Faculty of Dentistry, University of Toronto, 124 Edward Street, Toronto, ON, Canada M5G 1G6.
Neuroscience. 2011 Sep 29;192:721-31. doi: 10.1016/j.neuroscience.2011.06.083. Epub 2011 Jul 14.
Central sensitization is a crucial process underlying the increased neuronal excitability of nociceptive pathways following peripheral tissue injury and inflammation. Our previous findings have suggested that extracellular adenosine 5'-triphosphate (ATP) molecules acting at purinergic receptors located on presynaptic terminals (e.g., P2X2/3, P2X3 subunits) and glial cells are involved in the glutamatergic-dependent central sensitization induced in medullary dorsal horn (MDH) nociceptive neurons by application to the tooth pulp of the inflammatory irritant mustard oil (MO). Since growing evidence indicates that activation of P2X7 receptors located on glia is involved in chronic inflammatory and neuropathic pain, the aim of the present study was to test in vivo for P2X7 receptor involvement in this acute inflammatory pain model. Experiments were carried out in anesthetized Sprague-Dawley male rats. Single unit recordings were made in MDH functionally identified nociceptive neurons for which mechanoreceptive field, mechanical activation threshold and responses to noxious stimuli were tested. We found that continuous intrathecal (i.t.) superfusion over MDH of the potent P2X7 receptor antagonists brilliant blue G and periodated oxidized ATP could each significantly attenuate the MO-induced MDH central sensitization. MDH central sensitization could also be produced by i.t. superfusion of ATP and even more effectively by the P2X7 receptor agonist benzoylbenzoyl ATP. Superfusion of the microglial blocker minocycline abolished the MO-induced MDH central sensitization, consistent with reports that dorsal horn P2X7 receptors are mostly expressed on microglia. In control experiments, superfusion over MDH of vehicle did not produce any significant changes. These novel findings suggest that activation of P2X7 receptors in vivo may be involved in the development of central sensitization in an acute inflammatory pain model.
中枢敏化是外周组织损伤和炎症后伤害性通路神经元兴奋性增加的关键过程。我们之前的研究结果表明，位于突触前末梢（例如 P2X2/3、P2X3 亚基）和神经胶质细胞上的细胞外三磷酸腺苷（ATP）分子通过作用于炎性刺激物芥末油（MO）作用于牙髓时，可导致脊髓背角（MDH）伤害性神经元中的谷氨酸能依赖性中枢敏化，这些分子通过作用于嘌呤能受体而参与其中。由于越来越多的证据表明，位于神经胶质细胞上的 P2X7 受体的激活参与慢性炎症性和神经性疼痛，因此本研究旨在体内检测 P2X7 受体在这种急性炎症性疼痛模型中的作用。实验在麻醉的 Sprague-Dawley 雄性大鼠中进行。在 MDH 中功能性鉴定为伤害感受神经元，对其进行机械感受野、机械激活阈值和伤害性刺激反应测试，然后进行单细胞记录。我们发现，持续鞘内（i.t.）灌流 MDH 中的强效 P2X7 受体拮抗剂亮蓝 G 和碘化过氧 ATP 均可显著减弱 MO 诱导的 MDH 中枢敏化。i.t. 灌流 ATP 甚至 P2X7 受体激动剂苯甲酰苯甲酰基 ATP 也可产生 MDH 中枢敏化。微胶质细胞阻断剂米诺环素的灌流消除了 MO 诱导的 MDH 中枢敏化，这与背角 P2X7 受体主要表达在小胶质细胞上的报道一致。在对照实验中，MDH 上灌流载体未产生任何显著变化。这些新发现表明，体内 P2X7 受体的激活可能参与了急性炎症性疼痛模型中中枢敏化的发展。
