Postnatal development of right atrial injection of capsaicin-induced apneic response in rats

J Appl Physiol (1985). 2006 Jul;101(1):60-7. doi: 10.1152/japplphysiol.00085.2006. Epub 2006 Mar 30.


Apnea and respiratory failure often occur in infants with pulmonary disease. Bronchopulmonary C-fiber (PCF)-mediated apnea is an important component of respiratory dysfunction. This study was undertaken to define the postnatal development of PCF-mediated apnea. The experiments were conducted in five groups of anesthetized, tracheotomized, and spontaneously breathing rats with ages at postnatal days P1-3, P7-9, P14-16, P21-23, and P56-58. Right atrial bolus injection of three doses of capsaicin (Cap), equivalent to 2, 4, and 8 microg/kg used previously in 450-g rats, was applied to stimulate PCFs. We found that 1) Cap-induced apneic response [percent change from the baseline expiratory duration (Te) values (deltaTe%)] and the sensitivity of this response (deltaTe%.microg(-1)) were significantly greater in the rats <P10 than those >P10; 2) the Cap-induced apneas were vagally dependent in all rats tested; and 3) bivagotomy-induced prolongation of Te was much greater in the rats <P10 than those >P10. From these findings we concluded that, compared with the older rats (>P10), the newborn rats have a stronger PCF-mediated respiratory inhibition that may contribute to infants' vulnerability to respiratory failure.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aging / physiology
  • Animals
  • Animals, Newborn / physiology*
  • Apnea / chemically induced*
  • Apnea / physiopathology*
  • Capsaicin / administration & dosage
  • Capsaicin / pharmacology*
  • Exhalation / physiology
  • Heart Atria / drug effects
  • Heart Atria / physiopathology
  • Injections
  • Lung Volume Measurements
  • Male
  • Nerve Fibers, Unmyelinated / physiology*
  • Pulmonary Ventilation / physiology
  • Rats
  • Rats, Sprague-Dawley
  • Respiratory Physiological Phenomena / drug effects*
  • Respiratory System / drug effects
  • Respiratory System / growth & development
  • Respiratory System / innervation
  • Respiratory System / physiopathology
  • Time Factors
  • Vagus Nerve / physiopathology
  • Vagus Nerve / surgery


  • Capsaicin