Schomburg E D, Petersen N, Barajon I, Hultborn H
Department of Medical Physiology, The Panum Institute, University of Copenhagen, Denmark.
Exp Brain Res. 1998 Oct;122(3):339-50. doi: 10.1007/s002210050522.
The generation of locomotor-like spinal rhythms has been proposed to involve two neural centres with mutual reciprocal inhibition (Graham Brown's "half-centre" hypothesis). Much later a particular set of segmental flexor reflex pathways were described as being organized in accordance with this half-centre hypothesis. As these pathways became operative following injection of monoaminoxidase inhibitors and L-3,4-dihydroxyphenylalanine (L-dopa), i.e. under the same conditions under which a spontaneous locomotor activity may develop, it was assumed that these particular pathways and spinal rhythm generators involve the same neuronal networks. In order to give further evidence to this hypothesis, we investigated whether short trains to "flexor reflex afferents" (FRA) reset the spinal locomotor rhythm, i.e. shorten or lengthen the stimulated cycle after which the regular rhythm is resumed with step cycles of the original duration. The experiments were performed in anaemically decapitated, high-spinal curarized cats. A steady locomotor rhythm was induced by injection of nialamide and L-dopa and the influence of electrical stimulation (trains of 50-1000 ms) of FRA (joint, cutaneous, and group II and III muscle afferents) onto this rhythm was tested. Stimulation of FRA induced a clear resetting of the locomotor rhythm, which was mainly characterized by a flexion reflex pattern: during the extension phase the extensor activity was interrupted and a flexion phase was initiated; during the late flexion phase mainly a prolongation of that phase with a variable change of the following extension phase was induced. In addition to this prevailing pattern, stimulation of some nerves (in particular nerves to more distal extensors and the sural nerve) could often prolong extension, when stimulated during the late extension, or terminate the flexor burst and initiate a new extension phase, when stimulated during the late flexion phase. This pattern is probably due to the concomitant stimulation of group I afferents in the case of the muscle nerves and to separate non-FRA pathways in the case of the sural nerve. The results demonstrate that the interneurones of the FRA pathways, which are operative during L-dopa-induced locomotion in spinal animals, can be considered as neuronal elements of the rhythm-generating network for locomotion.
运动样脊髓节律的产生被认为涉及两个具有相互抑制作用的神经中枢（格雷厄姆·布朗的“半中枢”假说）。很久以后，一组特定的节段性屈肌反射通路被描述为按照这种半中枢假说进行组织。由于这些通路在注射单胺氧化酶抑制剂和L-3,4-二羟基苯丙氨酸（L-多巴）后开始起作用，即在可能产生自发运动活动的相同条件下，人们假定这些特定通路和脊髓节律发生器涉及相同的神经网络。为了进一步证明这一假说，我们研究了向“屈肌反射传入纤维”（FRA）施加短串刺激是否会重置脊髓运动节律，即缩短或延长受刺激的周期，之后以原始持续时间的步周期恢复正常节律。实验在贫血断头、高位脊髓箭毒化的猫身上进行。通过注射尼亚酰胺和L-多巴诱导出稳定的运动节律，并测试了对FRA（关节、皮肤以及Ⅱ和Ⅲ类肌肉传入纤维）进行电刺激（50 - 1000毫秒的串刺激）对该节律的影响。对FRA的刺激诱导了运动节律的明显重置，其主要特征为屈肌反射模式：在伸展期，伸肌活动被中断并启动一个屈曲期；在屈曲后期，主要是该期的延长以及随后伸展期的可变变化。除了这种主要模式外，刺激某些神经（特别是支配更远端伸肌的神经和腓肠神经），在伸展后期刺激时常常会延长伸展期，或者在屈曲后期刺激时会终止屈肌爆发并启动一个新的伸展期。这种模式可能是由于肌肉神经刺激时伴随的Ⅰ类传入纤维的刺激，以及腓肠神经刺激时单独的非FRA通路所致。结果表明，在脊髓动物中L-多巴诱导的运动过程中起作用的FRA通路的中间神经元，可被视为运动节律产生网络的神经元成分。
