AJP - Regulatory, Integrative and Comparative Physiology, Vol 257, Issue 4 889-R895, Copyright © 1989 by American Physiological Society

ARTICLES

Cardiac and abdominal vagal afferent inhibition of primate T9-S1 spinothalamic cells

S. F. Hobbs, U. T. Oh, M. J. Chandler and R. D. Foreman
Department of Physiology and Biophysics, University of Oklahoma Health Sciences Center, Oklahoma City 73190.

Effects of electrically stimulating vagal afferents were determined on lumbosacral spinothalamic tract (STT) neurons in the T9-S1 segments. Stimulating left or right vagal afferents inhibited 20 (50%) and excited 4 (10%) of 40 STT neurons. Vagal stimulation reduced activity of the 20 inhibited cells by 71 +/- 6% and reduced the average activity of all 40 STT neurons by 28% from 11.5 +/- 1.3 to 8.3 +/- 1.4 impulses/s (P less than 0.01). Effects of activating thoracic and abdominal or just abdominal vagal afferents were also determined. Stimulating right abdominal vagal afferents inhibited 4 (11%), excited 1 (3%), and did not affect 30 (86%) of the STT neurons and overall did not significantly affect STT cell activity. In contrast, in 33 of these cells stimulation of afferents in the right cervical vagus inhibited 16 (48%), excited 2 (6%), and did not affect 15 (45%) neurons and overall significantly reduced cell activity by 29% (P less than 0.01). These data and those of Ammons et al. (J. Neurophysiol. 50: 926-940, 1983; Circ Res. 53: 603-612, 1983; J. Neurophysiol. 54: 73-89, 1985) suggest that cardiopulmonary but not abdominal vagal afferent input reduces STT cell activity in many spinal segments. This inhibitory vagal reflex may play a role in protecting the heart.

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