Hayakawa T, Takanaga A, Maeda S, Ito H, Seki M
Department of Anatomy, Hyogo College of Medicine, Mukogawa, Nishinomiya, Japan.
Anat Embryol (Berl). 2000 Nov;202(5):411-20. doi: 10.1007/s004290000120.
The cricothyroid (CT) and the posterior cricoarytenoid (PCA) muscles in the larynx are activated by the laryngeal motoneurons located within the nucleus ambiguus; these motoneurons receive the laryngeal sensory information from the nucleus tractus solitarii (NTS) during respiration and swallowing. We investigated whether the neurons in the NTS projected directly to the laryngeal motoneurons, and what is the synaptic organization of their nerve terminals on the laryngeal motoneurons using the electron microscope. When wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) was injected into the NTS after cholera toxin subunit B-conjugated HRP (CT-HRP) was injected into the CT muscle or the PCA muscle, the anterogradely WGA-HRP-labeled terminals from the NTS were found to directly contact the retrogradely CT-HRP-labeled dendrites and soma of both the CT and the PCA motoneurons. The labeled NTS terminals comprised about 4% of the axosomatic terminals in a section through the CT motoneurons, and about 9% on both the small (PCA-A) and the large (PCA-B) PCA motoneurons. The number of labeled axosomatic terminals containing round vesicles and making asymmetric synaptic contacts (Gray's type I) was almost equal to that of the labeled terminals containing pleomorphic vesicles and making symmetric synaptic contacts (Gray's type II) on the CT motoneurons. The labeled axosomatic terminals were mostly Gray's type II on the PCA-A motoneurons, while the majority of them were Gray's type I on the PCA-B motoneurons. These results indicate that the laryngeal CT and PCA motoneurons receive a few direct excitatory and inhibitory inputs from the neurons in the NTS.
喉内的环甲肌（CT）和环杓后肌（PCA）由位于疑核内的喉运动神经元激活；这些运动神经元在呼吸和吞咽过程中从孤束核（NTS）接收喉部感觉信息。我们研究了NTS中的神经元是否直接投射到喉运动神经元，以及使用电子显微镜观察其在喉运动神经元上的神经末梢的突触组织是怎样的。在将霍乱毒素B亚基结合辣根过氧化物酶（CT-HRP）注入CT肌或PCA肌后，将小麦胚凝集素结合辣根过氧化物酶（WGA-HRP）注入NTS，发现来自NTS的顺行性WGA-HRP标记的末梢直接接触逆行性CT-HRP标记的CT和PCA运动神经元的树突和胞体。在通过CT运动神经元的切片中，标记的NTS末梢约占轴体末梢的4%，在小（PCA-A）和大（PCA-B）PCA运动神经元上约占9%。在CT运动神经元上，含有圆形囊泡并形成不对称突触接触（格雷I型）的标记轴体末梢数量几乎与含有多形性囊泡并形成对称突触接触（格雷II型）的标记末梢数量相等。在PCA-A运动神经元上，标记的轴体末梢大多为格雷II型，而在PCA-B运动神经元上，它们大多为格雷I型。这些结果表明，喉CT和PCA运动神经元从NTS中的神经元接收少量直接的兴奋性和抑制性输入。
