Fahim M A
Department of Physiology, Faculty of Medicine and Health Sciences, United Arab Emirates University, Al-Ain, Abu Dhabi.
Int J Dev Neurosci. 1993 Jun;11(3):303-10. doi: 10.1016/0736-5748(93)90002-u.
To evaluate the effect of partial denervation on age changes, morphological and physiological parameters were studied in young versus old extensor digitorum longus (EDL) muscles. The aims of this study were to elucidate synaptic maintenance in general and specifically to assess the adaptability of motor neurons from young and old animals to an enlarged field of innervation. Partial denervation was carried out in two groups of 30-40 g mice, aged within 6 or 24 months, by sectioning of the nerve supplying EDL muscle under methoxyfluorane anaesthesia. Sham operations were carried out on additional animals which served as controls. Five weeks' post-surgery, the safety factor of synaptic transmission was estimated by dividing the nerve-evoked twitch tension generated in 1 mM Ca2+ Krebs by that generated in 2.5 mM Ca2+ Krebs. Low Ca2+ Krebs caused a more pronounced decline in twitch tension in young control EDL muscles than old control. After partial denervation, young EDL twitch tensions were not significantly different while old were 20% of those in normal Krebs. Zinc Iodide Osmium (ZIO) stained nerve terminal parameters were significantly increased with aging. After partial denervation, nerve terminal areas were 46 and 39% larger in young and old mice, respectively, compared to their corresponding controls. Present data suggest that motor neurons of old mice are unable to develop and maintain an enlarged field of innervation.
为了评估部分去神经支配对衰老变化的影响，我们研究了年轻与年老的趾长伸肌（EDL）的形态学和生理学参数。本研究的目的是总体阐明突触维持情况，特别是评估年轻和年老动物的运动神经元对扩大的神经支配区域的适应性。在两组体重30 - 40克、年龄分别为6个月或24个月的小鼠中，通过在甲氧氟烷麻醉下切断供应EDL肌肉的神经进行部分去神经支配。对另外一些作为对照的动物进行假手术。术后五周，通过将在1 mM Ca2+ Krebs中产生的神经诱发抽搐张力除以在2.5 mM Ca2+ Krebs中产生的神经诱发抽搐张力来估计突触传递的安全系数。低钙Krebs溶液导致年轻对照EDL肌肉的抽搐张力下降比年老对照更明显。部分去神经支配后，年轻EDL的抽搐张力无显著差异，而年老的则为正常Krebs溶液中抽搐张力的20%。碘化锌锇（ZIO）染色的神经末梢参数随衰老显著增加。部分去神经支配后，年轻和年老小鼠的神经末梢面积分别比其相应对照大46%和39%。目前的数据表明，年老小鼠的运动神经元无法发展和维持扩大的神经支配区域。
