Nakamura Kouichi, Watakabe Akiya, Hioki Hiroyuki, Fujiyama Fumino, Tanaka Yasuyo, Yamamori Tetsuo, Kaneko Takeshi
Department of Morphological Brain Science, Graduate School of Medicine, Kyoto University, Kyoto 606-8501, Japan.
Eur J Neurosci. 2007 Dec;26(11):3054-67. doi: 10.1111/j.1460-9568.2007.05868.x.
Vesicular glutamate transporter 1 (VGLUT1) and VGLUT2 show complementary distribution in neocortex; VGLUT1 is expressed mainly in axon terminals of neocortical neurons, whereas VGLUT2 is located chiefly in thalamocortical axon terminals. However, we recently reported a frequent colocalization of VGLUT1 and VGLUT2 at a subset of axon terminals in postnatal developing neocortex. We here quantified the frequency of colocalization between VGLUT1 and VGLUT2 immunoreactivities at single axon terminals by using the correlation coefficient (CC) as an indicator in order to determine the time course and spatial extent of the colocalization during postnatal development of mouse neocortex. The colocalization was more frequent in the primary somatosensory (S1) area than in both the primary visual (V1) and the motor areas; of area S1 cortical layers, colocalization was most evident in layer IV barrels at postnatal day (P) 7 and in adulthood. CC in layer IV showed a peak at P7 in area S1, and at P10 in area V1 though the latter peak was much smaller than the former. These results suggest that thalamocortical axon terminals contained not only VGLUT2 but also VGLUT1, especially at P7-10. Double fluorescence in situ hybridization confirmed coexpression of VGLUT1 and VGLUT2 mRNAs at P7 in the somatosensory thalamic nuclei and later in the thalamic dorsal lateral geniculate nucleus. As VGLUT1 is often used in axon terminals that show synaptic plasticity in adult brain, the present findings suggest that VGLUT1 is used in thalamocortical axons transiently during the postnatal period when plasticity is required.
囊泡型谷氨酸转运体1（VGLUT1）和VGLUT2在新皮层中呈互补分布；VGLUT1主要表达于新皮层神经元的轴突终末，而VGLUT2主要位于丘脑皮质轴突终末。然而，我们最近报道在出生后发育中的新皮层的一部分轴突终末中，VGLUT1和VGLUT2经常共定位。我们在此通过使用相关系数（CC）作为指标，对单个轴突终末处VGLUT1和VGLUT2免疫反应性之间的共定位频率进行了量化，以确定小鼠新皮层出生后发育过程中共定位的时间进程和空间范围。共定位在初级体感（S1）区比在初级视觉（V1）区和运动区更频繁；在S1区皮质层中，共定位在出生后第（P）7天和成年期的IV层桶状结构中最为明显。IV层的CC在S1区于P7出现峰值，在V1区于P10出现峰值，尽管后者的峰值比前者小得多。这些结果表明丘脑皮质轴突终末不仅含有VGLUT2，还含有VGLUT1，尤其是在P7 - 10时。双荧光原位杂交证实了VGLUT1和VGLUT2 mRNA在P7时于体感丘脑核以及之后在丘脑背外侧膝状核中共表达。由于VGLUT1常用于在成体大脑中显示突触可塑性的轴突终末，目前的研究结果表明VGLUT1在出生后需要可塑性的时期在丘脑皮质轴突中短暂使用。
