AJP - Regulatory, Integrative and Comparative Physiology, Vol 255, Issue 6 961-R967, Copyright © 1988 by American Physiological Society
Inhibition of paraventricular neurons by subfornical organ and AV3V in cats
T. Osaka, H. Yamashita and K. Koizumi
Department of Physiology, State University of New York, Brooklyn 11203.
The study was designed to examine, by electrophysiological techniques,
influences of rostral periventricular structures on neurons in the
hypothalamic paraventricular nucleus (PVN) in a large animal (the cat) in
which stimulating and recording sites could be precisely identified.
Extracellular single action potentials were recorded from the PVN in
pentobarbital sodium-anesthetized and hemispherectomized cats. Of 246
neurons tested, 24-47% were inhibited and 9-21% were excited by electrical
stimulation of the subfornical organ (SFO), the nucleus preopticus medianus
(POMn), and the organum vasculosum of the lamina terminalis (OVLT). The
onset latencies of inhibition (19-26 ms) were shorter than those of
excitation (28-80 ms). Responses of both neurosecretory and
nonneurosecretory neurons were similar to the stimulation of all sites
tested. Among these sites, the POMn had the strongest influence on the PVN
in view of the proportion of the responsive neurons. Moreover,
antidromically evoked action potentials in the PVN neurons (n = 10) were
only observed after stimulation of the POMn. Chemical stimulation of POMn
and SFO by microinjection of sodium glutamate (50-100 nl, 0.5 M) also
inhibited 16 of 38 PVN cells; the remaining neurons were unaffected. These
results suggest that activation of the POMn, OVLT, and the SFO neurons
mainly inhibits the PVN neurons in the cat.
