Department of Neurobiology and Behavior, Gunma University Graduate School of Medicine, Maebashi 371-8511, Japan.
Neuroscience. 2010 Sep 15;169(4):1489-500. doi: 10.1016/j.neuroscience.2010.06.043. Epub 2010 Jun 25.
Glutamatergic synapses form onto both glutamatergic and GABAergic neurons. These two types of glutamatergic synapses differ in their electrical responses to high-frequency stimulation and postsynaptic density protein composition. However, it is not known whether they differ in the actin cytoskeleton composition. In the present study, we used hippocampal neuronal cultures prepared from glutamate decarboxylase 67 (GAD67)-GFP knock-in mice and analyzed the differences in the actin cytoskeleton at glutamatergic synapses contacting GABAergic and glutamatergic neurons. Drebrin-binding actin filaments enriched in dendritic spines are known to play a pivotal role in spine formation. Immunocytochemical analyses demonstrated that drebrin accumulated at glutamatergic synapses on GABAergic neurons as well as at those on glutamatergic neurons. However, the density of drebrin clusters along dendrites in GABAergic neurons was significantly lower than those of glutamatergic neurons. Furthermore, the level of drebrin accumulating at glutamatergic synapses was lower on GABAergic neurons than on glutamatergic neurons. In neurons overexpressing drebrin, drebrin cluster density and accumulation levels in GABAergic and glutamatergic neurons were similar, suggesting that the low drebrin levels in the glutamatergic postsynaptic sites on GABAergic neurons may be because GABAergic neurons express low levels of drebrin. On the other hand, pharmacological analysis demonstrated that the postsynaptic localization of drebrin depended on actin cytoskeleton organization in both GABAergic and glutamatergic neurons. Together these results indicated that, although GABAergic and glutamatergic neurons share common regulatory systems affecting drebrin localization, the density of drebrin-positive glutamatergic synapses formed on GABAergic neurons is lower than those on glutamatergic neurons. This is probably due to the low expression of drebrin in GABAergic neurons.
谷氨酸能突触形成于谷氨酸能和 GABA 能神经元上。这两种类型的谷氨酸能突触在高频刺激和突触后密度蛋白组成方面的电反应不同。然而，目前尚不清楚它们在肌动蛋白细胞骨架组成上是否存在差异。在本研究中，我们使用谷氨酸脱羧酶 67 (GAD67)-GFP 敲入小鼠制备的海马神经元培养物，并分析了与 GABA 能和谷氨酸能神经元接触的谷氨酸能突触处肌动蛋白细胞骨架的差异。已知富含 drebrin 的肌动蛋白纤维在树突棘形成中发挥关键作用。免疫细胞化学分析表明，drebrin 聚集在 GABA 能神经元上的谷氨酸能突触以及谷氨酸能神经元上的谷氨酸能突触上。然而，GABA 能神经元中沿着树突的 drebrin 簇密度明显低于谷氨酸能神经元。此外，在 GABA 能神经元上谷氨酸能突触处积累的 drebrin 水平低于谷氨酸能神经元。在过度表达 drebrin 的神经元中，GABA 能和谷氨酸能神经元中 drebrin 簇密度和积累水平相似，表明 GABA 能神经元上谷氨酸能突触处 drebrin 水平较低可能是因为 GABA 能神经元表达低水平的 drebrin。另一方面，药理学分析表明，drebrin 的突触后定位取决于 GABA 能和谷氨酸能神经元中肌动蛋白细胞骨架的组织。这些结果表明，尽管 GABA 能和谷氨酸能神经元共享影响 drebrin 定位的共同调节系统，但形成于 GABA 能神经元上的 drebrin 阳性谷氨酸能突触的密度低于谷氨酸能神经元。这可能是由于 GABA 能神经元中 drebrin 的低表达所致。
