AJP - Regulatory, Integrative and Comparative Physiology, Vol 264, Issue 1 169-R178, Copyright © 1993 by American Physiological Society
Identification of baroreceptor reflex interneurons in the caudal ventrolateral medulla
I. Jeske, S. F. Morrison, S. L. Cravo and D. J. Reis
Department of Neurology and Neuroscience, Cornell University Medical College, New York, New York 10021.
Interrupting neuronal activity in the caudal ventrolateral medulla (CVL)
abolishes baroreceptor-mediated sympathoinhibition and vasodepressor
responses. In the present study we identified CVL neurons that function as
interneurons in the baroreceptor reflex arc. The mean antidromic onset
latency of CVL neurons (5 ms) after stimulation in the rostral
ventrolateral medulla (RVL) suggests that they transmit information to the
RVL via unmyelinated axons. Stimulation of baroreceptor afferents in the
aortic depressor nerve (ADN) excited CVL neurons projecting to the RVL with
onset latencies between 15 and 45 ms. The short-latency ADN stimulus-evoked
excitation of CVL barosensory interneurons preceded the onset of the ADN
stimulus-evoked inhibition of RVL-spinal sympathoexcitatory neurons.
Longer-latency ADN-evoked CVL neuronal responses may arise from activation
of unmyelinated ADN afferents that can prolong the inhibition of RVL
sympathoexcitatory neurons. The excitation of CVL barosensory interneurons
resulting from the systolic pressure rise was followed by a period of
decreased excitability of RVL sympatho-excitatory neurons, which was of
comparable duration to the increase in the discharge probability of CVL
neurons. Our characterization of baroreceptor reflex interneurons in the
CVL suggests that transmission of baroreceptor information involves a
complex activation of medullary interneurons responding selectively to
different aspects of the arterial pressure stimulus.
