Abstract
Purpose: :
To visualize ultrastructural changes in the mouse retina in response to the systemic application of the retinotoxic compounds sodium iodate (NaIO3) and N-methyl-N-nitrosourea (MNU).
Methods: :
6-8 weeks old male C75 BL/6 mice were injected with 1% NaIO3 i.v. at a dose of 35 mg/ kg body weight (BW) or 1% MNU i.p. at a dose of 45 / 60 mg/ kg BW. The animals were sacrificed at different time points post injection (PI), eyes enucleated and fixed with Karnowsky fixation medium. The anterior part of the eye was dissected away and the eye cup postfixed in 4% osmium tetroxide and embedded in resin. Ultrathin sections (80 nm) were prepared and mounted on copper grids. The tissue was contrasted with 0.1 % lead citrate solution and visualized with a CM 12 electron microscope (Philips Applied Technologies, Eindhoven, Netherlands).
Results: :
Fourteen days after the application of 35 mg/ kg NaIO3, parts of the outer nuclear layer were still present. Apoptotic nuclei with condensed chromatin were seen therein. However, the RPE cell layer was almost totally destroyed and only single RPE cells with rounded shape and without microvillae present were left. Bruch’s membrane was visibly swollen three days after the application of NaIO3, but reverted to normal thickness after 10 days. Application of MNU led to total destruction of the outer nuclear layer within nine days. In contrast, the RPE cell monolayer appeared completely normal, even though multiple large vacuoles were visible. Furthermore, the RPE cells displayed microvillae despite the lacking of outer segments.
Conclusions: :
NaIO3 induced primary cell death in RPE cells, most probably by necrosis, which led to apoptotic cell death in the photoreceptor cells. In contrast, MNU directly induced cell death in photoreceptor cells without any adverse effects on the RPE cell layer. The recent data complete histological and immunohistochemical data shown earlier.
Keywords: apoptosis/cell death • microscopy: electron microscopy • retina