AJP - Regulatory, Integrative and Comparative Physiology, Vol 268, Issue 3 625-R633, Copyright © 1995 by American Physiological Society
Paraventricular nucleus neurons projecting to the spinal cord receive excitatory input from the subfornical organ
J. S. Bains and A. V. Ferguson
Department of Physiology, Queen's University, Kingston, Ontario, Canada.
The present study utilized electrophysiological techniques to determine the
effects of subfornical organ (SFO) stimulation on the activity of neurons
in the paraventricular nucleus (PVN) projecting to the spinal cord.
Single-unit recordings were obtained from 79 PVN neurons antidromically
identified as projecting to the intermediolateral cell column (IML).
Antidromically evoked action potentials showed a mean latency of 94.6 +/-
5.3 ms and a mean threshold for activation of 1.58 +/- 0.11 mA. Electrical
stimulation of SFO (100 microA-1.5 mA, 0.1 ms) resulted in excitatory
responses in 18 of the 27 neurons tested (67%). Peristimulus histogram
analysis of such effects demonstrated a duration of < 50 ms in 14 of the
18 cells so influenced (78%), whereas the remaining 4 cells (22%) showed
excitatory responses with a longer duration. Systemic administration of the
nonpeptidergic angiotensin II (ANG) type 1 (AT1) receptor antagonist
losartan (3 mg/kg) blocked the long-duration excitatory responses in 100%
(3 of 3) of the cells tested but was without effect on the short-duration
excitations (0 of 5). Twenty-two identified PVN neurons were also tested
for their responses to systemic ANG (20-500 ng), which had no observable
effect on the activity of any of these cells. These data demonstrate that
neurons in SFO provide excitatory input to PVN cells that project to the
IML. One of the neurotransmitters responsible for communication in this
pathway is ANG.
