Use of immunohistochemistry to follow the localization of GABA during retinal ischemia

[Extract] The mechanisms responsible for cellular damage and death after ischemia are not fully understood. Early reports of neuronal death in the retina and brain after administration of monosodium glutamate led to the hypothesis that ischemic damage results from excessive stimulation of excitatory amino acid receptors. While the early reports of the nurotoxicity of glutamate were recieved with scepticism there is now much evidence to support the idea that the pathogenesis of ischemic neuronal damage involves excessive activation of excitatory amino acid receptors and the crucial factor is an excessive influx of calcium.
Ischemia is caused be a stop in the blood flow and this in turn results in a lack of oxygen and depletion of cellular energy reserves such as glucose and ATP. This rapidly leads to impaired operation of membrane transport systems, depolarization and influx of calcium which in the case of neurons leads to the 'release' of their neurotransmitters and other components such as lactate dehydorgenase. Many of the substances, such as neurotransmitters, are specifically associated with defined neuron types in the CNS and can be located by immunocytochemistry. One strategy that we have used over the past few years is to examine how antigens associated with specific neurons are affected by ischemia or ischemia plus reperfusion. In this report we will focus on the neurotransmitter GABA.
In orger to study the effect of ischemia plus reperfusion it is essential to carry out experiments on the retina in the in situ state to allow for suitable periods of reperfusion. It has been recognized that free radical damage occurs during reperfusion when oxygen once again becomes available. Ischemia without reperfusion can also be conducted on the isolated retina where the influence of drugs can be more easily studied.