Anatomy and Neuroscience - Research Publications
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ItemThe Role of Histamine in the Retina: Studies on the Hdc Knockout Mouse(PUBLIC LIBRARY SCIENCE, 2014-12-29)The role of histamine in the retina is not well understood, despite it regulating a number of functions within the brain, including sleep, feeding, energy balance, and anxiety. In this study we characterized the structure and function of the retina in mice that lacked expression of the rate limiting enzyme in the formation of histamine, histidine decarboxylase (Hdc-/- mouse). Using laser capture microdissection, Hdc mRNA expression was assessed in the inner and outer nuclear layers of adult C57Bl6J wildtype (WT) and Hdc(-/-)-retinae. In adult WT and Hdc(-/-)-mice, retinal fundi were imaged, retinal structure was assessed using immunocytochemistry and function was probed by electroretinography. Blood flow velocity was assessed by quantifying temporal changes in the dynamic fluorescein angiography in arterioles and venules. In WT retinae, Hdc gene expression was detected in the outer nuclear layer, but not the inner nuclear layer, while the lack of Hdc expression was confirmed in the Hdc-/- retina. Preliminary examination of the fundus and retinal structure of the widely used Hdc-/- mouse strain revealed discrete lesions across the retina that corresponded to areas of photoreceptor abnormality reminiscent of the rd8 (Crb1) mutation. This was confirmed after genotyping and the strain designated Hdcrd8/rd8. In order to determine the effect of the lack of Hdc-alone on the retina, Hdc-/- mice free of the Crb1 mutation were bred. Retinal fundi appeared normal in these animals and there was no difference in retinal structure, macrogliosis, nor any change in microglial characteristics in Hdc-/- compared to wildtype retinae. In addition, retinal function and retinal blood flow dynamics showed no alterations in the Hdc-/- retina. Overall, these results suggest that histamine plays little role in modulating retinal structure and function.
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ItemStudying Age-Related Macular Degeneration Using Animal Models(LIPPINCOTT WILLIAMS & WILKINS, 2014-08)Over the recent years, there have been tremendous advances in our understanding of the genetic and environmental factors associated with the development of age-related macular degeneration (AMD). Examination of retinal changes in various animals has aided our understanding of the pathogenesis of the disease. Notably, mouse strains, carrying genetic anomalies similar to those affecting humans, have provided a foundation for understanding how various genetic risk factors affect retinal integrity. However, to date, no single mouse strain that develops all the features of AMD in a progressive age-related manner has been identified. In addition, a mutation present in some background strains has clouded the interpretation of retinal phenotypes in many mouse strains. The aim of this perspective was to describe how animals can be used to understand the significance of each sign of AMD, as well as key genetic risk factors.
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ItemATP-Induced Photoreceptor Death in a Feline Model of Retinal Degeneration(ASSOC RESEARCH VISION OPHTHALMOLOGY INC, 2014-12)PURPOSE: To develop and characterize a feline model of retinal degeneration induced by intravitreal injection of adenosine triphosphate (ATP). METHODS: Nineteen normally sighted adult cats received 100 μL intravitreal injections of ATP with a final concentration of 11, 22, or 55 mM at the retina. Four animals were euthanized 30 hours after injection and retinal sections examined for apoptosis using a TUNEL cell death assay. In the remaining animals, structural and functional changes were characterized over a 3-month period using a combination of electroretinography (ERG) and optical coherence tomography (OCT). RESULTS: Using a TUNEL cell death assay, we detected widespread photoreceptor death 30 hours after injection with 55 mM intravitreal ATP. All concentrations of ATP caused loss of retinal function and gross changes in retinal structure within 2 weeks of injection. Intravitreal injection of ATP led to a rapid loss of rod photoreceptor function and a gradual loss of cone photoreceptor function within 3 months. Outer nuclear layer thickness was globally reduced by 3 months, with the inner nuclear layer including the retinal nerve fiber layer remaining intact. Structural abnormalities were observed, including focal retinal detachment with evidence of both intravitreal and intraretinal inflammation in some eyes. CONCLUSIONS: Development of an ATP-induced feline model of retinal degeneration provides a rapid and effective large-eyed animal model for research into vision restoration.
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ItemAdenosine Triphosphate-Induced Photoreceptor Death and Retinal Remodeling In Rats(WILEY, 2014-09-01)Many common causes of blindness involve the death of retinal photoreceptors, followed by progressive inner retinal cell remodeling. For an inducible model of retinal degeneration to be useful, it must recapitulate these changes. Intravitreal administration of adenosine triphosphate (ATP) has recently been found to induce acute photoreceptor death. The aim of this study was to characterize the chronic effects of ATP on retinal integrity. Five-week-old, dark agouti rats were administered 50 mM ATP into the vitreous of one eye and saline into the other. Vision was assessed using the electroretinogram and optokinetic response and retinal morphology investigated via histology. ATP caused significant loss of visual function within 1 day and loss of 50% of the photoreceptors within 1 week. At 3 months, 80% of photoreceptor nuclei were lost, and total photoreceptor loss occurred by 6 months. The degeneration and remodeling were similar to those found in heritable retinal dystrophies and age-related macular degeneration and included inner retinal neuronal loss, migration, and formation of new synapses; Müller cell gliosis, migration, and scarring; blood vessel loss; and retinal pigment epithelium migration. In addition, extreme degeneration and remodeling events, such as neuronal and glial migration outside the neural retina and proliferative changes in glial cells, were observed. These extreme changes were also observed in the 2-year-old P23H rhodopsin transgenic rat model of retinitis pigmentosa. This ATP-induced model of retinal degeneration may provide a valuable tool for developing pharmaceutical therapies or for testing electronic implants aimed at restoring vision.
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ItemNo Preview AvailableA Naturally Occurring Mouse Model of Achromatopsia: Characterization of the Mutation in Cone Transducin and Subsequent Retinal Phenotype(ASSOC RESEARCH VISION OPHTHALMOLOGY INC, 2013-05)PURPOSE: This work investigates a novel, naturally occurring mouse model of achromatopsia. The specific missense mutation within the Gnat2 gene was identified and the subsequent retinal phenotype characterized. METHODS: The Gnat2 sequence was amplified using PCR from BALB/c and Gnat2(c.518A>G) retinae and the product sequenced. Retinal function was assessed at 3, 6, 9, and 12 months using the electroretinogram. Transducin and opsin expression were assessed at 3 and 12 months using immunohistochemistry and quantitative PCR. Retinal remodeling and Müller cell gliosis were investigated using immunocytochemistry. RESULTS: An A to G missense mutation at position 518 of the Gnat2 gene was identified that resulted in an aspartic acid to glycine substitution. Gnat2(c.518A>G) animals showed no cone response, while the rod response was normal except for a decrease in the photoreceptor response at 12 months (a-wave, -14%). Gnat2(c.518A>G) retinal sections showed no transducin immunolabeling; however, protein was detected via Western blot. Gnat2 gene expression was only decreased at 12 months of age (-27%). There was reduced cone number at 12 months (-27%) and M-opsin showed evidence of mislocalization. Displaced photoreceptor terminals and altered horizontal cell, cone/rod bipolar cell morphology were evident at 3 months, becoming more extensive at 12 months with the emergence of Müller cell gliosis. CONCLUSIONS: The Gnat2(c.518A>G) mouse contains a missense mutation that results in no cone function due to a misfolding of transducin. Cone photoreceptors also show signs of opsin mislocalization, retinal remodeling and degeneration. This naturally occurring model shows all the hallmark signs of achromatopsia.