Acute and chronic increases in osmolality increase excitatory amino acid drive of the rostral ventrolateral medulla in rats

Virginia Brooks, Korrina L. Freeman, Theresa L. O'Donaughy

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Abstract

Water deprivation is associated with increased excitatory amino acid (EAA) drive of the rostral ventrolateral medulla (RVLM), but the mechanism is unknown. This study tested the hypotheses that the increased EAA activity is mediated by decreased blood volume and/or increased osmolality. This was first tested in urethane-anesthetized rats by determining whether bilateral microinjection of kynurenate (KYN, 2.7 nmol) into the RVLM decreases arterial pressure less in water-deprived rats after normalization of blood volume by intravenous infusion of isotonic saline or after normalization of plasma osmolality by intravenous infusion of 5% dextrose in water (5DW). Water-deprived rats exhibited decreased plasma volume and elevated plasma osmolality, hematocrit, and plasma sodium, chloride, and protein levels (all P <0.05). KYN microinjection decreased arterial pressure by 24 ± 2 mmHg (P <0.05; n = 17). The depressor response was not altered following isotonic saline infusion but, while still present (P <0.05), was reduced (P <0.05) to -13 ± 2 mmHg soon after 5DW infusion. These data suggest that the high osmolality, but not low blood volume, contributes to the KYN depressor response. To further investigate the action of increased osmolality on EAA input to RVLM, water-replete rats were also studied after hypertonic saline infusion. Whereas KYN microinjection did not decrease pressure immediately following the infusion, a depressor response gradually developed over the next 3 h. Lumbar sympathetic nerve activity also gradually increased to up to 167 ± 19% of control (P <0.05) 3 h after hypertonic saline infusion. In conclusion, acute and chronic increases in osmolality appear to increase EAA drive of the RVLM.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Regulatory Integrative and Comparative Physiology
Volume287
Issue number6 56-6
DOIs
StatePublished - Dec 2004

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Excitatory Amino Acids
Osmolar Concentration
Microinjections
Blood Volume
Water
Intravenous Infusions
Arterial Pressure
Kynurenic Acid
Water Deprivation
Glucose
Plasma Volume
Urethane
Hematocrit
Sodium Chloride
Drive
Pressure
Proteins

Keywords

  • Blood pressure
  • Excitatory amino acid
  • Glutamate
  • Kynurenic acid
  • Sympathetic activity
  • Water deprivation

ASJC Scopus subject areas

  • Physiology

Cite this

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title = "Acute and chronic increases in osmolality increase excitatory amino acid drive of the rostral ventrolateral medulla in rats",
abstract = "Water deprivation is associated with increased excitatory amino acid (EAA) drive of the rostral ventrolateral medulla (RVLM), but the mechanism is unknown. This study tested the hypotheses that the increased EAA activity is mediated by decreased blood volume and/or increased osmolality. This was first tested in urethane-anesthetized rats by determining whether bilateral microinjection of kynurenate (KYN, 2.7 nmol) into the RVLM decreases arterial pressure less in water-deprived rats after normalization of blood volume by intravenous infusion of isotonic saline or after normalization of plasma osmolality by intravenous infusion of 5{\%} dextrose in water (5DW). Water-deprived rats exhibited decreased plasma volume and elevated plasma osmolality, hematocrit, and plasma sodium, chloride, and protein levels (all P <0.05). KYN microinjection decreased arterial pressure by 24 ± 2 mmHg (P <0.05; n = 17). The depressor response was not altered following isotonic saline infusion but, while still present (P <0.05), was reduced (P <0.05) to -13 ± 2 mmHg soon after 5DW infusion. These data suggest that the high osmolality, but not low blood volume, contributes to the KYN depressor response. To further investigate the action of increased osmolality on EAA input to RVLM, water-replete rats were also studied after hypertonic saline infusion. Whereas KYN microinjection did not decrease pressure immediately following the infusion, a depressor response gradually developed over the next 3 h. Lumbar sympathetic nerve activity also gradually increased to up to 167 ± 19{\%} of control (P <0.05) 3 h after hypertonic saline infusion. In conclusion, acute and chronic increases in osmolality appear to increase EAA drive of the RVLM.",
keywords = "Blood pressure, Excitatory amino acid, Glutamate, Kynurenic acid, Sympathetic activity, Water deprivation",
author = "Virginia Brooks and Freeman, {Korrina L.} and O'Donaughy, {Theresa L.}",
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doi = "10.1152/ajpregu.00104.2004",
language = "English (US)",
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journal = "American Journal of Physiology - Renal Fluid and Electrolyte Physiology",
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T1 - Acute and chronic increases in osmolality increase excitatory amino acid drive of the rostral ventrolateral medulla in rats

AU - Brooks, Virginia

AU - Freeman, Korrina L.

AU - O'Donaughy, Theresa L.

PY - 2004/12

Y1 - 2004/12

N2 - Water deprivation is associated with increased excitatory amino acid (EAA) drive of the rostral ventrolateral medulla (RVLM), but the mechanism is unknown. This study tested the hypotheses that the increased EAA activity is mediated by decreased blood volume and/or increased osmolality. This was first tested in urethane-anesthetized rats by determining whether bilateral microinjection of kynurenate (KYN, 2.7 nmol) into the RVLM decreases arterial pressure less in water-deprived rats after normalization of blood volume by intravenous infusion of isotonic saline or after normalization of plasma osmolality by intravenous infusion of 5% dextrose in water (5DW). Water-deprived rats exhibited decreased plasma volume and elevated plasma osmolality, hematocrit, and plasma sodium, chloride, and protein levels (all P <0.05). KYN microinjection decreased arterial pressure by 24 ± 2 mmHg (P <0.05; n = 17). The depressor response was not altered following isotonic saline infusion but, while still present (P <0.05), was reduced (P <0.05) to -13 ± 2 mmHg soon after 5DW infusion. These data suggest that the high osmolality, but not low blood volume, contributes to the KYN depressor response. To further investigate the action of increased osmolality on EAA input to RVLM, water-replete rats were also studied after hypertonic saline infusion. Whereas KYN microinjection did not decrease pressure immediately following the infusion, a depressor response gradually developed over the next 3 h. Lumbar sympathetic nerve activity also gradually increased to up to 167 ± 19% of control (P <0.05) 3 h after hypertonic saline infusion. In conclusion, acute and chronic increases in osmolality appear to increase EAA drive of the RVLM.

AB - Water deprivation is associated with increased excitatory amino acid (EAA) drive of the rostral ventrolateral medulla (RVLM), but the mechanism is unknown. This study tested the hypotheses that the increased EAA activity is mediated by decreased blood volume and/or increased osmolality. This was first tested in urethane-anesthetized rats by determining whether bilateral microinjection of kynurenate (KYN, 2.7 nmol) into the RVLM decreases arterial pressure less in water-deprived rats after normalization of blood volume by intravenous infusion of isotonic saline or after normalization of plasma osmolality by intravenous infusion of 5% dextrose in water (5DW). Water-deprived rats exhibited decreased plasma volume and elevated plasma osmolality, hematocrit, and plasma sodium, chloride, and protein levels (all P <0.05). KYN microinjection decreased arterial pressure by 24 ± 2 mmHg (P <0.05; n = 17). The depressor response was not altered following isotonic saline infusion but, while still present (P <0.05), was reduced (P <0.05) to -13 ± 2 mmHg soon after 5DW infusion. These data suggest that the high osmolality, but not low blood volume, contributes to the KYN depressor response. To further investigate the action of increased osmolality on EAA input to RVLM, water-replete rats were also studied after hypertonic saline infusion. Whereas KYN microinjection did not decrease pressure immediately following the infusion, a depressor response gradually developed over the next 3 h. Lumbar sympathetic nerve activity also gradually increased to up to 167 ± 19% of control (P <0.05) 3 h after hypertonic saline infusion. In conclusion, acute and chronic increases in osmolality appear to increase EAA drive of the RVLM.

KW - Blood pressure

KW - Excitatory amino acid

KW - Glutamate

KW - Kynurenic acid

KW - Sympathetic activity

KW - Water deprivation

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U2 - 10.1152/ajpregu.00104.2004

DO - 10.1152/ajpregu.00104.2004

M3 - Article

VL - 287

JO - American Journal of Physiology - Renal Fluid and Electrolyte Physiology

JF - American Journal of Physiology - Renal Fluid and Electrolyte Physiology

SN - 1931-857X

IS - 6 56-6

ER -