Retinal morphology in rats treated with a taurine transport antagonist

Previous studies have shown that chronic treatment of rats with guanidinoethyl sulfonate (GES), an antagonist of taurine uptake, leads to depletion of retinal taurine content and electroretinogram abnormalities. In this study we examined with the light- and electron microscope the retina and pigment epithelium of mother rats treated for 8 weeks with 1% GES in their drinking water. Pigment epithelial cells appeared swollen, sometimes with mitochondrial vacuolization and loss of cytoplasmic density, and changes in nuclear shape and chromatin distribution. Photoreceptor cells had shorter outer segments with disarray of disks, swollen inner segments and nuclei, and loss of synaptic terminal contents. These degenerative changes frequently led to cell death, indicated by loss of photoreceptor cell nuclei and shrinkage of the outer nuclear layer, and disappearance of photoreceptor synaptic terminals from the outer plexiform layer. Narrowing of the outer plexiform layer was due also to the retraction of cell processes from higher-order neurons. Quantitative studies of the retina along the vertical meridian passing through the optic nerve head showed that treatment resulted in significant reductions in the number of rod-cell nuclei per field, the width of the outer nuclear layer, and the width of the inner retina. Effects were more pronounced in the superior than the inferior hemisphere, reminiscent of findings in light-damage studies. A possible role for taurine in the cellular defence mechanisms against light- and oxygen-induced damage is suggested.