1
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Seo H, Chung WG, Kwon YW, Kim S, Hong YM, Park W, Kim E, Lee J, Lee S, Kim M, Lim K, Jeong I, Song H, Park JU. Smart Contact Lenses as Wearable Ophthalmic Devices for Disease Monitoring and Health Management. Chem Rev 2023; 123:11488-11558. [PMID: 37748126 PMCID: PMC10571045 DOI: 10.1021/acs.chemrev.3c00290] [Citation(s) in RCA: 16] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2023] [Indexed: 09/27/2023]
Abstract
The eye contains a complex network of physiological information and biomarkers for monitoring disease and managing health, and ocular devices can be used to effectively perform point-of-care diagnosis and disease management. This comprehensive review describes the target biomarkers and various diseases, including ophthalmic diseases, metabolic diseases, and neurological diseases, based on the physiological and anatomical background of the eye. This review also includes the recent technologies utilized in eye-wearable medical devices and the latest trends in wearable ophthalmic devices, specifically smart contact lenses for the purpose of disease management. After introducing other ocular devices such as the retinal prosthesis, we further discuss the current challenges and potential possibilities of smart contact lenses.
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Affiliation(s)
- Hunkyu Seo
- Department
of Materials Science and Engineering, Yonsei
University, Seoul 03722, Republic
of Korea
| | - Won Gi Chung
- Department
of Materials Science and Engineering, Yonsei
University, Seoul 03722, Republic
of Korea
| | - Yong Won Kwon
- Department
of Materials Science and Engineering, Yonsei
University, Seoul 03722, Republic
of Korea
| | - Sumin Kim
- Department
of Materials Science and Engineering, Yonsei
University, Seoul 03722, Republic
of Korea
| | - Yeon-Mi Hong
- Department
of Materials Science and Engineering, Yonsei
University, Seoul 03722, Republic
of Korea
| | - Wonjung Park
- Department
of Materials Science and Engineering, Yonsei
University, Seoul 03722, Republic
of Korea
| | - Enji Kim
- Department
of Materials Science and Engineering, Yonsei
University, Seoul 03722, Republic
of Korea
| | - Jakyoung Lee
- Department
of Materials Science and Engineering, Yonsei
University, Seoul 03722, Republic
of Korea
| | - Sanghoon Lee
- Department
of Materials Science and Engineering, Yonsei
University, Seoul 03722, Republic
of Korea
| | - Moohyun Kim
- Department
of Materials Science and Engineering, Yonsei
University, Seoul 03722, Republic
of Korea
| | - Kyeonghee Lim
- Department
of Materials Science and Engineering, Yonsei
University, Seoul 03722, Republic
of Korea
| | - Inhea Jeong
- Department
of Materials Science and Engineering, Yonsei
University, Seoul 03722, Republic
of Korea
| | - Hayoung Song
- Department
of Materials Science and Engineering, Yonsei
University, Seoul 03722, Republic
of Korea
| | - Jang-Ung Park
- Department
of Materials Science and Engineering, Yonsei
University, Seoul 03722, Republic
of Korea
- Department
of Neurosurgery, Yonsei University College
of Medicine, Seoul 03722, Republic of Korea
- Center
for Nanomedicine, Institute for Basic Science (IBS), Yonsei University, Seoul 03722, Republic
of Korea
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2
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Luessen DJ, Conn PJ. Allosteric Modulators of Metabotropic Glutamate Receptors as Novel Therapeutics for Neuropsychiatric Disease. Pharmacol Rev 2022; 74:630-661. [PMID: 35710132 PMCID: PMC9553119 DOI: 10.1124/pharmrev.121.000540] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Metabotropic glutamate (mGlu) receptors, a family of G-protein-coupled receptors, have been identified as novel therapeutic targets based on extensive research supporting their diverse contributions to cell signaling and physiology throughout the nervous system and important roles in regulating complex behaviors, such as cognition, reward, and movement. Thus, targeting mGlu receptors may be a promising strategy for the treatment of several brain disorders. Ongoing advances in the discovery of subtype-selective allosteric modulators for mGlu receptors has provided an unprecedented opportunity for highly specific modulation of signaling by individual mGlu receptor subtypes in the brain by targeting sites distinct from orthosteric or endogenous ligand binding sites on mGlu receptors. These pharmacological agents provide the unparalleled opportunity to selectively regulate neuronal excitability, synaptic transmission, and subsequent behavioral output pertinent to many brain disorders. Here, we review preclinical and clinical evidence supporting the utility of mGlu receptor allosteric modulators as novel therapeutic approaches to treat neuropsychiatric diseases, such as schizophrenia, substance use disorders, and stress-related disorders.
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3
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Young BK, Ramakrishnan C, Ganjawala T, Wang P, Deisseroth K, Tian N. An uncommon neuronal class conveys visual signals from rods and cones to retinal ganglion cells. Proc Natl Acad Sci U S A 2021; 118:e2104884118. [PMID: 34702737 PMCID: PMC8612366 DOI: 10.1073/pnas.2104884118] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/07/2021] [Indexed: 01/01/2023] Open
Abstract
Neurons in the central nervous system (CNS) are distinguished by the neurotransmitter types they release, their synaptic connections, morphology, and genetic profiles. To fully understand how the CNS works, it is critical to identify all neuronal classes and reveal their synaptic connections. The retina has been extensively used to study neuronal development and circuit formation. Here, we describe a previously unidentified interneuron in mammalian retina. This interneuron shares some morphological, physiological, and molecular features with retinal bipolar cells, such as receiving input from photoreceptors and relaying visual signals to retinal ganglion cells. It also shares some features with amacrine cells (ACs), particularly Aii-ACs, such as their neurite morphology in the inner plexiform layer, the expression of some AC-specific markers, and possibly the release of the inhibitory neurotransmitter glycine. Thus, we unveil an uncommon interneuron, which may play an atypical role in vision.
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Affiliation(s)
- Brent K Young
- Department of Ophthalmology & Visual Sciences, University of Utah, Salt Lake City, UT 84132
- Interdepartmental Neuroscience Program, University of Utah, Salt Lake City, UT 84114
| | | | - Tushar Ganjawala
- Department of Ophthalmology, Visual and Anatomical Sciences, Wayne State University School of Medicine, Detroit, MI 48202
| | - Ping Wang
- Department of Ophthalmology & Visual Sciences, University of Utah, Salt Lake City, UT 84132
| | - Karl Deisseroth
- Department of Bioengineering, Stanford University, Stanford, CA 94305
- Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305
| | - Ning Tian
- Department of Ophthalmology & Visual Sciences, University of Utah, Salt Lake City, UT 84132;
- Interdepartmental Neuroscience Program, University of Utah, Salt Lake City, UT 84114
- Department of Neurobiology, University of Utah, Salt Lake City, UT 84132
- Department of Biomedical Engineering, University of Utah, Salt Lake City, UT 84132
- Veterans Affairs Medical Center, Salt Lake City, UT 84148
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4
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Arora S, Surakiatchanukul T, Arora T, Cagini C, Lupidi M, Chhablani J. Sildenafil in ophthalmology: An update. Surv Ophthalmol 2021; 67:463-487. [PMID: 34175342 DOI: 10.1016/j.survophthal.2021.06.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2020] [Revised: 06/18/2021] [Accepted: 06/21/2021] [Indexed: 12/14/2022]
Abstract
Sildenafil citrate, a selective oral phosphodiesterase 5 inhibitor, is a widely used drug for erectile dysfunction that acts by elevating cGMP levels and causing smooth muscle relaxation. It also has 10% activity against PDE6, a key enzyme in phototransduction cascade in the retina. Recent ocular imaging developments have further revealed the influence of sildenafil on ocular hemodynamics, particularly choroidal perfusion. Choroidal thickness is increased, and choroidal perfusion is also enhanced by autoregulatory mechanisms that are further dependent on age and microvascular abnormalities. Studies demonstrating high intraocular pressure via a "parallel pathway" from increased choroidal volume and blood flow to the ciliary body have challenged previous concepts. Another new observation is the effect of sildenafil on bipolar cells and cyclic-nucleotide gated channels. We discuss potential deleterious effects (central serous chorioretinopathy, glaucoma, ischemic optic neuropathy, and risks to recessive carriers of retinitis pigmentosa), potential beneficial effects (ameliorate choroidal ischemia, prevent thickening of Bruch membrane, and promote recovery of the ellipsoid zone) in macular degeneration, as well as potential drug interactions of sildenafil.
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Affiliation(s)
- Supriya Arora
- Bahamas Vision Centre and Princess Margaret Hospital, Nassau NP, Bahamas.
| | - Thamolwan Surakiatchanukul
- Department of Ophthalmology, Jamaica Hospital Medical Center, New York Medical College, Jamaica, NY, USA
| | - Tarun Arora
- Bahamas Vision Centre and Princess Margaret Hospital, Nassau NP, Bahamas.
| | - Carlo Cagini
- Department of Biochemical and Surgical Sciences, Section of ophthalmology, University of Perugia, Perugia, Italy
| | - Marco Lupidi
- Department of Biochemical and Surgical Sciences, Section of ophthalmology, University of Perugia, Perugia, Italy
| | - Jay Chhablani
- University of Pittsburgh, UPMC Eye Center, Pittsburgh, PA, USA.
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5
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Palazzo E, Boccella S, Marabese I, Pierretti G, Guida F, Maione S. The Cold Case of Metabotropic Glutamate Receptor 6: Unjust Detention in the Retina? Curr Neuropharmacol 2020; 18:120-125. [PMID: 31573889 PMCID: PMC7324884 DOI: 10.2174/1570159x17666191001141849] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2019] [Revised: 08/20/2019] [Accepted: 09/29/2019] [Indexed: 02/03/2023] Open
Abstract
It is a common opinion that metabotropic glutamate receptor subtype 6 (mGluR6) is expressed exclusively in the retina, and in particular in the dendrites of ON-bipolar cells. Glutamate released in darkness from photoreceptors activates mGluR6, which is negatively associated with a membrane non-selective cation channel, the transient receptor potential melanoma-related 1, TRPM1, resulting in cell hyperpolarization. The evidence that mGluR6 is expressed not only in the retina but also in other tissues and cell populations has accumulated over time. The expression of mGluR6 has been identified in microglia, bone marrow stromal and prostate cancer cells, B lymphocytes, melanocytes and keratinocytes and non-neural tissues such as testis, kidney, cornea, conjunctiva, and eyelid. The receptor also appears to be expressed in brain areas, such as the hypothalamus, cortex, hippocampus, nucleus of tractus solitarius, superior colliculus, axons of the corpus callosum and accessory olfactory bulb. The pharmacological activation of mGluR6 in the hippocampus produced an anxiolytic-like effect and in the periaqueductal gray analgesic potential. This review aims to collect all the evidence on the expression and functioning of mGluR6 outside the retina that has been accumulated over the years for a broader view of the potential of the receptor whose retinal confinement appears understimated.
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Affiliation(s)
- E Palazzo
- Department of Experimental Medicine, Pharmacology Division, University of Campania "L. Vanvitelli", Naples, Italy
| | - S Boccella
- Department of Experimental Medicine, Pharmacology Division, University of Campania "L. Vanvitelli", Naples, Italy
| | - I Marabese
- Department of Experimental Medicine, Pharmacology Division, University of Campania "L. Vanvitelli", Naples, Italy
| | - G Pierretti
- Department of Plastic Surgery, University of Campania "L. Vanvitelli", Naples, Italy
| | - F Guida
- Department of Experimental Medicine, Pharmacology Division, University of Campania "L. Vanvitelli", Naples, Italy
| | - S Maione
- Department of Experimental Medicine, Pharmacology Division, University of Campania "L. Vanvitelli", Naples, Italy
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6
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Opere CA, Heruye S, Njie-Mbye YF, Ohia SE, Sharif NA. Regulation of Excitatory Amino Acid Transmission in the Retina: Studies on Neuroprotection. J Ocul Pharmacol Ther 2017; 34:107-118. [PMID: 29267132 DOI: 10.1089/jop.2017.0085] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Excitotoxicity occurs in neurons due to the accumulation of excitatory amino acids such as glutamate in the synaptic and extrasynaptic locations. In the retina, excessive glutamate concentrations trigger a neurotoxic cascade involving several mechanisms, including the elevation of intracellular calcium (Ca2+) and the activation of α-amino-3-hydroxy 5-methyl-4-iso-xazole-propionic acid/kainate (AMPA/KA) and N-methyl-d-aspartate (NMDA) receptors leading to retinal degeneration. Both ionotropic glutamate receptors (iGluRs) and metabotropic glutamate receptors (mGluRs) are present in the mammalian retina. Indeed, due to the abundant expression of GluRs, the mammalian retina is highly susceptible to excitotoxic neurodegeneration. Excitotoxicity has been postulated to present a common downstream mechanism for several stimuli, including hypoglycemia, hypoxia, ischemia, and chronic neurodegenerative diseases. Experimental approaches to the study of neuroprotection in the retina have utilized insults that trigger hypoxia, hypoglycemia, or excitotoxicity. Using these experimental approaches, the neuroprotective potential of GluR agents, including the NMDA receptor modulators (MK801, ifenprodil, memantine); AMPA/KA receptor antagonist (CNQX); Group II and III mGluR agonists (LY354740, quisqualate); and Ca2+-channel blockers (diltiazem, lomerizine, verapamil, ω-conotoxin), and others (pituitary adenylate cyclase activating polypeptide, neuropeptide Y, acetylcholine receptor agonists) have been elucidated. In addition to corroborating the exocytotic role of excitatory amino acids in retinal degeneration, these studies affirm that multiple mechanism/s contribute to the prevention of damage caused by excitotoxicity in the retina. Therefore, it is feasible that several pathways are involved in protecting the retina from toxic insults in ocular neurodegenerative conditions such as glaucoma and retinal ischemia. Furthermore, these experimental models are viable tools for evaluating therapeutic candidates in ocular neuropathies.
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Affiliation(s)
- Catherine A Opere
- 1 Department of Pharmacy Sciences, School of Pharmacy and Health Professions, Creighton University , Omaha, Nebraska
| | - Segewkal Heruye
- 1 Department of Pharmacy Sciences, School of Pharmacy and Health Professions, Creighton University , Omaha, Nebraska
| | - Ya-Fatou Njie-Mbye
- 2 Department of Environmental and Pharmaceutical Sciences, College of Pharmacy and Health Sciences, Texas Southern University , Houston, Texas
| | - Sunny E Ohia
- 2 Department of Environmental and Pharmaceutical Sciences, College of Pharmacy and Health Sciences, Texas Southern University , Houston, Texas
| | - Najam A Sharif
- 2 Department of Environmental and Pharmaceutical Sciences, College of Pharmacy and Health Sciences, Texas Southern University , Houston, Texas.,3 Santen Incorporated , Emeryville, California
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7
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Martemyanov KA, Sampath AP. The Transduction Cascade in Retinal ON-Bipolar Cells: Signal Processing and Disease. Annu Rev Vis Sci 2017; 3:25-51. [PMID: 28715957 DOI: 10.1146/annurev-vision-102016-061338] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Our robust visual experience is based on the reliable transfer of information from our photoreceptor cells, the rods and cones, to higher brain centers. At the very first synapse of the visual system, information is split into two separate pathways, ON and OFF, which encode increments and decrements in light intensity, respectively. The importance of this segregation is borne out in the fact that receptive fields in higher visual centers maintain a separation between ON and OFF regions. In the past decade, the molecular mechanisms underlying the generation of ON signals have been identified, which are unique in their use of a G-protein signaling cascade. In this review, we consider advances in our understanding of G-protein signaling in ON-bipolar cell (BC) dendrites and how insights about signaling have emerged from visual deficits, mostly night blindness. Studies of G-protein signaling in ON-BCs reveal an intricate mechanism that permits the regulation of visual sensitivity over a wide dynamic range.
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Affiliation(s)
| | - Alapakkam P Sampath
- Jules Stein Eye Institute, University of California, Los Angeles, California 90095;
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8
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Tummala SR, Dhingra A, Fina ME, Li JJ, Ramakrishnan H, Vardi N. Lack of mGluR6-related cascade elements leads to retrograde trans-synaptic effects on rod photoreceptor synapses via matrix-associated proteins. Eur J Neurosci 2016; 43:1509-22. [PMID: 27037829 DOI: 10.1111/ejn.13243] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2015] [Accepted: 03/29/2016] [Indexed: 12/23/2022]
Abstract
Heterotrimeric G-proteins couple metabotropic receptors to downstream effectors. In retinal ON bipolar cells, Go couples the metabotropic receptor mGluR6 to the TRPM1 channel and closes it in the dark, thus hyperpolarizing the cell. Light, via GTPase-activating proteins, deactivates Go , opens TRPM1 and depolarizes the cell. Go comprises Gαo1 , Gβ3 and Gγ13; all are necessary for efficient coupling. In addition, Gβ3 contributes to trafficking of certain cascade proteins and to maintaining the synaptic structure. The goal of this study was to determine the role of Gαo1 in maintaining the cascade and synaptic integrity. Using mice lacking Gαo1 , we quantified the immunostaining of certain mGluR6-related components. Deleting Gαo1 greatly reduced staining for Gβ3, Gγ13, Gβ5, RGS11, RGS7 and R9AP. Deletion of Gαo1 did not affect mGluR6, TRPM1 or PCP2. In addition, deleting Gαo1 reduced the number of rod bipolar dendrites that invaginate the rod terminal, similar to the effect seen in the absence of mGluR6, Gβ3 or the matrix-associated proteins, pikachurin, dystroglycan and dystrophin, which are localized presynaptically to the rod bipolar cell. We therefore tested mice lacking mGluR6, Gαo1 and Gβ3 for expression of these matrix-associated proteins. In all three genotypes, staining intensity for these proteins was lower than in wild type, suggesting a retrograde trans-synaptic effect. We propose that the mGluR6 macromolecular complex is connected to the presynaptic rod terminal via a protein chain that includes the matrix-associated proteins. When a component of the macromolecular chain is missing, the chain may fall apart and loosen the dendritic tip adherence within the invagination.
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Affiliation(s)
- Shanti R Tummala
- Department of Neuroscience, University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - Anuradha Dhingra
- Department of Neuroscience, University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - Marie E Fina
- Department of Neuroscience, University of Pennsylvania, Philadelphia, PA, 19104, USA
| | - Jian J Li
- Department of Neurology, University of Pennsylvania, Philadelphia, PA, USA
| | | | - Noga Vardi
- Department of Neuroscience, University of Pennsylvania, Philadelphia, PA, 19104, USA
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9
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Kuo SP, Schwartz GW, Rieke F. Nonlinear Spatiotemporal Integration by Electrical and Chemical Synapses in the Retina. Neuron 2016; 90:320-32. [PMID: 27068789 DOI: 10.1016/j.neuron.2016.03.012] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2015] [Revised: 02/02/2016] [Accepted: 03/06/2016] [Indexed: 10/22/2022]
Abstract
Electrical and chemical synapses coexist in circuits throughout the CNS. Yet, it is not well understood how electrical and chemical synaptic transmission interact to determine the functional output of networks endowed with both types of synapse. We found that release of glutamate from bipolar cells onto retinal ganglion cells (RGCs) was strongly shaped by gap-junction-mediated electrical coupling within the bipolar cell network of the mouse retina. Specifically, electrical synapses spread signals laterally between bipolar cells, and this lateral spread contributed to a nonlinear enhancement of bipolar cell output to visual stimuli presented closely in space and time. Our findings thus (1) highlight how electrical and chemical transmission can work in concert to influence network output and (2) reveal a previously unappreciated circuit mechanism that increases RGC sensitivity to spatiotemporally correlated input, such as that produced by motion.
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Affiliation(s)
- Sidney P Kuo
- Department of Physiology and Biophysics and Howard Hughes Medical Institute, University of Washington, Seattle, WA 98195, USA
| | - Gregory W Schwartz
- Department of Physiology and Biophysics and Howard Hughes Medical Institute, University of Washington, Seattle, WA 98195, USA
| | - Fred Rieke
- Department of Physiology and Biophysics and Howard Hughes Medical Institute, University of Washington, Seattle, WA 98195, USA.
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10
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The TRPM1 channel in ON-bipolar cells is gated by both the α and the βγ subunits of the G-protein Go. Sci Rep 2016; 6:20940. [PMID: 26883481 PMCID: PMC4756708 DOI: 10.1038/srep20940] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2015] [Accepted: 12/16/2015] [Indexed: 12/25/2022] Open
Abstract
Transmission from photoreceptors to ON bipolar cells in mammalian retina is mediated by a sign-inverting cascade. Upon binding glutamate, the metabotropic glutamate receptor mGluR6 activates the heterotrimeric G-protein Gαoβ3γ13, and this leads to closure of the TRPM1 channel (melastatin). TRPM1 is thought to be constitutively open, but the mechanism that leads to its closure is unclear. We investigated this question in mouse rod bipolar cells by dialyzing reagents that modify the activity of either Gαo or Gβγ and then observing their effects on the basal holding current. After opening the TRPM1 channels with light, a constitutively active mutant of Gαo closed the channel, but wild-type Gαo did not. After closing the channels by dark adaptation, phosducin or inactive Gαo (both sequester Gβγ) opened the channel while the active mutant of Gαo did not. Co-immunoprecipitation showed that TRPM1 interacts with Gβ3 and with the active and inactive forms of Gαo. Furthermore, bioluminescent energy transfer assays indicated that while Gαo interacts with both the N- and the C- termini of TRPM1, Gβγ interacts only with the N-terminus. Our physiological and biochemical results suggest that both Gαo and Gβγ bind TRPM1 channels and cooperate to close them.
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11
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Ramakrishnan H, Dhingra A, Tummala SR, Fina ME, Li JJ, Lyubarsky A, Vardi N. Differential function of Gγ13 in rod bipolar and ON cone bipolar cells. J Physiol 2015; 593:1531-50. [PMID: 25416620 DOI: 10.1113/jphysiol.2014.281196] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2014] [Accepted: 11/12/2014] [Indexed: 01/17/2023] Open
Abstract
Heterotrimeric G-proteins (comprising Gα and Gβγ subunits) are critical for coupling of metabotropic receptors to their downstream effectors. In the retina, glutamate released from photoreceptors in the dark activates metabotropic glutamate receptor 6 (mGluR6) receptors in ON bipolar cells; this leads to activation of Go , closure of transient receptor potential melastatin 1 channels and hyperpolarization of these cells. Go comprises Gαo , Gβ3 and a Gγ. The best Gγ candidate is Gγ13, although functional data to support this are lacking. Thus, we tested Gγ13 function by generating Gng13(-/-) knockout (KO) mice, recording electroretinograms (ERG) and performing immunocytochemical staining. The amplitude of scotopic ERG b-waves in KO mice was lower than in wild-type (WT) mice. Furthermore, in both KO and WT mice, the ERG b-wave decreased with age; this decrease was much more pronounced in KO mice. By contrast, the photopic ERG b-waves in KO mice were hardly affected at any age. In KO mice retinas, immunostaining for Gβ3 and for the GTPase activating proteins RGS7, RGS11, R9AP and Gβ5 decreased significantly in rod bipolar cells but not in ON cone bipolar cells. Staining for Gαo and certain other cascade elements decreased only slightly. Analysis of our ON bipolar cDNA library showed that these cells express mRNAs for Gγ5, Gγ10 and Gγ11. Quantitative RT-PCR of retinal cDNA showed greater values for these transcripts in retinas of KO mice, although the difference was not significant. Our results suggest that Gγ13 contributes to mGluR6 signalling in rod bipolar cells more than in ON cone bipolar cells, and that this contribution includes both coupling the receptor and maintaining a stable localization of the mGluR6-related cascade elements.
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Affiliation(s)
- Hariharasubramanian Ramakrishnan
- Department of Neuroscience, Department of Neurology and Department of Ophthalmology, University of Pennsylvania, Philadelphia, PA, 19104, USA
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12
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Dhingra A, Tummala SR, Lyubarsky A, Vardi N. PDE9A is expressed in the inner retina and contributes to the normal shape of the photopic ERG waveform. Front Mol Neurosci 2014; 7:60. [PMID: 25018695 PMCID: PMC4073215 DOI: 10.3389/fnmol.2014.00060] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2014] [Accepted: 06/09/2014] [Indexed: 11/19/2022] Open
Abstract
The ubiquitous second messenger cGMP is synthesized by guanylyl cyclase and hydrolyzed by phosphodiesterase (PDE). cGMP mediates numerous signaling pathways in multiple tissues. In the retina, cGMP regulates signaling in nearly every cell class including photoreceptors, bipolar cells, amacrine cells, and ganglion cells. In order to understand the specific role of cGMP and its regulating enzymes in different cell types, it is first necessary to localize these components and dissect their influence on the circuits. Here we tested the contribution of PDE9A to retinal processing by recording the electroretinograms (ERG) of PDE9A™/™ (KO) mice and by localizing the enzyme. We found that while the scotopic ERG of KO was the same as that of wild type (WT) in both amplitude and kinetics, the photopic ERG was greatly affected. The greatest effect was on the recovery of the b-wave; the falling phase and the b-wave duration were significantly longer in the KO mice for all photopic stimuli (UV, green, or saturating white flashes). The rising phase was slower in KO than in WT for UV and green stimuli. For certain stimuli, amplitudes of both the a- and b-waves were smaller than in WT. Using Lac-Z expression in KO retinas as a reporter for PDE9A expression pattern, we found that PDE9A is localized to GABA-positive and GABA-negative amacrine cells, and likely also to certain types of ganglion cells. Our results indicate that PDE9A, by controlling the level of cGMP, modulates inhibitory processes within the cone pathway. We speculate that these circuits involve NO/cGMP signaling pathways.
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Affiliation(s)
- Anuradha Dhingra
- Retina Lab, Department of Neuroscience, University of Pennsylvania Philadelphia, PA, USA
| | - Shanti R Tummala
- Retina Lab, Department of Neuroscience, University of Pennsylvania Philadelphia, PA, USA
| | - Arkady Lyubarsky
- Department of Ophthalmology, University of Pennsylvania Philadelphia, PA, USA
| | - Noga Vardi
- Retina Lab, Department of Neuroscience, University of Pennsylvania Philadelphia, PA, USA
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14
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Abstract
The transient receptor potential (TRP) channels play a wide variety of essential roles in the sensory systems of various species, both invertebrates and vertebrates. The TRP channel was first identified as a molecule required for proper light response in Drosophila melanogaster. We and another group recently revealed that TRPM1, the founding member of the melanoma-related transient receptor potential (TRPM) subfamily, is required for the photoresponse in mouse retinal ON-bipolar cells. We further demonstrated that Trpm1 is a component of the transduction cation channel negatively regulated by the metabotropic glutamate receptor 6 (mGulR6) cascade in ON-bipolar cells through a reconstitution experiment using CHO cells expressing Trpm1, mGluR6, and Goα. Furthermore, human TRPM1 mutations are associated with congenital stationary night blindness (CSNB), whose patients lack rod function and suffer from night blindness starting in early childhood. In addition to the function of transduction cation channel, TRPM1 is one of the retinal autoantigens in some paraneoplastic retinopathy (PR) associated with retinal ON-bipolar cell dysfunction. In this chapter, we describe physiological functions of the TRPM1 channel and its underlying biochemical mechanisms in retinal ON-bipolar cells in association with CSNB and PR.
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Affiliation(s)
- Shoichi Irie
- Laboratory for Molecular and Developmental Biology, Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka, 565-0871, Japan
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15
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Podda MV, Grassi C. New perspectives in cyclic nucleotide-mediated functions in the CNS: the emerging role of cyclic nucleotide-gated (CNG) channels. Pflugers Arch 2013; 466:1241-57. [PMID: 24142069 DOI: 10.1007/s00424-013-1373-2] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2013] [Revised: 09/27/2013] [Accepted: 09/28/2013] [Indexed: 01/07/2023]
Abstract
Cyclic nucleotides play fundamental roles in the central nervous system (CNS) under both physiological and pathological conditions. The impact of cAMP and cGMP signaling on neuronal and glial cell functions has been thoroughly characterized. Most of their effects have been related to cyclic nucleotide-dependent protein kinase activity. However, cyclic nucleotide-gated (CNG) channels, first described as key mediators of sensory transduction in retinal and olfactory receptors, have been receiving increasing attention as possible targets of cyclic nucleotides in the CNS. In the last 15 years, consistent evidence has emerged for their expression in neurons and astrocytes of the rodent brain. Far less is known, however, about the functional role of CNG channels in these cells, although several of their features, such as Ca(2+) permeability and prolonged activation in the presence of cyclic nucleotides, make them ideal candidates for mediators of physiological functions in the CNS. Here, we review literature suggesting the involvement of CNG channels in a number of CNS cellular functions (e.g., regulation of membrane potential, neuronal excitability, and neurotransmitter release) as well as in more complex phenomena, like brain plasticity, adult neurogenesis, and pain sensitivity. The emerging picture is that functional and dysfunctional cyclic nucleotide signaling in the CNS has to be reconsidered including CNG channels among possible targets. However, concerted efforts and multidisciplinary approaches are still needed to get more in-depth knowledge in this field.
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Affiliation(s)
- Maria Vittoria Podda
- Institute of Human Physiology, Medical School, Università Cattolica, Largo Francesco Vito 1, 00168, Rome, Italy
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16
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Machuca-Parra AI, Miledi R, Martínez-Torres A. Identification of the minimal promoter for specific expression of the GABAρ1 receptor in retinal bipolar cells. J Neurochem 2013; 124:175-88. [PMID: 23106649 DOI: 10.1111/jnc.12067] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2012] [Revised: 09/26/2012] [Accepted: 10/23/2012] [Indexed: 11/29/2022]
Abstract
γ-aminobutyric acid (GABA)ρ receptors regulate rapid synaptic ion currents in the axon end of retinal ON bipolar neurons, acting as a point of control along the visual pathway. In the GABAρ1 subunit knock out mouse, inhibition mediated by this receptor is totally eliminated, showing its role in neural transmission in retina. GABAρ1 mRNA is expressed in mouse retina after post-natal day 7, but little is known about its transcriptional regulation. To identify the GABAρ1 promoter, in silico analyses were performed and indicated that a 0.290-kb fragment, flanking the 5'-end of the GABAρ1 gene, includes putative transcription factor-binding sites, two Inr elements, and lacks a TATA-box. A rapid amplification of cDNA ends (RACE) assay showed three transcription start sites (TSS) clustered in the first exon. Luciferase reporter assays indicated that a 0.232-kb fragment upstream from the ATG is the minimal promoter in transfected cell lines and in vitro electroporated retinae. The second Inr and AP1 site are important to activate transcription in secretin tumor cells (STC-1) and retina. Finally, the 0.232-kb fragment drives green fluorescent protein (GFP) expression to the inner nuclear layer, where bipolar cells are present. This first work paves the way for further studies of molecular elements that control GABAρ1 transcription and regulate its expression during retinal development.
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Affiliation(s)
- Arturo Israel Machuca-Parra
- Departamento de Neurobiología Celular y Molecular, Universidad Nacional Autónoma de México, Instituto de Neurobiología, Querétaro, Mexico
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Dhingra A, Vardi N. "mGlu Receptors in the Retina" - WIREs Membrane Transport and Signaling. WILEY INTERDISCIPLINARY REVIEWS. MEMBRANE TRANSPORT AND SIGNALING 2012; 1:641-653. [PMID: 24003403 PMCID: PMC3755759 DOI: 10.1002/wmts.43] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Glutamate, a key neurotransmitter in the vertebrate retina, acts via ionotropic and metabotropic receptors. Retina expresses mRNA for all metabotropic glutamate receptors and proteins for all but mGluR3. Every retinal cell class expresses one or more of these receptors. In general, these receptors are present presynaptically and serve to modulate synaptic transmission. While mGluRs on the photoreceptor terminal act as autoreceptors to titer glutamate levels, those on horizontal cell processes seem to shape the light response. Similarly, autoreceptors on bipolar axon terminals modulate glutamate release and the receptors on amacrine and ganglion cells modulate feedforward signals by modulating K+ or Ca2+ current to fine tune light responses. Since most of the mGluR sub-types are present in amacrine and ganglion cells that belong to many cell types, the pathways downstream of mGluRs are highly diverse with primarily modulatory effects. An exception to most mGluRs which have modulatory function is mGluR6 because it plays a key role in the feedforward transmission from photoreceptors to ON bipolar cells and is also required for the correct localization of the synaptic proteins in the dendritic tips. In humans, mutations in the gene encoding mGluR6 cause autosomal recessive night blindness. In addition, mGluRs appear to play a trophic role in development and after retinal damage, suggesting potential future therapeutic implications.
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Pang JJ, Gao F, Wu SM. Ionotropic glutamate receptors mediate OFF responses in light-adapted ON bipolar cells. Vision Res 2012; 68:48-58. [PMID: 22842089 DOI: 10.1016/j.visres.2012.07.012] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2012] [Revised: 07/17/2012] [Accepted: 07/18/2012] [Indexed: 11/28/2022]
Abstract
Previous studies have suggested that photoreceptor synaptic inputs to depolarizing bipolar cells (DBCs or ON bipolar cells) are mediated by mGluR6 receptors and those to hyperpolarizing bipolar cells (HBCs or OFF bipolar cells) are mediated by AMPA/kainate receptors. Here we show that in addition to mGluR6 receptors which mediate the sign-inverting, depolarizing light responses, subpopulations of cone-dominated and rod/cone mixed DBCs use GluR4 AMPA receptors to generate a transient sign-preserving OFF response under light adapted conditions. These AMPA receptors are located at the basal junctions postsynaptic to rods and they are silent under dark-adapted conditions, as tonic glutamate release in darkness desensitizes these receptors. Light adaptation enhances rod-cone coupling and thus allows cone photocurrents with an abrupt OFF depolarization to enter the rods. The abrupt rod depolarization triggers glutamate activation of unoccupied AMPA receptors, resulting in a transient OFF response in DBCs. It has been widely accepted that the DNQX-sensitive, OFF transient responses in retinal amacrine cells and ganglion cells are mediated exclusively by HBCs. Our results suggests that this view needs revision as AMPA receptors in subpopulations of DBCs are likely to significantly contribute to the DNQX-sensitive OFF transient responses in light-adapted third- and higher-order visual neurons.
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Affiliation(s)
- Ji-Jie Pang
- Cullen Eye Institute, Baylor College of Medicine, Houston, TX 77030, United States
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19
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Topological analysis of small leucine-rich repeat proteoglycan nyctalopin. PLoS One 2012; 7:e33137. [PMID: 22485138 PMCID: PMC3317652 DOI: 10.1371/journal.pone.0033137] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2011] [Accepted: 02/10/2012] [Indexed: 11/24/2022] Open
Abstract
Nyctalopin is a small leucine rich repeat proteoglycan (SLRP) whose function is
critical for normal vision. The absence of nyctalopin results in the complete
form of congenital stationary night blindness. Normally, glutamate released by
photoreceptors binds to the metabotropic glutamate receptor type 6 (GRM6), which
through a G-protein cascade closes the non-specific cation channel, TRPM1, on
the dendritic tips of depolarizing bipolar cells (DBCs) in the retina.
Nyctalopin has been shown to interact with TRPM1 and expression of TRPM1 on the
dendritic tips of the DBCs is dependent on nyctalopin expression. In the current
study, we used yeast two hybrid and biochemical approaches to investigate
whether murine nyctalopin was membrane bound, and if so by what mechanism, and
also whether the functional form was as a homodimer. Our results show that
murine nyctalopin is anchored to the plasma membrane by a single transmembrane
domain, such that the LRR domain is located in the extracellular space.
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Vardi T, Fina M, Zhang L, Dhingra A, Vardi N. mGluR6 transcripts in non-neuronal tissues. J Histochem Cytochem 2011; 59:1076-86. [PMID: 22034516 DOI: 10.1369/0022155411425386] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
To study mGluR6 expression, the authors investigated two transgenic mouse lines that express enhanced green fluorescent protein (GFP) under control of mGluR6 promoter. In retina, GFP was expressed exclusively in all ON bipolar cell types, either uniformly across all cells of this class (line 5) or in a mosaic (patchy) fashion (line 1). In brain, GFP was found in certain cortical areas, superior colliculus, axons of the corpus callosum, accessory olfactory bulb, and cells of the subcommissural organ. Outside the nervous system, GFP was seen in the corneal endothelium, testis, the kidney's medulla, collecting ducts and parietal layer that surround the glomeruli, and B lymphocytes. Furthermore, RT-PCR showed that most tissues that expressed GFP in the transgenic mouse also transcribed two splice variants of mGluR6 in the wild-type mouse. The alternate variant was lacking exon 8, predicting a protein product of 545 amino acids that lacks the 7-transmembrane domains of the receptor. In cornea, immunostaining for mGluR6 gave strong staining in the endothelium, and this was stronger in wild-type than in mGluR6-null mice. Furthermore, calcium imaging with Fura-2 showed that application of L-AP4, an agonist for group III metabotropic glutamate receptors including mGluR6, elevated calcium in endothelial cells.
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Affiliation(s)
- Tamar Vardi
- Department of Neuroscience, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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Morgans CW, Brown RL, Duvoisin RM. TRPM1: the endpoint of the mGluR6 signal transduction cascade in retinal ON-bipolar cells. Bioessays 2011; 32:609-14. [PMID: 20544736 DOI: 10.1002/bies.200900198] [Citation(s) in RCA: 82] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
For almost 30 years the ion channel that initiates the ON visual pathway in vertebrate vision has remained elusive. Recent findings now indicate that the pathway, which begins with unbinding of glutamate from the metabotropic glutamate receptor 6 (mGluR6), ends with the opening of the transient receptor potential (TRP)M1 cation channel. As a component of the mGluR6 signal transduction pathway, mutations in TRPM1 would be expected to cause congenital stationary night blindness (CSNB), and several such mutations have already been identified in CSNB families. Furthermore, expression of TRPM1 in both the retina and skin raises the possibility that a genetic link exists between certain types of visual and skin disorders.
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Pang JJ, Gao F, Wu SM. Light responses and morphology of bNOS-immunoreactive neurons in the mouse retina. J Comp Neurol 2010; 518:2456-74. [PMID: 20503422 DOI: 10.1002/cne.22347] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Nitric oxide (NO), produced by NO synthase (NOS), modulates the function of all retinal neurons and ocular blood vessels and participates in the pathogenesis of ocular diseases. To further understand the regulation of ocular NO release, we systematically studied the morphology, topography, and light responses of NOS-containing amacrine cells (NOACs) in dark-adapted mouse retina. Immunohistological staining for neuronal NOS (bNOS), combined with retrograde labeling of ganglion cells (GCs) with Neurobiotin (NB, a gap junction permeable dye) and Lucifer yellow (LY, a less permeable dye), was used to identify NOACs. The light responses of ACs were recorded under whole-cell voltage clamp conditions and cell morphology was examined with a confocal microscope. We found that in dark-adapted conditions bNOS-immunoreactivity (IR) was present primarily in the inner nuclear layer and the ganglion cell layer. bNOS-IR somas were negative for LY, thus they were identified as ACs; nearly 6% of the cells were labeled by NB but not by LY, indicating that they were dye-coupled with GCs. Three morphological subtypes of NOACs (NI, NII, and displaced) were identified. The cell density, intercellular distance, and the distribution of NOACs were studied in whole retinas. Light evoked depolarizing highly sensitive ON-OFF responses in NI cells and less sensitive OFF responses in NII cells. Frequent (1-2 Hz) or abrupt change of light intensity evoked larger peak responses. The possibility for light to modify NO release from NOACs is discussed.
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Affiliation(s)
- Ji-Jie Pang
- Department of Ophthalmology, Baylor College of Medicine, Houston, Texas 77030, USA.
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Abstract
In the retina, several parallel channels originate that extract different attributes from the visual scene. This review describes how these channels arise and what their functions are. Following the introduction four sections deal with these channels. The first discusses the "ON" and "OFF" channels that have arisen for the purpose of rapidly processing images in the visual scene that become visible by virtue of either light increment or light decrement; the ON channel processes images that become visible by virtue of light increment and the OFF channel processes images that become visible by virtue of light decrement. The second section examines the midget and parasol channels. The midget channel processes fine detail, wavelength information, and stereoscopic depth cues; the parasol channel plays a central role in processing motion and flicker as well as motion parallax cues for depth perception. Both these channels have ON and OFF subdivisions. The third section describes the accessory optic system that receives input from the retinal ganglion cells of Dogiel; these cells play a central role, in concert with the vestibular system, in stabilizing images on the retina to prevent the blurring of images that would otherwise occur when an organism is in motion. The last section provides a brief overview of several additional channels that originate in the retina.
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24
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Quraishi S, Reed BT, Duvoisin RM, Taylor WR. Selective activation of mGluR8 receptors modulates retinal ganglion cell light responses. Neuroscience 2010; 166:935-41. [PMID: 20096339 DOI: 10.1016/j.neuroscience.2010.01.027] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2009] [Revised: 12/14/2009] [Accepted: 01/13/2010] [Indexed: 11/27/2022]
Abstract
Extracellular and whole-cell light-evoked responses of mouse retinal ganglion cells were recorded in the presence of the mGluR8 selective agonist, (S)-3,4-dicarboxy-phenylglycine (DCPG). Off-light responses were reversibly reduced in the presence of DCPG in wild-type but not in mGluR8-deficient retinas. On-responses were only marginally modulated by DCPG. During Off-responses, DCPG suppressed both excitatory and inhibitory synaptic conductances suggesting that mGluR8 receptor activity reduces glutamate release from bipolar cell terminals and possibly also the release of an inhibitory neurotransmitter from amacrine cell processes.
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Affiliation(s)
- S Quraishi
- Neurological Sciences Institute, Oregon Health & Science University, Beaverton, OR 97006, USA
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25
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TRPM1 is a component of the retinal ON bipolar cell transduction channel in the mGluR6 cascade. Proc Natl Acad Sci U S A 2009; 107:332-7. [PMID: 19966281 DOI: 10.1073/pnas.0912730107] [Citation(s) in RCA: 213] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
An essential step in intricate visual processing is the segregation of visual signals into ON and OFF pathways by retinal bipolar cells (BCs). Glutamate released from photoreceptors modulates the photoresponse of ON BCs via metabotropic glutamate receptor 6 (mGluR6) and G protein (Go) that regulates a cation channel. However, the cation channel has not yet been unequivocally identified. Here, we report a mouse TRPM1 long form (TRPM1-L) as the cation channel. We found that TRPM1-L localization is developmentally restricted to the dendritic tips of ON BCs in colocalization with mGluR6. TRPM1 null mutant mice completely lose the photoresponse of ON BCs but not that of OFF BCs. In the TRPM1-L-expressing cells, TRPM1-L functions as a constitutively active nonselective cation channel and its activity is negatively regulated by Go in the mGluR6 cascade. These results demonstrate that TRPM1-L is a component of the ON BC transduction channel downstream of mGluR6 in ON BCs.
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Ishii M, Morigiwa K, Takao M, Nakanishi S, Fukuda Y, Mimura O, Tsukamoto Y. Ectopic synaptic ribbons in dendrites of mouse retinal ON- and OFF-bipolar cells. Cell Tissue Res 2009; 338:355-75. [PMID: 19859741 PMCID: PMC2779389 DOI: 10.1007/s00441-009-0880-0] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2009] [Accepted: 09/08/2009] [Indexed: 11/12/2022]
Abstract
The ectopic distribution of synaptic ribbons in dendrites of mouse retinal bipolar cells was examined by using genetic ablation of metabotropic glutamate receptor subtype 6 (mGluR6), electron microscopy, and immunocytochemistry. Ectopic ribbons were observed in dendrites of rod and ON-cone bipolar cells in the mGluR6-deficient mouse but not in those of wild-type mice. The number of rod spherules facing the ectopic ribbons in mGluR6-deficient rod bipolar dendrites increased gradually during early growth and reached a plateau level of about 20% at 12 weeks. These ectopic ribbons were immunopositive for RIBEYE, a ribbon-specific protein, but the associated vesicles were immunonegative for synaptophysin, a synaptic-vesicle-specific protein. The presence of ectopic ribbons was correlated with an increase in the roundness of the invaginating dendrites of the rod bipolar cells. We further confirmed ectopic ribbons in dendrites of OFF-cone bipolar cells in wild-type retinas. Of the four types of OFF-cone bipolar cells (T1-T4), only the T2-type, which had a greater number of synaptic ribbons at the axon terminal and a thicker axon cylinder than the other types, had ectopic ribbons. Light-adapted experiments revealed that, in wild-type mice under enhanced-light adaptation (considered similar to the mGluR6-deficient state), the roundness in the invaginating dendrites and axon terminals of rod bipolar cells increased, but no ectopic ribbons were detected. Based on these findings and known mechanisms for neurotransmitter release and protein trafficking, the possible mechanisms underlying the ectopic ribbons are discussed on the basis of intracellular transport for the replenishment of synaptic proteins.
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Affiliation(s)
- Masaaki Ishii
- Department of Biology, Hyogo College of Medicine, Nishinomiya, Hyogo 663-8501 Japan
- Department of Ophthalmology, Hyogo College of Medicine, Nishinomiya, Hyogo 663-8501 Japan
| | | | - Motoharu Takao
- Department of Human and Information Science, Tokai University, Hiratsuka, Kanagawa 259-1292 Japan
| | | | - Yutaka Fukuda
- Department of Physiology, Osaka University Graduate School of Medicine, Suita, Osaka 565-0871 Japan
| | - Osamu Mimura
- Department of Ophthalmology, Hyogo College of Medicine, Nishinomiya, Hyogo 663-8501 Japan
| | - Yoshihiko Tsukamoto
- Department of Biology, Hyogo College of Medicine, Nishinomiya, Hyogo 663-8501 Japan
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27
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van Genderen MM, Bijveld MMC, Claassen YB, Florijn RJ, Pearring JN, Meire FM, McCall MA, Riemslag FCC, Gregg RG, Bergen AAB, Kamermans M. Mutations in TRPM1 are a common cause of complete congenital stationary night blindness. Am J Hum Genet 2009; 85:730-6. [PMID: 19896109 DOI: 10.1016/j.ajhg.2009.10.012] [Citation(s) in RCA: 159] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2009] [Revised: 10/16/2009] [Accepted: 10/16/2009] [Indexed: 11/19/2022] Open
Abstract
Congenital stationary night blindness (CSNB) is a clinically and genetically heterogeneous group of retinal disorders characterized by nonprogressive impaired night vision and variable decreased visual acuity. We report here that six out of eight female probands with autosomal-recessive complete CSNB (cCSNB) had mutations in TRPM1, a retinal transient receptor potential (TRP) cation channel gene. These data suggest that TRMP1 mutations are a major cause of autosomal-recessive CSNB in individuals of European ancestry. We localized TRPM1 in human retina to the ON bipolar cell dendrites in the outer plexifom layer. Our results suggest that in humans, TRPM1 is the channel gated by the mGluR6 (GRM6) signaling cascade, which results in the light-evoked response of ON bipolar cells. Finally, we showed that detailed electroretinography is an effective way to discriminate among patients with mutations in either TRPM1 or GRM6, another autosomal-recessive cCSNB disease gene. These results add to the growing importance of the diverse group of TRP channels in human disease and also provide new insights into retinal circuitry.
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TRPM1 is required for the depolarizing light response in retinal ON-bipolar cells. Proc Natl Acad Sci U S A 2009; 106:19174-8. [PMID: 19861548 DOI: 10.1073/pnas.0908711106] [Citation(s) in RCA: 226] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The ON pathway of the visual system, which detects increases in light intensity, is established at the first retinal synapse between photoreceptors and ON-bipolar cells. Photoreceptors hyperpolarize in response to light and reduce the rate of glutamate release, which in turn causes the depolarization of ON-bipolar cells. This ON-bipolar cell response is mediated by the metabotropic glutamate receptor, mGluR6, which controls the activity of a depolarizing current. Despite intensive research over the past two decades, the molecular identity of the channel that generates this depolarizing current has remained elusive. Here, we present evidence indicating that TRPM1 is necessary for the depolarizing light response of ON-bipolar cells, and further that TRPM1 is a component of the channel that generates this light response. Gene expression profiling revealed that TRPM1 is highly enriched in ON-bipolar cells. In situ hybridization experiments confirmed that TRPM1 mRNA is found in cells of the retinal inner nuclear layer, and immunofluorescent confocal microscopy showed that TRPM1 is localized in the dendrites of ON-bipolar cells in both mouse and macaque retina. The electroretinogram (ERG) of TRPM1-deficient (TRPM1(-/-)) mice had a normal a-wave, but no b-wave, indicating a loss of bipolar cell response. Finally, whole-cell patch-clamp recording from ON-bipolar cells in mouse retinal slices demonstrated that genetic deletion of TRPM1 abolished chemically simulated light responses from rod bipolar cells and dramatically altered the responses of cone ON-bipolar cells. Identification of TRPM1 as a mGluR6-coupled cation channel reveals a key step in vision, expands the role of the TRP channel family in sensory perception, and presents insights into the evolution of vertebrate vision.
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Nemargut JP, Wang GY. Inhibition of nitric oxide synthase desensitizes retinal ganglion cells to light by diminishing their excitatory synaptic currents under light adaptation. Vision Res 2009; 49:2936-47. [PMID: 19772868 DOI: 10.1016/j.visres.2009.09.011] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2009] [Revised: 09/11/2009] [Accepted: 09/16/2009] [Indexed: 10/20/2022]
Abstract
The effect of inhibiting nitric oxide synthase (NOS) on the visual responses of mouse retinal ganglion cells (RGCs) was studied under light adaptation by using patch-clamp recordings. The results demonstrated that NOS inhibitor, l-NAME, reduced the sensitivity of RGCs to light under light adaptation at different ambient light conditions. These observations were seen in all cells that recordings were made from. l-NAME diminished the excitatory synaptic currents (EPSCs), rather than increasing the inhibitory synaptic currents, of RGCs to reduce the sensitivity of RGCs to light. Cones may be the sites that l-NAME acted to diminish the EPSCs of RGCs.
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Affiliation(s)
- Joseph P Nemargut
- Department of Structural and Cellular Biology, School of Medicine, Tulane University, New Orleans, LA 70112, United States
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30
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Retina-specific GTPase accelerator RGS11/G beta 5S/R9AP is a constitutive heterotrimer selectively targeted to mGluR6 in ON-bipolar neurons. J Neurosci 2009; 29:9301-13. [PMID: 19625520 DOI: 10.1523/jneurosci.1367-09.2009] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Members of the R7 family of the regulators of G-protein signaling (R7 RGS) proteins form multi-subunit complexes that play crucial roles in processing the light responses of retinal neurons. The disruption of these complexes has been shown to lead to the loss of temporal resolution in retinal photoreceptors and deficient synaptic transmission to downstream neurons. Despite the well established role of one member of this family, RGS9-1, in controlling vertebrate phototransduction, the roles and organizational principles of other members in the retina are poorly understood. Here we investigate the composition, localization, and function of complexes containing RGS11, the closest homolog of RGS9-1. We find that RGS11 forms a novel obligatory trimeric complex with the short splice isoform of the type 5 G-protein beta subunit (G beta 5) and the RGS9 anchor protein (R9AP). The complex is expressed exclusively in the dendritic tips of ON-bipolar cells in which its localization is accomplished through a direct association with mGluR6, the glutamate receptor essential for the ON-bipolar light response. Although association with both R9AP and mGluR6 contributed to the proteolytic stabilization of the complex, postsynaptic targeting of RGS11 was not determined by its membrane anchor R9AP. Electrophysiological recordings of the light response in mouse rod ON-bipolar cells reveal that the genetic elimination of RGS11 has little effect on the deactivation of G alpha(o) in dark-adapted cells or during adaptation to background light. These results suggest that the deactivation of mGluR6 cascade during the light response may require the contribution of multiple GTPase activating proteins.
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31
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Abstract
RGS7, RGS11, and their binding partner Gbeta5 are localized to the dendritic tips of retinal ON bipolar cells (ON-BPC), where mGluR6 responds to glutamate released from photoreceptor terminals by activation of the RGS7/RGS11 substrate, Galphao. To determine their functions in retinal signaling, we investigated cell-specific expression patterns of RGS7 and RGS11 by immunostaining, and measured light responses by electroretinography in mice with targeted disruptions of the genes encoding them. RGS7 staining is present in dendritic tips of all rod ON-BPC, but missing in those for subsets of cone ON-BPC, whereas the converse was true for RGS11 staining. Genetic disruption of either RGS7 or RGS11 produced delays in the ON-BPC-derived electroretinogram b-wave, but no changes in the photoreceptor-derived a-wave. Homozygous RGS7 mutant mice had delays in rod-driven b-waves, whereas RGS11 mutant mice had delays in rod-driven, and especially in cone-driven b-waves. The b-wave delays were further enhanced in mice homozygous for both RGS7 and RGS11 gene disruptions. Thus, RGS7 and RGS11 act in parallel to regulate the kinetics of ON bipolar cell responses, with differential impacts on the rod and cone pathways.
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32
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A transient receptor potential-like channel mediates synaptic transmission in rod bipolar cells. J Neurosci 2009; 29:6088-93. [PMID: 19439586 DOI: 10.1523/jneurosci.0132-09.2009] [Citation(s) in RCA: 166] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
On bipolar cells are connected to photoreceptors via a sign-inverting synapse. At this synapse, glutamate binds to a metabotropic receptor which couples to the closure of a cation-selective transduction channel. The molecular identity of both the receptor and the G protein are known, but the identity of the transduction channel has remained elusive. Here, we show that the transduction channel in mouse rod bipolar cells, a subtype of On bipolar cell, is likely to be a member of the TRP family of channels. To evoke a transduction current, the metabotropic receptor antagonist LY341495 was applied to the dendrites of cells that were bathed in a solution containing the mGluR6 agonists L-AP4 or glutamate. The transduction current was suppressed by ruthenium red and the TRPV1 antagonists capsazepine and SB-366791. Furthermore, focal application of the TRPV1 agonists capsaicin and anandamide evoked a transduction-like current. The capsaicin-evoked and endogenous transduction current displayed prominent outward rectification, a property of the TRPV1 channel. To test the possibility that the transduction channel is TRPV1, we measured rod bipolar cell function in the TRPV1(-/-) mouse. The ERG b-wave, a measure of On bipolar cell function, as well as the transduction current and the response to TRPV1 agonists were normal, arguing against a role for TRPV1. However, ERG measurements from mice lacking TRPM1 receptors, another TRP channel implicated in retinal function, revealed the absence of a b-wave. Our results suggest that a TRP-like channel, possibly TRPM1, is essential for synaptic function in On bipolar cells.
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Nakajima Y, Moriyama M, Hattori M, Minato N, Nakanishi S. Isolation of ON bipolar cell genes via hrGFP-coupled cell enrichment using the mGluR6 promoter. J Biochem 2009; 145:811-8. [PMID: 19270057 DOI: 10.1093/jb/mvp038] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
mGluR6 expression is a characteristic property of retinal ON bipolar cells. mGluR6 is also the causal gene for a form of congenital night blindness. To elucidate physiological and pathological functions of ON bipolar cells and mGluR6, we thought it important to identify genes specifically expressed in them. We thus made transgenic mouse lines expressing humanized Renilla reniformis green fluorescent protein (hrGFP), under the control of the mGluR6 promoter. From their retina, we isolated hrGFP-positive cells by cell sorting, and analysed the gene-expression profile of these cells by using DNA microarray. Further analysis revealed that about half of the initially selected ON bipolar cell genes were expressed in the expected retinal layer. We confirmed previously ambiguous retinal localization of regulator of G-protein signalling 11 (RGS11) and transient receptor potential cation channel, subfamily M, member 1 (TRPM1). In addition, we showed the expression of calcium channel, voltage-dependent, alpha2/delta subunit 3 (Cacna2d3) in ON bipolar cells for the first time. Although we could not completely exclude the possibility that a small population of hrGFP-positive cells might not be ON bipolar cells, these mice as well as our strategy would be highly valuable for the further analysis of ON bipolar cells.
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Affiliation(s)
- Yoshiaki Nakajima
- Department of Biological Sciences, Faculty of Medicine, Graduate School of Biostudies, Kyoto University, Kyoto 606-8501, Japan.
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Dhingra A, Sulaiman P, Xu Y, Fina ME, Veh RW, Vardi N. Probing neurochemical structure and function of retinal ON bipolar cells with a transgenic mouse. J Comp Neurol 2008; 510:484-96. [PMID: 18671302 DOI: 10.1002/cne.21807] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Retinal ON bipolar cells make up about 70% of all bipolar cells. Glutamate hyperpolarizes these cells by binding to the metabotropic glutamate receptor mGluR6, activating the G-protein G(o1), and closing an unidentified cation channel. To facilitate investigation of ON bipolar cells, we here report on the production of a transgenic mouse (Grm6-GFP) in which enhanced green fluorescent protein (EGFP), under control of mGluR6 promoter, was expressed in all and only ON bipolar cells. We used the mouse to determine density of ON bipolar cells, which in central retina was 29,600 cells/mm(2). We further sorted the fluorescent cells and created a pure ON bipolar cDNA library that was negative for photoreceptor unique genes. With this library, we determined expression of 27 genes of interest. We obtained positive transcripts for G(o) interactors: regulators of G-protein signaling (RGS), Ret-RGS1 (a variant of RGS20), RGS16, RGS7, purkinje cell protein 2 (PCP2, also called L7 or GPSM4), synembryn (RIC-8), LGN (GPSM2), RAP1GAP, and Gbeta5; cGMP modulators: guanylyl cyclase (GC) 1alpha1, GC1beta1, phosphodiesterase (PDE) 1C, and PDE9A; and channels: inwardly rectifying potassium channel Kir2.4, transient receptor potential TRPC2, and sperm-specific cation channels CatSper 2-4. The following transcripts were not found in our library: AGS3 (GPSM1), RGS10, RGS19 (GAIP), calbindin, GC1alpha2, GC1beta2, PDE5, PDE2A, amiloride-sensitive sodium channel ACCN4, and CatSper1. We then localized Kir2.4 to several cell types and showed that, in ON bipolar cells, the channel concentrates in their dendritic tips. The channels and modulators found in ON bipolar cells likely shape their light response. Additional uses of the Grm6-GFP mouse are also discussed.
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Affiliation(s)
- Anuradha Dhingra
- Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6058, USA
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Kaneda M, Ishii T, Hosoya T. Pathway-dependent modulation by P2-purinoceptors in the mouse retina. Eur J Neurosci 2008; 28:128-36. [PMID: 18616561 DOI: 10.1111/j.1460-9568.2008.06317.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Adenosine trisphosphate (ATP) activates purinoceptors and acts as a neurotransmitter in the nervous system. In the retina, we previously reported that the immunohistochemical distribution of the subset of P2-purinoceptors differs between the ON and OFF pathways. Here, we investigated whether ATP activates P2-purinoceptors and modulates the physiological function of the mouse retina. We also examined if signal processing by P2-purinoceptors is pathway specific. Results showed that ATP activated both ON- and OFF-cholinergic amacrine cells. However, responses in OFF-cholinergic amacrine cells were greater than those in ON-cholinergic amacrine cells. Pharmacological studies in OFF-cholinergic amacrine cells showed that the response of OFF-cholinergic amacrine cells is mediated P2X(2)-purinoceptors. Further, ATP increased gamma-aminobutyric acid (GABA)ergic inhibitory postsynaptic currents (IPSCs) in OFF- but not ON-cholinergic amacrine cells. The increase in GABAergic IPSCs was mediated by P2-purinoceptors. P2-purinoceptor-mediated signals suppressed OFF ganglion cells but activated ON ganglion cells. Our findings indicate that ATP physiologically modulates signal processing of the ON and OFF pathways in a pathway-specific manner through P2-purinoceptors.
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Affiliation(s)
- Makoto Kaneda
- Department of Physiology, Keio University School of Medicine, Tokyo 160-8582, Japan.
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Retinal ON bipolar cells express a new PCP2 splice variant that accelerates the light response. J Neurosci 2008; 28:8873-84. [PMID: 18768681 DOI: 10.1523/jneurosci.0812-08.2008] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
PCP2, a member of the GoLoco domain-containing family, is present exclusively in cerebellar Purkinje cells and retinal ON bipolar cells. Its function in these tissues is unknown. Biochemical and expression system studies suggest that PCP2 is a guanine nucleotide dissociation inhibitor, although a guanine nucleotide exchange factor has also been suggested. Here, we studied the function of PCP2 in ON bipolar cells because their light response depends on Galpha(o1), which is known to interact with PCP2. We identified a new splice variant of PCP2 (Ret-PCP2) and localized it to rod bipolar and ON cone bipolar cells. Electroretinogram recordings from PCP2-null mice showed a normal a-wave but a slower falling phase of the b-wave (generated by the activity of ON bipolar cells) relative to the wild type. Whole-cell recordings from rod bipolar cells showed, both under Ames medium and after blocking GABA(A/C) and glycine receptors, that PCP2-null rod bipolar cells were more depolarized than wild-type cells with greater inward current when clamped to -60 mV. Also under both conditions, the rise time of the response to intense light was slower by 28% (Ames) and 44% (inhibitory blockers) in the null cells. Under Ames medium, we also observed >30% longer decay time in the PCP2-null rod bipolar cells. We conclude that PCP2 facilitates cation channels closure in the dark, shortens the rise time of the light response directly, and accelerates the decay time indirectly via the inhibitory network. These data can most easily be explained if PCP2 serves as a guanine nucleotide exchange factor.
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Tian N. Synaptic activity, visual experience and the maturation of retinal synaptic circuitry. J Physiol 2008; 586:4347-55. [PMID: 18669531 DOI: 10.1113/jphysiol.2008.159202] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
A fundamental feature of the synaptic organization of retina is the laminar-specific structure, in which specific types of retinal neurons form highly selective synapses to transfer distinct synaptic signals. In mature vertebrate retina, the dendrites of most retinal ganglion cells (RGCs) are narrowly stratified and ramified in specific strata of the inner plexiform layer (IPL) of retina to synapse with distinct subtypes of bipolar cells (BCs). However, little is known of how retinal neurons form this laminar-specific synaptic structure during development. Recent studies showed that the formation of retinal synaptic circuitry is regulated by both gene expression and neuronal activity. Here I will briefly discuss the recent advances in our understanding of how synaptic activity modulates the maturation of RGC synaptic connections.
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Affiliation(s)
- Ning Tian
- Department of Ophthalmology and Visual Science, Yale University School of Medicine, New Haven, CT 06520, USA.
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Abstract
Synaptic transmission from photoreceptors to all types of ON bipolar cells is primarily mediated by the mGluR6 receptor. This receptor, which is apparently expressed uniquely in the nervous system by ON bipolar cells, couples negatively to a nonselective cation channel. This arrangement results in a sign reversal at photoreceptor/ON bipolar cell synapse, which is necessary in order to establish parallel ON and OFF pathways in the retina. The synapse is an important target for second messenger molecules that are known to modulate synaptic transmission elsewhere in the nervous system, second messengers that act on a time scale ranging from milliseconds to minutes. This review focuses on two of these molecules, Ca2+ and cGMP, summarizing our current knowledge of how they modulate gain at the photoreceptor/ON bipolar cell synapse, as well as their proposed sites of action within the mGluR6 cascade. The implications of plasticity at this synapse for retinal function will also be examined.
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Affiliation(s)
- Josefin Snellman
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, 333 Cedar Street, SHM-B103, New Haven, CT 06520, USA
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Ping Y, Huang H, Zhang XJ, Yang XL. Melatonin potentiates rod signals to ON type bipolar cells in fish retina. J Physiol 2008; 586:2683-94. [PMID: 18388138 DOI: 10.1113/jphysiol.2008.152959] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Melatonin is involved in regulation of a variety of physiological functions through activation of specific G-protein coupled receptors. However, the neuromodulatory role of melatonin, released from photoreceptors in the retina, is poorly understood. Here we show that melatonin enhances the sensitivity of the rod signal pathway by potentiating signal transfer from rod photoreceptors to ON bipolar cells (Rod-ON-BCs). Whole-cell patch-clamp recordings showed that melatonin induced a sustained inward current from Rod-ON-BCs, through activation of the melatonin MT2 receptor, which was identified as one mediated by a cGMP-dependent cation channel. Consistent with this, melatonin was found, using immunocytochemistry, to increase intracellular cGMP levels, which was identified due to an inhibition of phosphodiesterase. Physiologically, melatonin potentiated responses of Rod-ON-BCs to simulated light flashes (brief puffs of CPPG, an mGluR6 antagonist, in the presence of l-AP4, an mGluR6 agonist), which was mediated by cGMP-dependent kinase, and increased the amplitude of the scotopic electroretinographic b-wave, a reflection of Rod-ON-BC activity. These results suggest that melatonin, being at a higher level at night, may improve the signal/noise ratio for rod signals in the outer retina by enhancing signal transfer from rods to BCs.
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Affiliation(s)
- Yong Ping
- Institute of Neurobiology, Fudan University, 138 Yixueyuan Road, Shanghai 200032, China
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Morgans CW, Wensel TG, Brown RL, Perez-Leon JA, Bearnot B, Duvoisin RM. Gbeta5-RGS complexes co-localize with mGluR6 in retinal ON-bipolar cells. Eur J Neurosci 2007; 26:2899-905. [PMID: 18001285 PMCID: PMC2435197 DOI: 10.1111/j.1460-9568.2007.05867.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The time course of G-protein-coupled responses is largely determined by the kinetics of GTP hydrolysis by the G protein alpha subunit, which is accelerated by interaction with regulator of G-protein signaling (RGS) proteins. Light responses of ON-bipolar cells of the vertebrate retina require rapid inactivation of the G protein Galphao, which is activated in the dark by metabotropic glutamate receptor, mGluR6, in their dendritic tips. It is not yet known, however, which RGS protein(s) might be responsible for rapid inactivation kinetics. By immunofluorescence and co-immunoprecipitation, we have identified complexes of the Galphao-selective RGS proteins RGS7 and RGS11, with their obligate binding partner, Gbeta5, that are localized to the dendritic tips of murine rod and cone ON-bipolar cells, along with mGluR6. Experiments using pre- and post-synaptic markers, and a dissociated bipolar cell preparation, clearly identified the location of these complexes as the ON-bipolar cell dendritic tips and not the adjacent photoreceptor terminals or horizontal cell dendrites. In mice lacking mGluR6, the distribution of RGS11, RGS7 and Gbeta5 shifts away from the dendritic tips, implying a functional relationship with mGluR6. The precise co-localization of Gbeta5-RGS7 and Gbeta5-RGS11 with mGluR6, and the dependence of localization on the presence of mGluR6, suggests that Gbeta5-RGS7 and Gbeta5-RGS11 function specifically in the mGluR6 signal transduction pathway, where they may stimulate the GTPase activity of Galphao, thus accelerating the ON-bipolar cell light response, in a manner analogous to the acceleration of photoreceptor light responses by the Gbeta5-RGS9-1 complex.
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Affiliation(s)
- Catherine W Morgans
- Neurological Sciences Institute, Oregon Health and Science University, Beaverton, OR 97006, USA.
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Gregg RG, Kamermans M, Klooster J, Lukasiewicz PD, Peachey NS, Vessey KA, McCall MA. Nyctalopin expression in retinal bipolar cells restores visual function in a mouse model of complete X-linked congenital stationary night blindness. J Neurophysiol 2007; 98:3023-33. [PMID: 17881478 PMCID: PMC2933657 DOI: 10.1152/jn.00608.2007] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Mutations in the NYX gene that encodes the protein nyctalopin cause congenital stationary night blindness type 1. In no b-wave (nob) mice, a mutation in Nyx results in a functional phenotype that includes the absence of the electroretinogram b-wave and abnormal spontaneous and light-evoked activity in retinal ganglion cells (RGCs). In contrast, there is no morphological abnormality in the retina at either the light or electron microscopic levels. These functional deficits suggest that nyctalopin is required for normal synaptic transmission between retinal photoreceptors and depolarizing bipolar cells (DBCs). However, the synaptic etiology and, specifically, the exact location and function of nyctalopin, remain uncertain. We show that nob DBCs fail to respond to exogenous application of the photoreceptor neurotransmitter, glutamate, thus demonstrating a postsynaptic deficit in photoreceptor to bipolar cell communication. To determine if postsynaptic expression of nyctalopin is necessary and sufficient to rescue the nob phenotype, we constructed transgenic mice that expressed an EYFP-nyctalopin fusion protein on the dendritic tips of the DBCs. Immunohistochemical and ultrastructural studies verified that fusion protein expression was limited to the DBC dendritic tips. Fusion gene expression in nob mice restored normal outer and inner visual function as determined by the electroretinogram and RGC spontaneous and evoked responses. Together, our data show that nyctalopin expression on DBC dendrites is required for normal function of the murine retina.
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Affiliation(s)
- Ronald G Gregg
- Department of Biochemistry and Molecular Biology, University of Louisville, KY 40202, USA.
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42
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Tamalu F, Watanabe SI. Glutamatergic input is coded by spike frequency at the soma and proximal dendrite of AII amacrine cells in the mouse retina. Eur J Neurosci 2007; 25:3243-52. [PMID: 17552993 DOI: 10.1111/j.1460-9568.2007.05596.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In the mammalian retina, AII amacrine cells play a crucial role in scotopic vision. They transfer rod signals from rod bipolar cells to the cone circuit, and divide these signals into the ON and OFF pathways at the discrete synaptic layers. AII amacrine cells have been reported to generate tetrodotoxin (TTX)-sensitive repetitive spikes of small amplitude. To investigate the properties of the spikes, we performed whole-cell patch-clamping of AII amacrine cells in mouse retinal slices. The spike frequency increased in proportion to the concentration of glutamate puffer-applied to the arboreal dendrite and to the intensity of the depolarizing current injection. The spike activity was suppressed by L-2-amino-4-phosphonobutyric acid, a glutamate analogue that hyperpolarizes rod bipolar cells, puffer-applied to the outer plexiform layer. Therefore, it is most likely that the spike frequency generated by AII amacrine cells is dependent on the excitatory glutamatergic input from rod bipolar cells. Gap junction blockers reduced the range of intensity of input with which spike frequency varies. Application of TTX to the soma and the proximal dendrite of AII amacrine cells blocked the voltage-gated Na(+) current significantly more than application to the arboreal dendrite, indicating that the Na(+) channels are mainly localized in these regions. Our results suggest that the intensity of the glutamatergic input from rod bipolar cells is coded by the spike frequency at the soma and the proximal dendrite of AII amacrine cells, raising the possibility that the spikes could contribute to the OFF pathway to enhance release of neurotransmitter.
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Affiliation(s)
- Fuminobu Tamalu
- Department of Physiology, Faculty of Medicine, Saitama Medical University, 38 Morohongo, Moroyama-machi, Saitama 350-0495, Japan.
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43
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Lüke M, Szurman P, Schneider T, Lüke C. The effects of the phosphodiesterase type V inhibitor sildenafil on human and bovine retinal function in vitro. Graefes Arch Clin Exp Ophthalmol 2007; 245:1211-5. [PMID: 17345091 DOI: 10.1007/s00417-007-0562-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2006] [Revised: 02/02/2007] [Accepted: 02/17/2007] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND After the ingestion of sildenafil (Viagra), visual adverse events have been reported, possibly caused by an inhibition of the phototransduction cascade by sildenafil via phosphodiesterase (PDE 6). Therefore, we investigated the effects of sildenafil on photoreceptors and postsynaptic neurons of human and bovine retinas using the isolated superfused vertebrate retina technique. METHODS Human and bovine retina preparations were perfused with an oxygen preequilibrated standard solution. The electroretinogram (ERG) was recorded using Ag/AgCl electrodes. After recording stable ERG amplitudes, sildenafil was added to the solution for 45 min. Thereupon, the preparations were reperfused with standard solution for 240 min. RESULTS Following the application of sildenafil (3 microMol/l), the b-wave amplitude of bovine and human preparations was reduced continuously and disappeared completely. After reperfusion with the standard solution for 4 h, the b-wave amplitude did not recover completely. Using the same sildenafil concentration (3 microMol/l), the a-wave amplitude of the human retina was not totally abolished, but reduced to 21% of the initial amplitude and remained reduced at washout. For all retinal preparations, the implicit time of the ERG amplitudes remained significantly extended at the end of the washout. CONCLUSIONS Strong similarities were detected in the drug-induced changes of the ERG when comparing human and bovine retinas. The results suggest that sildenafil impairs retinal function at not only the level of the photoreceptors, but it also affects the neuronal network of the inner retina at concentrations of approximately 30-fold higher than at therapeutic plasma concentrations.
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Affiliation(s)
- Matthias Lüke
- Institute of Neurophysiology, University of Cologne, Robert-Koch-Str. 39, 50931 Köln, Germany.
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Abstract
Pronounced multivesicular release (MVR) occurs at the ribbon synapses of sensory neurones that signal via graded potential changes. As MVR increases the likelihood of postsynaptic receptor saturation, it is of interest to consider how sensory synapses overcome this problem and use MVR to encode signals of widely varying intensities. Here, I discuss three postsynaptic mechanisms that permit three different retinal synapses to utilize MVR.
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Affiliation(s)
- Joshua H Singer
- Departments of Ophthalmology and Physiology, Northwestern University Feinberg School of Medicine, 303 E. Chicago Ave, Tarry 5-715, Chicago, IL 60611, USA.
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45
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Abstract
Complete X-linked congenital stationary night blindness (CSNB1) is a hereditary visual disease characterized by abnormalities in both the dark- and light-adapted electroretinogram, consistent with a defect in synaptic transmission between photoreceptors and ON-bipolar cells. The gene responsible for CSNB1, NYX, encodes a novel, leucine-rich repeat protein, nyctalopin. Consistent with its predicted glycosylphosphatidylinositol linkage, we show that recombinant nyctalopin is targeted to the extracellular cell surface in transfected HEK293 cells. Within the retina, strong nyctalopin immunoreactivity is present in the outer plexiform layer, the site of the photoreceptor to bipolar cell synapses. Double labelling of nyctalopin and known synaptic proteins in the outer plexiform layer indicate that nyctalopin is associated with the ribbon synapses of both rod and cone terminals. In the inner plexiform layer, nyctalopin immunoreactivity is associated with rod bipolar cell terminals. Our findings support a role for nyctalopin in synaptic transmission and/or synapse formation at ribbon synapses in the retina.
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Affiliation(s)
- Catherine W Morgans
- Neurological Sciences Institute, Oregon Health and Science University, Beaverton, 97006, USA.
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46
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Schein S, Ahmad KM. Efficiency of synaptic transmission of single-photon events from rod photoreceptor to rod bipolar dendrite. Biophys J 2006; 91:3257-67. [PMID: 16920838 PMCID: PMC1614493 DOI: 10.1529/biophysj.106.091744] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A rod transmits absorption of a single photon by what appears to be a small reduction in the small number of quanta of neurotransmitter (Q(count)) that it releases within the integration period ( approximately 0.1 s) of a rod bipolar dendrite. Due to the quantal and stochastic nature of release, discrete distributions of Q(count) for darkness versus one isomerization of rhodopsin (R*) overlap. We suggested that release must be regular to narrow these distributions, reduce overlap, reduce the rate of false positives, and increase transmission efficiency (the fraction of R* events that are identified as light). Unsurprisingly, higher quantal release rates (Q(rates)) yield higher efficiencies. Focusing here on the effect of small changes in Q(rate), we find that a slightly higher Q(rate) yields greatly reduced efficiency, due to a necessarily fixed quantal-count threshold. To stabilize efficiency in the face of drift in Q(rate), the dendrite needs to regulate the biochemical realization of its quantal-count threshold with respect to its Q(count). These considerations reveal the mathematical role of calcium-based negative feedback and suggest a helpful role for spontaneous R*. In addition, to stabilize efficiency in the face of drift in degree of regularity, efficiency should be approximately 50%, similar to measurements.
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Affiliation(s)
- Stan Schein
- Department of Psychology and Brain Research Institute, University of California, Los Angeles, 90095-1563, USA.
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47
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Hasegawa J, Obara T, Tanaka K, Tachibana M. High-Density Presynaptic Transporters Are Required for Glutamate Removal from the First Visual Synapse. Neuron 2006; 50:63-74. [PMID: 16600856 DOI: 10.1016/j.neuron.2006.02.022] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2005] [Revised: 01/24/2006] [Accepted: 02/17/2006] [Indexed: 10/24/2022]
Abstract
Reliable synaptic transmission depends not only on the release machinery and the postsynaptic response mechanism but also on removal or degradation of transmitter from the synaptic cleft. Accumulating evidence indicates that postsynaptic and glial excitatory amino acid transporters (EAATs) contribute to glutamate removal. However, the role of presynaptic EAATs is unclear. Here, we show in the mouse retina that glutamate is removed from the synaptic cleft at the rod to rod bipolar cell (RBC) synapse by presynaptic EAATs rather than by postsynaptic or glial EAATs. The RBC currents evoked by electrical stimulation of rods decayed slowly after pharmacological blockade of EAATs. Recordings of the evoked RBC currents from EAAT subtype-deficient mice and the EAAT-coupled anion current reveal that functional EAATs are localized to rod terminals. Model simulations suggest that rod EAATs are densely packed near the release site and that rods are equipped with an almost self-sufficient glutamate recollecting system.
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Affiliation(s)
- Jun Hasegawa
- Department of Psychology, Graduate School of Humanities and Sociology, The University of Tokyo, Tokyo 113-0033, Japan
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48
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Lüke M, Lüke C, Hescheler J, Schneider T, Sickel W. Effects of Phosphodiesterase Type 5 Inhibitor Sildenafil on Retinal Function in Isolated Superfused Retina. J Ocul Pharmacol Ther 2005; 21:305-14. [PMID: 16117694 DOI: 10.1089/jop.2005.21.305] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
After the oral ingestion of sildenafil, visual abnormalities have been reported constantly. The mechanism of these adverse events has been presumed to be a result of the interaction of sildenafil with the retinal phosphodiesterase (PDE) type 6. To investigate the physiological basis of the effects of sildenafil on retinal function, bovine retinas were isolated and perfused with an oxygen pre-equilibrated standard solution. The electroretinogram (ERG) was recorded as a transretinal potential using silver/silver-chloride electrodes. After reaching stable ERG amplitudes, sildenafil was added to the nurient solution at different concentrations, and its effect on the a- and b-wave amplitude was studied separately. The 0.1 microM and higher concentrations of sildenafil reduced the b-wave amplitude, while a reduction of the a-wave amplitude was observed at an elevated threshold of 0.3 microM. The changes of the ERG amplitudes were fully reversible for the b-wave at a concentration of 0.1 microM and for the a-wave at 0.3 microM sildenafil. At higher concentrations, sildenafil was found to be only partially reversible within recovery time. In conclusion, besides an inhibitory influence on photoreceptors, sildenafil performs additional effects on the postsynaptic neuronal network. Higher concentrations of sildenafil were found to have a potential for retinal degeneration, suggesting that further trials should be designed to evaluate the long-term effects of sildenafil. The physiological consequences of an abuse or long-term, daily use of sildenafil are not clear.
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Affiliation(s)
- Matthias Lüke
- Institute of Neurophysiology, University of Cologne, Köln, Germany
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Zhang DQ, Zhou T, Ruan GX, McMahon DG. Circadian rhythm of Period1 clock gene expression in NOS amacrine cells of the mouse retina. Brain Res 2005; 1050:101-9. [PMID: 15978557 DOI: 10.1016/j.brainres.2005.05.042] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2005] [Revised: 05/10/2005] [Accepted: 05/13/2005] [Indexed: 11/19/2022]
Abstract
The vertebrate retina contains self-sustained circadian clocks that broadly influence retinal physiology. In the present study, we have examined the relationship of nitric oxide, GABAergic and glycinergic inner retinal neurons with expression of a reporter for the circadian clock gene Period1 (Per1). Using Per1 : :GFP transgenic mice, we found that 72% of brain nitric oxide synthase (bNOS) expressing amacrine cells (NOS amacrine cells) sampled during the daytime were also immunoreactive for Per1-driven GFP. The number of bright GFP(+) NOS(+) cells was greater at Zeitgeber time (ZT) 10 than at 22, and this pattern persisted in retinas from animals which were placed in constant darkness [Circadian time (CT) 10 vs. 22]. Intensities of GFP-IR for individual NOS amacrine cells were analyzed at ZT4, 10, 16 and 22, with the peak value occurring at ZT10. Similar results were obtained from retinas sampled at CT4, 10, 16 and 22 in constant darkness, indicating that an endogenous circadian clock drives the transcription of the Per1 clock gene within NOS amacrine cells. The predominance of Per1 : :GFP(+) amacrine cells (82%), was immunoreactive to glutamate decarboxylase 65, but no Per1 : :GFP(+) amacrine cells colabeled with a glycine transporter 1 antibody. The results demonstrate circadian rhythms in Per1 promoter activation in nitric oxide (NO) and GABA secreting amacrine cells, and suggest that NO and GABA could be controlled by circadian clock mechanisms in the mammalian retina.
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Affiliation(s)
- Dao-Qi Zhang
- Department of Biological Sciences, Vanderbilt University, VU Station B, Box 35-1634, Nashville, TN 37235-1634, USA
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Fan SF, Yazulla S. Reciprocal inhibition of voltage-gated potassium currents (IK(V)) by activation of cannabinoid CB1and dopamine D1receptors in ON bipolar cells of goldfish retina. Vis Neurosci 2005; 22:55-63. [PMID: 15842741 DOI: 10.1017/s0952523805221089] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2004] [Indexed: 11/06/2022]
Abstract
Cannabinoid CB1receptor (viaGs) and dopamine D2receptor (viaGi/o) antagonistically modulate goldfish cone membrane currents. As ON bipolar cells have CB1and D1receptors, but not D2receptors, we focused on whether CB1receptor agonist and dopamine interact to modulate voltage-dependent outward membrane K+currentsIK(V)of the ON mixed rod/cone (Mb) bipolar cells. Whole-cell currents were recorded from Mb bipolar cells in goldfish retinal slices. Mb bipolar cells were identified by intracellular filling with Lucifer yellow. The bath solution was calcium-free and contained 1 mM cobalt to block indirect calcium-dependent effects. Dopamine (10 μM) consistently increasedIK(V)by a factor of 1.57 ± 0.12 (S.E.M.,n= 15). A CB receptor agonist, WIN 55212-2 (0.25–1 μM), had no effect, but 4 μM WIN 55212-2 suppressedIK(V)by 60%. IfIK(V)was first increased by 10 μM dopamine, application of WIN 55212-2 (0.25–1 μM) reversibly blocked the effect of dopamine even though these concentrations of WIN 55212-2 had no effect of their own. If WIN 55212-2 was applied first and dopamine (10 μM) was added to the WIN-containing solution, 0.1 μM WIN 55212-2 blocked the effect of dopamine. All effects of WIN 55212-2 were blocked by coapplication of SR 141716A (CB1antagonist) and pretreatment with pertussis toxin (blocker of Gi/o) indicating actionviaCB1receptor activation of G protein Gi/o. Coactivation of CB1and D1receptors on Mb bipolar cells produces reciprocal effects onIK(V). The CB1-evoked suppression ofIK(V)is mediated by G protein Gi/o, whereas the D1-evoked enhancement is mediated by G protein Gs. As dopamine is a retinal “light” signal, these data support our notion that endocannabinoids function as a “dark” signal, interacting with dopamine to set retinal sensitivity.
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Affiliation(s)
- Shih-Fang Fan
- Department of Neurobiology and Behavior, Stony Brook University, Stony Brook, NY 11794-5230, USA
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