Neuroimmunological activation of the afferent laryngeal neural circuit in experimentally induced laryngeal inflammation

Abstract

Conclusions These results show that laryngeal inflammatory reactions may induce the expression of proinflammatory cytokines along the afferent laryngeal circuit and in nuclei associated with the HPA axis. Local laryngeal inflammation may induce functional and physiologic alterations in the laryngeal neural system via neuroimmunologic reactions.

Objective Idiopathic laryngeal disorders associated with various neurologic conditions such as spasmodic dysphonia, idiopathic vocal fold paralysis and sudden infant death syndrome are causally related to upper respiratory tract infections, and it can be speculated that these disorders result in neurophysiologic alterations. The goal of this study was to identify the neurophysiologic effect on the central nervous system of local inflammatory alterations in the larynx.

Material and methods The expression of c-fos and IL-1β was identified after injecting saline solution, 10 μg of lipopolysaccharide or 100 μg of lipopolysaccharide into the larynx of 12 rats.

Results The inflammatory cytokine IL-1β was mainly expressed in the inferior olivary nucleus and raphe nucleus, which are associated with the hypothalamic–pituitary–adrenal (HPA) axis. IL-1β expression was also found in the nuclei of afferent nervous pathways of the superior laryngeal nerve, such as the nucleus tractus solitarius, nucleus ambiguus, lateral reticular nucleus, magnocellular reticular nucleus and paragigantocellular reticular nucleus.

• C-fos
• hypothalamic–pituitary–adrenal axis
• IL-1β
• laryngeal neural pathways
• laryngeal reflex
• larynx
• nucleus tractus solitarius
• proinflammatory cytokine