Smith D O, Rosenheimer J L
Exp Neurol. 1984 Feb;83(2):358-66. doi: 10.1016/S0014-4886(84)90104-3.
Impaired motor coordination is a widespread attribute of senescence. As this might be due to slower action potential propagation in peripheral nerves or to prolonged delays of neuromuscular transmission, axon conduction velocity, synaptic delays, and associated morphologic features governing speed of conduction were studied in the phrenic-diaphragm preparations of rats aged 10 (mature adult) and 28 (aged) months. Conduction velocity and synaptic delay of the motoneurons were measured with electrophysiologic recording techniques. Speed of conduction did not change with age, but the average synaptic delay increased from 0.28 in the younger rats to 0.40 ms in the 28-month-old animals. Nerve composition was examined using the electron microscope. There were no age-related changes in the number of myelinated or nonmyelinated axons, capillaries, or myelin sheath invaginations. Moreover, fiber diameter and myelin sheath width did not vary with age. The total extracellular space was about 32% larger in the aged rats: the synaptic cleft widths were 42.7 and 50.6 nm in the 10- and the 28-month animals, respectively. We concluded that in the rat age-related changes in the transmission properties of peripheral nerve are minor. Furthermore, temporal motor deficits during aging must be associated primarily with changes in central pathways or at the muscular apparatus.
运动协调受损是衰老的一个普遍特征。由于这可能是由于外周神经中动作电位传播较慢或神经肌肉传递延迟延长所致，因此研究了10个月大（成熟成年）和28个月大（老年）大鼠膈-膈肌标本中轴突传导速度、突触延迟以及控制传导速度的相关形态学特征。用电生理记录技术测量运动神经元的传导速度和突触延迟。传导速度不会随年龄变化，但平均突触延迟从年轻大鼠的0.28毫秒增加到28个月大动物的0.40毫秒。使用电子显微镜检查神经组成。有髓或无髓轴突、毛细血管或髓鞘内陷的数量没有与年龄相关的变化。此外，纤维直径和髓鞘宽度不会随年龄变化。老年大鼠的细胞外总空间大约大32%：10个月和28个月动物的突触间隙宽度分别为42.7纳米和50.6纳米。我们得出结论，在大鼠中，外周神经传递特性的年龄相关变化较小。此外，衰老过程中的时间性运动缺陷主要必须与中枢通路或肌肉器官的变化有关。
