Hauser Jessica L, Liu Xiaojin, Litvina Elizabeth Y, Chen Chinfei
Department of Neurology, F. M. Kirby Neurobiology Center, Children's Hospital, Boston, Massachusetts; and Program in Neuroscience, Harvard Medical School, Boston, Massachusetts.
Department of Neurology, F. M. Kirby Neurobiology Center, Children's Hospital, Boston, Massachusetts; and Program in Neuroscience, Harvard Medical School, Boston, Massachusetts
J Neurophysiol. 2014 Oct 1;112(7):1714-28. doi: 10.1152/jn.00451.2014. Epub 2014 Jun 25.
The retinogeniculate synapse, the connection between retinal ganglion cells (RGC) and thalamic relay neurons, undergoes robust changes in connectivity over development. This process of synapse elimination and strengthening of remaining inputs is thought to require synapse specificity. Here we show that glutamate spillover and asynchronous release are prominent features of retinogeniculate synaptic transmission during this period. The immature excitatory postsynaptic currents exhibit a slow decay time course that is sensitive to low-affinity glutamate receptor antagonists and extracellular calcium concentrations, consistent with glutamate spillover. Furthermore, we uncover and characterize a novel, purely spillover-mediated AMPA receptor current from immature relay neurons. The isolation of this current strongly supports the presence of spillover between boutons of different RGCs. In addition, fluorescence measurements of presynaptic calcium transients suggest that prolonged residual calcium contributes to both glutamate spillover and asynchronous release. These data indicate that, during development, far more RGCs contribute to relay neuron firing than would be expected based on predictions from anatomy alone.
视网膜-膝状体突触，即视网膜神经节细胞（RGC）与丘脑中继神经元之间的连接，在发育过程中其连接性会发生显著变化。这种突触消除以及剩余输入增强的过程被认为需要突触特异性。在此我们表明，谷氨酸溢出和异步释放是这一时期视网膜-膝状体突触传递的显著特征。未成熟的兴奋性突触后电流呈现出缓慢的衰减时间进程，对低亲和力谷氨酸受体拮抗剂和细胞外钙浓度敏感，这与谷氨酸溢出一致。此外，我们发现并表征了一种来自未成熟中继神经元的新型、纯粹由溢出介导的AMPA受体电流。这种电流的分离有力地支持了不同RGC终扣之间存在溢出。另外，对突触前钙瞬变的荧光测量表明，延长的残余钙对谷氨酸溢出和异步释放都有作用。这些数据表明，在发育过程中，对中继神经元放电有贡献的RGC数量比仅根据解剖学预测所预期的要多得多。
