Zeng X J, Tietz E I
Department of Pharmacology, Medical College of Ohio, Block Health Science Building, 3035 Arlington Ave., Toledo, OH 43614-5804, USA.
Brain Res. 2000 Jun 23;868(2):202-14. doi: 10.1016/s0006-8993(00)02330-1.
Chronic flurazepam treatment substantially impairs the function of GABAergic synapses on hippocampal CA1 pyramidal cells. Previous findings included a significant decrease in the synaptic and unitary conductance of CA1 pyramidal neuron GABA(A) receptor channels and the appearance of a GABA(A)-receptor mediated depolarizing potential. To investigate the ionic basis of the decreased conductance, whole-cell voltage-clamp techniques were used to record evoked, GABA(A) receptor-mediated IPSCs carried by HCO(3)(-)-Cl(-) or Cl(-) alone. Hippocampal slices were prepared from rats administered flurazepam orally for 1 week, 2 days after ending drug treatment. Slices were superfused with HCO(3)(-)-aCSF or with HEPES-aCSF (without HCO(3)(-)) plus 50 microM APV and 10 microM DNQX. The micropipette contained 130 mM CsCl and 1 microM QX-314. GABA(A) receptors located on pyramidal cell somata or dendrites were activated monosynaptically by maximal stimulation of GABAergic terminals at the stratum oriens-pyramidale (SO-SP) or stratum lacunosum-molecular (S-L-M) border, respectively. In HCO(3)(-)-aCSF, there was a significant reduction in synaptic-conductance in flurazepam-treated neurons following both SO-SP (control: 1058 pS, flurazepam: 226 pS, P<0.01) and S-L-M (control 998 pS, flurazepam: 179 pS, P<0.01) stimulation, as well as the total charge transfer, indicating a decreased HCO(3)(-)-Cl(-) flux. In HEPES-aCSF, the synaptic conductance and total charge transfer, and thus Cl(-) flux, was unchanged in flurazepam-treated neurons (SO-SP: control 588 pS, flurazepam: 580 pS, P>0.05; S-L-M: control 595 pS, flurazepam: 527 pS, P>0.05). Taken together, these findings suggest that a reduction in HCO(3)(-) flux may play a prominent role in mediating the action of GABA and that a loss of HCO(3)(-) conductance may significantly contribute to impaired GABA(A) receptor function after chronic benzodiazepine treatment.
长期使用氟西泮治疗会严重损害海马CA1锥体细胞上GABA能突触的功能。先前的研究结果包括CA1锥体神经元GABA(A)受体通道的突触和单位电导显著降低，以及出现GABA(A)受体介导的去极化电位。为了研究电导降低的离子基础，采用全细胞电压钳技术记录由HCO(3)(-)-Cl(-)或单独的Cl(-)介导的诱发GABA(A)受体介导的抑制性突触后电流（IPSCs）。从口服氟西泮1周的大鼠制备海马切片，在停药治疗2天后取材。切片用HCO(3)(-)-人工脑脊液（aCSF）或用HEPES-aCSF（不含HCO(3)(-)）加50微摩尔APV和10微摩尔DNQX进行灌流。微电极内含有130毫摩尔氯化铯和1微摩尔QX-314。分别通过最大刺激海马伞-锥体层（SO-SP）或腔隙-分子层（S-L-M）边界的GABA能终末，单突触激活位于锥体细胞胞体或树突上的GABA(A)受体。在HCO(3)(-)-aCSF中，在SO-SP（对照组：1058皮秒，氟西泮组：226皮秒，P<0.01）和S-L-M（对照组998皮秒，氟西泮组：179皮秒，P<0.01）刺激后，氟西泮处理的神经元的突触电导均显著降低，以及总电荷转移减少，表明HCO(3)(-)-Cl(-)通量降低。在HEPES-aCSF中，氟西泮处理的神经元的突触电导和总电荷转移，以及因此的Cl(-)通量没有变化（SO-SP：对照组588皮秒，氟西泮组：580皮秒，P>0.05；S-L-M：对照组595皮秒，氟西泮组：527皮秒，P>0.05）。综上所述，这些发现表明HCO(3)(-)通量的降低可能在介导GABA的作用中起重要作用，并且HCO(3)(-)电导的丧失可能在慢性苯二氮䓬治疗后显著导致GABA(A)受体功能受损。
