NMDAR-mediated EPSCs are maintained and accelerate in time course during maturation of mouse and rat auditory brainstem in vitro
NMDAR-mediated EPSCs are maintained and accelerate in time course during maturation of mouse and rat auditory brainstem in vitro
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DOI：
10.1113/jphysiol.2009.184317
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发表时间：
2010-02-01
影响因子：
5.5
通讯作者：
Forsythe, Ian D.
中科院分区：
文献类型：
--
作者：
Steinert, Joern R.;Postlethwaite, Michael;Forsythe, Ian D.
NMDA受体(NMDAR)在整个大脑的兴奋性谷氨酸能突触上介导缓慢的EPSC。在许多地区，NMDAR介导的EPSC的大小随着发育而下降，并与亚单位组成的变化有关，但成熟的通道组成往往未知。我们利用Hold末端及其靶点--斜方体内内侧核(MNTB)的主神经元，研究了从P10到P40突触成熟过程中NMDAR介导的EPSC。我们的数据显示，到18岁左右，花萼已经达到成熟状态。NMDAR介导的EPSC波幅(和主导衰减tau)从P10/11时的约5nA(tau：40-50ms)下降到P18时的0.3-0.5nA(tau：10-15ms)。成熟的NMDAR-EPSC对异丙苯地尔不敏感，提示缺乏NR2B亚基，亚微摩尔浓度的锌不阻断NMDAR-EPSC，与NR1-1b亚基的表达一致。此外，从P11到P18，电压依赖性阻断减小，[Mg~(2+)](O)(K-o)的表观离解常数从7.5 mm变为14 mm。定量聚合酶链式反应显示NR2A和NR2C的相对表达增加，免疫组织化学证实NR2A、NR2B和NR2C蛋白的存在。尽管成熟的NMDAR-EPSC很小，但正如DAR-4M成像所示，它很好地耦合到没有信号。我们的结论是，在Hold的花冠上，天然成熟的NMDAR通道具有较快的时间进程，并减少了[Mg2+](O)的阻断，这与NR2C亚基的优势和NR2B亚基的功能排斥是一致的。药理学提示为单通道类型，我们假设成熟的NMDAR由NR1-1b-NR2A-NR2C的异源三聚体组成。
NMDA receptors (NMDARs) mediate a slow EPSC at excitatory glutamatergic synapses throughout the brain. In many areas the magnitude of the NMDAR-mediated EPSC declines with development and is associated with changes in subunit composition, but the mature channel composition is often unknown. We have employed the calyx of Held terminal with its target, the principal neuron of the medial nucleus of the trapezoid body (MNTB), to examine the NMDAR-mediated EPSC during synapse maturation from P10 to P40. Our data show that the calyx has reached a mature state by around P18. The NMDAR-mediated EPSC amplitude (and dominant decay tau) fell from around 5 nA (tau: 40-50 ms) at P10/11 to 0.3-0.5 nA (tau: 10-15 ms) by P18. The mature NMDAR-EPSC showed no sensitivity to ifenprodil, indicating lack of NR2B subunits, and no block by submicromolar concentrations of zinc, consistent with NR1-1b subunit expression. Additionally, from P11 to P18 there was a reduction in voltage-dependent block and the apparent dissociation constant for [Mg2+](o) (K-o) changed from 7.5 to 14 mm. Quantitative PCR showed that the relative expression of NR2A and NR2C increased, while immunohistochemistry confirmed the presence of NR2A, NR2B and NR2C protein. Although the mature NMDAR-EPSC is small, it is well coupled to NO signalling, as indicated by DAR-4M imaging. We conclude that native mature NMDAR channels at the calyx of Held have a fast time course and reduced block by [Mg2+](o), consistent with dominance of NR2C subunits and functional exclusion of NR2B subunits. The pharmacology suggests a single channel type and we postulate that the mature NMDARs consist of heterotrimers of NR1-1b-NR2A-NR2C.