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1 Department of Internal Medicine and 3 Department of Pharmacology, University of California at Davis, Davis, California 95616; and 2 Department of Anatomy and Brain Science, Kobe University Graduate School of Medicine, Kobe 650-0017, Japan
A single bout of
exercise results in a postexercise hypotension (PEH) that is
accompanied by a reduced baroreflex function. Based on the role of
rostral ventrolateral medulla (RVLM) neurons in controlling sympathetic
nerve activity (SNA) and blood pressure, the role of 
-aminobutyric
acid (GABA) in controlling RVLM neuronal activity, and the reduced
baroreflex-SNA relationship during PEH, we determined whether:
1) RVLM neuronal activity is decreased during PEH,
2) GABAA-receptor mechanisms mediate the
decrease, and 3) baroreflex control of RVLM activity is
reduced. Spontaneously hypertensive rats (SHR) were subjected to 40 min
of treadmill or sham exercise (Sham PEH). PEH lasted 10 h in
conscious and anesthetized SHR, indicating that the anesthetics did not
affect the expression of PEH. Extracellular RVLM neuronal activity
having a cardiac and sympathetic rhythm, lumbar SNA, and blood pressure were recorded at rest and during baroreflex function curves. Resting RVLM neuronal activity was lower and was increased to a greater extent
by GABAA-receptor antagonism in PEH versus Sham PEH
(P < 0.05). Baroreflex control of RVLM neuronal
activity operated with a reduced gain (P < 0.05). Thus
increased GABA signaling at RVLM neurons may contribute to PEH.
spontaneously hypertensive rats; central sympathetic network; extracellular recording
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