Lorenzo Louis-Etienne, Magnussen Claire, Bailey Andrea L, St Louis Manon, De Koninck Yves, Ribeiro-da-Silva Alfredo
Department of Pharmacology and Therapeutics, McGill University, 3655 Promenade Sir-William-Osler, Montreal, Quebec H3G 1Y6, Canada.
Mol Pain. 2014 Sep 4;10:57. doi: 10.1186/1744-8069-10-57.
Inhibitory interneurons are an important component of dorsal horn circuitry where they serve to modulate spinal nociception. There is now considerable evidence indicating that reduced inhibition in the spinal dorsal horn contributes to neuropathic pain. A loss of these inhibitory neurons after nerve injury is one of the mechanisms being proposed to account for reduced inhibition; however, this remains controversial. This is in part because previous studies have focused on global measurements of inhibitory neurons without assessing the number of inhibitory synapses. To address this, we conducted a quantitative analysis of the spatial and temporal changes in the number of inhibitory terminals, as detected by glutamic acid decarboxylase 65 (GAD65) immunoreactivity, in the superficial dorsal horn of the spinal cord following a chronic constriction injury (CCI) to the sciatic nerve in rats. Isolectin B4 (IB4) labelling was used to define the location within the dorsal horn directly affected by the injury to the peripheral nerve. The density of GAD65 inhibitory terminals was reduced in lamina I (LI) and lamina II (LII) of the spinal cord after injury. The loss of GAD65 terminals was greatest in LII with the highest drop occurring around 3-4 weeks and a partial recovery by 56 days. The time course of changes in the number of GAD65 terminals correlated well with both the loss of IB4 labeling and with the altered thresholds to mechanical and thermal stimuli. Our detailed analysis of GAD65+ inhibitory terminals clearly revealed that nerve injury induced a transient loss of GAD65 immunoreactive terminals and suggests a potential involvement for these alterations in the development and amelioration of pain behaviour.
抑制性中间神经元是脊髓背角神经回路的重要组成部分，在其中发挥调节脊髓痛觉感受的作用。现在有大量证据表明，脊髓背角抑制作用的减弱会导致神经性疼痛。神经损伤后这些抑制性神经元的丧失是被提出的用于解释抑制作用减弱的机制之一；然而，这一点仍存在争议。部分原因在于先前的研究集中在对抑制性神经元的整体测量上，而没有评估抑制性突触的数量。为了解决这个问题，我们对大鼠坐骨神经慢性压迫损伤（CCI）后脊髓背角浅层中由谷氨酸脱羧酶65（GAD65）免疫反应性检测到的抑制性终末数量的时空变化进行了定量分析。使用异凝集素B4（IB4）标记来确定背角内直接受外周神经损伤影响的位置。损伤后脊髓I层（LI）和II层（LII）中GAD65抑制性终末的密度降低。GAD65终末的丧失在LII中最为明显，最高降幅出现在3 - 4周左右，到56天时部分恢复。GAD65终末数量变化的时间进程与IB4标记的丧失以及机械和热刺激阈值的改变密切相关。我们对GAD65 +抑制性终末的详细分析清楚地表明，神经损伤诱导了GAD65免疫反应性终末的短暂丧失，并提示这些改变可能参与疼痛行为的发展和改善。
