脊髓水平细胞外信号调节激酶激活参与吗啡依赖的形成及戒断反应的表达

在大鼠吗啡依赖和戒断模型上,采用行为学、免疫组织化学和Western blot方法观察吗啡依赖及戒断大鼠脊髓神经元磷酸化细胞外信号调节激酶（phospho-extracellular signal-regulated kinase,pERK）表达的变化,及鞘内注射促分裂原活化蛋白激酶激酶（mitogen-activated protein kinase kinase,MEK）抑制剂U0126或ERK反义寡核苷酸对吗啡依赖大鼠纳洛酮催促戒断反应、触诱发痛及脊髓神经元pERK表达的影响,探讨脊髓水平pERK在介导吗啡依赖和戒断过程中的作用。结果显示：（1）在吗啡依赖形成过程中,大鼠脊髓胞浆与胞核非磷酸化ERK表达没有改变,但pERK表达逐渐增加,纳洛酮催促戒断后,仍有进一步增加的趋势,戒断1h后,其表达量明显下降,但仍高于对照组。（2）鞘内预先注射MEK抑制剂U0126或ERK反义寡核苷酸能明显抑制吗啡戒断反应和戒断引起的痛觉异常;与行为学结果一致,脊髓背角pERK阳性神经元表达与脊髓胞浆和胞核pERK表达也明显降低。上述结果提示,脊髓水平ERK激活和核转位参与吗啡依赖的形成及戒断反应的表达。

Activation of the spinal extracellular signal-regulated kinase is involved in morphine dependence and naloxone-precipitated withdrawal response

Extracellular signal-regulated kinase (ERK),a mitogen-activated protein kinase (MAPK), transduces a broad range of extracellular stimuli into diverse intracellular responses. It has been reported that ERK is involved in the modulation of nociceptive information and central sensitization produced by intense noxious stimuli or peripheral tissue inflammation. Our previous studies showed that the spinal neurons sensitization was involved in morphine withdrawal response. This study was to investigate the role of the spinal ERK in morphine dependence and naloxone-precipitated withdrawal response. To set up morphine-dependent model, rats were subcutaneously injected with morphine (twice a day, for 5 d). The dose of morphine was 10 mg/kg on the first day and was increased by 10 mg/kg each day. On day 6,4 h after the injection of morphine (50 mg/kg), morphine withdrawal syndrome was precipitated by an injection of naloxone (4 mg/kg, i.p.). Using anti-phospho-ERK (pERK) antibody, the time course of pERK expression was detected by Western blot. U0126, a mitogen-activated protein kinase kinase (MEK) inhibitor, or phosphorothioate-modified antisense oligonucleotides (ODN) was intrathecally injected 30 min or 36, 24 and 12 h before naloxone-precipitated withdrawal. The scores of morphine withdrawal symptom and morphine withdrawal-induced allodynia were observed. One hour after naloxone-precipitated withdrawal, pERK expression in the spinal dorsal horn was assessed by immunohistochemical analysis and Western blot was used to detect the expression of cytosolic and nuclear fraction of pERK in the rat spinal cord. The results showed that the expression of cytosolic and nuclear fraction of pERK, not non-phospho-ERK, in the spinal cord was gradually increased following the injection of morphine. When morphine withdrawal was precipitated with naloxone, the expression of the spinal pERK further increased. Intrathecal administration of U0126 or antisense ODN against ERK decreased the scores of morphine withdrawal, attenuated morphine withdrawalinduced allodynia and also inhibited the increase of pERK expression in the spinal cord of morphine withdrawal rats. These results suggest that activation of the spinal ERK is involved in morphine-dependent and naloxone-precipitated withdrawal response.