Abstract：
Sympathetic neurons that innervate the heart are located primarily in the stellate ganglia (SG), which also contains neurons that project to brown adipose tissue (BAT). These studies were designed to examine the morphology of these two populations (cardiac- and BAT-projecting) and their target connectivity. We examined SG neurons in C57BL/6J mice following injections of the retrograde tracer cholera toxin B (CTb) conjugated to Alexa Fluor 488 and Alexa Fluor 555, into cardiac tissue and intrascapular BAT. BAT-projecting SG neurons were widely dispersed in SG, while cardiac-projecting SG neurons were localized primarily near the inferior cardiac nerve base. SG neurons were not dual-labeled, suggesting that sympathetic innervation is specific to the heart and BAT, supporting the idea of \"labeled lines\" of efferents. Morphologically, cardiac-projecting SG somata had more volume and were less abundant than BAT-projecting neurons using our tracer-labeling paradigm. We found a positive correlation between the number of primary dendrites per neuron and soma volume in cardiac-projecting SG neurons, though not in BAT-projecting neurons. In both SG subpopulations, the number of cholinergic inputs marked with vesicular acetylcholine transporter (VAChT) puncta contacting the soma was positively correlated to soma volume, suggesting scaling of inputs across a range of neuronal sizes. In separate studies using dual tracing from left and right BAT, we found that BAT-projecting SG neurons were located predominately ipsilateral to the injection, but a small subset of SG neurons project bilaterally to BAT. This tracing approach will allow the assessment of cell-specific mechanisms of plasticity within subpopulations of SG neurons.
摘要：
支配心脏的交感神经元主要位于星状神经节(SG),它还包含投射到棕色脂肪组织（BAT）的神经元。这些研究旨在检查这两个群体的形态（心脏和BAT投射）及其目标连通性。我们在将与AlexaFluor488和AlexaFluor555缀合的逆行示踪霍乱毒素B（CTb）注射到心脏组织和肩胛骨内BAT后，检查了C57BL/6J小鼠中的SG神经元。BAT投射的SG神经元广泛分散在SG中，而心脏投射的SG神经元主要位于下心神经基底附近。SG神经元没有双重标记，表明交感神经支配是心脏和BAT特有的，支持“标记线”的观点。形态学上,使用我们的示踪剂标记范式，心脏投射的SG躯体比BAT投射的神经元具有更大的体积，并且数量更少。我们发现每个神经元的初级树突数量与心脏投射SG神经元的体细胞体积之间呈正相关，尽管不在BAT投射神经元中。在两个SG亚群中，以囊泡乙酰胆碱转运蛋白（VAChT）点标记的胆碱能输入的数量与体细胞体积呈正相关，建议在一系列神经元大小上缩放输入。在使用左右BAT双重追踪的单独研究中，我们发现BAT投射的SG神经元主要位于注射的同侧，但是一小部分SG神经元双侧投射到BAT。这种追踪方法将允许评估SG神经元亚群内的细胞特异性可塑性机制。
