Gossard J P, Floeter M K, Degtyarenko A M, Simon E S, Burke R E
Laboratory of Neural Control, National Institutes of Health, Bethesda, MD 20892-4455, USA.
Exp Brain Res. 1996 May;109(2):277-88. doi: 10.1007/BF00231787.
This study compares some characteristics of the disynaptic excitatory pathways from the lateral vestibular nucleus (LVN) and medial longitudinal fasciculus (MLF) to lumbosacral alpha-motoneurons in the decerebrate cat. We used the spatial facilitation technique to test whether disynaptic LVN and MLF excitatory postsynaptic potentials (EPSPs) are produced by common last-order interneurons in the lumbosacral segments of the spinal cord. Of 77 motoneurons examined, 26 exhibited disynaptic EPSPs from both supraspinal sources. No spatial facilitation was found between LVN and MLF EPSPs in 21 of 24 cells that were adequately tested. In 3 of 23 cells (all flexor motoneurons), some spatial facilitation was found in some but not all trials. These observations suggest that stimulation of the LVN and MLF produces disynaptic EPSPs in motoneurons through largely separate populations of last-order interneurons. Disynaptic MLF and LVN EPSPs showed parallel patterns of modulation during fictive locomotion. Maximal disynaptic EPSP amplitudes occurred during the phase of the step cycle when the recorded motoneuron, whether flexor or extensor, exhibited depolarizing locomotor drive potentials and the corresponding muscle nerve was active. These observations, taken together, suggest that disynaptic LVN and MLF EPSPs are produced in motoneurons by at least four separate populations of segmental last-order excitatory interneurons, with separate populations projecting to flexor versus extensor cells. The results also suggest that the modulation of the disynaptic EPSPs during fictive locomotion is mainly due to premotoneuronal convergence of input from the respective descending systems and from the segmental central pattern generator for locomotion onto common interneurons.
本研究比较了去大脑猫中从外侧前庭核（LVN）和内侧纵束（MLF）到腰骶部α运动神经元的双突触兴奋性通路的一些特征。我们使用空间易化技术来测试双突触LVN和MLF兴奋性突触后电位（EPSP）是否由脊髓腰骶段共同的最后一级中间神经元产生。在检查的77个运动神经元中，26个表现出来自两个脊髓上源的双突触EPSP。在24个经过充分测试的细胞中的21个中，未发现LVN和MLF EPSP之间存在空间易化。在23个细胞中的3个（均为屈肌运动神经元）中，在部分而非所有试验中发现了一些空间易化。这些观察结果表明，刺激LVN和MLF通过很大程度上不同的最后一级中间神经元群体在运动神经元中产生双突触EPSP。双突触MLF和LVN EPSP在虚拟运动期间表现出平行的调制模式。最大双突触EPSP幅度出现在步周期的阶段，此时记录的运动神经元，无论是屈肌还是伸肌，都表现出去极化的运动驱动电位，并且相应的肌肉神经处于活动状态。综合这些观察结果表明，双突触LVN和MLF EPSP在运动神经元中由至少四个不同的节段性最后一级兴奋性中间神经元群体产生，不同的群体投射到屈肌和伸肌细胞。结果还表明，虚拟运动期间双突触EPSP的调制主要是由于来自各自下行系统和来自节段性运动中央模式发生器的输入在运动前神经元水平汇聚到共同的中间神经元。
