Modulation of the tongue muscle activity in response to bronchopulmonary C‐fiber activation following mid‐cervical contused in the rat

Abstract

The present study was designed to investigate the tongue muscle activity in response to bronchopulmonary C‐fiber activation following mid‐cervical spinal contusion in the rat. The esophageal pressure and electromyogram of extrinsic tongue muscles (genioglossus and hyoglossus) were monitored before and after inhalation of capsaicin (25 and 100 μg/ml) at the acute, subchronic and chronic injured stages after mid‐cervical contusion. The results demonstrated that pre‐inspiratory and inspiratory burst amplitude of tongue muscle were generally enhanced at the acute and subchronic injured stages in mid‐cervical contused animals vs. uninjured animals. Inhalation of capsaicin usually caused a rapid shallow breathing pattern associated with a reduction in pre‐inspiratory and inspiratory activity of the tongue muscle in uninjured animals at the acute injured stage; however, this altered breathing pattern and decreased tongue muscle activity were blunted in contused animals. During the chronic injured stage, the expiratory duration was prolonged to a similar degree in both uninjured and contused animals after inhalation of capsaicin. Notably, inhibition of genioglossus muscle activity during capsaicin inhalation is more severed in chronically contused animals. These results demonstrated that cervical spinal cord injury is associated with alteration of supraspinal respiratory activity, which may modulate upper airway motor outputs and bronchopulmonary C‐fiber mediated respiratory reflexes. The compensatory increase in the tongue muscle activity at the acute injured stage may be benefit to the maintenance of the upper airway patency; however, the susceptible tongue muscle activity during bronchopulmonary C‐fiber activation may increase the risk of airway obstruction during the chronic injured stage.Support or Funding InformationMOST (105‐2628‐B‐110‐002‐MY3 & 108‐2636‐B‐110‐001), Higher Education Sprout Project (07C030111), NSYSU‐KMU Joint Research Project (107‐I001)