Age related functional and morphological alterations in rat diaphragm and phrenic motoneuron

2年组膈运动神经元募集后各参数均无显著性差异，而非募集组运动神经元的基强度显著低于其他两组。1、2年组运动神经元动作电位平均间期较10周组延长，2年组放电模式不规则。高频刺激（20- 100 Hz）引起的强直张力在老年组明显低于对照组。老年人膈肌达到最大张力的时间和半松弛时间明显延长。老年膈肌FG纤维面积减少，SO纤维比例增加。

No significant differences were found in all parameters in recruited phrenic motoneuron, while the rheobase of the non-recruited motoneurons was significantly lower in the 2-year group than the other two groups. The mean interval of action potentials of the recruited motoneurons was longer in the 1- and 2-year groups than the 10-week group, and the firing pattern in 2-year group was considerably irregular. Although there were no significant differences in the twitch tension among the groups, tetanus tensions by high frequency stimulation (20-100Hz) were significantly lower in the older group. The time to peak tension and half relaxation time were significantly longer in aged diaphragm muscles. The histochemical profiles of aged diaphragm muscle showed a smaller area of FG fibers and higher percentage of SO fibers.