• Yan-li Zhu, Ming-juan Liu, Hua-dong Ni, Ming Yao, Bing Huang, Xu-yan Zhou, Jian-liang Sun, and Qing-quan Lian.
• Department of Anesthesiology, Wenzhou Medical College, China.
• Zhonghua Yi Xue Za Zhi. 2012 Oct 23;92(39):2785-8.

ObjectiveTo investigate the role of P2Y12 receptor in rat bone cancer pain model and its influence on p38MAPK (Mitogen-activated protein kinase).MethodA total of forty female SD rats, weighting 200 - 250 g, were randomly divided into 5 groups (n = 8): normal group (group N), sham group (group S), vehicle group (group DA), cancer group (group A), and analgesia group (group MA). Rats in group N were untreated, rats in group S were injected with Hank's solution 10 µl into the left tibial metaphysis; rats in group DA, group A and group MA were injected with Walker 256 cancer cells (10 µl, 2×10⁷ cells/ml) into the left tibial metaphysic to establish the model of bone cancer pain. Catheterization was simultaneously made in four groups between L3 and L4 vertebra except group N. Saline (0.9%, 15 µl) was injected in group S and group A, DMSO (5%, 15 µl) was injected in group DA, and MRS2395 (400 pmol/µl, 15 µl) was injected in group MA on day 9 to 12 post-inoculation. Mechanical withdrawal thresholds were measured on left hind paw before and every 10 min after intrathecal injection. Rats were euthanized after measuring mechanical withdrawal threshold at day 12 post-inoculation. L4-6 sections of spinal cord were collected to determine the expression of p-p38MAPK by immunohistochemistry and immunofluorescent.ResultCompared to that in group N (36.1 g ± 4.0 g) and group S (38.9 g ± 5.2 g), mechanical withdrawal thresholds in group MA (19.8 g ± 5.0 g) were decreased on day 9 post-inoculation (P < 0.01), and the expression of p-p38MAPK in spinal cord was increased on day 12 (P < 0.01). Compared to that in group DA (17.7 g ± 3.0 g) and group A (19.1 g ± 2.5 g), mechanical withdrawal threshold in group MA was obviously increased after intrathecal injection, peaked at (26.5 g ± 4.7 g) (P < 0.05); compared with group DA (number 43.4 ± 3.8, IOD 569 ± 27) and group A(number 45.0 ± 2.6, IOD 594 ± 22), the expression level of p-p38MAPK in spinal cord in group MA at day 12 was significantly decreased (number 20.9 ± 2.2, IOD 246 ± 25) (P < 0.01); Mechanical withdrawal threshold in group MA was still lower than group N and group S, while the expression of p-p38MAPK was higher than group N (number 9.9 ± 2.4, IOD 82 ± 28) and group S (number 10.9 ± 2.2, IOD 109 ± 25) (P < 0.01). Immunofluorescent showed that p-p38MAPK was colocalized with microglia in spinal dorsal horn, but not with neurons and astrocytes.ConclusionsThese results demonstrate rat bone cancer pain could partially relieved after intrathecal injection of P2Y12 receptor inhibitor MRS2395 through inhibiting the phosphorylation of p38MAPK in spinal dorsal horn.

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