Einsiedel L, Luff A R, Proske U
Department of Physiology, Monash University, Clayton, Victoria, Australia.
Exp Brain Res. 1992;90(2):369-74. doi: 10.1007/BF00227250.
Normally, gamma motoneurones innervate only the intrafusal fibres of muscle spindles. This is a report of sprouting of gamma motoneurones to innervate extrafusal muscle fibres following partial denervation of the soleus muscle of kittens. In eight newborn animals, the L7 ventral root was cut on one side under anaesthesia and the animals were then allowed to recover. At approximately 100 days of age animals were reanaesthetised and a study made of mechanical properties of motor units whose axons ran in the S1 ventral root and supplied the partially denervated soleus muscle. Evidence was obtained for sprouting of all surviving alpha motoneurones. In addition, in four experiments axons conducting within the gamma range, on stimulation, produced measurable tension. In one experiment, stimulation of one such gamma axon also produced specific fusimotor effects on four afferents identified as coming from primary endings of muscle spindles. The gamma axon was therefore a fusimotor axon. The effect observed on stimulation of the gamma axon suggested a largely dynamic action. Other examples of gamma axons were encountered that on stimulation produced tension, but which could not be specifically associated with spindles. In addition, a number of gamma axons that did not develop tension were shown, on stimulation, to have fusimotor effects that were static in action. It is concluded that in extensively denervated muscles gamma motoneurones may sometimes sprout to innervate extrafusal fibres. The mechanical properties of the extrafusal fibres innervated by such gamma axons were similar to those of ordinary alpha motor units.
正常情况下，γ运动神经元仅支配肌梭的梭内肌纤维。本文报道了小猫比目鱼肌部分去神经支配后，γ运动神经元发生芽生并支配梭外肌纤维的情况。对8只新生动物，在麻醉状态下切断一侧L7腹根，然后让动物恢复。在约100日龄时，再次对动物进行麻醉，并对其轴突走行于S1腹根并支配部分去神经的比目鱼肌的运动单位的力学特性进行研究。获得了所有存活的α运动神经元发生芽生的证据。此外，在4个实验中，刺激γ范围内传导的轴突可产生可测量的张力。在1个实验中，刺激1条这样的γ轴突也对4条被确定来自肌梭初级终末的传入纤维产生了特定的肌梭运动效应。因此，该γ轴突是一条肌梭运动轴突。刺激γ轴突时观察到的效应提示其主要起动态作用。还遇到了其他一些γ轴突，刺激时它们可产生张力，但无法明确与肌梭相关联。此外，一些不产生张力的γ轴突在刺激时显示出具有静态作用的肌梭运动效应。结论是，在广泛去神经支配的肌肉中，γ运动神经元有时可能会发生芽生以支配梭外肌纤维。由这些γ轴突支配的梭外肌纤维的力学特性与普通α运动单位的力学特性相似。
