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  • 174136_2_merged_1733936066

    Accepted author manuscript, 4.6 MB, PDF document

    Embargo ends: 12/01/26

DOI

  • Michael M Tymko
    University of Guelph, Ontario
  • Audrey Drapeau
    Université Laval
  • Maria Augusta Vieira-Coelho
    University of Porto
  • Lawrence Labrecque
    Université Laval
  • Sarah Imhoff
    Université Laval
  • Geoff B Coombs
    School of Psychology and Sport Science
  • Stephan Langevin
    Université Laval
  • Marc Fortin
    Université Laval
  • Nathalie Châteauvert
    Université Laval
  • Philip N Ainslie
    University of British Columbia, Okanagan
  • Patrice Brassard
    Université Laval

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.

Keywords

  • Humans, Baroreflex/physiology, Female, Male, Sympathetic Nervous System/physiology, Adult, Carbon Dioxide/metabolism, Norepinephrine/metabolism, Young Adult, Hypercapnia/physiopathology, Cerebrovascular Circulation/physiology, Lower Body Negative Pressure/methods, Brain/metabolism, Carotid Artery, Internal/physiology, Respiration, Blood Pressure/physiology, Jugular Veins/physiology, Chemoreceptor Cells/metabolism
Original languageEnglish
Pages (from-to)366-377
Number of pages12
JournalJournal of applied physiology (Bethesda, Md. : 1985)
Volume138
Issue number2
Early online date27 Jan 2025
DOIs
Publication statusPublished - 1 Feb 2025
Externally publishedYes
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