DNA FRAGMENTATION CHARACTERISTIC OF APOPTOSIS AND CELL LOSS INDUCED BY KAINIC ACID IN RABBIT RETINAS

We have examined whether ill vivo exposure to the glutamate analogue, kainic acid, induces cell loss through apoptosis and/or through necros is. The vulnerability of rabbit retinal cells was evaluated by routine histopathology. The DNA fragmentation Nas examined using an ill situ method (TUNEL: TdT-mediated biotin-dUTP nick-end labelling) and agaros e gel electrophoresis of extracted retinal DNA. Retinas were examined at 30 min, and 4, 16, 24 and 36 h, and 2-5 days following the intraocu lar administration of 140 nmol kainic acid. Although pyknotic cells co uld be seen already at 30 min, post-injection, TUNEL-labelled nuclei w ere first observed 4 h after the injection. A relatively large number of pyknotic cells and of TUNEL-labelled nuclei were still seen at 5 da ys post-injection. Pykrotic cells were seen throughout the inner nucle ar layer (mostly in the proximal half of the layer) and in the ganglio n cell layer. The TUNEL-labelled nuclei were almost only seen in the p roximal inner nuclear layer. Analysis of DNA by electrophoresis reveal ed the presence of large molecular weight fragments 4 h after the inje ction, and of oligonucleosome-size fragments between 16 h and 2 days a fter the injection. The present study thus presents evidence that, in our model, the retinal cell loss induced by kainic acid is preceded, p robably in most cells, by a fragmentation of DNA characteristic of apo ptotic cell death. The process of cell loss following kainic acid admi nistration was Found to be relatively slow, further suggesting that a programmed type of cell death, which eventually induces apoptosis, is involved. No indication that cells were lost also through necrosis was obtained. (C) 1997 Elsevier Science Ltd.