AJP - Heart and Circulatory Physiology, Vol 253, Issue 5 1127-H1135, Copyright © 1987 by American Physiological Society
Interactions in nucleus tractus solitarius between right and left carotid sinus nerves
R. B. Felder and C. M. Heesch
Department of Internal Medicine, College of Medicine, University of Iowa, Iowa City 52242.
Bilateral carotid sinus nerve stimulation was used as a model for studying
cardiovascular afferent interactions in the nucleus tractus solitarius
(NTS) region of dorso-medial medulla. Extracellular action potential
recordings were made from 69 single units, 33 of which were excited
independently by both right and left carotid sinus nerves (CSNs). Fifteen
of these were located in NTS. Peak latencies to electrical stimulation of
NTS neurons were 17.7 +/- 2.1 ms to ipsilateral CSN and 20.9 +/- 1.5 ms to
contralateral CSN. Summation of afferent input was routinely demonstrated.
In 10 units in NTS, a conditioning stimulus applied to one CSN caused
prolonged inhibition of the response to a test stimulus to the same or the
other CSN. The duration of inhibition was dependent on the intensity of the
conditioning stimulus, not on prior excitation of the unit by the
conditioning stimulus. In five additional excitability testing experiments,
we found limited evidence to suggest that primary afferent depolarization
of the central fibers of one CSN by stimulation of the contralateral CSN
might be contributing to this inhibitory interaction. The data suggest that
the outcome of integrative interactions between right and left CSN inputs
to NTS neurons may depend largely on the temporal sequence of convergent
afferent impulses.
