Nmda receptor blockade in cat dorsal horn blunts the reflex pressor
response to muscle contraction and stretch.
Hand, Gregory A., Andre F. Meintjes, Alan W. Keister, Ahmmed Ally, and
L. Britt Wilson.
Department of Physiology and The Harry S. Moss Heart Center,
University of Texas Southwestern Medical Center, Dallas, TX 75235
-9040
APStracts 2:0329H, 1995.
The role of N-Methyl-D-Aspartate (NMDA) receptors in the reflex
pressor response to static muscle contraction and passive stretch was
examined by microdialyzing the NMDA receptor antagonist, DL-2-amino
-5-phosphonovalerate (AP-5), into the L7, or L6 and S1, level of the
dorsal horn of anesthetized cats. Contraction, elicited by electrical
stimulation of the cut L7 and S1 ventral roots, increased mean
arterial pressure (MAP) and heart rate (HR). Passive stretch at
tensions similar to those generated by contraction also increased
these variables. These cardiovascular changes were unaffected by
dialyzing AP-5 (10 mM) into the L7 dorsal horn. Increasing the
syringe concentration of AP-5 to 100 mM attenuated the pressor and HR
responses from 62+/-8 mmHg to 31+/-6 mmHg, and 18+/-4 beats.min-1. to
12+/-4 beats.min-1. AP-5 blunted the increase in MAP (59+/-10 mmHg
vs. 41+/-10 mmHg) evoked by muscle stretch. Simultaneously
microdialyzing AP-5 (10 mM or 100 mM) into the dorsal horn at the L6
and S1 spinal levels also blunted the MAP and HR responses to
contraction and stretch. These results suggest that NMDA receptors
play a role in mediating the MAP and HR responses to static muscle
contraction at the spinal level of the central nervous system.
Further, these data demonstrate that collaterals from muscle
afferents partially mediate the reflex cardiovascular responses
evoked by muscle contraction and stretch.
Received 9 February 1995; accepted in final form 12 July 1995.
APS Manuscript Number H121-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 10 August 1995.