Role of excitatory amino acid receptors in cardiorespiratory coupling in the ventrolateral medulla. Miyawaki, Takashi, Jane Minson, Leonard Arnolda, John Chalmers, Ida Llewellyn-Smith, and Paul Pilowsky. Dept. of Medicine and Centre for Neuroscience, Flinders Medical Centre, Bedford Park SA 5042 AUSTRALIA
APStracts 3:0162R, 1996.
The role of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate and N-methyl-D-aspartic acid (NMDA) receptors in the rostral ventrolateral medulla (RVLM) and caudal ventrolateral medulla (CVLM) on the central respiratory-related activity of splanchnic sympathetic nerve activity (SNA) was examined in anaesthetized, vagotomized and paralyzed rats. Rat splanchnic SNA showed an increase in activity during early inspiration (inspiratory peak) and post -inspiration (post-inspiratory peak). The post-inspiratory peak was abolished after bilateral microinjection of either 6-cyano-7 -nitroquinoxaline-2,3-dione (CNQX, a selective AMPA/kainate receptor antagonist) or DL-2-amino-5-phosphonovaleric acid (APV, a selective NMDA receptor antagonist) into the RVLM, while the inspiratory peak was not affected. Non-selective blockade of excitatory amino acid receptors in RVLM with bilateral microinjection of kynurenate or a mixture of APV and CNQX also failed to eliminate the inspiratory peak. The sympathoexcitatory response evoked by electrical stimulation of the hind paw was abolished by CNQX injection into the RVLM, but was not affected by APV injection. Bilateral injection of CNQX, but not APV into the CVLM elicited a significant increase in the post-inspiratory peak of splanchnic nerve activity. The present findings therefore suggest that 1) both NMDA and AMPA/kainate receptors in the RVLM are involved in the coupling between the sympathetic nervous system and central respiratory drive which generates the post-inspiratory peak seen in splanchnic SNA. 2) The inspiratory peak of splanchnic SNA is independent of excitatory amino acid transmission within the RVLM. 3) There are different relative amounts of NMDA and AMPA/kainate receptors at the synapses where respiratory and somatic inputs converge onto RVLM neurons. 4) Glutamatergic inputs to CVLM neurons acting via AMPA/kainate receptors may modulate the coupling between SNA and central respiratory drive that occurs in the RVLM. 

Received 16 January 1996; accepted in final form 19 April 1996.
APS Manuscript Number R18-6.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 8 May 96