Apoptosis is present in the primate macula at all ages

Background: It has become increasingly clear that apoptosis is a main event in photoreceptor cell death in a variety of retinal degenerations. We inve stigated the role of apoptosis in the physiologically aging primate macula. Methods: Twenty maculae of rhesus monkeys, aged 6-34 years, were investigat ed. Apoptosis was determined in formalin-fixed, paraffin-embedded eyes usin g the TUNEL (TdT-mediated dUTP-biotin nick end labeling) method and quantit atively analyzed. Morphology of TUNEL positive cells was studied by confoca l laser microscopy and transmission electron microscopy. The thickness of t he outer nuclear layer (ONL) was determined by image analysis. Furthermore, expression of apoptosis-regulating proteins Bcl-x, Fas and Fas Ligand was studied by immunohistochemistry. Results: TUNEL-positive nuclei showed apoptotic features on confocal laser microscopy. They were scattered and sparsely found in the macula, most freq uently in the ONL. The thickness of the ONL decreased with increasing age. Apoptosis was found equally distributed at all ages, although in the two el dest maculae up to 13 times more apoptosis was found. Expression of Bcl-x, Fas and Fas Ligand was equal at all ages. Conclusion: Our findings indicate that apoptosis in the primate macula occu rs at all ages at similar rates, possibly increasing in the oldest age grou p, and may account for the decreasing thickness of the primate macula with age.