MINERALOCORTICOID RECEPTOR IN NTS STIMULATES SALT INTAKE DURING 4TH VENTRICULAR INFUSIONS OF ALDOSTERONE

Purpose: The purpose of this study was to determine if neurons within the NTS that possess the mineralocorticoid receptor (MR) play a role in aldosterone stimulation of salt intake. Methods: Adult WKY rats received microinjections of Adeno associated virus (AAV) with either short hairpin RNA for the MR (shRNA; n=9) or a scrambled RNA (scRNA; n=8) into the NTS. The vector used to knock-down the MR is AAV1/2-U6-Rat.Nr3c3/MR.shRNAterminator-CAG-EGFP-WPRE-BGH-polyA. Immediately after the viral construct injections, aldosterone-filled osmotic mini-pumps were implanted subcutaneously and connected to tubing within the 4th ventricle to infuse aldosterone (dissolved in aCSF) at a rate of 20ng/h. Prior to and after surgeries, rats had ad libitum access to food and two graduated drinking bottles filled with distilled water and 0.3M NaCl respectively. Salt intake was expressed as 100 X the ratio of 0.3M NaCl intake to total fluid intake (salt plus water). To verify that the shRNA reduced MR levels in the NTS, immunohistochemistry was performed for the MR and HSD2. Cells demonstrating immunoreactivity were counted in NTS sections from each rat and expressed as an average number per section. Results: Prior to surgeries, basal salt intake was 4.7% ± 2.9% in the scRNA group and 3.91% ± 2.6% in the shRNA group. 24 days post-surgery salt intake was 20.6% ± 2.9% in the scRNA group and 4.3% ± 2.8% in the shRNA group. Post-mortem immunohistochemistry revealed a significant reduction in the number of NTS neurons exhibiting immunoreactivity for the MR (scRNA 33 ± 2 cells/section; shRNA 23 ± 1 cells/section; p=.008) with no significant change in the number of HSD2 immunoreactive neurons. Conclusions: These results indicate 4th ventricular infusions of aldosterone stimulate salt intake and that at least part of the stimulation of salt intake during 4th ventricular infusions of aldosterone is mediated by hindbrain NTS neurons that possess the MR.