Home About us Contact
|
Home About us Contact | ||
|
|
||
Mammalian Retina (mammalian + retina)
Selected AbstractsRetina expresses a novel variant of the ryanodine receptorEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2007Varda Shoshan-Barmatz Abstract Calcium released from intracellular stores via the ryanodine receptor (RyR) mediates a variety of signalling processes. We previously showed that retina expresses the three known types of RyR, but retinal membrane preparations exhibit unique characteristics such as Ca2+ -independent [3H]ryanodine-binding and inhibition by caffeine. We have heretofore suggested that the major retinal RyR isoform is novel. The present study aimed to identify this receptor isoform and to localize RyR in mammalian retina. Immunoblotting with specific and pan-antibodies showed that the major retinal RyR has a mobility similar to that of RyR2 or RyR3. Real-time PCR revealed that the major type is RyR2, and RT-PCR followed by sequencing showed a transcript that encodes a protein with ~ 99% identity to RyR2, yet lacking two regions of seven and 12 amino acids and including an additional insertion of eight amino acids. An antibody against RyR2 localized this type to somas and primary dendrites of most retinal neurons. An antibody against RyR1 localized RyR to most somas but also revealed staining in photoreceptor outer segments, concentrated on the disk membranes at their rim. The ryanodine-binding properties and the electrophoretic mobility of RyR from the outer segments were similar to those of the whole retinal preparation. The results thus identify a novel variant of RyR2 which can contribute to regulating photoreceptor Ca2+ concentrations. The restricted localization of the outer segment RyR to the disk rim suggests that its activation mechanism involves a coupling between retinal RyR and the cGMP-gated channel. [source] Evidence for the involvement of purinergic P2X7 receptors in outer retinal processingEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2006Theresa Puthussery Abstract Extracellular ATP mediates fast excitatory neurotransmission in many regions of the central nervous system through activation of P2X receptors. Although several P2X receptor subunits have been identified in the mammalian retina, little is known about the functional role of these receptors in retinal signalling. The purpose of the present study was to investigate whether purinergic P2X7 receptors are involved in outer retinal processing by assessing receptor localization, degradation of extracellular ATP and the effect of functional activation of P2X7 receptors on the electroretinogram (ERG). Using light and electron microscopy, we demonstrated that P2X7 receptors are expressed postsynaptically on horizontal cell processes as well as presynaptically on photoreceptor synaptic terminals in both the rat and marmoset retina. Using an enzyme cytochemical method, we showed that ecto-ATPases are active in the outer plexiform layer of the rat retina, providing a mechanism by which purinergic synaptic transmission can be rapidly terminated. Finally, we evaluated the role of P2X7 receptors in retinal function by assessing changes to the ERG response of rats after intravitreal delivery of the P2X7 receptor agonist benzoyl benzoyl ATP (BzATP). Intravitreal injection of BzATP resulted in a sustained increase (up to 58%) in the amplitude of the photoreceptor-derived a-wave of the ERG. In contrast, BzATP caused a transient reduction in the rod- and cone-derived postreceptoral responses. These results provide three lines of evidence for the involvement of extracellular purines in outer retinal processing. [source] Visualization of local Ca2+ dynamics with genetically encoded bioluminescent reportersEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2005Kelly L. Rogers Abstract Measurements of local Ca2+ signalling at different developmental stages and/or in specific cell types is important for understanding aspects of brain functioning. The use of light excitation in fluorescence imaging can cause phototoxicity, photobleaching and auto-fluorescence. In contrast, bioluminescence does not require the input of radiative energy and can therefore be measured over long periods, with very high temporal resolution. Aequorin is a genetically encoded Ca2+ -sensitive bioluminescent protein, however, its low quantum yield prevents dynamic measurements of Ca2+ responses in single cells. To overcome this limitation, we recently reported the bi-functional Ca2+ reporter gene, GFP-aequorin (GA), which was developed specifically to improve the light output and stability of aequorin chimeras [V. Baubet, et al., (2000) PNAS, 97, 7260,7265]. In the current study, we have genetically targeted GA to different microdomains important in synaptic transmission, including to the mitochondrial matrix, endoplasmic reticulum, synaptic vesicles and to the postsynaptic density. We demonstrate that these reporters enable ,real-time' measurements of subcellular Ca2+ changes in single mammalian neurons using bioluminescence. The high signal-to-noise ratio of these reporters is also important in that it affords the visualization of Ca2+ dynamics in cell,cell communication in neuronal cultures and tissue slices. Further, we demonstrate the utility of this approach in ex-vivo preparations of mammalian retina, a paradigm in which external light input should be controlled. This represents a novel molecular imaging approach for non-invasive monitoring of local Ca2+ dynamics and cellular communication in tissue or whole animal studies. [source] Potassium channel Kir4.1 macromolecular complex in retinal glial cellsGLIA, Issue 2 2006Nathan C. Connors Abstract A major role for Müller cells in the retina is to buffer changes in the extracellular K+ concentration ([K+]o) resulting from light-evoked neuronal activity. The primary K+ conductance in Müller cells is the inwardly rectifying K+ channel Kir4.1. Since this channel is constitutively active, K+ can enter or exit Müller cells depending on the state of the [K+]o. This process of [K+]o buffering by Müller cells ("K+ siphoning") is enhanced by the precise accumulation of these K+ channels at discrete subdomains of Müller cell membranes. Specifically, Kir4.1 is localized to the perivascular processes of Müller cells in animals with vascular retinas and to the endfeet of Müller cells in all species examined. The water channel aquaporin-4 (AQP4) also appears to be important for [K+]o buffering and is expressed in Müller cells in a very similar subcellular distribution pattern to that of Kir4.1. To gain a better understanding of how Müller cells selectively target K+ and water channels to discrete membrane subdomains, we addressed the question of whether Kir4.1 and AQP4 associate with the dystrophin,glycoprotein complex (DGC) in the mammalian retina. Immunoprecipitation (IP) experiments were utilized to show that Kir4.1 and AQP4 are associated with DGC proteins in rat retina. Furthermore, AQP4 was also shown to co-precipitate with Kir4.1, suggesting that both channels are tethered together by the DGC in Müller cells. This work further defines a subcellular localization mechanism in Müller cells that facilitates [K+]o buffering in the retina. © 2005 Wiley-Liss, Inc. [source] Giant mitochondria in the retina cone inner segments of shrews of genus Sorex (Insectivora, Soricidae)THE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 2 2003Sara Lluch Abstract The retinas of three species of shrews (Sorex araneus, S. coronatus, and S. minutus) were analyzed. Two kinds of photoreceptors were identified according to (among other characteristics) the traits of the mitochondria of their inner segments. The rod inner segments contained several round or oval mitochondria distributed longitudinally inside the ellipsoid. The cone inner segment showed a few mitochondria, which we classified as megamitochondria (maximum length = 4.22 ,m in S. araneus, 5.68 ,m in S. coronatus, and 2.42 ,m in S. minutus). An analysis of serial thin sections in S. coronatus showed that these large organelles occurred in the apical and central portions of the ellipsoid. In the peripheral and basal regions of the ellipsoid, megamitochondria were frequently accompanied by smaller mitochondria. The giant mitochondria were irregular in form and densely packed, and a reduced cytosol was observed between each mitochondria. In general, they exhibited an electron-dense matrix and a complex system of cristae, which varied in length and array. In mammalian retina, megamitochondria have only been described in the ellipsoid of the tree shrews Tupaia glis and T. belangeri, two diurnal Scandentia with a rich-cone retina. In general terms, Sorex megamitochondria are morphologically very similar to those reported for Tupaia, especially in their arrangement in the cone ellipsoid. However, they differ in the orientation of the cristae. We propose that the ellipsoid of Sorex may serve two functions: as a source of energy for receptor cells, and as a device for improving the cone outer segment optics. Anat Rec Part A 272A:484,490, 2003. © 2003 Wiley-Liss, Inc. [source] Differential output of the high-sensitivity rod photoreceptor: AII amacrine pathwayTHE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 5 2008Artemis Petrides Abstract In the mammalian retina, the scotopic threshold of ganglion cells is in part dependent on how rod inputs are summed by their presynaptic cone bipolar cells. For ON cone bipolar cells, there are two anatomical routes for rod signals: 1) cone photoreceptors receive inputs via gap junctions with the surrounding, more numerous rods; and 2) ON cone bipolar cells receive highly convergent input via gap junctions with AII amacrine cells, which each receive input from hundreds of rods. Rod-cone coupling is thought to be utilized at higher photon fluxes relative to the AII-ON cone bipolar pathway due to the impedance mismatch of a single small rod driving a larger cone. Furthermore, it is widely held that the convergence of high-gain chemical synapses onto AIIs confers the highest sensitivity to ON cone bipolar cells and ganglion cells. A lack of coupling between one or more types of ON cone bipolar cells and AIIs would obviate this high-sensitivity pathway and explain the existence of ganglion cells with elevated scotopic thresholds. To investigate this possibility, we examined Neurobiotin and glycine diffusion from AIIs to bipolar cells and found that approximately one-fifth of ON cone bipolar cells are not coupled to AIIs. Unlike AII-AII coupling, which changes with ambient background intensity, the fraction of noncoupled ON cone bipolar cells was unaltered by dark or light adaptation. These data suggest that one of five morphologically distinct ON cone bipolar cell types is not coupled to AIIs and suggest that AII-ON cone bipolar coupling is modulated differently from AII-AII coupling. J. Comp. Neurol. 507:1653,1662, 2008. © 2008 Wiley-Liss, Inc. [source] Effects of optic nerve injury, glaucoma, and neuroprotection on the survival, structure, and function of ganglion cells in the mammalian retinaTHE JOURNAL OF PHYSIOLOGY, Issue 18 2008A. J. Weber Glaucoma is an optic neuropathy that originates with pressure-induced damage to the optic nerve. This results in the retrograde degeneration of ganglion cells in the retina, and a progressive loss of vision. Over the past several years, a number of studies have described the structural and functional changes that characterize ganglion cell degeneration in the glaucomatous eye, and following optic nerve injury. In addition, a variety of different strategies for providing neuroprotection to the injured retina have been proposed. Many of these are based on the use of brain-derived neurotrophic factor (BDNF), a particularly potent neuroprotectant in the mammalian eye and the basis of our research in this area. Of particular importance is the fact that BDNF not only promotes ganglion cell survival following damage to the optic nerve, but also helps to preserve the structural integrity of the surviving neurons, which in turn results in enhanced visual function. The studies presented here describe these attributes, and serve as the foundation for ongoing work that suggests a need to think beyond the eye in the development of future treatment strategies. [source] Defining Cytochemical Markers for Different Cell Types in the Equine RetinaANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 6 2006C. A. Deeg Summary The major cell types in the mammalian retina are photoreceptors, amacrine, horizontal, bipolar, ganglion and Mueller glial cells. Most of the specific cell types are conserved, but cytochemical markers vary between species. The aim of our study was to characterize cytochemically distinctive markers for different cell types in the equine retina. We were able to define specific markers for equine Mueller glial cells and photoreceptor cells. Furthermore, we describe markers for large ganglion cells, horizontal and amacrine cells and a subpopulation of bipolar cells. Additionally, discrimination between the inner plexiform layer and nerve fibre layer can be achieved by expression of syntaxin and neurofilament 200 respectively. [source] The Presence of Megamitochondria in the Ellipsoid of Photoreceptor Inner Segment of the Zebrafish RetinaANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 6 2005J. Kim Summary Although the megamitochondria (MM) were localized in various pathological conditions, normal retina of some mammalian species was reported to include MM for various physiological roles. However, it was not clearly confirmed whether the MM is present in the retina of lower vertebrate as well. In this study, we tried to show the presence of the MM in the zebrafish retina using electron microscopic technique. In all the photoreceptors including rods, cones and double cones of the zebrafish retina, MM were observed in the ellipsoid of inner segment. In the photoreceptor epllipsoid of the zebrafish retina, the mitochondria located in the central portion of the ellipsoid had a highly electron-dense matrix, which were accompanied by the mitochondria with electron-lucent matrix in the apical portion of the ellipsoid. The presence of MM was more clearly discernable in the rods, which were localized under the double cones. This finding is somewhat different from those observed in the previous studies because MM were localized in the inner segment of cones, but were not in those of rods in the case of mammalian retina. Although the exact physiological meaning for the presence of MM in some vertebrate species should be further studied, the present study could show that the MM in the ellipsoid of the retinal photoreceptors was not only restricted in some mammalian species. [source] | ||||||||||||||||||||||