Thurston C L, Starnes A, Randich A
Department of Biomedical Sciences, University of South Alabama, Mobile 36688.
Brain Res. 1993 May 28;612(1-2):70-7. doi: 10.1016/0006-8993(93)91645-9.
The present study shows that intravenous (i.v.) administration of morphine produces dose-dependent increases in tail flick and hot plate latencies in conscious rats. I.v. morphine also decreased heart rate, but had no significant effects on arterial blood pressure. Transection of the right vagus at the cervical level or pre-treatment with the peripherally acting opioid receptor antagonist naloxone methobromide attenuated the increased tail flick latency produced by either 1.75 or 2.5 mg/kg morphine. In addition, either right vagotomy or naloxone methobromide attenuated the increased hot plate latency produced by 1.75 mg/kg of morphine but not by 2.5 mg/kg of morphine. Following pre-treatment with naloxone methobromide, 1.75 and 2.5 mg/kg of morphine produced a small pressor response 1-3 min after injection. The bradycardia produced by 1.75 mg/kg of morphine was attenuated by naloxone methobromide, but not by right vagotomy. The bradycardia produced by 2.5 mg/kg of morphine was attenuated by either naloxone methobromide or vagotomy. These data obtained in the conscious rat are similar to previous reports using pentobarbital-anesthetized rats except for the following: (i) the dose-response function for inhibition of the tail flick was shifted to the right in conscious rats, (ii) the depressor response to morphine observed in anesthetized rats was attenuated in conscious rats, (iii) following naloxone methobromide, but not unilateral vagotomy, i.v. morphine produced a pressor response in the conscious rat, and (iv) unilateral vagotomy was not as effective in attenuating the antinociception and bradycardia in conscious rats as bilateral vagotomy is in pentobarbital-anesthetized rats.
本研究表明，静脉注射吗啡可使清醒大鼠的甩尾和热板潜伏期呈剂量依赖性增加。静脉注射吗啡还可降低心率，但对动脉血压无显著影响。在颈部水平切断右侧迷走神经或用外周作用的阿片受体拮抗剂甲溴纳洛酮预处理，可减弱1.75或2.5mg/kg吗啡引起的甩尾潜伏期增加。此外，右侧迷走神经切断术或甲溴纳洛酮可减弱1.75mg/kg吗啡引起的热板潜伏期增加，但不能减弱2.5mg/kg吗啡引起的热板潜伏期增加。用甲溴纳洛酮预处理后，1.75和2.5mg/kg的吗啡在注射后1 - 3分钟产生轻微的升压反应。1.75mg/kg吗啡引起的心动过缓可被甲溴纳洛酮减弱，但不能被右侧迷走神经切断术减弱。2.5mg/kg吗啡引起的心动过缓可被甲溴纳洛酮或迷走神经切断术减弱。在清醒大鼠中获得的这些数据与先前使用戊巴比妥麻醉大鼠的报告相似，但有以下不同：(i)清醒大鼠中抑制甩尾的剂量反应函数向右移动；(ii)麻醉大鼠中观察到的吗啡降压反应在清醒大鼠中减弱；(iii)用甲溴纳洛酮预处理后，静脉注射吗啡在清醒大鼠中产生升压反应，而单侧迷走神经切断术则不会；(iv)单侧迷走神经切断术在减弱清醒大鼠的抗伤害感受和心动过缓方面不如双侧迷走神经切断术在戊巴比妥麻醉大鼠中有效。
