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1 Department of Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
* To whom correspondence should be addressed. E-mail: sved{at}bns.pitt.edu.
The present study determined the effect of destruction of the RVLM-C1 cells on the integrated sympathetic and hormonal responses to hypotension or glucoprivation. Injection of anti-D
H-saporin into the RVLM resulted in 29-99% depletion of RVLM-C1 neurons and a ~60% reduction in A5 neurons. In unanesthetized rats, resting mean arterial pressure (MAP) was reduced by ~10 mmHg in rats with >80% depletion of RVLM-C1 cells compared to control rats, though resting heart rate (HR) did not differ significantly. In addition, hydralazine (HDZ)-evoked hypotension resulted in a smaller increase in HR in rats with >80% depletion of the RVLM-C1 cells compared to control rats. Plasma levels of norepinephrine evoked by hypotension were also attenuated in rats with >80% depletion of the RVLM-C1 cells compared to control rats. Furthermore, the elevated plasma levels of the posterior pituitary hormones, vasopressin and oxytocin evoked by HDZ were blunted in the RVLM-C1 lesioned rats compared to control rats, even though MAP fell to lower levels in the lesioned rats. Plasma renin activity, plasma osmolality, and plasma protein concentrations did not differ between control rats and rats with >80% depletion of RVLM-C1 neurons. The circulating level of epinephrine and the resulting hyperglycemia evoked by systemic administration of 2-deoxyglucose were attenuated in rats with >80% depletion of the RVLM-C1 cells compared to control rats. These results demonstrate that RVLM-C1 cells, in addition to playing a role in acute cardiovascular reflexes, play an important role in integrated sympathetic and hormonal responses to homeostatic challenges such as hypotension and glucoprivation.
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