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Topic: Visual phototransduction

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	Webvision: Visual Cortex
		After the complexities of phototransduction, lateral interactions provided by horizontal and amacrine cells, and integration of signals by ganglion cell dendrites only the constantly changing stream of action potentials propogating along ganglion cell axons is left to inform our visual perception.
		Visual input to the brain goes from eye to LGN and then to primary visual cortex, or area V1, which is located in the posterior of the occipital lobe.
		Maunsell JH, Gibson JR (1992) Visual response latencies in striate cortex of the macaque monkey.
	webvision.med.utah.edu /VisualCortex.html (9250 words)

	Salvador-Silva, Mol Vis 2005; 11:356-365.
		CRALBP in the visual cycle serves as an 11-cis-retinol acceptor for the enzymatic isomerization of all-trans-retinyl esters to 11-cis-retinol and as a substrate carrier for 11-cis-retinol dehydrogenase (RDH5) [15].
		We do not believe that the levels of many of the components of phototransduction and the retinoid visual cycle in bovine and human CE are present at the vestigial level or that they are due to tissue cross contamination with the retina.
		All-trans-retinyl esters are the substrates for isomerization in the vertebrate visual cycle.
	www.molvis.org /molvis/v11/a42 (5438 words)

	Institute of Ophthalmology
		Such aspects include the mechanisms of spectral tuning of visual pigments, the evolution of colour vision, the ecology of vision and the role of the photosensitive pineal organ of lower vertebrates.
		Visual pigments in vertebrates are divided into five phylogenetic families that probably evolved very early in vertebrate evolution, about 450-500 million years ago (MYA) and were most likely present in the early jawless fish of the Devonian period.
		Within each class, the visual pigments can be ‘tuned’ to be maximally sensitive at a particular wavelength (λmax) so that, for example, within the LWS family, a pigment in one species may be found with λmax at 570 nm whereas in another species at 500 nm.
	www.ucl.ac.uk /ioo/research/bowmaker.htm (1528 words)

	Pagina nueva 6
		Mutations in these receptors are responsible for a number of pathological processes, ranging from retinal degenerations in the case of the visual photoreceptor rhodopsin to precoucious puberty or heretitary obesity in others case.
		The activation and inactivation processes in which rhodopsin is involved, in the visual biochemical cycle, are precisely modulated by a number of very well organised sets of protein–protein interactions where metal ions play also an important role.
		In addition to its importance as a visual pathology, the study of CSNB is interesting because it can be a model of the first stages of RP.
	www.ct.upc.es /unitats/gbmi/cuerpo_investigaciones.htm (3072 words)

	Interactive Fly, Drosophila
		Drosophila visual signal transduction, the process by which incoming light is converted to neural signals that can be passed to the brain, provides an ideal system for the molecular dissection of the process by which extracellular signals are transduced across the plasma membrane leading to neuron activation.
		In the visual signal transduction pathway, light stimulates rhodopsin, which activates an eye-specific G protein (Galphaq).
		Both TRP (Transient receptor potential) and TRPL (TRP-like) are cation channels that are activated in the visual transduction process.
	www.sdbonline.org /fly/hjmuller/inad1.htm (1209 words)

	Annual Report on the Rare Diseases and Conditions Research Activities of the National Institutes of Health 1997 - ... (Site not responding. Last check: 2007-11-06)
		Photoreceptor cells of the retina, the rods and cones, are responsible for the capture of light and the initiation of an electrical signal to the brain in the process of vision.
		The study of signaling in the photoreceptor cells, termed the visual phototransduction cascade, has provided a detailed molecular description of this pathway.
		The goal of this research is to understand the pathogenesis of genetic mutations that may be responsible for a reduction of ocular pigmentation and the associated ocular morbidity with these diseases.
	rarediseases.info.nih.gov /html/reports/fy1997/nei.html (1316 words)

	ANU - The John Curtin School of Medical Research - JCSMR
		Phototransduction in vertebrate rods and cones: molecular mechanisms of amplification recovery and light adaptation.
		In Handbook of Biological Physics Vol 3, Molecular Mechanisms of Visual Transduction (ed DG Stavenga, WJ de Grip and EN Pugh Jr) Chapter 5, pp 183-255.
		Analysis of a wave amplification and kinetics in terms of the G protein cascade of phototransduction.
	jcsmr.anu.edu.au /org/dns/visual/publications.php (1467 words)

	Reduction of All-trans Retinal to All-trans Retinol in the Outer Segments of Frog and Mouse Rod Photoreceptors -- Chen ...
		that regenerate the vertebrate visual pigment rhodopsin, is
		photoreceptors is the photoisomerization of the visual pigment
		The structure and spectra of the chromophore of the visual pigments.
	www.biophysj.org /cgi/content/full/88/3/2278 (5854 words)

	Webvision: Photoreceptors
		It is from the base of the cilium that membrane evaginations and invaginations occur to produce the outer segment (o.s.) or the important visual pigment-bearing portion of the photoreceptor.
		The opsin part of the rhodopsin molecule (which is the visual pigment), is thought to be manufactured in the Golgi apparatus of the inner segment and presented to the outer membrane at the cilium, via fusion areas using G-proteins (Papermaster et al., 1985; Deretic and Papermaster, 1995).
		The visual pigment consists of a protein called opsin and a chromophore derived from vitamin A known as retinal.
	webvision.med.utah.edu /photo1.html (1648 words)

	NEUROSCIENCE : Julie Schnapf (Site not responding. Last check: 2007-11-06)
		To study the earliest stages of phototransduction we use suction electrodes to measure photocurrent in single rod and cone outer segments of human and monkey eyes and compare this to corresponding measures of human visual perception.
		The brightness of colored lights and the appearance of color mixtures could be predicted from the measured wavelength dependence of the responses in single rods and cones.
		After the photoreceptors, the next step in visual transduction is the excitation of retinal bipolar cells.
	www.ucsf.edu /neurosc/faculty/neuro_schnapf.html (476 words)

	NYU \| Department of Biology \| Faculty \| Daniel Tranchina
		A long-term goal is to be able to predict the responses of the various types of neurons in the visual system to arbitrary stimuli varying over time and space.
		Neurons are coupled via stochastic synapses, and the rate of excitatory/inhibitory input events for a target neuron is determined by the rate of action potentials in each of the presynaptic populations and by the average number of synapses the postsynaptic neuron receives from each of these populations.
		My newest project is a study of the role of feedback from visual cortex to the lateral geniculate nucleus (dLGN) of the thalamus.
	www.nyu.edu /fas/biology/faculty/tranchina/index.html (1082 words)

	Visual perception - Wikipedia, the free encyclopedia
		In psychology, visual perception is the end product of vision, consisting of the ability to detect light and interpret (see) the consequences of light stimulus.
		The remaining stages include the lateral geniculate nucleus, and the primary and secondary visual cortex of the brain.
		The Gestalt Laws of Organization have guided the study of how people perceive visual components as organized patterns or wholes, instead of many different parts.
	en.wikipedia.org /wiki/Visual_perception (729 words)

	Perceptual Adaptations
		The authors suggest that the basic structure of visual cortical maps is innate, but experience is essential for specific features as well as for maintaining the responsiveness and selectivity of cortical neurons.
		In all of this, the eyes themselves are optically normal after they are uncovered, the cells in the retina and in the lower visual centers appear to function normally in their response to visual input.
		But the deprived eye or deprived eyes are "blind", and the changes or lack of development responsible for this loss of visual function are in the visual cortex and are due to its plasticity, its dependence on appropriate input for the formation of working connections.
	cogweb.ucla.edu /ep/Perceptual.html (7517 words)

	Dr. Russell Hamer Lab
		We are working to develop a comprehensive model of vertebrate rod phototransduction that is able to account for rod responses over the full gamut of their response repertoire, from single-photon responses to highly light-adapted responses.
		His background is in experimental and theoretical psychophysics, as well as in state-of-the art visual evoked potential recordings, specializing in analyses of human temporal processing, contrast sensitivity, spatial vision, and human cortical visual development.
		He is primarily involved in the development and implementation of computational models of the vertebrate phototransduction cascade, and the numerical optimization of these models to account for a wide array of physiological data.
	www.ski.org /RHamer_lab (1035 words)

	Escribano, Mol Vis 2002; 8:315-332.
		The detection of these genes in the ciliary epithelium is not due to cross contamination from the retina, since their cellular distribution along the nonpigmented ciliary epithelium have been confirmed by indirect immunofluorescence at the pars plicata region of the ciliary epithelium, an area distant from the retina [15].
		In this tissue it may play a role in the phototransduction system, since in photoreceptors it is involved in the rod and rod-bipolar signaling cascades [34], hydrolyzing phosphatidylinositol 4,5-biphosphate to inositol triphosphate and diacylglycerol.
		PLC β4 is expressed in the brain and in neurons of the retina (bipolar cells, horizontal cells, and ganglion cells), modulating the visual response in mice.
	www.molvis.org /molvis/v8/a39 (9146 words)

	Cote Laboratory (Site not responding. Last check: 2007-11-06)
		Vision begins upon absorption of light by the visual pigment, is amplified by a series of highly regulated biochemical reactions, and ultimately results in closure of ion channels and membrane hyperpolarization.
		This phototransduction pathway in rods is the best understood G-protein-coupled receptor signaling system known, particularly the activation phase of the light response.
		Because precise regulation of cGMP metabolism is critical for the visual signaling pathway, any defect in the processes controlling cGMP levels can have serious consequences, including visual impairment, retinal degeneration, and total blindness.
	www.cote.unh.edu (189 words)

	ScienceWeek
		The thalamus acts as a relay station for the various sensory modalities, including vision, and the linkages between the thalamus and the parts of the cerebral cortex concerned with vision are essential in primates for the processing of visual information.
		The authors suggest that fusion events, in addition to being important for the presynaptic release of neurotransmitters, are also involved in some mechanism at the postsynaptic membrane, and thus contribute to long term potentiation.
		The authors suggest their findings challenge the belief that mammals are incapable of extraretinal circadian phototransduction, and that the findings also have implications for the development of more effective treatments of sleep and circadian rhythm disorders.
	scienceweek.com /1998/sw980130.htm (6235 words)

	Faculty Membership Application
		The research in my lab centers on the molecules involved in phototransduction-- the biochemical process by which photons are converted into a neural signal.
		The phototransduction enzyme cascade is an exquisitely sensitive system, being capable of producing a neural response to a single photon.
		One of the many exciting things about phototransduction is that much of the process is conserved across ALL animals that have eyes, from the slimy flatworms to the crunchy insects and right on up to humans.
	www.mbi.ufl.edu /people/fac-form.php?id=22 (377 words)

	Drosophila gene families: Visual signal transduction
		Among the proteins of critical importance in visual phototransduction is Inactivation-no-afterpotential D, a photoreceptor-specific protein containing five repeated protein interaction motifs known as PDZ repeats.
		A cycling trpl transcript could contribute to the visual sensitivity cycle: (1) the two phenomena are in the same phase with both sensitivity and trpl expression peaking around lights-off; (2) it is estimated that TRPL contributes about half of the wild-type conductance, allowing for a substantial range of modulation by reducing TRPL function.
		Interestingly, the contribution of visual photo-transduction to circadian photo-entrainment is apparently restricted to a few pacemaker neurons in the brain, a situation reminiscent of photo-entrainment of the clock circuits in the mammalian brain via the retina and the retino-hypothalamic tract.
	www.sdbonline.org /fly/aignfam/visual.htm (12868 words)

	Annual Report on the Rare Diseases and Conditions Research Activities of the National Institutes of Health FY 2000 - ... (Site not responding. Last check: 2007-11-06)
		RP is a group of blinding hereditary retinal degenerative diseases characterized by a progressive loss of vision due to the degeneration of photoreceptor cells.
		The absence of the RPE-65 gene produces a defect in the visual cycle, a series of biochemical events in the light-sensing retina that initiate vision.
		Clinical care for keratoconus is time-consuming for patients and physicians because of its chronic progression and the difficulty of achieving a stable contact lens fit for visual rehabilitation.
	rarediseases.info.nih.gov /html/reports/fy2000/nei.html (2281 words)

	Artur V. Cideciyan's Homepage
		Rod and cone visual cycle consequences of a null mutation in the 11-cis-retinol dehydrogenase gene in man.
		Null mutation in the rhodopsin kinase gene slows recovery kinetics of rod and cone phototransduction in man.
		An alternative phototransduction model for human rod and cone ERG a-waves: normal parameters and variation with age.
	mail.med.upenn.edu /~cideciya (217 words)

	Mammalian Homolog of Drosophila retinal degeneration B Rescues the Mutant Fly Phenotype -- Chang et al. 17 (15): 5881 ...
		Harris WA, Stark WS (1977) Hereditary retinal degeneration in Drosophila melanogaster: a mutant defect associated with the phototransduction process.
		Lee J, Della N, Chew CE, Zack DJ (1996) Rin, a neuron-specific and calmodulin-binding small-G protein, and Rit define a novel subfamily of Ras proteins.
		Pak WL, Grossfield J, Arnold K (1970) Mutants in the visual pathway of Drosophila melanogaster.
	www.jneurosci.org /cgi/content/full/17/15/5881 (6235 words)

	Encephalopsin: A Novel Mammalian Extraretinal Opsin Discretely Localized in the Brain -- Blackshaw and Snyder 19 (10): ...
		The molecular identity of the photopigments involved in nonvisual phototransduction is not fully known.
		of visual opsins in the pineal gland (Blackshaw and Snyder, 1997a
		Nathans J (1990) Determinants of visual pigment absorbance: identification of the retinylidene Schiff's base counterion in bovine rhodopsin.
	www.jneurosci.org /cgi/content/full/19/10/3681 (5024 words)

	[No title]
		The molecular phylogenetic tree of vertebrate visual pigments, constructed on the basis of amino acid sequence identity, suggests that the visual pigments can be classified into five groups (L, ML, MS, S and Rh) and that their genes have evolved along these five gene lines.
		In summary, the absorption maximum of a visual pigment is primarily regulated by the interaction of the chromophore charge distribution with dipolar residues in its opsin chromophore-binding pocket.
		The visual transduction processes in rod and cone photoreceptor cells are initiated by photon absorption by the different types of visual pigments.
	www.novartisfound.org.uk /catalog/224abs.htm (3304 words)

	UMBC Graduate Course Listing - Biological Sciences (Site not responding. Last check: 2007-11-06)
		Prerequisite: BIOL 305 or consent of the instructor.
		Topics included: visual pigments, biochemical basis of phototransduction, visual processing and organization of visual centers of the brain, eyes, optical arrays, and visual evolution and ecology.
		Prerequisites: BIOL 302 and BIOL 303, or consent of the instructor.
	www.umbc.edu /GradProg/biol-courses.html (2666 words)

	Reduction of All-trans Retinal to All-trans Retinol in the Outer Segments of Frog and Mouse Rod Photoreceptors ...
		The first step in the Visual Cycle, the series of reactions that regenerate the vertebrate visual pigment rhodopsin, is the reduction of all-trans retinal to all-trans retinol, a reaction that requires NADPH.
		The first step of the visual transduction process in vertebrate photoreceptors is the photoisomerization of the visual pigment chromophore from its 11-cis conformation to all-trans.
		The isomerization leads to the formation of photoactivated rhodopsin, which begins the cascade of reactions constituting visual phototransduction (for reviews see Ebrey and Koutalos, 2001; Fain et al., 2001).
	www.findarticles.com /p/articles/mi_qa3938/is_200503/ai_n13504369 (947 words)

	Rhodopsin: Structural Basis of Molecular Physiology -- Menon et al. 81 (4): 1659 -- Physiological Reviews
		The crystal structure of rod cell visual pigment rhodopsin was recently solved at 2.8-Å resolution.
		Visual pigments share a number of structural features (222).
		The molecular interactions between the opsin protein and RET define the spectral properties of a particular visual pigment.
	physrev.physiology.org /cgi/content/full/81/4/1659 (10457 words)

	GC1 Deletion Prevents Light-Dependent Arrestin Translocation in Mouse Cone Photoreceptor Cells -- Coleman and ...
		Light-dependent redistribution of visual arrestins and transducin subunits in mice with defective phototransduction.
		Visual pigment phosphorylation but not transducin translocation can contribute to light adaptation in zebrafish cones.
		GRK1-dependent phosphorylation of S and M opsins and their binding to cone arrestin during cone phototransduction in the mouse retina.
	www.iovs.org /cgi/content/full/46/1/12 (2955 words)

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