Ochs S, Jersild R A, Pourmand R, Potter C G
Department of Physiology, Indiana University School of Medicine, Indianapolis 46202.
Neuroscience. 1994 Jul;61(2):361-72. doi: 10.1016/0306-4522(94)90237-2.
When the nerves are lightly stretched and fixed by freeze-substitution, their fibers show the form-change termed "beading" which consists of a series of undulating constrictions and swellings in the internodes. This form change has not ordinarily been seen in chemically fixed nerves, or when it has, it has been ascribed to a pathological change or an artifact. We now report that beading is also retained in normal nerves when, following a light maintained stretch, they are fixed with aldehydes at a temperature close to 0 degrees C. The degree of beading in single fibers teased from the aldehyde fixed nerves was graded and found to be maximal at 0 degrees C, falling off with increased temperature until, at temperatures above 16 degrees C, most fibers showed no beading or a very mild beading. The fibers of nerves cold-fixed at 0 degrees C displayed the characteristics as freeze-substituted fibers, but with a somewhat smaller number of maximally beaded fibers and an 18% reduction in microtubule numbers in the axons. Desheathing or slitting the sheaths of the nerves before cold-fixation increased the probability of retaining beading. Exposure of stretched nerves to the aldehyde fixative at room temperatures for times as short as 3-5 min before they were cold-fixed showed a diminished degree of beading, indicating that aldehydes can have a deleterious effect on the beading mechanism which we hypothesize to be present in the fiber. This action is distinct from the general cross-linking action of aldehydes.
当神经通过冷冻置换被轻微拉伸并固定时，其纤维会呈现出一种称为“串珠化”的形态变化，这种变化由节间一系列起伏的收缩和肿胀组成。这种形态变化在化学固定的神经中通常不会出现，或者即使出现了，也被归因于病理变化或人为假象。我们现在报告，当正常神经在轻度持续拉伸后，于接近0摄氏度的温度下用醛类固定时，串珠化现象也会保留。对从醛类固定神经中分离出的单根纤维的串珠化程度进行分级，发现其在0摄氏度时最大，随温度升高而降低，直到在16摄氏度以上时，大多数纤维不再显示串珠化或仅有非常轻微的串珠化。在0摄氏度下冷固定的神经纤维表现出与冷冻置换纤维相似的特征，但最大串珠化纤维数量略少，轴突中的微管数量减少了18%。在冷固定前对神经进行去鞘或切开鞘膜会增加保留串珠化的可能性。在冷固定前，将拉伸的神经在室温下暴露于醛类固定剂3 - 5分钟，串珠化程度会降低，这表明醛类可能对我们假设存在于纤维中的串珠化机制产生有害影响。这种作用不同于醛类的一般交联作用。
