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.

Experimental model of ocular hypertension in the rat: study of the optic nerve capillaries and action of hypotensive drugs.

PURPOSE: To investigate quantitatively the effect of elevated intraocular pressure (IOP) on the microvasculature of the optic nerve with and without topical treatment with two hypotensive drugs, timolol and latanoprost. METHODS: Three groups of rats underwent cauterization of three episcleral veins to produce elevated IOP in the right eye. Two of these groups were treated with timolol or latanoprost for 3 months. Eyeballs were incubated with anti-GLUT-1 polyclonal antibody. GLUT-1-positive capillaries of the optic nerve head (ONH) and optic nerve exit (ON) were examined and analyzed for their number per square millimeter, volume fraction, length per unit volume, surface area per unit volume, and mean diameter. RESULTS: An increase in IOP resulted in a significant decrease in microvessel density in the laminar region (LR) and postlaminar region (PR) and ON compared with the control group. The other parameters fell significantly in all regions of the optic nerve. Topical treatment with timolol or latanoprost did not modify the density of the capillaries, although the other parameters increased significantly compared with the untreated experimental group. Additionally, the mean diameter of the capillaries in the LR and the PR recovered after treatment. CONCLUSIONS: The results indicate that the capillaries of the LR and the PR of the ONH are the most susceptible to IOP elevation. The authors suggest that timolol and latanoprost have a certain vascular action by increasing the available blood volume, surface area per unit volume, length per unit volume, and diameter of the capillaries of the ONH in these two regions.

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.

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.

Effects of aging on neurons and glial cells from the superficial layers of the superior colliculus in rats.

The aim of this study was to investigate the effect of aging on glial cells and neurons from the superficial layers of the superior colliculus in rats. We used stereological methods to estimate the volume of the superficial layers, neuron size, and the number of neurons and glial cells in Wistar male rats aged 3, 24, 26, and 28 months. A 32.6% volume increase was found in the stratum griseum superficiale between the ages of 3 and 26 months, while in the 28-month-old animals a 19% decrease was observed. The stratum opticum did not show any changes in volume with age. Also, our analysis revealed a process of somatic and nuclear atrophy in the neurons of the superficial layers in animals aged 26 and 28 months. On the other hand, no statistically significant differences were found in the numbers of neurons. The number of glial cells in the stratum griseum superficiale showed an increase between the 3rd and 26th month, while the stratum opticum suffered no change.

Stereological changes in the capillary network of the aging dorsal lateral geniculate nucleus.

In this work we studied the effect of aging on the capillaries of the dorsal lateral geniculate nucleus in 3-, 18-, 24-, and 28-month-old rats. The parameters analyzed were the capillary profile density, capillary volume fraction, length and surface area per unit volume, and capillary average diameter. The quantitative analysis showed in all parameters an increase between 3 and 18 months, and a significant decrease in capillary volume fraction (-18.75%) and diameter (-5.5%) between 18 and 24 months. No changes from 24 months onwards were observed. The increase observed in capillary profile density and capillary volume fraction between 3 and 18 months may indicate an increase of the capillary network. Furthermore, we observed an increase in the length and surface area per unit volume, which we interpret as an expansion of the exchange surface between blood and nerve tissue. The reduction in the capillary parameters that takes place between 18 and 24 months is slight, and may indicate the onset of decline characteristic of aging.

Quantitative age-related changes in NADPH-diaphorase-positive neurons in the ventral lateral geniculate nucleus.

Age-related changes in nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) were examined in the rat ventral lateral geniculate nucleus (vLGN) using histochemical methods. Eighteen rats aged 3, 24, and 26 months were studied using quantitative methods to investigate the number of neurons per mm(2), the cross-sectional area, and the orientation of dendritic processes of NADPH-d-positive neurons. We have described three types of neurons: types A and B are both located in the lateral and medial vLGN (vLGN-l and vLGN-m, respectively), and type C neurons over the optic tract. The number of NADPH-d-positive neurons was significantly reduced in the old rats (-39%) when compared with controls (3-month-old rats). The quantitative analysis of cell areas revealed a significant decrease of somatic size in type B neurons, both in the lateral and medial vLGN, and in C neurons; however, type A neurons did not show significant changes. By quantifying the orientation of dendritic processes, we observed a predominant dorsolateral orientation in type A and B neurons. During aging, there are no changes in the dendritic orientation of neurons located in the vLGN-m; however, vLGN-l neurons show an increase in dendritic processes with dorsoventral orientation. In type C neurons, our results show that 87.4% of dendritic processes are lateromedially oriented at 26 months old. Therefore, the types A and B neurons behave differently during senescence. Type A neurons do not change in size, but those located in the vLGN-l modify the orientation of their dendritic processes; however, type B neurons, reduce their size and those located in the vLGN-l also modify their dendritic process orientation. Finally, the type C neurons modify their size and dendritic process.