Hua Xiao-Ying, Svensson Camilla I, Matsui Tomohiro, Fitzsimmons Bethany, Yaksh Tony L, Webb Michael
Department of Anaesthesiology, University of California-San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0818, USA.
Eur J Neurosci. 2005 Nov;22(10):2431-40. doi: 10.1111/j.1460-9568.2005.04451.x.
Activation of p38 mitogen-activated protein kinase (p38) in spinal microglia is implicated in spinal nociceptive processing. Minocycline, a tetracycline derivative, displays selective inhibition of microglial activation, a function that is distinct from its antibiotic activity. In the present study we examined antinociceptive effects of intrathecal (IT) administration of minocycline in experimental models of inflammation-evoked hyperalgesia in addition to the effect of minocycline on stimulation-induced activation of p38 in spinal microglia. Intrathecal minocycline produced a dose-dependent reduction of formalin-evoked second-phase flinching behaviour in rats, and prevented thermal hyperalgesia induced by carrageenan injection into the paw. In contrast, systemic delivery (intraperitoneally) of minocycline inhibited the first but not the second phase of formalin-induced flinching, and it had no effect on carrageenan-induced hyperalgesia. Centrally mediated hyperalgesia induced by IT delivery of N-methyl-d-aspartate was completely blocked by IT minocycline. An increase in phosphorylation (activation) of p38 (P-p38) was observed in the dorsal spinal cord after carrageenan paw injection, assessed by both Western blotting and immunohistochemistry. The increased P-p38 immunoreactivity was seen primarily in microglia but also in a small population of neurons. Minocycline, at the IT dose that blocked carrageenan-induced hyperalgesia, also attenuated the increased P-p38 in microglia. In addition, minocycline suppressed lipopolysaccharide-evoked P-p38 in cultured spinal microglial cells. Taken together, these findings show that minocycline given IT produces a potent and consistent antinociception in models of tissue injury and inflammation-evoked pain, and they provide strong support for the idea that this effect is mediated by direct inhibition of spinal microglia and subsequent activation of p38 in these cells.
脊髓小胶质细胞中p38丝裂原活化蛋白激酶（p38）的激活与脊髓伤害性信息处理有关。米诺环素是一种四环素衍生物，可选择性抑制小胶质细胞激活，该功能与其抗菌活性不同。在本研究中，我们除了研究米诺环素对脊髓小胶质细胞中刺激诱导的p38激活的影响外，还在炎症诱发痛觉过敏的实验模型中研究了鞘内注射米诺环素的镇痛作用。鞘内注射米诺环素可使大鼠福尔马林诱发的第二相缩腿行为呈剂量依赖性减少，并预防角叉菜胶注射到爪部引起的热痛觉过敏。相比之下，米诺环素全身给药（腹腔注射）可抑制福尔马林诱导缩腿的第一相而非第二相，且对角叉菜胶诱导的痛觉过敏无影响。鞘内注射N-甲基-D-天冬氨酸诱导的中枢介导痛觉过敏被鞘内注射米诺环素完全阻断。通过蛋白质免疫印迹法和免疫组织化学评估发现，角叉菜胶注射爪部后，背侧脊髓中p38的磷酸化（激活）增加。p38免疫反应性增加主要见于小胶质细胞，但也见于少量神经元。在阻断角叉菜胶诱导的痛觉过敏的鞘内注射剂量下，米诺环素也减弱了小胶质细胞中p38的增加。此外，米诺环素抑制培养的脊髓小胶质细胞中脂多糖诱发的p38。综上所述，这些发现表明，鞘内注射米诺环素在组织损伤和炎症诱发疼痛的模型中产生强大且持续的镇痛作用，为这种作用是由直接抑制脊髓小胶质细胞并随后激活这些细胞中的p38介导的这一观点提供了有力支持。
