Submitted on March 15, 2005
Accepted on August 31, 2005
Carotid Sinus Nerve Is Involved in Cardiorespiratory Responses to Intracarotid Injection of Capsaicin in the Rat
Rurong Wang1, Fadi Xu1*, Jianguo Zhuang1, and Cancan Zhang1
1 Pathophysiology Program, Lovelace Respiratory Research Institute, Albuquerque, New Mexico, USA
* To whom correspondence should be addressed. E-mail: fxu{at}lrri.org.
The carotid sinus nerve (CSN), important in cardiorespiratory modulation, mainly contains Cfibers
(CSCFs). Previous studies have demonstrated that selective stimulation of bronchopulmonary C fibers (PCFs) via right atrial injection of capsaicin (CAP, ~0.25 µg) results
in an apnea (~3 sec) associated with hypotension and bradycardia. The present study was undertaken to determine the effects of activating CSCFs on cardiorespiratory activities. Intracarotid injection of CAP was performed before and after bilateral transection of the CSN in
anesthetized and spontaneously breathing rats. Our results showed that: (1) low doses of CAP (up to 2 ng) produced an increase in minute ventilation (VE) by elevating both tidal volume (VT) and respiratory frequency (f) with the threshold dosage at 1.0 ng (P < 0.05); (2) high doses (4-64 ng) generated an apnea (prolongation of expiratory duration by approximately eightfold) and hypertension (P < 0.05); (3) bilateral transection of the CSN reduced excitatory and inhibitory respiratory responses by 30% and 81%, respectively, and increased the hypertension by 88% (P < 0.05); and (4) the same doses of CAP delivered into the right atrium to stimulate bronchopulmonary C-fibers failed to evoke detectable cardiorespiratory responses. Our results suggest that as compared PCFs, CSCFs are more sensitive to CAP stimulation, and activation of these fibers significantly modulates cardiorespiratory activity in anesthetized rats.
