Ischemic Neuronal Death in the Fish Retina

Abstract

It has been postulated that ischemia leads to a loss of cellular homeostasis and a shortage of available adenosine triphosphate (ATP) (1–3). This causes a release of glutamate and other mediators, which results in a rapid cellular efflux of potassium and influxes of sodium, calcium, and chloride with obligated water. The neuronal damage is probably secondary to the influx and mobilization of calcium and activation of a variety of enzymes, such as protein kinases, proteases, and lipases (1, 4, 5). Glutamate N-methyl-D-aspartate (NMDA) receptors are thought to play a major role in the damaging effects elicited by an ischemic insult because the activation of these receptors results in an influx of calcium (1, 3, 6). Recent works have reported the involvement of oxygen radicals in the NMDA or ischemia induced neurotoxicity (7–9). However, such a direct evidence involving oxygen radicals during ischemia in vivo has not been studied. In the present study we first tested an availability of isolated fish retina to the ischemia in vitro. The nature of the ischemic insult to the retina in vitro can be precisely controlled by eliminating the glucose (hypoglycemia), oxygen (anoxia) or glucose and oxygen (ischemia) from the medium. Moreover, drugs can be added to the medium to reach the retina without having to cross barriers. We have used fish retinas in our neurobiological study (10–12). In spite of the useful and unique advantages (10, 12), very few study of ischemia with fish retina has been conducted. In such a line, we measured an accumulation of reactive oxygen species (ROS) and a cellular level of glutathione (GSH), which is a major antioxidant against oxidative stress, after ischemia in vitro with the isolated carp retina. We further investigated some metabolic respects of GSH, particularly the synthetic pathway of GSH from a precursor cysteine.