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1 Department of Behavioral Science and 2 The Neuroscience Program, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
To
characterize the baroreflex in central nervous system-intact
neuromuscular-blocked rats, we measured the vascular and cardiac responses and compared direct stimulation of the aortic depressor nerve (ADN) with a capacitance electrode (differentially activating either A or A + C fibers) to carotid sinus pressure with a micro-balloon (SINUS).
One-thousand-two-hundred-ninety-seven open-loop measurements
of systolic blood pressure (SBP), heart rate, venous pressure (VBP),
and mesenteric (msBF), femoral (fmBF), and skin (skBF) blood flow were
completed; the linear range of the effects was determined for each
response and stimulus mode. The rats were sinoaortic denervated (SAD).
The open-loop stimulation effect was very stable; e.g., the mean effect
of 790 ADN stimulations during >7 days was
9.8 mmHg,
with an average drift of +0.001 mmHg/h. In contrast, there was large
variability of the SBP baseline (e.g., SD = ±10.9), which was due
to SAD (±6.3 to ±16.3 mmHg, t =
13.9, df = 4, P < 0.0002) and was reversed by ganglionic block
(±10.8 to ± 2.9 mmHg, t =
12.9, df = 3, P < 0.001). The ADN stimuli produced larger depressor
responses than sinus stimuli (
66 vs.
45 mmHg); all component
responses paralleled the magnitude of the SBP effect, except interbeat
interval (IBI), for which the ADN
IBI was
10 times
that of SINUS. For all stimuli, fmBF increased and msBF did
not. Mesenteric and femoral vascular conductance both
increased, whereas VBP decreased and skBF followed SBP. We found that
for all baroreflex response components, with the exception of
SINUS-elicited
IBI, there was an orderly, substantially linear, relationship between stimulus strength and response magnitude.
baroreceptors; aortic depressor nerve; carotid sinus; sinoaortic denervation; noise; baroafferent stimulation
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