Takayama Chitoshi, Inoue Yoshiro
Department of Molecular Neuroanatomy, Hokkaido University School of Medicine, Kita-15 Nishi-7, Kita-Ku, Sapporo 060-8638, Japan.
Brain Res Dev Brain Res. 2005 Aug 8;158(1-2):41-9. doi: 10.1016/j.devbrainres.2005.05.007.
In the brain, gamma-amino butyric acid (GABA), released extrasynaptically and synaptically from GABAergic neurons, plays important roles in morphogenesis, expression of higher functions and so on. In the GABAergic transmission system, plasma membrane GABA transporters (GATs) mediate GABA-uptake from the synaptic cleft in the mature brain and are thought to mediate diacrine of cytosolic GABA in the immature brain. In the present study, we focused on two GATs (GAT-1 and GAT-3) in the mouse cerebellar cortex, which are widely localized in neural and glial cells. Firstly, we examined the localization of GATs in the dendrites and cell bodies of developing GABAergic neurons, where GABA is extrasynaptically distributed, to clarify the GABA-diacrine before synaptogenesis. Secondly, we examined the developmental changes in the localization of GATs to reveal the development of the GABA-uptake system. Neither transporter was detected within the dendrites and cell bodies of GABAergic neurons, including Purkinje, stellate, basket and Golgi cells, in the immature cerebellar cortex. GAT-1 was observed within the Golgi cell axon terminals after postnatal day 5 (P5) and presynaptic axons of stellate and basket cells after P7. GAT-3 was localized within the astrocyte processes, sealing the GABAergic synapses in the Purkinje cell and granular layers after P10. These results indicated that GABA-diacrine did not work in the mouse cerebellar cortex. The onset of GAT-1-expression was prior to that of GAT-3. GAT-1 started to be localized within the GABAergic axon terminals during synapse formation. GAT-3 started to be localized within astrocyte processes when they sealed the synapses.
在大脑中，γ-氨基丁酸（GABA）从GABA能神经元以突触外和突触方式释放，在形态发生、高级功能表达等方面发挥重要作用。在GABA能传递系统中，质膜GABA转运体（GATs）介导成熟大脑中突触间隙GABA的摄取，并被认为介导未成熟大脑中胞质GABA的旁分泌。在本研究中，我们聚焦于小鼠小脑皮质中的两种GATs（GAT-1和GAT-3），它们广泛定位于神经细胞和神经胶质细胞中。首先，我们检查了发育中的GABA能神经元的树突和细胞体中GATs的定位，GABA在这些部位以突触外方式分布，以阐明突触形成前的GABA旁分泌。其次，我们检查了GATs定位的发育变化，以揭示GABA摄取系统的发育。在未成熟的小脑皮质中，在包括浦肯野细胞、星状细胞、篮状细胞和高尔基细胞在内的GABA能神经元的树突和细胞体内均未检测到这两种转运体。出生后第5天（P5）后在高尔基细胞轴突终末观察到GAT-1，P7后在星状细胞和篮状细胞的突触前轴突中观察到GAT-1。P10后GAT-3定位于星形胶质细胞突起内，封闭浦肯野细胞和颗粒层中的GABA能突触。这些结果表明，GABA旁分泌在小鼠小脑皮质中不起作用。GAT-1的表达开始时间早于GAT-3。在突触形成过程中，GAT-1开始定位于GABA能轴突终末内。当星形胶质细胞突起封闭突触时，GAT-3开始定位于其突起内。
