TY - JOUR

T1 - New evidence for baroreflex and respiratory chemoreflex-mediated cerebral sympathetic activation in humans

AU - Tymko, Michael M

AU - Drapeau, Audrey

AU - Vieira-Coelho, Maria Augusta

AU - Labrecque, Lawrence

AU - Imhoff, Sarah

AU - Coombs, Geoff B

AU - Langevin, Stephan

AU - Fortin, Marc

AU - Châteauvert, Nathalie

AU - Ainslie, Philip N

AU - Brassard, Patrice

PY - 2025/2/1

Y1 - 2025/2/1

N2 - The brain is highly innervated by sympathetic nerve fibers; however, their physiological purpose is poorly understood. We hypothesized that unilateral cerebral norepinephrine (NE) spillover, an index of cerebral sympathetic nerve activity (SNA), would be elevated when engaging the baroreflex [via lower-body negative pressure (LBNP; -20 and -40 Torr)] and respiratory chemoreflexes [via carbon dioxide (CO2) administration (+8 Torr)], independently and in combination. Twelve young and healthy participants (five females) underwent simultaneous blood sampling from the right radial artery and internal jugular vein. Tritiated NE was infused through the participants' right forearm vein. Right internal jugular vein and internal carotid artery blood flow were measured using duplex ultrasound. Unilateral cerebral NE spillover remained unchanged when only LBNP was applied (P = 0.29) but increased with hypercapnia (P = 0.035) and -40 Torr LBNP + CO2 (P < 0.01). There were no changes in total NE spillover during the LBNP and LBNP + CO2 trials (both P = 0.66), nor during CO2 alone (P = 0.13). No correlations were present between the increase in unilateral cerebral NE spillover during -40 Torr LBNP + CO2 and reductions in internal carotid artery blood flow (P = 0.56). These results indicate that baroreflex and respiratory chemoreflex stressors elevate cerebral SNA; however, the observed cerebral sympathetic activation has no impact on blood flow regulation in the internal carotid artery.NEW & NOTEWORTHY The results of the current study suggest that baroreflex and respiratory chemoreflex stressors elevate cerebral sympathetic nervous activity, quantified using the brain norepinephrine spillover method. However, the observed cerebral sympathetic activation has no impact on blood flow regulation in the internal carotid artery.

AB - The brain is highly innervated by sympathetic nerve fibers; however, their physiological purpose is poorly understood. We hypothesized that unilateral cerebral norepinephrine (NE) spillover, an index of cerebral sympathetic nerve activity (SNA), would be elevated when engaging the baroreflex [via lower-body negative pressure (LBNP; -20 and -40 Torr)] and respiratory chemoreflexes [via carbon dioxide (CO2) administration (+8 Torr)], independently and in combination. Twelve young and healthy participants (five females) underwent simultaneous blood sampling from the right radial artery and internal jugular vein. Tritiated NE was infused through the participants' right forearm vein. Right internal jugular vein and internal carotid artery blood flow were measured using duplex ultrasound. Unilateral cerebral NE spillover remained unchanged when only LBNP was applied (P = 0.29) but increased with hypercapnia (P = 0.035) and -40 Torr LBNP + CO2 (P < 0.01). There were no changes in total NE spillover during the LBNP and LBNP + CO2 trials (both P = 0.66), nor during CO2 alone (P = 0.13). No correlations were present between the increase in unilateral cerebral NE spillover during -40 Torr LBNP + CO2 and reductions in internal carotid artery blood flow (P = 0.56). These results indicate that baroreflex and respiratory chemoreflex stressors elevate cerebral SNA; however, the observed cerebral sympathetic activation has no impact on blood flow regulation in the internal carotid artery.NEW & NOTEWORTHY The results of the current study suggest that baroreflex and respiratory chemoreflex stressors elevate cerebral sympathetic nervous activity, quantified using the brain norepinephrine spillover method. However, the observed cerebral sympathetic activation has no impact on blood flow regulation in the internal carotid artery.

KW - Humans

KW - Baroreflex/physiology

KW - Female

KW - Male

KW - Sympathetic Nervous System/physiology

KW - Adult

KW - Carbon Dioxide/metabolism

KW - Norepinephrine/metabolism

KW - Young Adult

KW - Hypercapnia/physiopathology

KW - Cerebrovascular Circulation/physiology

KW - Lower Body Negative Pressure/methods

KW - Brain/metabolism

KW - Carotid Artery, Internal/physiology

KW - Respiration

KW - Blood Pressure/physiology

KW - Jugular Veins/physiology

KW - Chemoreceptor Cells/metabolism

U2 - 10.1152/japplphysiol.00688.2024

DO - 10.1152/japplphysiol.00688.2024

M3 - Article

C2 - 39718204

VL - 138

SP - 366

EP - 377

JO - Journal of applied physiology (Bethesda, Md. : 1985)

JF - Journal of applied physiology (Bethesda, Md. : 1985)

SN - 8750-7587

IS - 2

ER -