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S-I Manabe, SA Lipton; NMDA Induces Divergent Signals Leading to Proapoptotic and Antiapoptotic Pathways in the Rat Retina . Invest. Ophthalmol. Vis. Sci. 2002;43(13):745.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:To investigate the involvement of the p38 mitogen-activated protein kinase (MAPK) and phosphatidylinositol-3 kinase (PI-3K)-Akt signaling pathways after pathological NMDA receptor stimulation of retinal neurons in vivo. Methods:Long-Evans rats were used for the experiments. We injected NMDA (2-200 nmol) with SB203580 (2 nmol, an inhibitor of p38 MAPK), LY294002 (6 nmol, an inhibitor of PI-3K), or control solution into the vitreous. To assess retinal ganglion cell (RGC) death quantitatively, we labeled RGCs retrogradely by injecting aminostilbamidine (FluoroGold) into the superior colliculus and subsequently counting fluorescent-labeled RGCs in retinal whole-mounts. Phosphorylation of p38 and Akt were assessed by immunoblotting using whole retinal lysates. To localize phospho-p38 and phospho-Akt, we performed immunohistochemistry using phospho-specific antibodies against p38 and Akt. TUNEL staining was also performed to assess apoptotic cell death. Results:Intravitreal injection of more than 10 nmol of NMDA induced RGC death. Prior to death, NMDA-stimulated retinas manifest increased phospho-p38 and phospho-Akt in the ganglion cell layer and the inner nuclear layer. Subsequently, pyknotic, TUNEL-positive cells were also localized to the ganglion cell layer and the inner nuclear layer. SB203580 partially rescued RGCs from NMDA-induced apoptosis, while LY294002 enhanced RGC death by NMDA. Conclusion:The p38 MAPK and PI-3K-Akt pathways are involved in signal transduction after excessive NMDA receptor stimulation in the retina. Our inhibitor studies suggest that the p38 MAPK pathway is proapoptotic, while the PI-3 kinase-Akt pathway is antiapoptotic in RGCs.
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