Plotkin M D, Snyder E Y, Hebert S C, Delpire E
Department of Medicine, Brigham and Women's Hospital, and Harvard Medical School, Boston, Massachusetts 02115, USA.
J Neurobiol. 1997 Nov 20;33(6):781-95. doi: 10.1002/(sici)1097-4695(19971120)33:6<781::aid-neu6>3.0.co;2-5.
An inhibitory neurotransmitter in mature brain, gamma-aminobutyric acid (GABA) also appears to be excitatory early in development. The mechanisms underlying this shift are not well understood. In vitro studies have suggested that Na-K-Cl cotransport may have a role in modulating immature neuronal and oligodendrocyte responses to the neurotransmitter GABA. An in vivo developmental study would test this view. Therefore, we examined the expression of the BSC2 isoform of the Na-K-2Cl cotransporter in the postnatal developing rat brain. A comparison of sections from developing rat brains by in situ hybridization revealed a well-delineated temporal and spatial pattern of first increasing and then diminishing cotransporter expression. Na-K-2Cl mRNA expression in the cerebral cortex and hippocampus was highest in the first week of postnatal life and then diminished from postnatal day (PND) 14 to adult. Cotransporter signal in white-matter tracts of the cerebrum, cerebellum, peaked at PND 14. Expression was detected in cerebellar progenitor cells of the external granular layer, in internal granular layer cells at least as early as PND 7, and in Purkinje cells beginning at PND 14. Double-labeling immunofluorescence of brain sections with anti-BSC2 antibody and cell type-specific antibodies confirmed expression of the cotransporter gene product in neurons and oligodendrocytes in the white matter in a pattern similar to that determined by in situ hybridization. The temporal pattern of expression of the Na-K-2Cl cotransporter in the postnatal rat brain supports the hypothesis that the cotransporter is the mechanism of intracellular Cl- accumulation in immature neurons and oligodendrocytes.
γ-氨基丁酸（GABA）是成熟大脑中的一种抑制性神经递质，在发育早期似乎也具有兴奋性。这种转变背后的机制尚不清楚。体外研究表明，钠-钾-氯共转运可能在调节未成熟神经元和少突胶质细胞对神经递质GABA的反应中起作用。一项体内发育研究将验证这一观点。因此，我们检测了钠-钾-2氯共转运体的BSC2亚型在出生后发育中的大鼠脑中的表达。通过原位杂交对发育中的大鼠脑切片进行比较，发现共转运体表达呈现出一种明确的时空模式，即先增加后减少。大脑皮层和海马体中的钠-钾-2氯mRNA表达在出生后的第一周最高，然后从出生后第14天到成年逐渐减少。大脑和小脑白质束中的共转运体信号在出生后第14天达到峰值。在外部颗粒层的小脑祖细胞中检测到表达，至少在出生后第7天在内部颗粒层细胞中检测到表达，从出生后第14天开始在浦肯野细胞中检测到表达。用抗BSC2抗体和细胞类型特异性抗体对脑切片进行双标记免疫荧光，证实了共转运体基因产物在白质中的神经元和少突胶质细胞中的表达模式与原位杂交确定的模式相似。钠-钾-2氯共转运体在出生后大鼠脑中的表达时间模式支持了这样一种假设，即共转运体是未成熟神经元和少突胶质细胞中细胞内氯离子积累的机制。
