NEUROTROPHIC AND NEUROTOXIC FACTORS EXPRESSED IN THE RETINA FOLLOWING OPTIC NERVE INJURY

培养的视网膜神经胶质细胞和神经元是研究视神经切断后视网膜状况的有效系统。用Fura-2荧光分光光度法检测了胶质细胞毒性氨基酸D，L，D，L-2-氨基己二酸选择性增加有或无视网膜神经元培养的Muller细胞内游离钙离子浓度的能力。D、L和D-型氨基酸在低浓度时激活神经元，L异构体在低浓度时激活Muller细胞。结果表明，AAA，尤其是D-异构体可能是兴奋性氨基酸受体的激动剂。下一项研究的重点是米勒细胞中的谷氨酸受体。细胞对谷氨酸受体激动剂和拮抗剂的反应也进行了类似的检测。结果表明，培养的Muller细胞具有AMPA/Kainate(非NMDA)受体。在没有视神经的视网膜中，谷氨酸受体相关事件不再被认为是神经元特有的。这种受体的作用可能是在病理条件下而不是生理条件下表达的。为了证实这一假设，比较了Muller细胞和视网膜神经元对激动剂(AMPA)的反应临界浓度。AMPA诱导的钙瞬变发生在神经元中的浓度低于Muller细胞，这表明Muller细胞中的受体起到了相当病理的作用。此外，在0.5 mM的AMPA作用下，暴露于神经毒剂海人酸组的反应细胞数明显高于对照组，提示Muller细胞对神经毒剂具有抵抗作用，可能参与了视网膜神经元的存活机制。

Cultured retinal glia and neurons are an efficient system to investigate retinal condition after optic nerve transection. The ability of the gliotoxic amino acid, D,L-, D-, L-2-aminoadipic acid (AAA) to increase selectively the intracellular concentration of free calcium ion was examined in Muller cells cultured with or without retinal neurons, by a spectrofluorophotometry using Fura-2. The D,L-and, D-forms of AAA activated neurons at low concentrations and the L-isomer activated Muller cells at low concentrations. The results indicated that AAA,especially the D-isomer, may be an agonist of excitatory amino acid receptor. The next study was focused on glutamate receptor in Muller cells. Cellular response to agonists and antagonists of glutamate receptor was examined similarly. The results indicated that cultured Muller cells possess the AMPA/kainate (non-NMDA) receptor. In the retina without optic nerve, glutamate receptor-linked events are no longer considered as specific to neurons. The action of this receptor may possibly be expressed under pathological rather than physiological conditions. To confirm the hypothesis, the critical concentration in response to the agonist (AMPA) between Muller cells and retinal neurons was compared. AMPA-induced calcium transients occurred in neurons at lower concentration than in Muller cells, suggesting the receptor in Muller cells to act rather pathologically. Furthermore, mhen AMPA at 0.5mM was administered, responsive cell number was higher for cells exposed with a neurotoxic agent, Kainate than control cells.Muller cells may be concluded to resist neurotoxic agents and possibly be involved in survival mechanisms of retinal neurons.