Capsaicin-induced activation of pulmonary vagal C fibers produces reflex laryngeal closure in the rat

Abstract

Our recent studies show that intravenous administration of capsaicin induces enhancement of the intralaryngeal thyroarytenoid (TA) branch but a reduction of the intralaryngeal abducent branch, suggesting that the glottis is likely closed by capsaicin. The aim of the present study was to examine whether the glottis is adducted by intravenous administration of capsaicin. Electromyographic (EMG) activity of the TA muscle, subglottal pressure (SGP), and glottal behavior were evaluated before and after intravenous administration of capsaicin in male Wistar rats that were anesthetized and tracheostomized. Catheters were placed in the femoral artery and vein, as well as in the right jugular vein. Low and high doses of capsaicin (0.625 and 1.25 microg/kg) produced apnea and increases in the amplitude of the TA EMG. This enhancement of the TA EMG was observed during apnea as well as during recovery from apnea. Moreover, the onset of the TA EMG was advanced such that it commenced earlier during inspiration. Concomitantly, the SGP substantially increased. Increases in both the TA EMG and SGP were abolished after bilateral sectioning of the recurrent laryngeal nerve. In some animals, movement of the vocal folds was recorded by taking a motion picture with a digital camera under a surgical microscope. With intravenous administration of capsaicin, a tight glottal closure, decreases in blood pressure, and bradycardia were observed. These results strongly suggest that glottal closure is reflexively induced by intravenous administration of capsaicin and that closure of the glottis is beneficial for the defense of the airway and lungs when an animal is exposed to environmental irritants.

Pulmonary C-fiber receptor activation abolishes uncoupled facial nerve activity from phrenic bursting during positive end-expired pressure in the rat

“…However, anandamide also induced a concomitant increase in burst amplitude with earlier onset in the adducent branch of the RLN. This coordinated response of the RLN branches resulted in a short period of glottal closure (47), similar to that reported in response to capsaicin (34). Moreover, a similar response occurs during pulmonary edema in lambs (8,9).…”

Ultrasonic output from the excised rat larynx

“…While there were upper outliers in these data that were excessive, the mean subglottal pressures observed were biologically realistic. 13 A significant main effect for adduction condition was found at airflow rates of 3 L/min (F ͓2,4͔ = 14.88, p = 0.01), 4 L/min (F ͓2,6͔ = 54.75, p = 0.0001), and 6 L/min (F ͓2,7͔ = 11.69, p Ͻ 0.01). Post-hoc paired comparisons revealed that modal frequency was significantly greater in both the anterior and the anterior/posterior adduction conditions at airflow rates of 3, 4, and 6 L/min compared with the open glottis condition ͑p Ͻ 0.05͒.…”

“…Although direct study of subglottal pressure during USV production is lacking, one study of rats reported subglottal pressures of 30 cm H 2 O during vocal fold closure. 13 Thus, it is likely that variations in laryngeal adduction, airflow, and subglottal pressure are used by the rat to achieve a wide frequency range of USVs in vivo.…”

“…Subglottal air pressure directly below the mounting tube was monitored with a U-tube manometer (Dwyer Instruments, Michigan City, IN) to ensure it remained within known physiologic limits. 13 A bat detector system (Anabat II with ZCAIM, AnaBat, East Brisbane, Australia) was mounted 10 cm away from the larynx out of the airstream to detect ultrasonic output. The Anabat II with ZCAIM (zero crossings analysis interface module) is a frequency division bat detector that uses zero crossings analysis to record fundamental frequency over time; amplitude and harmonics of the acoustic signal are not preserved.…”

Destructive effect of digitalis overdose on blood-brain barrier in rats; an experimental study

“…11 The endogenous opioid peptide-related behavior modulation may be disrupted with digoxin toxicity. 40 Digitalis toxicity may disrupt the sympathovagal control network, 41 which could lead to respiratory arrest due to vagal paralysis 42 and SAH probably due to hypothalamic damage. 12,43 Glycosides may be transported to the cerebrospinal fluid via choroidal arteries in patients with SAH.…”