去甲肾上腺素对SNI大鼠背根神经节神经元及其传入纤维兴奋性的影响

Effects of norepinephrine on the excitability of dorsal root ganglion neurons and their afferent fibers in SNI rats

目的:研究去甲肾上腺素(norepinephrine, NE)对保留性坐骨神经损伤(spared nerve injury,SNI)模型Sprague-Dawley大鼠背根神经节(dorsalrootganglion,DRG)神经元及其传入纤维兴奋性的影响。方法:(1)将40只雄性大鼠随机平均分为8组,每组5只。NE干预(SNI+NE)组、手术对照(SNI+Vehicle)组、去甲肾上腺素干预假手术(Sham+NE)组、假手术对照(Sham+Vehicle)组,每组再随机均分为C纤维记录组与A纤维记录组。SNI手术造模后7天内up-down法监测下肢痛阈变化,确认造模成功。术后第14天,采用在体脊髓诱发电位(spinal evoked field potential, SEFP)记录技术,研究外源性100μM NE干预L4、L5 DRG对刺激C纤维、A纤维诱发的脊髓背角SEFP的作用。(2)按前述将30只雄性大鼠随机平均分组。采用全细胞膜片钳技术研究100μM NE灌流对离体打散的手术侧L4、L5 DRG大、中、小直径神经元诱发动作电位基强度(current threshold, CT)和两倍基强度诱发动作电位次数(No. of APs at 2×rheobase)的作用。结果:(1)SEFP记录实验发现:100μM NE干预SNI侧DRG,可抑制A纤维诱发的脊髓背角SEFP (P <0.01)并增强C纤维诱发的脊髓背角SEFP (P <0.01)。(2)离体膜片钳实验发现:在钳制电压为-80 mV时,与Sham+Vehicle组相比,SNI+Vehicle组DRG神经元CT下降(P <0.001),两倍基强度诱发的动作电位放电次数增加(P <0.001),即SNI组神经元兴奋性增加;而100μM NE灌流,SNI+NE组和Sham+NE组的动作电位的放电次数与同组NE灌流前相比,未见明显变化(P> 0.05)。结论:NE通过抑制SNI大鼠DRG中大、中神经元的兴奋性,同时间接兴奋小神经元而参与痛觉传入信号的调控。

Objective: To investigate the effects of norepinephrine(NE) on the excitability of dorsal root ganglion(DRG) neurons and their afferent fibers in Sprague-Dawley rats with preserved sciatic nerve injury. Methods:(1) Forty male rats were randomly divided into 8 groups with 5 rats in each group. They are the NE intervention(SNI + NE) group, the surgical control(SNI + Vehicle) group, the norepinephrine intervention sham operation(Sham + NE) group, and the sham + Vehicle group. Rats in each group were randomly allocated to C fiber recording group or A fiber recording group. The up-down method was used to monitor the pain threshold changes of the lower limbs within 7 days after SNI surgery, confirming the successful modeling. On the 14 th day after surgery, the effect of exogenous 100 μM NE intervention on L4 and L5 DRG on the stimulation of C fiber and A fiber-induced spinal dorsal horn SEFP was studied by using local field potential(SEFP) recording technique.(2) Thirty male rats were randomly divided into groups and modeled as described above. Wholecell patch clamp technique was used to study the number of action potentials(current threshold, CT) and twice the base-induced evoked action potential of L4 and L5 DRG large and medium-diameter neurons on the surgical side of 100 μM(NE perfusion of APs at 2×rheobase). Results:(1) In the spinal cord field potential recording experiments, 100 μM NE intervention in the SNI side DRG inhibited the AFP-induced spinal dorsal horn SEFP(P < 0.01) and enhanced the C fiber-induced spinal dorsal horn SEFP(P < 0.01).(2) Ex vivo patch clamp experiments found that when the clamping voltage was-80 mV, the DRG neuron CT decreased in the SNI + Vehicle group compared with the Sham + Vehicle group(P < 0.001), twice the base-induced action potential. The number of discharges increased(P < 0.001), that is, the excitability of neurons in the SNI group increased. However, the number of discharges of action potentials in the SNI + NE group and the Sham + NE group was not significantly higher than that before the same group of NE perfusion in 100 μM NE perfusion changes(P > 0.05). Conclusion: Norepinephrine is involved in the regulation of pain signal transmission by inhibiting the excitability of large and medium-sized neurons in the dorsal root ganglia of SNI rats and meanwhile indirectly exciting small neurons.