PubMed Health⌕ Search

Biomedical subjects

P Gouras

Publications and source records attributed to P Gouras.

At least 19 recordsLinked to original sources
PubMed1992

Muller cells of chicken retina synthesize 11-cis-retinol.

The amounts of endogenous retinyl palmitate, retinol and retinaldehyde were measured in the neural retina and retinal pigment epithelium (RPE) of predominantly cone (chicken), rod (rat) and more mixed (cat, human) retinae. The ratio of 11-cis to all-trans isomers of retinyl palmitate and retinol in the neural retina and the RPE increases progressively with the increase in diurnality of the species from rat to chicken. The membrane fractions of both chicken and bovine RPE enzymically isomerize all-trans retinol to 11-cis-retinol. Chicken neural retina membranes enzymically form 11-cis-retinol and all-trans-retinyl palmitate from all-trans-retinol. Light and electron microscopy revealed no contamination of chicken neural retina by RPE. Muller cells from chicken retina were isolated, cultured and characterized by immunocytochemical localization of cellular retinaldehyde-binding protein. Cultured chicken Muller cells form all-trans-retinyl palmitate, 11-cis-retinol and 11-cis-retinyl palmitate from all-trans-retinol and release most of the 11-cis-retinol into the medium. The results indicate that chicken neural retina and Muller cells in particular synthesize 11-cis-retinoids from all-trans-retinol.

Animals↗
PubMed1992

The ultrastructure of transplanted rabbit retinal epithelium.

Retinal epithelial cells from pigmented rabbits have been cultured and radiolabelled during division with 3H-thymidine and transplanted to the subretinal space of albino rabbits using a pars plana transvitreal approach. The host rabbits were maintained on cyclosporine immunosuppression after transplantation surgery. The transplant cells survive and maintain a morphologically normal appearance for at least 5 months. The pigmented epithelial cells retain their pigmentation and become integrated with the host retinal epithelium forming junctional complexes with both the host and other transplant cells. The transplant cells contact host photoreceptors with their apical processes and phagocytize outer segments. There appears to be no significant cell division among the transplant cells.

Albinism↗
PubMed1992

Monitoring photoreceptor transplants with nuclear and cytoplasmic markers.

Two methods are described for identifying transplanted photoreceptors in a foreign host retina. One involves the use of [3H]thymidine to label the nuclei of photoreceptors which are dividing for 1 week after birth in myomorphic retina. These photoreceptors can be identified by autoradiography. The second involves the use of a transgenic mouse carrying a bovine rhodopsin promoter in tandem with the bacterial LacZ gene. These mice express beta-galactosidase in their rods. X-gal reaction allows these rods to be identified by routine light and electron microscopy. These methods have been used to follow photoreceptor transplants in adult Royal College of Surgeons strain rat and C3H mouse mutants which have lost virtually all their photoreceptors. Dissociated photoreceptors transplanted to the subretinal space of these animals survive for at least 3 months. The inner segment, cell body, and synaptic terminal of these transplanted photoreceptors remain morphologically normal; the outer segment, however, becomes rudimentary.

Animals↗
PubMed1992

Supernormal cone electroretinograms in central retinal vein occlusion.

In 12 successive cases of unilateral central retinal vein occlusion (CRVO), the strongly light-adapted cone electroretinogram (both a- and b-wave) was always slower and larger (supernormal) to long-wave stimuli compared with that of the unaffected eye. This supernormality became less as the level of light adaptation decreased; in the dark-adapted state, long-wave stimuli produced subnormal responses from the affected eye in all but two subjects. This supernormality was not caused by ineffectiveness of the adapting light related to a reduced cone quantal catch because it occurred in the dark. At any one state of adaptation, the supernormality increased with the wavelength of stimulation, paralleling the relative absorption ratio of long-middle wavelength-sensitive cones. This suggests that cones, especially long wavelength-sensitive cones, are less able to reduce their responsiveness to light with increasing levels of light adaptation in a retina affected by CRVO.

Adult↗
PubMed1992

Radiation retinopathy: electron microscopy of retina and optic nerve.

A 4 1/2 year old female was treated for embryonal rhabdomyosarcoma of the left orbit in 1975 with radiation (59.5 Gy in 5 weeks), followed by chemotherapy. An electroretinogram (ERG) in March, 1988 revealed cone responses 3% of normal and no rod responses in the left eye, and normal responses in the right eye. The eye was enucleated in April 1988. In the fovea no choroidocapillaris was seen at the intact Bruch's membrane, and the pigment epithelium was preserved only in small patches. No photoreceptor cells were seen in the areas devoid of pigment epithelial cells. The parafoveal and peripheral (30 degrees eccentricity) retina was better preserved. The thickness of the layer of rods and cones and of Henle's fiber layer was reduced. Very few outer segments were present. Macrophages had invaded the retinal tissue in moderate numbers. The retinal vessels were ensheathed by several layers of collagen fibrils. The spatial densities of pigment epithelial, cone, rod, and bipolar cells had been reduced. The optic nerve contained a total number of 1,022,000 nerve fibers.

Child, Preschool↗
PubMed1992

Reconstruction of degenerate rd mouse retina by transplantation of transgenic photoreceptors.

Photoreceptors from neonatal transgenic mice with normally developing retinas were transplanted to the subretinal spaces of 2-3-month-old rd mutant mice that lack photoreceptors. The transgenic mouse photoreceptors express high levels of the lac Z reporter gene product, beta-galactosidase, which facilitated tracking the transplanted cells. Two sources were used for these cells: (1) dissection of retinal microaggregates containing photoreceptors and (2) papain-dissociated photoreceptors. Host retinas were examined after transplantation. Both methods led to survival of photoreceptors for at least 2 mo after transplantation. Relatively mature outer segments were found only in transplanted microaggregates; this occurred optimally when the cells were adjacent to the retinal pigment epithelium (RPE). beta-galactosidase-labeled outer segments associated closely with the apical processes of the host RPE, which, together with labeled phagosomes in the RPE cells, suggested functional interaction between the transplanted photoreceptors and the host RPE. This study is the first to the authors' knowledge to show electron microscopically that a morphologically normal-appearing photoreceptor layer can be reconstructed in an otherwise photoreceptorless retina.

Animals↗
PubMed1991

Rhodopsin mutations in autosomal dominant retinitis pigmentosa.

DNA samples from 161 unrelated patients with autosomal dominant retinitis pigmentosa were screened for point mutations in the rhodopsin gene by using the polymerase chain reaction and denaturing gradient gel electrophoresis. Thirty-nine patients were found to carry 1 of 13 different point mutations at 12 amino acid positions. The presence or absence of the mutations correlated with the presence or absence of retinitis pigmentosa in 174 out of 179 individuals tested in 17 families. The mutations were absent from 118 control subjects with normal vision.

Base Sequence↗
PubMed1991

Survival and synapse formation of transplanted rat rods.

Isolated rods enzymatically removed from normal adult rat retina have been transplanted to the subretinal space of adult rats with a retinal dystrophy which has destroyed almost all the photoreceptors. These transplanted rods survive for months after transplantation during which time they form synapses with other retinal cells. Rod spherules with large amounts of synaptic vesicles and synaptic ribbons are found forming discreet contacts with pre- and post-synaptic densities in arrangements closely resembling those seen in the normal retina.

Animals↗
PubMed1991

Transplanted photoreceptors identified in dystrophic mouse retina by a transgenic reporter gene.

Dissociated photoreceptor cells from a transgenic strain of mice, containing a bovine promoter lac Z gene construct, were transplanted to the dystrophic retinas of a strain of mice (C3H, rd/rd) without obvious photoreceptors. The transgenic photoreceptor cells expressed beta-galactosidase and were distinguishable from the host retinal cells by light and electron microscopy after the 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside histochemical reaction. These results showed that transplanted transgenic photoreceptor cells survived at least 1 month in the host retina and had a primitive outer segment and a well-developed synaptic terminal.

Animals↗
PubMed1991

Transplantation of photoreceptors labeled with tritiated thymidine into RCS rats.

Tritiated thymidine was administered to newborn rats to label photoreceptors, about 50% of which are still dividing. These photoreceptors were enzymatically dissociated and separated from the remainder of the retina after the infant rat matured. These labeled photoreceptors were then transplanted into a foreign host retina in the region of the outer nuclear layer. The hosts were ocular, albinotic, Royal College of Surgeons (RCS) rats, congenic to the normal donors and at least 4 months old, a time when virtually all the photoreceptors have degenerated from their retinas. The transplant site was examined at various times after transplantation by light microscope autoradiography. Labeled photoreceptor cell bodies were found in clusters in the outer nuclear layer region for as long as 3 months after transplantation surgery.

Animals↗
PubMed1990

Synthesis of retinoids by human retinal epithelium and transfer to rod outer segments.

The synthesis and release of 11-cis-retinoids by primary cultures of human retinal pigment epithelium (RPE) and the transfer of these retinoids to co-incubated human rod outer segments (ROS) were studied. Monolayers of 2-3-week-old cultured RPE incorporate tritiated all-trans-retinol, esterify it to the corresponding retinyl palmitate, form 11-cis-retinol and 11-cis-retinaldehyde and release retinaldehyde into the culture medium. The ratio of 11-cis to all-trans isomers of retinol, retinyl palmitate and retinaldehyde formed in the cells along with retinaldehyde released and incorporated into the ROS progressively increases, indicating a progressive increase in the concentration of 11-cis isomer from the time it is formed in RPE cells until its transfer to ROS. Incorporation of 11-cis-retinaldehyde into the ROS is directly related to the amount of albumin present in the media, suggesting the transfer of retinoids from RPE to photoreceptor to be a protein-mediated process. Events leading to isomerization, esterification, oxidation and release of retinoids by human RPE and incorporation of retinoids into ROS can therefore be examined in vitro.

Adult↗
PubMed1990

Electroretinographic responses of the short-wavelength-sensitive cones.

An electroretinographic response of the human short wavelength (S) cone system can be distinguished from that of the longer wavelength (L or M) cone system by using ganzfeld short-wavelength stimulation at relatively high levels of retinal adaptation. The S cone response has both an a- and b-wave component in its ERG, both of which are slower than those of the L or M cone response at the same level of retinal adaptation. Proof that this is the S cone response is obtained by action spectra and by examination of a sex-linked achromat who is known to have only S cone and rod vision. This approach allows the simultaneous and rapid assessment of both the S and the L or M cone systems in the human retina using conventional electroretinogram (ERG) equipment, ganzfeld blue flashes on a white background, and computer averaging.

Adolescent↗
PubMed1989

Light adaptation of the electroretinogram. Diminished in retinitis pigmentosa.

The cone electroretinogram has been examined at different levels of ganzfeld adaptation in normals and subjects with retinitis pigmentosa (RP). As light adaptation increases, the amplitude and time course (measured as b-wave implicit time) of the cone ERG decrease in both normal and RP subjects. The same level of light adaptation, however, decreases the amplitude and the implicit time more in normal than in RP subjects. The ineffectiveness of light for adapting the ERG of RP subjects is most easily explained by assuming that RP cones absorb less light than normal cones. By comparing these parameters between normal and RP subjects at different levels of light adaptation, it is possible to estimate this ineffectiveness of cone absorption in RP subjects. The results imply that RP cones can transduce and adapt but fail to absorb light as effectively as normal cones. The quantitative relationship between cone b-wave implicit time and retinal illumination provides a unique method for examining cone function as well for standardizing ganzfeld backgrounds in ERG laboratories.

Adaptation, Physiological↗
PubMed1989

Growth in amplitude of the human cone electroretinogram with light adaptation.

The human cone electroretinogram gradually increases in amplitude an average of 75% (range 23 to 157%) during light adaptation, over a period of approximately 20 min. This increase involves both the a- and b-wave components of this response, and both waves follow a similar time course, implying that the photoreceptors themselves are responsible for the effect. The phenomenon occurs with suprathreshold, but not with threshold, levels of stimulation, and the stronger the test light, the greater the effect. An increase in the intensity of the adapting light shortens the time course of the ERG response, measured as b-wave implicit time, but this occurs almost immediately, and the implicit time then remains constant during the slow increase in response amplitude. The stronger the background adapting light, the smaller is the ERG amplitude, but the percentage growth (or rate of recovery) is unchanged. This slow increase in amplitude is thought to reflect the redepolarization of the cones, after their initial hyperpolarization to an adapting field. It does not reflect the d.c. potential of the eye (the EOG). It is essential to control this phenomenon in any studies of the human cone ERG, in order to minimize variability.

Adaptation, Physiological↗
PubMed1989

Transplanted retinal pigment epithelium modifies the retinal degeneration in the RCS rat.

Transplantation of dissociated retinal epithelial cells obtained from the retinas of normal, congenic pigmented strain of rats to Bruch's membrane and the subretinal space of dystrophic rats from the Royal College of Surgeon (RCS) strain can prevent photoreceptor cell degeneration in this retina for at least 4 months after transplantation. Host and transplant cells form close apposition with one another but can be distinguished by the presence of both phagosomes and melanin granules in the transplant and the absence of these inclusions in the host retinal epithelium. Transplanted cells show excessive amounts of phagosomal material within 48 hr after transplantation, implying that restoration of phagocytosis is responsible for the photoreceptor survival.

Animals↗
PubMed1988

Retinoid metabolism in cultured human retinal pigment epithelium.

Uptake, esterification and release of all-trans-retinol in primary cultures of human retinal epithelium were studied. Cultured cells were supplemented with 3H-labelled 11,12-all-trans-retinol, using fatty-acid-free albumin as the carrier. This led to incorporation of retinal and the formation of all-trans- and 11-cis-retinyl palmitate. The metabolism of the all-trans ester was monitored in a medium containing various concentrations of foetal-bovine serum (FBS). In 20% (v/v) FBS, the ester was hydrolysed, and all-trans-retinol was released into the culture medium. In the absence of FBS, little ester was hydrolysed and no retinol was found in the medium. Dialysed or heat-inactivated FBS or fatty-acid-free albumin was as effective as FBS in provoking ester hydrolysis and retinol release. The concentration-dependency of this effect on FBS was matched by the corresponding concentrations of albumin alone. A linear relationship was also found between interphotoreceptor retinoid-binding protein and retinoid release. Haemoglobin, which does not bind retinoids, is ineffective in this capacity. It is concluded that lipid-binding substances, mainly albumin, in FBS act as acceptors for retinol and drain the cultured cells of this molecule. The release of the retinol is coupled to the hydrolysis of retinyl esters in the cell, so that there is little or no net hydrolysis of ester if there is no acceptor for retinol in the culture medium. This effect explains why cultured human retinal epithelial cells are depleted of their stores of retinoids when maintained in medium supplemented with FBS.

Blood↗