Intrathecal blockade of both nmda and non-nmda receptors attenuates
the exercise pressor reflex in cats.
Adreani, Christine M., Janeen M. Hill, and Marc P. Kaufman.
Division of Cardiovascular Medicine, Departments of Internal
Medicine and Human Physiology, University of California, Davis
APStracts 2:0404A, 1995.
In decerebrate, unanesthetized cats we tested the hypothesis that
glutamatergic receptor blockade in the lumbosacral spinal cord
attenuated the reflex increases in mean arterial pressure (MAP),
minute ventilation (Vi), and renal sympathetic nerve activity (RSNA)
evoked by static contraction of the triceps surae muscles. Blockade
of N-methyl-d-Aspartate (NMDA) receptors by intrathecal injection of
(+/-) 2-amino-5-phosphonovaleric acid (AP-5) had no effect on the
initial phase of the pressor, ventilatory and RSNA responses to
contraction, but did attenuate the secondary phase of these
responses. Subsequent blockade of non-NMDA receptors in the
lumbosacral spinal cord by intrathecal injection of 6-cyano-7
-nitroquinoxaline-2,3-dione (CNQX) attenuated both the initial phase
of the pressor, RSNA and ventilatory responses to contraction and the
secondary phase of these responses. In addition, NMDA receptor
blockade had no effect?on the pressor or RSNA responses to tendon
stretch, whereas non-NMDA receptor blockade abolished these
responses. We confirmed that our results were not related to the
order of the antagonists injected by performing a series of
experiments in which a non-NMDA receptor antagonist was injected
first. Our findings suggest that non-NMDA receptors mediate the
spinal transmission of the initial and secondary phases of the
pressor, RSNA and ventilatory responses to contraction and to tendon
stretch. Therefore, non-NMDA receptors in the dorsal horn appear to
be involved in the spinal processing of input from mechanoreceptors
and metaboreceptors. Our findings also suggest that NMDA receptors
mediate the spinal transmission of the secondary phase of the
pressor, RSNA and ventilatory responses to contraction but do not
mediate the spinal transmission of the responses to tendon stretch.
Therefore, NMDA receptors in the dorsal horn appear to be involved in
the spinal processing of input from metaboreceptors.
Received 30 June 1995; accepted in final form 1 September 1995.
APS Manuscript Number A707-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 September 1995.