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Am J Physiol Regul Integr Comp Physiol (November 10, 2005). doi:10.1152/ajpregu.00541.2005
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Submitted on July 25, 2005
Accepted on November 7, 2005

Modulation of the Baroreceptor Reflex by the Dorsomedial Hypothalamic Nucleus and Perifornical Area

Lachlan M McDowall1, Jouji Horiuchi1, Suzanne Killinger1, and Roger A. L Dampney1*

1 Physiology, University of Sydney, Sydney, NSW, Australia

* To whom correspondence should be addressed. E-mail: rogerd{at}physiol.usyd.edu.au.

Neurons within the dorsomedial hypothalamic nucleus (DMH) and perifornical area (PeF), which lie within the classic hypothalamic defense area, subserve the cardiovascular response to psychological stress. Previous studies have shown that electrical stimulation of the hypothalamic defense area causes inhibition of the cardiac and (in some cases) sympathetic components of the baroreceptor reflex. In contrast, naturally evoked psychological stress does not appear to be associated with such inhibition. In this study we tested the effect of specific activation of neurons within the DMH and PeF on the baroreflex control of renal sympathetic nerve activity and heart rate in urethane-anesthetized rats. Microinjection of bicuculline (a GABAA receptor antagonist) into the DMH caused dose-dependent increases in heart rate and renal sympathetic activity, shifted the baroreflex control of both variables to higher levels (i.e. increased the upper and lower plateaus of the baroreflex function curves), and increased the threshold, midpoint and saturation levels of mean arterial pressure. The maximum gain of the sympathetic component of the baroreflex was also increased, while that of the cardiac component was not significantly changed. The increases in midpoint were very similar in magnitude to the evoked increases in baseline mean arterial pressure. Microinjection of bicuculline into the PeF evoked very similar effects. The results indicate that disinhibition of neurons in the DMH/PeF region not only increases sympathetic vasomotor activity and heart rate, but also resets the baroreceptor reflex such that it remains effective, without any decrease in sensitivity, over a higher operating range of arterial pressure.




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