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1 Department of Physiology, Universidade Federal de São Paulo-Escola Paulista de Medicina, São Paulo-SP 04023 - 060, Brazil and 2 Department of Neurology, University of Iowa and Veterans Affairs Medical Center, Iowa City, Iowa 52242
In this study, we
characterized the arterial pressure, heart rate, and regional vascular
conductance responses elicited by unilateral microinjection of
ionotropic glutamatergic agonists N-methyl-D-aspartic acid (NMDA and non-NMDA)
into the nucleus of tractus solitarius (NTS) of conscious rats.
Microinjections of NMDA and
S-
-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid
(AMPA) caused changes in mean arterial pressure (MAP). Lower doses
elicited decreases in MAP, whereas higher doses elicited biphasic
responses (decreases followed by increases). Both agonists induced
bradycardia and elicited dose-dependent vasoconstriction in the renal,
mesenteric, and hindquarter beds. AMPA elicited delayed vasodilation in
the hindquarter bed but NMDA did not. Bradycardia and initial
hypotension produced by each agonist were abolished by systemic
administration of the muscarinic antagonist methylatropine. However,
methylatropine did not affect either the vasoconstriction or the
vasodilatation. The contrasting hemodynamic effects produced by NMDA
and AMPA could be caused by activation of differential subsets of NTS
neurons. Preferential activation of one subset could produce
the NMDA-related responses, whereas activation of another subset would
elicit AMPA-related responses.
arterial pressure; regional vascular conductance; nucleus tractus solitarii
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