Exploration of endogenous novel ligands for glutamate receptors with a high sub-type specificities

在本研究项目中，我们获得了以下两个关于中枢氨基酸信号系统机制的发现：谷氨酸转运体在小脑中的特异性表达--脑组织中的Na^+依赖性、“高亲和力”的L-谷氨酸（GluT）转运已成为人们关注的焦点，特别是因为已经发现GluT异常可能与严重的神经系统疾病有关。使用定量放射自显影，我们研究了放射性配体结合位点的分布和药理学特征的底物识别/结合位点上的谷氨酸。我们测定<50>了非放射性对应物抑制[^3H]L-和[^3H]D-Asp结合的IC_值。这两种放射性配体在与前脑结合位点的相互作用中没有明显的差异，这与前脑中所有Na^+依赖性GluT结合位点没有立体选择性一致。 ...更多信息 或天冬氨酸对映体。然而，在小脑皮质中，数据表明存在一个GluT结合位点，该位点优选L-而不是D-天冬氨酸。这些发现与许多以前在小脑皮质的研究结果形成对比。一种新的中枢神经系统L-丝氨酸转运体--L-丝氨酸（Ser）可诱导突触后抑制电位，但其神经传递机制尚不清楚。我们在这里发现了一种新的高亲和力摄取活性的L-Ser在大鼠脑。其中一半不依赖于Na^+浓度，它由两个以上不同的转运系统组成。根据这些发现和本研究项目的其他结果，强烈建议除了经典的神经活性氨基酸外，D-Asp和L-Ser也在神经传递中发挥作用。少

In this research project we obtained two findings on the mechanism of central amino acids-signaling system as follows:Expression specifically in cerebellum of glutamate transporters with stereo-selectivity - The Na^+-dependent, "high-affinity" transport of L-glutamate (GluT) in brain tissue has become a significant focus of interest, particularly since it has been revealed that abnormalities of GluT may be associated with serious neurological disorders. Using quantitative autaradiography, we have studied the distribution and pharmacology of radioligand binding to sites with characteristics of the substrate-recognition/binding locus on GluT. We have determined IC_<50> values for the inhibition of [^3H]L- and [^3H]D-Asp binding by their non-radioactive counterparts. The two radioligands did not appreciably differ from each other in then interactions with the binding sites in the forebrain, consistent with all Na^+-dependent GluT binding sites in that region having no stereo-selectivity f … More or aspartate enantiomers. In the cerebellar cortex, however, the data indicated the presence of a GluT binding site mat preferred L- over D-aspartate. These findings contrast with many previous in cerebellar cortex. A possibility of an existence of hitherto unknown molecules with properties of a glutamate transporter should be considered.A novel L-serine transporters in central nervous system-It was reported that L-serine (Ser) induces postsynaptic inhibitory potentials; however, little is elucidated about the mechanism of its neuro-transmission. We found here a novel high affinity uptake activity for L-Ser in rat brain. A half of that is not dependent on Na^+ concentration and it was composed by more than two different transporters systems. Pharmacological characteristics of that was distinct from known amino acid transportersAccording to these findings and other results in this research project, it is strongly suggested that D-Asp and L-Ser play a role for neuronal transmission beside classical neuroactive amino acids. Less