AJP - Regulatory, Integrative and Comparative Physiology, Vol 254, Issue 3 544-R551, Copyright © 1988 by American Physiological Society
Subfornical organ and cardiovascular influences on identified septal neurons
S. D. Donevan and A. V. Ferguson
Department of Physiology, Queen's University, Kingston, Ontario, Canada.
We have identified, in urethan-anesthetized male Sprague-Dawley rats, a
polysynaptic pathway connecting the subfornical organ (SFO) with the
paraventricular nucleus (PVN) with a relay neuron in the medial
septum-diagonal band of Broca (MS-DBB). Extracellular recordings were
obtained from 136 MS-DBB neurons antidromically identified as projecting to
the PVN. SFO stimulation orthodromically activated 79% of these cells (mean
latency, 21.2 +/- 0.6 ms; mean duration, 6.0 +/- 0.2 ms), whereas
stimulation in the fornix or hippocampal commissure had no effect. Of 35
identified MS-DBB neurons tested with systemic angiotensin II (ANG II),
eight showed increases and six decreases in excitability that coincided
with the ANG II-induced increase in blood pressure. To determine whether
such changes were blood pressure related, 23 of the 35 identified MS-DBB
neurons tested with ANG II were tested with systemic epinephrine. In every
case the effect of epinephrine was similar to that of ANG II. These
findings suggest that neurons in the MS-DBB receive afferent information
from the SFO and the cardiovascular system. These cells in turn may
activate neurons involved in the control of a variety of autonomic
functions.
