糖皮质激素受体在慢性吗啡耐受大鼠脊髓背角神经元凋亡中的作用

in spinal dorsal horn in chronic morphine tolerant rats

目的 评价糖皮质激素受体在慢性吗啡耐受大鼠脊髓背角神经元凋亡中的作用.方法 鞘内置管成功的健康雄性SD大鼠20只,体重300～350 g,随机分为4组（n=5）：对照组（C组）、慢性吗啡耐受组（M组）、吗啡＋糖皮质激素受体拮抗剂组（MR组）和吗啡＋糖皮质激素受体激动剂组（MD组）分别于8：00和20：00鞘内注射生理盐水10μl、吗啡10μg、吗啡10μg＋RU38486 2μg、吗啡10μg＋地塞米松4μg,连续6 d.于每天8：00给药后30 min行甩尾实验,给药第7天处死大鼠,取L3～L5脊髓行TUNEL染色,光镜下观察脊髓背角神经元的凋亡情况,计算凋亡率.结果 地塞米松、RU38486分别对慢性吗啡耐受的形成起促进、抑制作用.与C组比较,M组和MD组脊髓背角神经元凋亡率升高（P＜0.05）;与M组比较,MR组脊髓背角神经元凋亡率降低,MD组脊髓背角神经元凋亡率升高（P＜0.05）.结论 糖皮质激素受体参与了慢性吗啡耐受形成中大鼠脊髓背角神经元凋亡的过程.

Objective To investigate the role of glucocorticoid receptor （GR） in the induction of neuronal apoptosis in spinal dorsal horn in chronic morphine tolerant rats. Methods Twenty healthy male SD rats weighing 300-350 g in which intrathecal （IT） catheter was successfully implanted without complication were randomized into 4 groups （ n = 5 each）： group Ⅰ control （ group C）;group Ⅱ morphine （ group M ）;group Ⅲ morphine ＋RU38486 （GR antagonist） （group MR） and group Ⅳ morphine ＋ dexamethasone （GR agonist） （group MD）.Normal saline 10 μl, morphine 10 μg, morphine 10 μg ＋ RU38486 2 μg and morphine 10μg ＋ dexamethasone 4 μg were injected IT twice a day at 8：00 and 20：00 for6 consecutive days in group C, M, MR and MD respectively. Tail flick latency （TFL） to a thermal nociceptive stimulus was measured every day at 30 min after IT administration in the morning （8：00）. Hyperalgesia was considered to be a sign of morphine tolerance. The animals were killed at 7 days after IT drug administration. The L3-5 segment of the spinal cord was isolated for determination of neuronal apoptosis in spinal dorsal horn by TUNEL staining. Apoptotic index was calculated （ the number of apoptotic neurons/the total number of neurons × 100% ）. Results TFL was significantly prolonged at day 1 and 3 of IT morphine 10 μg twice a day and returned to baseline at day 5 and 7 indicating morphine tolerance. RU38486 inhibited while dexamethasone enhanced morphine tolerance. IT morphine significantly increased the number of apoptotic neurons in spinal dorsal horn. Morphine-induced neuronal apoptosis was decreased by IT RU38486 and increased by IT dexamethasone. Conclusion Glucocorticoid receptors may be involved in morphine tolerance by inducing neuronal apoptosis in spinal dorsal horn.