3-DIMENSIONAL ULTRASTRUCTURE OF CRAYFISH NEUROMUSCULAR APPARATUS
3-DIMENSIONAL ULTRASTRUCTURE OF CRAYFISH NEUROMUSCULAR APPARATUS
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DOI：
10.1083/jcb.63.2.599
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发表时间：
1974-01-01
影响因子：
7.8
通讯作者：
ATWOOD, HL
中科院分区：
文献类型：
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作者：
JAHROMI, SS;ATWOOD, HL
用连续切片的电子显微照片重建了螯虾开肌的突触神经末梢。研究了兴奋性和抑制性轴突终末的分支模式以及神经肌肉和轴-轴突触的位置和大小。兴奋性和抑制性突触不仅可以根据突触囊泡的差异来区分，而且还可以通过突触前膜和突触后膜的密度差异来区分。两个轴突的突触通常有一个或多个明显局部化的突触前“致密体”，突触囊泡似乎聚集在周围。有些突触没有致密体。这些结构可能参与突触的生理活动。兴奋性轴突终末有更多的突触，和更大的百分比的终端表面积致力于突触接触，比抑制性轴突终末。然而，抑制性轴突的最大突触的表面积超过兴奋性轴突的。两个轴突都有许多来自主终端的侧支;通常，侧支通过狭窄的颈部与主终端相连。侧支的突触比主末梢的突触占表面积的百分比更大。只有一小部分的总表面积致力于轴-轴突触，但这些往往位于狭窄的颈部或收缩的兴奋性轴突。这种安排将导致有效地阻止尖峰侵入突触远端的末端区域，并且将允许相对较少的突触对兴奋性轴突的递质释放施加强大的影响。本文提出了一种解释神经肌肉器官发育的假说，认为新突触的产生比旧突触的扩大更重要，是轴突调节递质输出以满足肌肉功能需要的一种机制。螯虾开肌的神经支配由一个兴奋性（E）轴突和一个抑制性（I）轴突组成，这已经通过生理学方法和后来通过电子显微镜进行了广泛的研究（综述见2- 4）。该系统之所以令人感兴趣，是因为它具有一些
The synapse-bearing nerve terminals of the opener muscle of the crayfish Procambarus were reconstructed using electron micrographs of regions which had been serially sectioned. The branching patterns of the terminals of excitatory and inhibitory axons and the locations and sizes of neuromuscular and axo-axonal synapses were studied. Excitatory and inhibitory synapses could be distinguished not only on the basis of differences in synaptic vesicles, but also by a difference in density of pre-and postsynaptic membranes. Synapses of both axons usually had one or more sharply localized presynaptic" dense bodies" around which synaptic vesicles appeared to cluster. Some synapses did not have the dense bodies. These structures may be involved in the physiological activity of the synapse. Excitatory axon terminals had more synapses, and a larger percentage of terminal surface area devoted to synaptic contacts, than inhibitory axon terminals. However, the largest synapses of the inhibitory axon exceeded in surface area those of the excitatory axon. Both axons had many side branches coming from the main terminal; often, the side branches were joined to the main terminal by narrow necks. A greater percentage of surface area was devoted to synapses in side branches than in the main terminal. Only a small fraction of total surface area was devoted to axo-axonal synapses, but these were often located at narrow necks or constrictions of the excitatory axon. This arrangement would result in effective blockage of spike invasion of regions of the terminal distal to the synapse, and would allow relatively few synapses to exert a powerful effect on transmitter release from the excitatory axon. A hypothesis to account for the development of the neuromuscular apparatus is presented, in which it is suggested that production of new synapses is more important than enlargement of old ones as a mechanism for allowing the axon to adjust transmitter output to the functional needs of the muscle.The innervation of the crayfish opener muscle consists of a singe excitatory (E) axon and a single inhibitory (I) axon, which have been extensively investigated by physiological methods and later by means of electron microscopy (for reviews, see 2--4). The system is of interest because it has some