1
|
Bhoi JD, Goel M, Ribelayga CP, Mangel SC. Circadian clock organization in the retina: From clock components to rod and cone pathways and visual function. Prog Retin Eye Res 2023; 94:101119. [PMID: 36503722 PMCID: PMC10164718 DOI: 10.1016/j.preteyeres.2022.101119] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2020] [Revised: 08/22/2022] [Accepted: 08/25/2022] [Indexed: 12/13/2022]
Abstract
Circadian (24-h) clocks are cell-autonomous biological oscillators that orchestrate many aspects of our physiology on a daily basis. Numerous circadian rhythms in mammalian and non-mammalian retinas have been observed and the presence of an endogenous circadian clock has been demonstrated. However, how the clock and associated rhythms assemble into pathways that support and control retina function remains largely unknown. Our goal here is to review the current status of our knowledge and evaluate recent advances. We describe many previously-observed retinal rhythms, including circadian rhythms of morphology, biochemistry, physiology, and gene expression. We evaluate evidence concerning the location and molecular machinery of the retinal circadian clock, as well as consider findings that suggest the presence of multiple clocks. Our primary focus though is to describe in depth circadian rhythms in the light responses of retinal neurons with an emphasis on clock control of rod and cone pathways. We examine evidence that specific biochemical mechanisms produce these daily light response changes. We also discuss evidence for the presence of multiple circadian retinal pathways involving rhythms in neurotransmitter activity, transmitter receptors, metabolism, and pH. We focus on distinct actions of two dopamine receptor systems in the outer retina, a dopamine D4 receptor system that mediates circadian control of rod/cone gap junction coupling and a dopamine D1 receptor system that mediates non-circadian, light/dark adaptive regulation of gap junction coupling between horizontal cells. Finally, we evaluate the role of circadian rhythmicity in retinal degeneration and suggest future directions for the field of retinal circadian biology.
Collapse
Affiliation(s)
- Jacob D Bhoi
- Ruiz Department of Ophthalmology and Visual Science, McGovern Medical School, UTHEALTH-The University of Texas Health Science Center at Houston, Houston, TX, USA; Neuroscience Honors Research Program, William Marsh Rice University, Houston, TX, USA
| | - Manvi Goel
- Department of Neuroscience, Wexner Medical Center, College of Medicine, The Ohio State University, Columbus, OH, USA
| | - Christophe P Ribelayga
- Ruiz Department of Ophthalmology and Visual Science, McGovern Medical School, UTHEALTH-The University of Texas Health Science Center at Houston, Houston, TX, USA; Neuroscience Honors Research Program, William Marsh Rice University, Houston, TX, USA.
| | - Stuart C Mangel
- Department of Neuroscience, Wexner Medical Center, College of Medicine, The Ohio State University, Columbus, OH, USA.
| |
Collapse
|
2
|
Abstract
Voltage-gated Ca2+ (Cav) channels play pivotal roles in regulating gene transcription, neuronal excitability, and neurotransmitter release. To meet the spatial and temporal demands of visual signaling, Cav channels exhibit unusual properties in the retina compared to their counterparts in other areas of the nervous system. In this article, we review current concepts regarding the specific subtypes of Cav channels expressed in the retina, their intrinsic properties and forms of modulation, and how their dysregulation could lead to retinal disease.
Collapse
Affiliation(s)
- Brittany Williams
- Department of Cell Biology & Physiology, Carolina Institute for Developmental Disabilities, and Neuroscience Center, University of North Carolina, Chapel Hill, North Carolina, USA
| | - J Wesley Maddox
- Department of Neuroscience, University of Texas, Austin, Texas, USA;
| | - Amy Lee
- Department of Neuroscience, University of Texas, Austin, Texas, USA;
| |
Collapse
|
3
|
Li Q, Zhu H, Fan M, Sun J, Reinach PS, Wang Y, Qu J, Zhou X, Zhao F. Form-deprivation myopia downregulates calcium levels in retinal horizontal cells in mice. Exp Eye Res 2022; 218:109018. [PMID: 35240197 DOI: 10.1016/j.exer.2022.109018] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2021] [Revised: 02/14/2022] [Accepted: 02/25/2022] [Indexed: 11/25/2022]
Abstract
The process of eye axis lengthening in myopic eyes is regulated by multiple mechanisms in the retina, and horizontal cells (HCs) are an essential interneuron in the visual regulatory system. Wherein intracellular Ca2+ plays an important role in the events involved in the regulatory role of HCs in the retinal neural network. It is unknown if intracellular Ca2+ regulation in HCs mediates changes in the retinal neural network during myopia progression. We describe here a novel calcium fluorescence indicator system that monitors HCs' intracellular Ca2+ levels during form-deprivation myopia (FDM) in mice. AAV injection of GCaMP6s, as a protein calcium sensor, into a Gja10-Cre mouse monitored the changes in Ca2+signaling in HC that accompany FDM progression in mice. An alternative Gja10-Cre/Ai96-GCaMP6s mouse model was created by cross mating Gja10-Cre with Ai96 mice. Immunofluorescence imaging and live imaging of the retinal cells verified the identity of these animal models. Changes in retinal horizontal cellular Ca2+ levels were resolved during FDM development. The numbers of GCaMP6s and the proportion of HCs were tracked based on profiling changes in GCaMP6s+calbindin+/calbindin+ coimmunostaining patterns. They significantly decreased more after either two days (P < 0.01) or two weeks (P < 0.001) in form deprived eyes than in the untreated fellow eyes. These decreases in their proportion reached significance only in the retinal central region rather than also in the retinal periphery. A novel approach employing a GCaMP6s mouse model was developed that may ultimately clarify if HCs mediate Ca2+ signals that contribute to controlling FDM progression in mice. The results indicate so far that FDM progression is associated with declines in HC Ca2+ signaling activity.
Collapse
Affiliation(s)
- Qihang Li
- School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, China; State Key Laboratory of Optometry, Ophthalmology and Vision Science, Wenzhou, Zhejiang, China
| | - He Zhu
- School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, China; State Key Laboratory of Optometry, Ophthalmology and Vision Science, Wenzhou, Zhejiang, China
| | - Miaomiao Fan
- School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, China; State Key Laboratory of Optometry, Ophthalmology and Vision Science, Wenzhou, Zhejiang, China
| | - Jing Sun
- School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, China; State Key Laboratory of Optometry, Ophthalmology and Vision Science, Wenzhou, Zhejiang, China
| | - Peter S Reinach
- School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, China; State Key Laboratory of Optometry, Ophthalmology and Vision Science, Wenzhou, Zhejiang, China
| | - Yuhan Wang
- School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, China; State Key Laboratory of Optometry, Ophthalmology and Vision Science, Wenzhou, Zhejiang, China
| | - Jia Qu
- School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, China; State Key Laboratory of Optometry, Ophthalmology and Vision Science, Wenzhou, Zhejiang, China; Research Unit of Myopia Basic Research and Clinical Prevention and Control, Chinese Academy of Medical Sciences (2019RU025), Wenzhou, Zhejiang, China; Oujiang Laboratory, Zhejiang Lab for Regenerative Medicine, Vision and Brain Health, Wenzhou, Zhejiang, China
| | - Xiangtian Zhou
- School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, China; State Key Laboratory of Optometry, Ophthalmology and Vision Science, Wenzhou, Zhejiang, China; Research Unit of Myopia Basic Research and Clinical Prevention and Control, Chinese Academy of Medical Sciences (2019RU025), Wenzhou, Zhejiang, China; Oujiang Laboratory, Zhejiang Lab for Regenerative Medicine, Vision and Brain Health, Wenzhou, Zhejiang, China.
| | - Fuxin Zhao
- School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, China; State Key Laboratory of Optometry, Ophthalmology and Vision Science, Wenzhou, Zhejiang, China.
| |
Collapse
|
4
|
Alijevic O, Peng Z, Kellenberger S. Changes in H +, K +, and Ca 2+ Concentrations, as Observed in Seizures, Induce Action Potential Signaling in Cortical Neurons by a Mechanism That Depends Partially on Acid-Sensing Ion Channels. Front Cell Neurosci 2021; 15:732869. [PMID: 34720879 PMCID: PMC8553998 DOI: 10.3389/fncel.2021.732869] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Accepted: 09/27/2021] [Indexed: 11/13/2022] Open
Abstract
Acid-sensing ion channels (ASICs) are activated by extracellular acidification. Because ASIC currents are transient, these channels appear to be ideal sensors for detecting the onset of rapid pH changes. ASICs are involved in neuronal death after ischemic stroke, and in the sensation of inflammatory pain. Ischemia and inflammation are associated with a slowly developing, long-lasting acidification. Recent studies indicate however that ASICs are unable to induce an electrical signaling activity under standard experimental conditions if pH changes are slow. In situations associated with slow and sustained pH drops such as high neuronal signaling activity and ischemia, the extracellular K+ concentration increases, and the Ca2+ concentration decreases. We hypothesized that the concomitant changes in H+, K+, and Ca2+ concentrations may allow a long-lasting ASIC-dependent induction of action potential (AP) signaling. We show that for acidification from pH7.4 to pH7.0 or 6.8 on cultured cortical neurons, the number of action potentials and the firing time increased strongly if the acidification was accompanied by a change to higher K+ and lower Ca2+ concentrations. Under these conditions, APs were also induced in neurons from ASIC1a-/- mice, in which a pH of ≤ 5.0 would be required to activate ASICs, indicating that ASIC activation was not required for the AP induction. Comparison between neurons of different ASIC genotypes indicated that the ASICs modulate the AP induction under such changed ionic conditions. Voltage-clamp measurements of the Na+ and K+ currents in cultured cortical neurons showed that the lowering of the pH inhibited Na+ and K+ currents. In contrast, the lowering of the Ca2+ together with the increase in the K+ concentration led to a hyperpolarizing shift of the activation voltage dependence of voltage-gated Na+ channels. We conclude that the ionic changes observed during high neuronal activity mediate a sustained AP induction caused by the potentiation of Na+ currents, a membrane depolarization due to the changed K+ reversal potential, the activation of ASICs, and possibly effects on other ion channels. Our study describes therefore conditions under which slow pH changes induce neuronal signaling by a mechanism involving ASICs.
Collapse
Affiliation(s)
- Omar Alijevic
- Department of Biomedical Sciences, University of Lausanne, Lausanne, Switzerland
| | - Zhong Peng
- Department of Biomedical Sciences, University of Lausanne, Lausanne, Switzerland
| | - Stephan Kellenberger
- Department of Biomedical Sciences, University of Lausanne, Lausanne, Switzerland
| |
Collapse
|
5
|
Vila A, Shihabeddin E, Zhang Z, Santhanam A, Ribelayga CP, O'Brien J. Synaptic Scaffolds, Ion Channels and Polyamines in Mouse Photoreceptor Synapses: Anatomy of a Signaling Complex. Front Cell Neurosci 2021; 15:667046. [PMID: 34393723 PMCID: PMC8356055 DOI: 10.3389/fncel.2021.667046] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2021] [Accepted: 07/05/2021] [Indexed: 12/29/2022] Open
Abstract
Synaptic signaling complexes are held together by scaffold proteins, each of which is selectively capable of interacting with a number of other proteins. In previous studies of rabbit retina, we found Synapse-Associated Protein-102 (SAP102) and Channel Associated Protein of Synapse-110 (Chapsyn110) selectively localized in the tips of horizontal cell processes at contacts with rod and cone photoreceptors, along with several interacting ion channels. We have examined the equivalent suites of proteins in mouse retina and found similarities and differences. In the mouse retina we identified Chapsyn110 as the scaffold selectively localized in the tips of horizontal cells contacting photoreceptors, with Sap102 more diffusely present. As in rabbit, the inward rectifier potassium channel Kir2.1 was present with Chapsyn110 on the tips of horizontal cell dendrites within photoreceptor invaginations, where it could provide a hyperpolarization-activated current that could contribute to ephaptic signaling in the photoreceptor synapses. Pannexin 1 and Pannexin 2, thought to play a role in ephaptic and/or pH mediated signaling, were present in the outer plexiform layer, but likely not in the horizontal cells. Polyamines regulate many ion channels and control the degree of rectification of Kir2.1 by imposing a voltage-dependent block. During the day polyamine immunolabeling was unexpectedly high in photoreceptor terminals compared to other areas of the retina. This content was significantly lower at night, when polyamine content was predominantly in Müller glia, indicating daily rhythms of polyamine content. Both rod and cone terminals displayed the same rhythm. While polyamine content was not prominent in horizontal cells, if polyamines are released, they may regulate the activity of Kir2.1 channels located in the tips of HCs. The rhythmic change in polyamine content of photoreceptor terminals suggests that a daily rhythm tunes the behavior of suites of ion channels within the photoreceptor synapses.
Collapse
Affiliation(s)
- Alejandro Vila
- Richard S. Ruiz M.D. Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, Houston, TX, United States.,MD Anderson Cancer Center, UTHealth Graduate School of Biomedical Sciences, Houston, TX, United States
| | - Eyad Shihabeddin
- Richard S. Ruiz M.D. Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, Houston, TX, United States.,MD Anderson Cancer Center, UTHealth Graduate School of Biomedical Sciences, Houston, TX, United States
| | - Zhijing Zhang
- Richard S. Ruiz M.D. Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Abirami Santhanam
- Richard S. Ruiz M.D. Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Christophe P Ribelayga
- Richard S. Ruiz M.D. Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, Houston, TX, United States.,MD Anderson Cancer Center, UTHealth Graduate School of Biomedical Sciences, Houston, TX, United States
| | - John O'Brien
- Richard S. Ruiz M.D. Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, Houston, TX, United States.,MD Anderson Cancer Center, UTHealth Graduate School of Biomedical Sciences, Houston, TX, United States
| |
Collapse
|
6
|
Baer SM, Chang S, Crook SM, Gardner CL, Jones JR, Ringhofer C, Nelson RF. A multiscale continuum model of the vertebrate outer retina: The temporal dynamics of background-induced flicker enhancement. J Theor Biol 2021; 525:110763. [PMID: 34000285 DOI: 10.1016/j.jtbi.2021.110763] [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: 06/20/2020] [Revised: 04/28/2021] [Accepted: 05/07/2021] [Indexed: 11/25/2022]
Abstract
The retina is a part of the central nervous system that is accessible, well documented, and studied by researchers spanning the clinical, experimental, and theoretical sciences. Here, we mathematically model the subcircuits of the outer plexiform layer of the retina on two spatial scales: that of an individual synapse and that of the scale of the receptive field (hundreds to thousands of synapses). To this end we formulate a continuum spine model (a partial differential equation system) that incorporates the horizontal cell syncytium and its numerous processes (spines) within cone pedicles. With this multiscale modeling approach, detailed biophysical mechanisms at the synaptic level are retained while scaling up to the receptive field level. As an example of its utility, the model is applied to study background-induced flicker enhancement in which the onset of a dim background enhances the center flicker response of horizontal cells. Simulation results, in comparison with flicker enhancement data for square, slit, and disk test regions, suggest that feedback mechanisms that are voltage-axis modulators of cone calcium channels (for example, ephaptic and/or pH feedback) are robust in capturing the temporal dynamics of background-induced flicker enhancement. The value and potential of this continuum spine approach is that it provides a framework for mathematically modeling the input-output properties of the entire receptive field of the outer retina while implementing the latest models for transmission mechanisms at the synaptic level.
Collapse
Affiliation(s)
- Steven M Baer
- School of Mathematical and Statistical Sciences, Arizona State University, Tempe, AZ 85287, United States.
| | - Shaojie Chang
- School of Mathematical and Statistical Sciences, Arizona State University, Tempe, AZ 85287, United States; The High School Affiliated to Beijing Normal University, Beijing 100052, PR China
| | - Sharon M Crook
- School of Mathematical and Statistical Sciences, Arizona State University, Tempe, AZ 85287, United States
| | - Carl L Gardner
- School of Mathematical and Statistical Sciences, Arizona State University, Tempe, AZ 85287, United States
| | - Jeremiah R Jones
- School of Mathematical and Statistical Sciences, Arizona State University, Tempe, AZ 85287, United States
| | - Christian Ringhofer
- School of Mathematical and Statistical Sciences, Arizona State University, Tempe, AZ 85287, United States
| | - Ralph F Nelson
- Neural Circuits Unit, Basic Neuroscience Program, NINDS, NIH, Bethesda, MD 20892, United States
| |
Collapse
|
7
|
Efficient measurements for the dynamic range of human lightness perception. Jpn J Ophthalmol 2021; 65:432-438. [PMID: 33420857 DOI: 10.1007/s10384-020-00808-2] [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: 06/05/2020] [Accepted: 10/23/2020] [Indexed: 10/22/2022]
Abstract
PURPOSE Patients with an eye disease often report nyctalopia, hemianopia, and/or photophobia. We hypothesized that such symptoms are related to the disease impacting the dynamic range of lightness perception (DRL). However, there is currently no standardized approach for measuring DRL for clinical use. We developed an efficient measurement method to estimate DRL. STUDY DESIGN Clinical trial METHODS: Fifty-five photophobic patients with eye disease and 46 controls participated. Each participant judged the appearance of visual stimuli, a thick bar with luminance that gradually changed from maximum to minimum was displayed on uniform background. On different trials the background luminance changed pseudo-randomly between three levels. The participants repeatedly tapped a border on the bar that divided the appearance of grayish white/black and perfect white/black. We defined the DRL as the ratio between the luminance values at the tapped point of the border between gray and white/black. RESULTS The mean DRL of the patients was approximately 15 dB, significantly smaller than that of the controls (20 dB). The center of each patient's DRL shift depending on background luminance, which we named index of contextual susceptibility (iCS), was significantly larger than controls. The DRL of retinitis pigmentosa was smaller than controls for every luminance condition. Only the iCS of glaucoma was significantly larger than controls. CONCLUSIONS This measurement technique detects an abnormality of the DRL. The results support our hypothesis that the DRL abnormality characterizes lightness-relevant symptoms that may elucidate the causes of nyctalopia, hemeralopia, and photophobia.
Collapse
|
8
|
Hirano AA, Vuong HE, Kornmann HL, Schietroma C, Stella SL, Barnes S, Brecha NC. Vesicular Release of GABA by Mammalian Horizontal Cells Mediates Inhibitory Output to Photoreceptors. Front Cell Neurosci 2020; 14:600777. [PMID: 33335476 PMCID: PMC7735995 DOI: 10.3389/fncel.2020.600777] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2020] [Accepted: 11/04/2020] [Indexed: 12/14/2022] Open
Abstract
Feedback inhibition by horizontal cells regulates rod and cone photoreceptor calcium channels that control their release of the neurotransmitter glutamate. This inhibition contributes to synaptic gain control and the formation of the center-surround antagonistic receptive fields passed on to all downstream neurons, which is important for contrast sensitivity and color opponency in vision. In contrast to the plasmalemmal GABA transporter found in non-mammalian horizontal cells, there is evidence that the mechanism by which mammalian horizontal cells inhibit photoreceptors involves the vesicular release of the inhibitory neurotransmitter GABA. Historically, inconsistent findings of GABA and its biosynthetic enzyme, L-glutamate decarboxylase (GAD) in horizontal cells, and the apparent lack of surround response block by GABAergic agents diminished support for GABA's role in feedback inhibition. However, the immunolocalization of the vesicular GABA transporter (VGAT) in the dendritic and axonal endings of horizontal cells that innervate photoreceptor terminals suggested GABA was released via vesicular exocytosis. To test the idea that GABA is released from vesicles, we localized GABA and GAD, multiple SNARE complex proteins, synaptic vesicle proteins, and Cav channels that mediate exocytosis to horizontal cell dendritic tips and axonal terminals. To address the perceived relative paucity of synaptic vesicles in horizontal cell endings, we used conical electron tomography on mouse and guinea pig retinas that revealed small, clear-core vesicles, along with a few clathrin-coated vesicles and endosomes in horizontal cell processes within photoreceptor terminals. Some small-diameter vesicles were adjacent to the plasma membrane and plasma membrane specializations. To assess vesicular release, a functional assay involving incubation of retinal slices in luminal VGAT-C antibodies demonstrated vesicles fused with the membrane in a depolarization- and calcium-dependent manner, and these labeled vesicles can fuse multiple times. Finally, targeted elimination of VGAT in horizontal cells resulted in a loss of tonic, autaptic GABA currents, and of inhibitory feedback modulation of the cone photoreceptor Cai, consistent with the elimination of GABA release from horizontal cell endings. These results in mammalian retina identify the central role of vesicular release of GABA from horizontal cells in the feedback inhibition of photoreceptors.
Collapse
Affiliation(s)
- Arlene A. Hirano
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
- Veterans Administration Greater Los Angeles Healthcare System, Los Angeles, CA, United States
| | - Helen E. Vuong
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
| | - Helen L. Kornmann
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
| | - Cataldo Schietroma
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
| | - Salvatore L. Stella
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
| | - Steven Barnes
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
- Department of Ophthalmology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
- Doheny Eye Institute, University of California, Los Angeles, Los Angeles, CA, United States
| | - Nicholas C. Brecha
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
- Veterans Administration Greater Los Angeles Healthcare System, Los Angeles, CA, United States
- Department of Ophthalmology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
- Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
- Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
| |
Collapse
|
9
|
Tchernookova BK, Gongwer MW, George A, Goeglein B, Powell AM, Caringal HL, Leuschner T, Phillips AG, Schantz AW, Kiedrowski L, Chappell R, Kreitzer MA, Malchow RP. ATP-mediated increase in H + flux from retinal Müller cells: a role for Na +/H + exchange. J Neurophysiol 2020; 125:184-198. [PMID: 33206577 DOI: 10.1152/jn.00546.2020] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Small alterations in extracellular H+ can profoundly alter neurotransmitter release by neurons. We examined mechanisms by which extracellular ATP induces an extracellular H+ flux from Müller glial cells, which surround synaptic connections throughout the vertebrate retina. Müller glia were isolated from tiger salamander retinae and H+ fluxes examined using self-referencing H+-selective microelectrodes. Experiments were performed in 1 mM HEPES with no bicarbonate present. Replacement of extracellular sodium by choline decreased H+ efflux induced by 10 µM ATP by 75%. ATP-induced H+ efflux was also reduced by Na+/H+ exchange inhibitors. Amiloride reduced H+ efflux initiated by 10 µM ATP by 60%, while 10 µM cariporide decreased H+ flux by 37%, and 25 µM zoniporide reduced H+ flux by 32%. ATP-induced H+ fluxes were not significantly altered by the K+/H+ pump blockers SCH28080 or TAK438, and replacement of all extracellular chloride with gluconate was without effect on H+ fluxes. Recordings of ATP-induced H+ efflux from cells that were simultaneously whole cell voltage clamped revealed no effect of membrane potential from -70 mV to 0 mV. Restoration of extracellular potassium after cells were bathed in 0 mM potassium produced a transient alteration in ATP-dependent H+ efflux. The transient response to extracellular potassium occurred only when extracellular sodium was present and was abolished by 1 mM ouabain, suggesting that alterations in sodium gradients were mediated by Na+/K+-ATPase activity. Our data indicate that the majority of H+ efflux elicited by extracellular ATP from isolated Müller cells is mediated by Na+/H+ exchange.NEW & NOTEWORTHY Glial cells are known to regulate neuronal activity, but the exact mechanism(s) whereby these "support" cells modulate synaptic transmission remains unclear. Small changes in extracellular levels of acidity are known to be particularly powerful regulators of neurotransmitter release. Here, we show that extracellular ATP, known to be a potent activator of glial cells, induces H+ efflux from retinal Müller (glial) cells and that the bulk of the H+ efflux is mediated by Na+/H+ exchange.
Collapse
Affiliation(s)
| | | | - Alexis George
- Department of Biology, Indiana Wesleyan University, Marion, Indiana
| | - Brock Goeglein
- Department of Biology, Indiana Wesleyan University, Marion, Indiana
| | - Alyssa M Powell
- Department of Biology, Indiana Wesleyan University, Marion, Indiana
| | | | - Thomas Leuschner
- Department of Biology, Indiana Wesleyan University, Marion, Indiana
| | - Anna G Phillips
- Department of Biology, Indiana Wesleyan University, Marion, Indiana
| | - Adam W Schantz
- Department of Biology, Indiana Wesleyan University, Marion, Indiana
| | - Lech Kiedrowski
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois.,Spot Cells LLC, Chicago, Illinois
| | - Richard Chappell
- Department of Physiology and Biophysics, University at Buffalo, Buffalo, New York.,Eugene Bell Center, Marine Biological Laboratory, Woods Hole, Massachusetts
| | | | - Robert Paul Malchow
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois.,Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, Illinois
| |
Collapse
|
10
|
Barnes S, Grove JCR, McHugh CF, Hirano AA, Brecha NC. Horizontal Cell Feedback to Cone Photoreceptors in Mammalian Retina: Novel Insights From the GABA-pH Hybrid Model. Front Cell Neurosci 2020; 14:595064. [PMID: 33328894 PMCID: PMC7672006 DOI: 10.3389/fncel.2020.595064] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2020] [Accepted: 09/24/2020] [Indexed: 01/20/2023] Open
Abstract
How neurons in the eye feed signals back to photoreceptors to optimize sensitivity to patterns of light appears to be mediated by one or more unconventional mechanisms. Via these mechanisms, horizontal cells control photoreceptor synaptic gain and enhance key aspects of temporal and spatial center-surround receptive field antagonism. After the transduction of light energy into an electrical signal in photoreceptors, the next key task in visual processing is the transmission of an optimized signal to the follower neurons in the retina. For this to happen, the release of the excitatory neurotransmitter glutamate from photoreceptors is carefully regulated via horizontal cell feedback, which acts as a thermostat to keep the synaptic transmission in an optimal range during changes to light patterns and intensities. Novel findings of a recently described model that casts a classical neurotransmitter system together with ion transport mechanisms to adjust the alkaline milieu outside the synapse are reviewed. This novel inter-neuronal messaging system carries feedback signals using two separate, but interwoven regulated systems. The complex interplay between these two signaling modalities, creating synaptic modulation-at-a-distance, has obscured it’s being defined. The foundations of our understanding of the feedback mechanism from horizontal cells to photoreceptors have been long established: Horizontal cells have broad receptive fields, suitable for providing surround inhibition, their membrane potential, a function of stimulus intensity and size, regulates inhibition of photoreceptor voltage-gated Ca2+ channels, and strong artificial pH buffering eliminates this action. This review compares and contrasts models of how these foundations are linked, focusing on a recent report in mammals that shows tonic horizontal cell release of GABA activating Cl− and HCO3− permeable GABA autoreceptors. The membrane potential of horizontal cells provides the driving force for GABAR-mediated HCO3− efflux, alkalinizing the cleft when horizontal cells are hyperpolarized by light or adding to their depolarization in darkness and contributing to cleft acidification via NHE-mediated H+ efflux. This model challenges interpretations of earlier studies that were considered to rule out a role for GABA in feedback to cones.
Collapse
Affiliation(s)
- Steven Barnes
- Doheny Eye Institute, Los Angeles, CA, United States.,Department of Ophthalmology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States.,Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
| | - James C R Grove
- Neuroscience Graduate Program, University of California, San Francisco, San Francisco, CA, United States
| | | | - Arlene A Hirano
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States.,Veterans Administration Greater Los Angeles Healthcare System, Los Angeles, CA, United States
| | - Nicholas C Brecha
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States.,Veterans Administration Greater Los Angeles Healthcare System, Los Angeles, CA, United States.,Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States.,Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
| |
Collapse
|
11
|
Country MW, Htite ED, Samson IA, Jonz MG. Retinal horizontal cells of goldfish (Carassius auratus) display subtype-specific differences in spontaneous action potentials in situ. J Comp Neurol 2020; 529:1756-1767. [PMID: 33070331 DOI: 10.1002/cne.25054] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2020] [Revised: 09/25/2020] [Accepted: 10/06/2020] [Indexed: 11/11/2022]
Abstract
Horizontal cells (HCs) are neurons of the outer retina, which provide inhibitory feedback onto photoreceptors and contribute to image processing. HCs in teleosts are classified into four subtypes (H1-H4), each having different roles: H1-H3 feed back onto different sets of cones, H4 feed back onto rods, and only H1 store and release the inhibitory neurotransmitter, γ-aminobutyric acid (GABA). Dissociated HCs exhibit spontaneous Ca2+ -based action potentials (APs), yet it is unclear if APs occur in situ, or if all subtypes exhibit APs. We measured intracellular Ca2+ and report APs in slice preparations of the goldfish retina. In HCs furthest from photoreceptors (i.e., H3/H4), APs were less frequent, with greater duration and area under the curve (a measure of Ca2+ flux). Next, we classified acutely dissociated HCs into subtypes by integrating the ratio of dendritic field size vs. soma size (rd/s ). H1 and H2 subtypes had low rd/s values (<8); H3/H4 had high rd/s (>12). To verify this model, H1s were identified by immunoreactivity for GABA and 95% of these cells had an rd/s < 4. In Ca2+ imaging experiments, as rd/s increased, AP duration and area under the curve increased, while frequency decreased. Our results demonstrate the presence of Ca2+ -based APs in the goldfish retina in situ and show that HC subtypes H1 through H4 exhibit progressively longer and less frequent spontaneous APs. These results suggest that APs may play an important role in inhibitory feedback, and may have implications for understanding the relative contributions of HC subtypes in the outer retina.
Collapse
Affiliation(s)
- Michael W Country
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
| | - Elly Dimya Htite
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
| | - Isaiah A Samson
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
| | - Michael G Jonz
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada.,Brain and Mind Research Institute, University of Ottawa, Ottawa, Ontario, Canada
| |
Collapse
|
12
|
Controlling Horizontal Cell-Mediated Lateral Inhibition in Transgenic Zebrafish Retina with Chemogenetic Tools. eNeuro 2020; 7:ENEURO.0022-20.2020. [PMID: 33060180 PMCID: PMC7665903 DOI: 10.1523/eneuro.0022-20.2020] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2020] [Revised: 08/11/2020] [Accepted: 08/28/2020] [Indexed: 12/03/2022] Open
Abstract
Horizontal cells (HCs) form reciprocal synapses with rod and cone photoreceptors, an arrangement that underlies lateral inhibition in the retina. HCs send negative and positive feedback signals to photoreceptors, but how HCs initiate these signals remains unclear. Unfortunately, because HCs have no unique neurotransmitter receptors, there are no pharmacological treatments for perturbing membrane potential specifically in HCs. Here we use transgenic zebrafish whose HCs express alien receptors, enabling cell-type-specific control by cognate alien agonists. To depolarize HCs, we used the Phe-Met-Arg-Phe-amide (FMRFamide)-gated Na+ channel (FaNaC) activated by the invertebrate neuropeptide FMRFamide. To hyperpolarize HCs we used a pharmacologically selective actuator module (PSAM)-glycine receptor (GlyR), an engineered Cl– selective channel activated by a synthetic agonist. Expression of FaNaC or PSAM-GlyR was restricted to HCs with the cell-type selective promoter for connexin-55.5. We assessed HC-feedback control of photoreceptor synapses in three ways. First, we measured presynaptic exocytosis from photoreceptor terminals using the fluorescent dye FM1-43. Second, we measured the electroretinogram (ERG) b-wave, a signal generated by postsynaptic responses. Third, we used Ca2+ imaging in retinal ganglion cells (RGCs) expressing the Ca2+ indicator GCaMP6. Addition of FMRFamide significantly decreased FM1-43 destaining in darkness, whereas the addition of PSAM-GlyR significantly increased it. However, both agonists decreased the light-elicited ERG b-wave and eliminated surround inhibition of the Ca2+ response of RGCs. Taken together, our findings show that chemogenetic tools can selectively manipulate negative feedback from HCs, providing a platform for understanding its mechanism and helping to elucidate its functional roles in visual information processing at a succession of downstream stages.
Collapse
|
13
|
Furukawa T, Ueno A, Omori Y. Molecular mechanisms underlying selective synapse formation of vertebrate retinal photoreceptor cells. Cell Mol Life Sci 2020; 77:1251-1266. [PMID: 31586239 PMCID: PMC11105113 DOI: 10.1007/s00018-019-03324-w] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2019] [Revised: 09/21/2019] [Accepted: 09/25/2019] [Indexed: 11/29/2022]
Abstract
In vertebrate central nervous systems (CNSs), highly diverse neurons are selectively connected via synapses, which are essential for building an intricate neural network. The vertebrate retina is part of the CNS and is comprised of a distinct laminar organization, which serves as a good model system to study developmental synapse formation mechanisms. In the retina outer plexiform layer, rods and cones, two types of photoreceptor cells, elaborate selective synaptic contacts with ON- and/or OFF-bipolar cell terminals as well as with horizontal cell terminals. In the mouse retina, three photoreceptor subtypes and at least 15 bipolar subtypes exist. Previous and recent studies have significantly progressed our understanding of how selective synapse formation, between specific subtypes of photoreceptor and bipolar cells, is designed at the molecular level. In the ON pathway, photoreceptor-derived secreted and transmembrane proteins directly interact in trans with the GRM6 (mGluR6) complex, which is localized to ON-bipolar cell dendritic terminals, leading to selective synapse formation. Here, we review our current understanding of the key factors and mechanisms underlying selective synapse formation of photoreceptor cells with bipolar and horizontal cells in the retina. In addition, we describe how defects/mutations of the molecules involved in photoreceptor synapse formation are associated with human retinal diseases and visual disorders.
Collapse
Affiliation(s)
- Takahisa Furukawa
- Laboratory for Molecular and Developmental Biology, Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka, 565-0871, Japan.
| | - Akiko Ueno
- Laboratory for Molecular and Developmental Biology, Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka, 565-0871, Japan
| | - Yoshihiro Omori
- Laboratory for Molecular and Developmental Biology, Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka, 565-0871, Japan
| |
Collapse
|
14
|
Country MW, Campbell BFN, Jonz MG. Spontaneous action potentials in retinal horizontal cells of goldfish ( Carassius auratus) are dependent upon L-type Ca 2+ channels and ryanodine receptors. J Neurophysiol 2019; 122:2284-2293. [PMID: 31596629 DOI: 10.1152/jn.00240.2019] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Horizontal cells (HCs) are interneurons of the outer retina that undergo graded changes in membrane potential during the light response and provide feedback to photoreceptors. We characterized spontaneous Ca2+-based action potentials (APs) in isolated goldfish (Carassius auratus) HCs with electrophysiological and intracellular imaging techniques. Transient changes in intracellular Ca2+ concentration ([Ca2+]i) were observed with fura-2 and were abolished by removal of extracellular Ca2+ or by inhibition of Ca2+ channels by 50 µM Cd2+ or 100 µM nifedipine. Inhibition of Ca2+ release from stores with 20 µM ryanodine or 50 µM dantrolene abolished Ca2+ transients and increased baseline [Ca2+]i. This increased baseline was prevented by blocking L-type Ca2+ channels with nifedipine, suggesting that Ca2+-induced Ca2+ release from stores may be needed to inactivate membrane Ca2+ channels. Caffeine (3 mM) increased the frequency of Ca2+ transients, and the store-operated channel antagonist 2-aminoethyldiphenylborinate (100 μM) counteracted this effect. APs were detected with voltage-sensitive dye imaging (FluoVolt) and current-clamp electrophysiology. In current-clamp recordings, regenerative APs were abolished by removal of extracellular Ca2+ or in the presence of 5 mM Co2+ or 100 µM nifedipine, and APs were amplified with 15 mM Ba2+. Collectively, our data suggest that during APs Ca2+ enters through L-type Ca2+ channels and that Ca2+ stores (gated by ryanodine receptors) contribute to the rise in [Ca2+]i. This work may lead to further understanding of the possible role APs have in vision, such as transitioning from light to darkness or modulating feedback from HCs to photoreceptors.NEW & NOTEWORTHY Horizontal cells (HCs) are interneurons of the outer retina that provide inhibitory feedback onto photoreceptors. HCs respond to light via graded changes in membrane potential. We characterized spontaneous action potentials in HCs from goldfish and linked action potential generation to a rise in intracellular Ca2+ via plasma membrane channels and ryanodine receptors. Action potentials may play a role in vision, such as transitioning from light to darkness, or in modulating feedback from HCs to photoreceptors.
Collapse
Affiliation(s)
- Michael W Country
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
| | | | - Michael G Jonz
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
| |
Collapse
|
15
|
Thoreson WB, Dacey DM. Diverse Cell Types, Circuits, and Mechanisms for Color Vision in the Vertebrate Retina. Physiol Rev 2019; 99:1527-1573. [PMID: 31140374 DOI: 10.1152/physrev.00027.2018] [Citation(s) in RCA: 63] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Synaptic interactions to extract information about wavelength, and thus color, begin in the vertebrate retina with three classes of light-sensitive cells: rod photoreceptors at low light levels, multiple types of cone photoreceptors that vary in spectral sensitivity, and intrinsically photosensitive ganglion cells that contain the photopigment melanopsin. When isolated from its neighbors, a photoreceptor confounds photon flux with wavelength and so by itself provides no information about color. The retina has evolved elaborate color opponent circuitry for extracting wavelength information by comparing the activities of different photoreceptor types broadly tuned to different parts of the visible spectrum. We review studies concerning the circuit mechanisms mediating opponent interactions in a range of species, from tetrachromatic fish with diverse color opponent cell types to common dichromatic mammals where cone opponency is restricted to a subset of specialized circuits. Distinct among mammals, primates have reinvented trichromatic color vision using novel strategies to incorporate evolution of an additional photopigment gene into the foveal structure and circuitry that supports high-resolution vision. Color vision is absent at scotopic light levels when only rods are active, but rods interact with cone signals to influence color perception at mesopic light levels. Recent evidence suggests melanopsin-mediated signals, which have been identified as a substrate for setting circadian rhythms, may also influence color perception. We consider circuits that may mediate these interactions. While cone opponency is a relatively simple neural computation, it has been implemented in vertebrates by diverse neural mechanisms that are not yet fully understood.
Collapse
Affiliation(s)
- Wallace B Thoreson
- Department of Ophthalmology and Visual Sciences, Truhlsen Eye Institute, University of Nebraska Medical Center , Omaha, Nebraska ; and Department of Biological Structure, Washington National Primate Research Center, University of Washington , Seattle, Washington
| | - Dennis M Dacey
- Department of Ophthalmology and Visual Sciences, Truhlsen Eye Institute, University of Nebraska Medical Center , Omaha, Nebraska ; and Department of Biological Structure, Washington National Primate Research Center, University of Washington , Seattle, Washington
| |
Collapse
|
16
|
Grove JCR, Hirano AA, de los Santos J, McHugh CF, Purohit S, Field GD, Brecha NC, Barnes S. Novel hybrid action of GABA mediates inhibitory feedback in the mammalian retina. PLoS Biol 2019; 17:e3000200. [PMID: 30933967 PMCID: PMC6459543 DOI: 10.1371/journal.pbio.3000200] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2018] [Revised: 04/11/2019] [Accepted: 03/13/2019] [Indexed: 01/06/2023] Open
Abstract
The stream of visual information sent from photoreceptors to second-order bipolar cells is intercepted by laterally interacting horizontal cells that generate feedback to optimize and improve the efficiency of signal transmission. The mechanisms underlying the regulation of graded photoreceptor synaptic output in this nonspiking network have remained elusive. Here, we analyze with patch clamp recording the novel mechanisms by which horizontal cells control pH in the synaptic cleft to modulate photoreceptor neurotransmitter release. First, we show that mammalian horizontal cells respond to their own GABA release and that the results of this autaptic action affect cone voltage-gated Ca2+ channel (CaV channel) gating through changes in pH. As a proof-of-principle, we demonstrate that chemogenetic manipulation of horizontal cells with exogenous anion channel expression mimics GABA-mediated cone CaV channel inhibition. Activation of these GABA receptor anion channels can depolarize horizontal cells and increase cleft acidity via Na+/H+ exchanger (NHE) proton extrusion, which results in inhibition of cone CaV channels. This action is effectively counteracted when horizontal cells are sufficiently hyperpolarized by increased GABA receptor (GABAR)-mediated HCO3- efflux, alkalinizing the cleft and disinhibiting cone CaV channels. This demonstrates how hybrid actions of GABA operate in parallel to effect voltage-dependent pH changes, a novel mechanism for regulating synaptic output.
Collapse
Affiliation(s)
- James C. R. Grove
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
- Neuroscience Graduate Program, University of California, San Francisco, California, United States of America
| | - Arlene A. Hirano
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
- Veterans Administration Greater Los Angeles Healthcare System, Los Angeles, California, United States of America
| | - Janira de los Santos
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
| | - Cyrus F. McHugh
- Doheny Eye Institute, University of California, Los Angeles, California, United States of America
| | - Shashvat Purohit
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
| | - Greg D. Field
- Department of Neurobiology, Duke University School of Medicine, Durham, North Carolina, United States of America
| | - Nicholas C. Brecha
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
- Veterans Administration Greater Los Angeles Healthcare System, Los Angeles, California, United States of America
- Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
- Department of Ophthalmology, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
- Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
| | - Steven Barnes
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
- Doheny Eye Institute, University of California, Los Angeles, California, United States of America
- Department of Ophthalmology, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
- Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada
- Department of Ophthalmology and Visual Sciences, Dalhousie University, Halifax, Nova Scotia, Canada
| |
Collapse
|
17
|
Hirano AA, Liu X, Brecha NC, Barnes S. Analysis of Feedback Signaling from Horizontal Cells to Photoreceptors in Mice. Methods Mol Biol 2019; 1753:179-189. [PMID: 29564789 DOI: 10.1007/978-1-4939-7720-8_12] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/10/2023]
Abstract
Genetic manipulation of horizontal cells using a Connexin57-iCre mouse (Cx57-iCre) line combined with calcium imaging is proving to be a valuable method to study horizontal cell feedback inhibition onto photoreceptor terminals. While it is accepted that horizontal cells provide lateral inhibitory feedback to photoreceptors, the cellular mechanisms that underlie this feedback inhibition remain only partially elucidated. Feedback inhibition of photoreceptors acts via modulation of their voltage-gated calcium channels at their synaptic terminal. Calcium imaging of photoreceptors in retinal slices, therefore, reflects the impact of inhibitory feedback from horizontal cells. The development of a Cx57-iCre mouse line permits genetic manipulation of horizontal cells. In wild-type mouse retina, depolarization of horizontal cells by kainate provokes a decrease in photoreceptor Ca2+i, whereas hyperpolarization by NBQX elicits an increase in photoreceptor Ca2+i. These responses indicate increased feedback inhibition occurred when horizontal cells are depolarized, and decreased feedback inhibition, when hyperpolarized. This system was used to test the role of GABA release from horizontal cells in feedback inhibition by the selective elimination of VGAT/VIAAT, the inhibitory amino acid transmitter transporter that loads GABA into the synaptic vesicles of horizontal cells. Combined with calcium imaging of photoreceptors in retinal slices, the knockout of specific proteins, e.g., VGAT, provides a robust technique to test the role of GABA in feedback inhibition by horizontal cells.
Collapse
Affiliation(s)
- Arlene A Hirano
- Department of Neurobiology, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA. .,Veterans Administration of Greater Los Angeles Health System, Los Angeles, CA, USA.
| | - Xue Liu
- Department of Neurobiology, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.,Biomaterials and Live Cell Imaging Institute, Chongqing University of Science and Technology, Chongqing, People's Republic of China
| | - Nicholas C Brecha
- Department of Neurobiology, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.,Veterans Administration of Greater Los Angeles Health System, Los Angeles, CA, USA.,Departments of Medicine and Ophthalmology, Stein Eye Institute, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA
| | - Steven Barnes
- Department of Neurobiology, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.,Veterans Administration of Greater Los Angeles Health System, Los Angeles, CA, USA.,Departments of Physiology and Biophysics, Ophthalmology and Visual Sciences, Dalhousie University, Halifax, NS, Canada
| |
Collapse
|
18
|
Tikhonov DB, Magazanik LG, Nagaeva EI. Ligands of Acid-Sensing Ion Channel 1a: Mechanisms of Action and Binding Sites. Acta Naturae 2019; 11:4-13. [PMID: 31024743 PMCID: PMC6475867] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Indexed: 10/25/2022] Open
Abstract
The proton-gated cationic channels belonging to the ASIC family are widely distributed in the central nervous system of vertebrates and play an important role in several physiological and pathological processes. ASIC1a are most sensitive to acidification of the external medium, which is the reason for the current interest in their function and pharmacology. Recently, the list of ASIC1a ligands has been rapidly expanding. It includes inorganic cations, a large number of synthetic and endogenous small molecules, and peptide toxins. The information on the mechanisms of action and the binding sites of the ligands comes from electrophysiological, mutational and structural studies. In the present review, we attempt to present a systematic view of the complex pattern of interactions between ligands and ASIC1a.
Collapse
|
19
|
Localizing Proton-Mediated Inhibitory Feedback at the Retinal Horizontal Cell-Cone Synapse with Genetically-Encoded pH Probes. J Neurosci 2018; 39:651-662. [PMID: 30504272 DOI: 10.1523/jneurosci.1541-18.2018] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2018] [Revised: 11/12/2018] [Accepted: 11/17/2018] [Indexed: 11/21/2022] Open
Abstract
Lateral inhibition in the vertebrate retina depends on a negative feedback synapse between horizontal cells (HCs) and rod and cone photoreceptors. A change in pH is thought to be the signal for negative feedback, but its spatial profile in the synaptic cleft is unknown. Here we use three different membrane proteins, each fused to the same genetically-encoded pH-sensitive Green Fluorescent Protein (GFP) (pHluorin), to probe synaptic pH in retina from transgenic zebrafish (Danio rerio) of either sex. We used the cone transducin promoter to express SynaptopHluorin (pHluorin on vesicle-associated membrane protein (VAMP2)) or CalipHluorin (pHluorin on an L-type Ca2+ channel) and the HC-specific connexin-55.5 promoter to express AMPApHluorin (pHluorin on an AMPA receptor). Stimulus light led to increased fluorescence of all three probes, consistent with alkalinization of the synaptic cleft. The receptive field size, sensitivity to surround illumination, and response to activation of an alien receptor expressed exclusively in HCs, are consistent with lateral inhibition as the trigger for alkalinization. However, SynaptopHluorin and AMPApHluorin, which are displaced farther from cone synaptic ribbons than CalipHluorin, reported a smaller pH change. Hence, unlike feedforward glutamatergic transmission, which spills over to allow cross talk between terminals in the cone network, the pH change underlying HC feedback is compartmentalized to individual synaptic invaginations within a cone terminal, consistent with private line communication.SIGNIFICANCE STATEMENT Lateral inhibition (LI) is a fundamental feature of information processing in sensory systems, enhancing contrast sensitivity and enabling edge discrimination. Horizontal cells (HCs) are the first cellular substrate of LI in the vertebrate retina, but the synaptic mechanisms underlying LI are not completely understood, despite decades of study. This paper makes a significant contribution to our understanding of LI, by showing that each HC-cone synapse is a "private-line" that operates independently from other HC-cone connections. Using transgenic zebrafish expressing pHluorin, a pH-sensitive GFP variant spliced onto three different protein platforms expressed either in cones or HCs we show that the feedback pH signal is constrained to individual cone terminals, and more stringently, to individual synaptic contact sites within each terminal.
Collapse
|
20
|
Tchernookova BK, Heer C, Young M, Swygart D, Kaufman R, Gongwer M, Shepherd L, Caringal H, Jacoby J, Kreitzer MA, Malchow RP. Activation of retinal glial (Müller) cells by extracellular ATP induces pronounced increases in extracellular H+ flux. PLoS One 2018; 13:e0190893. [PMID: 29466379 PMCID: PMC5821311 DOI: 10.1371/journal.pone.0190893] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2017] [Accepted: 12/21/2017] [Indexed: 11/25/2022] Open
Abstract
Small alterations in extracellular acidity are potentially important modulators of neuronal signaling within the vertebrate retina. Here we report a novel extracellular acidification mechanism mediated by glial cells in the retina. Using self-referencing H+-selective microelectrodes to measure extracellular H+ fluxes, we show that activation of retinal Müller (glial) cells of the tiger salamander by micromolar concentrations of extracellular ATP induces a pronounced extracellular H+ flux independent of bicarbonate transport. ADP, UTP and the non-hydrolyzable analog ATPγs at micromolar concentrations were also potent stimulators of extracellular H+ fluxes, but adenosine was not. The extracellular H+ fluxes induced by ATP were mimicked by the P2Y1 agonist MRS 2365 and were significantly reduced by the P2 receptor blockers suramin and PPADS, suggesting activation of P2Y receptors. Bath-applied ATP induced an intracellular rise in calcium in Müller cells; both the calcium rise and the extracellular H+ fluxes were significantly attenuated when calcium re-loading into the endoplasmic reticulum was inhibited by thapsigargin and when the PLC-IP3 signaling pathway was disrupted with 2-APB and U73122. The anion transport inhibitor DIDS also markedly reduced the ATP-induced increase in H+ flux while SITS had no effect. ATP-induced H+ fluxes were also observed from Müller cells isolated from human, rat, monkey, skate and lamprey retinae, suggesting a highly evolutionarily conserved mechanism of potential general importance. Extracellular ATP also induced significant increases in extracellular H+ flux at the level of both the outer and inner plexiform layers in retinal slices of tiger salamander which was significantly reduced by suramin and PPADS. We suggest that the novel H+ flux mediated by ATP-activation of Müller cells and of other glia as well may be a key mechanism modulating neuronal signaling in the vertebrate retina and throughout the brain.
Collapse
Affiliation(s)
- Boriana K. Tchernookova
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois, United States of America
- * E-mail: (BKT); (RPM)
| | - Chad Heer
- Department of Biology, Indiana Wesleyan University, Marion, Indiana, United States of America
| | - Marin Young
- Department of Biology, Indiana Wesleyan University, Marion, Indiana, United States of America
| | - David Swygart
- Department of Biology, Indiana Wesleyan University, Marion, Indiana, United States of America
| | - Ryan Kaufman
- Department of Biology, Indiana Wesleyan University, Marion, Indiana, United States of America
| | - Michael Gongwer
- Department of Biology, Indiana Wesleyan University, Marion, Indiana, United States of America
| | - Lexi Shepherd
- Department of Biology, Indiana Wesleyan University, Marion, Indiana, United States of America
| | - Hannah Caringal
- Department of Biology, Indiana Wesleyan University, Marion, Indiana, United States of America
| | - Jason Jacoby
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois, United States of America
| | - Matthew A. Kreitzer
- Department of Biology, Indiana Wesleyan University, Marion, Indiana, United States of America
| | - Robert Paul Malchow
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois, United States of America
- Department of Ophthalmology & Visual Sciences, University of Illinois at Chicago, Chicago, Illinois, United States of America
- * E-mail: (BKT); (RPM)
| |
Collapse
|
21
|
Kreitzer MA, Swygart D, Osborn M, Skinner B, Heer C, Kaufman R, Williams B, Shepherd L, Caringal H, Gongwer M, Tchernookova BK, Malchow RP. Extracellular H + fluxes from tiger salamander Müller (glial) cells measured using self-referencing H +-selective microelectrodes. J Neurophysiol 2017; 118:3132-3143. [PMID: 28855292 DOI: 10.1152/jn.00409.2017] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2017] [Revised: 08/18/2017] [Accepted: 08/25/2017] [Indexed: 12/22/2022] Open
Abstract
Self-referencing H+-selective electrodes were used to measure extracellular H+ fluxes from Müller (glial) cells isolated from the tiger salamander retina. A novel chamber enabled stable recordings using H+-selective microelectrodes in a self-referencing format using bicarbonate-based buffer solutions. A small basal H+ flux was observed from the end foot region of quiescent cells bathed in 24 mM bicarbonate-based solutions, and increasing extracellular potassium induced a dose-dependent increase in H+ flux. Barium at 6 mM also increased H+ flux. Potassium-induced extracellular acidifications were abolished when bicarbonate was replaced by 1 mM HEPES. The carbonic anhydrase antagonist benzolamide potentiated the potassium-induced extracellular acidification, while 300 μM DIDS, 300 μM SITS, and 30 μM S0859 significantly reduced the response. Potassium-induced extracellular acidifications persisted in solutions lacking extracellular calcium, although potassium-induced changes in intracellular calcium monitored with Oregon Green were abolished. Exchange of external sodium with choline also eliminated the potassium-induced extracellular acidification. Removal of extracellular sodium by itself induced a transient alkalinization, and replacement of sodium induced a transient acidification, both of which were blocked by 300 μM DIDS. Recordings at the apical portion of the cell showed smaller potassium-induced extracellular H+ fluxes, and removal of the end foot region further decreased the H+ flux, suggesting that the end foot was the major source of acidifications. These studies demonstrate that self-referencing H+-selective electrodes can be used to monitor H+ fluxes from retinal Müller cells in bicarbonate-based solutions and confirm the presence of a sodium-coupled bicarbonate transporter, the activity of which is largely restricted to the end foot of the cell.NEW & NOTEWORTHY The present study uses self-referencing H+-selective electrodes for the first time to measure H+ fluxes from Müller (glial) cells isolated from tiger salamander retina. These studies demonstrate bicarbonate transport as a potent regulator of extracellular levels of acidity around Müller cells and point toward a need for further studies aimed at addressing how such glial cell pH regulatory mechanisms may shape neuronal signaling.
Collapse
Affiliation(s)
| | - David Swygart
- Department of Biology, Indiana Wesleyan University, Marion, Indiana
| | - Meredith Osborn
- Department of Biology, Indiana Wesleyan University, Marion, Indiana
| | - Blair Skinner
- Department of Biology, Indiana Wesleyan University, Marion, Indiana
| | - Chad Heer
- Department of Biology, Indiana Wesleyan University, Marion, Indiana
| | - Ryan Kaufman
- Department of Biology, Indiana Wesleyan University, Marion, Indiana
| | - Bethany Williams
- Department of Biology, Indiana Wesleyan University, Marion, Indiana
| | - Lexi Shepherd
- Department of Biology, Indiana Wesleyan University, Marion, Indiana
| | - Hannah Caringal
- Department of Biology, Indiana Wesleyan University, Marion, Indiana
| | - Michael Gongwer
- Department of Biology, Indiana Wesleyan University, Marion, Indiana
| | - Boriana K Tchernookova
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois; and
| | - Robert P Malchow
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois; and.,Ophthalmology & Visual Sciences, University of Illinois at Chicago, Chicago, Illinois
| |
Collapse
|
22
|
Deactivation kinetics of acid-sensing ion channel 1a are strongly pH-sensitive. Proc Natl Acad Sci U S A 2017; 114:E2504-E2513. [PMID: 28265090 DOI: 10.1073/pnas.1620508114] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Acid-sensing ion channels (ASICs) are trimeric cation-selective ion channels activated by protons in the physiological range. Recent reports have revealed that postsynaptically localized ASICs contribute to the excitatory postsynaptic current by responding to the transient acidification of the synaptic cleft that accompanies neurotransmission. In response to such brief acidic transients, both recombinant and native ASICs show extremely rapid deactivation in outside-out patches when jumping from a pH 5 stimulus to a single resting pH of 8. Given that the resting pH of the synaptic cleft is highly dynamic and depends on recent synaptic activity, we explored the kinetics of ASIC1a and 1a/2a heteromers to such brief pH transients over a wider [H+] range to approximate neuronal conditions better. Surprisingly, the deactivation of ASICs was steeply dependent on the pH, spanning nearly three orders of magnitude from extremely fast (<1 ms) at pH 8 to very slow (>300 ms) at pH 7. This study provides an example of a ligand-gated ion channel whose deactivation is sensitive to agonist concentrations that do not directly activate the receptor. Kinetic simulations and further mutagenesis provide evidence that ASICs show such steeply agonist-dependent deactivation because of strong cooperativity in proton binding. This capacity to signal across such a large synaptically relevant bandwidth enhances the response to small-amplitude acidifications likely to occur at the cleft and may provide ASICs with the ability to shape activity in response to the recent history of the synapse.
Collapse
|
23
|
Acid-Sensing Ion Channels Activated by Evoked Released Protons Modulate Synaptic Transmission at the Mouse Calyx of Held Synapse. J Neurosci 2017; 37:2589-2599. [PMID: 28159907 DOI: 10.1523/jneurosci.2566-16.2017] [Citation(s) in RCA: 60] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2016] [Revised: 01/10/2017] [Accepted: 01/13/2017] [Indexed: 12/30/2022] Open
Abstract
Acid-sensing ion channels (ASICs) regulate synaptic activities and play important roles in neurodegenerative diseases. We found that these channels can be activated in neurons of the medial nucleus of the trapezoid body (MNTB) of the auditory system in the CNS. A drop in extracellular pH induces transient inward ASIC currents (IASICs) in postsynaptic MNTB neurons from wild-type mice. The inhibition of IASICs by psalmotoxin-1 (PcTx1) and the absence of these currents in knock-out mice for ASIC-1a subunit (ASIC1a-/-) suggest that homomeric ASIC-1as are mediating these currents in MNTB neurons. Furthermore, we detect ASIC1a-dependent currents during synaptic transmission, suggesting an acidification of the synaptic cleft due to the corelease of neurotransmitter and H+ from synaptic vesicles. These currents are capable of eliciting action potentials in the absence of glutamatergic currents. A significant characteristic of these homomeric ASIC-1as is their permeability to Ca2+ Activation of ASIC-1a in MNTB neurons by exogenous H+ induces an increase in intracellular Ca2+ Furthermore, the activation of postsynaptic ASIC-1as during high-frequency stimulation (HFS) of the presynaptic nerve terminal leads to a PcTx1-sensitive increase in intracellular Ca2+ in MNTB neurons, which is independent of glutamate receptors and is absent in neurons from ASIC1a-/- mice. During HFS, the lack of functional ASICs in synaptic transmission results in an enhanced short-term depression of glutamatergic EPSCs. These results strongly support the hypothesis of protons as neurotransmitters and demonstrate that presynaptic released protons modulate synaptic transmission by activating ASIC-1as at the calyx of Held-MNTB synapse.SIGNIFICANCE STATEMENT The manuscript demonstrates that postsynaptic neurons of the medial nucleus of the trapezoid body at the mouse calyx of Held synapse express functional homomeric Acid-sensing ion channel-1a (ASIC-1as) that can be activated by protons (coreleased with neurotransmitter from acidified synaptic vesicles). These ASIC-1as contribute to the generation of postsynaptic currents and, more relevant, to calcium influx, which could be involved in the modulation of presynaptic transmitter release. Inhibition or deletion of ASIC-1a leads to enhanced short-term depression, demonstrating that they are concerned with short-term plasticity of the synapse. ASICs represent a widespread communication system with unique properties. We expect that our experiments will have an impact in the neurobiology field and will spread in areas related to neuronal plasticity.
Collapse
|
24
|
Country MW, Jonz MG. Calcium dynamics and regulation in horizontal cells of the vertebrate retina: lessons from teleosts. J Neurophysiol 2017; 117:523-536. [PMID: 27832601 PMCID: PMC5288477 DOI: 10.1152/jn.00585.2016] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2016] [Accepted: 11/02/2016] [Indexed: 01/20/2023] Open
Abstract
Horizontal cells (HCs) are inhibitory interneurons of the vertebrate retina. Unlike typical neurons, HCs are chronically depolarized in the dark, leading to a constant influx of Ca2+ Therefore, mechanisms of Ca2+ homeostasis in HCs must differ from neurons elsewhere in the central nervous system, which undergo excitotoxicity when they are chronically depolarized or stressed with Ca2+ HCs are especially well characterized in teleost fish and have been used to unlock mysteries of the vertebrate retina for over one century. More recently, mammalian models of the retina have been increasingly informative for HC physiology. We draw from both teleost and mammalian models in this review, using a comparative approach to examine what is known about Ca2+ pathways in vertebrate HCs. We begin with a survey of Ca2+-permeable ion channels, exchangers, and pumps and summarize Ca2+ influx and efflux pathways, buffering, and intracellular stores. This includes evidence for Ca2+-permeable α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors and N-methyl-d-aspartate receptors and for voltage-gated Ca2+ channels. Special attention is given to interactions between ion channels, to differences among species, and in which subtypes of HCs these channels have been found. We then discuss a number of unresolved issues pertaining to Ca2+ dynamics in HCs, including a potential role for Ca2+ in feedback to photoreceptors, the role for Ca2+-induced Ca2+ release, and the properties and functions of Ca2+-based action potentials. This review aims to highlight the unique Ca2+ dynamics in HCs, as these are inextricably tied to retinal function.
Collapse
Affiliation(s)
- Michael W Country
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
| | - Michael G Jonz
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
| |
Collapse
|
25
|
Storozhuk M, Kondratskaya E, Nikolaenko L, Krishtal O. A modulatory role of ASICs on GABAergic synapses in rat hippocampal cell cultures. Mol Brain 2016; 9:90. [PMID: 27760555 PMCID: PMC5070181 DOI: 10.1186/s13041-016-0269-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2016] [Accepted: 10/05/2016] [Indexed: 12/27/2022] Open
Abstract
Rapid acidification occurring during synaptic vesicle release can activate acid-sensing ion channels (ASICs) both on pre- and postsynaptic neurons. In the latter case, a fraction of postsynaptic current would be mediated by cation-selective acid-sensing ion channels. Additionally, in both cases, activation of acid-sensing ion channels could modulate synaptic strength by affecting transmitter release and/or sensitivity of postsynaptic receptors. To address potential involvement of acid-sensing ion channels in mediation/modulation of synaptic transmission at hippocampal GABAergic synapses, we studied effects of three structurally different blockers of acid-sensing ion channels on evoked postsynaptic currents using the patch-clamp technique. We found that GABAergic postsynaptic currents, recorded below their reversal potential as inward currents, are suppressed by all the employed blockers of acid-sensing ion channels. These currents were suppressed by ~ 20 % in the presence of a novel blocker 5b (1 μM) and by ~30 % in the presence of either amiloride (25 μM) or diminazene (20 μM). In the same cells the suppression of postsynaptic currents, recorded above their reversal potential as outward currents was statistically insignificant. These results imply that the effects of blockers in our experiments are at least partially postsynaptic. On the other hand, in the case of mediation of a fraction of postsynaptic current by acid-sensing ion channels, an increase of outward currents would be expected under our experimental conditions. Our analysis of a bicuculline-resistant fraction of postsynaptic currents also suggests that effects of the blockers are predominantly modulatory. In this work we present evidence for the first time that acid-sensing ion channels play a functional role at hippocampal GABAergic synapses. The suppressing effect of the blockers of acid-sensing ion channels on GABAergic transmission is due, at least partially, to a postsynaptic but (predominantly) modulatory mechanism. We hypothesize that the modulatory effect is due to functional crosstalk between ASICs and GABAA-receptors recently reported in isolated neurons, however, verification of this hypothesis is necessary.
Collapse
Affiliation(s)
- Maksim Storozhuk
- Bogomoletz Institute of Physiology, Bogomoletz st. 4, Kiev, Ukraine. .,State Key Laboratory of Molecular and Cellular Biology, Bogomoletz st. 4, Kiev, Ukraine.
| | - Elena Kondratskaya
- Bogomoletz Institute of Physiology, Bogomoletz st. 4, Kiev, Ukraine.,State Key Laboratory of Molecular and Cellular Biology, Bogomoletz st. 4, Kiev, Ukraine
| | | | - Oleg Krishtal
- Bogomoletz Institute of Physiology, Bogomoletz st. 4, Kiev, Ukraine.,State Key Laboratory of Molecular and Cellular Biology, Bogomoletz st. 4, Kiev, Ukraine
| |
Collapse
|
26
|
Kinetics of Inhibitory Feedback from Horizontal Cells to Photoreceptors: Implications for an Ephaptic Mechanism. J Neurosci 2016; 36:10075-88. [PMID: 27683904 DOI: 10.1523/jneurosci.1090-16.2016] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2016] [Accepted: 08/12/2016] [Indexed: 11/21/2022] Open
Abstract
UNLABELLED Inhibitory feedback from horizontal cells (HCs) to cones generates center-surround receptive fields and color opponency in the retina. Mechanisms of HC feedback remain unsettled, but one hypothesis proposes that an ephaptic mechanism may alter the extracellular electrical field surrounding photoreceptor synaptic terminals, thereby altering Ca(2+) channel activity and photoreceptor output. An ephaptic voltage change produced by current flowing through open channels in the HC membrane should occur with no delay. To test for this mechanism, we measured kinetics of inhibitory feedback currents in Ambystoma tigrinum cones and rods evoked by hyperpolarizing steps applied to synaptically coupled HCs. Hyperpolarizing HCs stimulated inward feedback currents in cones that averaged 8-9 pA and exhibited a biexponential time course with time constants averaging 14-17 ms and 120-220 ms. Measurement of feedback-current kinetics was limited by three factors: (1) HC voltage-clamp speed, (2) cone voltage-clamp speed, and (3) kinetics of Ca(2+) channel activation or deactivation in the photoreceptor terminal. These factors totaled ∼4-5 ms in cones meaning that the true fast time constants for HC-to-cone feedback currents were 9-13 ms, slower than expected for ephaptic voltage changes. We also compared speed of feedback to feedforward glutamate release measured at the same cone/HC synapses and found a latency for feedback of 11-14 ms. Inhibitory feedback from HCs to rods was also significantly slower than either measurement kinetics or feedforward release. The finding that inhibitory feedback from HCs to photoreceptors involves a significant delay indicates that it is not due to previously proposed ephaptic mechanisms. SIGNIFICANCE STATEMENT Lateral inhibitory feedback from horizontal cells (HCs) to photoreceptors creates center-surround receptive fields and color-opponent interactions. Although underlying mechanisms remain unsettled, a longstanding hypothesis proposes that feedback is due to ephaptic voltage changes that regulate photoreceptor synaptic output by altering Ca(2+) channel activity. Ephaptic processes should occur with no delay. We measured kinetics of inhibitory feedback currents evoked in photoreceptors with voltage steps applied to synaptically coupled HCs and found that feedback is too slow to be explained by ephaptic voltage changes generated by current flowing through continuously open channels in HC membranes. By eliminating the proposed ephaptic mechanism for HC feedback regulation of photoreceptor Ca(2+) channels, our data support earlier proposals that synaptic cleft pH changes are more likely responsible.
Collapse
|
27
|
Vila A, Whitaker CM, O'Brien J. Membrane-associated guanylate kinase scaffolds organize a horizontal cell synaptic complex restricted to invaginating contacts with photoreceptors. J Comp Neurol 2016; 525:850-867. [PMID: 27558197 DOI: 10.1002/cne.24101] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2016] [Revised: 08/02/2016] [Accepted: 08/15/2016] [Indexed: 12/21/2022]
Abstract
Synaptic processes and plasticity of synapses are mediated by large suites of proteins. In most cases, many of these proteins are tethered together by synaptic scaffold proteins. Scaffold proteins have a large number and typically a variety of protein interaction domains that allow many different proteins to be assembled into functional complexes. Because each scaffold protein has a different set of protein interaction domains and a unique set of interacting partners, the presence of synaptic scaffolds can provide insight into the molecular mechanisms that regulate synaptic processes. In studies of rabbit retina, we found SAP102 and Chapsyn110 selectively localized in the tips of B-type horizontal cell processes, where they contact cone and rod photoreceptors. We further identified some known SAP102 binding partners, kainate receptor GluR6/7 and inward rectifier potassium channel Kir2.1, closely associated with SAP102 in photoreceptor invaginations. The kainate receptor occupies a position distinct from that of the majority of AMPA receptors that dominate the horizontal cell postsynaptic response. GluR6/7 and Kir2.1 presumably are involved in synaptic processes that govern cell-to-cell communication and could both contribute in different ways to synaptic currents that mediate feedback signaling. Notably, we failed to find evidence for the presence of Cx57 or Cx59 that might be involved in ephaptic feedback signaling in this complex. The presence of SAP102 and its binding partners in both cone and rod invaginating synapses suggests that whatever mechanism is supported by this protein complex is present in both types of photoreceptors. J. Comp. Neurol. 525:850-867, 2017. © 2016 Wiley Periodicals, Inc.
Collapse
Affiliation(s)
- Alejandro Vila
- Richard S. Ruiz M.D. Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, Houston, Texas, 77030.,University of Texas Graduate School of Biomedical Sciences at Houston, Houston, Texas, 77030
| | - Christopher M Whitaker
- Richard S. Ruiz M.D. Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, Houston, Texas, 77030
| | - John O'Brien
- Richard S. Ruiz M.D. Department of Ophthalmology and Visual Science, University of Texas Health Science Center at Houston, Houston, Texas, 77030.,University of Texas Graduate School of Biomedical Sciences at Houston, Houston, Texas, 77030
| |
Collapse
|
28
|
Boscardin E, Alijevic O, Hummler E, Frateschi S, Kellenberger S. The function and regulation of acid-sensing ion channels (ASICs) and the epithelial Na(+) channel (ENaC): IUPHAR Review 19. Br J Pharmacol 2016; 173:2671-701. [PMID: 27278329 DOI: 10.1111/bph.13533] [Citation(s) in RCA: 108] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2016] [Revised: 05/19/2016] [Accepted: 06/02/2016] [Indexed: 12/30/2022] Open
Abstract
Acid-sensing ion channels (ASICs) and the epithelial Na(+) channel (ENaC) are both members of the ENaC/degenerin family of amiloride-sensitive Na(+) channels. ASICs act as proton sensors in the nervous system where they contribute, besides other roles, to fear behaviour, learning and pain sensation. ENaC mediates Na(+) reabsorption across epithelia of the distal kidney and colon and of the airways. ENaC is a clinically used drug target in the context of hypertension and cystic fibrosis, while ASIC is an interesting potential target. Following a brief introduction, here we will review selected aspects of ASIC and ENaC function. We discuss the origin and nature of pH changes in the brain and the involvement of ASICs in synaptic signalling. We expose how in the peripheral nervous system, ASICs cover together with other ion channels a wide pH range as proton sensors. We introduce the mechanisms of aldosterone-dependent ENaC regulation and the evidence for an aldosterone-independent control of ENaC activity, such as regulation by dietary K(+) . We then provide an overview of the regulation of ENaC by proteases, a topic of increasing interest over the past few years. In spite of the profound differences in the physiological and pathological roles of ASICs and ENaC, these channels share many basic functional and structural properties. It is likely that further research will identify physiological contexts in which ASICs and ENaC have similar or overlapping roles.
Collapse
Affiliation(s)
- Emilie Boscardin
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland
| | - Omar Alijevic
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland
| | - Edith Hummler
- Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland
| | | | | |
Collapse
|
29
|
Warren TJ, Van Hook MJ, Supuran CT, Thoreson WB. Sources of protons and a role for bicarbonate in inhibitory feedback from horizontal cells to cones in Ambystoma tigrinum retina. J Physiol 2016; 594:6661-6677. [PMID: 27345444 DOI: 10.1113/jp272533] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2016] [Accepted: 06/16/2016] [Indexed: 12/13/2022] Open
Abstract
KEY POINTS In the vertebrate retina, photoreceptors influence the signalling of neighbouring photoreceptors through lateral-inhibitory interactions mediated by horizontal cells (HCs). These interactions create antagonistic centre-surround receptive fields important for detecting edges and generating chromatically opponent responses in colour vision. The mechanisms responsible for inhibitory feedback from HCs involve changes in synaptic cleft pH that modulate photoreceptor calcium currents. However, the sources of synaptic protons involved in feedback and the mechanisms for their removal from the cleft when HCs hyperpolarize to light remain unknown. Our results indicate that Na+ -H+ exchangers are the principal source of synaptic cleft protons involved in HC feedback but that synaptic cleft alkalization during light-evoked hyperpolarization of HCs also involves changes in bicarbonate transport across the HC membrane. In addition to delineating processes that establish lateral inhibition in the retina, these results contribute to other evidence showing the key role for pH in regulating synaptic signalling throughout the nervous system. ABSTRACT Lateral-inhibitory feedback from horizontal cells (HCs) to photoreceptors involves changes in synaptic cleft pH accompanying light-evoked changes in HC membrane potential. We analysed HC to cone feedback by studying surround-evoked light responses of cones and by obtaining paired whole cell recordings from cones and HCs in salamander retina. We tested three potential sources for synaptic cleft protons: (1) generation by extracellular carbonic anhydrase (CA), (2) release from acidic synaptic vesicles and (3) Na+ /H+ exchangers (NHEs). Neither antagonizing extracellular CA nor blocking loading of protons into synaptic vesicles eliminated feedback. However, feedback was eliminated when extracellular Na+ was replaced with choline and significantly reduced by an NHE inhibitor, cariporide. Depriving NHEs of intracellular protons by buffering HC cytosol with a pH 9.2 pipette solution eliminated feedback, whereas alkalinizing the cone cytosol did not, suggesting that HCs are a major source for protons in feedback. We also examined mechanisms for changing synaptic cleft pH in response to changes in HC membrane potential. Increasing the trans-membrane proton gradient by lowering the extracellular pH from 7.8 to 7.4 to 7.1 strengthened feedback. While maintaining constant extracellular pH with 1 mm HEPES, removal of bicarbonate abolished feedback. Elevating intracellular bicarbonate levels within HCs prevented this loss of feedback. A bicarbonate transport inhibitor, 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS), also blocked feedback. Together, these results suggest that NHEs are the primary source of extracellular protons in HC feedback but that changes in cleft pH accompanying changes in HC membrane voltage also require bicarbonate flux across the HC membrane.
Collapse
Affiliation(s)
- Ted J Warren
- Department of Pharmacology & Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, 68198, USA.,Truhlsen Eye Institute and Department of Ophthalmology & Visual Sciences, University of Nebraska Medical Center, Omaha, NE, 68198, USA
| | - Matthew J Van Hook
- Truhlsen Eye Institute and Department of Ophthalmology & Visual Sciences, University of Nebraska Medical Center, Omaha, NE, 68198, USA
| | - Claudiu T Supuran
- University of Florence, Neurofarba Department, Sesto Fiorentino, Italy
| | - Wallace B Thoreson
- Department of Pharmacology & Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, 68198, USA.,Truhlsen Eye Institute and Department of Ophthalmology & Visual Sciences, University of Nebraska Medical Center, Omaha, NE, 68198, USA
| |
Collapse
|
30
|
Liu X, Grove JCR, Hirano AA, Brecha NC, Barnes S. Dopamine D1 receptor modulation of calcium channel currents in horizontal cells of mouse retina. J Neurophysiol 2016; 116:686-97. [PMID: 27193322 DOI: 10.1152/jn.00990.2015] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2015] [Accepted: 05/12/2016] [Indexed: 12/22/2022] Open
Abstract
Horizontal cells form the first laterally interacting network of inhibitory interneurons in the retina. Dopamine released onto horizontal cells under photic and circadian control modulates horizontal cell function. Using isolated, identified horizontal cells from a connexin-57-iCre × ROSA26-tdTomato transgenic mouse line, we investigated dopaminergic modulation of calcium channel currents (ICa) with whole cell patch-clamp techniques. Dopamine (10 μM) blocked 27% of steady-state ICa, an action blunted to 9% in the presence of the L-type Ca channel blocker verapamil (50 μM). The dopamine type 1 receptor (D1R) agonist SKF38393 (20 μM) inhibited ICa by 24%. The D1R antagonist SCH23390 (20 μM) reduced dopamine and SKF38393 inhibition. Dopamine slowed ICa activation, blocking ICa by 38% early in a voltage step. Enhanced early inhibition of ICa was eliminated by applying voltage prepulses to +120 mV for 100 ms, increasing ICa by 31% and 11% for early and steady-state currents, respectively. Voltage-dependent facilitation of ICa and block of dopamine inhibition after preincubation with a Gβγ-blocking peptide suggested involvement of Gβγ proteins in the D1R-mediated modulation. When the G protein activator guanosine 5'-O-(3-thiotriphosphate) (GTPγS) was added intracellularly, ICa was smaller and showed the same slowed kinetics seen during D1R activation. With GTPγS in the pipette, additional block of ICa by dopamine was only 6%. Strong depolarizing voltage prepulses restored the GTPγS-reduced early ICa amplitude by 36% and steady-state ICa amplitude by 3%. These results suggest that dopaminergic inhibition of ICa via D1Rs is primarily mediated through the action of Gβγ proteins in horizontal cells.
Collapse
Affiliation(s)
- Xue Liu
- Biomaterials and Live Cell Imaging Institute, Chongqing University of Science and Technology, Chongqing, People's Republic of China; Department of Neurobiology and Jules Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, California
| | - James C R Grove
- Department of Neurobiology and Jules Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, California
| | - Arlene A Hirano
- Department of Neurobiology and Jules Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, California; Department of Veterans Affairs Greater Los Angeles Healthcare System, Los Angeles, California; and
| | - Nicholas C Brecha
- Department of Neurobiology and Jules Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, California; Department of Veterans Affairs Greater Los Angeles Healthcare System, Los Angeles, California; and
| | - Steven Barnes
- Department of Neurobiology and Jules Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, California; Department of Veterans Affairs Greater Los Angeles Healthcare System, Los Angeles, California; and Department of Physiology and Biophysics and Department of Ophthalmology and Visual Sciences, Dalhousie University, Halifax, Nova Scotia, Canada
| |
Collapse
|
31
|
Vester M, Grueter A, Finkler B, Becker R, Jung G. Biexponential photon antibunching: recombination kinetics within the Förster-cycle in DMSO. Phys Chem Chem Phys 2016; 18:10281-8. [PMID: 27020473 DOI: 10.1039/c6cp00718j] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Time-resolved experiments with pulsed-laser excitation are the standard approach to map the dynamic evolution of excited states, but ground-state kinetics remain hidden or require pump-dump-probe schemes. Here, we exploit the so-called photon antibunching, a purely quantum-optical effect related to single molecule detection to assess the rate constants for a chemical reaction in the electronic ground state. The measurement of the second-order correlation function g((2)), i.e. the evaluation of inter-photon arrival times, is applied to the reprotonation in a Förster-cycle. We find that the antibunching of three different photoacids in the aprotic solvent DMSO significantly differs from the behavior in water. The longer decay constant of the biexponential antibunching tl is linked to the bimolecular reprotonation kinetics of the fully separated ion-pair, independent of the acidic additives. The value of the corresponding bimolecular rate constant, kp = 4 × 10(9) M(-1) s(-1), indicates diffusion-controlled reprotonation. The analysis of tl also allows for the extraction of the separation yield of proton and the conjugated base after excitation and amounts to approximately 15%. The shorter time component ts is connected to the decay of the solvent-separated ion pair. The associated time constant for geminate reprotonation is approximately 3 ± 1 ns in agreement with independent tcspc experiments. These experiments verify that the transfer of quantum-optical experiments to problems in chemistry enables mechanistic conclusions which are hardly accessible by other methods.
Collapse
Affiliation(s)
- Michael Vester
- Biophysical Chemistry, Saarland University, 66123 Saarbrücken, Germany.
| | | | | | | | | |
Collapse
|
32
|
Targeted Deletion of Vesicular GABA Transporter from Retinal Horizontal Cells Eliminates Feedback Modulation of Photoreceptor Calcium Channels. eNeuro 2016; 3:eN-NWR-0148-15. [PMID: 27022629 PMCID: PMC4785380 DOI: 10.1523/eneuro.0148-15.2016] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2015] [Revised: 01/20/2016] [Accepted: 01/28/2016] [Indexed: 11/21/2022] Open
Abstract
The cellular mechanisms underlying feedback signaling from horizontal cells to photoreceptors, which are important for the formation of receptive field surrounds of early visual neurons, remain unsettled. Mammalian horizontal cells express a complement of synaptic proteins that are necessary and sufficient for calcium-dependent exocytosis of inhibitory neurotransmitters at their contacts with photoreceptor terminals, suggesting that they are capable of releasing GABA via vesicular release. To test whether horizontal cell vesicular release is involved in feedback signaling, we perturbed inhibitory neurotransmission in these cells by targeted deletion of the vesicular GABA transporter (VGAT), the protein responsible for the uptake of inhibitory transmitter by synaptic vesicles. To manipulate horizontal cells selectively, an iCre mouse line with Cre recombinase expression controlled by connexin57 (Cx57) regulatory elements was generated. In Cx57-iCre mouse retina, only horizontal cells expressed Cre protein, and its expression occurred in all retinal regions. After crossing with a VGATflox/flox mouse line, VGAT was selectively eliminated from horizontal cells, which was confirmed immunohistochemically. Voltage-gated ion channel currents in horizontal cells of Cx57-VGAT−/− mice were the same as Cx57-VGAT+/+ controls, as were the cell responses to the ionotropic glutamate receptor agonist kainate, but the response to the GABAA receptor agonist muscimol in Cx57-VGAT−/− mice was larger. In contrast, the feedback inhibition of photoreceptor calcium channels, which in control animals is induced by horizontal cell depolarization, was completely absent in Cx57-VGAT−/− mice. The results suggest that vesicular release of GABA from horizontal cells is required for feedback inhibition of photoreceptors.
Collapse
|
33
|
Abstract
Lateral inhibition at the first synapse in the retina is important for visual perception, enhancing image contrast, color discrimination, and light adaptation. Despite decades of research, the feedback signal from horizontal cells to photoreceptors that generates lateral inhibition remains uncertain. GABA, protons, or an ephaptic mechanism have all been suggested as the primary mediator of feedback. However, the complexity of the reciprocal cone to horizontal cell synapse has left the identity of the feedback signal an unsolved mystery.
Collapse
|
34
|
Huang Y, Jiang N, Li J, Ji YH, Xiong ZG, Zha XM. Two aspects of ASIC function: Synaptic plasticity and neuronal injury. Neuropharmacology 2015; 94:42-8. [PMID: 25582290 DOI: 10.1016/j.neuropharm.2014.12.010] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2014] [Revised: 12/06/2014] [Accepted: 12/09/2014] [Indexed: 12/17/2022]
Abstract
Extracellular brain pH fluctuates in both physiological and disease conditions. The main postsynaptic proton receptor is the acid-sensing ion channels (ASICs). During the past decade, much progress has been made on protons, ASICs, and neurological disease. This review summarizes the recent progress on synaptic role of protons and our current understanding of how ASICs contribute to various types of neuronal injury in the brain. This article is part of the Special Issue entitled 'Acid-Sensing Ion Channels in the Nervous System'.
Collapse
Affiliation(s)
- Yan Huang
- School of Pharmacy, Anhui Medical University, Hefei, China; Neuroscience Institute, Morehouse School of Medicine, Atlanta GA 30310, USA
| | - Nan Jiang
- Department of Physiology and Cell Biology, University of South Alabama College of Medicine, Mobile, AL 36688, USA; Lab of Neuropharmacology and Neurotoxicology, Shanghai University, Shanghai, China
| | - Jun Li
- School of Pharmacy, Anhui Medical University, Hefei, China
| | - Yong-Hua Ji
- Lab of Neuropharmacology and Neurotoxicology, Shanghai University, Shanghai, China
| | - Zhi-Gang Xiong
- Neuroscience Institute, Morehouse School of Medicine, Atlanta GA 30310, USA.
| | - Xiang-ming Zha
- Department of Physiology and Cell Biology, University of South Alabama College of Medicine, Mobile, AL 36688, USA.
| |
Collapse
|
35
|
Szikra T, Trenholm S, Drinnenberg A, Jüttner J, Raics Z, Farrow K, Biel M, Awatramani G, Clark DA, Sahel JA, da Silveira RA, Roska B. Rods in daylight act as relay cells for cone-driven horizontal cell-mediated surround inhibition. Nat Neurosci 2014; 17:1728-35. [PMID: 25344628 DOI: 10.1038/nn.3852] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2014] [Accepted: 09/29/2014] [Indexed: 12/18/2022]
Abstract
Vertebrate vision relies on two types of photoreceptors, rods and cones, which signal increments in light intensity with graded hyperpolarizations. Rods operate in the lower range of light intensities while cones operate at brighter intensities. The receptive fields of both photoreceptors exhibit antagonistic center-surround organization. Here we show that at bright light levels, mouse rods act as relay cells for cone-driven horizontal cell-mediated surround inhibition. In response to large, bright stimuli that activate their surrounds, rods depolarize. Rod depolarization increases with stimulus size, and its action spectrum matches that of cones. Rod responses at high light levels are abolished in mice with nonfunctional cones and when horizontal cells are reversibly inactivated. Rod depolarization is conveyed to the inner retina via postsynaptic circuit elements, namely the rod bipolar cells. Our results show that the retinal circuitry repurposes rods, when they are not directly sensing light, to relay cone-driven surround inhibition.
Collapse
Affiliation(s)
- Tamas Szikra
- Neural Circuit Laboratories, Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | - Stuart Trenholm
- 1] Neural Circuit Laboratories, Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland. [2] Department of Biology, University of Victoria, Victoria, British Columbia, Canada
| | - Antonia Drinnenberg
- 1] Neural Circuit Laboratories, Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland. [2] University of Basel, Basel, Switzerland
| | - Josephine Jüttner
- Neural Circuit Laboratories, Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | - Zoltan Raics
- Neural Circuit Laboratories, Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | - Karl Farrow
- Neural Circuit Laboratories, Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| | - Martin Biel
- Department of Pharmacy-Center for Drug Research, Center for Integrated Protein Science Munich, Ludwig-Maximilians University, Munich, Germany
| | - Gautam Awatramani
- Department of Biology, University of Victoria, Victoria, British Columbia, Canada
| | - Damon A Clark
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut, USA
| | - José-Alain Sahel
- 1] Université Pierre et Marie Curie-Sorbonne Universités, Institut de la Vision, Paris, France. [2] Institut national de la santé et de la recherche médicale, Institut de la Vision, Paris, France. [3] Centre national de la recherche scientifique, Institut de la Vision, Paris, France. [4] Centre Hospitalier National d'Ophtalmologie des Quinze-Vingts, Département Hospitalo-Universitaire ViewMaintain, Paris, France. [5] Fondation Ophtalmologique Adolphe de Rothschild, Paris, France
| | - Rava Azeredo da Silveira
- 1] Department of Physics, École Normale Supérieure, Paris, France. [2] Laboratoire de Physique Statistique, Centre National de la Recherche Scientifique, Université Pierre et Marie Curie, Université Denis Diderot, Paris, France
| | - Botond Roska
- Neural Circuit Laboratories, Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland
| |
Collapse
|
36
|
Differential regulation of cone calcium signals by different horizontal cell feedback mechanisms in the mouse retina. J Neurosci 2014; 34:11826-43. [PMID: 25164677 DOI: 10.1523/jneurosci.0272-14.2014] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Controlling neurotransmitter release by modulating the presynaptic calcium level is a key mechanism to ensure reliable signal transmission from one neuron to the next. In this study, we investigated how the glutamatergic output of cone photoreceptors (cones) in the mouse retina is shaped by different feedback mechanisms from postsynaptic GABAergic horizontal cells (HCs) using a combination of two-photon calcium imaging and pharmacology at the level of individual cone axon terminals. We provide evidence that hemichannel-mediated (putative ephaptic) feedback sets the cone output gain by defining the basal calcium level, a mechanism that may be crucial for adapting cones to the ambient light level. In contrast, pH-mediated feedback did not modulate the cone basal calcium level but affected the size and shape of light-evoked cone calcium signals in a contrast-dependent way: low-contrast light responses were amplified, whereas high-contrast light responses were reduced. Finally, we provide functional evidence that GABA shapes light-evoked calcium signals in cones. Because we could not localize ionotropic GABA receptors on cone axon terminals using electron microscopy, we suggest that GABA may act through GABA autoreceptors on HCs, thereby possibly modulating hemichannel- and/or pH-mediated feedback. Together, our results suggest that at the cone synapse, hemichannel-mediated (ephaptic) and pH-mediated feedback fulfill distinct functions to adjust the output of cones to changing ambient light levels and stimulus contrasts and that the efficacy of these feedback mechanisms is likely modulated by GABA release in the outer retina.
Collapse
|
37
|
Gardner CL, Jones JR, Baer SM, Crook SM. Drift-diffusion simulation of the ephaptic effect in the triad synapse of the retina. J Comput Neurosci 2014; 38:129-42. [PMID: 25260382 DOI: 10.1007/s10827-014-0531-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2013] [Revised: 08/28/2014] [Accepted: 09/12/2014] [Indexed: 12/18/2022]
Abstract
Experimental evidence suggests the existence of a negative feedback pathway between horizontal cells and cone photoreceptors in the outer plexiform layer of the retina that modulates the flow of calcium ions into the synaptic terminals of cones. However, the underlying mechanism for this feedback is controversial and there are currently three competing hypotheses: the ephaptic hypothesis, the pH hypothesis, and the GABA hypothesis. The goal of this investigation is to demonstrate the ephaptic hypothesis by means of detailed numerical simulations. The drift-diffusion (Poisson-Nernst-Planck) model with membrane boundary current equations is applied to a realistic two-dimensional cross-section of the triad synapse in the goldfish retina to verify the existence of strictly electrical feedback, as predicted by the ephaptic hypothesis. The effect on electrical feedback from the behavior of the bipolar cell membrane potential is also explored. The computed steady-state cone calcium transmembrane current-voltage curves for several cases are presented and compared with experimental data on goldfish. The results provide convincing evidence that an ephaptic mechanism can produce the feedback effect seen in experiments. The model and numerical methods presented here can be applied to any neuronal circuit where dendritic spines are invaginated in presynaptic terminals or boutons.
Collapse
Affiliation(s)
- Carl L Gardner
- School of Mathematical & Statistical Sciences, Arizona State University, Tempe, AZ, 85287, USA,
| | | | | | | |
Collapse
|
38
|
Hoon M, Okawa H, Della Santina L, Wong ROL. Functional architecture of the retina: development and disease. Prog Retin Eye Res 2014; 42:44-84. [PMID: 24984227 DOI: 10.1016/j.preteyeres.2014.06.003] [Citation(s) in RCA: 337] [Impact Index Per Article: 33.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2014] [Revised: 06/08/2014] [Accepted: 06/22/2014] [Indexed: 12/22/2022]
Abstract
Structure and function are highly correlated in the vertebrate retina, a sensory tissue that is organized into cell layers with microcircuits working in parallel and together to encode visual information. All vertebrate retinas share a fundamental plan, comprising five major neuronal cell classes with cell body distributions and connectivity arranged in stereotypic patterns. Conserved features in retinal design have enabled detailed analysis and comparisons of structure, connectivity and function across species. Each species, however, can adopt structural and/or functional retinal specializations, implementing variations to the basic design in order to satisfy unique requirements in visual function. Recent advances in molecular tools, imaging and electrophysiological approaches have greatly facilitated identification of the cellular and molecular mechanisms that establish the fundamental organization of the retina and the specializations of its microcircuits during development. Here, we review advances in our understanding of how these mechanisms act to shape structure and function at the single cell level, to coordinate the assembly of cell populations, and to define their specific circuitry. We also highlight how structure is rearranged and function is disrupted in disease, and discuss current approaches to re-establish the intricate functional architecture of the retina.
Collapse
Affiliation(s)
- Mrinalini Hoon
- Department of Biological Structure, University of Washington, 1959 NE Pacific Street, Seattle, WA 98195, USA
| | - Haruhisa Okawa
- Department of Biological Structure, University of Washington, 1959 NE Pacific Street, Seattle, WA 98195, USA
| | - Luca Della Santina
- Department of Biological Structure, University of Washington, 1959 NE Pacific Street, Seattle, WA 98195, USA
| | - Rachel O L Wong
- Department of Biological Structure, University of Washington, 1959 NE Pacific Street, Seattle, WA 98195, USA.
| |
Collapse
|
39
|
Acid-sensing ion channels contribute to synaptic transmission and inhibit cocaine-evoked plasticity. Nat Neurosci 2014; 17:1083-91. [PMID: 24952644 PMCID: PMC4115047 DOI: 10.1038/nn.3750] [Citation(s) in RCA: 150] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2014] [Accepted: 05/27/2014] [Indexed: 12/14/2022]
Abstract
Acid-sensing ion channel 1A (ASIC1A) is abundant in the nucleus accumbens (NAc), a region known for its role in addiction. Because ASIC1A has been suggested to promote associative learning, we hypothesized that disrupting ASIC1A in the NAc would reduce drug-associated learning and memory. However, contrary to this hypothesis, we found that disrupting ASIC1A in the mouse NAc increased cocaine-conditioned place preference, suggesting an unexpected role for ASIC1A in addiction-related behavior. Moreover, overexpressing ASIC1A in rat NAc reduced cocaine self-administration. Investigating the underlying mechanisms, we identified a previously unknown postsynaptic current during neurotransmission that was mediated by ASIC1A and ASIC2 and thus well positioned to regulate synapse structure and function. Consistent with this possibility, disrupting ASIC1A altered dendritic spine density and glutamate receptor function, and increased cocaine-evoked plasticity, which resemble changes previously associated with cocaine-induced behavior. Together, these data suggest that ASIC1A inhibits the plasticity underlying addiction-related behavior and raise the possibility of developing therapies for drug addiction by targeting ASIC-dependent neurotransmission.
Collapse
|
40
|
Protons are a neurotransmitter that regulates synaptic plasticity in the lateral amygdala. Proc Natl Acad Sci U S A 2014; 111:8961-6. [PMID: 24889629 DOI: 10.1073/pnas.1407018111] [Citation(s) in RCA: 196] [Impact Index Per Article: 19.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Stimulating presynaptic terminals can increase the proton concentration in synapses. Potential receptors for protons are acid-sensing ion channels (ASICs), Na(+)- and Ca(2+)-permeable channels that are activated by extracellular acidosis. Those observations suggest that protons might be a neurotransmitter. We found that presynaptic stimulation transiently reduced extracellular pH in the amygdala. The protons activated ASICs in lateral amygdala pyramidal neurons, generating excitatory postsynaptic currents. Moreover, both protons and ASICs were required for synaptic plasticity in lateral amygdala neurons. The results identify protons as a neurotransmitter, and they establish ASICs as the postsynaptic receptor. They also indicate that protons and ASICs are a neurotransmitter/receptor pair critical for amygdala-dependent learning and memory.
Collapse
|
41
|
Vroman R, Klaassen LJ, Howlett MH, Cenedese V, Klooster J, Sjoerdsma T, Kamermans M. Extracellular ATP hydrolysis inhibits synaptic transmission by increasing ph buffering in the synaptic cleft. PLoS Biol 2014; 12:e1001864. [PMID: 24844296 PMCID: PMC4028192 DOI: 10.1371/journal.pbio.1001864] [Citation(s) in RCA: 64] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2013] [Accepted: 04/10/2014] [Indexed: 11/18/2022] Open
Abstract
A slow mechanism of retinal synaptic inhibition involves hydrolysis of ATP released from pannexin 1 channels (from the tips of horizontal cell dendrites); the resulting protons and phosphates acidify the synaptic cleft, which inhibits neurotransmitter release. Neuronal computations strongly depend on inhibitory interactions. One such example occurs at the first retinal synapse, where horizontal cells inhibit photoreceptors. This interaction generates the center/surround organization of bipolar cell receptive fields and is crucial for contrast enhancement. Despite its essential role in vision, the underlying synaptic mechanism has puzzled the neuroscience community for decades. Two competing hypotheses are currently considered: an ephaptic and a proton-mediated mechanism. Here we show that horizontal cells feed back to photoreceptors via an unexpected synthesis of the two. The first one is a very fast ephaptic mechanism that has no synaptic delay, making it one of the fastest inhibitory synapses known. The second one is a relatively slow (τ≈200 ms), highly intriguing mechanism. It depends on ATP release via Pannexin 1 channels located on horizontal cell dendrites invaginating the cone synaptic terminal. The ecto-ATPase NTPDase1 hydrolyses extracellular ATP to AMP, phosphate groups, and protons. The phosphate groups and protons form a pH buffer with a pKa of 7.2, which keeps the pH in the synaptic cleft relatively acidic. This inhibits the cone Ca2+ channels and consequently reduces the glutamate release by the cones. When horizontal cells hyperpolarize, the pannexin 1 channels decrease their conductance, the ATP release decreases, and the formation of the pH buffer reduces. The resulting alkalization in the synaptic cleft consequently increases cone glutamate release. Surprisingly, the hydrolysis of ATP instead of ATP itself mediates the synaptic modulation. Our results not only solve longstanding issues regarding horizontal cell to photoreceptor feedback, they also demonstrate a new form of synaptic modulation. Because pannexin 1 channels and ecto-ATPases are strongly expressed in the nervous system and pannexin 1 function is implicated in synaptic plasticity, we anticipate that this novel form of synaptic modulation may be a widespread phenomenon. At the first retinal synapse, specific cells—horizontal cells (HCs)—inhibit photoreceptors and help to organize the receptive fields of another retinal cell type, bipolar cells. This synaptic interaction is crucial for visual contrast enhancement. Here we show that horizontal cells feed back to photoreceptors via a very fast ephaptic mechanism and a relatively slow mechanism. The slow mechanism requires ATP release via Pannexin 1 (Panx1) channels that are located on HC dendrites near the site where photoreceptors release the neurotransmitter glutamate to HCs and bipolar cells. The released ATP is hydrolyzed to produce AMP, phosphate groups, and protons; these phosphates and protons form a pH buffer, which acidifies the synaptic cleft. This slow acidification inhibits presynaptic calcium channels and consequently reduces the neurotransmitter release of photoreceptors. This demonstrates a new way in which ATP release can be involved in synaptic modulation. Surprisingly, the action of ATP is not purinergic but is mediated via changes in the pH buffer capacity in the synaptic cleft. Given the broad expression of Panx1 channels in the nervous system and the suggestion that Panx1 function underlies stabilization of synaptic plasticity and is needed for learning, we anticipate that this mechanism will be more widespread than just occurring at the first retinal synapse.
Collapse
Affiliation(s)
- Rozan Vroman
- Netherlands Institute for Neuroscience, Amsterdam, the Netherlands
| | - Lauw J. Klaassen
- Netherlands Institute for Neuroscience, Amsterdam, the Netherlands
| | | | | | - Jan Klooster
- Netherlands Institute for Neuroscience, Amsterdam, the Netherlands
| | | | - Maarten Kamermans
- Netherlands Institute for Neuroscience, Amsterdam, the Netherlands
- * E-mail:
| |
Collapse
|
42
|
Gao F, Pang JJ, Wu SM. Sign-preserving and sign-inverting synaptic interactions between rod and cone photoreceptors in the dark-adapted retina. J Physiol 2013; 591:5711-26. [PMID: 24000179 DOI: 10.1113/jphysiol.2013.260984] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
We show that various types of rods and cones in the dark-adapted salamander retina are electrically coupled with linear and symmetrical junctional conductances G(j) (40-223 pS) and a rank order: Rod(C)-large single cone, rod-large single cone, rod-small single cone, rod-accessory double cone and rod-principal double cone. By systematically comparing the transjunctional current-voltage (I(j)-V(j)) relations and average G(j) values of the five types of rod-cone pairs recorded at day and night times, our results suggest that the differences in G(j) values among various types of rod-cone pairs are not caused by circadian differences, and the circadian-dependent changes in rod-cone coupling observed in the fish and rodent retinas are not present in the tiger salamander. In addition to rod-cone coupling, there is a sign-inverting, unidirectional rod→cone current I(RC), and the I(RC)-V(Cone) relations are linear, with a reversal potential near the chloride reversal potential E(Cl). I(RC) can be observed in rods and cones separated by at least 260 μm, and its waveform resembles that of the rod-elicited horizontal cell (HC) response I(HC). A glutamate transporter-associated chloride channel blocker TBOA suppresses I(RC) but not I(HC). These results suggest that I(RC) is largely mediated by HCs via a sign-inverting feedback chemical synapse associated with a chloride channel. I(RC) significantly reduced rod→cone coupling in the frequency range below 15 Hz, allowing better separation of rod and cone signals in the dark-adapted retina.
Collapse
Affiliation(s)
- Fan Gao
- S. M. Wu: Cullen Eye Institute, Baylor College of Medicine, One Baylor Plaza, NC-205, Houston, TX 77030, USA.
| | | | | |
Collapse
|
43
|
Kranz K, Dorgau B, Pottek M, Herrling R, Schultz K, Bolte P, Monyer H, Penuela S, Laird DW, Dedek K, Weiler R, Janssen-Bienhold U. Expression of Pannexin1 in the outer plexiform layer of the mouse retina and physiological impact of its knockout. J Comp Neurol 2013; 521:1119-35. [PMID: 22965528 DOI: 10.1002/cne.23223] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2012] [Revised: 07/09/2012] [Accepted: 09/05/2012] [Indexed: 11/09/2022]
Abstract
Pannexin1 (Panx1) belongs to a class of vertebrate proteins that exhibits sequence homology to innexins, the invertebrate gap junction proteins, and which also shares topological similarities with vertebrate gap junction proteins, the connexins. Unlike gap junctional channels, Panx1 forms single-membrane channels, whose functional role in neuronal circuits is still unsettled. We therefore investigated the subcellular distribution of Panx1 in the mouse retina of wildtype and Panx1-null mice by reverse-transcription polymerase chain reaction (RT-PCR), immunohistochemistry, and electron microscopy. Use of Panx1-deficient mice served as a model to assess the physiological role of Panx1 by electroretinographic recordings and also to ensure the specificity of the anti-Panx1 antibody labeling. Expression of Panx1 was found in type 3a OFF bipolar cells and in dendrites and axonal processes of horizontal cells. Panx1 was also found in horizontal cell dendrites representing the lateral elements of the triad synapse at cone and rod terminals. In vivo electroretinography of Panx1 knockout mice indicated an increased a- and b-wave compared to Panx1 wildtype mice under scotopic conditions. The effect on the b-wave was confirmed by in vitro electroretinograms from the inner retina. These results suggest that Panx1 channels serve as sinks for extracellular current flow making them possible candidates for the mediation of feedback from horizontal cells to photoreceptors.
Collapse
Affiliation(s)
- Katharina Kranz
- Department of Neurobiology, University of Oldenburg, D-26111 Oldenburg, Germany
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
44
|
Liu X, Hirano AA, Sun X, Brecha NC, Barnes S. Calcium channels in rat horizontal cells regulate feedback inhibition of photoreceptors through an unconventional GABA- and pH-sensitive mechanism. J Physiol 2013; 591:3309-24. [PMID: 23613534 DOI: 10.1113/jphysiol.2012.248179] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Horizontal cells send inhibitory feedback to photoreceptors, helping form antagonistic receptive fields in the retina, but the neurotransmitter and the mechanisms underlying this signalling are not known. Since the proteins responsible for conventional Ca(2+)-dependent release of GABAergic synaptic vesicles are present in mammalian horizontal cells, we investigated this conventional mechanism as the means by which horizontal cells inhibit photoreceptors. Using Ca(2+) imaging in rat retinal slices, we confirm that horizontal cell depolarization with kainate inhibits and horizontal cell hyperpolarization with NBQX disinhibits the Ca(2+) signals produced by pH-sensitive activation of voltage-gated calcium channels (Ca channels) in photoreceptors. We show that while 100 μm Co(2+) reduces photoreceptor Ca(2+) signals, it disinhibits them at 10 μm, an effect reminiscent of earlier studies where low [Co(2+)] eliminated feedback. The low [Co(2+)] disinhibition is pH sensitive. We localized L-, N- and P/Q-type Ca channels in rat horizontal cells, and showed that both the N-type Ca channel blocker -conotoxin GVIA and the P/Q-type Ca channel blocker -agatoxin IVA increased Ca(2+) signals in photoreceptors in a pH-sensitive manner. Pronounced actions of GABAergic agents on feedback signals to photoreceptors were observed, and are pH sensitive, but are inconsistent with direct inhibition by GABA of photoreceptor [Ca(2+)]. Patch-clamp studies revealed that GABA activates a conductance having high bicarbonate permeability in isolated horizontal cells, suggesting that the commonality of pH sensitivity throughout the results could arise from a GABA autofeedback action in horizontal cells. This could change cleft pH with concomitant inhibitory influences on photoreceptor Ca channels.
Collapse
Affiliation(s)
- Xue Liu
- S. Barnes: Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
| | | | | | | | | |
Collapse
|
45
|
Hanneken AM, Babai N, Thoreson WB. Oral proton pump inhibitors disrupt horizontal cell-cone feedback and enhance visual hallucinations in macular degeneration patients. Invest Ophthalmol Vis Sci 2013; 54:1485-9. [PMID: 23341015 DOI: 10.1167/iovs.12-11091] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE Visual hallucinations (VHs) occur in macular degeneration patients with poor vision but normal cognitive function. The underlying mechanisms are poorly understood. We report the identification of pharmaceutical agents that enhance VH and use these agents to examine the contribution of retinal neurons to this syndrome. METHODS We detail clinical observations on VH in five macular degeneration patients treated with proton pump inhibitors having the core structure, 2-pyridyl-methylsulfinyl-benzimidazole. We tested possible retinal mechanisms using paired whole cell recordings to examine effects of these compounds on feedback interactions between horizontal cells and cones in amphibian retina. RESULTS Five patients with advanced wet macular degeneration described patterned VHs that were induced or enhanced by oral proton pump inhibitors. The abnormal images increased with light, disappeared in the dark, and originated in the retina, based on ophthalmodynamometry. Simultaneous paired whole cell recordings from amphibian cones and horizontal cells showed that 2-pyridyl-methylsulfinyl-benzimidazoles blocked the negative shift in voltage dependence and increase in amplitude of the calcium current (ICa) in cones that is induced by changes in horizontal cell membrane potential. These effects disrupt the negative feedback from horizontal cells to cones that is important for the formation of center-surround receptive fields in bipolar and ganglion cells, and thus for normal spatial and chromatic perception. CONCLUSIONS Our study suggests that changes in the output of retinal neurons caused by disturbances in outer retinal feedback mechanisms can enhance patterned visual hallucinations.
Collapse
Affiliation(s)
- Anne M Hanneken
- Department of Molecular & Experimental Medicine, The Scripps Research Institute, 10550 North Torrey Pines Road, SP-201, La Jolla, CA 92037, USA.
| | | | | |
Collapse
|
46
|
Allman E, Waters K, Ackroyd S, Nehrke K. Analysis of Ca2+ signaling motifs that regulate proton signaling through the Na+/H+ exchanger NHX-7 during a rhythmic behavior in Caenorhabditis elegans. J Biol Chem 2013; 288:5886-95. [PMID: 23319594 DOI: 10.1074/jbc.m112.434852] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Membrane proton transporters contribute to pH homeostasis but have also been shown to transmit information between cells in close proximity through regulated proton secretion. For example, the nematode intestinal Na(+)/H(+) exchanger NHX-7 causes adjacent muscle cells to contract by transiently acidifying the extracellular space between the intestine and muscle. NHX-7 operates during a Ca(2+)-dependent rhythmic behavior and contains several conserved motifs for regulation by Ca(2+) input, including motifs for calmodulin and phosphatidylinositol 4,5-bisphosphate binding, protein kinase C- and calmodulin-dependent protein kinase type II phosphorylation, and a binding site for calcineurin homologous protein. Here, we tested the idea that Ca(2+) input differentiates proton signaling from pH housekeeping activity. Each of these motifs was mutated, and their contribution to NHX-7 function was assessed. These functions included pH recovery from acidification in cells in culture expressing recombinant NHX-7, extracellular acidification measured during behavior in live moving worms, and muscle contraction strength as a result of this acidification. Our data suggest that multiple levels of Ca(2+) input regulate NHX-7, whose transport capacity normally exceeds the minimum necessary to cause muscle contraction. Furthermore, extracellular acidification limits NHX-7 proton transport through feedback inhibition, likely to prevent metabolic acidosis from occurring. Our findings are consistent with an integrated network whereby both Ca(2+) and pH contribute to proton signaling. Finally, our results obtained by expressing rat NHE1 in Caenorhabditis elegans suggest that a conserved mechanism of regulation may contribute to cell-cell communication or proton signaling by Na(+)/H(+) exchangers in mammals.
Collapse
Affiliation(s)
- Erik Allman
- Department of Pharmacology and Physiology, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642, USA
| | | | | | | |
Collapse
|
47
|
|
48
|
Ablation of retinal horizontal cells from adult mice leads to rod degeneration and remodeling in the outer retina. J Neurosci 2012; 32:10713-24. [PMID: 22855819 DOI: 10.1523/jneurosci.0442-12.2012] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
In the brain, including the retina, interneurons show an enormous structural and functional diversity. Retinal horizontal cells represent a class of interneurons that form triad synapses with photoreceptors and ON bipolar cells. At this first retinal synapse, horizontal cells modulate signal transmission from photoreceptors to bipolar cells by feedback and feedforward inhibition. To test how the fully developed retina reacts to the specific loss of horizontal cells, these interneurons were specifically ablated from adult mice using the diphtheria toxin (DT)/DT-receptor system and the connexin57 promoter. Following ablation, the retinal network responded with extensive remodeling: rods retracted their axons from the outer plexiform layer and partially degenerated, whereas cones survived. Cone pedicles remained in the outer plexiform layer and preserved synaptic contacts with OFF but not with ON bipolar cells. Consistently, the retinal ON pathway was impaired, leading to reduced amplitudes and prolonged latencies in electroretinograms. However, ganglion cell responses showed only slight changes in time course, presumably because ON bipolar cells formed multiple ectopic synapses with photoreceptors, and visual performance, assessed with an optomotor system, was only mildly affected. Thus, the loss of an entire interneuron class can be largely compensated even by the adult retinal network.
Collapse
|
49
|
Buldyrev I, Taylor WR. Inhibitory mechanisms that generate centre and surround properties in ON and OFF brisk-sustained ganglion cells in the rabbit retina. J Physiol 2012; 591:303-25. [PMID: 23045347 DOI: 10.1113/jphysiol.2012.243113] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Lateral inhibition produces the centre-surround organization of retinal receptive fields, in which inhibition driven by the mean luminance enhances the sensitivity of ganglion cells to spatial and temporal contrast. Surround inhibition is generated in both synaptic layers; however, the synaptic mechanisms within the inner plexiform layer are not well characterized within specific classes of retinal ganglion cell. Here, we compared the synaptic circuits generating concentric centre-surround receptive fields in ON and OFF brisk-sustained ganglion cells (BSGCs) in the rabbit retina. We first characterized the synaptic inputs to the centre of ON BSGCs, for comparison with previous results from OFF BSGCs. Similar to wide-field ganglion cells, the spatial extent of the excitatory centre and inhibitory surround was larger for the ON than the OFF BSGCs. The results indicate that the surrounds of ON and OFF BSGCs are generated in both the outer and the inner plexiform layers. The inner plexiform layer surround inhibition comprised GABAergic suppression of excitatory inputs from bipolar cells. However, ON and OFF BSGCs displayed notable differences. Surround suppression of excitatory inputs was weaker in ON than OFF BSGCs, and was mediated largely by GABA(C) receptors in ON BSGCs, and by both GABA(A) and GABA(C) receptors in OFF BSGCs. Large ON pathway-mediated glycinergic inputs to ON and OFF BSGCs also showed surround suppression, while much smaller GABAergic inputs showed weak, if any, spatial tuning. Unlike OFF BSGCs, which receive strong glycinergic crossover inhibition from the ON pathway, the ON BSGCs do not receive crossover inhibition from the OFF pathway. We compare and discuss possible roles for glycinergic inhibition in the two cell types.
Collapse
Affiliation(s)
- Ilya Buldyrev
- Casey Eye Institute, Department of Ophthalmology, School of Medicine, Oregon Health and Science University, Portland, OR 97239, USA
| | | |
Collapse
|
50
|
Thoreson WB, Mangel SC. Lateral interactions in the outer retina. Prog Retin Eye Res 2012; 31:407-41. [PMID: 22580106 PMCID: PMC3401171 DOI: 10.1016/j.preteyeres.2012.04.003] [Citation(s) in RCA: 136] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2012] [Revised: 03/05/2012] [Accepted: 03/09/2012] [Indexed: 10/28/2022]
Abstract
Lateral interactions in the outer retina, particularly negative feedback from horizontal cells to cones and direct feed-forward input from horizontal cells to bipolar cells, play a number of important roles in early visual processing, such as generating center-surround receptive fields that enhance spatial discrimination. These circuits may also contribute to post-receptoral light adaptation and the generation of color opponency. In this review, we examine the contributions of horizontal cell feedback and feed-forward pathways to early visual processing. We begin by reviewing the properties of bipolar cell receptive fields, especially with respect to modulation of the bipolar receptive field surround by the ambient light level and to the contribution of horizontal cells to the surround. We then review evidence for and against three proposed mechanisms for negative feedback from horizontal cells to cones: 1) GABA release by horizontal cells, 2) ephaptic modulation of the cone pedicle membrane potential generated by currents flowing through hemigap junctions in horizontal cell dendrites, and 3) modulation of cone calcium currents (I(Ca)) by changes in synaptic cleft proton levels. We also consider evidence for the presence of direct horizontal cell feed-forward input to bipolar cells and discuss a possible role for GABA at this synapse. We summarize proposed functions of horizontal cell feedback and feed-forward pathways. Finally, we examine the mechanisms and functions of two other forms of lateral interaction in the outer retina: negative feedback from horizontal cells to rods and positive feedback from horizontal cells to cones.
Collapse
Affiliation(s)
- Wallace B. Thoreson
- Departments of Ophthalmology & Visual Sciences and Pharmacology & Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE 68198 USA
| | - Stuart C. Mangel
- Department of Neuroscience, The Ohio State University College of Medicine, Columbus, OH 43210 USA
| |
Collapse
|