slowly adapting type 1 impulses. Furthermore, the treatment of whisker hair follicles with
methamphetamine resulted in serotonin release from whisker hair follicles. Taken together,
our results suggest that serotonin transporters play a role in regulating tactile
transmission at Merkel discs.
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Affiliation(s)
- Weipang Chang
- Department of Anesthesiology and Perioperative Medicine, School of Medicine, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Jianguo G Gu
- Department of Anesthesiology and Perioperative Medicine, School of Medicine, University of Alabama at Birmingham, Birmingham, AL, USA
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8
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Pathogenic mechanisms of lipid mediator lysophosphatidic acid in chronic pain. Prog Lipid Res 2020; 81:101079. [PMID: 33259854 DOI: 10.1016/j.plipres.2020.101079] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2020] [Revised: 11/22/2020] [Accepted: 11/23/2020] [Indexed: 02/07/2023]
Abstract
A number of membrane lipid-derived mediators play pivotal roles in the initiation, maintenance, and regulation of various types of acute and chronic pain. Acute pain, comprising nociceptive and inflammatory pain warns us about the presence of damage or harmful stimuli. However, it can be efficiently reversed by opioid analgesics and anti-inflammatory drugs. Prostaglandin E2 and I2, the representative lipid mediators, are well-known causes of acute pain. However, some lipid mediators such as lipoxins, resolvins or endocannabinoids suppress acute pain. Various types of peripheral and central neuropathic pain (NeuP) as well as fibromyalgia (FM) are representatives of chronic pain and refractory owing to abnormal pain processing distinct from acute pain. Accumulating evidence demonstrated that lipid mediators represented by lysophosphatidic acid (LPA) are involved in the initiation and maintenance of both NeuP and FM in experimental animal models. The LPAR1-mediated peripheral mechanisms including dorsal root demyelination, Cavα2δ1 expression in dorsal root ganglion, and LPAR3-mediated amplification of central LPA production via glial cells are involved in the series of molecular mechanisms underlying NeuP. This review also discusses the involvement of lipid mediators in emerging research directives, including itch-sensing, sexual dimorphism, and the peripheral immune system.
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9
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Peripheral Mechanobiology of Touch-Studies on Vertebrate Cutaneous Sensory Corpuscles. Int J Mol Sci 2020; 21:ijms21176221. [PMID: 32867400 PMCID: PMC7504094 DOI: 10.3390/ijms21176221] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2020] [Revised: 08/19/2020] [Accepted: 08/24/2020] [Indexed: 12/21/2022] Open
Abstract
The vertebrate skin contains sensory corpuscles that are receptors for different qualities of mechanosensitivity like light brush, touch, pressure, stretch or vibration. These specialized sensory organs are linked anatomically and functionally to mechanosensory neurons, which function as low-threshold mechanoreceptors connected to peripheral skin through Aβ nerve fibers. Furthermore, low-threshold mechanoreceptors associated with Aδ and C nerve fibers have been identified in hairy skin. The process of mechanotransduction requires the conversion of a mechanical stimulus into electrical signals (action potentials) through the activation of mechanosensible ion channels present both in the axon and the periaxonal cells of sensory corpuscles (i.e., Schwann-, endoneurial- and perineurial-related cells). Most of those putative ion channels belong to the degenerin/epithelial sodium channel (especially the family of acid-sensing ion channels), the transient receptor potential channel superfamilies, and the Piezo family. This review updates the current data about the occurrence and distribution of putative mechanosensitive ion channels in cutaneous mechanoreceptors including primary sensory neurons and sensory corpuscles.
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10
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Hoffman BU, Baba Y, Griffith TN, Mosharov EV, Woo SH, Roybal DD, Karsenty G, Patapoutian A, Sulzer D, Lumpkin EA. Merkel Cells Activate Sensory Neural Pathways through Adrenergic Synapses. Neuron 2018; 100:1401-1413.e6. [PMID: 30415995 DOI: 10.1016/j.neuron.2018.10.034] [Citation(s) in RCA: 74] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2018] [Revised: 09/21/2018] [Accepted: 10/22/2018] [Indexed: 01/06/2023]
Abstract
Epithelial-neuronal signaling is essential for sensory encoding in touch, itch, and nociception; however, little is known about the release mechanisms and neurotransmitter receptors through which skin cells govern neuronal excitability. Merkel cells are mechanosensory epidermal cells that have long been proposed to activate neuronal afferents through chemical synaptic transmission. We employed a set of classical criteria for chemical neurotransmission as a framework to test this hypothesis. RNA sequencing of adult mouse Merkel cells demonstrated that they express presynaptic molecules and biosynthetic machinery for adrenergic transmission. Moreover, live-cell imaging directly demonstrated that Merkel cells mediate activity- and VMAT-dependent release of fluorescent catecholamine neurotransmitter analogs. Touch-evoked firing in Merkel-cell afferents was inhibited either by pre-synaptic silencing of SNARE-mediated vesicle release from Merkel cells or by neuronal deletion of β2-adrenergic receptors. Together, these results identify both pre- and postsynaptic mechanisms through which Merkel cells excite mechanosensory afferents to encode gentle touch. VIDEO ABSTRACT.
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Affiliation(s)
- Benjamin U Hoffman
- Department of Physiology & Cellular Biophysics, Columbia University, New York, NY, USA; Program in Neurobiology & Behavior, Columbia University, New York, NY, USA
| | - Yoshichika Baba
- Department of Physiology & Cellular Biophysics, Columbia University, New York, NY, USA
| | - Theanne N Griffith
- Department of Physiology & Cellular Biophysics, Columbia University, New York, NY, USA
| | - Eugene V Mosharov
- Departments of Psychiatry, Neurology, and Pharmacology, Columbia University: Division of Molecular Therapeutics, New York State Psychiatric Institute, New York, NY, USA
| | - Seung-Hyun Woo
- The Scripps Research Institute & Howard Hughes Medical Institute, La Jolla, CA, USA
| | - Daniel D Roybal
- Pharmacology Graduate Program, Columbia University, New York, NY, USA
| | - Gerard Karsenty
- Department of Genetics and Development, Columbia University, New York, NY, USA
| | - Ardem Patapoutian
- The Scripps Research Institute & Howard Hughes Medical Institute, La Jolla, CA, USA
| | - David Sulzer
- Departments of Psychiatry, Neurology, and Pharmacology, Columbia University: Division of Molecular Therapeutics, New York State Psychiatric Institute, New York, NY, USA
| | - Ellen A Lumpkin
- Department of Physiology & Cellular Biophysics, Columbia University, New York, NY, USA; Program in Neurobiology & Behavior, Columbia University, New York, NY, USA; Department of Dermatology, Columbia University, New York, NY, USA.
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11
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Hyperpolarization-activated current I h in mouse trigeminal sensory neurons in a transgenic mouse model of familial hemiplegic migraine type-1. Neuroscience 2017; 351:47-64. [DOI: 10.1016/j.neuroscience.2017.03.033] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2016] [Revised: 03/15/2017] [Accepted: 03/20/2017] [Indexed: 12/19/2022]
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