Allan A M, Baier L D, Zhang X
Department of Psychiatry, Washington University School of Medicine, Saint Louis, Missouri.
J Pharmacol Exp Ther. 1992 May;261(2):395-402.
Mice were treated with 4 mg/kg of lorazepam for 7 days via implanted osmotic mini pumps. After chronic drug treatment, brains were assayed for GABA-mediated chloride flux (GABA-Cl-). Compared to control, brain membranes from lorazepam-tolerant mice were resistant to flunitrazepam stimulation of GABA-Cl-. Lorazepam tolerance did not affect [3H]diazepam binding affinity but did lower binding number slightly. Membranes from lorazepam-tolerant mice were cross-tolerant to both ethanol and phenobarbital stimulation of GABA-Cl-. Pentobarbital-stimulation of GABA-Cl- was equivalent in the two treatment groups. An increase in maximum inhibition of chloride flux produced by the benzodiazepine partial inverse agonist, n-methyl-beta-carboline-3-carboxamide (FG-7142) in membranes from lorazepam-tolerant mice was observed. FG-7142 was also found to be a more potent inhibitor of [3H]diazepam binding in membranes from lorazepam-tolerant mice. Withdrawal from chronic treatment by an acute injection with the benzodiazepine antagonist RO-15-1788 (flumazenil), restored functioning of the channel complex to control levels. There were no differences between membranes from control and lorazepam withdrawn mice in stimulation by flunitrazepam, ethanol, phenobarbital and pentobarbital or inhibition by FG-7142 of GABA-Cl-. [3H]Diazepam-saturated binding parameters and inhibition of binding by FG-7142 were similar. Chronic administration of lorazepam reduces the coupling between the benzodiazepine agonist site and the chloride channel and concomitantly increases coupling between the channel and the inverse agonist site. Furthermore, these findings offer neurochemical evidence for cross-tolerance to ethanol and phenobarbital after induction of lorazepam tolerance.
通过植入式渗透微型泵，给小鼠连续7天注射4mg/kg的劳拉西泮。经过长期药物治疗后，对小鼠大脑进行γ-氨基丁酸介导的氯通量（GABA-Cl-）检测。与对照组相比，劳拉西泮耐受小鼠的脑膜对氟硝西泮刺激GABA-Cl-具有抗性。劳拉西泮耐受性不影响[3H]地西泮的结合亲和力，但结合数略有降低。劳拉西泮耐受小鼠的脑膜对乙醇和苯巴比妥刺激GABA-Cl-具有交叉耐受性。两个治疗组中，戊巴比妥刺激GABA-Cl-的效果相当。观察到苯二氮䓬部分反向激动剂n-甲基-β-咔啉-3-甲酰胺（FG-7142）对劳拉西泮耐受小鼠脑膜中氯通量最大抑制作用增加。还发现FG-7142对劳拉西泮耐受小鼠脑膜中[3H]地西泮结合的抑制作用更强。通过急性注射苯二氮䓬拮抗剂RO-15-1788（氟马西尼）撤去长期治疗药物后，通道复合物功能恢复至对照水平。在氟硝西泮、乙醇、苯巴比妥和戊巴比妥刺激或FG-7142对GABA-Cl-的抑制方面，对照组和撤去劳拉西泮小鼠的脑膜之间没有差异。[3H]地西泮饱和结合参数以及FG-7142对结合的抑制作用相似。长期给予劳拉西泮会降低苯二氮䓬激动剂位点与氯通道之间的偶联，并同时增加通道与反向激动剂位点之间的偶联。此外，这些发现为劳拉西泮耐受诱导后对乙醇和苯巴比妥的交叉耐受性提供了神经化学证据。
