Stimulation of the N-methyl-d-aspartate receptor promotes the biochemical differentiation of cerebellar granule neurons and not astrocytes
Stimulation of the N-methyl-d-aspartate receptor promotes the biochemical differentiation of cerebellar granule neurons and not astrocytes
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DOI：
10.1016/0006-8993(89)91272-9
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发表时间：
1989-05
期刊：
影响因子：
2.9
通讯作者：
J. Morán;A. J. Patel
中科院分区：
文献类型：
--
作者：
J. Morán;A. J. Patel
小脑颗粒细胞被认为是谷氨酸能细胞，但是，当它们接受来自苔藓纤维的兴奋性氨基酸输入时，它们也具有n -甲基-d-天冬氨酸（NMDA）受体。这些NMDA受体可能参与了培养的颗粒神经元的生化分化，根据磷酸盐激活谷氨酰胺酶的特定活性进行了研究，谷氨酰胺酶在合成假定的谷氨酸神经递质库中起重要作用。部分去极化细胞经NMDA处理后3天（即体外2 ~ 5天），谷氨酰胺酶的特异性活性呈剂量依赖性和时间依赖性升高。当NMDA浓度为10 μM时，效果达到了一半，而当NMDA浓度为50 μM时，效果达到了最大，在5 d龄的培养物中产生了约2.7倍的效果。这种谷氨酰胺酶的增加被NMDA受体拮抗剂2-氨基-5-磷酸戊酸和NMDA受体连接的Ca2+离子通道阻滞剂mk801和Mg2+完全阻断。NMDA的作用与颗粒细胞的存活无关，因为实验是在培养中颗粒细胞的存活依赖于高K+之前进行的，并且在研究期间，所使用的化合物都没有损害这些细胞的存活。谷氨酰胺酶活性的增强是由于酶蛋白的诱导，因为它被环己亚胺和放线菌素d完全阻断。与颗粒神经元相比，NMDA处理对培养的小脑星形胶质细胞的谷氨酰胺酶和谷氨酰胺合成酶活性没有显著影响。我们目前对谷氨酰胺酶的研究结果表明，通过NMDA介导的细胞游离Ca2+浓度的增加诱导Ca2+电导的增加，导致小脑颗粒神经元分化的长期变化，并且可能这种生理刺激通常是由突触前谷氨酸能苔藓纤维在体内提供的。
Cerebellar granule cells are believed to be glutamatergic, but, as they receive excitatory amino acidergic input from mossy fibers, they also possessN-methyl-d-aspartate (NMDA) receptors. The possible involvement of these NMDA receptors in the biochemical differentiation of cultured granule neurons was studied in terms of the specific activity of phosphate-activated glutaminase, an enzyme important in the synthesis of the putative neurotransmitter pool of glutamate. When the partially depolarized cells were treated with NMDA for the last 3 days (i.e. between 2 and 5 days in vitro), it elevated specific activity of glutaminase in the dose- and time-dependent manners. The half-maximal effect was obtained at about 10 μM NMDA, whereas the maximum concentration, which produced about a 2.7-fold increase in 5-day-old cultures, was about 50 μM NMDA. This increase in glutaminase was completely blocked by the NMDA receptor antagonist, 2-amino-5-phosphonovaleric acid, and by the NMDA receptor-linked Ca2+ion channel blockers, MK 801 and Mg2+. The effect of NMDA was not related to the survival of the granule cells, as the experiments were carried out before the dependence on high K+for the survival of granule cells develops in culture, and during the period of investigation none of the compounds used compromised the survival of these cells. The enhancement of glutaminase activity was due to an induction in enzyme protein, since it was completely blocked by cycloheximide and actinomycin D. In contrast to granule neurons, the treatment with NMDA had no significant effect on the activity of glutaminase and glutamine synthetase in cultured cerebellar astroglial cells. Our present results on glutaminase enzyme would indicate that an increase in the cellular concentration of free Ca2+mediated through the NMDA induced increase in Ca2+conductance, leads to long term changes in differentiating cerebellar granule neurons, and it is possible that this kind of physiological stimulation of granule cells is normally provided in vivo by the presynaptic glutamatergic mossy fibers.