Synaptic and extrasynaptic NMDA receptor NR2 subunits in cultured hippocampal neurons
Synaptic and extrasynaptic NMDA receptor NR2 subunits in cultured hippocampal neurons
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DOI：
10.1152/jn.00771.2005
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发表时间：
2006-03-01
影响因子：
2.5
通讯作者：
Westbrook, GL
中科院分区：
文献类型：
--
作者：
Thomas, CG;Miller, AJ;Westbrook, GL
在发育早期，神经元仅表达含有 NR1/NR2B 的 N-甲基-D-天冬氨酸 (NMDA) 受体。随后，NR2A 亚基在突触快速形成期间上调。这种模式通常被解释为表明含有 NR2A 的受体是突触性的，而含有 NR2B 的受体是突触外的。我们使用培养的海马神经元的全细胞记录重新检查了这个问题。正如预期的那样，NR2B 特异性拮抗剂艾芬地尔对全细胞电流的抑制从 69.5 +/- 2.4% [ 6 天体外 (DIV)] 逐渐下降至 54.9 +/- 2.6% ( 8 DIV)，然后在第二周达到稳定水平 (42.5 +/- 2%，12 - 19 DIV)。在仅表达含 NR1/NR2B 的 NMDA 受体的 NR2A(-/-) 神经元中，自动兴奋性突触后电流 (EPSC；>= 12 DIV) 对艾芬地尔更敏感，并且比野生型神经元中的 EPSC 衰减得更慢。因此，突触中并没有排除含有 NR2B 的受体。我们在诱发递质释放期间用 MK-801 阻断突触 NMDA 受体，从而使我们能够分离突触外受体。艾芬地尔对突触外群体的抑制作用在不同神经元中存在很大差异。此外，自动培养物中的突触外受体仅被艾芬地尔部分阻断，表明含有 NR2A 的受体并不完全局限于突触。在用全长 NR2A 转染的 NR2A(-/-) 神经元中也检测到了包含突触外 NR2A 的受体。 NR2A C 末端的截断并没有消除含有 NR2A 的受体的突触表达。我们的结果表明，含有 NR2A 和 NR2B 的受体可以位于突触或突触外区室中。
Early in development, neurons only express NR1/NR2B-containing N-methyl-D-aspartate (NMDA) receptors. Later, NR2A subunits are upregulated during a period of rapid synapse formation. This pattern is often interpreted to indicate that NR2A-containing receptors are synaptic and that NR2B-containing receptors are extrasynaptic. We re-examined this issue using whole cell recordings in cultured hippocampal neurons. As expected, the inhibition of whole cell currents by the NR2B-specific antagonist, ifenprodil, progressively decreased from 69.5 +/- 2.4% [ 6 days in vitro (DIV)] to 54.9 +/- 2.6% ( 8 DIV), before reaching a plateau in the second week (42.5 +/- 2%, 12 - 19 DIV). In NR2A(-/-) neurons, which express only NR1/NR2B-containing NMDA receptors, autaptic excitatory postsynaptic currents (EPSCs; >= 12 DIV) were more sensitive to ifenprodil and decayed more slowly than EPSCs in wild-type neurons. Thus NR2B-containing receptors were not excluded from synapses. We blocked synaptic NMDA receptors with MK-801 during evoked transmitter release, thus allowing us to isolate extrasynaptic receptors. Ifenprodil inhibition of this extrasynaptic population was highly variable in different neurons. Furthermore, extrasynaptic receptors in autaptic cultures were only partially blocked by ifenprodil, indicating that NR2A-containing receptors are not exclusively confined to the synapse. Extrasynaptic NR2A-containing receptors were also detected in NR2A(-/-) neurons transfected with full-length NR2A. Truncation of the NR2A C terminus did not eliminate synaptic expression of NR2A-containing receptors. Our results indicate that NR2A- and NR2B-containing receptors can be located in either synaptic or extrasynaptic compartments.