Gong Kerui, Kung Ling-Hsuan, Magni Giulia, Bhargava Aditi, Jasmin Luc
Department of Oral and Maxillofacial Surgery, University of California San Francisco, San Francisco, California, United States of America; Department of Anatomy, University of California San Francisco, San Francisco, California, United States of America.
Department of Anatomy, University of California San Francisco, San Francisco, California, United States of America.
PLoS One. 2014 Apr 18;9(4):e95491. doi: 10.1371/journal.pone.0095491. eCollection 2014.
Glutamate in the peripheral nervous system is involved in neuropathic pain, yet we know little how nerve injury alters responses to this neurotransmitter in primary sensory neurons. We recorded neuronal responses from the ex-vivo preparations of the dorsal root ganglia (DRG) one week following a chronic constriction injury (CCI) of the sciatic nerve in adult rats. We found that small diameter DRG neurons (<30 µm) exhibited increased excitability that was associated with decreased membrane threshold and rheobase, whereas responses in large diameter neurons (>30 µm) were unaffected. Puff application of either glutamate, or the selective ionotropic glutamate receptor agonists alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and kainic acid (KA), or the group I metabotropic receptor (mGluR) agonist (S)-3,5-dihydroxyphenylglycine (DHPG), induced larger inward currents in CCI DRGs compared to those from uninjured rats. N-methyl-D-aspartate (NMDA)-induced currents were unchanged. In addition to larger inward currents following CCI, a greater number of neurons responded to glutamate, AMPA, NMDA, and DHPG, but not to KA. Western blot analysis of the DRGs revealed that CCI resulted in a 35% increase in GluA1 and a 60% decrease in GluA2, the AMPA receptor subunits, compared to uninjured controls. mGluR1 receptor expression increased by 60% in the membrane fraction, whereas mGluR5 receptor subunit expression remained unchanged after CCI. These results show that following nerve injury, small diameter DRG neurons, many of which are nociceptive, have increased excitability and an increased response to glutamate that is associated with changes in receptor expression at the neuronal membrane. Our findings provide further evidence that glutamatergic transmission in the periphery plays a role in nociception.
外周神经系统中的谷氨酸参与神经性疼痛，但我们对神经损伤如何改变初级感觉神经元对这种神经递质的反应知之甚少。我们记录了成年大鼠坐骨神经慢性压迫损伤（CCI）一周后背根神经节（DRG）离体标本的神经元反应。我们发现，小直径DRG神经元（<30 µm）表现出兴奋性增加，这与膜阈值和基强度降低有关，而大直径神经元（>30 µm）的反应未受影响。与未受伤大鼠相比，在CCI DRG中，微量注射谷氨酸、选择性离子型谷氨酸受体激动剂α-氨基-3-羟基-5-甲基-4-异恶唑丙酸（AMPA）和 kainic 酸（KA）或 I 型代谢型受体（mGluR）激动剂（S）-3,5-二羟基苯甘氨酸（DHPG）可诱导更大的内向电流。N-甲基-D-天冬氨酸（NMDA）诱导的电流没有变化。除了CCI后内向电流更大外，更多神经元对谷氨酸、AMPA、NMDA和DHPG有反应，但对KA没有反应。DRG的蛋白质免疫印迹分析显示，与未受伤对照相比，CCI导致AMPA受体亚基GluA1增加35%，GluA2减少60%。mGluR1受体表达在膜组分中增加60%，而CCI后mGluR5受体亚基表达保持不变。这些结果表明，神经损伤后，许多为伤害性感受神经元的小直径DRG神经元兴奋性增加，对谷氨酸的反应增强，这与神经元膜上受体表达的变化有关。我们的研究结果进一步证明外周谷氨酸能传递在伤害感受中起作用。
