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Biomedical subjects

Peter Gouras

Publications and source records attributed to Peter Gouras.

At least 19 recordsLinked to original sources
PubMed2006

Alteration in choroidal blood flow produced by local pressure.

BACKGROUND: To investigate how transient pressure applied to the retinal pigment epithelium (RPE) layer and choroid affects choroidal blood flow in rabbits. METHODS: Twelve rabbits underwent vitrectomy and local retinectomy. In nine of the rabbits a glass rod was used to exert brief pressure on the RPE layer and choroid. Three of the rabbits had no pressure indentation and were considered to be controls. The choroidal circulation was studied by indocyanine green (ICG) angiography. The retina and choroid were studied by postmortem histology. RESULTS: Pressure on the RPE layer and choroid caused nonfluorescence in segments of retinal arteries and veins and reduced fluorescence in adjacent choroidal capillaries, producing a black region at the pressure site in the angiograms. The size of this region decreased during the angiogram, often accompanied by the appearance of fine channels considered to be flow through the partially blocked vessels; the obstructed ends of the vessels became increasingly hyperfluorescent. These changes lasted for about 24 h before the choroidal circulation recovered. Histology showed evidence of thrombotic-like material in choroidal arteries and veins at the areas of absent perfusion. After local retinectomies, there was no evidence of thrombosis in control eyes where no pressure had been applied. CONCLUSION: Brief pressure on the RPE and choroid causes immediate reduction in flow through choroidal vessels, which appears to be due to local thrombosis in small segments of these vessels that resolves slowly. This may reflect a tendency for thrombi to form rapidly in choroidal vessels; it may also depend on neural reflexes causing vasoconstriction. The long time course of recovery could result in retinal ischemia and may underlie the pathophysiology of other pressure insults to the choroid.

Animals↗
PubMed2005

Retinal degeneration associated with RDH12 mutations results from decreased 11-cis retinal synthesis due to disruption of the visual cycle.

Retinoid dehydrogenases/reductases catalyze key oxidation-reduction reactions in the visual cycle that converts vitamin A to 11-cis retinal, the chromophore of the rod and cone photoreceptors. It has recently been shown that mutations in RDH12, encoding a retinol dehydrogenase, result in severe and early-onset autosomal recessive retinal dystrophy (arRD). In a cohort of 1011 individuals diagnosed with arRD, we have now identified 20 different disease-associated RDH12 mutations, of which 16 are novel, in a total of 22 individuals (2.2%). Haplotype analysis suggested a founder mutation for each of the three common mutations: p.L99I, p.T155I and c.806_810delCCCTG. Patients typically presented with early disease that affected the function of both rods and cones and progressed to legal blindness in early adulthood. Eleven of the missense variants identified in our study exhibited profound loss of catalytic activity when expressed in transiently transfected COS-7 cells and assayed for ability to convert all-trans retinal to all-trans retinol. Loss-of-function appeared to result from decreased protein stability, as expression levels were significantly reduced. For the p.T49M variant, differing activity profiles were associated with each of the alleles of the common p.R161Q RDH12 polymorphism, suggesting that genetic background may act as a modifier of mutation effect. A locus (LCA3) for Leber congenital amaurosis, a severe, early-onset form of arRD, maps close to RDH12 on chromosome 14q24. Haplotype analysis in the family in which LCA3 was mapped excluded RDH12 as the LCA3 gene and thus suggests the presence of a novel arRD gene in this region.

Alcohol Oxidoreductases↗
PubMed2004

Age-related changes in the basement membrane of the retinal pigment epithelium of Rpe65 -/- and wild-type mice.

PURPOSE: To investigate unusual changes in the basal surface of the retinal pigment epithelium (RPE) cell layer in aging Rpe65 -/- and wild-type mice. METHODS: The retinas of Rpe65 -/- and wild-type mice of different ages-6 weeks and 3, 6, 12-13 and 16 months-were examined by electron microscopy. RESULTS: There was an age-related increase in the width of the basement membrane of both Rpe65 -/- and wild-type mice which was associated with loss of basal infoldings of the plasma membrane of the RPE cells and protrusions of basement membrane material deep into the cytoplasm of these cells. These changes were evident at 6 months of age in RPE65 -/- mice and became extensive at 1 year of age. Similar changes occurred in wild-type mice but were less extensive and were only evident after 1 year of age. CONCLUSIONS: There is an age-dependent abnormality that develops at the basal surface of murine RPE cells, which resembles some of the changes observed in human age-related macular degeneration. These changes occur earlier in life and are more extensive in Rpe65 mutant mice.

Aging↗
PubMed2004

Assessing macular pigment from SLO images.

PURPOSE: To assess the spectral characteristics and spatial distribution of macular pigment by comparing relative retinal reflectance at four different wavelengths. METHODS: A Rodenstock scanning laser opththalmoscope (SLO) with four spectral beams, 488, 544, 633 and 780 nm, was used to obtain images of the normal macula from five eyes of three normal subjects. The relative spectral reflectance was determined along a horizontal path extending from nasal to temporal retina through the fovea for each image. A comparison of this data provided an indication of the relative density and the actual spatial extent of macular pigmentation. RESULTS: There is an area of hyper-pigmentation obtained from averaging the data from all five eyes that extends from about 6 deg symmetrically into nasal and temporal macula surrounding a small zone of greater hyper-pigmentation that extends about 3 deg on each side of the fovea. The smaller central zone has a relatively high absorption for blue light and is considered to represent macular pigment. The larger less hyper-pigmented zone is considered to represent melanin in the retinal pigment epithelium. CONCLUSION: The circularly symmetrical hyper-pigmented central macula including the yellow macular pigment can be assessed by comparing different spectral images obtained from an SLO.

Adult↗
PubMed2004

Auto-immune-like cone dystrophy.

PURPOSE: To describe rapid loss of cone vision in an adult due to putative auto-immune rejection. METHODS: Clinical and electrophysiological examination, including full-field and multi-focal electroretinograms (ERGs), were used to assess retinal function. Serum was analyzed for antibodies to retinal antigens. RESULTS: The patient lost cone vision in the course of several months while rod vision remained unaffected. Initially short wavelength (S) cone function appeared more resistant to the degeneration. Cancer associated retinal antibodies were present in the sera of the patient but no cancer has been found. CONCLUSION: Rapid loss of cone function can occur in an adult without a concomitant neoplasm although serum antibodies to retinal antigens suggest an autoimmune cause.

Aged↗
PubMed2004

Why do mice have ultra-violet vision?

Murine vision has become a fascinating entity due to discoveries about the histology and physiology of its retina over the past decade. It has two varieties of cones, one serving the traditional green-yellow region of the vision spectrum and another serving the ultra-violet region, essentially invisible to man and many other mammal. This puts unusual constraints on the optical transmission of the murine eye, in particular its relatively large lens. Its ultra-violet vision appears to involve its upper much more than its lower visual field, providing a heuristic clue to its purpose. In addition behavioural evidence exists for colour vision in mice. On the other hand there is unequivocal evidence that many murine cones contain both cone photopigments, an unrealistic but not impossible arrangement for colour vision. A better understanding of how ultra-violet vision is interwoven into cone and rod vision and possible colour vision can be clarified by analysing the responses of single retinal neurons. This paper reviews the current information on this topic and provides new insights from single retinal ganglion cell recordings.

Animals↗
PubMed2004

Transient immunosuppression stops rejection of virus-transduced enhanced green fluorescent protein in rabbit retina.

The expression of lentivirus-transduced enhanced green fluorescent protein (EGFP) was detectable in rabbit retinal pigment epithelium (RPE) within 3 to 5 days after subretinal injection of the vector. Within 2 to 3 weeks, EGFP-expressing cells were eliminated by rejection. In the current experiments, we monitor serum antibody titers for EGFP before and after transduction and determine whether systemic immunosuppression prevents recognition of EGFP by the immune system. While all control rabbits developed antibodies against EFGP and showed signs of rejection, no such evidence was observed with animals which received immunosuppression. One month of systemic immunosuppression permanently prevented rejection of RPE with EGFP expression. Fluorescence has been maintained for more than a year. If a control eye was injected with the same virus after terminating immunosuppression, both eyes showed signs of rejection. The lack of rejection is not due to tolerance but to a failure of the animals to detect the foreign protein. Detection must depend upon a brief window of time after surgery needed to introduce the vector, perhaps related to a concurrent but transient inflammation. This strategy may be useful in managing other types of rejection in the retina.

Animals↗
PubMed2003

Changes in the choroidal circulation of rabbit following RPE removal.

PURPOSE: To examine the effects of surgical removal of the retinal pigment epithelium (RPE) on the choroidal circulation of the rabbit. METHODS: The retina and choroid were examined by biomicroscopy, scanning laser ophthalmoscopy, fluorescein and indocyanine green angiography and histology at various times after the surgical removal of the RPE by gentle aspiration following a prior local vitrectomy and bleb detachment. Comparison was made between small and large areas of RPE removal, or only slight pressure to the retina without removal of RPE. RESULTS: Removal of the RPE layer causes transient leakage of vascular fluid into the subretinal space for at least a week after surgery and loss of perfusion in the underlying choroidal vessels and choriocapillaris at the débridement site. This reduction in local choroidal blood flow can occur within 15 min after RPE débridement and can be transient or permanent. Histology indicates that permanent changes are due to fibroblastic infiltration that compresses the choroidal vessels. Permanent changes tend to occur after removal of relatively large areas of RPE. The removal of small areas of RPE or slight pressure on the retina causes a transient loss of local choroidal perfusion, and fibroblastic infiltration into the choroid does not occur. CONCLUSION: Removal of the RPE causes changes throughout the underlying choroid. It reduces the circulation in the large choroidal vessels as well as the choriocapillaris. If large areas of RPE are removed, this choroidal non-perfusion can be permanent due to fibroblastic infiltration. Small areas of RPE removal or slight pressure on the retina lead to only transient reduction of the choroidal flow. The rapidity with which the choroidal blood flow can be reduced implies a reflex mechanism that responds to sudden RPE pressure and/or trauma. These changes are best observed with ICG angiography.

Angiography↗
PubMed2003

Ultrastructure of adult rd mouse retina.

PURPOSE: To examine the ultrastructure of the adult rd mouse retina in order to determine what structures are altered or lost and thus to better interpret changes produced by photoreceptor and/or retinal transplantation in this model of retinal degeneration. METHODS: rd mutant mice expressing a LacZ reporter gene in rod bipolars were used in order to identify these cells and their processes. Mice of age 6 weeks to 5 months were studied by electron microscopy, concentrating on the posterior pole where retinal transplants are usually placed. RESULTS: The adult rd mouse retina contains degenerating cones, cone outer segments, cone synaptic pedicles with synaptic vesicles and post-synaptic contacts. The major abnormalities occur in the subretinal space where all traces of rods are gone and the main structures are inner segments of cones. These inner segments are smaller than normal, contain fewer and smaller mitochondria, have organized arrays of microtubules, resembling those in cone axonal processes, and are completely engulfed by massive proliferation of apical processes of the retinal epithelium. The subretinal space is well defined by the external limiting membrane vitreally and the retinal epithelium choroidally. Muller cells extend globular rather than filamentous processes into the subretinal space which contact the apical processes of the epithelium. Rod bipolar cells survive and retain processes in the external plexiform layer. CONCLUSIONS: The adult rd mouse retains structural elements necessary for phototransduction and transmission of signals to the inner layers of the retina by the cone system. The major deficits are located in the subretinal space where all rods are lost and cone inner segments undergo a slow degeneration. Rod bipolar cells survive but appear to be de-afferented; there was no evidence that they contact residual cone processes in the external plexiform layer. The rd mouse is a logical model to study the effects of transplantation of photoreceptors because second- and third-order retinal neurons as well as degenerating cones survive in the adult retina.

Animals↗
PubMed2003

Survival and integration of neural retinal transplants in rd mice.

PURPOSE: To examine the ultrastructure of the rd retina after transplantation of small micro-aggregates of neural retina in order to determine their survival and integration with the host retina and for sites of communication between transplant and host neurons. METHODS: Neonatal micro-aggregates from transgenic mice expressing a LacZ gene reporter gene in their rods were transplanted into the subretinal space of transgenic rd mice expressing a LacZ reporter gene in their rod bipolar cells. The mice were killed at various times after transplantation surgery and studied by light and electron microscopy. RESULTS: Retinal transplants survived well, as long as 8 months, without signs of rejection and were well integrated into the host retina. Cell bodies of transplanted rods made membrane-to-membrane contacts with rod bipolar cells of the host at areas where there were gaps in the host external plexiform layer. One synaptic process of a transplanted rod was found on the vitreal side of the host's external limiting membrane. In two cases, a postsynaptic process in a transplanted rod spherule contained an Xgal label, implying that it belonged to a host rod bipolar. There was evidence of extension of processes between host and transplant retinas involving astrocytic rather than neural structures. CONCLUSIONS: Retinal allografts to the subretinal space of rd mice survive indefinitely. Close but non-synaptic contacts occur between transplant and host neurons that could allow ephaptic communication between these two retinas. Evidence of synaptic contacts between transplant and host was difficult to find.

Animals↗
PubMed2003

The effect of body temperature on the murine electroretinogram.

PURPOSE: To study the effect of body temperature on the murine electroretinogram (ERG). METHODS: The corneal ERG elicited by a strobe flash from dark-adapted mice was recorded using a saline wick electrode while measuring rectal temperature continuously. The mouse was placed within a cylindrical coil of tubing through which water circulated from a temperature controlled bath. The body temperature of the mouse was changed stepwise between 30 and 37 degrees C. RESULTS: ERGs of approximately normal configuration were recorded at body temperature ranging between 30 and 37 degrees C. The maximum amplitude of the a- and b-waves varied linearly with temperature. The rate of change of b-wave amplitude was about 100 microV/degree. At 30 degrees C, maximum b-wave amplitude was about 400 microV; at 37 degrees C it was about 1000 microV. A change in body temperature produced a rapid change in ERG amplitude. CONCLUSION: The murine ERG is very sensitive to changes in temperature. In order to monitor the ERG accurately over time, continuous recording of body temperature is essential.

Animals↗
PubMed2003

The role of S-cones in human vision.

The human S-cone ERG and single neuron responses from cells mediating the signals of short wavelength sensitive cones (S-cones) were examined and compared with the responses of long (L) and middle (M) wavelength sensitive cones. The S-cone system contributes a relatively small signal to the total cone ERG; it can be selectively light adapted; its b-wave is slower than that of L- and M-cone b-wave; and it lacks a d-wave. Transient tritanopia, a striking feature of S-cone on-retinal ganglion cells, is relatively weak at the level of the ERG. The responses of geniculate neurons were studied using a slowly moving border of energy and wavelength contrast. The ability of cells to respond to wavelength contrast across a border in which energy contrast was reversed was tested in all major varieties of retino-geniculate neurons in the macaque monkey. Cells mediating the signals of S-cones are unique in responding to wavelength rather than energy contrast. The most effective stimulus for such cells is white/yellow wavelength contrast at minimum energy contrast. It is suggested that the S-cone system's major role is to detect wavelength (chromatic) contrast and in particular white and grey from yellow and brown at minimal energy (brightness) contrast.

Electroretinography↗
PubMed2002

Macular pigment and visual acuity in Stargardt macular dystrophy.

PURPOSE: To test the hypothesis that macular pigment reflects foveal cone function and possibly the presence of foveal cones in recessive Stargardt macular dystrophy. METHODS: Sixteen patients (32 eyes) diagnosed to have Stargardt macular dystrophy by clinical criteria were studied with a scanning laser ophthalmoscope (SLO) comparing argon laser blue (488 nm), green (514), helium-neon laser red (633 nm) and infrared diode laser (780 nm) images for the presence or absence of macular pigment in the fovea. Fifteen of the patients were screened for mutations in the ABCR gene. Eyes were graded into three categories: those without foveal macular pigment, those with partial pigment and those with normal amounts of macular pigment. These categories were compared with visual acuity determined by the Snellen chart. RESULTS: All patients with a visual acuity of 20/200 or worse had no macular pigment in the fovea. All patients with visual acuity of 20/40 or better had a normal amount of macular pigment in the fovea. Patients with partial macular pigment had intermediary acuity values except for two eyes, one with 20/20 and another with 20/200 acuity. Infrared light revealed more retinal abnormalities than blue light at early stages of the disease. CONCLUSION: Foveal macular pigment is related to foveal cone acuity in Stargardt macular dystrophy and may be a marker for the presence of foveal cones. Infrared light is a sensitive monitor of early Stargardt macular dystrophy.

Adolescent↗
PubMed2002

Muscle expression of human retinol-binding protein (RBP). Suppression of the visual defect of RBP knockout mice.

Mice lacking retinol-binding protein (RBP) have low circulating retinol levels. They have severe visual defects due to a low content of retinol or retinyl esters in the eye. A transgenic mouse strain that expresses human RBP under the control of the muscle creatine kinase promoter in the null background was generated. The exogenous protein bound retinol and transthyretin in the circulation and effectively delivered retinol to the eye. Thus, RBP expressed from an ectopic source suppresses the visual phenotype, and retinoids accumulate in the eye. No human RBP was found in the retinal pigment epithelium of the transgenic mice, indicating that retinol uptake by the eye does not entail endocytosis of the carrier RBP.

Animals↗
PubMed2002

Long-term effects of short-term retinal bleb detachments in rabbits.

PURPOSE: To examine the effects of saline-induced bleb detachments in rabbit retina. METHODS: Retinal bleb detachments were produced by the injection of 50 microl of balanced salt solution (BSS) into the subretinal space of one eye of each of six rabbits using a glass pipette with a flat tip, 50 microm in diameter. The retina was examined by biomicroscopy, scanning laser ophthalmoscopy (SLO), auto-fluorescence and simultaneous fluorescein and indocyanine green (ICG) angiography. Histological examination was carried out at 1, 2, 3 and 4 months after surgery. RESULTS: All rabbits showed leakage of fluorescein for at least a day after detachment, but within 1 month the leakage ceased. ICG staining developed gradually at the level of the RPE or Bruch's membrane near sites of previous staining. Lipofuscin fluorescence also developed gradually around areas of staining. Histology revealed the source of the excessive lipofuscin to be in the RPE layer, especially in cells migrating away from Bruch's membrane. CONCLUSIONS: Short-term bleb detachments cause a transient breakdown in the blood-retinal barrier, long-term ICG staining at or deep to the RPE layer, hyperlipofuscinosis and migration of the RPE. The abnormal lipofuscin accumulation is apparent on fluorescence ophthalmoscopy and can be confused with markers such as green fluorescent protein.

Animals↗
PubMed2002

The positive role of the carboxyl terminus of the gamma subunit of retinal cGMP-phosphodiesterase in maintaining phosphodiesterase activity in vivo.

The inhibitory rod cyclic GMP-phosphodiesterase gamma subunit, PDEgamma, is a key component of the photoresponse and is required to support rod integrity. Pdeg(tm1)/Pdeg(tm1) mice that lack PDEgamma due to a targeted disruption of the gene encoding PDEgamma, (Pdeg) suffer from a very rapid and severe photoreceptor degeneration. Previously, deletions in the carboxyl-terminal domain of PDEgamma blocked its ability to inhibit trypsin-activated PDE activity, in vitro. In other words, these mutations eliminated PDEgamma's control on the catalytic activity of PDEalpha and PDEbeta. To study the in vivo effects resulting from the deletion of the last seven amino acids of the PDEgamma carboxyl terminal, this PDEgamma allele (Del7C) was introduced as a transgene Pdeg(tm1)/Pdeg(tm1) mice. These animals could only synthesize transgenic mutant PDEgamma. The mutant retinas were expected to display a higher basal level of PDE activity and lower cGMP levels in light and darkness than the PDEgamma knockout mice, which would allow the rescue of their photoreceptors. Instead, our results showed that the Del7C transgene could not complement the Pdeg(tm1)/Pdeg(tm1) mutant for photoreceptor survival. In fact, animals carrying the Del7C transgene have low PDE activity as well as reduced PDEalpha and PDEbeta content.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed2002

Targeted disruption of the mouse cis-retinol dehydrogenase gene: visual and nonvisual functions.

It has been proposed that cis-retinol dehydrogenase (cRDH) acts within the body to catalyze the oxidation of 9-cis-retinol, an oxidative step needed for 9-cis-retinoic acid synthesis, the oxidation of 11-cis-retinol [an oxidative step needed for 11-cis-retinal (visual chromophore) synthesis], and 3 alpha-hydroxysteroid transformations. To assess in vivo the physiological importance of each of these proposed actions of cRDH, we generated cRDH-deficient (cRDH-/-) mice. The cRDH-/- mice reproduce normally and appear to be normal. However, the mutant mice do have a mild visual phenotype of impaired dark adaptation. This phenotype is evidenced by electroretinagram analysis of the mice and by biochemical measures of eye levels of retinoid intermediates during recovery from an intense photobleach. Although it is thought that cRDH is expressed in the eye almost solely in retinal pigment epithelial cells, we detected cRDH expression in other retinal cells, including ganglion cells, amacrine cells, horizontal cells, and the inner segments of the rod photoreceptor cells. Aside from the eye, there are no marked differences in retinoid levels in other tissues throughout the body for cRDH-/- compared with cRDH+/+ mice. Moreover, we did not detect any non-visual phenotypic changes for cRDH-/- mice, suggesting that these mice do not have problems in metabolizing 3 alpha-hydroxysteroids.Thus, cRDH may act essentially in the visual cycle but is redundant for catalyzing 9-cis-retinoic acid formation and 3 alpha-hydroxysteroid metabolism.

Alcohol Oxidoreductases↗