Transient direct corticomotoneuronal connections during development in rodents, an electrophysiological study
Transient direct corticomotoneuronal connections during development in rodents, an electrophysiological study
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啮齿类动物发育过程中短暂的直接皮质运动神经元连接，一项电生理学研究
DOI：
10.1016/j.neuroscience.2021.09.006
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发表时间：
2021
期刊：
影响因子：
3.3
通讯作者：
Sakurai M
中科院分区：
文献类型：
--
作者：
Ohno T;Fukuda S;Murabe N;Niido M;Sakurai M
我们先前在啮齿类动物中观察到，在出生后第2周，皮质脊髓轴突与运动神经元形成单突触连接。在这一发现之前，人们一直认为这种接触只发生在高等灵长类动物中。虽然体外电生理研究是研究突触连接发育时间过程的先决条件，但在2周龄以上的动物中可靠地记录脊髓运动神经元的突触反应的技术困难阻碍了这项研究。相反，我们使用了逆行跨突触标记与基因修饰的狂犬病病毒，以确认直接的皮质-肌肉-神经元连接在早期发育阶段的存在，并表明这些连接随后被消除。本研究通过改进切片制备方法和保持切片活力，采用全细胞膜片钳技术，对大鼠生后第7周前的前臂运动神经元进行逆行标记，记录突触后反应。我们检查了皮质-运动神经元单突触连接的程度，并研究了它们积累和丢失的时间过程。单突触皮质-运动神经元EPSC阳性率从P6到P8逐渐增加，然后趋于稳定（P8-P13：65%）。此后，单突触连接下降，直到P21，在这个时候，他们不再被检测到。通过使用光遗传学刺激的实验证实了下降期和消除的时间过程。消除的时间落在我们早期使用逆行跨突触标记的研究中估计的相同范围内（P18-22）。
We previously observed in rodents that during the 2nd postnatal week corticospinal axons make monosynaptic connections with motoneurons. Prior to that finding, it had been believed that such contacts only occur in higher primates. Although anin vitroelectrophysiological study is prerequisite for studying the developmental time course of synaptic connections, the technical difficulty of reliably recording synaptic responses from spinal motoneurons in animals over 2 weeks old hampered the study. Instead, we used retrograde transsynaptic labeling with a genetically modified rabies virus to confirm the presence of direct corticomotoneuronal connections at an early developmental stage and to show that these connections were subsequently eliminated. However, determination of an accurate elimination time course and quantitative evaluation of synaptic connectivity cannot be achieved through viral-tracing experiments.For the present study, we improved the slice preparation procedure and maintenance of slice viability, which enabled us to record postsynaptic responses using the whole cell patch-clamp technique from retrogradely labeled forearm motoneurons up until postnatal week 7. We examined the extent of corticomotoneuronal monosynaptic connections and studied the time course of their accumulation and loss. Positive ratios of monosynaptic corticomotoneuronal EPSCs increased from P6 to P8 and then plateaued (P8–P13: 65%). Thereafter, the monosynaptic connections declined until P21, at which time they were no longer detected. The time course of the falling phase and elimination was confirmed by experiments using optogenetic stimulation. The timing of the elimination fell within the same range (P18-22) estimated in our earlier study using retrograde transsynaptic labeling.