Rheuben M B
Department of Anatomy, College of Veterinary Medicine, Michigan State University, East Lansing 48824-1316.
J Exp Biol. 1992 Jun;167:119-54. doi: 10.1242/jeb.167.1.119.
During the degenerative processes that precede and accompany metamorphosis of the larval mesothoracic dorsal longitudinal muscles of Manduca sexta, the motor nerves and neuromuscular junctions undergo a variety of structural changes that are largely secondary to the changing morphologies of their respective glia. In the central region of the main motor nerve, the multiple layers of glial processes surrounding each of the large axons withdraw, leaving them apposed. In the peripheral region of the main motor nerve and in the secondary and tertiary nerve branches supplying the muscle, the outer glial processes of the nerve sheath and those that loosely wrap accompanying small neurosecretory axons all swell. Phagocytic cells and cells of unknown function invade the outer region of the nerve. In the neuromuscular junctions, the glial cells withdraw their processes from a complicated interdigitation with processes from the muscle fiber and from their relationship with the nerve terminal. As degeneration proceeds, this allows a greater area of contact between each nerve terminal and the muscle fiber. Within each junction there is a mixture of both functional and non-functional regions and active zones, as determined by both thin-section and freeze-fracture observations. No correlation was found between the degree of degeneration of a neuromuscular junction and its association with a particular muscle fiber or its position on the fiber relative to the origin or insertion.
在烟草天蛾幼虫中胸背纵肌变态之前及伴随变态过程的退化过程中，运动神经和神经肌肉接头会发生多种结构变化，这些变化在很大程度上继发于各自神经胶质细胞形态的改变。在主运动神经的中央区域，围绕每条大轴突的多层神经胶质细胞突起缩回，使它们相互并置。在主运动神经的外周区域以及供应肌肉的二级和三级神经分支中，神经鞘的外层神经胶质细胞突起以及松散包裹伴随小神经分泌轴突的那些突起都会肿胀。吞噬细胞和功能未知的细胞侵入神经的外层区域。在神经肌肉接头处，神经胶质细胞将其突起从与肌纤维突起的复杂交叉以及与神经末梢的关系中撤回。随着退化的进行，这使得每个神经末梢与肌纤维之间有更大的接触面积。通过超薄切片和冷冻断裂观察确定，每个接头内都存在功能区和非功能区以及活性区的混合。未发现神经肌肉接头的退化程度与其与特定肌纤维的关联或其在纤维上相对于起点或插入点的位置之间存在相关性。
