AJP - Regulatory, Integrative and Comparative Physiology, Vol 255, Issue 6 946-R951, Copyright © 1988 by American Physiological Society
Blockade of spinal pathways decreases pre- and postganglionic discharge differentially
L. Qu, R. Sherebrin and L. C. Weaver
John P. Robarts Research Institute, University of Western Ontario, London, Canada.
Although discharge of many sympathetic nerves decreases substantially on
transection of the spinal cord in cats, firing of splenic and mesenteric
postganglionic nerves continues unabated (R. L. Meckler and L. C. Weaver,
Brain Res. 338: 123-135, 1985; R. D. Stein and L. C. Weaver. J. Physiol.
Lond. 396: 155-172, 1988). Therefore, ongoing sympathetic outflow directed
to the splanchnic circulation was proposed to be less dependent on
supraspinal excitatory drive than that directed to other vascular beds.
Blockade or transection of cervical spinal pathways in
chloralose-anesthetized cats significantly decreased firing of gastric,
hepatic, adrenal, and lumbar chain sympathetic nerves. Discharge of gastric
and hepatic nerves decreased as much as that of adrenal and lumbar chain
nerves; therefore, sustained discharge in the absence of bulbospinal
excitation is not a characteristic of all sympathetic nerves innervating
the splanchnic circulation. In contrast, discharge of the preganglionic
greater splanchnic nerves was not decreased after spinal transection,
although it changed from a rhythmic to an asynchronous pattern. This
provocative finding suggests that rhythmicity of preganglionic discharge
may be important for effective synaptic transmission to some postganglionic
neurons, since postganglionic gastric, hepatic, and adrenal nerve firing
decreased in the presence of sustained but asynchronous preganglionic
input.
