Northington F J, Traystman R J, Koehler R C, Rothstein J D, Martin L J
Department of Pediatrics, The Johns Hopkins Medical Institutions, Baltimore, MD 21287, USA.
Neuroscience. 1998 Aug;85(4):1183-94. doi: 10.1016/s0306-4522(97)00673-8.
Glutamate transport is a primary mechanism for regulating extracellular levels of glutamate which can have either neurotrophic or neurotoxic effects in the developing brain, depending on its concentration. Using immunoblotting and immunocytochemistry, we tested the hypotheses that expression of neuronal and glial glutamate transporter proteins was regionally and temporally regulated in the developing ovine brain and that expression of the glial isoform early in development was not cell-type specific. Immunoblots for the neuronal glutamate transporter EAAC1 revealed a major band of immunoreactivity at 69,000 nmol. wt, whereas glial glutamate transporter-1 (GLT1) immunoreactivity was observed as 73,000 and 146,000 mol. wt proteins. EAAC1 and GLT1 are regulated differently during development, with EAAC1 immunoreactivity being most abundant at 60 and 71 days completed gestation (term=145 days) and dissipating thereafter, while GLT1 immunoreactivity was most abundant at 136 days gestation. By immunocytochemistry EAAC1 expression is neuronal throughout gestation with intense labelling of dendrites within the telencephalon evident at 60 days. Neuropil, neuronal cell bodies and processes are EAAC1-immunoreactive throughout gestation with no evidence of astrocytic or oligodendroglial immunoreactivity. In contrast, GLT1 is expressed by neuronal and non-neuronal cell types during midgestation with astrocyte selectivity developing by 136 days. During midgestation, GLT1 is transiently expressed in neurons of the subplate, cranial nerve nuclei, basal ganglia, and cerebellar cortex. The major finding of this study, that GLT1 is transiently expressed in various neuronal populations at midgestation demonstrates that the cell-type specificity of the GLT1 phenotype is developmentally regulated and depends on brain maturity.
谷氨酸转运是调节细胞外谷氨酸水平的主要机制，在发育中的大脑中，谷氨酸根据其浓度可产生神经营养或神经毒性作用。我们运用免疫印迹法和免疫细胞化学方法，检验了以下假设：在发育中的绵羊大脑中，神经元和胶质细胞谷氨酸转运蛋白的表达在区域和时间上受到调控，并且在发育早期胶质细胞亚型的表达并非细胞类型特异性的。神经元谷氨酸转运体EAAC1的免疫印迹显示，在69,000 nmol. wt处有一条主要的免疫反应带，而胶质细胞谷氨酸转运体-1（GLT1）的免疫反应性表现为73,000和146,000 mol. wt的蛋白质。EAAC1和GLT1在发育过程中受到不同的调控，EAAC1免疫反应性在妊娠60天和71天（足月为145天）时最为丰富，此后逐渐消散，而GLT1免疫反应性在妊娠136天时最为丰富。通过免疫细胞化学方法发现，EAAC1在整个妊娠期均表达于神经元，在60天时端脑内的树突有强烈标记。在整个妊娠期，神经纤维、神经元细胞体和突起均有EAAC1免疫反应性，没有星形胶质细胞或少突胶质细胞免疫反应性的证据。相比之下，GLT1在妊娠中期由神经元和非神经元细胞类型表达，到136天时出现星形胶质细胞选择性表达。在妊娠中期，GLT1在板下层、脑神经核、基底神经节和小脑皮质的神经元中短暂表达。本研究的主要发现，即GLT1在妊娠中期在各种神经元群体中短暂表达，表明GLT1表型的细胞类型特异性受到发育调控，并且取决于大脑成熟度。
