Data from: Mapping and analysis of the connectome of sympathetic premotor neurons in the rostral ventrolateral medulla of the rat using a volumetric brain atlas

Spinally projecting neurons in the rostral ventrolateral medulla (RVLM) play a critical role in the generation of vasomotor sympathetic tone and are thought to receive convergent input from neurons at every level of the neuraxis; the factors that determine their ongoing activity remain unresolved. In this study we use a genetically restricted viral tracing strategy to definitively map their spatially diffuse connectome.
We infected bulbospinal RVLM neurons with recombinant rabies variant that drives reporter expression in monosynaptically connected input neurons and mapped their distribution using a MRI-based volumetric atlas and a novel image alignment and visualization tool that efficiently translates the positions of neurons captured in conventional photomicrographs to Cartesian coordinates.
We identified prominent inputs from well-established neurohumoral and viscero-sympathetic sensory actuators, medullary autonomic and respiratory subnuclei, and supramedullary autonomic nuclei. The majority of inputs lay within the brainstem (88 – 94%), and included putative respiratory neurons in the pre-Bötzinger Complex and post-inspiratory complex that are therefore likely to underlie respiratory-sympathetic coupling. We also discovered a substantial and previously unrecognized input from the region immediately ventral to nucleus prepositus hypoglossi. In contrast, RVLM sympathetic premotor neurons were only sparsely innervated by suprapontine structures including the paraventricular nucleus, lateral hypothalamus, periaqueductal grey and superior colliculus, and we found almost no evidence of direct inputs from the cortex or amygdala.
Our approach can be used to quantify, standardize and share complete neuroanatomical datasets, and therefore provides researchers with a platform for presentation, analysis and independent analysis of connectomic data.

延髓嘴侧腹外侧区 (rostral ventrolateral medulla, RVLM) 的脊髓投射神经元对血管运动交感紧张的产生至关重要，且被认为接受来自神经轴各层级神经元的会聚性输入；但其调控其持续放电活动的因素仍未明确。本研究采用遗传限制性病毒示踪策略，首次明确绘制了其空间弥散的连接组。
我们将可在单突触连接的输入神经元中驱动报告基因表达的重组狂犬病毒变体，感染球脊髓性RVLM神经元；并通过基于磁共振成像 (MRI) 的体积图谱，以及一款可将常规显微照片中捕获的神经元位置高效转换为笛卡尔坐标的新型图像配准与可视化工具，绘制了这些神经元的分布情况。
本研究鉴定出多个显著的输入来源，包括已被证实的神经体液与内脏交感感觉效应器、延髓自主神经及呼吸亚核，以及延髓上自主神经核团。大部分输入信号来自脑干（88%~94%），其中包含前包钦格复合体 (pre-Bötzinger Complex) 和吸气后复合体中的疑似呼吸神经元，这些神经元或为呼吸-交感耦合的结构基础。我们还发现了来自舌下神经前置核 (nucleus prepositus hypoglossi) 腹侧紧邻区域的大量、此前未被报道的输入信号。与之相对，RVLM交感前运动神经元仅接受来自桥脑上位结构的稀疏神经支配，这些结构包括室旁核、外侧下丘脑、中脑导水管周围灰质及上丘；且我们几乎未发现来自大脑皮层或杏仁核的直接输入证据。
本研究方法可用于量化、标准化并共享完整的神经解剖学数据集，从而为研究者提供一个用于展示、分析及独立解析连接组数据的平台。