大鼠正常与退变性髓核突出导致神经根性疼痛的对比研究

A comparative study of the effects of normal and degenerated nucleus pulposus on radicular pain in rats

目的探讨正常与退变髓核突出对大鼠疼痛阈值以及背根神经节中TNF-α表达的影响,研究椎间盘退变与神经根性疼痛之间的关系。方法72只大鼠随机分为4组:正常对照组(n=18)、假手术组(n=19)、正常髓核(N-NP)组(n=16)和退变髓核(P-NP)组(n=19)。对P-NP组大鼠利用尾椎椎间盘纤维环穿刺的方法建立椎间盘退变模型。分别取出N-NP组和P-NP组大鼠自体的正常髓核与退变髓核组织,置于手术显露后的腰5左侧神经根处,建立髓核突出致神经根性疼痛动物模型。采用行为学测试的方法分别观察各组大鼠术前1天,术后1、4、7、10、14、21天机械刺激阈值与热刺激阈值的变化;采用免疫组化方法分别检测术后第4、14天各组大鼠背根神经节中TNF-α的表达。结果行尾椎间盘纤维环穿刺后2周,组织学与MRI检查均证实椎间盘组织发生明显退变。对照组和假手术组动物未出现明显的痛觉过敏现象,N-NP组和P-NP组大鼠机械性刺激阈值均显著下降,该痛觉过敏现象持续至术后2周消失;与正常髓核组织相比,退变髓核所致机械性刺激阈值下降程度更为严重。各实验组均未发生热刺激阈值的规律性变化。术后第4、14天对照组和假手术组背根神经节中未见TNF-α明显表达,而正常及退变髓核组TNF-α表达量均显著升高。结论大鼠尾椎纤维环穿刺是建立大鼠椎间盘退变模型的一种有效方法。与正常髓核组织相比,发生退变的髓核组织可导致神经根性疼痛的加重,提示椎间盘退变过程中释放的炎症因子在疼痛的发生机制中可能起到了重要作用。

Objective To evaluate the effects of normal and degenerated nucleus pulposus （NP） on pain threshold of hindlimbs in rats and the expression of TNF-α in L5 dorsal root ganglion （DRG）,subsequently to study the relationship between disc degeneration and radicular pain.Methods Seventy-two rats were randomly divided into 4 groups：normal control （NC） group （n =18）,sham-operation control （SC） group （n =19）,normal NP （N-NP） group （n =16） and punctured NP （P-NP） group （n =19）.Annular needle puncture model of intervertebral disc degeneration in rat tail was established in P-NP group.Normal and punctured NP tissue were obtained and placed onto the L5 left nerve root following hemilaminectomy.Behavioral tests including mechanical threshold and thermal withdrawal latency were performed at 1 day before surgery and 1,4,7,10,14,21 days after surgery.The expression of TNF-α in L5 DRG were examined through immunohisto-chemical analysis at 4 and 14 days postoperatively.Results The punctured discs showed significant degeneration two weeks after intervention.Application of both normal and punctured NP induced mechanical hyperalgesia in the ipisilateral paw postoperatively,while NC and SC group had no positive results.Furthermore,hyperalgesia were more severe in P-NP group than in N-NP group.No statistically significant changes in thermal withdrawal latency over time were found in four groups.Significant increase of the expression of TNF-α positive neurons in DRG were found in both N-NP and P-NP groups at 4 and 14 days after operation,while no obvious expression of TNF-α in NC and SC group.Conclusions Needle puncture in rat tail is an effective method to establish intervertebral disc degeneration model.Compared with normal NP,the degenerated NP enhances mechanical hyperalgesia by the application of NP onto lumbar nerve root.The results suggest that inflammatory mediators produced during disc degeneration may play a key role in the mechanism of pain symptoms.