TRIGEMINAL AND CHEMORECEPTOR CONTRIBUTIONS TO BRADYCARDIA DURING VOLUNTARY DIVES IN RATS

This study investigates the importance of chemoreceptive and trigemina l information during voluntarily initiated diving in rats. The heart r ate responses to simulated diving are unaffected by chemoreceptor driv e [McCulloch, P. F., and N. H. West. Am. J. Physiol. 263 (Regulatory I ntegrative Comp. Physiol. 32): R1049-R1056, 1992] but are reversibly e liminated by infusion of glutamate receptor antagonists into the spina l trigeminal nuclei [McCulloch, P. F., I. A. Paterson, and N. H. West. Am. J. Physiol. 269 (Regulatory Integrative Comp. Physiol. 38): R669- R677, 1995]. To investigate the role of chemoreceptor drive in conscio us dives, rats mere made hypercapnic, hyperoxic, or hypoxic predive. T he role of trigeminal input was explored by infusing the glutamatergic antagonists D-2-amino-7-phosphoheptanoic acid and 6,7-dinitroquinoxal ine-2,3-dione into the region of the trigeminal nuclei. The alteration of arterial blood gases predive had no effect on diving bradycardia. Trigeminal blockade reduced the intensity of the bradycardia but did n ot abolish it. Chemoreceptor input does not play a significant role in determining heart rate during conscious diving in rats. The attenuati on, rather than abolition, of bradycardia on trigeminal blockade sugge sts either that we achieved incomplete blockade or that an additional spectrum of sensory inputs not present in simulated diving is importan t in determining the underwater heart rate during conscious diving in rats.