AJP - Regulatory, Integrative and Comparative Physiology, Vol 243, Issue 1 25-R33, Copyright © 1982 by American Physiological Society
Fastigial nucleus stimulation and excitatory spinal sympathetic activity in dog
K. J. Dormer, R. D. Foreman and C. A. Ohata
To locate the cerebellar-activated descending sympathetic pathways in the
dog the fastigial nucleus (FN) was electrically stimulated in
chloralose-anesthetized dogs while recording from sympathetic preganglionic
neurons. Physiological interventions included lesions in the dorsolateral
funiculus (DLF) of the spinal cord, myelotomy, arterial pressure changes,
bilateral occlusion of the carotid arteries, and administration of
clonidine. Multiunit activity at the T2 on T3 white ramus communicans was
recorded on-line during rest and FN stimulation. Descending sympathetic
activity (averaging 3.5 m/s) in the DLF was increased in response to FN
stimulation but was significantly reduced by ipsilateral and eliminated by
bilateral FN lesions. When testing for the effects of baroreceptor reflexes
on the sympathetic pathway phenylephrine-induced hypertension decreased,
but moderate hemorrhage increased the amount of preganglionic activity at
rest and during FN stimulation. During hypertension and simultaneous
carotid artery occlusion the amount of sympathetic activity that could be
evoked was comparable to that evoked during normotensive states. Clonidine
(IV) reduced the FN sympathoexcitation, but direct stimulation of the DLF
indicated that clonidine had sympathoinhibitory activity at both medullary
and spinal sites. In summary, rostral FN primarily excited ipsilateral
descending sympathetic pathways in DLF, and this sympathoexcitation was
partially inhibited by baroreceptor intervention.
