吗啡对新生期大鼠脊髓背角长时程增强的作用

Effect of Morphine on Synaptic Long-Term Potentiation in Spinal Dorsal Horn Evoked by Electric Stimulation of Sciatic Nerve in Neonatal Rats

目的:评价吗啡对电刺激坐骨神经诱发新生期大鼠脊髓背角浅层长时程增强(LTP)的影响。方法:雄性SD大鼠20只,日龄18-21d,体重60-65g,随机分为对照组、吗啡组(M组)、纳洛酮组(N组),纳洛酮+吗啡组(MN组),每组8例。麻醉下分离左侧坐骨神经,记录电极插于左侧T13-L1脊髓背角浅层,刺激电极刺激左侧坐骨神经,给予4V、0.5ms、1/60Hz单个方波电刺激30min以诱发场电位,抽取生理盐水10μl、吗啡10μl(15μg/μl)、纳洛酮10μl(2.5μg/μl)、纳洛酮(2.5μg/μl)和吗啡(15μg/μl)各5μl的混合液,在脊髓上方3mm,经2min内缓慢滴注,给药后5min时,给予4串条件电刺激(8V、0.5ms、100Hz、串长1s、串间隔10s)后,再给予单个方波电刺激120min以上,记录强直刺激前30min、条件电刺激后0-30,35-60,65-120min时段平均场电位幅值及潜伏期。结果:与强直刺激前30min比较,C组和N组A类特征的波在强直刺激后各时段平均场电位幅值升高,潜伏期缩短,M组A类特征的波在强直刺激后各时段平均场电位幅值降低,潜伏期延长,MN组A类特征的波在强直刺激后0-30min平均场电位幅值升高,潜伏期缩短,35-120min时段平均场电位幅值降低,潜伏期延长,以上P<0.05或0.01,C类特征的波在刺激前后变化不明显。结论:吗啡可抑制电刺激新生期大鼠坐骨神经诱发脊髓背角以A类特征波的突触LTP,可能是其所处神经发育阶段决定的。

Objective. To evaluate the effect of morphine on synaptic long-term potentiation（LTP） in the spinal dorsal horn evoked by electric stimulation of sciatic nerve in neonate rats. Methods, Twen- ty healthy male SD rats aged 18-21 days weighing 60-65 g were randomly divided into control group （group C, n=8）, morphine group （group M, n=8）, naloxone group （group N, n=8）, and morphineq-naloxone group （group MN, n=8）. The animals were anesthetized, intubated, and then mechanically ventilated. The bipolar insulated stainless steel recording electrode was in- serted into the left side of the spinal dorsal horn at T13 to L1 to stimulate the left side of the sci- atic nerve. Single square pulse （4 V, 0.5 ms, 1/60 Hz for 30 min） was applied to evoke spinal field potentials. Normal saline 10 ml, morphine 10 gl （15μg/μl）, naloxone 10 μl （2.5μg/μl）, and the mixture of naloxone 5 /al （2.5 μg/μl） and morphine 5 /,1 （15 μg/μl） was gradually in- stilled over 2 min in the four groups respectively. Five minutes later, high-frequency stimulation was used to induce LTP. Then single aqnare stimuli （8 V, 5 ms, 1/60 Hz） were applied to the sciatic never for 120 min. The amplitude and latency period of the field potential were recorded 30 min before tetanic stimulation, and 0-30 min, 35-60 min, 65-120 min respectively after tetanic stimulation. Results： Compared with that respectively in group C, the amplitude of the field po- tential was significantly decreased and the latency period was prolonged in group M and MN dur- ing 35-60 min and 65-120 min, but there was no significant difference in the above indices between group N and C. Compared with that respectively in group M, the amplitude of the field potential was significantly increased and the latency period shortened during 0-60 min of group MN. Conclusion： Morphine can inhibit synaptic LTP in the spinal dorsal horn evoked by electric stimu- lation of sciatic nerve in neonatal rats during their neurodevelopmental stage.