Role of ampa/kainate receptors in transmission of the sympathetic baroreflex in rat caudal ventrolateral medulla. Miyawaki, Takashi, Satoshi Suzuki, Jane Minson, Leonard Arnolda, Ida Llewellyn-Smith, John Chalmers, and Paul Pilowsky. Dept. of Medicine and Centre for Neuroscience, Flinders Medical Centre, Bedford Park SA 5042 AUSTRALIA
APStracts 3:0347R, 1996.
We examined the role of alpha-amino-3-hydroxy-5-methyl-4 -isoxazolepropionic acid (AMPA)/kainate receptors within the caudal ventrolateral medulla (CVLM) in mediating the sympathetic baroreceptor reflex in anaesthetised and paralysed rats. Bilateral microinjection into CVLM of either DL-2-amino-5-phosphonovaleric acid (APV; a selective N-methyl-D-aspartic acid (NMDA) receptor antagonist, 20 mM, 100 nl) or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; a selective AMPA/kainate receptor antagonist, 2 mM, 100 nl) alone, into CVLM, failed to eliminate the aortic nerve stimulation evoked hypotension and inhibition of splanchnic sympathetic nerve activity (SNA), or the cardiac-related rhythmicity of SNA. All components of the sympathetic-baroreceptor reflex were abolished when kynurenate (100 mM, 30 nl) or mixtures of APV and CNQX (10 mM and 1 mM, respectively, 100 or 30 nl) were injected into CVLM. Injection of APV or CNQX into CVLM reduced aortic nerve evoked inhibitory responses of bulbospinal sympathoexcitatory neurons in rostral ventrolateral medulla (RVLM). The extent of this reduction was variable. Usually, significant inhibition was preserved. In seven RVLM neurons, intravenous injection of MK-801 (NMDA receptor antagonist, 2 mg/Kg) failed to eliminate aortic nerve evoked inhibitory responses. However, inhibitory responses were abolished when CNQX was injected into CVLM after intravenous MK-801. We conclude that both NMDA and AMPA/kainate receptors in CVLM transmit baroreceptor information. 

Received 10 January 1996; accepted in final form 28 August 1996.
APS Manuscript Number R10-6.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 September 1996