AMERICAN JOURNAL OF PHYSIOLOGY Vol. 228, No. 2, February 1975. Printed in U.S.A. Central nervous system control of cardiorespiratory nasopharyngeal reflexes in the rabbit SAXON WHITE, ROBERT J. McRITCHIE, AND PAUL I. KORNER Debartment of Medicine, Universitv of Svdnav. and Hallstrom Instituta of Cardiology, WHITE, SAXON, ROBERT J. MCRITCHIE, AND PAUL I. CORNER. Central nervous system control of cardiorespiratory nasopharyngeal refi7exes in the rabbit. Am. J. Physiol. 228(2) : 404-409. 1975.--The role of different central nervous regions in the reflex apnea, bradycardia, and mesenteric vasoconstriction evoked by nasopharyngeal stimu- lation with cigarette smoke was examined in unanesthetized sham- operated, thalamic, and pontine rabbits with intact and sectioned carotid sinus and aortic nerves (CS and AN). Apnea occurred in all preparations. In pontine animals with intact CS and AN, the heart rate response was reduced but not the mesenteric vasocon- striction. The role of suprabulbar and bulbospinal regions became more apparent when individual components of the input profile were examined in animals with controlled ventilation. The brady- cardia and mesenteric vasoconstriction evoked by apnea without smoke, but not by smoke without apnea, were reduced in pontine animals. Prior section of the CS and AN attenuated the response in all neural preparations but to the least extent when cerebral hemispheres were intact. The data indicate that the respiratory reflex is predominantly integrated at bulbospinal sites, but the cardiovascular reflex is integrated at both bulbospinal and supra- bulbar sites, or is integrated at bulbospinal and modulated from suprabulbar sites. central nervous cardiovascular control; central nervous respiratory control; smoke reflex; trigeminal; carotid sinus and aortic nerves; asnea NAS~PHARYSGEAL STIMULATION in the rabbit with cigarette smoke and many other vapors evokes a reflex response con- sisting of apnea in expiration, bradycardia, a rise in blood pressure, and widespread peripheral vasoconstriction (5, 20, 2 1 ), Trigeminal afferents and those from the arterial baroreceptors contribute to the circulatory response, and the input from the chemoreceptors influences the duration of the apnea ( 14) l The question arises as to whether supra- pontine mechanisms play a role in the ‘%moke” reflex as they do in other reflex disturbances (9-11, 19). No analysis of the role of the central nervous system (CNS) in the smoke reflex of the rabbit has been made so far. However, the reflex resembles the diving response of aquatic birds, in which Huxley (6) and Andersen (1) demonstrated that reflex apnea and bradycardia were unaffected by decerebra- tian. They therefore considered the diving reflex was inte- grated predominantly by bulbar mechanisms. The purpose of the present study was to examine the role of suprapontine and bulbospinal regions in the reflex re- sponse to nasal smoke inhalation in unanesthetized rabbits. We studied the responses of spontaneously breathing sham- operated, thalamic, and pontine rabbits in which the input from the carotid sinus and aortic nerves was intact and also when these nerves were sectioned. In these same prepara- tions we also analyzed under conditions of controlled ven- tilation the effects of apnea without smoke stimulation and of smoke without apnea. METHODS The experiments were performed with New Zealand white rabbits, weighing between 2.4 and 3.5 kg. Preliminary operations were performed lo-14 days before an experi- ment, with halothane anesthesia. At this operation, a Doppler ultrasonic flow transducer was placed around the superior mesenteric artery, as described previously (2 1) . On the day of the experiment the central ear artery was cannulated under local lidocaine anesthesia. A fronto- parietal craniotomy was then performed with halothane anesthesia. Sham-operated rabbits, thalamic rabbits (with cerebral hemispheres and basal ganglia removed and thalamus and hypothalamus left intact), and pontine ani- mals (infracollicular decerebration) were prepared as de- scribed previously (11). Th ere were four rabbits in each of these groups. In four additional animals of each group the carotid sinus and aortic nerves were cut bilaterally in the neck (7) immediately after neurosurgical procedures while the rabbits were anesthetized with halothane. Sham-oper- ated and thalamic animals recovered normal movement and posture within .5-l h from the end of anesthesia. The pontine animals lay on their side until .5 h before the start of the experiment, and their body temperatures were main- tained with an electric blanket. Details of the postoperative management were as described previously (11). Conduct of experiments and statistical methods. Experiments began 3 h after the operation. The sham-operated and thalamic animals sat quietly in their rabbit box, while the pontine animals were placed in a special holder and studied in the posture of a normally sitting rabbit. Nasopharyngeal stimulation was produced by blowing cigarette smoke through a narrow polyvinyl chloride tube. One puff of smoke was blown gently in front of the animal’s nostrils and the cardiorespiratory response was observed (see below). The response was highly reproducible in a given animal (20). A given response in a particular animal was estimated from the mean of three puffs of cigarette smoke adminis- tered at 3- to 5-min intervals. For each test, measurements by 10.220.32.246 on May 8, 2017 http://ajplegacy.physiology.org/ Downloaded from