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1 From the Laboratoire de Physiopathologie Cellulaire et Moléculaire de la Rétine, Institute National de la Santé et de la Recherche Médicale, Université Louis Pasteur E9918, Clinique Médicale A, Centre Hospitalier et Universitaire de Strasbourg, France; and 2 Ciba VisionNovartis Pharma, Basel, Switzerland.
PURPOSE. Excitotoxicity is proposed to play a prominent role in retinal ganglion cell (RGC) death ensuing from diseases such as glaucoma and ischemia, but cell culture studies have used tissue from newborn rodents, yielding conflicting data that implicate either N-methyl D-aspartate (NMDA) or non-NMDA glutamate (Glu) receptormediated pathways. Excitotoxic RGC death was examined in vitro in this study, using adult pigs, a large-animal model for human retina.
METHODS. Adult pig retina (and for comparative purposes young and adult rat retina) were dissociated and maintained in monolayer culture. Medium was supplemented with Glu or pharmacologic agonists or antagonists, and surviving RGCs and other retinal neurons were quantified using specific immunolabeling methods. Electrophysiological responses to externally applied Glu of RGCs in culture were recorded using whole-cell patchclamp techniques.
RESULTS. Application of Glu led to selective, dose-dependent losses in large
RGCs (maximal 37% decrease at 1 mM; median effective dose
[ED50],
80 µM) and neurite damage in surviving RGCs.
Application of Glu agonists and Glu receptor subclass antagonists
showed that large RGC death was mediated through both NMDA and non-NMDA
receptor pathways. Small RGCs, amacrine cells, and all other retinal
neurons were resistant to Glu-induced death. By comparison, rat retinal
cultures displayed heightened RGC vulnerability to Glu, mediated
exclusively by non-NMDA receptormediated pathways. Amacrine cells
were unaffected by NMDA but were very sensitive to kainate application
(>90% loss). Other retinal neurons were unaffected by any treatment.
CONCLUSIONS. The molecular pathways underlying excitotoxic RGC death in vitro (non-NMDA or NMDA-preferring Glu receptors) vary among species and developmental stages. The selective elimination of adult pig large RGCs by NMDA receptormediated pathways more closely resembles human and animal glaucoma in vivo than other published culture models, providing a simplified experimental system for investigating the pharmacologic and toxicologic bases of glaucoma-like neuronal death.
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