Zeng X, Tietz E I
Department of Pharmacology, Medical College of Ohio, Toledo 43699-0008, USA.
Synapse. 1997 Feb;25(2):125-36. doi: 10.1002/(SICI)1098-2396(199702)25:2<125::AID-SYN3>3.0.CO;2-E.
GABAergic synaptic responses were studied by direct, monosynaptic activation of GABAergic interneurons in the CA1 region of in vitro hippocampal slices from rats made tolerant to the benzodiazepine, flurazepam. Monosynaptic IPSPs were elicited in CA1 pyramidal neurons, following 1 week oral flurazepam administration, by electrical stimulation at the stratum oriens/stratum pyramidale or stratum radiatum/ stratum-lacanosum border < or = 0.5 mm from the recording electrode plane. Excitatory input to pyramidal cells and interneurons was eliminated by prior superfusion of the glutamate receptor antagonists, APV (50 microM) and DNQX (10 microM). GABAA receptor-mediated early IPSPs were further isolated by perfusion of the GABAB antagonist, CGP 35348 (25 microM) or by diffusion of Cs- from the recording electrode. GABAB receptor-mediated late IPSPs were pharmacologically isolated by perfusion of the GABAA antagonist, picrotoxin (50 microM). There was a significant decrease in the amplitude of pharmacologically isolated early and late IPSPs in FZP-treated neurons without a change in passive membrane properties. A shift of the early IPSP, but not the late IPSP, reversal potential in FZP-treated neurons suggested that a change in the driving force for anions, presumably Cl, in CA1 neurons was one important factor related to the decreased early IPSP amplitude after prolonged activation of GABAA receptors by flurazepam. A decreased early IPSP amplitude accompanied by a decreased late IPSP amplitude suggested that presynaptic GABA release onto FZP-treated pyramidal cells may also be reduced. We conclude from these data that an impairment of GABAergic transmission in CA1 pyramidal neurons associated with the development of tolerance during chronic benzodiazepine treatment may be related to the regulation of both pre- and postsynaptic mechanisms at the GABA synapse.
通过直接、单突触激活来自对苯二氮䓬氟西泮产生耐受性的大鼠的体外海马切片CA1区的GABA能中间神经元，研究了GABA能突触反应。在口服氟西泮1周后，通过在距记录电极平面≤0.5mm的海马齿状回原层/锥体层或辐射层/腔隙下层边界处进行电刺激，在CA1锥体神经元中诱发单突触抑制性突触后电位（IPSPs）。通过预先灌注谷氨酸受体拮抗剂APV（50μM）和DNQX（10μM），消除了对锥体细胞和中间神经元的兴奋性输入。通过灌注GABAB拮抗剂CGP 35348（25μM）或通过从记录电极扩散Cs+，进一步分离出GABAA受体介导的早期IPSPs。通过灌注GABAA拮抗剂印防己毒素（50μM），从药理学上分离出GABAB受体介导的晚期IPSPs。在氟西泮处理的神经元中，药理学分离的早期和晚期IPSPs的幅度显著降低，而被动膜特性没有变化。氟西泮处理的神经元中早期IPSPs的反转电位发生了偏移，但晚期IPSPs没有，这表明CA1神经元中阴离子（可能是Cl-）驱动力的变化是与氟西泮长期激活GABAA受体后早期IPSP幅度降低相关的一个重要因素。早期IPSP幅度降低伴随着晚期IPSP幅度降低，这表明向氟西泮处理的锥体细胞的突触前GABA释放可能也减少了。从这些数据中我们得出结论，慢性苯二氮䓬治疗期间与耐受性发展相关的CA1锥体神经元中GABA能传递受损可能与GABA突触处突触前和突触后机制的调节有关。
