Jakowec M W, Fox A J, Martin L J, Kalb R G
Department of Neurology, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
Neuroscience. 1995 Aug;67(4):893-907. doi: 10.1016/0306-4522(95)00026-f.
Synaptic activity in early postnatal life is important for the acquisition of mature structural and functional properties of neurons. Previous studies indicate that the mature molecular features of spinal motor neurons emerge during a period of activity-dependent development in early postnatal life. Since glutamatergic synaptic transmission provides the major excitatory drive into motor neurons, glutamate receptors are likely to play a central role in motor neuron activity-dependent development. To gain insight into this process, we have used receptor autoradiography, immunoblotting and immunohistochemistry to determine the distribution, temporal expression and potential subunit composition of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid subtype glutamate receptors in the developing rat spinal cord. Using two different ligands, [3H]-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and [3H]-6-cyano-7-nitroquinoxaline-2,3-dione, we find that alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid binding sites in the adult are largely restricted to the substantia gelatinosa. In marked contrast, during early postnatal life, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid binding sites are transiently expressed at high levels in the ventral horn. This parallels previous findings on the developmental regulation of N-methyl-D-aspartate receptor expression. Using alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subunit-specific antibodies we show by immunoblot analysis and immunohistology that, to varying degrees, the expression patterns of glutamate receptor subunit 1 and glutamate receptor subunits 2/3 are significantly developmentally regulated. The most conspicuous change is the downregulation of glutamate receptor 1 expression within motor neurons over the first three weeks of postnatal life. The qualitative and quantitative changes we observe in glutamate receptor expression in early postnatal life are likely to have a major impact on the electrophysiological properties of young motor neurons and thus may contribute to their activity-dependent development.
出生后早期的突触活动对于神经元获得成熟的结构和功能特性至关重要。先前的研究表明，脊髓运动神经元的成熟分子特征在出生后早期依赖活动的发育阶段出现。由于谷氨酸能突触传递为运动神经元提供主要的兴奋性驱动，谷氨酸受体可能在运动神经元依赖活动的发育中起核心作用。为了深入了解这一过程，我们使用受体放射自显影、免疫印迹和免疫组织化学来确定发育中大鼠脊髓中α-氨基-3-羟基-5-甲基-4-异恶唑丙酸亚型谷氨酸受体的分布、时间表达和潜在亚基组成。使用两种不同的配体，[3H]-α-氨基-3-羟基-5-甲基-4-异恶唑丙酸和[3H]-6-氰基-7-硝基喹喔啉-2,3-二酮，我们发现成体中的α-氨基-3-羟基-5-甲基-4-异恶唑丙酸结合位点主要局限于胶状质。与之形成鲜明对比的是，在出生后早期，α-氨基-3-羟基-5-甲基-4-异恶唑丙酸结合位点在腹角短暂高水平表达。这与先前关于N-甲基-D-天冬氨酸受体表达的发育调节的研究结果相似。使用α-氨基-3-羟基-5-甲基-4-异恶唑丙酸受体亚基特异性抗体，我们通过免疫印迹分析和免疫组织学表明，谷氨酸受体亚基1和谷氨酸受体亚基2/3的表达模式在不同程度上受到显著的发育调节。最明显的变化是出生后前三周运动神经元内谷氨酸受体1表达的下调。我们在出生后早期观察到的谷氨酸受体表达的定性和定量变化可能对年轻运动神经元的电生理特性产生重大影响，从而可能有助于它们依赖活动的发育。
