Objective: To examine the effect of acetylcholine (ACh) on the electric activities of pain-excitation neurons (PEN) and pain-inhibitation neurons (PIN) in the hippocampal CA1 area of normal rats or morphinistic rats, and to explore the role of ACh in regulation of pain perception in CA1 area under normal condition and morphine addiction.
Methods: The trains of electric impulses applied to sciatic nerve were set as noxious stimulation. The discharges of PEN and PIN in the CA1 area were recorded extracellularly by glass microelectrode. We observed the influence of intracerebroventricular (i.c.v.) injection of ACh and atropine on the noxious stimulation-evoked activities of PEN and PIN in the CA1 area.
Results: Noxious stimulation enhanced the electric activity of PEN and depressed that of PIN in the CA1 area of both normal and addiction rats. In normal rats, ACh decrease the pain-evoked discharge frequency of PEN, while increased the frequency of PIN. These effects reached the peak value at 4 min after injection of ACh. In morphinistic rats, ACh also inhibited the PEN electric activity and potentialized the PIN electric activity, but the maximum effect appeared at 6 min after administration. The ACh-induced responses were significantly blocked by muscarinic receptor antagonist atropine.
Conclusion: Cholinergic neurons and muscarinic receptors in the hippocampal CA1 area are involved in the processing of nociceptive information and they may play an analgesia role in pain modulation. Morphine addiction attenuated the sensitivity of pain-related neurons to the noxious information.
目的: 研究 ACh 对正常大鼠和吗啡成瘾大鼠海马CA1 区痛兴奋神经元(pain-excitation neurons, PEN)和痛抑制神经元(pain-inhibitation neurons, PIN)电活动的影响, 进一步探讨ACh对正常和吗啡成瘾状态下CA1区痛觉调制的作用及机制。
方法: 电刺激坐骨神经作为伤害性电刺激, 在细胞外用?璃微电极记录CA1区PEN和 PIN 的放电, 观察ACh 对正常大鼠和吗啡成瘾大鼠CA1 区PEN 和PIN 电活动的影响。
结果: 伤害性刺激能够增强PEN 的电活动, 而减弱PIN 的电活动。正常大鼠中, ACh 使PEN 的痛诱发放电频率降低, PIN 的放电频率增加; ACh 的作用在注射后4 min 达到峰值。吗啡成瘾大鼠中, ACh 同样也抑制了PEN 的电活动, 兴奋PIN 的电活动, 但是作用的高峰出现在注射后6 min。胆碱能受体拮抗剂阿托品可阻断ACh的作用。
结论: 海马CA1 区内的胆碱能神经元和毒蕈碱受体参与了伤害性信息的处理, 并且起到了镇痛作用。吗啡成瘾可以降低CA1区痛反应神经元对伤害性刺激的敏感性。