Biomedical subjects

G F Vrensen

Publications and source records attributed to G F Vrensen.

At least 73 records · Page 4Linked to original sources

PubMed1994

Effects of platelet-derived growth factor on endothelial wound healing of human corneas.

PURPOSE: To investigate the effects of platelet-derived growth factor (PDGF) on endothelial wound healing of organ-cultured human corneas. METHODS: The endothelia of paired human donor corneas (age, 71 +/- 11 years; total 84 pairs) were mechanically wounded (area, 5.6 +/- 0.8 mm2). Of each pair, one cornea was treated with 10 ng/ml human recombinant PDGF-BB while its mate served as control. The endothelial wound closure time was assessed by daily staining of the corneas with trypan blue. Morphometric data (endothelial cell density, shape, coefficient of variations) were obtained in the wound area after alizarin red staining. DNA synthesis was assessed using 3H-thymidine autoradiography. RESULTS: Although significant, the time of complete wound closure shortened only marginally on addition of PDGF to the culture medium. In the closed wound center (between 4 and 9 days), all corneas exposed to PDGF had significantly higher endothelial cell densities (737 +/- 126 cells/mm2) than the control corneas (515 +/- 89 cells/mm2). Fifteen days after wounding, the mean endothelial cell density averaged 526 +/- 93 and 708 +/- 135 cells/mm2 in the control and PDGF-treated groups, respectively. PDGF did not affect the final cell shape within the closed wounds. DNA synthesis was significantly but only marginally enhanced in PDGF-treated corneas. CONCLUSION: In organ-cultured human corneas, PDGF-BB promotes endothelial wound healing predominantly by cell migration, at least in corneas from senior donors.

Adult↗

PubMed1994

Heterogeneity in ultrastructure and elemental composition of perinuclear lens retrodots.

PURPOSE: To unravel the cataractogenic process(es) leading to the birefringent lenticular bodies known as perinuclear retrodots. METHODS: Ten human lenses containing biomicroscopically verified perinuclear retrodots were systematically screened and analyzed using scanning electron microscopy and energy dispersive x-ray microanalysis to verify their ultrastructure and elemental composition. RESULTS: Three types of retrodots were distinguished, different in size, ultrastructure, and origin. Two of them contained calcium phosphate, the third probably contained calcium oxalate. All three types were separated from surrounding normal fibers and the crystalline inclusions were sequestered within membrane-lined bodies. CONCLUSIONS: Because of these observations and data found in the literature it is postulated that elevated free calcium is the initiating factor in the formation of retrodots, trapped by either oxalate or phosphate and sequestered in the retrodots. It is suggested that the oxalate is derived from ascorbate because of impaired protection against oxidative stress in the older lens. Phosphoric acid is believed to be released by calcium-induced hydrolysis of membrane phospholipids.

Calcium Oxalate↗

PubMed1993

The peripheral and central projections of the Edinger-Westphal nucleus in the rat. A light and electron microscopic tracing study.

The peripheral and central efferent projections of the rostral part of the Edinger-Westphal nucleus in the rat were investigated at the light and electron microscopic level by means of iontophoretic injections of the anterograde tracer Phaseolus vulgaris-leucoagglutinin and retrograde tracer injections of Fast blue and Nuclear yellow into the facial nucleus and into the principal olive. Two pathways leaving the rostral part of the Edinger-Westphal nucleus were studied, a peripheral and a central descending pathway. Fluorescent experiments demonstrated that the central pathway fibers originated from distinct individual Edinger-Westphal neurons. These neurons were mainly distributed throughout the rostral part of the Edinger-Westphal nucleus and had fusiform cell bodies. The neurons rarely form collateral projections. The central descending pathway left the Edinger-Westphal nucleus medially and terminated bilaterally in the principal olive, in the subnuclei A, B and C of the inferior olive and ipsilaterally in the medial accessory olive. The central pathway also terminated contralaterally in the lateral parabrachial nucleus, the facial nucleus, the trigeminal brainstem nuclear complex, the lateral reticular nucleus and the rostroventral reticular nucleus. The projection to the facial nucleus provides evidence for the existence of a polysynaptic loop forming the central part of the corneal blink reflex. Projections from the Edinger-Westphal nucleus to the cerebellar cortex or the deep nuclei, as described in cat and primate, could not be confirmed. The peripheral pathway left the Edinger-Westphal nucleus ventrally and terminated on dendrites of ciliary ganglion cells, along smooth muscle cells of ciliary ganglion associated arterioles and in the proximity of ciliary ganglion associated venules. The central and peripheral terminals that originate in the Edinger-Westphal nucleus all had similar ultrastructural features: clear, round vesicles and electron dense mitochondria. The terminals originating from the central descending pathway were often found to be arranged in glomerular-like structures. The central and peripheral terminals made asymmetric synaptic membrane specializations (Gray type one), except terminals innervating the ciliary ganglion associated vessels, which showed no synaptic contacts.

Amidines↗

PubMed1993

Local variations in protein structure in the human eye lens: a Raman microspectroscopic study.

Confocal Raman microspectroscopy was used to monitor local and age-related changes in protein conformation in human eye lenses. In clear human lenses of varying age (range 17-80 years) spectra were recorded along the visual axis, using laser light of 660 nm wavelength. The Raman vibrations in the 650-1750 cm-1 spectral region were analyzed. Difference spectra between central core and different positions along the visual axis were calculated after calibration for protein content using the I(1450) cm-1 CH2/CH3 vibration peak. Tryptophan content was quantified using the peak at 760 cm-1 calibrated for protein. Changes in the 'exposed' vs. 'buried' position of tryptophan were analyzed using the peak heights at I(880) and I(760) cm-1. The difference spectra revealed an excess of tryptophan, tyrosine, phenylalanine, beta-sheet conformation and molecules or molecular groups responsible for a 1425 cm-1 peak in the core region in all lenses investigated. The excess peaks disappeared at about 0.6-0.9 mm below the surface. The tryptophan content increased from superficial to deep layers, levelling off between 0.4-0.8 mm below the surface. Upon aging, the tryptophan content increases in the core not in the cortex. No changes in the 'exposed' vs. 'buried' position of tryptophan were observed. Changes in tryptophan and tyrosine probably reflect the maturational shift from cortex to core in the relative content of alpha, beta and gamma crystallines. The age-related increase in tryptophan in the core may reflect the preferential breakdown by endo- and exopeptidases of alpha-crystallins damaged upon aging. The increase in beta-sheet conformation may indicate a post-translational shift in secondary conformation upon aging. These changes in protein conformation are largely completed in a small superficial zone, i.e., in the early life span of the crystallins.

Adolescent↗

PubMed1993

Spectral sensitivity of the blood-retinal barrier at the pigment epithelium for blue light in the 400-500 nm range.

To specify the spectral sensitivity of the retinal pigment epithelium (RPE) for blue light damage, pigmented rabbits were exposed to light of 408, 418, 439, 455, 485, and 500 nm (half-peak bandwidth approximately 12 nm). The range of radiant exposure was 15-275 J cm-2 (1.7-19 mW cm-2 for 0.5-5 h). Vitreous fluorophotometry was used to functionally evaluate the blood-retinal barrier at the RPE in vivo, and electron microscopy to visualize RPE ultrastructure in vitro. A significant increase in permeability of the blood-retinal barrier was seen only after exposure to light of 418 nm. Radiant exposure at threshold for permeability increase was 18 J cm-2. Electron microscopy of the RPE demonstrated dispersion and clumping of melanin granules. The results suggest that the RPE is most sensitive to light in the range 412-425 nm, possibly due to damage-mediating chromophores such as cytochrome c oxidase and lipofuscin.

Animals↗

PubMed1993

Early morphogenesis of persistent hyperplastic tunica vasculosa lentis and primary vitreous (PHTVL/PHPV). Scanning electron microscopic observations.

This study provides scanning electron microscopic observations on the early morphogenesis of persistent hyperplastic tunica vasculosa lentis and primary vitreous (PHTVL/PHPV) in canine fetuses at days 28 35 postcoitum (D28 and D35). From previous studies regarding PHTVL/PHPV it is known that a retrolental plaque of fibrovascular tissue is present in eyes of affected canine fetuses from the D33 stage. The contribution of vitreous cells to the formation of the plaque is supported by the results of this study. The lens capsules at the stages described were not found to contain abnormalities such as transparent (thinner) parts or rents, as have been described for postnatal cases of PHTVL/PHPV. These findings support the hypothesis that the capsular anomalies observed in postnatal patients are secondary entities.

Animals↗

PubMed1993

Is cortical spoke cataract due to lens fibre breaks? The relationship between fibre folds, fibre breaks, waterclefts and spoke cataract.

Fibre folds, previously called lamellar separation of the lens, have been found by electron microscopy to be associated with fibre breaks, which are seen in vivo as the circular shades of Obazawa. This led to the present study to determine the relationship between fibre folds, fibre breaks, waterclefts and spoke cataract. All lenses with fibre folds were found to have circular shades. A few instances of circular shades without fibre folds were found, suggesting that the fibre break may be the primary pathology. It was found that circular shades occurred in association with spoke cataract only when fibre folds were also present. Thus there is no essential causal relationship between fibre breaks and spoke cataract. The occurrence of waterclefts was unrelated to the presence of the other features. The lower nasal quadrant of the lens was the most common site for the four features. The depth of spoke cataracts was found to be unrelated to the age of the patient, which makes it unlikely that accommodational stress at the time of onset of presbyopia is causative.

Age of Onset↗

PubMed1993

Substance P in rat corneal and iridal nerves: an ultrastructural immunohistochemical study.

The distribution of substance P (SP) within the nerve fibers of the rat cornea and iris was studied using electron microscopic immunohistochemistry. Numerous SP-immunoreactive fibers were found throughout the corneal and iridal stroma. The most intense staining was found within varicosities containing numerous vesicles. Similar SP-immunoreactive varicosities were found in fibers in close proximity to the iris sphincter and dilator muscles. On account of previous ultrastructural work the SP-containing fibers and varicosities must be assumed to be of trigeminal origin. Additionally, the distribution of SP and calcitonin gene-related peptide (CGRP) in corneal and iridal fibers of rats is similar, suggesting that CGRP and SP are colocalized and may be coreleased from the same varicosities.

Animals↗

PubMed1993

Facial parasympathetic innervation of the rat choroid, lacrimal glands and ciliary ganglion. An ultrastructural pterygopalatine tracing and immunohistochemical study.

The pterygopalatine parasympathetic innervation of the rat choroid, lacrimal glands and ciliary ganglion was ultrastructurally studied by anterograde 3H-leucine tracing. Numerous unmyelinated fibers and vesicle-containing terminals were labeled in these structures. No direct synaptic contacts were found. In the choroid, similar terminals were immunoreactive to vasoactive intestinal polypeptide (VIP). A regulatory feedback loop within the eye-related peripheral nervous system is endorsed by the present results. The finding of fibers and terminals of pterygopalatine origin in the lacrimal glands agrees with earlier studies in cats and monkeys. In the ciliary ganglion, pterygopalatine terminals most likely influence the ganglion cells by nonsynaptic release of neurotransmitters or neuromodulators including VIP.

Animals↗

PubMed1993

Morphologic characteristics and chemical composition of Christmas tree cataract.

PURPOSE: Christmas tree cataract consists of highly refractile multicolored "needles" crisscrossing the lens fibers of the deep cortex. The fact that the colors vary according to the angle of the incident light, and that in retroillumination only a dim outline of the cataract is seen, would suggest that Christmas tree cataract is a diffractive phenomenon. This study was performed to unravel the ultrastructure and chemical composition of the Christmas tree needles. METHODS: Eight lenses from donor eyes and four extracapsularly extracted lenses with Christmas tree cataract were investigated by scanning and transmission electron microscopy. The chemical composition was studied with energy-dispersive x-ray microanalysis and Raman microspectroscopy. RESULTS: Scanning electron microscope examination showed that the needles are smooth, rectangular, plate-like elements bordered by membranes and amorphous material and running crisscross through the lens. In the specimens for transmission electron microscopic examination, the needles proved to be largely dissolved, but the remains showed regular spacings of approximately 5 nm. Material identical in spacing and electron density was found in neighboring cells bound to a reticular membranous network originating from the fiber-limiting membranes. Energy-dispersive x-ray and Raman microanalysis showed that the needles have a high sulfur content and pronounced S-S, CS-SC, and C-S vibrations. The cytoplasm adjacent to the needles and reticular meshwork had an elevated Ca++ content. CONCLUSIONS: It is concluded that cystine is the most likely candidate for the Christmas tree needles and that the needles probably are formed as the result of an age-related aberrant breakdown of crystallins induced by elevated Ca++ levels.

Aged↗

PubMed1993

Platelet-derived growth factor: receptor expression in corneas and effects on corneal cells.

PURPOSE: Platelet-derived growth factor (PDGF), a major mitogen and chemoattractant, is a dimeric molecule of disulfide-bonded A and/or B polypeptide chains (PDGF-AA/AB/BB). Two PDGF receptors (PDGFR) exist, alpha and beta, which dimerize after ligand exposure. The alpha-receptor binds both A- and B-chains, whereas the beta-receptor preferentially binds the B-chain. Whether PDGFR are present on, and whether PDGF is mitogenic for, corneal cells was investigated. METHODS: For receptor determination, a two-step immunoperoxidase technique with monoclonal antibodies against both alpha- and beta-receptors was applied on frozen sections of human and bovine corneas. To test the mitogenic activity of PDGF-BB, two proliferation assays, the DNA synthesis assay (3H-thymidine incorporation) and the colorimetric MTT assay, were used for cultured bovine corneal endothelial cells (BCEC) and human corneal fibroblast (HCF). RESULTS: Both receptors were present on epithelial cells, stromal fibroblasts, and endothelial cells, the beta-receptor being most abundant. In BCEC, minimal and maximal effects on DNA synthesis occurred at 10 ng/ml and 50-100 ng/ml PDGF, respectively. For HCF, the minimal and maximal effective doses were 1 ng/ml and 25-100 ng/ml of PDGF, respectively. The MTT assay, carried out in BCEC only, showed a minimal and maximal cell activity at 1 ng/ml and 10-100 ng/ml of PDGF, respectively. CONCLUSIONS: The presence of PDGFR in human corneal epithelium, fibroblasts, and endothelium and the mitogenic effects of PDGF on corneal cells indicate that PDGF may play a role in corneal wound healing.

Aged↗

PubMed1992

Quantitative aspects of synapses on Golgi-impregnated neurons.

With the classical Golgi techniques, numerous types of neurons can be distinguished in the cerebral cortex, each with a specific dendritic geometry and pattern of axonal ramifications. In the present review we describe two techniques which allow quantification of synapses on identified neurons: (1) Golgi-rapid impregnation-gold toning-electron microscopy, and (2) Golgi-Kopsch impregnation-gold toning-electron microscopy in combination with staining of the tissue with ethanolic phosphotungstic acid (E-PTA). Both techniques were applied on neurons in the visual cortex of young and adult rabbits. By means of rotating and tilting specimens in the electron microscope, the nondistinctive ultrastructure of obliquely sectioned synapses can be circumvented, leading to precise estimates of asymmetrical vs. symmetrical synapses without complete reconstruction of the neuron.

Animals↗

PubMed1992

Toxicity of 1-(beta-D-arabinofuranosyl)cytosine after intravitreal injection in the rabbit eye.

The retinal toxicity of intravitreally injected 1-(beta-D-arabinofuranosyl)cytosine (cytarabine) was examined in 7 chinchilla rabbits to determine if cytarabine can be used as local therapy for vitreoretinal non-Hodgkin's lymphoma. Fractionated dose of 600 micrograms, 1500 micrograms, and 2700 micrograms cytarabine in stabilized saline were given intravitreally in one eye (2 x 300 micrograms, 5 x 300 micrograms, and 3 x 900 micrograms, respectively, with an interval time of 24 h) and stabilized saline in the other eye as control. Toxic effects were evaluated with biomicroscopy, direct ophthalmoscopy, fluorophotometry, electroretinography, light, and electron microscopy. Toxic effects were found with the 1500 micrograms and 2700 micrograms doses only. They consisted of a temporary impairment of the blood retina barrier function for fluorescein as measured by fluorophotometry and an irreversible change of the b-wave in the electroretinograms. No histopathologic changes were seen under the light microscope. Electron microscopic examination showed aberrations in the synaptic pedicles of the photoreceptor cells at a dose of 1500 micrograms cytarabine. The results suggest that the cytarabine dose that is expected to be therapeutic for vitreoretinal non-Hodgkin's lymphoma (about 90 micrograms given in three doses of 30 micrograms) is non-toxic for ocular structures.

Animals↗

PubMed1992

Ageing and changes in protein conformation in the human lens: a Raman microspectroscopic study.

Using confocal Raman microspectroscopy with laser light of 660 nm the secondary and tertiary conformation of crystallins was studied in human lenses of varying age (20-75 years). Differences in cortical and nuclear proteins in individual lenses and among lenses of different age and differences between small equatorial opacities and adjacent clear sites were analysed using a difference spectrum approach. Intensity calibration allows assessment of local variations in protein content. The main findings and conclusions are as follows. (1) Irrespective of the age of the lens nuclear proteins proved to contain more aromatic amino acids, i.e. tryptophan, tyrosine and phenylalanine. This change most probably reflects differences in crystallin composition between nucleus and cortex as described in biochemical studies. (2) Changes in the amide bands indicate a more pronounced beta-sheet conformation of the nuclear proteins. Taking into account available biochemical evidence this most probably reflects a true post-translational change in the secondary conformation of the crystallins. (3) Cortical proteins in 'old' and 'young' lenses are largely identical indicating that ageing is not accompanied by gross alterations in the transcription/translation of the crystallin genes. (4) 'Old' and 'young' nuclear proteins deviate with respect to the amount of aromatic amino acids, being more abundant in 'young' nuclear proteins. (5) Proteins in small early opacities do not exhibit alterations in conformation. (6) A pronounced peak in the difference spectra in the region 1425-1435 cm-1 for nuclear proteins especially when compared with equatorial cortical proteins may be considered as evidence for the advanced photooxidation of tryptophan and/or deamidation of asparagine from superficial to deep regions of the lens.

Adult↗

PubMed1992

Dysfunction and repair of the blood-retina barrier following white light exposure: a fluorophotometric and histologic study.

The purpose of this study was to pinpoint the site of blood-retina barrier disruption after white light exposure and determine the course of barrier repair. The retinas of 25 anaesthetized pigmented rabbits were exposed for 1 hr to the light of a xenon arc lamp filtered to eliminate ultraviolet and infrared light. The light intensities selected were near the threshold intensity causing visible retinal lesions in order to evaluate the function of the blood-retina barrier (BRB) in this range. Functional assessment of the BRB was made with vitreous fluorophotometry (VF), and electron microscopy (EM) after intra-arterial administration of horseradish peroxidase (HRP) as tracer. In 11 of the 14 rabbits exposed to threshold intensity (90-110 mW cm-2; retinal field of illumination, 0.64 cm2), a breakdown of the BRB was demonstrated by a 2-40-fold increase in the permeability of the BRB for fluorescein and by transcellular passage of HRP through the retina pigment epithelium (RPE). All 11 rabbits developed oedematous fundus lesions. Within a week, pigmentary alterations of the fundus were seen on ophthalmoscopy, while the BRB permeability for fluorescein and HRP had returned to normal. EM of the retina showed slight swelling of RPE during the period of increased permeability but no alterations of the neuroretina. After functional barrier repair, the RPE cells demonstrated irregularity of the melanin pigment alignment and some loss of the monocellular arrangement. In six rabbits exposed to subthreshold light intensity (65-89 mW cm-2) no fundus lesion developed and EM evaluation of the BRB was normal.2+ remains altered.

Animals↗

PubMed1992

The pathology of after-cataract. A minireview.

After-cataract can be defined as the retropupillary, non-vitreal opacification of the lens remnants occurring after extracapsular cataract extraction (ECCE) leading to disturbance of transparency and impairment of vision. The synonymous secondary cataract is confusing, since it is also and more frequently used as cataract secondary to ocular diseases (Duke-Elder 1969). The synonymous opacification of the posterior capsule is, in fact, a misnomer, since histological observations revealed that after-cataract is not proven to be the result of changes in the remaining posterior capsule itself, but is caused by proliferation of lenticular epithelial cells, fibroblasts, macrophages and even iris-derived pigment cells on the posterior capsule (Fig. 1).

Animals↗

PubMed1992

Ultrastructural identification of trigeminal nerve endings in the rat cornea and iris.

Trigeminal nerve terminals in the rat cornea and iris were ultrastructurally identified using anterograde tracing with Phaseolus vulgaris-leukoagglutinin (PHA-L). Electron microscopic immunohistochemistry was used to demonstrate the presence and localization of calcitonin gene-related peptide (CGRP) in cornea and iris. In the cornea and iris, nerve fibers were labelled with PHA-L throughout the stroma. Labelling was most obvious within varicosities, densely packed with mainly clear and a few granular vesicles and containing dark mitochondria. Numerous fibers in the stroma of cornea and iris were CGRP-positive. CGRP-positive staining was most intense within varicosities, containing mainly clear and incidentally granular vesicles and dark mitochondria, similar to the structures labelled with PHA-L. CGRP-positive varicosities packed with mainly clear and few granular vesicles also were demonstrated in fibers adjacent to the sphincter and dilator muscles of the iris. In the corneal epithelium, small terminals containing vesicles were CGRP-positive. Trigeminal nerve fibers innervating the rat cornea and iris contained numerous varicosities packed with vesicles. These areas are CGRP-positive, so it can be implied that CGRP is released from these varicosities as a response to triggering impulses. This agrees with the hypothesis that in addition to their afferent function, sensory fibers also exert an efferent modulating function.

Animals↗

PubMed1992

Blood-retinal barrier dysfunction at the pigment epithelium induced by blue light.

Exposure to low-intensity white light can induce dysfunction of the blood-retinal barrier (BRB) at the retinal pigment epithelium (RPE). To determine whether the shorter wavelengths white light are responsible for this dysfunction, rabbit retinas were exposed to blue light (400-520 nm) or yellow light (510-740 nm). The permeability of the BRB, a parameter for the integrity of the barrier, was quantified with vitreous fluorophotometry. Morphologically, the barrier at the RPE was visualized on light and electron microscopy using horseradish peroxidase (HRP) as a tracer. Seventeen pigmented rabbits were exposed to blue light and 11 were exposed to yellow light. Vitreous fluorescein leakage increased with the exposure energy according to a power function (correlation coefficient > 0.79). The threshold energy for an increase in BRB permeability was 50 J/cm2 (0.014 W/cm2 for 1 hr) after blue and 1600 J/cm2 after yellow light. HRP tracing demonstrated that after blue light exposure, a significant fluorescein leakage on fluorophotometry corresponded to the presence of HRP in the RPE cells and in the subretinal space. After yellow light exposures of < 3700 J/cm2 and in rabbits with no significant fluorescein leakage, the HRP was limited to the choroidal capillaries and Bruch's membrane. These results demonstrate that the blue component of white light causes dysfunction of the BRB at the RPE 30 times more effectively than the longer wavelength fraction of white light. As a result, a blue light blocking filter should be used in ocular surgery on humans when an operating microscope is being used (light power 0.1-0.9 W/cm2).

Animals↗