CHANGES IN NADPH-DIAPHORASE EXPRESSION INDUCED BY EXCITOTOXICITY IN THE GOLDFISH RETINA - RELATION WITH SOME MORPHOLOGICAL AND BIOCHEMICAL ASPECTS

We report alterations in the pattern of NADPH-diaphorase staining, a m arker of nitric oxide, in the goldfish retina after kainic acid admini stration. The heavily stained ellipsoids of the photoreceptors, the he avily stained neurons of the inner plexiform layer and the labeled neu rons of the ganglion cell layer are spared by excitotoxic insult, whil e the faintly medium sized neurons of the inner plexiform layer disapp ear after kainic acid administration. Furthermore, in the bipolar and in the horizontal retinal neurons we observe an induction of NADPH-dia phorase expression. The kainic acid-induced neurotoxicity evaluated by morphological observations and by measuring the levels of choline ace tyltranferase in retinal homogenates, is not prevented by the administ ration of a nitric oxide synthase inhibitor.