Jørum E, Shyu B-C
Institute of Neurophysiology, University of Oslo, N-0162 Oslo 1 Norway Department of Physiology, University of Göteborg, S-400 33 GöteborgSweden.
Pain. 1988 Mar;32(3):357-366. doi: 10.1016/0304-3959(88)90048-6.
Several authors claim that analgesia by low-frequency peripheral nerve stimulation (transcutaneously or through inserted needles) depends on the activation of small-diameter A delta afferents. In the present study, a marked increase in pain threshold assessed by the squeak threshold test (vocalization to electric shocks delivered to the tail) was obtained by 2 Hz sciatic or radial nerve low-intensity stimulation, using single pulses. Conduction velocities of the activated nerve fibers ranged between 33.6 and 46.4 m/sec, which is consistent with activation of large afferent A fibers. This analgesic effect was reversed by naloxone (3 mg/kg i.v.). Thus, low-threshold afferents may contribute to the analgesic effect in addition to the previously reported high-threshold induced effect. High-intensity stimulation (5-6 times the threshold for visible muscular twitches), activating small-diameter afferents (A delta fibers) resulted in a decrease in pain threshold. Hyperalgesia also resulted from low-intensity stimulation using trains of pulses. The analgesic or hyperalgesic effects were correlated with the animal's behavior during stimulation. Analgesia was obtained in calm rats, who went to sleep regularly. When the rats showed signs of being distressed, hyperalgesia resulted. These findings may explain the occasional failure to obtain reduction in pain in anxious human patients by peripheral stimulation.
几位作者声称，通过低频外周神经刺激（经皮或通过插入针）产生的镇痛作用取决于小直径Aδ传入神经的激活。在本研究中，使用单脉冲对坐骨神经或桡神经进行2 Hz的低强度刺激，通过尖叫阈值测试（对施加于尾巴的电击发出叫声）评估的疼痛阈值显著增加。被激活的神经纤维的传导速度在33.6至46.4米/秒之间，这与大传入A纤维的激活一致。这种镇痛作用被纳洛酮（3毫克/千克静脉注射）逆转。因此，除了先前报道的高阈值诱导效应外，低阈值传入神经可能也有助于镇痛作用。高强度刺激（可见肌肉抽搐阈值的5 - 6倍）激活小直径传入神经（Aδ纤维）会导致疼痛阈值降低。使用脉冲串进行低强度刺激也会导致痛觉过敏。镇痛或痛觉过敏效应与刺激期间动物的行为相关。在平静且能正常入睡的大鼠中可获得镇痛效果。当大鼠表现出痛苦迹象时，则会产生痛觉过敏。这些发现可能解释了在外周刺激时，焦虑的人类患者偶尔无法减轻疼痛的原因。
