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Water deprivation increases respiratory rhythmic sympathetic discharge through a mechanism that depends on neuronal activity in the hypothalamic paraventricular nucleus (PVN)

As in specific neurogenic cardiovascular diseases, activation of the hypothalamic PVN during water deprivation likely plays a key role in supporting sympathetic nerve activity (SNA) and arterial blood pressure (ABP). To determine if PVN support of SNA in water deprived (WD) rats involves increasing specific rhythmic bursting patterns, vagal intact euhydrated (control) and 48 h WD male rats were instrumented to record ABP, ECG, expired CO2, and splanchnic SNA (SSNA) or renal SNA (RSNA). Autospectral analysis (0.2 Hz resolution) revealed that respiratory power (1.3 ‐ 1.7 Hz) of SSNA and RSNA was greater in WD rats (n=3/4) than controls (n=3). Bilateral inhibition of PVN with the GABA‐AR agonist muscimol (100pmol in 100nl/side) reduced mean ABP (P<0.001), SSNA and RSNA (P<0.05/0.005) in WD rats but not controls. Muscimol also tended to reduce respiratory power of SSNA only in WD rats (P<0.09) such that respiratory power : total power (0.2 – 15 Hz) ratios were no longer different between groups. PVN muscimol did not affect respiratory power of RSNA in either group. These data indicate that PVN neuronal activity in WD rats supports respiratory rhythmic bursting of SSNA, but not RSNA. Ongoing studies seek to determine if reduced respiratory rhythmic SSNA by PVN muscimol in WD rats is a direct effect of suppressed PVN output to respiratory/sympathetic networks or an indirect effect of reduced mean ABP. Support: HL102310 (GMT)