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Departments of 1 Anesthesiology and 3 Neuroscience and Anatomy, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033; and 2 Hypertension Center, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157
Ischemic
stimulation of cardiac receptors evokes excitatory sympathetic
reflexes. Although the nucleus of the solitary tract (NTS) is an
important site for integration of visceral afferents, its involvement
in the cardiac-renal sympathetic reflex remains to be fully defined.
This study examined the role of glutamate receptor subtypes in the
commissural NTS in the sympathetic responses to stimulation of cardiac
receptors. Renal sympathetic nerve activity (RSNA) was recorded in
anesthetized rats. Cardiac receptors were stimulated by epicardial
application of bradykinin (BK; 10 µg/ml). Application of BK
significantly increased the mean arterial pressure from 78.2 ± 2.2 to 97.5 ± 2.9 mmHg and augmented RSNA by 38.5 ± 2.5%
(P < 0.05). Bilateral microinjection of 10 pmol of
6-cyano-7-nitroquinoxaline-2,3-dione, a
non-N-methyl-D-aspartate (NMDA) antagonist, into
the commissural NTS eliminated the pressor and RSNA responses to BK
application in 10 rats. However, microinjection of
2-amino-5-phosphonopentanoic acid (0.1 and 1 nmol, n = 8), an NMDA- receptor antagonist, or 
-methyl-4-carboxyphenylglycine
(0.1 and 1 nmol, n = 5), a glutamate metabotropic
receptor antagonist, failed to attenuate significantly the pressor and
RSNA responses to stimulation of cardiac receptors with BK. Thus this
study suggests that non-NMDA, but not NMDA and glutamate metabotropic,
receptors in the commissural NTS play an important role in the
sympathoexcitatory reflex response to activation of cardiac receptors
during myocardial ischemia.
cardiac nociceptors; sympathetic nervous system; cardiovascular reflexes; bradykinin; N-methyl-D-aspartate receptors; myocardial ischemia
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