AJP - Heart and Circulatory Physiology, Vol 243, Issue 3 463-H470, Copyright © 1982 by American Physiological Society
Sympathetic nerve discharge in chronic spinal cat
J. L. Ardell, S. M. Barman and G. L. Gebber
A study was made of external carotid, renal, and splanchnic sympathetic
nerve discharge (SND) in chloralose-anesthetized cats subjected to
transection of the sixth cervical spinal segment 2-37 days earlier. Minimal
activity was observed under normocapnic conditions 2 days after spinal
transection, and ganglionic blockade failed to lower blood pressure.
Moderate hypercapnia increased SND and led to synchronization of activity
into 1-6 cycle/s slow waves. Such slow-wave activity was present under
normocapnic conditions in cats 9-37 days after spinal transection.
Ganglionic blockade significantly reduced blood pressure in these
preparations. The interval between successive 1-6 cycle/s slow waves was
variable. Thus, unlike the case in baroreceptor-denervated cats with an
intact neuraxis [Barman and Gebber, Am. J. Physiol. 239 (Regulatory
Integrative Comp. Physiol. 8): R42-R47, 1980], chronic spinal cats are
incapable of rhythm generation in the 1-6 cycle/s frequency range.
Crosscorrelation analysis revealed that the discharges of pairs of
segmental (but not intersegmental) sympathetic nerves were related in the
chronic spinal cat. This situation differs from that in the
baroreceptor-denervated cat in which the discharges of pairs of
intersegmental as well as segmental sympathetic nerves are related. Thus
coordination of activity in sympathetic nerves that arise from different
spinal segments requires the integrity of bulbospinal connections. Finally,
no evidence was obtained for the existence of a baroreceptor-like reflex
mechanism acting to control SND in the chronic spinal cat.
