Florentina Díaz

Ultrastructural and quantitative age-related changes in capillaries of the dorsal lateral geniculate nucleus.

An ultrastructural and quantitative study of age-related changes in the capillaries of the dorsal lateral geniculate nucleus was carried out using male Wistar rats aged 3, 24, and 28 months. The most important structural changes were found in the basal lamina: thickenings either homogeneously distributed or in specific points; spurs towards the astrocyte sheath; and osmiophilic membrane-like inclusions located within the basal lamina. Endothelial cells and pericytes showed an increase in inclusions and dense bodies in the cytoplasm. The quantitative study showed that the most pronounced alteration was the thickening of the basal lamina, which existed at 24 months. Later, at 28 months, thinning of the endothelial cells was observed together with an increase in mitochondria size and the number of pinocytic vesicles. These changes could be an endothelial cell response to compensate for the increasing transport difficulties caused by the thickening of the basal lamina. The progressive age-related changes observed in the structure of the capillaries might have an effect on the regulation of blood and brain tissue exchanges, and thus might contribute to the development of degenerative alterations in surrounding aging neurones.

Reaction of Müller cells in an experimental rat model of increased intraocular pressure following timolol, latanoprost and brimonidine

The aim of this study was to evaluate the reaction of Müller cells in an experimental rat model of intraocular pressure (IOP) and their response to treatment with ocular hypotensive drugs. Episcleral vein cauterization in unilateral eyes of Wistar rats was performed to produce elevated IOP. The animals were divided into five groups: control, experimental, and experimental treated with timolol, latanoprost or brimonidine. Histological sections of retina were studied by immunochemistry with antibodies to glial fibrillary acidic protein (GFAP), and the percentage of labeled area was measured to evaluate the degree of reactive gliosis. In the experimental group, the Müller cells showed hypertrophy and a significant increase in GFAP (4.39+/-0.32%) in relation to retinas of the control group (2.05+/-0.14%). Gliosis was detected in all three treated groups, with a varying increase in GFAP intensity. The timolol-treated group showed the most intense and persistent glial reactivity after 3 months of treatment (13.89+/-0.63%). Treatment with brimonidine, however, resulted in a decrease in the level of GFAP immunoreactivity (8.37+/-0.4%). The group treated with latanoprost showed the lowest glial reactivity (4.8+/-0.36%). Given that all three drugs are effective hypotensive agents, their neuroprotective effect could be related with other factors, such as gliosis, which, over long periods may have noxious effects on the neurons. Thus, hypotensives like brimonidine, and specially latanoprost, may afford greater neuroprotection to the ganglion cells by attenuating the retinal glial reaction.

Nitric oxide synthase in retina and optic nerve head of rat with increased intraocular pressure and effect of timolol

We investigated the expression of nitric oxide synthase (NOS) isoforms -1, -2 and -3 in the retina and optic nerve head (ONH) in an experimental rat model of elevated intraocular pressure (IOP) before and after treatment with timolol, to assess whether its neuroprotective action is associated with the activity of these enzymes. Episcleral vein cauterization in unilateral eyes of Wistar rats was performed to produce elevated IOP. Histological sections of retina and ONH from animals with normal IOP, with elevated IOP, and elevated IOP treated with timolol, were studied by immunohistochemistry with antibodies to NOS-1, NOS-2, and NOS-3. In the control rats, NOS-1 was localized to photoreceptor inner segments, amacrine cells and bipolar cells in the retina, and in astrocytes, pericytes and vascular nitrergic terminals in the ONH. NOS-3 immunostaining localized to the endothelial cells. The rats with elevated IOP showed increased expression of NOS-1 in the plexiform layers of the retina and reactive astrocytes in the ONH. These cells also showed NOS-2 positivity. The rats treated with timolol showed reduced expression of NOS-1 in the retina and ONH. NOS-2 was only detected in a few groups of astrocytes in the ONH. NOS-3 was unchanged in both elevated IOP and timolol-treated groups. These results show that excessive levels of NO synthesized by the NOS-1 and -2 isoforms, considered neurotoxic, might contribute to the progressive lesions of retinal ganglion cell axons. Their reduction after treatment suggests a possible neuroprotective effect of timolol in neurons exposed to excessive amounts of NO.

Quantitative age-related changes in dorsal lateral geniculate nucleus relay neurons of the rat

An ultrastructural and quantitative study of the age-related changes occurring in the relay neurons of the dorsal lateral geniculate nucleus (dLGN) was carried out using male Wistar rats aged 3, 18, 24, and 28 months. Morphometric techniques were used to obtain data regarding cellular activity including soma, nuclear, and nucleolar size. Volume fractions for rough endoplasmic reticulum (RER), mitochondria, and lipofuscin, as well as numbers and sizes of mitochondria and dense bodies (DB) was also calculated. Among the few alterations found in the perikaryon, we can highlight the redistribution and fragmentation of RER and an increase and progressive aggregation of lipofuscin. Quantitative data show a significant decrease in the volume of the soma (-42.77%) and the nucleus (-33.66%), and in the volume fraction of the RER (-18.81%) and mitochondria (-10.16%). A significant increase in lipofuscin (+213.29%), and variations in size and number of mitochondria and dense bodies were also found. Some histophysiological considerations about the findings are discussed. The findings lead to the conclusion that a relative degree of morphological stability is exhibited by relay neurons, although the quantitative data show evident intracellular changes, especially from 24 to 28 months. These changes suggest that accompanying physiological alterations may occur, with putative effects on visual function during ageing.

Stereological Age-Related Changes in Neurons of the Rat Dorsal Lateral Geniculate Nucleus

Quantitative methods were used to compare the changes taking place in the volume of the dorsal lateral geniculate nucleus (dLGN) and corresponding neurons of young, adult and old rats. The study was carried out on male albino rats aged 3, 18, 24 and 28 months. In order to estimate the volume of the dLGN, neuronal volume density, numerical density and total number of neurons, we used serial sections stained according to the Klüver‐Barrera technique and stereological methods. We found that dorsal lateral geniculate nucleus volume increases between 3 and 28 months, with a larger increase between 24 and 28 months. Neuronal volume density and numerical density of neurons are greater at 3 months and undergo a significant decrease between 24 and 28 months. Finally, the total number of neurons is shown to be smaller in adult and old animals than in younger ones, even though no significant variations are found between 18 and 28 months. Furthermore, this study confirms the need to analyze the total number of neurons and not just neuronal density if we want to correctly evaluate some of the microscopic changes occurring during senescence. Anat Rec 255:396–400, 1999.

Quantitative morphological changes in neurons from the dorsal lateral geniculate nucleus of young and old rats

We studied the morphological changes occurring in neurons from the dorsal lateral geniculate nucleus (dLGN) during aging by analysing the size and shape of cell bodies and nuclei.

Evolution of neuronal density in the ageing thalamic reticular nucleus

In this paper we present an analysis of the visual sector of the Thalamic Reticular Nucleus (TRN) from 3, 6, 18, 24 and 30 month old Wistar rats using stereological methods. The volume density (Vv), the number of neurones per surface unit (Na) and the neurone numerical density (Nv) showed a progressive decrease between the 3rd and the 24th months as the animals aged, whereas a significant increase was observed between the 24th and the 30th month, the period at which these rodents have fully entered old age.

Cytochrome oxidase activity in the lateral geniculate nucleus of postnatal rats

We have studied the cytochrome oxidase activity and its pattern of distribution in the dorsal lateral geniculate nucleus of the rat during postnatal development. Between the 1st and the 8th postnatal days, the geniculate nucleus is seen to have a homogeneous enzymatic pattern with high neuronal density and moderately reactive neuropil. On the 15th postnatal day, different levels of neuronal enzymatic activity are found, and adult morphology is attained as of the 21st. The densitometric study has revealed that moderate and lightly reactive neurons are predominant between the 1st and the 8th postnatal days, whereas dark neurons are more numerous and optical density maximum on the 15th postnatal day. No variation in the enzymatic pattern was observed between the 21st and the 42nd days.

Quantitative histochemical study of cytochrome oxidase in the dLGN of aging rats

We carried out a quantitative histochemical study of the enzyme cytochrome oxidase (CO) in neurons of the dorsal lateral geniculate nucleus (dLGN) of male Wistar rats aged 3, 18, 24 and 28 months. The results show that the activity of cytochrome oxidase decreases significantly between 24 and 28 months. We also checked whether a correlation existed between neuronal size and enzymatic activity. Low correlation coefficients were obtained which were between 0.4139 at 3 months 0.2092 at 28 months. Nevertheless, we observed a certain relationship between both parameters, and therefore we classified the neurons as light, moderate and dark according to their optical density, which correlates with enzyme cytochrome oxidase activity, and as small, medium and large depending on their size. We found that light neurons were scarcely represented in the dLGN. At the age of 3 months, the most frequent neurons were moderate, medium-size ones, and dark, small ones. The population of moderate neurons increased with age, reaching 74.5% at the 28th month, 52.2% of which corresponded to medium-size neurons. In the same group dark neurons decreased, falling to a total of 15.3% made up of medium and large-size ones. These results could be interpreted as reflecting a decrease in the bioenergetic competence of the neurons of this nucleus in old age.

Study of the effects of ocular hypotensive drugs on number of neurons in the retinal ganglion layer in a rat experimental glaucoma

Purpose We investigated the effects of antiglaucomatous drugs on neurons in the retinal ganglion layer (RGL) in an experimental model of elevated intraocular pressure (IOP). Methods Three episcleral veins of rats with normal IOP were cauterized. Three months later, we examined the effects on the number of neurons in the RGL as well as in rats submitted to treatment with timolol, latanoprost, or brimonidine. The IOP was measured using a calibrated Tono-Pen XL tonometer before and immediately after cauterization and every 2 weeks for the following 3 months as well as immediately before perfusion. Results The IOP was 14.85±0.65 mmHg in the control group, whereas it was 1.25-fold higher (33.5±1.06 mmHg) in the experimental group. After treatment, the IOP returned to baseline levels. The mean number of neurons per mm2 in the RGL was 33% lower in the experimental group (283±10 cells/mm2) compared with the control group (423±11 cells/mm2). In the groups treated with timolol, latanoprost, or brimonidine, the neuronal loss was less (331±10, 360±15, and 333±3 cells/mm2, respectively), although values did not return to baseline levels. Conclusions This experimental model provokes an immediate, constant, and prolonged increase in IOP and the application of hypotensive agents affords a certain degree of protection to neurons in the RGL.