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Supplemental material, sj-pdf-1-jcb-10.1177_0271678X20928011 for Optical measurement of microvascular oxygenation and blood flow responses in awake mouse cortex during functional activation by İkbal Şencan, Tatiana Esipova, Kıvılcım Kılıç, Baoqiang Li, Michèle Desjardins, Mohammad A Yaseen, Hui Wang, Jason E Porter, Sreekanth Kura, Buyin Fu, Timothy W Secomb, David A Boas, Sergei A Vinogradov, Anna Devor and Sava Sakadžić in Journal of Cerebral Blood Flow & Metabolism

Supplemental material, sj-pdf-1-jcb-10.1177_0271678X20928011 for Optical measurement of microvascular oxygenation and blood flow responses in awake mouse cortex during functional activation by İkbal Şencan, Tatiana Esipova, Kıvılcım Kılıç, Baoqiang Li, Michèle Desjardins, Mohammad A Yaseen, Hui Wang, Jason E Porter, Sreekanth Kura, Buyin Fu, Timothy W Secomb, David A Boas, Sergei A Vinogradov, Anna Devor and Sava Sakadžić in Journal of Cerebral Blood Flow & Metabolism

Summary Efforts to deepen our understanding of the nervous system depends on high resolution sampling of neuronal activity. We leveraged clinically necessary intracranial monitoring performed during surgical resections to record from the cortical surface (N=30) using high spatial resolution, low impedance PEDOT:PSS microelectrodes. We identified three classes of activity. The first included relatively fast repeated waveforms with kinetics similar to, but not perfectly matching, extracellular single unit activity. The other two discrete unitary events with slower waveforms had event frequencies which were selectively modulated by auditory stimuli, electrical stimuli, pharmacological manipulation, and cold saline application. Furthermore, different classes had small but significant causal co-occurrences. We speculate that these different events could reflect axonal action potentials, dendritic calcium spikes, backpropagating action potentials or pre and post-synaptic phenomena, opening the possibility that we can sample information beyond typical extracellular somatic action potentials via high-density, low impedance electrodes on the cortical surface.

PURPOSE: The primary goal of this study was to estimate the value of β, the exponent in the power law relating changes of the transverse relaxation rate and intra-extravascular local magnetic susceptibility differences as [Formula: see text]. The secondary objective was to evaluate any differences that might exist in the value of β obtained using a deoxyhemoglobin-weighted [Formula: see text] distribution versus a constant [Formula: see text] distribution assumed in earlier computations. The third objective was to estimate the value of β relevant for methods based on susceptibility contrast agents with a concentration of [Formula: see text] higher than that used for BOLD fMRI calculations. METHODS: Our recently developed model of real microvascular anatomical networks is utilized to extend the original simplified Monte-Carlo simulations to compute [Formula: see text] from first principles. RESULTS: Our results show that [Formula: see text] for most BOLD fMRI measurements of real vascular networks as opposed to earlier predictions of [Formula: see text] using uniform [Formula: see text] distributions. For perfusion or functional MRI methods based on contrast agents, which generate larger values for [Formula: see text] , [Formula: see text] for [Formula: see text] , while at 14 T [Formula: see text] can drop below 1 and the variation across subjects is large, which indicates that a lower concentration of contrast agent with a lower value of [Formula: see text] is desired for experiments at high [Formula: see text]. CONCLUSION: These results improve our understanding of the relationship between R(2)* and the underlying microvascular properties. The findings will help to infer the cerebral metabolic rate of oxygen (CMRO(2)) and cerebral blood volume (CBV) from BOLD and perfusion MRI respectively.

The cerebral metabolic rate of oxygen ([Formula: see text]) is an essential parameter for evaluating brain function and pathophysiology. However, the currently available approaches for quantifying [Formula: see text] rely on complex multimodal imaging and mathematical modeling. Here, we introduce a method that allows estimation of [Formula: see text] based on a single measurement modality-two-photon imaging of the partial pressure of oxygen ([Formula: see text]) in cortical tissue. We employed two-photon phosphorescence lifetime microscopy (2PLM) and the oxygen-sensitive nanoprobe PtP-C343 to map the tissue [Formula: see text] distribution around cortical penetrating arterioles. [Formula: see text] is subsequently estimated by fitting the changes of tissue [Formula: see text] around arterioles with the Krogh cylinder model of oxygen diffusion. We measured the baseline [Formula: see text] in anesthetized rats and modulated tissue [Formula: see text] levels by manipulating the depth of anesthesia. This method provides [Formula: see text] measurements localized within [Formula: see text] and it may provide oxygen consumption measurements in individual cortical layers or within confined cortical regions, such as in ischemic penumbra and the foci of functional activation.

Background: Recent genome-wide association studies (GWAS) have identified a large number of genetic risk factors for schizophrenia (SCZ) featuring ion channels and calcium transporters. For some of these risk factors, independent prior investigations have examined the effects of genetic alterations on the cellular electrical excitability and calcium homeostasis. In the present proof-of-concept study, we harnessed these experimental results for modeling of computational properties on layer V cortical pyramidal cell and identify possible common alterations in behavior across SCZ-related genes. Methods: We applied a biophysically detailed multi-compartmental model to study the excitability of a layer V pyramidal cell. We reviewed the literature on functional genomics for variants of genes associated with SCZ, and used changes in neuron model parameters to represent the effects of these variants. Results: We present and apply a framework for examining the effects of subtle single nucleotide polymorphisms in ion channel and Ca2+ transporter-encoding genes on neuron excitability. Our analysis indicates that most of the considered SCZ- related genetic variants affect the spiking behavior and intracellular calcium dynamics resulting from summation of inputs across the dendritic tree. Conclusions: Our results suggest that alteration in the ability of a single neuron to integrate the inputs and scale its excitability may constitute a fundamental mechanistic contributor to mental disease, alongside with the previously proposed deficits in synaptic communication and network behavior.

© 2014 Macmillan Publishers Limited. All rights reserved. What is the organization of cerebral microvascular oxygenation and morphology that allows adequate tissue oxygenation at different activity levels? We address this question in the mouse cerebral cortex using microscopic imaging of intravascular O2partial pressure and blood flow combined with numerical modelling. Here we show that parenchymal arterioles are responsible for 50% of the extracted O2at baseline activity, and the majority of the remaining O2exchange takes place within the first few capillary branches. Most capillaries release little O2at baseline acting as an O2reserve that is recruited during increased neuronal activity or decreased blood flow. Our results challenge the common perception that capillaries are the major site of O2delivery to cerebral tissue. The understanding of oxygenation distribution along arterio-capillary paths may have profound implications for the interpretation of blood-oxygen-level dependent (BOLD) contrast in functional magnetic resonance imaging and for evaluating microvascular O2delivery capacity to support cerebral tissue in disease.

Measurements of oxygen partial pressure (pO(2)) with high temporal and spatial resolution in three dimensions is crucial for understanding oxygen delivery and consumption in normal and diseased brain. Among existing pO(2) measurement methods, phosphorescence quenching is optimally suited for the task. However, previous attempts to couple phosphorescence with two-photon laser scanning microscopy have faced substantial difficulties because of extremely low two-photon absorption cross-sections of conventional phosphorescent probes. Here we report to our knowledge the first practical in vivo two-photon high-resolution pO(2) measurements in small rodents' cortical microvasculature and tissue, made possible by combining an optimized imaging system with a two-photon-enhanced phosphorescent nanoprobe. The method features a measurement depth of up to 250 microm, sub-second temporal resolution and requires low probe concentration. The properties of the probe allowed for direct high-resolution measurement of cortical extravascular (tissue) pO(2), opening many possibilities for functional metabolic brain studies.

Functional hemodynamic responses are the composite results of underlying variations in cerebral oxygen consumption and the dilation of arterial vessels after neuronal activity. The development of biophysically based models of the cerebral vasculature allows the separation of the neuro-metabolic and neuro-vascular influences on measurable hemodynamic signals such as functional magnetic resonance imaging or optical imaging. We describe a multicompartment model of the vascular and oxygen transport dynamics associated with stimulus-driven neuronal activation. Our model offers several unique features compared with previous formulations such as the ability to estimate baseline blood flow, volume, and oxygen consumption from functional data. In addition, we introduce a capillary compliance model, arterial and venous oxygen permeability, and model the dynamics of extravascular tissue oxygenation. We apply this model to multimodal optical spectroscopic and laser speckle imaging of the rat somato-sensory cortex during nine conditions of whisker stimulation. By fitting the model using a psuedo-Bayesian framework to incorporate multimodal observations, we estimate baseline blood flow to be 94 (+/-15) mL/100 g min and baseline oxygen consumption to be 6.7 (+/-1.3) mL O(2)/100 g min. We calculate parametric, linear increases in arterial dilation (R(2)=0.96) and CMRO(2) (R(2)=0.87) responses over the nine conditions. Other parameters estimated by the model include vascular transit time and volume reserve, oxygen content, saturation, diffusivity rate constants, and partial pressure of oxygen in the vascular compartments and in the extravascular tissue. Finally, we compare this model to earlier work and find that the multicompartment model more accurately describes the observed oxygenation changes when compared with a single compartment version.

The Brain Research through Advancing Innovative Neurotechnologies (BRAIN) Initiative has focused scientific attention on the necessary tools to understand the human brain and mind. Here, we outline our collective vision for what we can achieve within a decade with properly targeted efforts and discuss likely technological deliverables and neuroscience progress.