Experience-dependent GluR trafficking in visual cortex

尽管视觉体验在视觉皮质的正常和病理发育中具有重要作用，但视觉活动导致皮层突触功能发生长期变化的分子机制尚不清楚。哺乳动物视皮层中兴奋性神经元之间高度可变的突触使用谷氨酸作为神经递质。作为突触释放谷氨酸的主要效应器，突触后谷氨酸受体(GluRs)的数量和/或功能的变化可能会显著影响突触的强度。这一建议使用双眼和单眼剥夺范式来调节大鼠视皮层突触连接的强度，并检验了以下假设：经验诱导的突触强度增加是由GluRs的传递介导的，而剥夺引起的突触强度的下降是由于突触GluRs的移除。Glur水平的分析是在突触神经体中进行的，突触神经体是一种亚细胞成分，富含完整的、代谢活性的谷氨酸能突触。通过观察突触神经体GluR水平与突触GluRs的生理和药理反应特性的变化高度相关，并事实上高度预测突触强度的变化，揭示了这一过程的力量。突触蛋白合成在长期依赖经验维持突触Glur水平中的作用也将在体内和体外的分离代谢活性突触图谱中得到检验。对突触GluR成分的双向、活性依赖的控制将代表着一种新的机制来调节发育中的视皮层的突触效能，并识别潜在的药物干预靶点(Glur或Glur转运蛋白)，特别是在严重的、治疗耐受的弱视的情况下。

Despite the importance of visual experience in the normal and pathological development of the visual cortex, the molecular mechanisms by which visual activity induces long-lasting changes in the function of cortical synapses have not been defined. The highly modifiable synapses between excitatory neurons in the mammalian visual cortex use glutamate as a neurotransmitter. As the primary effectors of synaptic glutamate release, changes in the number and/or function of post-synaptic glutamate receptors (GluRs) are likely to dramatically effect synaptic strength. This proposal uses binocular and monocular deprivation paradigms to regulate the strength of synaptic connections in the rat visual cortex, and tests the hypothesis that an experience-induced increase in synaptic strength is mediated by delivery of GluRs, while a deprivation-induced decrease in synaptic strength is due to the removal of synaptic GluRs. Analysis of GluR levels is performed in synatoneurosomes, a subcellular fraction which is enriched for intact, metabolically active glutamatergic synapses. The power of this procedure is revealed by the observation that levels of synaptoneurosomal GluRs are highly correlated with changes in the physiological and pharmacological response properties of synaptic GluRs, and in fact are highly predictive of changes in synaptic strength. The role of synaptic protein synthesis in the long-term experience- dependent maintenance of synaptic GluR levels will also be examined in vivo, and in isolated metabolically active synaptic profiles in vitro. Bidirectional, activity-dependent control of synaptic GluR composition would represent a novel mechanism for the regulation of synaptic efficacy in the developing visual cortex, and identify potential targets (GluR or GluR trafficking proteins) for pharmacological intervention, especially in the case of severe, therapy-resistant amblyopia.