AJP - Regulatory, Integrative and Comparative Physiology, Vol 247, Issue 5 761-R767, Copyright © 1984 by American Physiological Society
Spinal interneurons with sympathetic nerve-related activity
S. M. Barman and G. L. Gebber
This study tested the hypothesis that at least some brain stem and reflex
control of sympathetic outflow is mediated over pathways containing spinal
interneurons. The vicinity of the intermediolateral nucleus (IML) of the
third thoracic spinal segment was searched for neurons with spontaneous
activity correlated to that in the inferior cardiac post-ganglionic
sympathetic nerve of 16 baroreceptor-denervated cats anesthetized with
Dial-urethane. Section of the carotid sinus, aortic depressor, and vagus
nerves prevented the coupling of sympathetic and nonsympathetic networks by
pulse synchronous baroreceptor activity. Spike-triggered averaging revealed
the existence of two types of spinal neurons with sympathetic nerve-related
activity. Preganglionic sympathetic neurons (PSN; n = 33) were
antidromically activated by electrical stimulation of their axons in the
third thoracic white ramus. Four observations suggest that the second group
of neurons with sympathetic nerve-related activity (n = 18) were spinal
interneurons (SIN) in pathways that excite PSN. First, these neurons could
not be antidromically activated by stimulation of the segmental white
ramus. Second, the intervals between spontaneous unit spike occurrence and
inferior cardiac nerve activity were similar for SIN and PSN. Third, SIN
and PSN were activated with nearly identical onset latencies by electrical
stimulation of medullary sympathoexcitatory sites. Fourth, SIN were excited
by intensities of cardiac sympathetic afferent stimulation that also
activated PSN and the inferior cardiac nerve. SIN and PSN were
distinguished on the basis of their spontaneous firing patterns; i.e.,
interspike intervals of SIN were significantly shorter than those of
PSN.(ABSTRACT TRUNCATED AT 250 WORDS)
