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Water deprivation does not enhance sympathetic and pressor responses to sciatic nerve stimulation or chemical activation of RVLM neurons
Author(s) -
Stocker Sean D,
Wenner Megan M,
Farquhar William B
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.849.5
Subject(s) - rostral ventrolateral medulla , endocrinology , medicine , stimulation , chemistry , sciatic nerve , osmole , plasma osmolality , sympathetic nervous system , sodium , sed , blood pressure , heart rate , anesthesia , vasopressin , organic chemistry
Water deprivation produces a volume contraction and elevation in plasma sodium concentrations and osmolality. Together, these changes activate the sympathetic nerve activity (SNA) to support arterial blood pressure (ABP). Prior studies suggest that dietary salt intake raises plasma sodium concentrations to sensitize central autonomic networks including the rostral ventrolateral medulla (RVLM), exaggerate sympathetic reflexes, and increase blood pressure variability. The purpose of the present study was to examine whether water deprivation produced similar changes in RVLM neurons and enhanced sympathetic responses from activation of sciatic afferent nerves. Male Sprague‐Dawley rats (300–450g) were deprived of water but not food for 48h. Control rats were given free access to both. Then, animals were anesthetized with Inactin (120mg/kg, IV), artificially‐ventilated, and prepared for recording brachial ABP and SNA. Sciatic afferents were electrically stimulated (500uA, 1s pulse, 5s duration) at various frequencies (2, 5, 10, and 20 Hz). Water deprivation (H 2 OD) vs control rats significantly elevated plasma sodium concentrations (143±1 vs 137±1 mM, respectively; P<0.01) and osmolality (310±4 vs 294±2 mOsm/L, respectively; P<0.01). Activation of sciatic afferents produced frequency‐dependent increases in all variables in both control and water‐deprived animals. However, there were no statistical differences at any frequency between groups in mean ABP (5Hz ‐ control: 18±3 mmHg vs H 2 OD: 21±2 mmHg; n=6–8), lumbar SNA (5Hz – control: 139±11% vs H 2 OD: 129±10%, n=6–8), renal SNA (5Hz – control: 169±20% vs H 2 OD: 178±18%, n=6–8 per group), or splanchnic SNA (5Hz – control: 163±17% vs H 2 OD: 162±5%, n=6–8 per group). In a second set of experiments, chemical stimulation of RVLM neurons by microinjection of L‐glutamate (10mM, 35nL) produced significant increases in SNA and ABP in control and water‐deprived groups; however, there were no significant differences in mean ABP (control: 15±4mmHg vs H 2 OD: 11±2mmHg; n=4 per group), lumbar SNA (control: 124±4% vs H 2 OD: 131±10%), renal SNA (control: 133±5% vs H 2 OD: 131±4%), or splanchnic SNA (control: 131±3% vs H 2 OD: 140±17%). Inhibition of RVLM by unilateral injection of GABA (100mM, 35nL) produced similar decreases in mean ABP (control: ‐31±3mmHg vs H 2 OD: −29±2mmHg; n=3–4 per group), lumbar SNA (control: −26±1% vs H 2 O: −27±8%), renal SNA (control: −41±8% vs H 2 OD: −30±7%), and splanchnic SNA (control: −39±11% vs H 2 OD: −43±7%). Collectively, these findings suggest that water deprivation raises plasma sodium concentrations and osmolality but does not alter sympathetic reflexes or alter the excitability of RVLM neurons. Support or Funding Information AHA Established Investigator Award (SDS), NIH R01 HL113270 (SDS), NIH R01 HL128388 (SDS, WBF)