Tyc F, Vrbová G
Department of Anatomy and Developmental Biology, University College London, Gower Street, London WC1E 6BT, UK.
Brain Res Dev Brain Res. 1998 Aug 8;109(2):149-55. doi: 10.1016/s0165-3806(98)00075-3.
Partial denervation of the neonatal rat extensor digitorum longus muscles by removing the L4 spinal nerve and thus 80% of its innervation [A.L. Connold, T.J. Fisher, S. Maudarbocus, G. Vrbová, Response of developing fast muscles to partial denervation, Neuroscience 46 (1992) 981-988; F. Tyc, G. Vrbová, The effect of partial denervation of developing rat fast muscles on their motor unit properties, J. Physiol. 482 (1995) 651-660] results in its permanent weakness. The possibility that the weakness that follows partial denervation is due to the effects of reducing activity of the muscle during a critical stage of development was studied here. Partial denervation was carried out in 3-day-old pups by removing the L4 spinal nerve. To enhance motor activity two days later some animals had injections of l-Dopa twice a day for 8 days. This treatment induced locomotor activity for at least 2 h/day. The muscles from treated and untreated animals were examined 2 months later. There was a significantly smaller reduction of weight and force production in the muscles from l-Dopa treated animals. Both twitch and tetanic force developed by the EDL muscle from the treated group was twice that of the control untreated group. This effect was due mainly to the larger size of the motor units (MUs) in the l-Dopa treated muscles compared to the controls. The mean motor unit force in the untreated group was 69% of that in the control muscle, whereas this value was 127% in the l-Dopa treated animals. Thus it appears that the activity induced by treatment with l-Dopa could to some extent prevent the loss of weight and force output seen after partial denervation of young fast muscles.
通过切除L4脊髓神经，使新生大鼠趾长伸肌80%的神经支配被去除，从而造成部分去神经支配 [A.L. 康诺德、T.J. 费舍尔、S. 莫达尔博库斯、G. 弗尔博娃，发育中的快肌对部分去神经支配的反应，《神经科学》46 (1992) 981 - 988；F. 泰克、G. 弗尔博娃，发育中的大鼠快肌部分去神经支配对其运动单位特性的影响，《生理学杂志》482 (1995) 651 - 660]，这会导致该肌肉永久性无力。本研究探讨了部分去神经支配后出现的无力是否是由于在发育关键阶段肌肉活动减少所致。在3日龄幼崽中通过切除L4脊髓神经进行部分去神经支配。两天后，为增强运动活动，一些动物每天注射两次左旋多巴，持续8天。这种治疗诱导至少每天2小时的运动活动。2个月后检查经治疗和未治疗动物的肌肉。接受左旋多巴治疗的动物的肌肉重量和力量产生的减少明显较小。治疗组的趾长伸肌产生的单收缩和强直收缩力均为未治疗对照组的两倍。这种效应主要是由于与对照组相比，接受左旋多巴治疗的肌肉中运动单位（MU）更大。未治疗组的平均运动单位力为对照肌肉的69%，而在接受左旋多巴治疗的动物中该值为127%。因此，似乎左旋多巴治疗诱导的活动在一定程度上可以防止幼年快肌部分去神经支配后出现的重量和力量输出的损失。
