Effect of carotid chemoreceptor denervation on breathing during ventrolateral medullary cooling in goats. Pan, L. G., H. V. Forster, P. J. Ohtake, T. F. Lowry, M. J. Korducki, and A. L. Forster. Department of Physiology, Medical College of Wisconsin, Milwaukee, WI 53226; Zablocki Veterans Affairs Medical Center, Milwaukee, WI 53295; and Program in Physical Therapy, Marquette Univ., Milwaukee, WI 53233
APStracts 2:0217A, 1995.
It has been postulated that the so-called area S of the ventrolateral medulla (VLM) integrates peripheral chemoreceptor activity; thus cooling induced dysfunction of neurons in this VLM area should functionally eliminate carotid chemoreceptor stimulation of breathing. Accordingly, carotid chemoreceptor denervation (CBD) should not alter the breathing effects of VLM neuronal dysfunction. To test this hypothesis in awake goats, chronically implanted thermodes were used to cool the VLM, and thereby cause reversible neuronal dysfunction in all or portions of VLM areas M and S. Within 5 seconds after initiation of cooling approximately 60-100% of areas M and S in intact goats, pulmonary ventilation (I) decreased by approximately 40% (P<.05) uniformly over conditions of eupnea, hypercapnia, and hypoxia. Between 10 and 20 seconds of cooling, the reduction in I was about 10% greater (<.05) during hypercapnia than during eupnea and hypoxia. For the remaining 10 seconds of cooling and for about 1 minute after cooling, I increased to and above control for all conditions. For all conditions, CBD accentuated the depression of I during cooling, causing I to decrease (P<.05) 10 -40% more than pre-CBD. After CBD, the greatest effect on I of cooling was again during hypercapnia. Thus the carotid bodies in intact goats appear to sense blood gas errors caused during VLM cooling to minimize the decreases in I. We conclude that the data from this study does not support the concept that the VLM integrates carotid chemoreceptor activity. 

Received 23 January 1995; accepted in final form 10 May 1995.
APS Manuscript Number A85-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 May 1995.