AJP - Regulatory, Integrative and Comparative Physiology, Vol 258, Issue 1 10-R20, Copyright © 1990 by American Physiological Society
Urinary bladder and hindlimb stimuli inhibit T1-T6 spinal and spinoreticular cells
S. F. Hobbs, U. T. Oh, T. J. Brennan, M. J. Chandler, K. S. Kim and R. D. Foreman
Department of Physiology and Biophysics, University of Oklahoma, Health Sciences Center, Oklahoma City 73190.
Upper thoracic spinal neurons are primarily excited by cardiopulmonary
spinal afferent input but are excited and inhibited by splanchnic afferent
input. These data suggest that the greater the number of segments between a
spinal neuron and spinal afferent input the greater the probability that
the afferent input will inhibit the spinal neuron. Based on this idea we
hypothesized that visceral (urinary bladder) and somatic (hindlimb)
afferent input would inhibit upper thoracic spinal neurons. To test this
hypothesis the activities of 69 spinal and 27 spinoreticular tract neurons
in 45 alpha-chloralose-anesthetized cats were studied. Only neurons excited
by both visceral and somatic thoracic afferent input were studied. Urinary
bladder distension (UBD) inhibited 48 (50%), excited 6 (6%), and did not
affect 41 (43%) of these neurons. Also, UBD inhibited the excitatory
responses of these cells to noxious visceral and somatic stimuli. Hindlimb
pinch also inhibited greater than 50% of the neurons. These data indicate
that visceral and somatic afferent input to the lumbosacral spinal cord
inhibits the activity of upper thoracic neurons. This inhibitory effect may
play a role in localization of sensory and motor responses to noxious
stimuli.
