Sustained Effects of Capsaicin Infusion into the Oropharynx on Swallowing in Perfused Rats.

Abstract

To examine the sustained effects of oropharyngeal capsaicin stimulation on the regulation of swallowing, we recorded the swallowing-related nerve activities during continuous infusion of capsaicin solution into the oropharynx. In 33 in situ perfused brainstem preparation of rats, we recorded the activities of the vagus, hypoglossal, and phrenic nerves during fictive swallowing. The interburst intervals (IBIs) of the swallowing-related nerves during sequential pharyngeal swallowing (sPSW) elicited by electrical stimulation of the superior laryngeal nerve (SLN) during concurrent capsaicin stimulation of 10, 1, and 0.1 μM (n = 28) were compared with those during oropharyngeal infusion of saline (control) (n = 5). The IBIs during SLN-induced sPSW were reduced at 5 min after initiation of continuous infusion of 10 and 1 μM capsaicin solution. The IBIs showed significant decreases to -25.8 ± 6.9%, -25.9 ± 5.3, -18.3 ± 3.7, and -12.0 ± 1.6 at 30 min following 1 μM capsaicin stimulation at SLN stimulus conditions at 5 Hz of 1.2 times threshold, 10 Hz of 40 μA, 5 Hz of 60 μA, and 10 Hz of 60 μA, respectively. Continuous capsaicin stimulation of 0.1 μM solution did not show significant sustained effects. Pharmacological stimulation of capsaicin could provide time-dependent effects on the likelihood of swallowing, particularly subserving sustained facilitation of swallowing reflex with appropriate concentration of capsaicin. NA Laryngoscope, 134:305-314, 2024.