Light-induced retinal degeneration is accompanied by changes in the expression of endothelin-1 immunoreactivity

SUBURO AM

Il Ciocco, Barga

Congreso; Gordon Conference Visual System: development and degeneration.; 2006

Gordon Research Conferences

Purpose: We have investigated the expression of endothelin-1 immunoreactivity in various stages of retinal degeneration induced BY continuous illumination. Methods: BALB-c mice were exposed to 1,500 lux for 1, 3, 6 or 18 days, euthanized and fixed for immunohistochemical and morphometric analyses. Changes in the relationship between retinal arteries and glial cell processes were studied with immunohistochemistry for smooth muscle actin (SMA), glial fibrillary acidic protein (GFAP), endothelin-1 (ET-1) and glutamine synthase (GS). Diameters of radial branches of the retinal artery were measured in retinal wholemounts stained for NADPH-diaphorase activity. Results: Under these illumination conditions a decrease in the thickness of the outer nuclear layer became apparent after 6 days. No modifications of other nuclear layers were detected during this period. In normal retinas, GFAP immunoreactivity was only present in astrocytes. At difference with brain astrocytes, which only express ET-1 after activation, normal retinal astrocytes always exhibited strong ET-1 immunoreactivity. In animals submitted to continuous illumination, GFAP immunoreactivity also appeared in Müller cells. These cells, however, could be recognized by GS immunoreactivity, whereas ET-1 labeling could identify astrocytes. Marked astrocytic changes appeared in 3-day illuminated retinas. As demonstrated by ET-1 immunoreactivity, these changes included an increase in the complexity of the astrocytic plexus and a larger number of astrocytic processes surrounding the smooth muscle layer of retinal arterioles. By contrast, no significant differences in the association of Müller cell end-feet with arterioles could be detected in illuminated retinas. Conclusions: Continuous illumination induced a large increase of perivascular astrocytic processes before a decrease in the outer nuclear layer could be detected. Since astrocytic processes express strong ET-1 immunoreactivity, endothelin-1 release might reduce retinal blood flow and might also enhance the retinal injury induced by light.