Marvizón J C, Martínez V, Grady E F, Bunnett N W, Mayer E A
CURE: Digestive Diseases Research Center, Neuroenteric Disease Program, Department of Medicine, University of California, Los Angeles, California 90073, USA.
J Neurosci. 1997 Nov 1;17(21):8129-36. doi: 10.1523/JNEUROSCI.17-21-08129.1997.
The excitability of spinal neurons that transmit pain is modulated by glutamate and substance P (SP). Glutamate is an excitatory neurotransmitter in the dorsal horn, and its effects are enhanced by SP acting on neurokinin 1 receptors (NK1Rs). We assessed activation of NK1Rs by studying their internalization in spinal cord slices. NK1Rs were localized in sections from the slices by using immunohistochemistry combined with fluorescence and confocal microscopy. Incubating the slices with SP induced internalization in most NK1R-positive neurons in laminae I, IIo, and X and in half of NK1R-positive neurons in laminae III-V. SP-induced internalization was abolished by the specific NK1R antagonist L-703,606 (1 microM). Stimulating the dorsal root with long-duration (0.4 msec) pulses evoked EPSPs in dorsal horn neurons with latencies consistent with the conduction speed of A partial differential- and C-fibers. High-frequency (100 Hz) stimulation of the dorsal root with these pulses induced NK1R internalization in neurons in laminae I-IIo of the stimulated side of the slice but not in the contralateral side or in other laminae. Stimulation at lower frequencies (1 and 10 Hz) failed to elicit significant internalization, suggesting that the release of SP is frequency-dependent. Internalization produced by the 100 Hz tetanus was mimicked by NMDA and blocked by an NMDA antagonist, 2-amino-5-phosphonopentanoic acid, but not by the AMPA and kainate antagonist CNQX. The NK1R antagonist L-703,606 abolished the internalization produced by 100 Hz stimulation or NMDA. Therefore, the release of SP in the dorsal horn appears to be controlled by NMDA receptors.
传递疼痛的脊髓神经元的兴奋性受谷氨酸和P物质（SP）调节。谷氨酸是背角中的一种兴奋性神经递质，SP作用于神经激肽1受体（NK1Rs）可增强其作用。我们通过研究脊髓切片中NK1Rs的内化来评估其激活情况。利用免疫组织化学结合荧光和共聚焦显微镜对切片中的NK1Rs进行定位。用SP孵育切片可诱导I层、IIo层和X层中大多数NK1R阳性神经元以及III - V层中一半的NK1R阳性神经元发生内化。特异性NK1R拮抗剂L - 703,606（1微摩尔）可消除SP诱导的内化。用长时间（0.4毫秒）脉冲刺激背根可在背角神经元中诱发兴奋性突触后电位（EPSPs），其潜伏期与Aδ纤维和C纤维的传导速度一致。用这些脉冲对背根进行高频（100赫兹）刺激可诱导切片受刺激侧I - IIo层神经元中的NK1R内化，但对侧或其他层则无此现象。较低频率（1和10赫兹）刺激未能引发明显的内化，表明SP的释放具有频率依赖性。100赫兹强直刺激产生的内化可被N - 甲基 - D - 天冬氨酸（NMDA）模拟，并被NMDA拮抗剂2 - 氨基 - 5 - 膦酰基戊酸阻断，但不被α - 氨基 - 3 - 羟基 - 5 - 甲基 - 4 - 异恶唑丙酸（AMPA）和海人酸拮抗剂6 - 氰基 - 7 - 硝基喹喔啉 - 2,3 - 二酮（CNQX）阻断。NK1R拮抗剂L - 703,606可消除100赫兹刺激或NMDA产生的内化。因此，背角中SP的释放似乎受NMDA受体控制。
