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

在本研究项目中，我们获得了关于中枢氨基酸信号系统机制的两个发现：具有立体选择性的谷氨酸转运体在小脑中的特异性表达-依赖Na^+的l -谷氨酸（GluT）在脑组织中的“高亲和力”转运已成为一个重要的关注焦点，特别是因为已经揭示了GluT的异常可能与严重的神经系统疾病有关。利用定量放射自显影技术，我们研究了放射配体与GluT上具有底物识别/结合位点特征的位点结合的分布和药理学。我们已经确定了非放射性对应物对[^3H]L-和[^3H]D-Asp结合抑制的IC_<50>值。这两种放射性配体在与前脑结合位点的相互作用方面没有明显差异，这与该区域所有依赖Na^+的GluT结合位点对…More或天门草氨酸对映体没有立体选择性一致。然而，在小脑皮层，数据表明存在一个GluT结合位点，它更倾向于L-而不是d -天冬氨酸。这些发现与先前在小脑皮层的许多发现形成对比。应该考虑存在迄今为止未知的具有谷氨酸转运体性质的分子的可能性。一种新型的l -丝氨酸转运体在中枢神经系统中的作用——据报道，l -丝氨酸（Ser）诱导突触后抑制电位；但其神经传递机制尚不清楚。我们在大鼠脑中发现了一种新的高亲和力的l -丝氨酸摄取活性。其中一半不依赖于Na^+浓度它由两种以上不同的转运体系统组成。根据这些发现和本研究项目的其他结果，强烈建议D-Asp和L-Ser在经典神经活性氨基酸的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