Abstract
Abstract: :
Purpose: To study structural and ultrastructural changes of rabbit Retinal Ganglion Cells (RGCs) which survive after optic nerve section (ONS). It is reported that 1 month after ONS more than 90% of RGCs die (Germain et al., Exp. Eye Res., In press) and that the surviving cells show dendroaxonic processes spreading out of the normal dendritic field (Germain et al., Eur. J. Neurosci. 2003). However, very little is known about the functionality and synaptic connections of these cells. Methods: Adult New Zealand rabbits weighing 1000–1500 g were used in this study. All experimental procedures were carried out in accordance with the ARVO and European Communities Council Directives (86/609/ECC) for the use of laboratory animals. The right optic nerve was completely sectioned 4 mm behind the eyeball and the left optic nerve was used as control. One month after the optic nerve section (ONS) the retinas were removed and the surviving RGCs were labelled by intracellular injection of Neurobiotin or by immunocytochemistry using antibodies anti–b tubulin Isotype III (SIGMA). The labelled cells were studied using standard light and electon–microscope techniques. Results: The surviving RGCs have a longer dendritic length and almost all axomized RGCs studied showed dendro–axonic processes that frequently ended in growth cones. Some of these thicker dendrites had blebs and frequently ended in bulbous swellings. Dendritic loops were also observed, especially at the distal end of the dendrites. In the inner plexiform layer, many processes showed vesicular accumulations and electro–dense inclusions. Several labelled processes showed synapses suggesting that one month after axotomy RGCs maintain certain degree of functionality. Axons were thicker and visible along the retina until the optic disc. In the optic fiber layer, we found labelled axons with normal appearance together with many degenerating axons. Conclusions: After axotomy most RGCs die. Surviving cells experience a growth and show vitality signs. However, at the same time, these cells undergoing important ultrastructural damage that finally causes its death.
Keywords: ganglion cells • retinal degenerations: cell biology • plasticity