Broadie K S, Bate M
Department of Zoology, University of Cambridge, United Kingdom.
J Neurosci. 1993 Jan;13(1):144-66. doi: 10.1523/JNEUROSCI.13-01-00144.1993.
We have examined the embryonic development of an identified neuromuscular junction (NMJ) of Drosophila melanogaster using whole-cell patch-clamp and a variety of physiological and morphological techniques. Synaptic current at the embryonic NMJ is carried through a large-conductance (200 pS) L-glutamate receptor. Early synaptic communication is characterized by frequent, brief (< 10 msec) currents carried through few (1-10) receptors and relatively rare, prolonged currents (up to seconds) of similar amplitude. The brief currents have a time course similar to the mature larval excitatory junction currents (EJCs), but the prolonged currents are restricted to early stages of synaptogenesis. The amplitude of EJCs rapidly increases, and the frequency of the prolonged currents decreases, after the initial stages of synaptogenesis. Early prolonged (seconds), nonspiking synaptic potentials are replaced with rapid (< 0.10 sec), spiking synaptic potentials later in development. The early synapse appears tenuous, easily fatiguable, and with inconsistent communication properties. Synaptogenesis can be divided into a sequence of progressive stages. (1) Motor axon filopodia begin neurotransmitter expression and concurrent exploration of the myotube surface. (2) Myotubes uncouple to form single-cell units soon after motor axon contact. (3) A small number of transmitter receptors are homogeneously displayed on the myotube surface immediately following myotube uncoupling. (4) Endogenous transmitter release from pioneering growth cones is detected; nerve stimulation elicits postsynaptic EJC response. (5) Motor axon filopodia and transmitter receptors are localized to the mature synaptic zone; filopodial localization is complete in advance of receptor localization. (6) A functional neuromuscular synapse is formed; endogenous muscular activity begins; nerve stimulation leads to muscle contraction. (7) Morphological presynaptic specializations develop; synapse develops mature morphology. (8) A second motor axon synapses on the myotube at the pre-established synaptic zone. (9) Vigorous neuromuscular activity, characteristic of larval locomotory movements, begins. (10) A second stage of receptor expression begins and continues through the end of embryogenesis. In general, Drosophila neuromuscular synaptogenesis appears similar to neuromuscular synaptogenesis in known vertebrate preparations. We suggest that this system provides a model for synaptogenesis in which investigation can be readily extended to a genetic and molecular level.
我们使用全细胞膜片钳以及多种生理和形态学技术，研究了黑腹果蝇一个已确定的神经肌肉接头（NMJ）的胚胎发育过程。胚胎期NMJ处的突触电流通过一种大电导（200皮秒）的L-谷氨酸受体传导。早期突触通讯的特征是，通过少数（1 - 10个）受体传导的频繁、短暂（<10毫秒）电流，以及相对罕见的、持续时间较长（长达数秒）且幅度相似的电流。短暂电流的时间进程与成熟幼虫兴奋性接头电流（EJC）相似，但持续时间较长的电流仅限于突触发生的早期阶段。在突触发生的初始阶段之后，EJC的幅度迅速增加，而持续时间较长的电流频率降低。早期持续时间较长（数秒）、非尖峰状的突触电位在发育后期被快速（<0.10秒）、尖峰状的突触电位所取代。早期的突触看起来很脆弱，容易疲劳，且通讯特性不一致。突触发生可分为一系列渐进阶段。（1）运动轴突丝状伪足开始表达神经递质，并同时探索肌管表面。（2）运动轴突接触后不久，肌管解偶联形成单细胞单元。（3）肌管解偶联后，少数递质受体立即均匀地分布在肌管表面。（4）检测到先驱生长锥释放内源性递质；神经刺激引发突触后EJC反应。（5）运动轴突丝状伪足和递质受体定位于成熟的突触区；丝状伪足的定位在受体定位之前完成。（6）形成功能性神经肌肉突触；内源性肌肉活动开始；神经刺激导致肌肉收缩。（7）形态学上的突触前特化形成；突触发育成熟形态。（8）第二条运动轴突在预先建立的突触区与肌管形成突触。（9）开始出现幼虫运动特征的剧烈神经肌肉活动。（10）受体表达的第二阶段开始，并持续到胚胎发育结束。总体而言，果蝇神经肌肉突触发生过程似乎与已知脊椎动物标本中的神经肌肉突触发生过程相似。我们认为，这个系统为突触发生提供了一个模型，在此模型中，研究可以很容易地扩展到基因和分子水平。
