Respiratory modulation of sympathetic nerve activity: effect of mk
-801.
Morrison, Shaun F.
Department of Physiology, Northwestern University Medical School,
Chicago, IL 60611
APStracts 2:0284R, 1995.
The modulation of splanchnic sympathetic nerve activity (SNA) by
brainstem neural networks generating the respiratory rhythm was
examined in decerebrate, unanesthetized, vagotomized, artificially
ventilated rats before and after blockade of the NMDA channel with
intravenous administration of MK-801 (dizocilpine). NMDA channel
blockade (1) prolonged inspiration and reduced the phrenic nerve
amplitude, (2) reduced SNA to 40% of control levels and (3) decreased
mean arterial pressure by 20 mmHg. A strong synchronization of SNA to
the central respiratory cycle (monitored by the activity on the
phrenic nerve) was maintained following MK-801 administration,
although a brief inhibition of SNA during early inspiration and a
sympathetic excitation during early expiration were eliminated. These
results suggest (1) the existence of an NMDA-independent mechanism by
which some elements of the brainstem respiratory network excite
sympathetic outflow, (2) that the NMDA-mediated influence of specific
classes of brainstem respiratory neurons can modulate this excitation
during portions of the respiratory cycle, and (3) that an NMDA
-dependent excitation in the brainstem or spinal cord plays a
significant role in maintaining basal levels of splanchnic SNA.
Received 31 March 1995; accepted in final form 4 October 1995.
APS Manuscript Number R214-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 14 November 95