Experience-dependent GluR trafficking in visual cortex

尽管视觉体验在视觉皮层的正常和病理发育中具有重要意义，但视觉活动诱导皮层突触功能长期变化的分子机制尚未明确。哺乳动物视觉皮层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。作为突触谷氨酸释放的主要效应器，突触后谷氨酸受体（GluRs）数量和/或功能的变化可能会显著影响突触强度。本研究采用双眼和单眼剥夺模式来调节大鼠视觉皮层突触连接的强度，并验证了经验诱导的突触强度增加是由GluRs的传递介导的，而剥夺诱导的突触强度下降是由于突触GluRs的去除。GluR水平的分析是在突触体中进行的，这是一种亚细胞部分，富含完整的、代谢活跃的谷氨酸突触。通过观察突触eurosomal GluRs的水平与突触GluRs的生理和药理学反应特性的变化高度相关，并且实际上可以高度预测突触强度的变化，揭示了这一过程的力量。突触蛋白合成在突触GluR水平长期依赖维持中的作用也将在体内和体外分离代谢活跃的突触中进行研究。突触GluR组成的双向、活动依赖控制将代表发育中的视觉皮层突触疗效调节的新机制，并确定药物干预的潜在靶点（GluR或GluR转运蛋白），特别是在严重的、治疗抵抗性弱视的情况下。

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.