Counter S A
J Morphol. 1978 Dec;158(3):361-5. doi: 10.1002/jmor.1051580306.
The ultrastructure of neuromuscular junctions in the twitch fibers of the stapedius muscle of Gallus gallus (domesticus) was investigated as part of a series of neurophysiological studies. Among the morphological features observed were elongated end-plates with numerous large and clear synaptic vesicles mixed with larger dense core vesicles and irregular or aperiodic "active sites" in the presynaptic membrane where synaptic vesicles were focused. The most remarkable features of these junctions were large synaptic clefts (50-80 nm) and the absence of junctional folds in the sarcolemmal surface. Unlike the large periodic junctional folds seen in the neuromuscular junctions of frogs and in the fast twitch fibers of the mammalian stapedius, the preparations studied only show small aperiodic invaginations (primitive folds) in the postsynaptic membranes. This morphological feature remains essentially constant from newly hatched to adult chickens. While these smooth junctions are consistent with earlier findings of inconspicuous junctional folds in the twitch fibers of the chicken posterior latissimus dorsi they are unlike those seen in the fast twitch fibers of the mammalian stapedius muscle, or other twitch fibers in general. The morphological findings of the present study may also suggest that the simple, unmodified neuromuscular junctions in the stapedius of Gallus may be a useful preparation for studies of synaptic membrane structures that employ the freeze-fracture technique.
作为一系列神经生理学研究的一部分，对家鸡镫骨肌快肌纤维中神经肌肉接头的超微结构进行了研究。观察到的形态学特征包括拉长的终板，其中有许多大而清亮的突触小泡，与较大的致密核心小泡混合，以及突触前膜上不规则或无周期性的“活性部位”，突触小泡在此聚集。这些接头最显著的特征是大的突触间隙（50 - 80纳米）以及肌膜表面缺乏接头褶皱。与青蛙神经肌肉接头和哺乳动物镫骨肌快肌纤维中所见的大的周期性接头褶皱不同，所研究的标本仅在突触后膜上显示出小的无周期性内陷（原始褶皱）。从新孵化的小鸡到成年鸡，这种形态学特征基本保持不变。虽然这些平滑的接头与早期在鸡背阔肌快肌纤维中不明显的接头褶皱的发现一致，但它们与哺乳动物镫骨肌快肌纤维或一般其他快肌纤维中所见的不同。本研究的形态学发现也可能表明，家鸡镫骨肌中简单、未修饰的神经肌肉接头可能是利用冷冻断裂技术研究突触膜结构的有用标本。
