Witte S, Stier H, Cline H T
Department of Physiology & Biophysics, University of Iowa City 52245, USA.
J Neurobiol. 1996 Oct;31(2):219-34. doi: 10.1002/(SICI)1097-4695(199610)31:2<219::AID-NEU7>3.0.CO;2-E.
Changes in neuronal structure can contribute to the plasticity of neuronal connections in the developing and mature nervous system. However, the expectation that they would occur slowly precluded many from considering structural changes as a mechanism underlying synaptic plasticity that occurs over a period of minutes to hours. We took time-lapse confocal images of retinotectal axon arbors to determine the timecourse, magnitude, and distribution of changes in axon arbor structure within living Xenopus tadpoles. Images of axons were collected at intervals of 3 min, 30 min, and 2 h over total observation periods up to 8 h. Branch additions and retractions in arbors imaged at 3 or 30 min intervals were confined to shorter branches. Sites of additions and retractions were distributed throughout the arbor. The average lifetime of branches was about 10 min. Branches of up to 10 microns could be added to the arbor within a single 3 min observation interval. Observations of arbors at 3 min intervals showed rapid changes in the structure of branchtips, including transitions from lamellar growth cones to more streamlined tips, growth cone collaps, and re-extension. Simple branchtips were motile and appeared capable of exploratory behavior when viewed in time-lapse movies. In arbors imaged at 2-h intervals over a total of 8 h, morphological changes included longer branches, tens of microns in length. An average of 50% of the total branch length in the arbor was remodeled within 8 h. The data indicate that the elaboration of the arbor occurs by the random addition of branches throughout the arbor, followed by the selective stabilization of a small fraction of the new branches and the retraction of the majority of branches. Stabilized branches can then elongate and support the addition of more branches. These data show that structural changes in presynaptic axons can occur very rapidly even in complex arbors and can therefore play a role in forms of neuronal plasticity that operate on a timescale of minutes.
神经元结构的变化有助于发育中和成熟神经系统中神经元连接的可塑性。然而，由于人们预期这些变化会缓慢发生，所以许多人没有将结构变化视为在数分钟到数小时内发生的突触可塑性的潜在机制。我们对视网膜顶盖轴突树突进行了延时共聚焦成像，以确定非洲爪蟾蝌蚪体内轴突树突结构变化的时间进程、幅度和分布。在长达8小时的总观察期内，每隔3分钟、30分钟和2小时收集轴突图像。以3分钟或30分钟间隔成像的树突中，分支的添加和回缩仅限于较短的分支。添加和回缩的部位分布在整个树突中。分支的平均寿命约为10分钟。在单个3分钟的观察间隔内，树突中可添加长达10微米的分支。以3分钟间隔对树突进行观察时，发现分支尖端的结构变化迅速，包括从片状生长锥向更流线型尖端的转变、生长锥塌陷和重新延伸。简单的分支尖端具有运动性，在延时电影中观察时似乎能够进行探索行为。在总共8小时内以2小时间隔成像的树突中，形态变化包括更长的分支，长度可达数十微米。在8小时内，树突中平均50%的总分支长度发生了重塑。数据表明，树突的细化是通过在整个树突中随机添加分支，随后一小部分新分支选择性稳定以及大多数分支回缩来实现的。稳定的分支随后可以伸长并支持添加更多分支。这些数据表明，即使在复杂的树突中，突触前轴突的结构变化也可以非常迅速地发生，因此可以在以分钟为时间尺度的神经元可塑性形式中发挥作用。
