Contribution of glutamate transporter GLT-1 to removal of synaptically released glutamate in Purkinje cell synapses

在这项研究中，我旨在阐明胶质谷氨酸转运体GLT-1在谷氨酸能突触中的作用。1.比较了野生型(WT)、GLAST(-/-)和GLT-1(-/-)小鼠小脑浦肯野细胞(PC)对平行纤维(CF)刺激诱发的兴奋性突触后电流(EPSCs)的衰减动力学。Cf-EPSCs的衰变时间常数(τ_w)在GLT-1(-/-)小鼠比WT小鼠慢。然而，与τ(-/-)小鼠相比，GLAST_w延长的程度不那么显著。2.GLT-1(-/-)和GLAST(-/-)小鼠在10 nM和100 nM加入有效的神经胶质细胞谷氨酸转运体阻断剂(2S，3S)-3-[3-(4-甲氧基苯甲酰氨基)苯甲氧基]天冬氨酸(PMB-TBOA)后，τ_w值与WT小鼠相当，这使Cf刺激BG引起的谷氨酸转运体电流的幅度分别降低到？81%和？28%。我们的结论是，与GLAST相比，GLT-1在清除Cf-PC突触释放的谷氨酸方面发挥的作用较小。3.药物阻断神经胶质细胞谷氨酸转运体功能导致突触释放的谷氨酸从单个CF端溢出到相邻的PC，这表明胶质谷氨酸转运体是通过防止谷氨酸溢出来维持CFPC突触的一对一关系所必需的。4.在尚未形成谷氨酸突触的新生大鼠海马CA1区神经元中，药物阻断神经胶质细胞谷氨酸转运体可引起NMDA受体激活所介导的自发去极化振荡，提示神经胶质细胞转运体在清除非突触释放的谷氨酸以维持细胞外低浓度谷氨酸的过程中起着关键作用。

In this study, I aimed to clarify roles of glial glutamate transporter GLT-1 in glutamatergic synapses. The results are summarized as follows: 1. We compared the decay kinetics of excitatory postsynaptic currents (EPSCs) in cerebellar Purkinje cells (PCs) evoked by parallel fiber (CF) stimulation among wild-type (WT), GLAST (-/-) and GLT-1 (-/-) mice. The decay time constant of CF-EPSCs (τ_w) in GLT-1 (-/-) mice was slower than that in WT mice. However, the degree of this prolongation of τ_w was less prominent compared to that in GLAST (-/-) mice. 2. The values of τ_w in GLT-1 (-/-) mice and GLAST (-/-) mice were comparable to those estimated in WT mice in the presence of a potent blocker of glial glutamate transporters (2S,3S)-3- [3- (4-methoxybenzoylamino) benzyloxy] aspartate (PMB-TBOA) at 10 nM and 100 nM, which reduced the amplitudes of glutamate transporter currents elicited by CF stimulation in BG to ?81% and ?28%, respectively. We conclude that GLT-1 plays a minor role compared to GLAST in clearing synaptically released glutamate at CF-PC synapses. 3. Pharmacological blockage of glial glutamate transporter functions caused a spillover of synaptically released glutamate from a single CF terminal over to neighboring PCs, indicating that glial glutamate transporters are indispensable to maintain one-to-one relationship at CF-PC synapses by preventing glutamate spillover. 4. In hippocampal CA1 neurons of newborn rats in which the glutamate synapses are not formed yet, pharmacological blockage of glial glutamate transporters caused a spontaneous depolarizing oscillations mediated by activation of NMDA receptors, suggesting that glial transporters play a pivotal role in clearing non-synaptically released glutamate to maintain its extracellular concentration at a low level.