Itier V, Granger P, Perrault G, Depoortere H, Scatton B, Avenet P
Synthélabo Recherche, Central Nervous System Research Department, Bagneux, France.
J Pharmacol Exp Ther. 1996 Dec;279(3):1092-9.
Tolerance to benzodiazepines (BZs) is thought to involve alterations of the gamma-aminobutyric acid (GABA)A receptor as a result of the prolonged occupancy of its modulatory BZ recognition site. We used the whole-cell patch-clamp technique to compare the functional and pharmacological properties of GABAA receptors in acutely dissociated hippocampal neurons from the control or diazepam-tolerant rats. Administration of diazepam (15 mg/kg p.o.) twice a day for 10 days induced tolerance as demonstrated by the decreased potency of acute diazepam i.p. injections to protect against pentylenetetrazole-induced clonictonic convulsions (10.5% of tolerant rats protected by 0.1 mg/kg of diazepam against 55% of nontreated rats, 48 hr after the last dose of the chronic treatment). The specific current induced by 1 microM GABA in acutely dissociated hippocampal neurons 48 hr after withdrawal (10.5 +/- 1.3 microA/cm2) was similar to that observed in the control rats (8.7 +/- 0.8 microA/cm2). The EC50 value for GABA was unchanged by the chronic treatment [6.3 (5.4-7.1) and 7.5 (6.2-8.7) microM in neurons from the control and treated rats, respectively]. The potency of the nonselective allosteric modulator diazepam to stimulate Cl- currents was identical in cells from treated rats [EC50 values of 25 (20-30) and 34 (26-41) nM in the control and treated rats, respectively; P < .05], but the potency of the selective BZ1-site ligand zolpidem was decreased [EC50 values of 99 (88-111) and 267 (221-313) nM in the control and treated rats, respectively; P < .05]. The maximal potentiation of the GABA-induced current was significantly decreased with diazepam (maximal potentiation: 168.0 +/- 16.2 and 124.0 +/- 8.9% in the control and treated rats, respectively). These results suggest that tolerance to diazepam is accompanied in hippocampal neurons by a decrease in BZ1 binding sites and in the functional coupling of BZ/GABA recognition sites.
苯二氮䓬（BZs）耐受性被认为是由于其调节性BZ识别位点长期被占据，导致γ-氨基丁酸（GABA）A受体发生改变。我们使用全细胞膜片钳技术，比较了来自对照或地西泮耐受大鼠的急性分离海马神经元中GABAA受体的功能和药理学特性。每天两次给予地西泮（15mg/kg口服），持续10天可诱导耐受性，末次慢性给药后48小时，腹腔注射急性地西泮预防戊四氮诱导的阵挛性惊厥的效力降低可证明这一点（0.1mg/kg地西泮保护10.5%的耐受大鼠，而未处理大鼠的保护率为55%）。撤药后48小时，急性分离海马神经元中1μM GABA诱导的特异性电流（10.5±1.3μA/cm2）与对照大鼠中观察到的电流（8.7±0.8μA/cm2）相似。慢性处理后GABA的EC50值未改变（对照大鼠和处理大鼠神经元中分别为6.3（5.4 - 7.1）和7.5（6.2 - 8.7）μM）。非选择性变构调节剂地西泮刺激Cl-电流的效力在处理大鼠的细胞中相同（对照大鼠和处理大鼠中EC50值分别为25（20 - 30）和34（26 - 41）nM；P <.05），但选择性BZ1位点配体唑吡坦的效力降低（对照大鼠和处理大鼠中EC50值分别为99（88 - 111）和267（221 - 313）nM；P <.05）。地西泮使GABA诱导电流的最大增强显著降低（最大增强：对照大鼠和处理大鼠中分别为168.0±16.2%和124.0±8.9%）。这些结果表明，海马神经元对地西泮的耐受性伴随着BZ1结合位点的减少以及BZ/GABA识别位点的功能偶联的降低。
