Regulatory mechanisms on the postsynaptic receptor sensitivity

突触的可塑性部分是由突触后受体的变化产生的。在这个项目中，我们试图阐明突触后受体敏感性变化的机制。首先，我们发现突触后密度(PSD)部分的AMPA受体可以钙和钙调蛋白依赖的方式被磷酸化，这支持了AMPA受体的磷酸化参与了突触效能的长时程增强的表达的假说。接下来，我们通过将膜片钳技术应用于NMDA受体亚单位被基因靶向消融的小鼠，研究了NMDA受体亚单位在小脑颗粒细胞中的作用。我们发现，epsilon1亚基有助于缩短NMDA受体介导的突触电流，而epsilon3亚基降低NMDA受体对镁阻滞剂的敏感性，从而两者都有助于形成成熟的突触后受体。关于海马区的NMDA受体，我们发现epsilon 2亚单位在新生动物Schaffer Colatral-CA1锥体突触的长期抑郁(LTD)的形成中起着至关重要的作用。最后，我们检测了蛋白激酶C(PKC)激动剂对斜方体内侧核听觉中继神经元记录的EPSCs的影响。佛波醇酯PDBu通过贴片吸管注入神经元，可显著增强NMDA受体介导的EPSCs，而不影响AMPA受体介导的EPSCs。佛波酯的这种作用不是由于镁的解封。我们认为，PKC激活对NMDA-EPSCs的增强作用可能有助于LTP的诱导。

Synaptic plasticity is produced in part by changes in postsynaptic receptors. In this project, we attempted to elucidate a mechanism underlying changes in postsynaptic receptor sensitivity. First we found that AMPA receptor in the postsynaptic density (PSD) fraction can be phosphorylated in a Ca and calmodulin-dependent manner, supporting the hypothesis that phosphorylation of AMPA receptor is involved in the expression of long-term potentiation of synaptic efficacy in hippocampus. We next addressed a role of NMDA receptor subunits in cerebellar granule cells by applying patch clamp techniques to the mice with their NMDA receptor subunits ablated by gene targeting. We found that epsilonl subunit contributes to shortening of NMDA receptor-mediated synaptic currents, whereas epsilon3 subunit reduces the sensitivity of NMDA rcceptor to Mg block, thereby both contributing to form mature postsynaptic rcceptors. About NMDA receptors in hippocampus, we have found that epsilon2 subunit play a crucial role in the formation of long-term depression (LTD) at the Schaffer collatral-CA1 pyramidal synapses in neonatal animals. Lastly, we tested the effect of the protein kinase C (PKC) activator on EPSCs recorded from thc auditory relay neuron in the medial nucleus of trapezoid body. A phorbol ester PDBu applied into the neuron through patch pipette perfusion greatly augmented the NMDA receptor-mediated EPSCs without affecting the AMPA rcceptor-mediated ones. This effect of phorbol ester was not due to the Mg unblock. We suggest that potentiation of NMDA-EPSCs by PKC activation would contribute to the induction of LTP.