Influence of gabaergic mechanisms on baroreceptor inputs to the
nucleus tractus solitarii of rats.
Ruggeri, Piero, Carla E. Cogo, Viviana Picchio, Claudio Molinari, Rosa
Ermirio, and Franco R. Calaresu.
Istituto di Fisiologia Umana, Facolt di Medicina e Chirurgia,
Universit di Genova, 16132 Genova, Italy, Department of Physiology,
University of Western Ontario, London, Ontario, Canada, N6A 5C1
APStracts 3:0078H, 1996.
The firing frequency of baroreceptive neurons in the nucleus tractus
solitarii (NTS) during microiontophoretic application of muscimol, a
GABAA agonist, or baclofen, a GABAB agonist, were monitored in
anesthetized rats. Muscimol decreased the spontaneous discharge of 69
of 73 (94.5%) NTS baroreceptive neurons without affecting the
remaining 4 neurons (5.5%). The statistical comparison on a bin-by
-bin basis of the peri-REwave interval histograms of the discharge of
each NTS neuron showed that the inhibitory action of muscimol was
always exerted on the whole neuronal discharge independently of its
correlation to the cardiac cycle. Baclofen inhibited 60 of 73 (82.2%)
NTS neurons without affecting the remaining 13 neurons (17.8%). In 31
of the 60 (51.7%) neurons inhibited by baclofen, this substance
significantly affected only pulse-synchronous peaks of neuronal
discharge without significant inhibition of the neuronal firing
between cardiac cycle-related peaks. Fifty-eight of the 73 (79.5%)
NTS neurons studied were inhibited by both muscimol and baclofen, 11
neurons (15%) only by muscimol, 2 neurons (2.7%) only by baclofen and
2 neurons (2.7%) were unaffected by both substances. These results
demonstrate that both GABAA and GABAB receptors mediate inhibition of
the spontaneous discharge in the great majority of the NTS
baroreceptive neurons studied and suggest different functions of the
two types of GABA receptors in influencing baroreceptor inputs to the
NTS.
Received 14 September 1995; accepted in final form 9 February
1996.
APS Manuscript Number H864-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 March 96