Background: The spinal cord's central pattern generators (CPGs) have been explained by the symmetrical half-center hypothesis, the bursts generator, computational models, and more recently by connectome circuits. Asymmetrical models, at odds with the half-center paradigm, are composed of extensor and flexor CPG modules. Other models include not only flexor and extensor motoneurons but also motoneuron pools controlling biarticular muscles. It is unknown whether a preferred model can explain some particularities that fictive scratching (FS) in the cat presents. The first aim of this study was to investigate FS patterns considering the aiming and the rhythmic periods, and second, to examine the effects of serotonin (5HT) on and segmental inputs to FS. Methods: The experiments were carried out first in brain cortex-ablated cats (BCAC), then spinalized (SC), and for the midcollicular (MCC) preparation. Subjects were immobilized and the peripheral nerves were used to elicit the Monosynaptic reflex (MR), to modify the scratching patterns and for electroneurogram recordings. Results: In BCAC, FS was produced by pinna stimulation and, in some cases, by serotonin. The scratching aiming phase (AP) initiates with the activation of either flexor or extensor motoneurons. Serotonin application during the AP produced simultaneous extensor and flexor bursts. Furthermore, WAY 100635 (5HT1A antagonist) produced a brief burst in the tibialis anterior (TA) nerve, followed by a reduction in its electroneurogram (ENG), while the soleus ENG remained silent. In SC, rhythmic phase (RP) activity was recorded in the soleus motoneurons. Serotonin or WAY produced FS bouts. The electrical stimulation of Ia afferent fibers produced heteronymous MRes waxing and waning during the scratch cycle. In MCC, FS began with flexor activity. Electrical stimulation of either deep peroneus (DP) or superficial peroneus (SP) nerves increased the duration of the TA electroneurogram. Medial gastrocnemius (MG) stretching or MG nerve electrical stimulation produced a reduction in the TA electroneurogram and an initial MG extensor burst. MRes waxed and waned during the scratch cycle. Conclusion: Descending pathways and segmental afferent fibers, as well as 5-HT and WAY, can change the FS pattern. To our understanding, the half-center hypothesis is the most suitable for explaining the AP in MCC.

中文翻译：

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大脑皮层消融，中脑无脊椎和脊柱猫的虚拟划痕模式。

背景：脊髓的中央模式发生器（CPG）已通过对称的半中心假说，爆发发生器，计算模型以及最近的连接套电路进行了解释。与半中心范式不一致的非对称模型由伸肌和屈肌CPG模块组成。其他模型不仅包括屈肌和伸肌运动神经元，还包括控制双关节肌肉的运动神经元池。尚不清楚首选模型能否解释猫的虚构性抓挠（FS）表现出的某些特殊性。这项研究的第一个目标是考虑目标和节律周期来研究FS模式，其次，检查5-羟色胺（5HT）对FS和分段输入的影响。方法：实验首先在大脑皮层切除的猫（BCAC）中进行，然后进行脊柱（SC）手术，并准备中颈（MCC）手术。固定受试者，并使用周围神经引发单突触反射（MR），修改抓挠模式并进行电镜记录。结果：在BCAC中，FS是通过耳廓刺激产生的，在某些情况下是通过血清素产生的。划痕瞄准阶段（AP）从屈肌或伸肌运动神经元的激活开始。在AP期间应用5-羟色胺会同时引起伸肌和屈肌爆发。此外，WAY 100635（5HT1A拮抗剂）在胫骨前（TA）神经中产生短暂爆发，随后其电描记图（ENG）减少，而比目鱼ENG保持沉默。在SC中，比目鱼运动神经元中记录有节律相（RP）活性。血清素或WAY产生FS发作。Ia传入纤维的电刺激在刮擦周期中产生异质性MRes蜡化和减弱。在MCC中，FS开始于屈肌活动。深部腓骨（DP）或浅表腓骨（SP）的电刺激增加了TA电镜的持续时间。内侧腓肠肌（MG）拉伸或MG神经电刺激导致TA电子神经图的减少和初始MG伸肌爆发。MRes在刮擦周期中起伏不定。结论：下降途径和节段传入纤维以及5-HT和WAY可改变FS模式。据我们了解，半中心假设最适合解释MCC中的AP。深部腓骨（DP）或浅表腓骨（SP）的电刺激增加了TA电镜的持续时间。内侧腓肠肌（MG）拉伸或MG神经电刺激导致TA电子神经图的减少和初始MG伸肌爆发。MRes在刮擦周期中起伏不定。结论：下降路径和节段传入纤维以及5-HT和WAY可以改变FS模式。据我们了解，半中心假设最适合解释MCC中的AP。深部腓骨（DP）或浅表腓骨（SP）的电刺激增加了TA电镜的持续时间。内侧腓肠肌（MG）拉伸或MG神经电刺激导致TA电子神经图的减少和初始MG伸肌爆发。MRes在刮擦周期中起伏不定。结论：下降途径和节段传入纤维以及5-HT和WAY可以改变FS模式。据我们了解，半中心假设最适合解释MCC中的AP。MRes在刮擦周期中起伏不定。结论：下降路径和节段传入纤维以及5-HT和WAY可以改变FS模式。据我们了解，半中心假设最适合解释MCC中的AP。MRes在刮擦周期中起伏不定。结论：下降路径和节段传入纤维以及5-HT和WAY可以改变FS模式。据我们了解，半中心假设最适合解释MCC中的AP。