van Raamsdonk W, Smit-Onel M J, Diegenbach P C
Department of Experimental Zoology, University of Amsterdam.
Eur J Morphol. 1993 Sep;31(3):175-91.
We investigated the relationship between the enzyme histochemical properties of motoneurons and the size of their peripheral target. The study was carried out on zebrafish (Brachydanio rerio) of 18 to 53 mm body length. Motoneurons of the white, fast glycolytic muscle (WMN) and of the slower red and intermediate oxidative muscle (RIMN) were investigated. We determined the average soma size of the WMNs and the RMNs and the following histochemical characteristics: Glucose 6-phosphate dehydrogenase (G6PDH), a marker for reductive biosynthesis; Phosphofructokinase (PFK), a marker for glycolytic activity; Succinate dehydrogenase (SDH) enzyme of the citric acid cycle and NADH tetrazolium reductase (NADH-TR) a marker for oxidative activity. The product of enzyme activity and the soma volume was denoted the enzyme capacity of a soma. As a measure for the average target of the motoneurons, we took the number of endplate regions within the white and the red-intermediate muscle. The age dependent increase in G6PDH capacity of motoneuron somata correlates significantly with the increase in the number of endplate regions. On the basis of changes in the soma size, enzyme capacity and target size, we estimate that in 18 mm fish about 45% and in 53 mm fish about 60% of the oxidative capacity is used to maintain connections with the target. This holds for WMNs as well as for RIMNs. Similar calculations, on basis of data known from the literature, indicate that in motoneurons of the cat, less than 10% of the oxidative capacity is used for connections with the target. The PFK capacity increased unproportionally with age in WMNs but not in RIMNs. This indicates that the energy metabolism in WMNs of large fish tends to be anaerobic glycolytic. The study shows that enzyme histochemical characteristics of motoneurons should be interpreted in a morphological context, regarding motoneuron soma size and target size.
我们研究了运动神经元的酶组织化学特性与其外周靶标的大小之间的关系。该研究以体长为18至53毫米的斑马鱼（短担尼鱼）为对象。对白色快速糖酵解型肌肉运动神经元（WMN）以及较慢的红色和中间型氧化型肌肉运动神经元（RIMN）进行了研究。我们测定了WMN和RIMN的平均胞体大小以及以下组织化学特征：6-磷酸葡萄糖脱氢酶（G6PDH），一种还原生物合成的标志物；磷酸果糖激酶（PFK），一种糖酵解活性的标志物；柠檬酸循环中的琥珀酸脱氢酶（SDH）以及作为氧化活性标志物的NADH四氮唑还原酶（NADH-TR）。酶活性与胞体体积的乘积被定义为胞体的酶容量。作为运动神经元平均靶标的衡量指标，我们采用了白色和红色-中间型肌肉内终板区域的数量。运动神经元胞体的G6PDH容量随年龄增长的增加与终板区域数量的增加显著相关。基于胞体大小、酶容量和靶标大小的变化，我们估计在18毫米长的鱼中，约45%的氧化能力以及在53毫米长的鱼中约60%的氧化能力用于维持与靶标的连接。这适用于WMN以及RIMN。基于文献中已知的数据进行的类似计算表明，在猫的运动神经元中，用于与靶标连接的氧化能力不到10%。WMN中PFK容量随年龄增长不成比例地增加，而RIMN中则不然。这表明大型鱼类的WMN中的能量代谢倾向于无氧糖酵解。该研究表明，运动神经元的酶组织化学特征应结合运动神经元胞体大小和靶标大小的形态学背景来进行解释。
