Owens D F, Boyce L H, Davis M B, Kriegstein A R
Department of Neurology, College of Physicians and Surgeons of Columbia University, New York, New York 10025, USA.
J Neurosci. 1996 Oct 15;16(20):6414-23. doi: 10.1523/JNEUROSCI.16-20-06414.1996.
Gramicidin perforated-patch-clamp recordings in brain slices were used to obtain an accurate assessment of the developmental change in the GABAA receptor reversal potential (EGABAA) in embryonic and early postnatal rat neocortical cells including neuroepithelial precursor cells, cortical plate neurons, and postnatal neocortical neurons. Our results demonstrate that there is a progressive negative shift in EGABAA with the most positive values found in the youngest cortical precursor cells. At the early stages of neocortical development, EGABAA is determined by the chloride (Cl-) gradient, and the internal chloride concentration ([Cl-]i) decreases with development. EGABAA is positive to the resting potential, indicating that GABA serves to depolarize developing neocortical cells. Consistent with this conclusion, GABAA receptor activation with muscimol was found-to increase the internal calcium concentration ([Ca2+]i) in both embryonic and early postnatal neocortical cells through the activation of voltage-gated calcium channels (VGCCs). Postnatal cells exhibit spontaneous postsynaptic synaptic currents, which are eliminated by bicuculline methiodide (BMI) but not glutamate receptor antagonists and reverse at the Cl- equilibrium potential. Likewise, brief spontaneous increases in [Ca2+]i, sensitive to BMI and TTX, are observed at the same ages, suggesting that endogenous synaptic GABAA receptor activation can depolarize cells and activate VGCCs. These results suggest that GABAA receptor-mediated depolarization may influence early neocortical developmental events, including neurogenesis and synaptogenesis, through the activation of Ca(2+)-dependent signal transduction pathways.
采用脑片上的短杆菌肽穿孔膜片钳记录技术，对胚胎期和出生后早期大鼠新皮质细胞（包括神经上皮前体细胞、皮质板神经元和出生后新皮质神经元）中γ-氨基丁酸A受体（GABAA受体）反转电位（EGABAA）的发育变化进行了准确评估。我们的结果表明，EGABAA呈逐渐负向偏移，在最年幼的皮质前体细胞中发现其值最为正向。在新皮质发育的早期阶段，EGABAA由氯离子（Cl-）梯度决定，且细胞内氯离子浓度（[Cl-]i）随发育而降低。EGABAA相对于静息电位为正，这表明γ-氨基丁酸（GABA）可使发育中的新皮质细胞去极化。与这一结论一致的是，发现用蝇蕈醇激活GABAA受体会通过激活电压门控钙通道（VGCCs）来增加胚胎期和出生后早期新皮质细胞内的钙浓度（[Ca2+]i）。出生后的细胞表现出自发性突触后突触电流，该电流可被甲磺酸荷包牡丹碱（BMI）消除，但不能被谷氨酸受体拮抗剂消除，且在Cl-平衡电位处反转。同样，在相同年龄段观察到对BMI和河豚毒素（TTX）敏感的[Ca2+]i短暂自发性升高，这表明内源性突触GABAA受体激活可使细胞去极化并激活VGCCs。这些结果表明，GABAA受体介导的去极化可能通过激活钙（Ca2+）依赖的信号转导途径影响早期新皮质发育事件，包括神经发生和突触形成。
