Response of respiratory-related hypoglossal nerve activity to capsaicin-induced pulmonary C-fiber activation in rats.
This study was designed to examine respiratory-related hypoglossal nerve activity in response to activation of pulmonary C-fibers by capsaicin. Rats were anesthetized with urethane (1.2 g/kg, i.p.). Tracheostomy was performed. Catheters were introduced into the femoral vein and artery. Another catheter was placed near the entrance of the right atrium via the right jugular vein. Rats were paralyzed with gallamine triethiodide (5 mg/kg, i.v.), and ventilated artificially. Activities of the phrenic nerve (PNA) and the hypoglossal nerve (HNA) were recorded simultaneously. Varied doses of capsaicin (0.625, 1.25, and 5 microg/kg) were delivered into the right atrium to activate pulmonary C-fibers. Before bilateral vagotomy, apnea, decreases in PNA and HNA were observed in response to pulmonary C-fiber activation by the low and moderate doses of capsaicin. The high dose of capsaicin evoked an increase in PNA, an immediate tonic discharge of the hypoglossal nerve, and a decrease in phasic HNA. The onset time of HNA preceding PNA was abolished and replaced by a time lagged pattern as pulmonary C-fibers were activated. Raising CO(2) concentration did not attenuate the inhibitory effect of pulmonary C-fiber activation upon PNA and HNA. After bilateral sectioning of the vagi, administration of the moderate dose of capsaicin to activate non-vagal C-fibers produced increases in PNA and HNA. These results suggest that pulmonary vagal C-fiber activation may narrow the diameter at the oropharyngeal level by a decrease in phasic HNA, which may be disadvantageous for the maintenance of a patent upper airway.
Lee
Kun-Ze
KZ
Department of Life Science, National Taiwan Normal University, Taipei, Taiwan, ROC.
Lu
I-Jung
IJ
Ku
Li-Chi
LC
Lin
Jin-Tun
JT
Hwang
Ji-Chuu
JC
D000818:Animals; D002211:Capsaicin / Q000494:pharmacology*; D002245:Carbon Dioxide / Q000494:pharmacology; D007002:Hypoglossal Nerve / Q000502:physiology*; D008168:Lung / Q000294:innervation*; D008297:Male; D036421:Nerve Fibers, Unmyelinated / Q000187:drug effects*; D010791:Phrenic Nerve / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012119:Respiration; D014628:Vagotomy
D002245:Carbon Dioxide; D002211:Capsaicin