Neural drive to tongue protrudor and retractor muscles following pulmonary C-fiber activation

• Published in: Journal of applied physiology (1985) 2007-01, Vol.102 (1), p.434-444
• Main Authors: Lee, Kun-Ze, Fuller, David D, Lu, I-Jung, Lin, Jin-Tun, Hwang, Ji-Chuu
• Format: Article
• Language: English
• Subjects: Action Potentials - drug effects; Analgesics, Non-Narcotic - pharmacology; Anatomy & physiology; Animals; Biological and medical sciences; Blood Pressure - drug effects; Capsaicin - pharmacology; Dose-Response Relationship, Drug; Drugs; Fundamental and applied biological sciences. Psychology; Heart Rate - drug effects; Hypoglossal Nerve - drug effects; Hypoglossal Nerve - physiology; Inhalation - physiology; Lung - innervation; Lung - physiology; Male; Motor Neurons - drug effects; Motor Neurons - physiology; Muscle, Smooth - innervation; Muscle, Smooth - physiology; Nerve Fibers, Unmyelinated - drug effects; Nerve Fibers, Unmyelinated - physiology; Neurons; Phrenic Nerve - drug effects; Phrenic Nerve - physiology; Rats; Rats, Wistar; Rodents; Tongue; Tongue - innervation
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00982.2005

1 Department of Life Science, National Taiwan Normal University, Taipei, Taiwan, Republic of China; and 2 Department of Physical Therapy, University of Florida, Gainesville, Florida Submitted 11 August 2005 ; accepted in final form 30 August 2006 ABSTRACT Hypoglossal (XII) nerve recordings indicate that pulmonary C-fiber (PCF) receptor activation reduces inspiratory bursting and triggers tonic discharge. We tested three hypotheses related to this observation: 1 ) PCF receptor activation inhibits inspiratory activity in XII branches innervating both tongue protrudor muscles (medial branch; XII MED ) and retractor muscles (lateral branch; XII LAT ); 2 ) reduced XII neurogram amplitude reflects decreased XII motoneuron discharge rate; and 3 ) tonic XII activity reflects recruitment of previously silent motoneurons. Phrenic, XII MED , and XII LAT neurograms were recorded in anesthetized, paralyzed, and ventilated rats. Capsaicin delivered to the jugular vein reduced phrenic bursting at doses of 0.625 and 1.25 µg/kg but augmented bursting at 5 µg/kg. All doses reduced inspiratory amplitude in XII MED and XII LAT ( P < 0.05), and these effects were eliminated following bilateral vagotomy. Single-fiber recordings indicated that capsaicin causes individual XII motoneurons to either decrease discharge rate ( n = 101/153) or become silent ( n = 39/153). Capsaicin also altered temporal characteristics such that both XII MED and XII LAT inspiratory burst onset occurred after the phrenic burst ( P < 0.05). Increases in tonic discharge after capsaicin were greater in XII MED vs. XII LAT ( P < 0.05); single-fiber recordings indicated that tonic discharge reflected recruitment of previously silent motoneurons. We conclude that PCF receptor activation reduces inspiratory XII motoneuron discharge and transiently attenuates neural drive to both tongue protrudor and retractor muscles. However, tonic discharge appears to be selectively enhanced in tongue protrudor muscles. Accordingly, reductions in upper airway stiffness associated with reduced XII burst amplitude may be offset by enhanced tonic activity in tongue protrudor muscles. hypoglossal motoneurons; rat Address for reprint requests and other correspondence: J.-C. Hwang, Dept. of Life Science, National Taiwan Normal Univ., Taipei, Taiwan, ROC (e-mail: jchwang{at}ntnu.edu.tw )