SUBGROUPS OF ROSTRAL VENTROLATERAL MEDULLARY AND CAUDAL MEDULLARY RAPHE
NEURONS BASED ON PATTERNS OF RELATIONSHIP TO SYMPATHETIC NERVE DISCHARGE AND
Barman, Susan M. and Gerard L. Gebber.
Department of Pharmacology and Toxicology, Michigan State University, East
Lansing, MI 48824-1317.
APStracts 3:0186N, 1996.
This study was designed to answer three questions concerning rostral
ventrolater al medullary (RVLM) and caudal medullary raphe (CMR) neurons with
activity correlated to sympathetic nerve discharge (SND). What are the
proportions of RVLM and CMR neurons that have activity correlated to both the
cardiac-related and 10-Hz rhythms in SND, to only the 10-Hz rhythm, and to
only the cardiac-related rhythm? 2) Which of these cell types project to the
spinal cord? 3) Do the outputs of the cardiac-related and 10-Hz rhythm
generators converge at the level of bulbospinal neurons or their antecedent
interneurons? To address these issues we recorded from 44 RVLM and 48 CMR
neurons with sympathetic nerve-related activity in urethan-anesthetized cats
with intact carotid sinus nerves, but sectioned aortic depressor and vagus
nerves. Spike-triggered averaging, arterial pulse-triggered analysis, and
coherence analysis revealed that the naturally occurring discharges of 24 of
these RVLM neurons and 41 of these CMR neurons were correlated to both the 10-
Hz and cardiac-related rhythms in inferior cardiac postganglionic SND. The
discharges of the other neurons were correlated to only the 10-Hz rhythm (15
RVLM and 6 CMR neurons) or to only the cardiac-related rhythm (5 RVLM neurons
and 1 CMR neuron) in SND. The time-controlled collision test verified that 16
of 18 RVLM and 31 of 34 CMR neurons with activity correlated to both rhythms
were antidromically activated by stimulation of the white matter of the first
thoracic (T1) segment of the spinal cord. In contrast, only 1 of 10 RVLM
neurons and 0 of 4 CMR neurons with activity correlated to only the 10-Hz
rhythm could be antidromically activated by stimulation at T1. Also 0 of 3
RVLM neurons with activity correlated to only the cardiac-related rhythm in
SND were antidromically activated by spinal stimulation. These data show for
the first time that bulbospinal sympathetic pathways emanating from the RVLM
and CMR are comprised almost exclusively of neurons whose discharges are
correlated to both the cardiac-related and 10-Hz rhythms in SND. Moreover, the
data support the hypothesis that the outputs of the cardiac-related and 10-Hz
rhythm generators converge on RVLM and CMR bulbospinal neurons rather than on
their antecedent interneurons. Finally, the data demonstrate that a
substantial proportion of RVLM neurons and a small group of CMR neurons with
activity correlated to SND do not project to the thoracic spinal cord. Their
discharges were correlated to only one of the rhythms in SND. Their axonal
trajectories and functions are unknown.
Received 18 July 1996; accepted in final form 28 August 1996.
APS Manuscript Number J575-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 7 October 1996