Rumbaugh G, Vicini S
Department of Pharmacology, Georgetown University School of Medicine, Washington, DC 20007, USA.
J Neurosci. 1999 Dec 15;19(24):10603-10. doi: 10.1523/JNEUROSCI.19-24-10603.1999.
In rat cerebellar granule neurons, mRNA and protein levels of the NR2A and NR2C subunits of the NMDA receptor increase during the second postnatal week. At this time, mRNA and protein levels of the NR2B subunit begin to fall. To investigate targeting of NMDA receptor subunits, we performed whole-cell recordings from rat cerebellar granule neurons at different times during development and investigated the pharmacological and biophysical properties of mossy fiber-evoked NMDA EPSCs. Isolated NMDA EPSCs from newly formed synapses in the first postnatal week exhibited partial block by the NR2B subunit-specific antagonist (1S, 2S)-1-(4-hydroxyphenyl)-2-(4-hydroxy-4-phenylpiperidino)-1-propanol (CP 101,606). By the end of the second postnatal week, NMDA EPSCs were virtually unaffected by the NR2B antagonist. In parallel, NMDA EPSC decay times decreased over a similar developmental time course. We compared properties of synaptic NMDA receptors with extrasynaptic receptors that are present on the cell body with rapid application of glutamate to excised nucleated patches. Deactivation of patch responses accelerated with development and closely resembled evoked NMDA EPSCs in rats of the same age. However, patch responses were highly sensitive to CP 101,606 through the second postnatal week, and sensitivity was seen in some neurons up to the fourth postnatal week. Spermine potentiated peak NMDA patch responses from postnatal days 10-14 rats but had little effect on evoked NMDA EPSCs. Our data suggest selective targeting of a distinct NMDA receptor subtype to synaptic receptor populations in cerebellar granule neurons. Later in development, similar changes occur in the extrasynaptic receptor population.
在大鼠小脑颗粒神经元中，NMDA受体的NR2A和NR2C亚基的mRNA和蛋白质水平在出生后第二周升高。此时，NR2B亚基的mRNA和蛋白质水平开始下降。为了研究NMDA受体亚基的靶向作用，我们在发育的不同时间对大鼠小脑颗粒神经元进行了全细胞记录，并研究了苔藓纤维诱发的NMDA兴奋性突触后电流（EPSCs）的药理学和生物物理特性。出生后第一周新形成突触的分离NMDA EPSCs表现出被NR2B亚基特异性拮抗剂（1S，2S）-1-（4-羟苯基）-2-（4-羟基-4-苯基哌啶基）-1-丙醇（CP 101,606）部分阻断。到出生后第二周结束时，NMDA EPSCs实际上不受NR2B拮抗剂的影响。同时，NMDA EPSC衰减时间在相似的发育时间进程中缩短。我们将突触NMDA受体的特性与存在于细胞体上的突触外受体的特性进行了比较，通过快速应用谷氨酸到切除的有核膜片上来进行研究。膜片反应的失活随着发育而加速，并且与相同年龄大鼠中诱发的NMDA EPSCs非常相似。然而，在出生后第二周，膜片反应对CP 101,606高度敏感，并在一些神经元中直至出生后第四周仍可见到这种敏感性。精胺增强了出生后第10 - 14天大鼠的NMDA膜片反应峰值，但对诱发的NMDA EPSCs几乎没有影响。我们的数据表明，在小脑颗粒神经元中，一种独特的NMDA受体亚型选择性地靶向突触受体群体。在发育后期，突触外受体群体也发生了类似的变化。
