Ultrastructural Differences Between Adrenalectomized and Sham Operated Rats in Light Induced Retinal Degeneration

Abstract

Abstract: : Purpose: Previous studies have shown that adrenalectomy partially prevents light–induced retinal degeneration (LIRD). The aim of the present work was to perform an ultrastructural study during LIRD in sham operated control animals (CTL), to characterize the neuronal death that occurs in this tissue, and to compare the ultrastructural changes between adrenalectomized rats (ADX) and CTL animals. Methods: Animal experiments were conducted in compliance with the ARVO Guidelines of Animal Use Statement. Sprague Dawley rats were adrenalectomized under Ketamine anesthesia (50 mg/kg, IP). After 18 hours of recovery; adrenalectomized (ADX) and CTL rats were submitted to continuous illumination (CI) (12000 lux) up to 7 days. Animals were offered water (CTL) or saline solution (NaCl, 0.9%) (ADX) and food ad libitum. Rats were anesthetized with chloral hydrate (350 mg/kg, IP) and sacrificed either before or after 1, 2, 5 and 7 days of CI. The eyes were fixed by immersion in a solution containing 2.5% glutaraldehyde and were dehydrated and embedded in Durcupan. Ultrathin sections were stained with lead citrate and were observed with a Zeiss 110 electron microscope. Results: After 24 hs of CI, alterations of outer and inner photoreceptor segments were observed. Retinal degeneration increased along days 2 and 5, and was maximal after 7 days of CI, when cell debris were observed between the swollen retinal pigment epithelium and the thin outer nuclear layer (ONL). Pycnotic nuclei and nuclear fragmentation were observed in ONL of both CTL and ADX illuminated retinas although changes were more prominent in CTL rats. Inflammatory infiltrates were not observed in the retinas in any condition. Mitochondrial alterations were detected in inner nuclear layer of CTL rats after 1 and 2 days of CI and in ADX animals after 5 days of CI. Degenerated cells and thick electron dense processes of Muller cells were observed in ganglion cell layer in both groups after 5 days of CI. Conclusions: These results show that LIRD occurs by apoptosis. As changes were more pronounced in CTL than in ADX rats, these evidences further support the idea that adrenal hormones could facilitate LIRD.

Keywords: apoptosis/cell death • microscopy: electron microscopy • retinal degenerations: cell biology