Cardiac sympathetic premotor neurons.
Campos, R. R., and R. M. McAllen.
Howard Florey Institute of Experimental Physiology and Medicine,
University of Melbourne, Parkville, Vic. 3052, Australia
APStracts 3:0320R, 1996.
To locate premotor neurons controlling the cardiac sympathetic supply
and to determine their relation to brainstem vasomotor pathways, the
rostral ventrolateral medulla (RVLM) was mapped in 7 chloralose
-anesthetized cats, using microinjections of sodium glutamate (5-10
nl, 0.1 M) to excite neuronal cell bodies. Cardiac sympathetic
responses were recorded from the ipsilateral inferior cardiac nerve,
while recordings were made simultaneously from postganglionic
vasoconstrictor fibers to skeletal muscle (ipsilateral peroneal
nerve). Baroreceptors were denervated to eliminate the reflex effects
of blood pressure changes. Most of the 115 injected RVLM sites
excited both sympathetic nerves. Inferior cardiac nerve activity
increased by up to 395% (mean 105 % +/- 86%, S.D.) and muscle
vasoconstrictor activity by up to 487% (110 +/-107%). Their relative
response varied with injection site, however. For 16 of the most
rostromedial injections, the inferior cardiac nerve:muscle
vasoconstrictor response ratio exceeded that expected by 2-7 fold;
for 9 very caudolateral injections that ratio was strongly reversed,
favoring muscle vasoconstrictors by 2-5 fold. Intervening sites gave
more equal responses. Overall, the response ratio varied
systematically with injection site. These findings demonstrate that
neurons with preferential or selective actions on the cardiac
sympathetic outflow are present in the RVLM, and are organized
topographically. The simplest interpretation is that a population of
selective cardiac sympathetic premotor neurons occupies a territory
substantially overlapping, but centered rostromedially to, the
population controlling vasoconstriction in muscle.
Received 4 March 1996; accepted in final form 8 August 1996.
APS Manuscript Number R132-6.
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