Coordinated Respiratory Motor Activity in Nerves Innervating the Upper Airway Muscles in Rats

Abstract

Maintaining the patency of the upper airway during breathing is of vital importance. The activity of various muscles is related to the patency of the upper airway. In the present study, we examined the respiratory motor activity in the efferent nerves innervating the upper airway muscles to determine the movements of the upper airway during respiration under normocapnic conditions (pH = 7.4) and in hypercapnic acidosis (pH = 7.2). Experiments were performed on arterially perfused decerebrate rats aged between postnatal days 21–35. We recorded the efferent nerve activity in a branch of the cervical spinal nerve innervating the infrahyoid muscles (CN), the hypoglossal nerve (HGN), the external branch of the superior laryngeal nerve (SLN), and the recurrent laryngeal nerve (RLN) with the phrenic nerve (PN). Inspiratory nerve discharges were observed in all these nerves under normocapnic conditions. The onset of inspiratory discharges in the CN and HGN was slightly prior to those in the SLN and RLN. When the CO2 concentration in the perfusate was increased from 5% to 8% to prepare for hypercapnic acidosis, the peak amplitudes of the inspiratory discharges in all the recorded nerves were increased. Moreover, hypercapnic acidosis induced pre-inspiratory discharges in the CN, HGN, SLN, and RLN. The onset of pre-inspiratory discharges in the CN, HGN, and SLN was prior to that of discharges in the RLN. These results suggest that the securing of the airway that occurs a certain time before dilation of the glottis may facilitate ventilation and improve hypercapnic acidosis.

Recovery of respiratory function and autonomic diaphragm movement following unilateral recurrent laryngeal nerve to phrenic nerve anastomosis in rabbits

“…2). Similarly, Tachikawa et al found that the discharge frequency of the RLN synchronized with that of the PN whether in a normocapnic condition or hypercapnic acidosis, 26 and other studies found that RLN-innervated muscles contracted simultaneously with the abdominal muscles during forced expiration, such as when coughing. 7,24 In addition, we showed that most of the fibers in the RLN are motor fibers using AChE staining, even though the number of motor fibers in the RLN was much less than that in the PN (Fig.…”

“…1 Tachikawa et al found that the discharge frequency of the RLN synchronized with that of the PN, and this demonstrated the theoretical possibility of reestablishing autonomic and physiological respiration with RLN-PN anastomosis. 26 Gauthier et al found that spontaneous discharge from an anastomosed PN could be detected even after complete transection of the spinal cord at the C2 level in a rat model. 12 Using a rabbit model, Derrey et al studied the effect of anastomosis of the inferior laryngeal nerve (ILN) to the PN and found poor neurogenic electrical activity of the diaphragm.…”

Coordinated control of the tongue during suckling-like activity and respiration

“…In such preparations, respiratory rhythms (19) and firing patterns of the medullary respiratory neurons (20) are similar to those of adult in vivo mammal preparations. Thus, we used this experimental model to examine respiratory motor activity during normo-and hypercapnia in efferent nerves innervating the upper airway muscles, such as the HGN innervating the tongue; the first, second, and third cervical spinal nerves (CN) innervating the infrahyoid muscles; the external branch of the superior laryngeal nerve (SLN) innervating the cricothyroid and inferior pharyngeal constrictor muscles; and the recurrent laryngeal nerve (RLN) innervating the laryngeal abductors and laryngeal adductors (21).…”

“…Under normocapnic conditions (5% CO 2 ), stable inspiratory activity of the phrenic nerve (PN)-which innervates the main inspiratory muscle, the diaphragmspontaneously occurs at a frequency of ≈0.3 Hz in the perfused preparations (21). The integrated PN activity exhibited an augmenting pattern ( Fig.…”