Abstract
Somatosensory feedback from the larynx plays a critical role in regulation of normal upper airway functions, such as breathing, deglutition, and voice production, while altered laryngeal sensory feedback is known to elicit a variety of pathological reflex responses, including persistent coughing, dysphonia, and laryngospasm. Despite its clinical impact, the central mechanisms underlying the development of pathological laryngeal responses remain poorly understood. We examined the effects of persistent vocal fold (VF) inflammation and trauma, as frequent causes of long-lasting modulation of laryngeal sensory feedback, on brainstem immunoreactivity in the rat. Combined VF inflammation and trauma were induced by injection of lipopolysaccharide (LPS) solution and compared to VF trauma alone from injection of vehicle solution and to controls without any VF manipulations. Using a c-fos marker, we found significantly increased Fos-like immunoreactivity (FLI) in the bilateral intermediate/parvicellular reticular formation (IRF/PCRF) with a trend in the left solitary tract nucleus (NTS) only in animals with combined LPS-induced VF inflammation and trauma. Further, FLI in the right NTS was significantly correlated with the severity of LPS-induced VF changes. However, increased brainstem FLI response was not associated with FLI changes in the first-order neurons of the laryngeal afferents located in the nodose and jugular ganglia in either group. Our data indicate that complex VF alterations (i.e., inflammation/trauma vs. trauma alone) may cause prolonged excitability of the brainstem nuclei receiving a direct sensory input from the larynx, which, in turn, may lead to (mal)plastic changes within the laryngeal central sensory control.
Highlights
Sensory feedback from the larynx is an integral component of the central control of upper airway functions, including breathing, deglutition, and voice production
Using a c-fos marker, we found significantly increased Fos-like immunoreactivity (FLI) in the bilateral intermediate/parvicellular reticular formation (IRF/PCRF) with a trend in the left solitary tract nucleus (NTS) only in animals with combined LPS-induced vocal fold (VF) inflammation and trauma
We hypothesized that persistent VF inflammation combined with trauma but not VF trauma alone would elicit an immunoreactivity response in the brainstem regions of laryngeal somatosensory control in the rat
Summary
Sensory feedback from the larynx is an integral component of the central control of upper airway functions, including breathing, deglutition, and voice production. Alterations of the laryngeal sensory feedback often result in a variety of pathological laryngeal reflex responses, such as effortful swallowing, laryngospasm, central apnea, reflexive coughing, and chronic dysphonia (Sasaki and Suzuki, 1976; Loughlin and Koufman, 1996; Nishino et al, 1996; Jafari et al, 2003; Bolser, 2004). Some of these pathological responses in humans may represent a lifethreatening condition (e.g., laryngospasm), while others may have a profound effect on persons’ quality of life (e.g., chronic dysphonia and coughing).
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