Locomotion allows us to move and interact with our surroundings. Spinal networks that control locomotion produce rhythm and left–right and flexor–extensor coordination. Several glutamatergic populations, Shox2 non-V2a, Hb9-derived interneurons, and, recently, spinocerebellar neurons have been proposed to be involved in the mouse rhythm generating networks. These cells make up only a smaller fraction of the excitatory cells in the ventral spinal cord. Here, we set out to identify additional populations of excitatory spinal neurons that may be involved in rhythm generation or other functions in the locomotor network. We use RNA sequencing from glutamatergic, non-glutamatergic, and Shox2 cells in the neonatal mice from both sexes followed by differential gene expression analyses. These analyses identified transcription factors that are highly expressed by glutamatergic spinal neurons and differentially expressed between Shox2 neurons and glutamatergic neurons. From this latter category, we identified the Lhx9-derived neurons as having a restricted spinal expression pattern with no Shox2 neuron overlap. They are purely glutamatergic and ipsilaterally projecting. Ablation of the glutamatergic transmission or acute inactivation of the neuronal activity of Lhx9-derived neurons leads to a decrease in the frequency of locomotor-like activity without change in coordination pattern. Optogenetic activation of Lhx9-derived neurons promotes locomotor-like activity and modulates the frequency of the locomotor activity. Calcium activities of Lhx9-derived neurons show strong left–right out-of-phase rhythmicity during locomotor-like activity. Our study identifies a distinct population of spinal excitatory neurons that regulates the frequency of locomotor output with a suggested role in rhythm-generation in the mouse alongside other spinal populations.

运动使我们能够移动并与周围环境互动。控制运动的脊柱网络产生节奏以及左右和屈伸肌的协调。一些谷氨酸能群体、Shox2 非 V2a、Hb9 衍生的中间神经元以及最近的脊髓小脑神经元已被提议参与小鼠节律生成网络。这些细胞仅占腹侧脊髓兴奋性细胞的一小部分。在这里，我们着手识别可能参与节律生成或运动网络中其他功能的其他兴奋性脊髓神经元群体。我们对两性新生小鼠的谷氨酸能、非谷氨酸能和 Shox2 细胞进行 RNA 测序，然后进行差异基因表达分析。这些分析确定了谷氨酸能脊髓神经元高表达且在 Shox2 神经元和谷氨酸能神经元之间差异表达的转录因子。从后一类中，我们发现 Lhx9 衍生的神经元具有受限的脊髓表达模式，没有 Shox2 神经元重叠。它们是纯谷氨酸能的并且向同侧突出。谷氨酸传递的消融或 Lhx9 衍生神经元的神经元活动的急性失活导致运动样活动频率的降低，而协调模式没有改变。 Lhx9 衍生神经元的光遗传学激活可促进运动样活动并调节运动活动的频率。 Lhx9 衍生神经元的钙活动在运动样活动期间表现出强烈的左右异相节律性。我们的研究确定了一个独特的脊髓兴奋性神经元群体，它们调节运动输出的频率，与其他脊髓群体一样，在小鼠节律生成中发挥着潜在的作用。