Concurrent Optical Imaging Spectroscopy and Laser-Doppler Flowmetry: The Relationship between Blood Flow, Oxygenation, and Volume in Rodent Barrel Cortex

Jones, Myles; Berwick, Jason; Johnston, Dave; Mayhew, John E. W.

doi:10.1006/nimg.2001.0808

Cited by 235 publications

(275 citation statements)

References 35 publications

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“…This biphasic response was similar to brain haemodynamic changes reported in studies using different imaging modalities, such as optical imaging of deoxyhaemoglobin (Jones et al . 2001) and functional magnetic resonance imaging (fMRI) of blood‐oxygenation‐level‐dependent (BOLD) responses (Menon et al . 1995; Kim et al .…”

Section: Discussionmentioning

confidence: 99%

Abnormal oxygen homeostasis in the nucleus tractus solitarii of the spontaneously hypertensive rat

Hosford

Millar

Ramage

et al. 2017

Experimental Physiology

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New Findings What is the central question of this study? Arterial hypertension is associated with impaired neurovascular coupling in the somatosensory cortex. Abnormalities in activity‐dependent oxygen consumption in brainstem regions involved in the control of cardiovascular reflexes have not been explored previously. What is the main finding and its importance? Using fast‐cyclic voltammetry, we found that changes in local tissue PnormalO2 in the nucleus tractus solitarii induced by electrical stimulation of the vagus nerve are significantly impaired in spontaneously hypertensive rats. This is consistent with previous observations showing that brainstem hypoxia plays an important role in the pathogenesis of arterial hypertension. The effects of arterial hypertension on cerebral blood flow remain poorly understood. Haemodynamic responses within the somatosensory cortex have been shown to be impaired in the spontaneously hypertensive rat (SHR) model. However, it is unknown whether arterial hypertension affects oxygen homeostasis in vital brainstem areas that control cardiovascular reflexes. In this study, we assessed vagus nerve stimulation‐induced changes in local tissue PnormalO2 (PnormaltO2) in the caudal nucleus tractus solitarii (cNTS) of SHRs and normotensive Wistar rats. Measurements of PnormaltO2 were performed using a novel application of fast‐cyclic voltammetry, which allows higher temporal resolution of O2 changes than traditional optical fluorescence techniques. Electrical stimulation of the central cut end of the vagus nerve (ESVN) caused profound reductions in arterial blood pressure along with biphasic changes in PnormaltO2 in the cNTS, characterized by a rapid decrease in PnormaltO2 (‘initial dip’) followed by a post‐stimulus overshoot above baseline. The initial dip was found to be significantly smaller in SHRs compared with normotensive Wistar rats even after ganglionic blockade. The post‐ESVN overshoot was similar in both groups but was reduced in Wistar rats after ganglionic blockade. In conclusion, neural activity‐dependent changes in tissue oxygen in brainstem cardiovascular autonomic centres are significantly impaired in animals with arterial hypertension.

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Section: Discussionmentioning

confidence: 99%

Abnormal oxygen homeostasis in the nucleus tractus solitarii of the spontaneously hypertensive rat

Hosford

Millar

Ramage

et al. 2017

Experimental Physiology

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“…Some investigators have reported an initial dip of the BOLD signal lasting 1-2 s before the standard BOLD signal increase (Ernst and Hennig, 1994;Hu et al, 1997;Menon et al, 1995;Yacoub and Hu, 2001), and a corresponding transient increase of deoxyhemoglobin has been reported in optical imaging studies (Malonek and Grinvald, 1996). The effect is small and not always present (Buxton, 2001;Jones et al, 2001;Lindauer et al, 2001), but it has stirred interest because it may reflect a rapid increase of CMRO 2 before the CBF increase, and this phenomenon may be better localized to the area of increased metabolism (i.e., the CBF increase may cover a wider area) (Malonek and Grinvald, 1996). 5.…”

Section: Experimental Characterization Of the Hemodynamic Responsementioning

confidence: 93%

Modeling the hemodynamic response to brain activation

et al. 2004

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Neural activity in the brain is accompanied by changes in cerebral blood flow (CBF) and blood oxygenation that are detectable with functional magnetic resonance imaging (fMRI) techniques. In this paper, recent mathematical models of this hemodynamic response are reviewed and integrated. Models are described for: (1) the blood oxygenation level dependent (BOLD) signal as a function of changes in cerebral oxygen extraction fraction (E) and cerebral blood volume (CBV); (2) the balloon model, proposed to describe the transient dynamics of CBV and deoxyhemoglobin (Hb) and how they affect the BOLD signal; (3) neurovascular coupling, relating the responses in CBF and cerebral metabolic rate of oxygen (CMRO 2 ) to the neural activity response; and (4) a simple model for the temporal nonlinearity of the neural response itself. These models are integrated into a mathematical framework describing the steps linking a stimulus to the measured BOLD and CBF responses. Experimental results examining transient features of the BOLD response (post-stimulus undershoot and initial dip), nonlinearities of the hemodynamic response, and the role of the physiologic baseline state in altering the BOLD signal are discussed in the context of the proposed models. Quantitative modeling of the hemodynamic response, when combined with experimental data measuring both the BOLD and CBF responses, makes possible a more specific and quantitative assessment of brain physiology than is possible with standard BOLD imaging alone. This approach has the potential to enhance numerous studies of brain function in development, health, and disease. D

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“…The CBF changes are paralleled by changes in oxygenation and blood volume. [47][48][49][50][51][52] The temporal dynamics of the CBF response thus suggest a close relation to oxygen rather than glucose availability.…”

Section: Differences Of Oxygen and Glucose Supplymentioning

confidence: 94%

The Oxygen Paradox of Neurovascular Coupling

Leithner

Royl

2013

J Cereb Blood Flow Metab

119

110

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The coupling of cerebral blood flow (CBF) to neuronal activity is well preserved during evolution. Upon changes in the neuronal activity, an incompletely understood coupling mechanism regulates diameter changes of supplying blood vessels, which adjust CBF within seconds. The physiologic brain tissue oxygen content would sustain unimpeded brain function for only 1 second if continuous oxygen supply would suddenly stop. This suggests that the CBF response has evolved to balance oxygen supply and demand. Surprisingly, CBF increases surpass the accompanying increases of cerebral metabolic rate of oxygen (CMRO 2 ). However, a disproportionate CBF increase may be required to increase the concentration gradient from capillary to tissue that drives oxygen delivery. However, the brain tissue oxygen content is not zero, and tissue pO 2 decreases could serve to increase oxygen delivery without a CBF increase. Experimental evidence suggests that CMRO 2 can increase with constant CBF within limits and decreases of baseline CBF were observed with constant CMRO 2 . This conflicting evidence may be viewed as an oxygen paradox of neurovascular coupling. As a possible solution for this paradox, we hypothesize that the CBF response has evolved to safeguard brain function in situations of moderate pathophysiological interference with oxygen supply. Keywords: brain; CMRO 2 ; functional hyperemia; neurovascular coupling; oxygen A quick glance at basic numbers of oxygen and glucose delivery to the brain and cerebral energy metabolism suggests that the most delicate function of cerebral blood flow (CBF) is the delivery of sufficient amounts of oxygen to the tissue where the oxygen reserve is so low that ATP production declines almost immediately once blood flow ceases. Therefore, the intuitive explanation for the rapid and large CBF response to neuronal activation is the supply of the additional oxygen needed. Experimental observations of large CBF responses accompanying small increases of cerebral metabolic rate of oxygen (CMRO 2 ), however, have cast doubt on this intuitive assumption. A number of alternative hypotheses may reconcile the seemingly conflicting findings: (1) A small increase of CMRO 2 may only be possible with a large increase in CBF due to physical limitations of oxygen delivery. Journal of Cerebral Blood(2) The large CBF response may be necessary to ensure oxygen delivery to the areas most distant from blood supply. (3) The large CBF response may not be necessary in its full extent but may have evolved as a safety mechanism ensuring sufficient oxygen supply in situations where oxygen delivery to the brain is impaired. (4) The large CBF response may be necessary for reasons other than oxygen delivery.In this opinion paper, we discuss studies on brain energy metabolism and neurovascular coupling. Based on the available evidence, we hypothesize that the surprisingly large CBF response to neuronal activation has evolved as a safety mechanism for oxygen delivery. To support this hypothesis, we first review basic facts on ...

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Concurrent Optical Imaging Spectroscopy and Laser-Doppler Flowmetry: The Relationship between Blood Flow, Oxygenation, and Volume in Rodent Barrel Cortex

Cited by 235 publications

References 35 publications

Abnormal oxygen homeostasis in the nucleus tractus solitarii of the spontaneously hypertensive rat

Abnormal oxygen homeostasis in the nucleus tractus solitarii of the spontaneously hypertensive rat

Modeling the hemodynamic response to brain activation

The Oxygen Paradox of Neurovascular Coupling

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