Putative acidic amino acid transmitters in the cerebellum I. Depolarization-induced release
Putative acidic amino acid transmitters in the cerebellum I. Depolarization-induced release
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小脑中假定的酸性氨基酸递质 I. 去极化诱导的释放
DOI：
10.1016/0006-8993(82)90520-0
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发表时间：
1982
期刊：
影响因子：
2.9
通讯作者：
R. Bala´zs
中科院分区：
文献类型：
--
作者：
G. Levi;R. Gordon;V. Gallo;G. Wilkin;R. Bala´zs
本实验研究了大鼠体外小脑制剂中酸性氨基酸去极化诱导释放的放射自显影定位和特征。在非代谢的谷氨酸类似物-[3H]天冬氨酸存在下预孵卵的小脑切片的光镜放射自显影显示，胶质细胞上有大量的放射性积累，而颗粒细胞的标记很少，其假定的神经递质可能是谷氨酸。尽管d-[3H]天冬氨酸（和[14C]谷氨酸）主要定位于胶质细胞，但它以Ca2+依赖的方式从高[K+]去极化的小脑片中释放出来，并且由缬草碱引起的释放被TTX阻止。这些发现，再加上观察到新鲜分离或培养的神经胶质细胞没有显示出任何Ca2+依赖性，去极化诱导的d-[3H]天冬氨酸释放，表明从切片中释放的放射性氨基酸具有神经元来源。过量的小脑突触体制剂中外源性放射性酸性氨基酸的高[K+]诱导释放至多显示出适度的Ca2+依赖性，这可能是由于从污染制剂的胶质碎片中存在大量非Ca2+依赖性氨基酸释放的结果。然而，无论是K+诱发的内源性谷氨酸的释放，还是先前由[14C]谷氨酰胺合成的[14C]谷氨酸的释放，都在很大程度上依赖于Ca2+，这表明神经末梢是参与刺激偶联分泌的主要部位。在用[14C]谷氨酰胺预先标记突触体的实验中，对释放的谷氨酸的特定放射性的研究，以及在突触体开始和结束时出现的谷氨酸的研究，提供了支持新合成的[14C]谷氨酸优先释放的证据。与谷氨酸相反，内源性天冬氨酸不以Ca2+依赖的方式释放，新形成的[14C]天冬氨酸的外排仅被Ca2+轻微增强，这表明谷氨酸和天冬氨酸不是从同一位点释放的。对未成熟8日龄小脑的制备（切片和突触体）的研究表明，K+诱发的ofd-[3H]天冬氨酸和内源性谷氨酸的释放都不依赖于Ca2+。总之，提出的数据与谷氨酸在小脑中具有神经递质作用的命题是一致的。
In the present investigation we studied the autoradiographic localization and the characteristics of the depolarization-induced release of acidic amino acids in in vitro rat cerebellar preparations. Light microscopy autoradiography of cerebellar slices preincubated in the presence of the non-metabolized glutamate analogued-[3H]aspartate showed a large accumulation of radioactivity over glial cells, and very little labelling of the granule cells, whose putative neurotransmitter may be glutamate. In spite of its predominant localization in glia,d-[3H]aspartate (and [14C]glutamate) was released from cerebellar slices depolarized with high [K+] in a Ca2+-dependent way, and the release elicited by veratrine was prevented by TTX. These findings, together with the observation that freshly isolated or cultured glial cells did not show any Ca2+-dependent, depolarization-induced release ofd-[3H]aspartate, suggest that the radio-active amino acid released from slices has a neuronal origin. The high [K+]-induced release of exogenous radioactive acidic amino acids from superfused cerebellar synaptosomal preparations exhibited, at best, a modest Ca2+-dependence, a result probably due to the existence of a substantial non-Ca2+-dependent release of the amino acid from glial fragments contaminating the preparation. However, both the K+-evoked release of endogenous glutamate, and that of [14C]glutamate previously synthesized from [14C]glutamine were largely Ca2+-dependent, suggesting that nerve endings are the main sites involved in the stimulus-coupled secretion. In the experiments in which synaptosomes had been prelabelled with [14C]glutamine, a study of the specific radioactivity of the glutamate released and of that present in synaptosomes at the beginning and at the end of superfusion period provided evidence in favour of a preferential release of the newly synthesized [14C]glutamate. In contrast to glutamate, endogenous aspartate was not released in a Ca2+-dependent manner, and the efflux of newly formed [14C]aspartate was only slightly potentiated by Ca2+, which suggests that glutamate and aspartate are not released from the same sites. Studies on preparations (slices and synaptosomes) from immature, 8-day-old cerebella showed that neither the K+-evoked released ofd-[3H]aspartate, nor that of endogenous glutamate was Ca2+-dependent. In conclusion, the data presented are consistent with the proposition that glutamate has a neurotransmitter role in the cerebellum.