Study of the fundamental neural circuitry for respiratory rhythmogenesis

为了分析呼吸中枢的神经网络，我们采用细胞内记录和神经生物素标记的方法研究了呼气减弱神经元（E-DEC）和呼气增强神经元（E-AUG）的形态学特征。本研究结果首次揭示了腹侧呼吸组（VRG）区E-DEC神经元和Botzinger复合体（BOT）神经元的详细形态。它们广泛的髓内投射表明这些尾侧VRG E-DEC神经元在呼吸中起重要作用。特别是，从尾侧VRG E-DEC神经元同时投射到脊髓和模糊核（NA）表明这些神经元在包括发声、呕吐和排便在内的非呼吸行为中发挥综合作用。2.BOT的E-AUG神经元向脑干有广泛的轴突投射。此外，本研究还揭示了BOT E-AUG神经元的一些新的投射模式。首先，几个BOT - E-AUG神经元向脑桥发送长长的上行侧支，一个标记良好的轴突到达同侧臂旁核并分布束。其次，发现这些上升侧支的分支在面核吻端水平的面核背外侧区域有明显的突起。第三，向对侧的侧枝在髓质背内侧形成细分支，称为副神经节背核。因此，本研究结果揭示了由E-DEC和E-AUG神经元组成的网络的解剖学基础，并为呼吸中枢的组织提供了新的见解。

In order to analyze the neuronal network of the respiratory center, the morphological properties of decrementing expiratory (E-DEC) neurons and augmenting expiratory (E-AUG) neurons were studied using intracellular recording and labeling with Neurobiotin. 1.The present results have revealed, for the first time, the detailed morphology of E-DEC neurons of the ventral respiratory group (VRG) area as well as those of the Botzinger complex (BOT). Their extensive intramedullary projections suggest that these caudal VRG E-DEC neurons play a significant role in respiration. In particular, the simultaneous projections from the caudal VRG E-DEC neurons to both the spinal cord and the ambiguus nucleus (NA) suggest that these neurons play integrative roles in non-respiratory behaviors including vocalization, vomiting and defecation. 2.E-AUG neurons of the BOT had extensive axonal projections to the brainstem as expected. In addition, the present study revealed a number of new projection patterns of the BOT E-AUG neurons. First, several BOT E-AUG neurons sent long ascending collaterals to the pons and one well-labeled axon reached the ipsilateral parabrachial nuclei and distributed boutons. Second, conspicuous projections from branches of these ascending collaterals to the area dorsolateral to the facial nucleus (FN) at the level of the rostral end of the FN were found. Third, a collateral that coursed toward the contralateral side issued a thin branch with boutons in the dorsomedial medulla called the dorsal paragigantoculluar nucleus. Thus, the present results have shown an anatomical substrate for the network formed by E-DEC and E-AUG neurons and provided new insights into the organization of the respiratory center.