Robert A, Howe J R, Waxman S G
Department of Neurology and Paralyzed Veterans of America-Eastern Paralyzed Veterans Association Neuroscience Research Center, Yale University School of Medicine, New Haven, CT 06510, USA.
J Neurophysiol. 2000 Feb;83(2):659-70. doi: 10.1152/jn.2000.83.2.659.
The development of glutamatergic synapses involves a sequence of events that are still not well understood. We have studied the time course of the development of glutamatergic synapses in cultured spinal neurons by characterizing spontaneous synaptic currents recorded from cells maintained in vitro for different times. At short times in culture (2 days in vitro; DIV2), spontaneous synaptic activity consisted almost solely of N-methyl-D-aspartate (NMDA) receptor (NMDAR) openings. In contrast, older neurons (DIV5 to DIV8) displayed clear alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor (AMPAR)-mediated synaptic currents, while the NMDAR-mediated activity remained small. Between 8 and 14 days in vitro there was a large increase in the density of synaptically activated NMDARs, although there was no significant increase in the density of the NMDAR-mediated current activated by exogenous glutamate. The results indicate that there is a switch in NMDAR targeting from somatic to synaptic regions during the course of the second in vitro week. Finally, our results support the conclusion that the spontaneous synaptic activity displayed in culture depends on ongoing NMDAR-mediated activity, even when the expression of synaptic NMDARs is low.
谷氨酸能突触的发育涉及一系列尚未完全理解的事件。我们通过对体外培养不同时间的细胞记录的自发突触电流进行表征，研究了培养的脊髓神经元中谷氨酸能突触发育的时间进程。在培养的短时间内（体外培养2天；DIV2），自发突触活动几乎完全由N-甲基-D-天冬氨酸（NMDA）受体（NMDAR）开放组成。相比之下，较成熟的神经元（DIV5至DIV8）表现出明显的α-氨基-3-羟基-5-甲基-4-异恶唑丙酸（AMPA）受体（AMPAR）介导的突触电流，而NMDAR介导的活动仍然很小。在体外培养8至14天之间，突触激活的NMDAR密度大幅增加，尽管外源性谷氨酸激活的NMDAR介导电流密度没有显著增加。结果表明，在体外培养的第二周过程中，NMDAR的靶向从体细胞区域转变为突触区域。最后，我们的结果支持这样的结论，即培养中显示的自发突触活动依赖于持续的NMDAR介导的活动，即使突触NMDAR的表达很低。
