De Gois Stéphanie, Schäfer Martin K-H, Defamie Norah, Chen Chu, Ricci Anthony, Weihe Eberhard, Varoqui Hélène, Erickson Jeffrey D
Neuroscience Center of Excellence, Louisiana State University Health Sciences Center, New Orleans, Louisiana 70112, USA.
J Neurosci. 2005 Aug 3;25(31):7121-33. doi: 10.1523/JNEUROSCI.5221-04.2005.
Homeostatic control of pyramidal neuron firing rate involves a functional balance of feedforward excitation and feedback inhibition in neocortical circuits. Here, we reveal a dynamic scaling in vesicular excitatory (vesicular glutamate transporters VGLUT1 and VGLUT2) and inhibitory (vesicular inhibitory amino acid transporter VIAAT) transporter mRNA and synaptic protein expression in rat neocortical neuronal cultures, using a well established in vitro protocol to induce homeostatic plasticity. During the second and third week of synaptic differentiation, the predominant vesicular transporters expressed in neocortical neurons, VGLUT1 and VIAAT, are both dramatically upregulated. In mature cultures, VGLUT1 and VIAAT exhibit bidirectional and opposite regulation by prolonged activity changes. Endogenous coregulation during development and homeostatic scaling of the expression of the transporters in functionally differentiated cultures may serve to control vesicular glutamate and GABA filling and adjust functional presynaptic excitatory/inhibitory balance. Unexpectedly, hyperexcitation in differentiated cultures triggers a striking increase in VGLUT2 mRNA and synaptic protein, whereas decreased excitation reduces levels. VGLUT2 mRNA and protein are expressed in subsets of VGLUT1-encoded neocortical neurons that we identify in primary cultures and in neocortex in situ and in vivo. After prolonged hyperexcitation, downregulation of VGLUT1/synaptophysin intensity ratios at most synapses is observed, whereas a subset of VGLUT1-containing boutons selectively increase the expression of VGLUT2. Bidirectional and opposite regulation of VGLUT1 and VGLUT2 by activity may serve as positive or negative feedback regulators for cortical synaptic transmission. Intracortical VGLUT1/VGLUT2 coexpressing neurons have the capacity to independently modulate the level of expression of either transporter at discrete synapses and therefore may serve as a plastic interface between subcortical thalamic input (VGLUT2) and cortical output (VGLUT1) neurons.
锥体神经元放电频率的稳态控制涉及新皮质回路中前馈兴奋和反馈抑制的功能平衡。在此，我们利用一种成熟的体外实验方案诱导稳态可塑性，揭示了大鼠新皮质神经元培养物中囊泡兴奋性（囊泡谷氨酸转运体VGLUT1和VGLUT2）和抑制性（囊泡抑制性氨基酸转运体VIAAT）转运体mRNA及突触蛋白表达的动态缩放。在突触分化的第二和第三周，新皮质神经元中表达的主要囊泡转运体VGLUT1和VIAAT均显著上调。在成熟培养物中，VGLUT1和VIAAT通过延长的活动变化表现出双向且相反的调节。发育过程中的内源性共调节以及功能分化培养物中转运体表达的稳态缩放可能有助于控制囊泡谷氨酸和GABA的填充，并调节功能性突触前兴奋/抑制平衡。出乎意料的是，分化培养物中的过度兴奋会引发VGLUT2 mRNA和突触蛋白的显著增加，而兴奋降低则会使其水平降低。VGLUT2 mRNA和蛋白在我们在原代培养物以及原位和体内新皮质中鉴定出的VGLUT1编码的新皮质神经元亚群中表达。在长时间过度兴奋后，观察到大多数突触处VGLUT1/突触素强度比下调，而一部分含VGLUT1的突触小体选择性增加VGLUT2的表达。活动对VGLUT1和VGLUT2的双向且相反调节可能作为皮质突触传递的正反馈或负反馈调节因子。皮质内共表达VGLUT1/VGLUT2的神经元有能力在离散突触处独立调节任一转运体的表达水平，因此可能作为皮质下丘脑输入（VGLUT2）和皮质输出（VGLUT1）神经元之间的可塑性界面。
