General and variable features of varicosity spacing along unmyelinated axons in the hippocampus and cerebellum
General and variable features of varicosity spacing along unmyelinated axons in the hippocampus and cerebellum
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DOI：
10.1073/pnas.052151299
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发表时间：
2002-04-30
影响因子：
11.1
通讯作者：
Andersen, P
中科院分区：
文献类型：
--
作者：
Shepherd, GMG;Raastad, M;Andersen, P
沿着无髓鞘的中央轴突，突触发生在称为轴突静脉曲张（终扣）的局灶性轴突上。调节突触和静脉曲张沿着轴突发生频率的机制仍然知之甚少。在这里，调查静脉曲张的分布模式和在何种程度上，他们可以在不同的轴突保守，我们分析了静脉曲张的数量和位置沿着荧光标记的轴突分支在海马区CA 1（CA 3-CA 1“谢弗侧支”轴突）和其他5个突触区域的大鼠海马和小脑。静脉曲张间距因区域而异;例如，3.7 CA 3-至-CA 1轴突为+/- 0.6 μ m（平均值+/- SD），小脑平行纤维为5.2 +/- 1.0 μ m。令人惊讶的是，当来自这些不同区域的56个轴突被汇集到一个单一的异质组中时，出现了一个一般的关系：间距变异性（SD）是平均间距的恒定分数，这表明沿着不同轴突的变异性以基本相似的比例方式分布。静脉曲张间距既不规则也不随机，但遵循的模式与随机突触分布和多突触扣的发生一致。一个定量模型再现了数据的显着特点，并区分两个拟议的机制轴突形态发生和突触。
Along unmyelinated central axons, synapses occur at focal swellings called axonal varicosities (boutons). The mechanisms regulating how frequently synapses and varicosities occur along axons remain poorly understood. Here, to investigate varicosity distribution patterns and the extent to which they may be conserved across different axons, we analyzed varicosity numbers and positions along fluorescently labeled axon branches in hippocampal area CA1 (CA3-to-CA1 "Schaffer collateral" axons) and five other synaptic regions of rat hippocampus and cerebellum. Varicosity spacing varied by region; e.g., 3.7 +/- 0.6 mum (mean +/- SD) for CA3-to-CA1 axons and 5.2 +/- 1.0 mum for cerebellar parallel fibers. Surprisingly, when 56 axons from these different regions were pooled into a single heterogeneous group, a general relationship emerged: the spacing variability (SD) was a constant fraction of the mean spacing, suggesting that varicosities along different axons are distributed in a fundamentally similar, scaled manner. Varicosity spacing was neither regular nor random but followed a pattern consistent with random synaptic distributions and the occurrence of multiple-synapse boutons. A quantitative model reproduced the salient features of the data and distinguished between two proposed mechanisms relating axonal morphogenesis and synaptogenesis.