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1 Department of Anatomy and
Physiology,
The
following experiments were done to determine whether changes in
baroreflex sensitivity evoked by cervical vagus nerve stimulation are
due to sympathoexcitation mediated by the parabrachial nucleus. The
relative contribution of cardiopulmonary and general gastric afferents
within the cervical vagus nerve to the depression in baroreflex
sensitivity are also investigated. Male Sprague-Dawley rats
anesthetized with thiobutabarbital sodium (50 mg/kg) were instrumented
to measure blood pressure and heart rate or for the continuous
monitoring of renal sympathetic nerve activity. Baroreflex sensitivity
was measured using bolus injections of phenylephrine. Electrical
stimulation of the cervical vagus (with or without the aortic depressor
nerve) or the abdominal vagus nerve produced a significant increase in
renal nerve activity and a decrease in baroreflex sensitivity. Both of
these effects were blocked after the microinjection of lidocaine into
the parabrachial nucleus before nerve stimulation. Therefore, we
conclude that an increase in the activity of cardiac, pulmonary, or
general gastric afferents mediated the increased sympathetic output and
decreased baroreflex sensitivity via a pathway involving the
parabrachial nucleus.
cervical vagus; abdominal vagus; renal sympathetic activity; parabrachial nucleus; lidocaine
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