ACTIVITY-DEPENDENT DISINHIBITION .3. DESENSITIZATION AND GABAB RECEPTOR-MEDIATED PRESYNAPTIC INHIBITION IN THE HIPPOCAMPUS INVITRO
ACTIVITY-DEPENDENT DISINHIBITION .3. DESENSITIZATION AND GABAB RECEPTOR-MEDIATED PRESYNAPTIC INHIBITION IN THE HIPPOCAMPUS INVITRO
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DOI：
10.1152/jn.1989.61.3.524
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发表时间：
1989-03-01
影响因子：
2.5
通讯作者：
GAHWILER, BH
中科院分区：
文献类型：
--
作者：
THOMPSON, SM;GAHWILER, BH
从器官型海马切片培养物中的CA 3锥体细胞进行单电极电压钳记录，用于测量γ-β细胞和海马细胞的膜电流。氨基丁酸（GABA）介导的，Cl-依赖性抑制性突触后电位（IPSC），诱发响应苔藓纤维通路的刺激，和响应离子电渗应用GABA。研究了介导IPSC（gIPSC）电导的活性依赖性降低的突触前和突触后机制。在99秒的应用GABA，平均诱发电导（gGABA）下降43%，初始时间常数为51秒。脱敏从未完成。在细胞内Cs+存在下，用100 ms至15 s持续时间的去极化电压命令激活的Ca 2+内流对GABA反应没有影响。离子电渗应用GABAA受体激动剂蝇蕈醇引起去极化膜电位（Vm）诱发的IPSC振幅迅速下降80-100%。在30 s内恢复80%。蝇蕈醇的两个配对应用中的第二个，以相同的离子电渗强度递送，振幅降低35%。这被证明是由于减少驱动力，而不是从脱敏。我们得出结论，蝇蕈醇减少IPSCs引起细胞内Cl-浓度的增加。GABAB-受体激动剂（. ±.）-的离子电渗应用巴氯芬引起在去极化Vms诱发的IPSC的振幅仅降低30%。这种效应持续时间超过巴氯芬的突触后效应;在60和90秒之间恢复完成80%。发现（-）-巴氯芬的浴施降低gIPSC而不影响IPSC逆转电位。这种作用开始迅速，在低至1 × 10 - 6的浓度下就可以观察到。10-7 M，恢复得很快。EC 50约为5倍。10-7 M和出现类似的，在突触后电导的baclitazone激活的增加。未观察到对离子电渗施加的GABA的响应的影响，表明巴氯芬通过减少经由GABAB受体的突触前释放来降低gIPSC。GABA的离子电渗应用以剂量依赖性方式减少IPSC。在低离子电渗强度下，IPSC仅减少30%并且恢复缓慢，与巴氯芬离子电渗一样。在更高的离子电渗强度，IPSCs被更完全地阻断。恢复最初很快，但需要60-90秒才能完成。第二个两对离子电渗应用GABA的幅度相对于第一个大离子电渗电流强度，但低离子电渗强度不变。在较高的离子电渗强度的第二个脉冲的幅度降低被证明是由于在驱动力的减少，而不是从脱敏。我们的结论是，GABA可以减少IPSCs的GABAB受体介导的突触前抑制释放在低浓度和GABAA受体介导的增加[Cl-]i在较高浓度。这些机制可以解释重复刺激对GABA能抑制的影响。
Single-electrode voltage-clamp recordings were made from CA3 pyramidal cells in organotypic hippocampal slice cultures for measurement of membrane currents underlying both the .gamma.-aminobutyric acid (GABA)-mediated, Cl--dependent inhibitory postsynaptic potential (IPSC), evoked in response to stimulation of the mossy fiber pathway, and responses to iontophoretically applied GABA. Pre- and postsynaptic mechanisms mediating activity-dependent reductions in the conductance underlying the IPSC (gIPSC) were investigated. During 99-s applications of GABA, the mean evoked conductance (gGABA) decreased 43% with an initial time constant of 51 s. Desensitization was never complete. Ca2+-influx, activated with depolarizing voltage commands of 100-ms to 15-s duration in the presence of intracellular Cs+, had no effect on GABA responses. Iontophoretic application of the GABAA-receptor agonist muscimol caused a rapid decrease of 80-100% in the amplitude of IPSCs evoked at depolarized membrane potentials (Vm). Recovery was 80% complete in 30 s. The second of two paired applications of muscimol, delivered at the same iontophoretic intensity, was reduced in amplitude 35%. This was shown to result from a decrease in driving force rather than from desensitization. We conclude that muscimol decreases IPSCs by causing an increase in the intracellular Cl- concentration. Ionotophoretic application of the GABAB-receptor agonist (.+-.)-baclofen caused a decrease of only 30% in the amplitude of IPSCs evoked at depolarized Vms. This effect outlasted the postsynaptic effects of baclofen; recovery was 80% complete between 60 and 90 s. Bath application of (-)-baclofen was found to decrease gIPSC without affecting the IPSC reversal potential. This effect was rapid in onset, could be observed at concentrations as low as 1 .times. 10-7 M, and recovered quickly. For EC50 was roughly 5 .times. 10-7 M and appeared similar, to that for the baclofen-activated increase in postsynaptic conductance. No effect on responses to iontophoretically applied GABA was observed, demonstrating that baclofen decreases gIPSC by reducing presynaptic release via GABAB receptors. Ionotophoretic application of GABA reduced IPSCs in a dose-dependent manner. At low iontophoretic intensities, IPSCs were reduced only 30% and recovered slowly, as with baclofen iontophoresis. At higher iontophoretic intensities, IPSCs were more completely blocked. Recovery was initially fast, but took 60-90 s to be complete. The second of two paired iontophoretic application of GABA was reduced in amplitude relative to the first for large iontophoretic current intensities, but was unchanged for low iontophoretic intensities. The decreased amplitude of the second pulse at higher iontophoretic intensities was shown to result from a decrease in driving force and not from desensitization. We conclude that GABA can decrease IPSCs by both a GABAB receptor-mediated presynaptic inhibition of release at low concentrations and by a GABAA receptor-mediated increase in [Cl-]i at higher concentrations. These mechanisms can account for the effects of repetitive stimulation on GABAergic inhibition.