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Berry MH, Holt A, Salari A, Veit J, Visel M, Levitz J, Aghi K, Gaub BM, Sivyer B, Flannery JG, Isacoff EY. Restoration of high-sensitivity and adapting vision with a cone opsin. Nat Commun 2019; 10:1221. [PMID: 30874546 PMCID: PMC6420663 DOI: 10.1038/s41467-019-09124-x] [Citation(s) in RCA: 67] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2018] [Accepted: 02/20/2019] [Indexed: 01/27/2023] Open
Abstract
Inherited and age-related retinal degenerative diseases cause progressive loss of rod and cone photoreceptors, leading to blindness, but spare downstream retinal neurons, which can be targeted for optogenetic therapy. However, optogenetic approaches have been limited by either low light sensitivity or slow kinetics, and lack adaptation to changes in ambient light, and not been shown to restore object vision. We find that the vertebrate medium wavelength cone opsin (MW-opsin) overcomes these limitations and supports vision in dim light. MW-opsin enables an otherwise blind retinitis pigmenotosa mouse to discriminate temporal and spatial light patterns displayed on a standard LCD computer tablet, displays adaption to changes in ambient light, and restores open-field novel object exploration under incidental room light. By contrast, rhodopsin, which is similar in sensitivity but slower in light response and has greater rundown, fails these tests. Thus, MW-opsin provides the speed, sensitivity and adaptation needed to restore patterned vision.
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Affiliation(s)
- Michael H Berry
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, 94720, USA
- Department of Physiology and Pharmacology, Oregon Health and Sciences University, Portland, OR, 97239, USA
| | - Amy Holt
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, 94720, USA
| | - Autoosa Salari
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, 94720, USA
| | - Julia Veit
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, 94720, USA
- Helen Wills Neuroscience Institute, University of California, Berkeley, CA, 94720, USA
| | - Meike Visel
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, 94720, USA
| | - Joshua Levitz
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, 94720, USA
- Department of Biochemistry, Weill Cornell Medicine, New York, NY, 10024, USA
| | - Krisha Aghi
- Helen Wills Neuroscience Institute, University of California, Berkeley, CA, 94720, USA
| | - Benjamin M Gaub
- Helen Wills Neuroscience Institute, University of California, Berkeley, CA, 94720, USA
- Department of Biosystems Science Engineering, ETH Zürich, Mattenstrasse 26, Basel, 8092, Switzerland
| | - Benjamin Sivyer
- Department of Physiology and Pharmacology, Oregon Health and Sciences University, Portland, OR, 97239, USA
- Department of Ophthalmology, Casey Eye Institute, Oregon Health and Science University, Portland, OR, 97239, USA
| | - John G Flannery
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, 94720, USA
- Helen Wills Neuroscience Institute, University of California, Berkeley, CA, 94720, USA
- School of Optometry, University of California, Berkeley, CA, 94720, USA
| | - Ehud Y Isacoff
- Department of Molecular and Cell Biology, University of California, Berkeley, CA, 94720, USA.
- Helen Wills Neuroscience Institute, University of California, Berkeley, CA, 94720, USA.
- Bioscience Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
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2
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Verdaguer D, Jansen MAK, Llorens L, Morales LO, Neugart S. UV-A radiation effects on higher plants: Exploring the known unknown. PLANT SCIENCE : AN INTERNATIONAL JOURNAL OF EXPERIMENTAL PLANT BIOLOGY 2017; 255:72-81. [PMID: 28131343 DOI: 10.1016/j.plantsci.2016.11.014] [Citation(s) in RCA: 103] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2016] [Revised: 11/28/2016] [Accepted: 11/29/2016] [Indexed: 05/02/2023]
Abstract
Ultraviolet-A radiation (UV-A: 315-400nm) is a component of solar radiation that exerts a wide range of physiological responses in plants. Currently, field attenuation experiments are the most reliable source of information on the effects of UV-A. Common plant responses to UV-A include both inhibitory and stimulatory effects on biomass accumulation and morphology. UV-A effects on biomass accumulation can differ from those on root: shoot ratio, and distinct responses are described for different leaf tissues. Inhibitory and enhancing effects of UV-A on photosynthesis are also analysed, as well as activation of photoprotective responses, including UV-absorbing pigments. UV-A-induced leaf flavonoids are highly compound-specific and species-dependent. Many of the effects on growth and development exerted by UV-A are distinct to those triggered by UV-B and vary considerably in terms of the direction the response takes. Such differences may reflect diverse UV-perception mechanisms with multiple photoreceptors operating in the UV-A range and/or variations in the experimental approaches used. This review highlights a role that various photoreceptors (UVR8, phototropins, phytochromes and cryptochromes) may play in plant responses to UV-A when dose, wavelength and other conditions are taken into account.
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Affiliation(s)
- Dolors Verdaguer
- Environmental Sciences Department, Faculty of Sciences, University of Girona, Campus de Montilivi, C/Maria Aurèlia Capmany I Farnés, 69, E-17003 Girona, Spain.
| | - Marcel A K Jansen
- School of Biological, Earth and Environmental Sciences, University College Cork, Distillery Field, North Mall, Cork, Ireland.
| | - Laura Llorens
- Environmental Sciences Department, Faculty of Sciences, University of Girona, Campus de Montilivi, C/Maria Aurèlia Capmany I Farnés, 69, E-17003 Girona, Spain.
| | - Luis O Morales
- Division of Plant Biology, Department of Biosciences, Viikki Plant Science Center, University of Helsinki, FI-00014 Helsinki, Finland.
| | - Susanne Neugart
- Leibniz-Institute of Vegetable and Ornamental Crops Grossbeeren/Erfurt e.V., Theodor-Echtermeyer-Weg 1, 14979, Grossbeeren, Germany.
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3
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Regulation of Neuronal Oxygen Responses in C. elegans Is Mediated through Interactions between Globin 5 and the H-NOX Domains of Soluble Guanylate Cyclases. J Neurosci 2016; 36:963-78. [PMID: 26791224 DOI: 10.1523/jneurosci.3170-15.2016] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Soluble guanylate cyclases (sGCs) are gas-binding proteins that control diverse physiological processes such as vasodilation, platelet aggregation, and synaptic plasticity. In the nematode Caenorhabditis elegans, a complex of sGCs, GCY-35 and GCY-36, functions in oxygen (O2) sensing. Previous studies suggested that the neuroglobin GLB-5 genetically interacts with GCY-35, and that the inhibitory effect of GLB-5 on GCY-35 function is necessary for fast recovery from prolonged hypoxia. In this study, we identified mutations in gcy-35 and gcy-36 that impact fast recovery and other phenotypes associated with GLB-5, without undermining sGC activity. These mutations, heb1 and heb3, change conserved amino acid residues in the regulatory H-NOX domains of GCY-35 and GCY-36, respectively, and appear to suppress GLB-5 activity by different mechanisms. Moreover, we observed that short exposure to 35% O2 desensitized the neurons responsible for ambient O2 sensing and that this phenomenon does not occur in heb1 animals. These observations may implicate sGCs in neuronal desensitization mechanisms far beyond the specific case of O2 sensing in nematodes. The conservation of functionally important regions of sGCs is supported by examining site-directed mutants of GCY-35, which suggested that similar regions in the H-NOX domains of O2 and NO-sensing sGCs are important for heme/gas interactions. Overall, our studies provide novel insights into sGC activity and regulation, and implicate similar structural determinants in the control of both O2 and NO sensors. Significance statement: Soluble guanylate cyclases (sGCs) control essential and diverse physiological processes, including memory processing. We used Caenorhabditis elegans to explore how a neuroglobin inhibits a complex of oxygen-sensing sGCs, identifying sGC mutants that resist inhibition. Resistance appears to arise by two different mechanisms: increased basal sGC activity or disruption of an interaction with neuroglobin. Our findings demonstrate that the inhibition of sGCs by neuroglobin is essential for rapid adaptation to either low or high oxygen levels, and that similar structural regions are key for regulating both oxygen and nitric oxide sensors. Based on our structural and functional analyses, we present the hypothesis that neuroglobin-sGC interactions may be generally important for adaptation processes, including those in organisms with more complex neurological functions.
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Sund P, Månsson LG, Båth M. Development and evaluation of a method of calibrating medical displays based on fixed adaptation. Med Phys 2015; 42:2018-28. [DOI: 10.1118/1.4915531] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
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5
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Nikolić D. Practopoiesis: or how life fosters a mind. J Theor Biol 2015; 373:40-61. [PMID: 25791287 DOI: 10.1016/j.jtbi.2015.03.003] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2014] [Revised: 12/16/2014] [Accepted: 03/03/2015] [Indexed: 12/25/2022]
Abstract
The mind is a biological phenomenon. Thus, biological principles of organization should also be the principles underlying mental operations. Practopoiesis states that the key for achieving intelligence through adaptation is an arrangement in which mechanisms laying at a lower level of organization, by their operations and interaction with the environment, enable creation of mechanisms laying at a higher level of organization. When such an organizational advance of a system occurs, it is called a traverse. A case of traverse is when plasticity mechanisms (at a lower level of organization), by their operations, create a neural network anatomy (at a higher level of organization). Another case is the actual production of behavior by that network, whereby the mechanisms of neuronal activity operate to create motor actions. Practopoietic theory explains why the adaptability of a system increases with each increase in the number of traverses. With a larger number of traverses, a system can be relatively small and yet, produce a higher degree of adaptive/intelligent behavior than a system with a lower number of traverses. The present analyses indicate that the two well-known traverses - neural plasticity and neural activity - are not sufficient to explain human mental capabilities. At least one additional traverse is needed, which is named anapoiesis for its contribution in reconstructing knowledge e.g., from long-term memory into working memory. The conclusions bear implications for brain theory, the mind-body explanatory gap, and developments of artificial intelligence technologies.
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Affiliation(s)
- Danko Nikolić
- Department of Neurophysiology, Max Planck Institute for Brain Research, Deutschordenstraße 46, D-60528 Frankfurt/M, Germany; Frankfurt Institute for Advanced Studies (FIAS), Ruth-Moufang-Straße 1, D-60438 Frankfurt/M, Germany; Ernst Strüngmann Institute (ESI) for Neuroscience in Cooperation with Max Planck Society, Deutschordenstraße 46, D-60528 Frankfurt/M, Germany; Department of Psychology, Faculty of Humanities and Social Sciences, University of Zagreb, Zagreb, Croatia.
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ALSAM ALI, RIVERTZ HANSJAKOB, SHARMA PUNEET. WHAT THE EYE DID NOT SEE — A FUSION APPROACH TO IMAGE CODING. INT J ARTIF INTELL T 2013. [DOI: 10.1142/s0218213013600142] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The concentration of the cones and ganglion cells is much higher in the fovea than the rest of the retina. This non-uniform sampling results in a retinal image that is sharp at the fixation point, where a person is looking, and blurred away from it. This difference between the sampling rates at the different spatial locations presents us with the question of whether we can employ this biological characteristic to achieve better image compression. This can be achieved by compressing an image less at the fixation point and more away from it. It is, however, known that the vision system employs more that one fixation to look at a single scene which presents us with the problem of combining images pertaining to the same scene but exhibiting different spatial contrasts. This article presents an algorithm to combine such a series of images by using image fusion in the gradient domain. The advantage of the algorithm is that unlike other algorithms that compress the image in the spatial domain our algorithm results in no artifacts. The algorithm is based on two steps, in the first we modify the gradients of an image based on a limited number of fixations and in the second we integrate the modified gradient. Results based on measured and predicted fixations verify our approach.
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Affiliation(s)
- ALI ALSAM
- Department of Informatics & e-Learning (AITeL), Sør-Trøndelag University College (HiST), Trondheim, Norway
| | - HANS JAKOB RIVERTZ
- Department of Informatics & e-Learning (AITeL), Sør-Trøndelag University College (HiST), Trondheim, Norway
| | - PUNEET SHARMA
- Department of Informatics & e-Learning (AITeL), Sør-Trøndelag University College (HiST), Trondheim, Norway
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7
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Vasserman G, Schneidman E, Segev R. Adaptive colour contrast coding in the salamander retina efficiently matches natural scene statistics. PLoS One 2013; 8:e79163. [PMID: 24205373 PMCID: PMC3813611 DOI: 10.1371/journal.pone.0079163] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2012] [Accepted: 09/19/2013] [Indexed: 11/19/2022] Open
Abstract
The visual system continually adjusts its sensitivity to the statistical properties of the environment through an adaptation process that starts in the retina. Colour perception and processing is commonly thought to occur mainly in high visual areas, and indeed most evidence for chromatic colour contrast adaptation comes from cortical studies. We show that colour contrast adaptation starts in the retina where ganglion cells adjust their responses to the spectral properties of the environment. We demonstrate that the ganglion cells match their responses to red-blue stimulus combinations according to the relative contrast of each of the input channels by rotating their functional response properties in colour space. Using measurements of the chromatic statistics of natural environments, we show that the retina balances inputs from the two (red and blue) stimulated colour channels, as would be expected from theoretical optimal behaviour. Our results suggest that colour is encoded in the retina based on the efficient processing of spectral information that matches spectral combinations in natural scenes on the colour processing level.
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Affiliation(s)
- Genadiy Vasserman
- Department of Life Sciences and the Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Elad Schneidman
- Department of Neurobiology, Weizmann Institute of Science, Rehovot, Israel
| | - Ronen Segev
- Department of Life Sciences and the Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva, Israel
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Lindeberg T. Invariance of visual operations at the level of receptive fields. PLoS One 2013; 8:e66990. [PMID: 23894283 PMCID: PMC3716821 DOI: 10.1371/journal.pone.0066990] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2012] [Accepted: 05/14/2013] [Indexed: 11/29/2022] Open
Abstract
The brain is able to maintain a stable perception although the visual stimuli vary substantially on the retina due to geometric transformations and lighting variations in the environment. This paper presents a theory for achieving basic invariance properties already at the level of receptive fields. Specifically, the presented framework comprises (i) local scaling transformations caused by objects of different size and at different distances to the observer, (ii) locally linearized image deformations caused by variations in the viewing direction in relation to the object, (iii) locally linearized relative motions between the object and the observer and (iv) local multiplicative intensity transformations caused by illumination variations. The receptive field model can be derived by necessity from symmetry properties of the environment and leads to predictions about receptive field profiles in good agreement with receptive field profiles measured by cell recordings in mammalian vision. Indeed, the receptive field profiles in the retina, LGN and V1 are close to ideal to what is motivated by the idealized requirements. By complementing receptive field measurements with selection mechanisms over the parameters in the receptive field families, it is shown how true invariance of receptive field responses can be obtained under scaling transformations, affine transformations and Galilean transformations. Thereby, the framework provides a mathematically well-founded and biologically plausible model for how basic invariance properties can be achieved already at the level of receptive fields and support invariant recognition of objects and events under variations in viewpoint, retinal size, object motion and illumination. The theory can explain the different shapes of receptive field profiles found in biological vision, which are tuned to different sizes and orientations in the image domain as well as to different image velocities in space-time, from a requirement that the visual system should be invariant to the natural types of image transformations that occur in its environment.
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Affiliation(s)
- Tony Lindeberg
- Department of Computational Biology, School of Computer Science and Communication, KTH Royal Institute of Technology, Stockholm, Sweden.
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9
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Fold-change detection and scalar symmetry of sensory input fields. Proc Natl Acad Sci U S A 2010; 107:15995-6000. [PMID: 20729472 DOI: 10.1073/pnas.1002352107] [Citation(s) in RCA: 135] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Recent studies suggest that certain cellular sensory systems display fold-change detection (FCD): a response whose entire shape, including amplitude and duration, depends only on fold changes in input and not on absolute levels. Thus, a step change in input from, for example, level 1 to 2 gives precisely the same dynamical output as a step from level 2 to 4, because the steps have the same fold change. We ask what the benefit of FCD is and show that FCD is necessary and sufficient for sensory search to be independent of multiplying the input field by a scalar. Thus, the FCD search pattern depends only on the spatial profile of the input and not on its amplitude. Such scalar symmetry occurs in a wide range of sensory inputs, such as source strength multiplying diffusing/convecting chemical fields sensed in chemotaxis, ambient light multiplying the contrast field in vision, and protein concentrations multiplying the output in cellular signaling systems. Furthermore, we show that FCD entails two features found across sensory systems, exact adaptation and Weber's law, but that these two features are not sufficient for FCD. Finally, we present a wide class of mechanisms that have FCD, including certain nonlinear feedback and feed-forward loops. We find that bacterial chemotaxis displays feedback within the present class and hence, is expected to show FCD. This can explain experiments in which chemotaxis searches are insensitive to attractant source levels. This study, thus, suggests a connection between properties of biological sensory systems and scalar symmetry stemming from physical properties of their input fields.
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10
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Moriondo A, Rispoli G. The contribution of cationic conductances to the potential of rod photoreceptors. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2009; 39:889-902. [PMID: 19234695 DOI: 10.1007/s00249-009-0419-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2008] [Revised: 01/27/2009] [Accepted: 02/02/2009] [Indexed: 11/29/2022]
Abstract
The contribution of cationic conductances in shaping the rod photovoltage was studied in light adapted cells recorded under whole-cell voltage- or current-clamp conditions. Depolarising current steps (of size comparable to the light-regulated current) produced monotonic responses when the prepulse holding potential (V (h)) was -40 mV (i.e. corresponding to the membrane potential in the dark). At V (h) = -60 mV (simulating the steady-state response to an intense background of light) current injections <35 pA (mimicking a light decrement) produced instead an initial depolarisation that declined to a plateau, and voltage transiently overshot V (h) at the stimulus offset. Current steps >40 pA produced a steady depolarisation to approximately -16 mV at both V (h). The difference between the responses at the two V (h) was primarily generated by the slow delayed-rectifier-like K(+) current (I (Kx)), which therefore strongly affects both the photoresponse rising and falling phase. The steady voltage observed at both V (h) in response to large current injections was instead generated by Ca-activated K(+) channels (I (KCa)), as previously found. Both I (Kx) and I (KCa) oppose the cation influx, occurring at the light stimulus offset through the cGMP-gated channels and the voltage-activated Ca(2+) channels (I (Ca)). This avoids that the cation influx could erratically depolarise the rod past its normal resting value, thus allowing a reliable dim stimuli detection, without slowing down the photovoltage recovery kinetics. The latter kinetics was instead accelerated by the hyperpolarisation-activated, non-selective current (I (h)) and I (Ca). Blockade of all K(+) currents with external TEA unmasked a I (Ca)-dependent regenerative behaviour.
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Affiliation(s)
- Andrea Moriondo
- Dipartimento di Biologia ed Evoluzione, Sezione di Fisiologia e Biofisica, National Institute of Neuroscience and Neuroscience Center, Università di Ferrara, Via L. Borsari 46, Ferrara, Italy
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11
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Miller JA, Denning KS, George JS, Marshak DW, Kenyon GT. A high frequency resonance in the responses of retinal ganglion cells to rapidly modulated stimuli: a computer model. Vis Neurosci 2006; 23:779-94. [PMID: 17020633 PMCID: PMC3350093 DOI: 10.1017/s0952523806230104] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2006] [Accepted: 05/09/2006] [Indexed: 11/05/2022]
Abstract
Brisk Y-type ganglion cells in the cat retina exhibit a high frequency resonance (HFR) in their responses to large, rapidly modulated stimuli. We used a computer model to test whether negative feedback mediated by axon-bearing amacrine cells onto ganglion cells could account for the experimentally observed properties of HFRs. Temporal modulation transfer functions (tMTFs) recorded from model ganglion cells exhibited HFR peaks whose amplitude, width, and locations were qualitatively consistent with experimental data. Moreover, the wide spatial distribution of axon-mediated feedback accounted for the observed increase in HFR amplitude with stimulus size. Model phase plots were qualitatively similar to those recorded from Y ganglion cells, including an anomalous phase advance that in our model coincided with the amplification of low-order harmonics that overlapped the HFR peak. When axon-mediated feedback in the model was directed primarily to bipolar cells, whose synaptic output was graded, or else when the model was replaced with a simple cascade of linear filters, it was possible to produce large HFR peaks but the region of anomalous phase advance was always eliminated, suggesting the critical involvement of strongly non-linear feedback loops. To investigate whether HFRs might contribute to visual processing, we simulated high frequency ocular tremor by rapidly modulating a naturalistic image. Visual signals riding on top of the imposed jitter conveyed an enhanced representation of large objects. We conclude that by amplifying responses to ocular tremor, HFRs may selectively enhance the processing of large image features.
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Affiliation(s)
- J A Miller
- Applied Modern Physics, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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12
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Abstract
This review presents a new unified view of the pathogenesis of three common causes of acquired retinal degenerative disease-diabetic retinopathy, age related macular degeneration, and retinopathy of prematurity. In these three conditions, angiogenesis has a predominant role in the development of sight threatening pathology. Angiogenesis is controlled by among other factors the expression of vascular endothelial growth factor (VEGF), which in turn is regulated by absolute and relative lack of oxygen. The severe pathological manifestations of these three conditions are not part of a general underlying disease process because they are peculiar to the eye, and the profound hypoxia that develops in normal retina during dark adaptation (rod driven hypoxia) is an adequate and elegant additional factor to explain their pathogenesis. A large number of experimental reports support this conclusion, although rod driven anoxia is not generally considered as a causal factor in ocular disease. However, the hypothesis can be critically tested, and also suggests novel methods of treatment and prevention of these conditions that may be simpler and more inexpensive than current therapies and that have a smaller potential for adverse effects.
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Affiliation(s)
- G B Arden
- Henry Wellcome Laboratories, Applied Vision Research Centre, Department of Optometry and Visual Science, City University, Northampton Square, London EC1V 0HB, UK.
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13
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He F, Mao M, Wensel TG. Enhancement of phototransduction g protein-effector interactions by phosphoinositides. J Biol Chem 2003; 279:8986-90. [PMID: 14699118 DOI: 10.1074/jbc.m311488200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Light responses in photoreceptor cells are mediated by the action of the G protein transducin (G(t)) on the effector enzyme cGMP phosphodiesterase (PDE6) at the surface of disk membranes. The enzymatic components needed for phosphoinositide-based signaling are known to be present in rod cells, but it has remained uncertain what role phosphoinositides play in vertebrate phototransduction. Reconstitution of PDE6 and activated G(alphat), on the surface of large unilamellar vesicles containing d-myo-phosphatidylinositol-4,5-bisphosphate (PI(4,5)P(2)), stimulated PDE activity nearly 4-fold above the level observed with membranes containing no phosphoinositides, whereas G protein-independent activation by trypsin was unaffected by the presence of phosphoinositides. PDE activity was similarly stimulated by d-myo-phosphatidylinositol-3,4-bisphosphate and d-myo-phosphatidylinositol-4-phosphate (PI(4)P), but much less by d-myo-phosphatidylinositol-5-phosphate (PI(5)P) or d-myo-phosphatidylinositol-3,5-bisphosphate. Incubation of rod outer segment membranes with phosphoinositide-specific phospholipase C decreased G protein-stimulated activation of endogenous PDE6, but not trypsin-stimulated PDE activity. Binding experiments using phosphoinositide-containing vesicles revealed patterns of PDE6 binding and PDE6-enhanced G(alphat)-GTPgammaS binding, consistent with the activation profile PI(4,5)P(2) > PI(4)P > PI(5)P approximately control vesicles. These results suggest that enhancement of effector-G protein interactions represents a possible mechanism for modulation of phototransduction gain by changes in phosphoinositide levels, perhaps occurring in response to longterm changes in illumination or other environmental cues.
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Affiliation(s)
- Feng He
- Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030, USA
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14
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Abstract
Small GTP binding proteins regulate diverse biological processes including gene expression, cytoskeleton reorganization, and protein and vesicular transport. While small GTPases have been investigated in a wide variety of cells, few studies have addressed their role in photoreceptors. In vertebrate retinal rods, the light stimulus is transmitted from rhodopsin via the pathway mediated by the heterotrimeric G protein transducin. To increase their sensitivity to light, photoreceptors accumulate remarkably high concentrations of rhodopsin and transducin in specialized cellular compartments, the outer segments (OS). Transport of these proteins from the inner segments is regulated by the small GTPases Rab6 and Rab8, which do not enter OS. Here, we asked if small G proteins have other functions in photoreceptors. We show that OS contain the small GTPase Rac-1, a member of the Rho family. In contrast to other cells, Rac-1 in OS is exclusively associated with the membranes and resides in lipid rafts. Most importantly, Rac-1 is activated by light. This activation is specifically blocked by a synthetic peptide corresponding to the Asn-Pro-X-X-Tyr motif found in rhodopsin, and Rac-1 coprecipitates with rhodopsin on Concanavalin A Sepharose. These data provide the first direct evidence for the existence of a novel pathway activated by rhodopsin.
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Affiliation(s)
- Nagaraj Balasubramanian
- Department of Molecular and Cellular Pharmacology and the Neuroscience Program, University of Miami School of Medicine, Miami, FL 33136, USA
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