AJP - Regulatory, Integrative and Comparative Physiology, Vol 243, Issue 1 49-R59, Copyright © 1982 by American Physiological Society
Classification of raphe neurons with cardiac-related activity
S. F. Morrison and G. L. Gebber
The cardiac-related component of sympathetic nerve discharge (SND) results
from entrainment of a rhythm of brain stem origin by the baroreceptor
reflexes [Gebber, Am. J. Physiol. 239 (Heart Circ. Physiol. 8): H143-H155,
1980]. As a consequence, changes in heart rate are accompanied by shifts in
the phase relations between SND and the arterial pulse wave. This
observation presented us with the opportunity of distinguishing brain stem
neurons whose discharges are locked to SND from other neuronal types that
exhibit cardiac-related activity. Raphe neurons in the cat medulla with
cardiac-related activity were identified using post-R wave interval
analysis. The discharges of one group of these neurons remained locked to
inferior cardiac SND during changes in ventricular rate which shifted the
phase relations between SND and the arterial pulse wave. Most importantly,
the lag between unit spike occurrence and the peak of the cardiac-related
component of SND was unchanged during ventricular pacing (as demonstrated
with cross-correlation analysis). It is suggested that these neurons were
contained in brain stem networks which control SND. The discharges of two
additional types of raphe neurons remained locked to the arterial pulse
wave during ventricular pacing. Neurons of the first type exhibited an
increase in discharge probability in late diastole and early systole.
Neurons of the second type exhibited a period of reduced activity
time-locked to systole.
