Hayasaki H, Sohma Y, Kanbara K, Maemura K, Kubota T, Watanabe M
Department of Anatomy, Osaka Medical College, Takatsuki, Osaka 569-8686, Japan.
Eur J Neurosci. 2006 Feb;23(3):745-57. doi: 10.1111/j.1460-9568.2006.04602.x.
We investigated the GABAergic system within the Sprague-Dawley rat (2-3-weeks old) trigeminal ganglion (TG). Reverse transcription-polymerase chain reaction (RT-PCR) analysis revealed expression of glutamate decarboxylase (GAD) 65 and GAD67 mRNAs and mRNAs encoding GABA(A) receptor subunits alpha1-6, beta1-3, gamma1-3, and delta. In situ hybridization revealed that GAD65 and GAD67 mRNAs were expressed in neuronal cell bodies but not satellite cells. Immunohistochemical analysis showed that only GAD65 was expressed in all neuronal cell bodies, and approximately 70% of all neurons exhibited GABA immunoreactivity. Satellite cells were strongly immunopositive for GABA. GABA(A) receptor alpha1, alpha5, beta2/3 and gamma1/2/3 subunit immunoreactivities were observed in the majority of neurons, but no immunoreactivity for alpha2 was observed. Two types of cells were identified in TG based on cell size and morphology, type A and B. The percentage of cells expressing alpha3, alpha4, alpha6, and delta subunits appeared to be dependent on cell size, as delta and alpha6 expression were only observed in small (B-type) neurons. In whole-cell patch clamp experiments, GABA application induced inward Cl- currents in all neurons examined. The EC50 for GABA varied from 5.3 to 240 microm, and the Hill Coefficient (nH) varied between 0.98 and 2.6 at -60 mV. We found that GABA was released from TG cells by increasing extracellular K+ concentration to 100 mm. We speculate that GABA acts as a nonsynaptically released diffusible neurotransmitter, which may modulate somatic inhibition of neurons within the TG.
我们研究了2至3周龄的Sprague-Dawley大鼠三叉神经节（TG）内的GABA能系统。逆转录-聚合酶链反应（RT-PCR）分析显示，谷氨酸脱羧酶（GAD）65和GAD67 mRNA以及编码GABA(A)受体亚基α1-6、β1-3、γ1-3和δ的mRNA均有表达。原位杂交显示，GAD65和GAD67 mRNA在神经元细胞体中表达，但在卫星细胞中不表达。免疫组织化学分析表明，只有GAD65在所有神经元细胞体中表达，并且约70%的神经元表现出GABA免疫反应性。卫星细胞对GABA呈强免疫阳性。在大多数神经元中观察到GABA(A)受体α1、α5、β2/3和γ1/2/3亚基的免疫反应性，但未观察到α2亚基的免疫反应性。根据细胞大小和形态，在三叉神经节中鉴定出两种类型的细胞，即A型和B型。表达α3、α4、α6和δ亚基的细胞百分比似乎取决于细胞大小，因为仅在小（B型）神经元中观察到δ和α6的表达。在全细胞膜片钳实验中，施加GABA可在所有检测的神经元中诱导内向Cl-电流。在-60 mV时，GABA的半数有效浓度（EC50）在5.3至240 μmol之间，希尔系数（nH）在0.98至2.6之间。我们发现，将细胞外K+浓度提高到100 mmol/L可使GABA从三叉神经节细胞中释放出来。我们推测，GABA作为一种非突触释放的可扩散神经递质，可能调节三叉神经节内神经元的躯体抑制。
