代谢型谷氨酸受体5在吗啡耐受大鼠脊髓中的表达

Expression of metabotropic glutamate receptor 5 in spinal cord of morphine tolerant rats

目的研究吗啡耐受大鼠脊髓代谢型谷氨酸受体5（mGluR5）的表达变化及mGluR5拮抗剂MPEP对其表达的影响。方法雄性SD大鼠随机分为4组：对照组（NS），吗啡耐受组（Mor），吗啡加MPEP组（Mor＋MPEP）和MPEP组。采用鞘内重复给药方式建立慢性吗啡耐受模型，鞘内注射吗啡10μg，每日给药2次，连续7d。通过甩尾实验，观察给药前和给药后30min大鼠甩尾潜伏期并计算最大镇痛效应百分比[MPE％=（给药后阈值一基础阈值）／（最大阈值一基础阈值）×100％]。采用免疫荧光和免疫印迹（Westernblot）方法检测并比较各组L4-5,脊髓组织mGluR5的表达。结果鞘内重复注射吗啡后，吗啡组MPE％逐渐下降，到第7天与NS组比较，差异无统计学意义（P〉0．05），吗啡加MPEP组第7天仍表现出较强的镇痛效应（P〈0．05）。免疫荧光和Westernblot显示吗啡耐受组mGluR5表达升高，吗啡加MPEP组mGluR5的表达低于吗啡耐受组（P〈0．05），但高于Ns组（P〈0．05）。结论mGluR5拮抗剂MPEP有延缓吗啡耐受的作用。吗啡耐受大鼠脊髓背角mGluR5表达上调，MPEP可能通过部分抑制mGluR5的上调节拮抗吗啡耐受。

Objective To investigate the expression of metabotropic glutamate receptor 5 （ mGluR5 ） in spinal cord of morphine tolerant rats and understand the influence of mGluR5 antagonist MPEP upon the expression of mGluR5. Methods Male Sprague-Dawley rats were randomly divided into four groups with 8 rats each ：control group （ NS）, morphine group, morphine plus MPEP group and MPEP group. A morphine tolerance model of rat was established by repeated administration of 10 μg morphine intrathecally twice daily for 7 days. The effects of morphine co-administrated with MPEP upon the thermal pain threshold were examined by tail flick test. Tail flick latency （TFL） was measured at 30 min pre- and postdosing. MPE% （percentage of maximal possible effect） was calculated by the equation： MPE （%） = [ （test response time-basal response time）/（cut-off time-basal response time）] × 100%. The rats were sacrificed and L4_5 spinal cord tissue was removed. The expression of mGluR5 in every group was examined by immunofluorescence and Western blot. Results MPE% of morphine group decreased gradually after chronic administration of morphine intrathecally. There was no significant difference between morphine group and control group at Day 7 （ P 〉 0. 05 ）. Morphine plus MPEP group had significant analgesic effect as compared with morphine group at Day 7 （ P 〈 0. 05 ）. The expression of mGluR5 was up-regulated in the dorsal horn of spinal cord in morphine tolerant rats. The protein level of mGluR5 in morphine plus MPEP group was lower than that in morphine group （ P 〈 0. 05 ）, but higher than control group （ P 〈 0. 05 ）. Conclusion The mGluR5 antagonist MPEP can prevent the development of morphine tolerance. The expression of mGluR5 protein increases in the spinal cord of morphine tolerant rats. MPEP plays its role in morphine tolerance by partly inhibiting the expression of mGluR5.