Brizzi L, Ting L H, Zytnicki D
Centre National de la Recherche Scientifique 2361, Unité Mixte de Recherche 8119, Université René Descartes, 75270 Paris, France.
J Neurophysiol. 2002 Nov;88(5):2207-14. doi: 10.1152/jn.01051.2001.
Pretibial flexor motoneurons were recorded intracellularly in anesthetized cats during unfused isometric contractions of a subpopulation of motor units from either tibialis anterior (TA) or extensor digitorum longus (EDL) muscles. The contractions elicited excitatory postsynaptic potentials in 23 of 28 pretibial flexor motoneurons. No effect was observed in the remaining motoneurons. In control experiments, the effects of electrical stimulation of afferents within the TA nerve were investigated to help identify afferents responsible for the contraction-induced positive feedback. This feedback was ascribed to actions of Ia fibers because the pattern of the contraction-induced excitatory potentials was consistent with the known pattern of Ia discharge; in control experiments, electrical stimulation of group I fibers elicited only monosynaptic excitatory potentials; and the distribution of both the contraction-induced positive feedback among motor nuclei as well as the electrically evoked Ia excitatory monosynaptic potentials were restricted to homonymous and synergic motoneurons. Observation of the Ia contraction-induced positive feedback was facilitated by the absence of Ib autogenic inhibition. This contraction-induced Ia excitatory feedback in ankle flexors might either reinforce Ia-induced reflexes when these muscles are lengthened or help to lift the leg over an obstacle.
在麻醉猫中，当来自胫骨前肌（TA）或趾长伸肌（EDL）的一部分运动单位进行非融合等长收缩时，对胫前屈肌运动神经元进行细胞内记录。在28个胫前屈肌运动神经元中，有23个在收缩时引发了兴奋性突触后电位。其余运动神经元未观察到效应。在对照实验中，研究了电刺激TA神经内传入纤维的效应，以帮助确定负责收缩诱导正反馈的传入纤维。这种反馈归因于Ia纤维的作用，因为收缩诱导的兴奋性电位模式与已知的Ia放电模式一致；在对照实验中，电刺激I组纤维仅引发单突触兴奋性电位；收缩诱导的正反馈在运动核间的分布以及电诱发的Ia兴奋性单突触电位均局限于同名和协同运动神经元。Ib自身抑制的缺失有助于观察到Ia收缩诱导的正反馈。踝关节屈肌中这种收缩诱导的Ia兴奋性反馈，在这些肌肉被拉长时可能会增强Ia诱导的反射，或者有助于将腿部抬起越过障碍物。
