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

视网膜胶质细胞和神经元的培养是视神经断裂后视网膜状况的有效研究系统。用Fura-2分光光度法检测了胶质毒性氨基酸D，L-, D-， L-2-氨基二酸（AAA）在有或没有视网膜神经元培养的Muller细胞中选择性增加细胞内游离钙离子浓度的能力。AAA的D、l和D型在低浓度下激活神经元，l -异构体在低浓度下激活Muller细胞。结果表明，AAA，特别是d -异构体，可能是兴奋性氨基酸受体的激动剂。接下来的研究重点是Muller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研究。结果表明，Muller细胞具有AMPA/kainate （non-NMDA）受体。在没有视神经的视网膜中，谷氨酸受体相关的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而非生理条件下表达的。为了证实这一假设，我们比较了Muller细胞和视网膜神经元对激动剂（AMPA）反应的临界浓度。ampa诱导的钙瞬变发生在浓度低于Muller细胞的神经元中，表明Muller细胞中的受体在病理上起作用。此外，当给予0.5mM AMPA时，暴露于神经毒性药物Kainate的细胞的应答细胞数量高于对照细胞。Muller细胞可以抵抗神经毒性药物，并可能参与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.