吗啡对电刺激坐骨神经诱发大鼠脊髓背角突触长时程增强的影响

Effect of morphine on synaptic long-term potentiation in spinal dorsal horn evoked by electric stimulation of sciatic nerve in rats

目的评价吗啡对电刺激坐骨神经诱发大鼠脊髓背角突触长时程增强（LTP）的影响。方法雄性SD大鼠27只，日龄60～90d，体重180～200g，随机分为4组：对照组（C组，n=7）、吗啡组（M组，n=7）、纳洛酮组（N组，n=6），纳洛酮＋吗啡组（MN组，n=7）。麻醉下分离左侧坐骨神经，记录电极插入左侧T13～L1脊髓背角，刺激电极刺激左侧坐骨神经，给予15V、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3～5mm，经2min内缓慢滴注，给药后5min时，给予4串高频高强度强直电刺激后，再给予15V、0．5ms、1／60Hz单个方波电刺激210min，记录强直刺激前30min、强直刺激后即刻～30min、35～60min、65～120min、125～210min时段平均场电位幅值及潜伏期。结果与C组比较，M组和MN组平均场电位幅值降低，潜伏期延长（P〈0．05或0．01），N组上述指标差异无统计学意义（P〉0，05）。与M组比较，MN组平均场电位幅值升高，潜伏期缩短（P〈0．05或0．01）。与强直刺激前30min比较，C组和N组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组在强直刺激后即刻-30min和35～60min时段平均场电位幅值升高，强直刺激后即刻～30min时段潜伏期缩短，65～120min和125-210min时段平均场电位幅值降低，潜伏期延长（P〈0．05或0．01）。结论吗啡可抑制电刺激坐骨神经诱发大鼠脊髓背角突触LTP，可能是其抑制中枢敏化的机制之一。

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 rats. Methods Twenty-seven healthy male SD rats aged 60-90 d weighing D80-200 g were randomly divided into 4 groups： group Ⅰ control （group C, n = 7）, group Ⅱ morphine （group M, n = 7）, group Ⅲ naloxone （group N, n = 6）, and group Ⅳ morphine ＋ naloxone （group MN, n = 7）. The animals were anesthetized with intraperitoneal 10% urethane 1 g/kg, intubated and then mechanically ventilated. The bipolar insulated stainless steel recording electrode （impedance 0.5-1 MΩ, diameter 0.1 mm） was inserted into the left side of the spinal dorsal horn at T13 -L1 to stimulate the left side of the sciatic nerve. Single square pulses （D5 V, 0.5 ms, 1/60 Hz for 30 min） was applied to evoke spinal field potentials. Normal saline 10μl, morphine 10 μl （15 μg/μl）, naloxone 10μl （2.5 μg/μl）, and the mixture 10 μl of naloxone 5 μl （2.5 μg/μl） and morphine 5 μl （ 15 μg/μl） was gradually instilled over 2 min in the 4 groups respectively. Five minutes later, high-frequency and intensity tetanic stimulation （30-40 V, 0.5 ms, 100 Hz, given in 4 trains of 1-s duration at 10-s intervals） was used to induce LTP. Then single square stimuli （15 V, 5 ms, 1/60 Hz） were applied to the sciatic nerve for 210 min. The amplitude and latency period of the field potential were recorded 30 min before tetanic stimulation, and 0-30, 35-60, 65-120 and 125-210 min after titanic stimulation. Results Compared with group C, the amplitude of the field potential was significantly decreased and the latency period prolonged in group M and MN, but there was no significant difference in the above indices between group N and C. Compared with group M, the amplitude of the field potential was significantly increased and the latency period shortened in group MN. Compared with those 30 min before the tetanic stimulation, the amplitude of the field potential was significantly increased and latency period shorted at the time points after the tetanic stimulation in group C and N, the amplitude of the field potential was significantly decreased and latency period prolonged at the time points after the tetanic stimulation in group M, and the amplitude of the field potential was significantly increased 0-30 and 35-60 min after the tetanic stimulation and latency period shortened 0-30 min after the tetanic stimulation, the amplitude of the field potential was significantly decreased and latency period prolonged 65-120 and 125-210 min after the tetanic stimulation in group MN. Conclusion Morphine can inhibit synaptic LTP in the spinal dorsal horn evoked by electric stimulation of sciatic nerve in rats, and it may be one of the mechanisms of the central sensitization inhibition.