Janos Feher

Age-related changes in the human retina

BACKGROUND In a previous study, scanning electron microscopy (SEM) showed age-related changes in the rat retina. We carried out a study to evaluate age-related changes in the human retina. METHODS Samples of fresh retinal tissue obtained from younger (age 22 years or less) and older (age 66 years or more) donors were studied by means of traditional histologic methods and by SEM. Eight retinas were obtained from four donors whose corneas had been used for transplantation, and four retinas were obtained from four subjects whose eyes had been enucleated owing to injury. All morphologic results were subjected to quantitative analysis of images. The concentration of cytoplasmic (free) and structural (tissue-associated) protein in retinal tissue homogenates was determined by means of biochemical methods. RESULTS There was a decrease in all features studied with the exception of structural protein concentration. The mean retinal thickness (and standard error of the mean) was 426 (34.2) microm in the younger subjects and 261 (18.9) microm in the older subjects. The mean numbers of ganglion cells (and standard error of the mean) were 413.5/mm2 (32.3/mm2) and 256.2/mm2 (26.8/mm2) respectively, of capillaries 3.6/mm2 (1.4/mm2) and 1.8/mm2 (1.2/mm2) respectively, of synaptic bodies 122.4 (4.9) conventional units (CU)/area observed and 38.5 (1.6) CU/area observed respectively, of cellular processes 82.3 (3.1) CU/area observed and 13.1 (1.5) CU/ area observed respectively, and of intercellular connections 36.4 (2.5) CU/area observed and 14.3 (1.4) CU/area observed respectively. The mean concentration of total protein per milligram of fresh tissue (and standard error of the mean) was 92.1 (1.8) microg in the younger subjects and 78.7 (1.3) microg in the older subjects; the corresponding values for cytoplasmic protein were 27.6 (1.3) microg and 11.8 (0.8) microg, and for structural protein, 64.4 (1.6) microg and 86.9 (1.4) microg. All differences between the younger and older subjects were significant (p < 0.001) with the exception of mean concentration of cytoplasmic and of structural protein. INTERPRETATION The human retina undergoes specific changes with aging. SEM provides new morphometric information regarding age-related changes in photoreceptor cells, bipolar cells and ganglion cells that increases our understanding of this topic. Our results may be adopted as a model or as normal values when studying other changes that may occur in the human retina in pathological conditions.

Age-related changes in the human optic nerve

BACKGROUND Recent morphologic research has demonstrated the presence of nerve fibres of different diameters in the human optic nerve. The purpose of this study was to investigate age-related changes in fibres of the human optic nerve. METHODS We studied the left optic nerve of 50 male cadaveric donors, 16 aged 18 to 22 years (mean 20 [standard deviation 1.2] years) and 34 aged 68 to 76 years (mean 72 [standard deviation 1.6] years). The samples were carefully harvested during autopsy from the intracranial portion of the optic nerve. Each nerve was cut into four 4-mm segments. After morphologic, histochemical and immunohistochemical staining, the optic nerve fibres were counted and measured. Each segment was evaluated under light microscopy for microanatomic details, glial cells and glial fibrillary acidic protein (GFAP) staining. The protein content was determined under biochemical analysis. We performed morphometric analysis by examining the optic nerve images quantitatively. RESULTS Compared with the younger group, in the older group there was an increase in mean diameter of the optic nerve (p < 0.001), due to an increase in the optic nerve:meningeal membrane ratio. There was also an increase in mean optic nerve area (p < 0.001) and in mean number of astrocytes and the related GFAP-immunoreactive area (p < 0.001). The mean number of nerve fibres of large diameter (greater than 4 pm) was decreased (p < 0.001). There was no difference in mean protein content of the fibres between the two groups. INTERPRETATION The human optic nerve is sensitive to the aging process and may be considered as a model for studies on neuronal aging.

Localization of dopamine receptors in the rabbit cornea.

PURPOSE To analyze the pharmacologic profile and the anatomic localization of the dopamine D1 and D2 receptors in sections of the rabbit cornea in normal conditions. METHODS Samples of rabbit cornea were drawn. Biochemical and autoradiographic techniques were used on frozen sections. [3H]SCH-23390 was used as a ligand of dopamine D1 receptors and [3H]spiroperidol as a ligand of dopamine D2 receptors. RESULTS [3H]SCH-23390 and [3H]spiroperidol were bound by sections of the rabbit cornea. The pharmacologic profile of the binding was consistent with the labeling of D1 and D2 receptors, respectively. Light microscopic analysis of the localization of D1 and D2 receptors revealed an accumulation of the two radioligands in the epithelial and in the endothelial layers of the cornea. CONCLUSION A possible role of the dopaminergic system in the control of the corneal functions is suggested.

Age-related Changes in Rat Retina

PURPOSE To describe the changes in rat retina occurring with ageing by means of histological methods, scanning electron microscopic observations and morphometrical data; and to study by means of biochemical methods the amount of protein content in retinal tissues. METHODS Samples of fresh retinal tissue obtained from young, adult, and aged rats were studied by means of traditional histological methods and by scanning electron microscopy. Particular attention was paid to morphometrical data and to the changes which occur with ageing. With the aid of a quantitative analysis of images, a large amount of morphometrical data was collected. Moreover, the amount of protein content in retinal tissues has been determined. RESULTS Retinal thickness significantly decreases with age. The ganglion cells seem to be more vulnerable to age-related loss than other retinal cells. The number of retinal capillaries is diminished with age. The intercellular connections between photoreceptors, the number of cellular processes, and the number of synaptic bodies of the bipolar cells also decrease significantly with age. These results were all confirmed by scanning electron microscopy observations and morphometrical findings. Biochemical dosage of proteins demonstrates that retinal tissues decrease with age. CONCLUSIONS All morphological, morphometrical, ultrastructural and biochemical data are concordant in demonstrating that the retinal tissues of rats undergo specific changes with age. Our findings are in agreement with those described by previous authors and underline that the rat retina can be considered an optimal model for studies on neuronal maturation and/or neuronal ageing. Since our data have confirmed that many changes occur in rat retina with ageing, we can hypothesize that rat retina is particularly sensitive to developmental changes and to senile decay.

Metabolic Changes in Rabbit Lens Induced by Treatment with Dexamethasone

Metabolic changes in the rabbit lens have been studied by means of nuclear magnetic resonance spectroscopy. These changes have been induced by prolonged topical treatment with dexamethasone. Our results demonstrate an increase in sorbitol, sorbitol-3-phosphate, fructose-3-phosphate, glycerol-3-phosphate and glucose-6-phosphate levels and a decrease in glutathione sulphate (GSH) and myo-inositol levels, in agreement with what was observed in lenses from streptozocin-diabetic rats before lens opacity. The hyperglycaemia can only partially explain all these observed biochemical variations. The lack of increase in the intermediates of pentose cycle, such as sedoheptulose-7-phosphate, seems to support the hypothesis of an inhibition of glucose-6-phosphate dehydrogenase by dexamethasone treatment. Finally dexamethasone treatment induces a decrease in GSH. The decreasing or the loss of GSH has been suggested as a possible pathogenic mechanism in the cataract formation.

Microvessels of the human optic nerve head: ultrastructural and radioreceptorial changes in eyes with increased IOP.

BACKGROUND Ultrastructural, morphological modifications in the microvessels of the optic nerve head were studied in human eyes with normal intraocular pressure (IOP), with slightly increased IOP, and with strongly increased IOP. Moreover, the distribution of beta-adrenergic receptors was analyzed in the same samples. METHODS Six enucleated human eyes were studied. Small pieces of the optic nerve head and of iridocorneal angle (including trabecular meshwork) were dissected immediately after autopsy. The sections were studied with transmission electron microscopy and autoradiography. Radiolabelled pindolol was used to locate beta-adrenergic receptors topographically on fresh sections of human eye. RESULTS Transmission electron microscopy demonstrated that elevated IOP induces ultrastructural modifications of the microvessels of the optic nerve head. Autoradiographic experiments showed the presence and distribution of beta-adrenergic receptors in the optic nerve head of eyes with both normal and increased IOP. INTERPRETATION Increased IOP initially compresses the microvessels of the optic nerve head. The number of beta-adrenergic receptors increased markedly in the eyes with raised IOP. Further studies are needed to clarify the physiological and pathological roles of these receptors.

The human choriocapillaris: evidence for an intrinsic regulation of the endothelium?

The aim of the present study was to describe the ultrastructure of particular cells observed in the microvascular bed of the healthy human choroid, in close relation to the wall of the microvessels and resembling the periadventitial cells of other vascular areas of the human body. Serial sections of 12 fresh human eyes were studied by transmission electron microscopy. In all the eyes, the sections were obtained by cutting from the same zones (inner and outer choroid at the posterior pole of the eye). Standard techniques were used for transmission electron microscopy. Round cell bodies were found in the inner choroid at the posterior pole of the eye, mainly located in the intercapillary connective tissue. The cells were composed of an electron‐transparent cytoplasm containing a few small mitochondria, and a dilated smooth surface of endoplasmic reticulum, at some points continuous with the nuclear membrane. These cells showed processes forming contact with the capillary wall. Some of these processes extended to the elastic layer of Bruchs membrane, but none had contact with the retinal pigment epithelium. A thin basement membrane surrounded both the cell bodies and processes. We believe that these cells are special cells resembling some type of periendothelial cells also localized in other microvascular districts of the human body. The close topographic correlation with the endothelial cells seems to indicate that these special cells play a role in the intrinsic control of proper endothelial functions.

Glycosaminoglycans in Human Trabecular Meshwork: Age-Related Changes

Glycosaminoglycans play a central role in maintaining the normal outflow resistance in the human trabecular meshwork. We evaluated the possible morphological, histochemical and morphometrical age-related changes in glycosaminoglycans of the trabecular meshwork. Small human samples were drawn from 24 eyes after exitus from young and old humans. Samples were harvested from the anterior chamber of the eye, without any aesthetic damage for the face. They were divided into three fragments, each used for morphological, histochemical and ultrastructural staining. Quantitative analysis of images was performed to evaluate morphometrical data that were statistically analysed. Our findings demonstrate the following age-related changes: (1) deposition of fibrous granular material in the trabecular meshwork; (2) increased electron density of the structures; (3) strong decrease in the hyaluronic acid content, and (4) increase in sulphated proteoglycans. Glycosaminoglycans of human trabecular meshwork undergo age-related changes, as demonstrated by our morphological, histochemical and morphometrical results.

Ultrastructure of neurovascular changes in human diabetic retinopathy

The previous concept regarding diabetic retinopathy assigned a primary role to hyperglycemia-induced microvascular alterations, while neuronal and glial abnormalities were considered to be secondary to either ischemia or exudation. The aim of this study was to reveal the potential role of neuronal and glial cells in initial and advanced alterations of the retinopathy in human type 2 diabetes. Electron microscopy and histochemical studies were performed on 38 surgically removed human eyes (28 obtained from diabetic patients and 10 from non-diabetic patients). Morphometric analysis of basement membrane material and lipids was performed. An accumulation of metabolic by-products was found in the capillary wall with aging: this aspect was significantly more pronounced in diabetics. Müller glial cells were found to contribute to alterations of the capillary wall and to occlusion, as well as to the development of proliferative retinopathy and cystoid degeneration of the retina. Our results showed morphological evidence regarding the role of neuronal and glial cells in the pathology of diabetic retinopathy, prior and in addition to microangiopathy. These morphological findings support a neurovascular pathogenesis at the origin of diabetic retinopathy, thus the current treatment approach should be completed by neuroprotective measures.