Retinal ischemia, caused by one of several retinal vascular disorders, can result in vision impairment and blindness. The overall aim of the laboratory is to delineate the cellular mechanisms involved in retinal neurodegeneration and in particular, to elaborate the role played by glutamate and NMDA receptors in the neurodegeneration associated with metabolic stress encountered in conditions of retinal ischemia, hypoxia and hypoglycemia. The current application is an extension of past efforts and is designed to understand the early cellular events that occur during inhibition of retinal cellular metabolism which lead to irreversible cell death. Studies will utilize an ex vivo chick retinal preparation which we have used extensively in prior work.
Aim 1 will determine the contribution of acute cellular swelling induced by metabolic stress or direct glutamate receptor overstimulation to irreversible delayed cell death. Acute cell swelling is a rapid consequence of both ischemia and acute excitotoxicity. Previous studies with the retinal model have shown an intimate link between inhibition of energy metabolism and activation of excitotoxic processes initially involving the NMDA subtype of glutamate receptor. The current studies will test the hypothesis that, in retina, metabolic stress or excitatory amino acid (EAA) induced acute cell swelling is caused by reversal of the GABA transporter and that this swelling contributes to delayed cell death.
Aim 2 will examine the contribution of glial metabolism to NMDA receptor mediated damage due to metabolic stress. Studies will test the hypothesis that metabolic stress in the Muller cells contributes to neuronal damage. The extent to which glial metabolism will selectively be inhibited with fluorocitrate or fluoroacetate and the effect on neurons evaluated. Additionally, glial metabolism will be inhibited during an EAA challenge or general mild metabolic stress to determine if inhibition of glial metabolism potentiates neuronal damage.
Aim 3 will examine the role of endothelin (ET) in retina and in mediation of damage due to metabolic stress. The location of ET in retina will be determined. Signal transduction mechanisms linked to ET's action in retina will be examined and include activation of Ca2+ channels, protein kinase C and regulation of cAMP and cGMP. The effect of ET on neurotransmitter release and on modulation of metabolic stress induced damage in retina will be investigated. Overall, these studies are expected to expand upon previous findings to develop a more detailed knowledge of the cellular mechanisms underlying retinal cell damage due to metabolic stress. An understanding of such mechanisms may lead to future strategies to prevent damage due to retinal ischemia.
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| Zeevalk, G D; Davis, N; Hyndman, A G et al. (1998) Origins of the extracellular glutamate released during total metabolic blockade in the immature retina. J Neurochem 71:2373-81 |
| Zeevalk, G D; Bernard, L P; Sinha, C et al. (1998) Excitotoxicity and oxidative stress during inhibition of energy metabolism. Dev Neurosci 20:444-53 |
| Zeevalk, G D; Nicklas, W J (1997) Activity at the GABA transporter contributes to acute cellular swelling produced by metabolic impairment in retina. Vision Res 37:3463-70 |
| Zeevalk, G D; Nicklas, W J (1997) Contribution of glial metabolism to neuronal damage caused by partial inhibition of energy metabolism in retina. Exp Eye Res 65:397-405 |
| Zeevalk, G D; Nicklas, W J (1996) Hypothermia and metabolic stress: narrowing the cellular site of early neuroprotection. J Pharmacol Exp Ther 279:332-9 |
