title: Baroreceptor afferents modulate brain excitation and influence susceptibility to toxic effects of hyperbaric oxygen.
abstract: Unexplained adjustments in baroreflex sensitivity occur in conjunction with exposures to potentially toxic levels of hyperbaric oxygen. To investigate this, we monitored central nervous system, autonomic and cardiovascular responses in conscious and anesthetized rats exposed to hyperbaric oxygen at 5 and 6 atmospheres absolute, respectively. We observed two contrasting phases associated with time-dependent alterations in the functional state of the arterial baroreflex. The first phase, which conferred protection against potentially neurotoxic doses of oxygen, was concurrent with an increase in baroreflex sensitivity and included decreases in cerebral blood flow, heart rate, cardiac output, and sympathetic drive. The second phase was characterized by baroreflex impairment, cerebral hyperemia, spiking on the electroencephalogram, increased sympathetic drive, parasympatholysis, and pulmonary injury. Complete arterial baroreceptor deafferentation abolished the initial protective response, whereas electrical stimulation of intact arterial baroreceptor afferents prolonged it. We concluded that increased afferent traffic attributable to arterial baroreflex activation delays the development of excessive central excitation and seizures. Baroreflex inactivation or impairment removes this protection, and seizures may follow. Finally, electrical stimulation of intact baroreceptor afferents extends the normal delay in seizure development. These findings reveal that the autonomic nervous system is a powerful determinant of susceptibility to sympathetic hyperactivation and seizures in hyperbaric oxygen and the ensuing neurogenic pulmonary injury.
authors.affiliation: Center for Hyperbaric Medicine and Environmental Physiology, and Departments of Anesthesiology and Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russia.
authors.forename: Ivan T
authors.initials: IT
authors.lastname: Demchenko
authors.affiliation: Center for Hyperbaric Medicine and Environmental Physiology, and Departments of Anesthesiology and.
authors.forename: Heath G
authors.initials: HG
authors.lastname: Gasier
authors.affiliation: Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russia.
authors.forename: Sergei Yu
authors.initials: SY
authors.lastname: Zhilyaev
authors.affiliation: Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russia.
authors.forename: Alexander N
authors.initials: AN
authors.lastname: Moskvin
authors.affiliation: Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russia.
authors.forename: Alexander I
authors.initials: AI
authors.lastname: Krivchenko
authors.affiliation: Center for Hyperbaric Medicine and Environmental Physiology, and Departments of Anesthesiology and Medicine, Duke University Medical Center, Durham, North Carolina;
authors.forename: Claude A
authors.initials: CA
authors.lastname: Piantadosi
authors.affiliation: Center for Hyperbaric Medicine and Environmental Physiology, and Departments of Anesthesiology and barry.w.allen@duke.edu.
authors.forename: Barry W
authors.initials: BW
authors.lastname: Allen
mesh_terms: D000818:Animals; D001921:Brain / Q000502:physiology*; D004558:Electric Stimulation; D006439:Hemodynamics / Q000502:physiology; D006931:Hyperbaric Oxygenation / Q000009:adverse effects*; D008297:Male; D009475:Neurons, Afferent / Q000502:physiology*; D010100:Oxygen / Q000633:toxicity*; D011311:Pressoreceptors / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000502:physiology
chemical_list: D010100:Oxygen
keywords: afferent stimulation; autonomic nervous system; baroreflex sensitivity; hyperbaric oxygen; oxygen seizures