Continuous illumination of the retina: ultrastructural and immunocytochemical study of apoptosis in control and adrenalectomized rats

LOPEZ-COSTA, J.J; LOPEZ, E.M.; ACKERMAN, M.; PIAGGIO, M.B.; SÁNCHEZ DE BUSTAMANTE, J.; COIRINI, H.

Hilton Buenos Aires, Puerto Madero, Ciudad Autónoma de Buenos Aires, Argentina

Congreso; XVII International Congress of Eye Research.; 2006

International Society for Eye Research

Adrenalectomy partially prevents light-induced retinal degeneration (LIRD). In the present work, the ultrastructural alterations of the retina and the immunocytochemical characterization of apoptotic nuclei was performed in both sham operated (CTL) and adrenalectomized (ADX) rats. Animal experiments were conducted in compliance with the ARVO Guidelines of Animal Use Statement. Sprague Dawley rats were adrenalectomized under Ketamine anesthesia. After 18 hours of recovery; 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 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. The eyes from another group of CTL and ADX animals were fixed using a 4 % paraformaldehyde solution and cryostat sections were processed by immunocytochemistry using a Caspase-3 antibody. 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. RPE showed an important phagocytic activity after 48 hs of illumination in CTL rats while maximal alterations in RPE from ADX rats were observed after 5 days of CI. An important quantity of pycnotic nuclei and nuclear fragmentation were observed in ONL in CTL rats but these changes were less prominent in ADX rats. Degenerated cells were observed in GCL in both groups after 5 days of CI but thick electron dense processes of Muller cells were predominatly observed in CTL retinas. Immunocytochemical studies revealed caspase-3 immunolabeled nuclei in ONL in both conditions confirming that apoptosis is involved in LIRD. As changes were more pronounced in CTL than in ADX rats, these evidences further support the hypothesis that adrenal hormones could facilitate LIRD. (UBACYT-M020 and CONICET-PIP-5785).