Department of Biological Sciences, Columbia University, New York, New York 10027, USA.
J Comp Neurol. 2011 Dec 15;519(18):3713-26. doi: 10.1002/cne.22684.
Neural connections in the adult nervous system are established with a high degree of precision. Several examples throughout the nervous system indicate that this precision is achieved by first establishing an initial exuberant immature pattern of connectivity that is then sculpted into the adult pattern via pruning. This often emerges as an activity-dependent process. In the olfactory system, sensory axons from neurons expressing the same odorant receptor project with high precision to specific glomerular structures in the olfactory bulb. This process undergoes maturation-dependent refinements that are not fully understood. Due to technical impediments that have made it difficult to focus on single axons, it is unknown whether olfactory sensory projections are established in an exuberant fashion. Here we developed a novel technique of electroporation that allowed us to simultaneously label single olfactory sensory neuron (OSN) axonal arbors and their presynaptic specializations. Using this method we were able to incorporate plasmids into OSNs at an immature stage, thereby allowing a time-course study of axonal arbor development and synapse formation in single olfactory sensory axons. We observed that the number of branch points, the total branch length, and the number and density of presynaptic specializations peaked at postnatal day 8 and decreased afterwards. Our data demonstrate that olfactory sensory axons develop in an exuberant way, both in terms of branch growth and synaptic composition. We hypothesize that exuberant branches and synapses are eliminated to achieve the mature pattern in a process likely to be regulated by neural activity.
成人神经系统中的神经连接具有高度的精确性。神经系统中的几个例子表明，这种精确性是通过首先建立初始过度的不成熟连接模式来实现的，然后通过修剪将其塑造成成人模式。这通常是一个依赖于活动的过程。在嗅觉系统中，表达相同气味受体的神经元的感觉轴突以高精度投射到嗅球中的特定肾小球结构。这个过程经历了成熟依赖性的细化，但尚未完全理解。由于技术障碍使得难以关注单个轴突，因此尚不清楚嗅觉感觉投射是否以过度的方式建立。在这里，我们开发了一种新的电穿孔技术，允许我们同时标记单个嗅觉感觉神经元（OSN）轴突树突及其突触前特化结构。使用这种方法，我们能够在不成熟阶段将质粒掺入 OSN 中，从而可以在单个嗅觉感觉轴突中进行轴突树突发育和突触形成的时程研究。我们观察到分支点的数量、总分支长度以及突触前特化结构的数量和密度在出生后第 8 天达到峰值，然后减少。我们的数据表明，嗅觉感觉轴突以过度的方式发育，无论是在分支生长还是突触组成方面。我们假设过度的分支和突触被消除，以在可能受神经活动调节的过程中实现成熟模式。
