Johnston Ian N, Westbrook R Frederick
Department of Psychology, University of Colorado, Campus Box 0345, Boulder, CO 80309, USA.
Behav Brain Res. 2004 May 5;151(1-2):151-8. doi: 10.1016/j.bbr.2003.08.022.
Intraperitoneal (i.p.) administration of lithium chloride (LiCl) has two effects on pain sensation: (1) it induces a transient hyperalgesia that is reversed by intracerebroventricular (i.c.v.) or intrathecal (i.t.) administration of the opioid receptor antagonist naloxone or by peripheral administration of the quaternary compound naloxone methiodide [Behav. Neurosci. 114 (2000) 1183]; (2) it produces a long-lasting (24 h) reduction in morphine analgesia and does so in the absence of hyperalgesia [Behav. Brain Res. 142 (2003) 89]. We confirmed that rats administered with LiCl showed a reduction in analgesia when administered morphine 24 h later. We also found that morphine analgesia was restored if LiCl had been preceded by i.p. or i.c.v. administration of naloxone or by i.p. administration of naloxone methiodide. However, i.p. administration of naloxone methiodide prior to testing 24 h after an injection with LiCl did not restore morphine analgesia. Thus, activity at peripheral and central opioid receptors is necessary for the inhibition of morphine analgesia by LiCl, but peripheral opioid receptors are not critical for the expression of this inhibition.
腹腔注射氯化锂（LiCl）对痛觉有两种影响：（1）它会诱发短暂的痛觉过敏，脑室内（i.c.v.）或鞘内（i.t.）注射阿片受体拮抗剂纳洛酮或外周注射季铵化合物甲碘化纳洛酮可逆转这种痛觉过敏[《行为神经科学》114（2000）1183]；（2）它会使吗啡镇痛作用持续长时间（24小时）降低，且在没有痛觉过敏的情况下发生[《行为脑科学研究》142（2003）89]。我们证实，腹腔注射LiCl的大鼠在24小时后注射吗啡时镇痛作用降低。我们还发现，如果在腹腔注射LiCl之前先进行腹腔或脑室内注射纳洛酮或腹腔注射甲碘化纳洛酮，吗啡镇痛作用会恢复。然而，在注射LiCl 24小时后进行测试前腹腔注射甲碘化纳洛酮并不能恢复吗啡镇痛作用。因此，外周和中枢阿片受体的活性对于LiCl抑制吗啡镇痛作用是必需的，但外周阿片受体对于这种抑制作用的表达并不关键。
