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Department of Physiology, Health Science Center, University of Western Ontario, London, Ontario, Canada N6A 5C1
GABAergic inputs
have been demonstrated in the central nucleus of the amygdala (ACe).
However, the contribution of these inhibitory inputs to the
cardiovascular responses elicited from the ACe is not known.
Experiments were done in chloralose-anesthetized, paralyzed, and
artificially ventilated male Wistar rats to investigate the effects of
microinjections of GABA, the selective
GABAA-receptor antagonist
bicuculline, or the GABAB-receptor
antagonist phaclofen, in the ACe on the mean arterial
pressure (MAP) and heart rate (HR) responses elicited by
L-glutamate (Glu) stimulation of the ACe. Microinjections
of Glu in the ACe elicited decreases in MAP (
13.7 ± 1.6 mmHg) and HR (
5.3 ± 1.9 beats/min). The MAP and HR responses
elicited by Glu stimulation of the ACe were significantly reduced
(89%) by the prior microinjection of GABA in the same ACe site. In
addition, at some sites in the ACe at which microinjection of Glu did
not elicit depressor responses, Glu injections in the presence of
phaclofen elicited decreases in MAP (
9.5 ± 1.0 mmHg) and
variable changes in HR. On the other hand, the magnitude of the
depressor responses elicited during stimulation of the ACe site in the
presence of bicuculline was significantly attenuated (60%), whereas
phaclofen had no effect on the magnitude of the depressor responses
elicited by Glu stimulation of the ACe. These data suggest that
GABAergic mechanisms in the ACe alter the excitability of ACe neurons
involved in mediating changes in systemic arterial pressure and HR.
cardiovascular regulation; arterial pressure;
-aminobutyric acid
A receptor;
-aminobutyric acid B receptor
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