AJP - Regulatory, Integrative and Comparative Physiology, Vol 269, Issue 3 669-R677, Copyright © 1995 by American Physiological Society

ARTICLES

An intact glutamatergic trigeminal pathway is essential for the cardiac response to simulated diving

P. F. McCulloch, I. A. Paterson and N. H. West
Department of Physiology, College of Medicine, University of Saskatchewan, Saskatoon, Canada.

Nasal water flow plus concomitant expiratory apnea in anesthetized (Innovar-Vet), paralyzed, and artificially ventilated rats produces immediate bradycardia. To investigate the origin of this response, four procedures were used to block the trigeminal pathway. 1) Trigeminal receptors within the nasal passages were anesthetized by infusing local anesthetic through the external nares. 2) Trigeminal nerves that innervate the nasal passages were sectioned bilaterally as they passed through the orbit. 3) The trigeminal neural pathway was blocked within the brain stem by either electrolytically lesioning or infusing local anesthetic into the spinal trigeminal nucleus interpolaris (Sp5I). 4) Synaptic transmission within Sp5I was prevented by infusing glutamate receptor antagonists D-2-amino-7-phosphonoheptanoic acid and 6,7-dinitroquinoxaline-2,3-dione. After each of the procedures was completed, the cardiovascular responses to nasal water flow plus apnea were either attenuated or eliminated. The major conclusion of this study is that an intact glutamatergic trigeminal pathway is required for manifestation of the cardiovascular responses to nasal stimulation. Evidence also suggests that N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptors are both required for synaptic neurotransmission within Sp5I.

This article has been cited by other articles:

				G. P. Ollenberger and N. H. West Contribution of hypercapnia and trigeminal stimulation to cerebrovascular dilation during simulated diving Am J Physiol Regulatory Integrative Comp Physiol, April 1, 1998; 274(4): R921 - R930. [Abstract] [Full Text] [PDF]