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Am J Physiol Regul Integr Comp Physiol (December 11, 2003). doi:10.1152/ajpregu.00494.2003
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Submitted on August 27, 2003
Accepted on December 7, 2003

Acute inhibition of the hypothalamic paraventricular nucleus decreases renal sympathetic nerve activity and arterial blood pressure in water-deprived rats

Sean D Stocker1*, Kimberly J Keith1, and Glenn M Toney1

1 Department of Physiology, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA

* To whom correspondence should be addressed. E-mail: stocker{at}uthscsa.edu.

The present study was performed to determine whether sympathetic outflow and arterial blood pressure in water-deprived rats is dependent upon the ongoing neuronal activity of the hypothalamic paraventricular nucleus (PVN). Renal sympathetic nerve activity (RSNA), mean arterial blood pressure (MAP), and heart rate were recorded in urethane/{alpha}-chloralose anesthetized rats that were deprived of water but not food for 48 h before experiments. Acute inhibition of the PVN by bilateral microinjection of the GABAA agonist muscimol (100 pmol per side) significantly decreased RSNA in water-deprived rats (-26.7 ± 4.7%, n = 7) but was without effect in control rats (1.3 ± 6.3%, n = 7). Similarly, injection of muscimol produced a greater decrease in MAP in water-deprived rats than in control rats (-46 ± 3 mmHg vs -16 ± 3 mmHg, respectively), although baseline MAP was not different between groups (105 ± 4 mmHg vs 107 ± 4 mmHg, respectively). Neither bilateral microinjection of isotonic saline vehicle (100 nl per side) into the PVN nor muscimol (100 pmol per side) outside the PVN altered RSNA or MAP in either group. In addition, ganglionic blockade with hexamethonium (30 mg/kg, iv) significantly decreased MAP in both groups; however, the decrease in MAP was significantly greater in water-deprived rats than in control rats (62 ± 2 mmHg vs 48 ± 2 mmHg, respectively). Collectively, these findings suggest that sympathetic outflow contributes more to the maintenance of blood pressure in the water-deprived rat, and this depends, at least partly, on the ongoing activity of PVN neurons.




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