Wen Zhi-Hong, Chang Yi-Chen, Wong Chih-Shung
Department of Anesthesiology, Tri-Service General Hospital, National Defense Medical Center, #325, Chenggung Road, Section 2, Neihu 114, Taipei, Taiwan, R.O.C.
Acta Anaesthesiol Sin. 2003 Dec;41(4):187-96.
Like opioid tolerance, neuropathic pain syndrome manifested by hyperalgesia and allodynia responds poorly to opioids. Hitherto, its development is still not clear and its treatment and prevention are still disputable. Pertussis toxin (PTX) which ADP-ribosylates the alpha-subunit of inhibitory guanine nucleotide binding regulatory proteins (Gi/Go), is used to induce morphine tolerance through intrathecal (i.t.) injection. It decreases the antinociceptive effect of opioid receptor agonists, and produces a thermal hyperalgesia as well. With treatment of PTX the inhibitory Gi- and Go-proteins signal transduction is inactivated. Inhibition of the inhibitory system would likely lead to a predominance of the excitatory system. Intrathecal PTX administration has also been suggested as a model for study of the central mechanisms of neuropathic pain. In our previous studies, with intrathecal microdialysis and drug delivery techniques, we correlated the biochemical and pharmacological effects on the behavioral expressions of i.t. PTX-treated rats. Intrathecal PTX administration would induce thermal hyperalgesia in rats, with accompaniments of a prolonged increase in the concentrations of excitatory amino acids (EAAs), glutamate and aspartate, and a decrease in the concentration of the inhibitory amino acid (IAA) glycine in the spinal CSF dialysates. The PTX-induced thermal hyperalgesia peaked between day 2 and 4, but no cold allodynia is observed; i.t. administration of N-methyl-D-aspartate (NMDA) receptor antagonist, D-2-amino-5-phosponovaleric acid (D-AP5), glycine and protein kinase C (PKC) inhibitor chelerythrine attenuated the thermal hyperalgesia. The PKC gamma content of both synaptosomal and cytosolic fractions were significantly increased in PTX-treated rats. In contrast, the levels of PKC alpha, beta I, or beta II isozymes in these fractions were unaffected. Infusion of NMDA antagonist D-AP5 prevented both the thermal hyperalgesia and the increase in PKC gamma expression in PTX-treated rats. Similar to our previous report, i.t. PTX reduced morphine's analgesic effect. PKC inhibitor chelerythrine attenuated this reduction of morphine's analgesia, and an inhibition of the morphine-evoked EAAs release was observed in PTX-treated rats as well. Taken together, i.t. PTX-induced neuropathic pain syndrome is accompanied by increasing of EAAs, decreasing of IAA release, and a selective increasing of PKC gamma expression in the spinal cord. Inhibition of PKC not only blocked thermal hyperalgesia, but also reversed the reduction of morphine's analgesic effect in PTX-rats. These results suggest that PTX-induced neuropathic pain syndromes are involved in EAAs, IAAs and PKC alternations.
与阿片类药物耐受性一样，以痛觉过敏和异常性疼痛为特征的神经病理性疼痛综合征对阿片类药物反应不佳。迄今为止，其发病机制仍不明确，治疗和预防方法仍存在争议。百日咳毒素（PTX）可使抑制性鸟嘌呤核苷酸结合调节蛋白（Gi/Go）的α亚基发生ADP核糖基化，通过鞘内注射诱导吗啡耐受性。它降低了阿片受体激动剂的镇痛作用，还产生了热痛觉过敏。PTX处理后，抑制性Gi-和Go-蛋白信号转导失活。抑制抑制系统可能会导致兴奋系统占主导地位。鞘内注射PTX也被认为是研究神经病理性疼痛中枢机制的模型。在我们之前的研究中，利用鞘内微透析和药物递送技术，我们将鞘内注射PTX处理的大鼠的生化和药理作用与行为表现相关联。鞘内注射PTX会诱导大鼠出现热痛觉过敏，同时伴有脊髓脑脊液透析液中兴奋性氨基酸（EAA）谷氨酸和天冬氨酸浓度的持续升高，以及抑制性氨基酸（IAA）甘氨酸浓度的降低。PTX诱导的热痛觉过敏在第2天至第4天达到峰值，但未观察到冷异常性疼痛；鞘内注射N-甲基-D-天冬氨酸（NMDA）受体拮抗剂D-2-氨基-5-磷酸戊酸（D-AP5）、甘氨酸和蛋白激酶C（PKC）抑制剂白屈菜红碱可减轻热痛觉过敏。PTX处理的大鼠突触体和胞质部分的PKCγ含量均显著增加。相比之下，这些部分中PKCα、βI或βII同工酶的水平未受影响。注入NMDA拮抗剂D-AP5可预防PTX处理的大鼠的热痛觉过敏和PKCγ表达的增加。与我们之前的报告相似鞘内注射PTX降低了吗啡的镇痛作用。PKC抑制剂白屈菜红碱减弱了吗啡镇痛作用的这种降低，并且在PTX处理的大鼠中也观察到对吗啡诱发的EAA释放的抑制。综上所述，鞘内注射PTX诱导的神经病理性疼痛综合征伴有EAA增加、IAA释放减少以及脊髓中PKCγ表达的选择性增加。抑制PKC不仅阻断了热痛觉过敏，还逆转了PTX处理大鼠中吗啡镇痛作用的降低。这些结果表明，PTX诱导的神经病理性疼痛综合征与EAA、IAA和PKC的变化有关。
