Monosynaptic inputs from the nucleus tractus solitarii to the laryngeal motoneurons in the nucleus ambiguus of the rat

Abstract

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.

Distribution of Fos-Like Immunoreactivity, Catecholaminergic and Serotoninergic Neurons Activated by the Laryngeal Chemoreflex in the Medulla Oblongata of Rats

“…Tracing studies revealed the laryngeal pre-motor neurons [14,61,62], showing overlaps with our finding. Pharmaceutical and functional approaches even provided the role of NTS in the LCR [40,63].…”

“…Previous studies indicated that some medullary nuclei were potentially involved in the LCR [14,40,61–63]. Tracing studies revealed the laryngeal pre-motor neurons [14,61,62], showing overlaps with our finding.…”

Inhibitory connections among rostral medullary expiratory neurones detected with cross-correlation in the decerebrate rat*

“…John 1998). Many are motoneurones (Bryant et al 1993;Saito et al 2002;Zheng et al 1991a), especially those caudal to the obex, which may be laryngeal motoneurones (Hayakawa et al 2000;Saito et al 2002). However, some in the caudal VRG project to the spinal cord and the nucleus ambiguus Zheng et al 1991a) and may either play a role as premotor neurones to laryngeal and spinal motoneurones (Bianchi et al 1990;Dutschmann and Paton 2002;Saito et al 2002), or act as inhibitory interneurones (Bianchi et al 1989).…”

Caudal nuclei of the rat nucleus of the solitary tract differentially innervate respiratory compartments within the ventrolateral medulla

“…Hayakawa et al, 1998, 2000). In many cases, these afferent pathways to the nucleus ambiguus are undoubtedly also labeled by tracer injections into compartments of the VRC and may complicate the identification of differences amongst the NTS nuclei innervating functional cardiorespiratory compartments.…”