Department of Biomedical Engineering, Northwestern University, Chicago, Illinois, USA.
J Neurophysiol. 2010 Mar;103(3):1580-90. doi: 10.1152/jn.00961.2009. Epub 2010 Jan 20.
Previous studies have demonstrated that "locomotor-like" rhythmic patterns can be evoked in the isolated neonatal rat spinal cord by several means, including pharmacological neuromodulation and electrical stimulation of various pathways. Recent studies have used stimulation of afferent pathways to evoke rhythmic patterns, relying on synaptic activation of interneuronal systems rather than global imposition of neuromodulatory state by pharmacological agents. We use the in vitro neonatal rat spinal cord with attached hindlimb to examine the muscle activation patterns evoked by stimulation of these different pathways and evaluate whether stimulation of these pathways all evoke the same patterns. We find that the patterns evoked by bath application of serotonin (5-HT) and N-methyl-D-aspartic acid (NMDA) consisted of alternation between hip flexors and extensors and similar alternation was observed in the patterns evoked by electrical stimulation of the cauda equina (CE) or contralateral fifth lumbar (L(5)) dorsal nerve root. In contrast, the knee extensor/hip flexor rectus femoris (RF) and knee flexor/hip extensor semitendinosus (ST) were activated differentially across stimulation conditions. In 5-HT/NMDA patterns, RF was active in late flexion and ST in late extension. In CE patterns, these two muscles switched places with RF typically active in late extension and ST active in flexion. In L(5) patterns, ST was activated in extension and RF was silent or weakly active during flexion. There were also systematic differences in the consistency of rhythms evoked by each stimulation method: patterns evoked by electrical stimulation of CE or L(5) were less consistently modulated with the rhythm when compared with 5-HT/NMDA-evoked patterns. All differences were preserved following deafferentation, demonstrating that they reflect intrinsic properties of spinal systems. These results highlight the intrinsic flexibility of motor pattern generation by spinal motor circuitry which is present from birth and provides important information to many studies examining spinal pattern generating networks.
先前的研究表明，通过多种手段，包括药理学神经调节和各种途径的电刺激，可以在分离的新生大鼠脊髓中诱发“类似运动”的节律模式。最近的研究使用刺激传入途径来诱发节律模式，依赖于中间神经元系统的突触激活，而不是通过药理学制剂全局施加神经调节状态。我们使用附有后肢的体外新生大鼠脊髓来检查这些不同途径刺激所诱发的肌肉激活模式，并评估这些途径的刺激是否都能诱发相同的模式。我们发现，5-羟色胺（5-HT）和 N-甲基-D-天冬氨酸（NMDA）的浴应用所诱发的模式包括髋关节屈肌和伸肌的交替，并且在马尾（CE）或对侧第五腰椎（L5）背根神经的电刺激所诱发的模式中也观察到类似的交替。相比之下，膝伸肌/髋关节屈肌股直肌（RF）和膝屈肌/髋关节伸肌半腱肌（ST）在不同的刺激条件下被激活。在 5-HT/NMDA 模式中，RF 在晚期屈曲中活跃，ST 在晚期伸展中活跃。在 CE 模式中，这两块肌肉的位置发生了变化，RF 通常在晚期伸展中活跃，ST 在屈曲中活跃。在 L（5）模式中，ST 在伸展中被激活，而 RF 在屈曲中处于沉默或弱激活状态。每种刺激方法诱发的节律的一致性也存在系统差异：与 5-HT/NMDA 诱发的模式相比，CE 或 L（5）电刺激诱发的模式的节律变化不太一致。去传入后，所有差异均得以保留，表明这些差异反映了脊髓系统的内在特性。这些结果突出了脊髓运动电路产生运动模式的内在灵活性，这种灵活性从出生时就存在，并为许多研究脊髓模式产生网络的研究提供了重要信息。
