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Demchenko IT, Suliman HB, Zhilyaey SY, Alekseeva OS, Platonova TF, Makowski MS, Piantadosi CA, Gasier HG. GAT inhibition preserves cerebral blood flow and reduces oxidant damage to mitochondria in rodents exposed to extreme hyperbaric oxygen. Front Mol Neurosci 2023; 15:1062410. [PMID: 36704328 PMCID: PMC9871636 DOI: 10.3389/fnmol.2022.1062410] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2022] [Accepted: 12/22/2022] [Indexed: 01/11/2023] Open
Abstract
Oxygen breathing at elevated partial pressures (PO2's) at or more than 3 atmospheres absolute (ATA) causes a reduction in brain γ-aminobutyric acid (GABA) levels that impacts the development of central nervous system oxygen toxicity (CNS-OT). Drugs that increase brain GABA content delay the onset of CNS-OT, but it is unknown if oxidant damage is lessened because brain tissue PO2 remains elevated during hyperbaric oxygen (HBO2) exposures. Experiments were performed in rats and mice to measure brain GABA levels with or without GABA transporter inhibitors (GATs) and its influence on cerebral blood flow, oxidant damage, and aspects of mitochondrial quality control signaling (mitophagy and biogenesis). In rats pretreated with tiagabine (GAT1 inhibitor), the tachycardia, secondary rise in mean arterial blood pressure, and cerebral hyperemia were prevented during HBO2 at 5 and 6 ATA. Tiagabine and the nonselective GAT inhibitor nipecotic acid similarly extended HBO2 seizure latencies. In mice pretreated with tiagabine and exposed to HBO2 at 5 ATA, nuclear and mitochondrial DNA oxidation and astrocytosis was attenuated in the cerebellum and hippocampus. Less oxidant injury in these regions was accompanied by reduced conjugated microtubule-associated protein 1A/1B-light chain 3 (LC3-II), an index of mitophagy, and phosphorylated cAMP response element binding protein (pCREB), an initiator of mitochondrial biogenesis. We conclude that GABA prevents cerebral hyperemia and delays neuroexcitation under extreme HBO2, limiting oxidant damage in the cerebellum and hippocampus, and likely lowering mitophagy flux and initiation of pCREB-initiated mitochondrial biogenesis.
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Affiliation(s)
- Ivan T. Demchenko
- The Duke Center for Hyperbaric Medicine and Environmental Physiology, Duke University Medical Center, Durham, NC, United States
- Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russia
| | - Hagir B. Suliman
- Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russia
| | - Sergey Y. Zhilyaey
- Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russia
| | - Olga S. Alekseeva
- Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russia
| | - Tatyana F. Platonova
- Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russia
| | - Matthew S. Makowski
- The Duke Center for Hyperbaric Medicine and Environmental Physiology, Duke University Medical Center, Durham, NC, United States
| | - Claude A. Piantadosi
- The Duke Center for Hyperbaric Medicine and Environmental Physiology, Duke University Medical Center, Durham, NC, United States
| | - Heath G. Gasier
- The Duke Center for Hyperbaric Medicine and Environmental Physiology, Duke University Medical Center, Durham, NC, United States
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Dean JB, Stavitzski NM. The O2-sensitive brain stem, hyperoxic hyperventilation, and CNS oxygen toxicity. Front Physiol 2022; 13:921470. [PMID: 35957982 PMCID: PMC9360621 DOI: 10.3389/fphys.2022.921470] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2022] [Accepted: 06/27/2022] [Indexed: 11/13/2022] Open
Abstract
Central nervous system oxygen toxicity (CNS-OT) is a complex disorder that presents, initially, as a sequence of cardio-respiratory abnormalities and nonconvulsive signs and symptoms (S/Sx) of brain stem origin that culminate in generalized seizures, loss of consciousness, and postictal cardiogenic pulmonary edema. The risk of CNS-OT and its antecedent “early toxic indications” are what limits the use of hyperbaric oxygen (HBO2) in hyperbaric and undersea medicine. The purpose of this review is to illustrate, based on animal research, how the temporal pattern of abnormal brain stem responses that precedes an “oxtox hit” provides researchers a window into the early neurological events underlying seizure genesis. Specifically, we focus on the phenomenon of hyperoxic hyperventilation, and the medullary neurons presumed to contribute in large part to this paradoxical respiratory response; neurons in the caudal Solitary complex (cSC) of the dorsomedial medulla, including putative CO2 chemoreceptor neurons. The electrophysiological and redox properties of O2-/CO2-sensitive cSC neurons identified in rat brain slice experiments are summarized. Additionally, evidence is summarized that supports the working hypothesis that seizure genesis originates in subcortical areas and involves cardio-respiratory centers and cranial nerve nuclei in the hind brain (brainstem and cerebellum) based on, respectively, the complex temporal pattern of abnormal cardio-respiratory responses and various nonconvulsive S/Sx that precede seizures during exposure to HBO2.
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Reaction of the Hippocampal Microglia to Hyperbaric Oxygen. Bull Exp Biol Med 2022; 173:655-659. [PMID: 36210418 PMCID: PMC9548419 DOI: 10.1007/s10517-022-05607-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2022] [Indexed: 11/21/2022]
Abstract
We studied the reaction of rat hippocampal microgliocytes to hyperbaric oxygen at a pressure of 5 ata (absolute atmosphere). Immunohistochemical analysis with selective macrophage marker CD68 (ED1) and microglial marker Iba-1 allowed separate analysis of these two cell populations. It was shown that macrophages do not significantly contribute to reactive changes in the total pool of Iba-1+ hippocampal cells induced by hyperbaric oxygen.
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Ciarlone GE, Hinojo CM, Stavitzski NM, Dean JB. CNS function and dysfunction during exposure to hyperbaric oxygen in operational and clinical settings. Redox Biol 2019; 27:101159. [PMID: 30902504 PMCID: PMC6859559 DOI: 10.1016/j.redox.2019.101159] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2019] [Revised: 02/20/2019] [Accepted: 03/01/2019] [Indexed: 12/26/2022] Open
Abstract
Hyperbaric oxygen (HBO2) is breathed during hyperbaric oxygen therapy and during certain undersea pursuits in diving and submarine operations. What limits exposure to HBO2 in these situations is the acute onset of central nervous system oxygen toxicity (CNS-OT) following a latent period of safe oxygen breathing. CNS-OT presents as various non-convulsive signs and symptoms, many of which appear to be of brainstem origin involving cranial nerve nuclei and autonomic and cardiorespiratory centers, which ultimately spread to higher cortical centers and terminate as generalized tonic-clonic seizures. The initial safe latent period makes the use of HBO2 practical in hyperbaric and undersea medicine; however, the latent period is highly variable between individuals and within the same individual on different days, making it difficult to predict onset of toxic indications. Consequently, currently accepted guidelines for safe HBO2 exposure are highly conservative. This review examines the disorder of CNS-OT and summarizes current ideas on its underlying pathophysiology, including specific areas of the CNS and fundamental neural and redox signaling mechanisms that are thought to be involved in seizure genesis and propagation. In addition, conditions that accelerate the onset of seizures are discussed, as are current mitigation strategies under investigation for neuroprotection against redox stress while breathing HBO2 that extend the latent period, thus enabling safer and longer exposures for diving and medical therapies.
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Affiliation(s)
- Geoffrey E Ciarlone
- Undersea Medicine Department, Naval Medical Research Center, 503 Robert Grant Ave., Silver Spring, MD, USA
| | - Christopher M Hinojo
- Department of Molecular Pharmacology and Physiology, Hyperbaric Biomedical Research Laboratory, Morsani College of Medicine, University of South Florida, Tampa, FL, USA
| | - Nicole M Stavitzski
- Department of Molecular Pharmacology and Physiology, Hyperbaric Biomedical Research Laboratory, Morsani College of Medicine, University of South Florida, Tampa, FL, USA
| | - Jay B Dean
- Department of Molecular Pharmacology and Physiology, Hyperbaric Biomedical Research Laboratory, Morsani College of Medicine, University of South Florida, Tampa, FL, USA.
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Demchenko IT, Zhilyaev SY, Alekseeva OS, Krivchenko AI, Piantadosi CA, Gasier HG. Increased Antiseizure Effectiveness with Tiagabine Combined with Sodium Channel Antagonists in Mice Exposed to Hyperbaric Oxygen. Neurotox Res 2019; 36:788-795. [PMID: 31148118 DOI: 10.1007/s12640-019-00063-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2019] [Revised: 04/24/2019] [Accepted: 05/09/2019] [Indexed: 10/26/2022]
Abstract
Hyperbaric oxygen (HBO2) is acutely toxic to the central nervous system, culminating in EEG spikes and tonic-clonic convulsions. GABA enhancers and sodium channel antagonists improve seizure latencies in HBO2 when administered individually, while combining antiepileptic drugs from different functional classes can provide greater seizure latency. We examined the combined effectiveness of GABA enhancers (tiagabine and gabapentin) with sodium channel antagonists (carbamazepine and lamotrigine) in delaying HBO2-induced seizures. A series of experiments in C57BL/6 mice exposed to 100% oxygen at 5 atmospheres absolute (ATA) were performed. We predicted equally effective doses from individual drug-dose response curves, and the combinations of tiagabine + carbamazepine or lamotrigine were tested to determine the maximally effective combined doses to be used in subsequent experiments designed to identify the type of pharmacodynamic interaction for three fixed-ratio combinations (1:3, 1:1, and 3:1) using isobolographic analysis. For both combinations, the maximally effective combined doses increased seizure latency over controls > 5-fold and were determined to interact synergistically for fixed ratios 1:1 and 3:1, additive for 1:3. These results led us to explore whether the benefits of these drug combinations could be extended to the lungs, since a centrally mediated mechanism is believed to mediate hyperoxic-induced cardiogenic lung injury. Indeed, both combinations attenuated bronchoalveolar lavage protein content by ~ 50%. Combining tiagabine with carbamazepine or lamotrigine not only affords greater antiseizure protection in HBO2 but also allows for lower doses to be used, minimizing side effects, and attenuating acute lung injury.
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Affiliation(s)
- Ivan T Demchenko
- Center for Hyperbaric Medicine and Environmental Physiology, Duke University Medical Center, Durham, NC, USA.,Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russia
| | - Sergei Yu Zhilyaev
- Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russia
| | - Olga S Alekseeva
- Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russia
| | - Alexander I Krivchenko
- Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russia
| | - Claude A Piantadosi
- Center for Hyperbaric Medicine and Environmental Physiology, Duke University Medical Center, Durham, NC, USA.,Department of Anesthesiology, Duke University Medical Center, Durham, NC, USA.,Department of Medicine, Duke University Medical Center, Durham, NC, USA
| | - Heath G Gasier
- Department of Military and Emergency Medicine, Uniformed Services University of the Health Sciences, Bethesda, MD, USA.
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Yi H, Yu S, Zhang Y, Li R, Zhang D, Zhang D, Xu W. Preventive effects of ketone ester BD-AcAc 2 on central nervous system oxygen toxicity and concomitant acute lung injury. Diving Hyperb Med 2019; 48:235-240. [PMID: 30517956 DOI: 10.28920/dhm48.4.235-240] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2018] [Accepted: 10/28/2018] [Indexed: 02/01/2023]
Abstract
BACKGROUND Recent studies indicated that ketone ester R,S-1,3-butanediol acetoacetate diester (BD-AcAc2) may be effective in preventing central nervous system oxygen toxicity (CNS-OT) and concomitant acute lung injury, a serious medical problem to be faced when breathing hyperbaric oxygen (HBO). This study aimed to further investigate the protective effects of BD-AcAc2 against CNS-OT and concomitant acute lung injury (ALI) in mice. METHODS Mice were treated with BD-AcAc2 in peanut oil vehicle (2.5, 5.0 or 10.0 g·kg⁻² body weight) by gavage 20 minutes before 600 kPa HBO exposure. Control mice received the vehicle only. Seizure latency was recorded. Malondialdehyde content in brain and lung tissues, total protein level in bronchoalveolar lavage fluid (BLF) and lung water content were measured 60 minutes after the hyperbaric exposure. Histopathology of lung tissue was undertaken. RESULTS Compared with the vehicle alone, BD-AcAc2 prolonged seizure latency in a dose-dependent manner (P < 0.01). The HBO-induced increase in brain malondialdehyde, BLF protein and lung water were significantly reduced by BD-AcAc2 (P < 0.01). CONCLUSION Oral administration of the ketone ester BD-AcAc2 significantly protected against CNS-OT and concomitant ALI. Alleviation of oxidative stress may be one underlying mechanism providing this effect.
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Affiliation(s)
- Hongjie Yi
- Department of Diving and Hyperbaric Medicine, Naval Medical University, Shanghai, P R China
| | - Shichong Yu
- Department of Organic Chemistry, Naval Medical University, Shanghai
| | - Yanan Zhang
- Department of Diving and Hyperbaric Medicine, Naval Medical University, Shanghai, P R China
| | - Runping Li
- Department of Diving and Hyperbaric Medicine, Naval Medical University, Shanghai, P R China
| | - Dazhi Zhang
- Department of Organic Chemistry, Naval Medical University, Shanghai
| | - Dazhi Zhang
- Department of Diving and Hyperbaric Medicine, Naval Medical University, Shanghai, P R China
| | - Weigang Xu
- Department of Diving and Hyperbaric Medicine, Naval Medical University, Shanghai, P R China.,Corresponding author: Department of Diving and Hyperbaric Medicine, Naval Medical University, Shanghai 200433, China,
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Gasier HG, Demchenko IT, Zhilyaev SY, Moskvin AN, Krivchenko AI, Piantadosi CA. Adrenoceptor blockade modifies regional cerebral blood flow responses to hyperbaric hyperoxia: Protection against CNS oxygen toxicity. J Appl Physiol (1985) 2018; 125:1296-1304. [PMID: 30024340 DOI: 10.1152/japplphysiol.00540.2018] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Exposure to extreme-hyperbaric oxygen (HBO2), > 5-6 atmospheres absolute (ATA), produces baroreflex impairment, sympathetic hyperactivation, hypertension, tachycardia, and cerebral hyperemia, known as Phase II, culminating in seizures. We hypothesized that attenuation of the effects of high sympathetic outflow would preserve regional cerebral blood flow (rCBF) and protect against HBO2-induced seizures. To explore this possibility, we tested four adrenoceptor antagonists in conscious and anesthetized rats exposed to HBO2 at 5 and 6 ATA, respectively: phentolamine (nonselective α1 and 2), prazosin (selective α1), propranolol (nonselective β1 and 2) and atenolol (selective β1). In conscious rats, 4 drug-doses were administered to rats prior to HBO2 exposures, and seizure latencies were recorded. Drug-doses that provided similar protection against seizures were administered before HBO2 exposures in anesthetized rats to determine the effects of adrenoceptor blockade on mean arterial pressure, heart rate, rCBF and EEG spikes. All four drugs modified cardiovascular and rCBF responses in HBO2 that aligned with epileptiform discharges, but only phentolamine and propranolol effectively increased EEG spike latencies by ~20 and 36 min, respectively. When phentolamine and propranolol were delivered during HBO2 at the onset of phase II, only propranolol led to sustained reductions in heart rate and rCBF, preventing the appearance of epileptiform discharges. The enhanced effectiveness of propranolol may extend beyond β-adrenoceptor blockade, i.e. membrane stability and reduced metabolic activity. These results indicate that adrenoceptor drug pre-treatment will minimize the effects of excessive sympathetic outflow on rCBF and extend HBO2 exposure time.
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Affiliation(s)
- Heath G Gasier
- Department of Military & Emergency Medicine, Uniformed Services University of the Health Sciences, United States
| | - Ivan T Demchenko
- Center for Hyperbaric Medicine and Environmental Physiology, Duke University, United States
| | - Sergei Yu Zhilyaev
- Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russia
| | - Alexander N Moskvin
- Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russia
| | - Alexander I Krivchenko
- Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russia
| | - Claude A Piantadosi
- Center for Hyperbaric Medicine and Environmental Physiology, Duke University, United States
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Freiberger JJ, Derrick BJ, Natoli MJ, Akushevich I, Schinazi EA, Parker C, Stolp BW, Bennett PB, Vann RD, Dunworth SAS, Moon RE. Assessment of the interaction of hyperbaric N2, CO2, and O2 on psychomotor performance in divers. J Appl Physiol (1985) 2016; 121:953-964. [PMID: 27633739 DOI: 10.1152/japplphysiol.00534.2016] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Accepted: 09/02/2016] [Indexed: 11/22/2022] Open
Abstract
Diving narcosis results from the complex interaction of gases, activities, and environmental conditions. We hypothesized that these interactions could be separated into their component parts. Where previous studies have tested single cognitive tasks sequentially, we varied inspired partial pressures of CO2, N2, and O2 in immersed, exercising subjects while assessing multitasking performance with the Multi-Attribute Task Battery II (MATB-II) flight simulator. Cognitive performance was tested under 20 conditions of gas partial pressure and exercise in 42 male subjects meeting U.S. Navy age and fitness profiles. Inspired nitrogen (N2) and oxygen (O2) partial pressures were 0, 4.5, and 5.6 ATA and 0.21, 1.0, and 1.22 ATA, respectively, at rest and during 100-W immersed exercise with and without 0.075-ATA CO2 Linear regression modeled the association of gas partial pressure with task performance while controlling for exercise, hypercapnic ventilatory response, dive training, video game frequency, and age. Subjects served as their own controls. Impairment of memory, attention, and planning, but not motor tasks, was associated with N2 partial pressures >4.5 ATA. Sea level O2 at 0.925 ATA partially rescued motor and memory reaction time impaired by 0.075-ATA CO2; however, at hyperbaric pressures an unexpectedly strong interaction between CO2, N2, and exercise caused incapacitating narcosis with amnesia, which was augmented by O2 Perception of narcosis was not correlated with actual scores. The relative contributions of factors associated with diving narcosis will be useful to predict the effects of gas mixtures and exercise conditions on the cognitive performance of divers. The O2 effects are consistent with O2 narcosis or enhanced O2 toxicity.
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Affiliation(s)
- J J Freiberger
- Duke Center for Hyperbaric Medicine and Environmental Physiology and Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina
| | - B J Derrick
- Duke Center for Hyperbaric Medicine and Environmental Physiology and Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina
| | - M J Natoli
- Duke Center for Hyperbaric Medicine and Environmental Physiology and Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina
| | - I Akushevich
- Duke Center for Hyperbaric Medicine and Environmental Physiology and Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina
| | - E A Schinazi
- Duke Center for Hyperbaric Medicine and Environmental Physiology and Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina
| | - C Parker
- Duke Center for Hyperbaric Medicine and Environmental Physiology and Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina
| | - B W Stolp
- Duke Center for Hyperbaric Medicine and Environmental Physiology and Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina
| | - P B Bennett
- Duke Center for Hyperbaric Medicine and Environmental Physiology and Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina
| | - R D Vann
- Duke Center for Hyperbaric Medicine and Environmental Physiology and Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina
| | - S A S Dunworth
- Duke Center for Hyperbaric Medicine and Environmental Physiology and Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina
| | - R E Moon
- Duke Center for Hyperbaric Medicine and Environmental Physiology and Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina
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Abstract
INTRODUCTION The use of hyperbaric oxygen (O2) as a therapeutic agent carries with it the risk of central nervous system (CNS) O2 toxicity. METHODS To further the understanding of this risk and the nature of its molecular mechanism, a review was conducted on the literature from various fields. RESULTS Numerous physiological changes are produced by increased partial pressures of oxygen (Po2), which may ultimately result in CNS O2 toxicity. The human body has several equilibrated safeguards that minimize effects of reactive species on neural networks, believed to play a primary role in CNS O2 toxicity. Increased partial pressure of oxygen (Po2) appears to saturate protective enzymes and unfavorably shift protective reactions in the direction of neural network overstimulation. Certain regions of the CNS appear more susceptible than others to these effects. Failure to decrease the elevated Po2 can result in a tonic-clonic seizure and death. Randomized, controlled studies in human populations would require a multicenter trial over a long period of time with numerous endpoints used to identify O2 toxicity. CONCLUSIONS The mounting scientific evidence and apparent increase in the number of hyperbaric O2 treatments demonstrate a need for further study in the near future.
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Gasier HG, Demchenko IT, Allen BW, Piantadosi CA. Effects of striatal nitric oxide production on regional cerebral blood flow and seizure development in rats exposed to extreme hyperoxia. J Appl Physiol (1985) 2015; 119:1282-8. [PMID: 26338456 DOI: 10.1152/japplphysiol.00432.2015] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2015] [Accepted: 08/31/2015] [Indexed: 02/04/2023] Open
Abstract
The endogenous vasodilator and signaling molecule nitric oxide has been implicated in cerebral hyperemia, sympathoexcitation, and seizures induced by hyperbaric oxygen (HBO2) at or above 3 atmospheres absolute (ATA). It is unknown whether these events in the onset of central nervous system oxygen toxicity originate within specific brain structures and whether blood flow is diverted to the brain from peripheral organs with high basal flow, such as the kidney. To explore these questions, total and regional cerebral blood flow (CBF) were measured in brain structures of the central autonomic network in anesthetized rats in HBO2 at 6 ATA. Electroencephalogram (EEG) recordings, cardiovascular hemodynamics, and renal blood flow (RBF) were also monitored. As expected, mean arterial blood pressure and total and regional CBF increased preceding EEG spikes while RBF was unaltered. Of the brain structures examined, the earliest rise in CBF occurred in the striatum, suggesting increased neuronal activation. Continuous unilateral or bilateral striatal infusion of the nitric oxide synthase inhibitor N(ω)-nitro-L-arginine methyl ester attenuated CBF responses in that structure, but global EEG discharges persisted and did not differ from controls. Our novel findings indicate that: 1) cerebral hyperemia in extreme HBO2 in rats does not occur at the expense of renal perfusion, highlighting the remarkable autoregulatory capability of the kidney, and 2) in spite of a sentinel increase in striatal blood flow, additional brain structure(s) likely govern the pathogenesis of HBO2-induced seizures because EEG discharge latency was unchanged by local blockade of striatal nitric oxide production and concomitant hyperemia.
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Affiliation(s)
- Heath G Gasier
- Center for Hyperbaric Medicine and Environmental Physiology, Duke University Medical Center, Durham, North Carolina; Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina; and
| | - Ivan T Demchenko
- Center for Hyperbaric Medicine and Environmental Physiology, Duke University Medical Center, Durham, North Carolina; Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina; and
| | - Barry W Allen
- Center for Hyperbaric Medicine and Environmental Physiology, Duke University Medical Center, Durham, North Carolina; Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina; and
| | - Claude A Piantadosi
- Center for Hyperbaric Medicine and Environmental Physiology, Duke University Medical Center, Durham, North Carolina; Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina; and Department of Medicine, Duke University Medical Center, Durham, North Carolina
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