AJP - Regulatory, Integrative and Comparative Physiology, Vol 273, Issue 2 814-R822, Copyright © 1997 by American Physiological Society
Trigeminal and chemoreceptor contributions to bradycardia during voluntary dives in rats
P. F. McCulloch, G. P. Ollenberger, L. K. Bekar and N. H. West
Department of Physiology, College of Medicine, University of Saskatchewan, Saskatoon, Canada.
This study investigates the importance of chemoreceptive and trigeminal
information during voluntarily initiated diving in rats. The heart rate
responses to simulated diving are unaffected by chemoreceptor drive
[McCulloch, P.F., and N. H. West. Am. J. Physiol. 263 (Regulatory
Integrative Comp. Physiol. 32): R1049-R1056, 1992] but are reversibly
eliminated by infusion of glutamate receptor antagonists into the spinal
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 conscious dives, rats
were made hypercapnic, hyperoxic, or hypoxic predive. The role of
trigeminal input was explored by infusing the glutamatergic antagonists
D-2-amino-7-phosphoheptanoic acid and 6,7-dinitroquinoxaline-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 not abolish it. Chemoreceptor
input does not play a significant role in determining heart rate during
conscious diving in rats. The attenuation, rather than abolition, of
bradycardia on trigeminal blockade suggests either that we achieved
incomplete blockade or that an additional spectrum of sensory inputs not
present in simulated diving is important in determining the underwater
heart rate during conscious diving in rats.
