Glial and neuronal control of brain blood flow

Degree of PEGylatation of Lumbricus terrestris Hemoglobin Improves Microcirculatory Blood Flow but Increases the Rate of Auto-Oxidation

INTRODUCTION

The demand for red blood cells (RBCs) is on the rise due to the increasing diagnosis of chronic diseases such as sickle cell anemia, malaria, and thalassemia. Despite many commercial attempts, there are no U.S. FDA-approved artificial RBCs for use in humans. Existing RBC substitutes have employed various strategies to transport oxygen, extend the circulation time, and reduce organ toxicity, but none have replicated the natural protective mechanisms of RBCs, which prevent hemoglobin (Hb) dimerization and heme iron oxidation. Lumbricus terrestris (earthworm) erythrocruorin (LtEc) is a naturally occurring extracellular hemoglobin (Hb) with promising attributes: large molecular diameter (30 nm), high molecular weight (3.6 MDa), low auto-oxidation rate, and limited nitric oxide-scavenging properties. These characteristics make LtEc an ideal candidate as an RBC substitute. However, LtEc has a significant drawback, its short circulatory half-life. To address this issue, we explored thiol-mediated surface PEGylation of LtEc (PEG-LtEc) at varying polyethylene glycol (PEG) surface coverages. Increasing PEG surface coverage beyond 40% destabilizes LtEc into smaller subunits that are 1/12th the size of LtEc. Therefore, we evaluated two PEG surface coverage options: PEG-LtEc-0.2 (20% PEGylation) and PEG-LtEc-1.0 (100% PEGylation).

METHODS

We conducted experiments using golden Syrian hamsters with dorsal window chambers and catheters to assess the efficacy of these solutions. We measured microvascular parameters, organ function, cerebral blood flow, circulation time, mean arterial pressure, heart rate, and blood gases and performed histology to screen for toxicity.

CONCLUSION

Our findings indicate that both PEG-LtEc molecules offer significant benefits in restoring microvascular parameters, organ function, cerebral blood flow, and circulation time compared to LtEc alone. Notably, PEG-LtEc-1.0 showed superior microvascular perfusion, although it exhibited a higher rate of auto-oxidation compared to PEG-LtEc-0.2. These results underscore the advantages of PEGylation in terms of tissue perfusion and organ health while highlighting its limitations.

Spatiotemporal cerebral blood flow dynamics underlies emergence of the limbic-sensorimotor-association cortical gradient in human infancy

Infant cerebral blood flow (CBF) delivers nutrients and oxygen to fulfill brain energy consumption requirements for the fastest period of postnatal brain development across the lifespan. However, organizing principle of whole-brain CBF dynamics during infancy remains obscure. Leveraging a unique cohort of 100+ infants with high-resolution arterial spin labeled MRI, we found the emergence of the cortical hierarchy revealed by the highest-resolution infant CBF maps available to date. Infant CBF across cortical regions increased in a biphasic pattern with initial rapid and sequentially slower rate, with break-point ages increasing along the limbic-sensorimotor-association cortical gradient. Increases in CBF in sensorimotor cortices were associated with enhanced language and motor skills, and frontoparietal association cortices for cognitive skills. The study discovered emergence of the hierarchical limbic-sensorimotor-association cortical gradient in infancy, and offers standardized reference of infant brain CBF and insight into the physiological basis of cortical specialization and real-world infant developmental functioning.

Neurodegenerative disorders: Mechanisms of degeneration and therapeutic approaches with their clinical relevance

Neurodegenerative disorders (NDs) are expected to pose a significant challenge for both medicine and public health in the upcoming years due to global demographic changes. NDs are mainly represented by degeneration/loss of neurons, which is primarily accountable for severe mental illness. This neuronal degeneration leads to many neuropsychiatric problems and permanent disability in an individual. Moreover, the tight junction of the brain, blood-brain barrier (BBB)has a protective feature, functioning as a biological barrier that can prevent medicines, toxins, and foreign substances from entering the brain. However, delivering any medicinal agent to the brain in NDs (i.e., Multiple sclerosis, Alzheimer's, Parkinson's, etc.) is enormously challenging. There are many approved therapies to address NDs, but most of them only help treat the associated manifestations. The available therapies have failed to control the progression of NDs due to certain factors, i.e., BBB and drug-associated undesirable effects. NDs have extremely complex pathology, with many pathogenic mechanisms involved in the initiation and progression; thereby, a limited survival rate has been observed in ND patients. Hence, understanding the exact mechanism behind NDs is crucial to developing alternative approaches for improving ND patients' survival rates. Thus, the present review sheds light on different cellular mechanisms involved in NDs and novel therapeutic approaches with their clinical relevance, which will assist researchers in developing alternate strategies to address the limitations of conventional ND therapies. The current work offers the scope into the near future to improve the therapeutic approach of NDs.

Cerebral Small Vessel Disease in Population-Based Research: What are We Looking at - and What not?

Cerebral small vessel disease (CSVD) is considered as one of the main causes of cognitive decline and dementia. However, despite extensive research, the pathogenesis of CSVD and the mechanisms through which CSVD leads to its clinical manifestations remain largely unclear. The challenging in vivo quantification of CSVD hampers progress in further unraveling the pathogenesis and pathophysiology of CSVD. Currently, markers of CSVD are mainly brain abnormalities attributed to CSVD, but these are limited in reflecting morphological and functional changes of the microvasculature. We describe aspects of CSVD that are reflected by currently used techniques and those that are still insufficiently captured.

Risk factors for neurological disability outcomes in patients under extracorporeal membrane oxygenation following cardiac arrest: An observational study

OBJECTIVES

This study aimed to identify factors associated with neurological and disability outcomes in patients who underwent ECMO following cardiac arrest.

METHODS

This retrospective, single-center, observational study included adult patients who received ECMO treatment for in-hospital cardiac arrest (IHCA) or out-of-hospital cardiac arrest (OHCA) between February 2016 and March 2020. Factors associated with neurological and disability outcomes in these patients who underwent ECMO were assessed.

SETTING

Hamad General Hospital, Qatar.

MAIN OUTCOME MEASURES

Neurological disability outcomes were assessed using the Modified Rankin Scale (mRS) and the Cerebral Performance Category (CPC) scale.

RESULTS

Among the 48 patients included, 37 (77 %) experienced OHCA, and 11 (23 %) had IHCA. The 28-day survival rate was 14 (29.2 %). Of the survivors, 9 (64.3 %) achieved a good neurological outcome, while 5 (35.7 %) experienced poor neurological outcomes. Regarding disability, 5 (35.7 %) of survivors had no disability, while 9 (64.3 %) had some form of disability. The results showed significantly shorter median time intervals in minutes, including collapse to cardiopulmonary resuscitation (CPR) (3 vs. 6, P = 0.001), CPR duration (12 vs. 35, P = 0.001), CPR to extracorporeal cardiopulmonary resuscitation (ECPR) (20 vs. 40, P = 0.001), and collapse-to-ECPR (23 vs. 45, P = 0.001), in the good outcome group compared to the poor outcome group.

CONCLUSION

This study emphasizes the importance of minimizing the time between collapse and CPR/ECMO initiation to improve neurological outcomes and reduce disability in cardiac arrest patients. However, no significant associations were found between outcomes and other demographic or clinical variables in this study. Further research with a larger sample size is needed to validate these findings.

IMPLICATIONS FOR CLINICAL PRACTICE

The study underscores the significance of reducing the time between collapse and the initiation of CPR and ECMO. Shorter time intervals were associated with improved neurological outcomes and reduced disability in cardiac arrest patients.

Blood-brain barrier alterations and their impact on Parkinson's disease pathogenesis and therapy

There is increasing evidence for blood-brain barrier (BBB) alterations in Parkinson's disease (PD), the second most common neurodegenerative disorder with rapidly rising prevalence. Altered tight junction and transporter protein levels, accumulation of α-synuclein and increase in inflammatory processes lead to extravasation of blood molecules and vessel degeneration. This could result in a self-perpetuating pathophysiology of inflammation and BBB alteration, which contribute to neurodegeneration. Toxin exposure or α-synuclein over-expression in animal models has been shown to initiate similar pathologies, providing a platform to study underlying mechanisms and therapeutic interventions. Here we provide a comprehensive review of the current knowledge on BBB alterations in PD patients and how rodent models that replicate some of these changes can be used to study disease mechanisms. Specific challenges in assessing the BBB in patients and in healthy controls are discussed. Finally, a potential role of BBB alterations in disease pathogenesis and possible implications for therapy are explored. The interference of BBB alterations with current and novel therapeutic strategies requires more attention. Brain region-specific BBB alterations could also open up novel opportunities to target specifically vulnerable neuronal subpopulations.

Cellular Components of the Blood-Brain Barrier and Their Involvement in Aging-Associated Cognitive Impairment

Human life expectancy has been significantly extended, which poses major challenges to our healthcare and social systems. Aging-associated cognitive impairment is attributed to endothelial dysfunction in the cardiovascular system and neurological dysfunction in the central nervous system. The central nervous system is considered an immune-privileged tissue due to the exquisite protection provided by the blood-brain barrier. The present review provides an overview of the structure and function of blood-brain barrier, extending the cell components of blood-brain barrier from endothelial cells and pericytes to astrocytes, perivascular macrophages and oligodendrocyte progenitor cells. In particular, the pathological changes in the blood-brain barrier in aging, with special focus on the underlying mechanisms and molecular changes, are presented. Furthermore, the potential preventive/therapeutic strategies against aging-associated blood-brain barrier disruption are discussed.

Beyond hypertrophy: Changing views of astrocytes in glaucoma

Astrocytes serve multiple roles in helping to maintain homeostatic physiology of central nervous system tissue, ranging from metabolic support to coupling between vascular and neural elements. Astrocytes are especially critical in axonal tracts such as the optic nerve, where axons propagate energy-demanding action potentials great distances. In disease, astrocyte remodeling is a dynamic, multifaceted process that is often over-simplified between states of quiescence and reactivity. In glaucoma, axon degeneration in the optic nerve is characterized by progressive stages. So too is astrocyte remodeling. Here, using quantitative analysis of light and electron micrographs of myelinated optic nerve sections from the DBA/2J mouse model of glaucoma, we offer further insight into how astrocyte organization reflects stages of degeneration. This analysis indicates that even as axons degenerate, astrocyte gliosis in the nerve increases without abject proliferation, similar to results in the DBA/2J retina. Gliosis is accompanied by reorganization. As axons expand prior to frank degeneration, astrocyte processes retract from the extra-axonal space and reorient towards the nerve edge. After a critical threshold of expansion, axons drop out, and astrocyte processes distribute more evenly across the nerve reflecting gliosis. This multi-stage process likely reflects local rather than global cues from axons and the surrounding tissue that induce rapid reorganization to promote axon survival and extend functionality of the nerve.

Novel therapeutic targets for reperfusion injury in ischemic stroke: Understanding the role of mitochondria, excitotoxicity and ferroptosis

Ischemic reperfusion injury (IRI) remains a significant challenge in various clinical settings, including stroke. Despite advances in reperfusion strategies, the restoration of blood flow to ischemic tissues often exacerbates tissue damage through a complex cascade of cellular and molecular events. In recent years, there has been growing interest in identifying novel therapeutic targets to ameliorate the detrimental effects of IRI and improve patient outcomes. This review critically evaluates emerging therapeutic targets and strategies for IRI management, such as R-spondin 3, neurolysin, glial cell gene therapy and inter alpha inhibitors. Diverse pathophysiology involved in IRI stroke such as oxidative stress, inflammation, mitochondrial dysfunction, and ferroptosis are also closely discussed. Additionally, we explored the intricate interplay between inflammation and IRI, focusing on cell-mediated gene therapy approaches and anti-inflammatory agents that hold promise for attenuating tissue damage. Moreover, we delve into novel strategies aimed at preserving endothelial function, promoting tissue repair, and enhancing cellular resilience to ischemic insults. Finally, we discuss challenges, future directions, and translational opportunities for the development of effective therapies targeting ischemic reperfusion injury.

Cellular and molecular mechanisms of the blood-brain barrier dysfunction in neurodegenerative diseases

BACKGROUND

Maintaining the structural and functional integrity of the blood-brain barrier (BBB) is vital for neuronal equilibrium and optimal brain function. Disruptions to BBB performance are implicated in the pathology of neurodegenerative diseases.

MAIN BODY

Early indicators of multiple neurodegenerative disorders in humans and animal models include impaired BBB stability, regional cerebral blood flow shortfalls, and vascular inflammation associated with BBB dysfunction. Understanding the cellular and molecular mechanisms of BBB dysfunction in brain disorders is crucial for elucidating the sustenance of neural computations under pathological conditions and for developing treatments for these diseases. This paper initially explores the cellular and molecular definition of the BBB, along with the signaling pathways regulating BBB stability, cerebral blood flow, and vascular inflammation. Subsequently, we review current insights into BBB dynamics in Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and multiple sclerosis. The paper concludes by proposing a unified mechanism whereby BBB dysfunction contributes to neurodegenerative disorders, highlights potential BBB-focused therapeutic strategies and targets, and outlines lessons learned and future research directions.

CONCLUSIONS

BBB breakdown significantly impacts the development and progression of neurodegenerative diseases, and unraveling the cellular and molecular mechanisms underlying BBB dysfunction is vital to elucidate how neural computations are sustained under pathological conditions and to devise therapeutic approaches.

Distinct potassium channel types in brain capillary pericytes

Capillaries, composed of electrically coupled endothelial cells and overlying pericytes, constitute the vast majority of blood vessels in the brain. The most arteriole-proximate three to four branches of the capillary bed are covered by α-actin-expressing, contractile pericytes. These mural cells have a distinctive morphology and express different markers compared with their smooth muscle cell (SMC) cousins but share similar excitation-coupling contraction machinery. Despite this similarity, pericytes are considerably more depolarized than SMCs at low intravascular pressures. We have recently shown that pericytes, such as SMCs, possess functional voltage-dependent Ca2+ channels and ATP-sensitive K+ channels. Here, we further investigate the complement of pericyte ion channels, focusing on members of the K+ channel superfamily. Using NG2-DsRed-transgenic mice and diverse configurations of the patch-clamp technique, we demonstrate that pericytes display robust inward-rectifier K+ currents that are primarily mediated by the Kir2 family, based on their unique biophysical characteristics and sensitivity to micromolar concentrations of Ba2+. Moreover, multiple lines of evidence, including characteristic kinetics, sensitivity to specific blockers, biophysical attributes, and distinctive single-channel properties, established the functional expression of two voltage-dependent K+ channels: KV1 and BKCa. Although these three types of channels are also present in SMCs, they exhibit distinctive current density and kinetics profiles in pericytes. Collectively, these findings underscore differences in the operation of shared molecular features between pericytes and SMCs and highlight the potential contribution of these three K+ ion channels in setting pericyte membrane potential, modulating capillary hemodynamics, and regulating cerebral blood flow.

Synaptic signaling modeled by functional connectivity predicts metabolic demands of the human brain

PURPOSE

The human brain is characterized by interacting large-scale functional networks fueled by glucose metabolism. Since former studies could not sufficiently clarify how these functional connections shape glucose metabolism, we aimed to provide a neurophysiologically-based approach.

METHODS

51 healthy volunteers underwent simultaneous PET/MRI to obtain BOLD functional connectivity and [18F]FDG glucose metabolism. These multimodal imaging proxies of fMRI and PET were combined in a whole-brain extension of metabolic connectivity mapping. Specifically, functional connectivity of all brain regions were used as input to explain glucose metabolism of a given target region. This enabled the modeling of postsynaptic energy demands by incoming signals from distinct brain regions.

RESULTS

Functional connectivity input explained a substantial part of metabolic demands but with pronounced regional variations (34 - 76%). During cognitive task performance this multimodal association revealed a shift to higher network integration compared to resting state. In healthy aging, a dedifferentiation (decreased segregated/modular structure of the brain) of brain networks during rest was observed. Furthermore, by including data from mRNA maps, [11C]UCB-J synaptic density and aerobic glycolysis (oxygen-to-glucose index from PET data), we show that whole-brain functional input reflects non-oxidative, on-demand metabolism of synaptic signaling. The metabolically-derived directionality of functional inputs further marked them as top-down predictions. In addition, the approach uncovered formerly hidden networks with superior efficiency through metabolically informed network partitioning.

CONCLUSIONS

Applying multimodal imaging, we decipher a crucial part of the metabolic and neurophysiological basis of functional connections in the brain as interregional on-demand synaptic signaling fueled by anaerobic metabolism. The observed task- and age-related effects indicate promising future applications to characterize human brain function and clinical alterations.

Neuroprotective effects of lactate and ketone bodies in acute brain injury

The goal of neurocritical care is to prevent and reverse the pathologic cascades of secondary brain injury by optimizing cerebral blood flow, oxygen supply and substrate delivery. While glucose is an essential energetic substrate for the brain, we frequently observe a strong decrease in glucose delivery and/or a glucose metabolic dysregulation following acute brain injury. In parallel, during the last decades, lactate and ketone bodies have been identified as potential alternative fuels to provide energy to the brain, both under physiological conditions and in case of glucose shortage. They are now viewed as integral parts of brain metabolism. In addition to their energetic role, experimental evidence also supports their neuroprotective properties after acute brain injury, regulating in particular intracranial pressure control, decreasing ischemic volume, and leading to an improvement in cognitive functions as well as survival. In this review, we present preclinical and clinical evidence exploring the mechanisms underlying their neuroprotective effects and identify research priorities for promoting lactate and ketone bodies use in brain injury.

Astrocyte morphology

Astrocytes are predominant glial cells that tile the central nervous system (CNS). A cardinal feature of astrocytes is their complex and visually enchanting morphology, referred to as bushy, spongy, and star-like. A central precept of this review is that such complex morphological shapes evolved to allow astrocytes to contact and signal with diverse cells at a range of distances in order to sample, regulate, and contribute to the extracellular milieu, and thus participate widely in cell-cell signaling during physiology and disease. The recent use of improved imaging methods and cell-specific molecular evaluations has revealed new information on the structural organization and molecular underpinnings of astrocyte morphology, the mechanisms of astrocyte morphogenesis, and the contributions to disease states of reduced morphology. These insights have reignited interest in astrocyte morphological complexity as a cornerstone of fundamental glial biology and as a critical substrate for multicellular spatial and physiological interactions in the CNS.

Intrinsic organization of the corpus callosum

The corpus callosum-the largest commissural fiber system connecting the two cerebral hemispheres-is considered essential for bilateral sensory integration and higher cognitive functions. Most studies exploring the corpus callosum have examined either the anatomical, physiological, and neurochemical organization of callosal projections or the functional and/or behavioral aspects of the callosal connections after complete/partial callosotomy or callosal lesion. There are no works that address the intrinsic organization of the corpus callosum. We review the existing information on the activities that take place in the commissure in three sections: I) the topographical and neurochemical organization of the intracallosal fibers, II) the role of glia in the corpus callosum, and III) the role of the intracallosal neurons.

tPA supplementation preserves neurovascular and cognitive function in Tg2576 mice

INTRODUCTION

Amyloid beta (Aβ) impairs the cerebral blood flow (CBF) increase induced by neural activity (functional hyperemia). Tissue plasminogen activator (tPA) is required for functional hyperemia, and in mouse models of Aβ accumulation tPA deficiency contributes to neurovascular and cognitive impairment. However, it remains unknown if tPA supplementation can rescue Aβ-induced neurovascular and cognitive dysfunction.

METHODS

Tg2576 mice and wild-type littermates received intranasal tPA (0.8 mg/kg/day) or vehicle 5 days a week starting at 11 to 12 months of age and were assessed 3 months later.

RESULTS

Treatment of Tg2576 mice with tPA restored resting CBF, prevented the attenuation in functional hyperemia, and improved nesting behavior. These effects were associated with reduced cerebral atrophy and cerebral amyloid angiopathy, but not parenchymal amyloid.

DISCUSSION

These findings highlight the key role of tPA deficiency in the neurovascular and cognitive dysfunction associated with amyloid pathology, and suggest potential therapeutic strategies involving tPA reconstitution.

HIGHLIGHTS

Amyloid beta (Aβ) induces neurovascular dysfunction and impairs the increase of cerebral blood flow induced by neural activity (functional hyperemia). Tissue plasminogen activator (tPA) deficiency contributes to the neurovascular and cognitive dysfunction caused by Aβ. In mice with florid amyloid pathology intranasal administration of tPA rescues the neurovascular and cognitive dysfunction and reduces brain atrophy and cerebral amyloid angiopathy. tPA deficiency plays a crucial role in neurovascular and cognitive dysfunction induced by Aβ and tPA reconstitution may be of therapeutic value.

Beyond life: Exploring hemodynamic patterns in postmortem mice brains

We utilize Laser Speckle Contrast Imaging (LSCI) for visualizing cerebral blood flow in mice during and post-cardiac arrest. Analyzing LSCI images, we noted temporal blood flow variations across the brain surface for hours postmortem. Fast Fourier Transform (FFT) analysis depicted blood flow and microcirculation decay post-death. Continuous Wavelet Transform (CWT) identified potential cerebral hemodynamic synchronization patterns. Additionally, non-negative matrix factorization (NMF) with four components segmented LSCI images, revealing structural subcomponent alterations over time. This integrated approach of LSCI, FFT, CWT, and NMF offers a comprehensive tool for studying cerebral blood flow dynamics, metaphorically capturing the 'end of the tunnel' experience. Results showed primary postmortem hemodynamic activity in the olfactory bulbs, followed by blood microflow relocations between somatosensory and visual cortical regions via the superior sagittal sinus. This method opens new avenues for exploring these phenomena, potentially linking neuroscientific insights with mysteries surrounding consciousness and perception at life's end.

Establishing the distribution of cerebrovascular resistance using computational fluid dynamics and 4D flow MRI

Cerebrovascular resistance (CVR) regulates blood flow in the brain, but little is known about the vascular resistances of the individual cerebral territories. We present a method to calculate these resistances and investigate how CVR varies in the hemodynamically disturbed brain. We included 48 patients with stroke/TIA (29 with symptomatic carotid stenosis). By combining flow rate (4D flow MRI) and structural computed tomography angiography (CTA) data with computational fluid dynamics (CFD) we computed the perfusion pressures out from the circle of Willis, with which CVR of the MCA, ACA, and PCA territories was estimated. 56 controls were included for comparison of total CVR (tCVR). CVR were 33.8 ± 10.5, 59.0 ± 30.6, and 77.8 ± 21.3 mmHg s/ml for the MCA, ACA, and PCA territories. We found no differences in tCVR between patients, 9.3 ± 1.9 mmHg s/ml, and controls, 9.3 ± 2.0 mmHg s/ml (p = 0.88), nor in territorial CVR in the carotid stenosis patients between ipsilateral and contralateral hemispheres. Territorial resistance associated inversely to territorial brain volume (p < 0.001). These resistances may work as reference values when modelling blood flow in the circle of Willis, and the method can be used when there is need for subject-specific analysis.

Metabolic flexibility ensures proper neuronal network function in moderate neuroinflammation

Microglia, brain-resident macrophages, can acquire distinct functional phenotypes, which are supported by differential reprogramming of cell metabolism. These adaptations include remodeling in glycolytic and mitochondrial metabolic fluxes, potentially altering energy substrate availability at the tissue level. This phenomenon may be highly relevant in the brain, where metabolism must be precisely regulated to maintain appropriate neuronal excitability and synaptic transmission. Direct evidence that microglia can impact on neuronal energy metabolism has been widely lacking, however. Combining molecular profiling, electrophysiology, oxygen microsensor recordings and mathematical modeling, we investigated microglia-mediated disturbances in brain energetics during neuroinflammation. Our results suggest that proinflammatory microglia showing enhanced nitric oxide release and decreased CX3CR1 expression transiently increase the tissue lactate/glucose ratio that depends on transcriptional reprogramming in microglia, not in neurons. In this condition, neuronal network activity such as gamma oscillations (30-70 Hz) can be fueled by increased ATP production in mitochondria, which is reflected by elevated oxygen consumption. During dysregulated inflammation, high energy demand and low glucose availability can be boundary conditions for neuronal metabolic fitness as revealed by kinetic modeling of single neuron energetics. Collectively, these findings indicate that metabolic flexibility protects neuronal network function against alterations in local substrate availability during moderate neuroinflammation.

Integrative neurovascular coupling and neurotransmitter analyses in anisometropic and visual deprivation amblyopia children

The association between visual abnormalities and impairments in cerebral blood flow and brain region potentially results in neural dysfunction of amblyopia. Nevertheless, the differences in the complex mechanisms of brain neural network coupling and its relationship with neurotransmitters remain unclear. Here, the neurovascular coupling mechanism and neurotransmitter activity in children with anisometropic amblyopia (AA) and visual deprivation amblyopia (VDA) was explored. The neurovascular coupling of 17 brain regions in amblyopia children was significantly abnormal than in normal controls. The classification abilities of coupling units in brain regions differed between two types of amblyopia. Correlations between different coupling effects and neurotransmitters were different. The findings of this study demonstrate a correlation between the neurovascular coupling and neurotransmitter in children with AA and VDA, implying their impaired neurovascular coupling function and potential molecular underpinnings. The neuroimaging evidence revealed herein offers potential for the development of neural therapies for amblyopia.

Ultra-High Dose Rate Helium Ion Beams: First In Vivo Evidence for Neuroprotective FLASH Effect

Purpose

To investigate ultra-high-dose rate helium ion irradiation and its potential FLASH sparing effect with the endpoint acute brain injury in preclinical in vivo settings.

Material and methods

Raster-scanned helium ion beams were administered to explore and compare the impact of dose rate variations between standard dose rate (SDR at 0.2 Gy/s) and FLASH (at 141 Gy/s) radiotherapy (RT). Irradiation-induced brain injury was investigated in healthy C57BL/6 mice via DNA damage response kinetic studies using nuclear γH2AX as a surrogate for double-strand breaks (DSB). The integrity of the neurovascular and immune compartments was assessed via CD31+ microvascular density and microglia/macrophages activation. Iba1+ ramified and CD68+ phagocytic microglia/macrophages were quantified, together with the expression of inducible nitric oxide synthetase (iNOS).

Results

Helium FLASH RT significantly prevented acute brain tissue injury compared with SDR. This was demonstrated by reduced levels of DSB and structural preservation of the neurovascular endothelium after FLASH RT. Moreover, FLASH RT exhibited reduced activation of neuroinflammatory signals compared with SDR, as detected by quantification of CD68+ iNOS+ microglia/macrophages.

Conclusion

To our knowledge, this is the first report on the FLASH-sparing neuroprotective effect of raster scanning helium ion radiotherapy in vivo.

Hemodynamic responses in the rat hippocampus are simultaneously controlled by at least two independently acting neurovascular coupling mechanisms

We combined electrical perforant pathway stimulation with electrophysiological and fMRI recordings in the hippocampus to investigate the effects of neuronal afterdischarges (nAD) on subsequent fMRI BOLD signals in the presence of isoflurane and medetomidine. These two drugs already alter basal hemodynamics in the hippocampus, with isoflurane being mildly vasodilatory and medetomidine being mildly vasoconstrictive. The perforant pathway was stimulated once for 8 seconds with either continuous 20 Hz pulses (continuous stimulation) or 8 bursts of 20 high-frequency pulses (burst stimulation). Burst stimulation in the presence of medetomidine elicited long-lasting nAD that coincided with a brief positive BOLD response and a subsequent long-lasting decrease in BOLD signals. Under isoflurane, this stimulation elicited only short-lasting nAD and only a short-lasting decline in BOLD signals. In contrast, continuous stimulation under isoflurane and medetomidine caused a similar duration of nAD. Under isoflurane, this caused only a sharp and prolonged decline in BOLD signals, whereas under medetomidine, again, only a brief positive BOLD response was elicited, followed by a shorter and moderate decline in BOLD signals. Our results suggest that nAD simultaneously activate different neurovascular coupling mechanisms that then independently alter local hemodynamics in the hippocampus, resulting in an even more complex neurovascular coupling mechanism.

pH regulating mechanisms of astrocytes: A critical component in physiology and disease of the brain

Strict homeostatic control of pH in both intra- and extracellular compartments of the brain is fundamentally important, primarily due to the profound impact of free protons ([H+]) on neuronal activity and overall brain function. Astrocytes, crucial players in the homeostasis of various ions in the brain, actively regulate their intracellular [H+] (pHi) through multiple membrane transporters and carbonic anhydrases. The activation of astroglial pHi regulating mechanisms also leads to corresponding alterations in the acid-base status of the extracellular fluid. Notably, astrocyte pH regulators are modulated by various neuronal signals, suggesting their pivotal role in regulating brain acid-base balance in both health and disease. This review presents the mechanisms involved in pH regulation in astrocytes and discusses their potential impact on extracellular pH under physiological conditions and in brain disorders. Targeting astrocytic pH regulatory mechanisms represents a promising therapeutic approach for modulating brain acid-base balance in diseases, offering a potential critical contribution to neuroprotection.

The effects of long-term high-altitude exposure on cognition: A meta-analysis

Long-term high altitudes (HA) exposure's impact on cognition has yielded inconsistent findings in previous research. To address this, we conducted a meta-analysis of 49 studies (6191 individuals) to comprehensively evaluate this effect. Moderating factors such as cognitive task type, altitude (1500-2500 m, 2500-4000 m, and above 4000 m), residential type (chronic and lifelong), adaptation level and demographic factors were analyzed. Cognitive tasks were classified into eight categories: perceptual processes, psychomotor function, long-term memory, working memory, inhibitory control, problem-solving, language, and others. Results revealed a moderate negative effect of HA on cognitive performance (g = -.40, SE =.18, 95% CI = -.76 to -.05). Psychomotor function and long-term memory notably experience the most pronounced decline, while working memory and language skills show moderate decreases due to HA exposure. However, perceptual processes, inhibitory control, and problem-solving abilities remain unaffected. Moreover, residing at altitudes above 4000 m and being a HA immigrant are associated with significant cognitive impairment. In summary, our findings indicate a selective adaptation of cognitive performance to HA conditions.

Combined treatment with naloxone and the alpha2 adrenoceptor antagonist atipamezole reversed brain hypoxia induced by a fentanyl-xylazine mixture in a rat model

Xylazine, a veterinary tranquillizer known by drug users as "Tranq", is being increasingly detected in people who overdose on opioid drugs, indicating enhanced health risk of fentanyl-xylazine mixtures. We recently found that xylazine potentiates fentanyl- and heroin-induced brain hypoxia and eliminates the rebound-like post-hypoxic oxygen increases. Here, we used oxygen sensors coupled with high-speed amperometry in rats of both sexes to explore the treatment potential of naloxone plus atipamezole, a selective α2-adrenoceptor antagonist, in reversing brain (nucleus accumbens) and periphery (subcutaneous space) hypoxia induced by a fentanyl-xylazine mixture. Pretreatment with naloxone (0.2 mg/kg, IV) fully blocked brain and peripheral hypoxia induced by fentanyl (20 μg/kg, IV), but only partially decreased hypoxia induced by a fentanyl-xylazine mixture. Pretreatment with atipamezole (0.25 mg/kg, IV) fully blocked the hypoxic effects of xylazine (1.0 mg/kg, IV), but not fentanyl. Pretreatment with atipamezole + naloxone was more potent than naloxone alone in blocking the hypoxic effects of the fentanyl-xylazine mixture. Both naloxone and naloxone + atipamezole, delivered at the peak of brain hypoxia (3 min post fentanyl-xylazine exposure), reversed the rapid initial brain hypoxia, but only naloxone + atipamezole decreased the prolonged weaker hypoxia. There were no sex differences in the effects of the different drugs and their combinations on brain and peripheral oxygen responses. Results indicate that combined treatment with naloxone and atipamezole is more effective than naloxone alone in reversing the hypoxic effects of fentanyl-xylazine mixtures. Naloxone + atipamezole treatment should be considered in preventing overdoses induced by fentanyl-xylazine mixtures in humans.

Imaging bioluminescence by detecting localized haemodynamic contrast from photosensitized vasculature

Bioluminescent probes are widely used to monitor biomedically relevant processes and cellular targets in living animals. However, the absorption and scattering of visible light by tissue drastically limit the depth and resolution of the detection of luminescence. Here we show that bioluminescent sources can be detected with magnetic resonance imaging by leveraging the light-mediated activation of vascular cells expressing a photosensitive bacterial enzyme that causes the conversion of bioluminescent emission into local changes in haemodynamic contrast. In the brains of rats with photosensitized vasculature, we used magnetic resonance imaging to volumetrically map bioluminescent xenografts and cell populations virally transduced to express luciferase. Detecting bioluminescence-induced haemodynamic signals from photosensitized vasculature will extend the applications of bioluminescent probes.

Systematic review and dosage analysis: hyperbaric oxygen therapy efficacy in the treatment of posttraumatic stress disorder

Background

Studies of hyperbaric oxygen therapy (HBOT) treatment of mild traumatic brain injury persistent postconcussion syndrome in military and civilian subjects have shown simultaneous improvement in posttraumatic stress disorder (PTSD) or PTSD symptoms, suggesting that HBOT may be an effective treatment for PTSD. This is a systematic review and dosage analysis of HBOT treatment of patients with PTSD symptoms.

Methods

PubMed, CINAHL, and the Cochrane Systematic Review Database were searched from September 18 to November 23, 2023, for all adult clinical studies published in English on HBOT and PTSD. Randomized trials and studies with symptomatic outcomes were selected for final analysis and analyzed according to the dose of oxygen and barometric pressure on symptom outcomes. Outcome assessment was for statistically significant change and Reliable Change or Clinically Significant Change according to the National Center for PTSD Guidelines. Methodologic quality and bias were determined with the PEDro Scale.

Results

Eight studies were included, all with < 75 subjects/study, total 393 subjects: seven randomized trials and one imaging case-controlled study. Six studies were on military subjects, one on civilian and military subjects, and one on civilians. Subjects were 3-450 months post trauma. Statistically significant symptomatic improvements, as well as Reliable Change or Clinically Significant changes, were achieved for patients treated with 40-60 HBOTS over a wide range of pressures from 1.3 to 2.0 ATA. There was a linear dose-response relationship for increased symptomatic improvement with increasing cumulative oxygen dose from 1002 to 11,400 atmosphere-minutes of oxygen. The greater symptomatic response was accompanied by a greater and severe reversible exacerbation of emotional symptoms at the highest oxygen doses in 30-39% of subjects. Other side effects were transient and minor. In three studies the symptomatic improvements were associated with functional and anatomic brain imaging changes. All 7 randomized trials were found to be of good-highest quality by PEDro scale scoring.

Discussion

In multiple randomized and randomized controlled clinical trials HBOT demonstrated statistically significant symptomatic improvements, Reliable Changes, or Clinically Significant Changes in patients with PTSD symptoms or PTSD over a wide range of pressure and oxygen doses. The highest doses were associated with a severe reversible exacerbation of emotional symptoms in 30-39% of subjects. Symptomatic improvements were supported by correlative functional and microstructural imaging changes in PTSD-affected brain regions. The imaging findings and hyperbaric oxygen therapy effects indicate that PTSD can no longer be considered strictly a psychiatric disease.

Mapping glymphatic solute transportation through the perivascular space of hippocampal arterioles with 14 Tesla MRI

The perivascular space (PVS) plays a crucial role in facilitating the clearance of waste products and the exchange of cerebrospinal fluid and interstitial fluid in the central nervous system. While optical imaging methods identify the glymphatic transport of fluorescent tracers through PVS of surface-diving arteries, their limited depth penetration impedes the study of glymphatic dynamics in deep brain regions. In this study, we introduced a novel high-resolution dynamic contrast-enhanced MRI mapping approach based on single-vessel multi-gradient-echo methods. This technique allowed the differentiation of penetrating arterioles and venules from adjacent parenchymal tissue voxels and enabled the detection of Gd-enhanced signals coupled to PVS of penetrating arterioles in the deep cortex and hippocampus. By directly infusing Gd into the lateral ventricle, we eliminated delays in cerebrospinal fluid flow and focused on PVS Gd transport through PVS of hippocampal arterioles. The study revealed significant PVS-specific Gd signal enhancements, shedding light on glymphatic function in deep brain regions. These findings advance our understanding of brain-wide glymphatic dynamics and hold potential implications for neurological conditions characterized by impaired waste clearance, warranting further exploration of their clinical relevance and therapeutic applications.

Loss of Katnal2 leads to ependymal ciliary hyperfunction and autism-related phenotypes in mice

Autism spectrum disorders (ASD) frequently accompany macrocephaly, which often involves hydrocephalic enlargement of brain ventricles. Katnal2 is a microtubule-regulatory protein strongly linked to ASD, but it remains unclear whether Katnal2 knockout (KO) in mice leads to microtubule- and ASD-related molecular, synaptic, brain, and behavioral phenotypes. We found that Katnal2-KO mice display ASD-like social communication deficits and age-dependent progressive ventricular enlargements. The latter involves increased length and beating frequency of motile cilia on ependymal cells lining ventricles. Katnal2-KO hippocampal neurons surrounded by enlarged lateral ventricles show progressive synaptic deficits that correlate with ASD-like transcriptomic changes involving synaptic gene down-regulation. Importantly, early postnatal Katnal2 re-expression prevents ciliary, ventricular, and behavioral phenotypes in Katnal2-KO adults, suggesting a causal relationship and a potential treatment. Therefore, Katnal2 negatively regulates ependymal ciliary function and its deletion in mice leads to ependymal ciliary hyperfunction and hydrocephalus accompanying ASD-related behavioral, synaptic, and transcriptomic changes.

Genetic deletion of hormone-sensitive lipase in mice reduces cerebral blood flow but does not aggravate the impact of diet-induced obesity on memory

Hormone-sensitive lipase (HSL) is active throughout the brain and its genetic ablation impacts brain function. Its activity in the brain was proposed to regulate bioactive lipid availability, namely eicosanoids that are inflammatory mediators and regulate cerebral blood flow (CBF). We aimed at testing whether HSL deletion increases susceptibility to neuroinflammation and impaired brain perfusion upon diet-induced obesity. HSL-/-, HSL+/-, and HSL+/+ mice of either sex were fed high-fat diet (HFD) or control diet for 8 weeks, and then assessed in behavior tests (object recognition, open field, and elevated plus maze), metabolic tests (insulin and glucose tolerance tests and indirect calorimetry in metabolic cages), and CBF determination by arterial spin labeling (ASL) magnetic resonance imaging (MRI). Immunofluorescence microscopy was used to determine coverage of blood vessels, and morphology of astrocytes and microglia in brain slices. HSL deletion reduced CBF, most prominently in cortex and hippocampus, while HFD feeding only lowered CBF in the hippocampus of wild-type mice. CBF was positively correlated with lectin-stained vessel density. HSL deletion did not exacerbate HFD-induced microgliosis in the hippocampus and hypothalamus. HSL-/- mice showed preserved memory performance when compared to wild-type mice, and HSL deletion did not significantly aggravate HFD-induced memory impairment in object recognition tests. In contrast, HSL deletion conferred protection against HFD-induced obesity, glucose intolerance, and insulin resistance. Altogether, this study points to distinct roles of HSL in periphery and brain during diet-induced obesity. While HSL-/- mice were protected against metabolic syndrome development, HSL deletion reduced brain perfusion without leading to aggravated HFD-induced neuroinflammation and memory dysfunction.

Remazolam affects the phenotype and function of astrocytes to improve traumatic brain injury by regulating the Cx43

PURPOSE

To explore the mechanism by which Remazolam affects the phenotype and function of astrocytes to improve traumatic brain injury (TBI).

METHODS

The oxygen -glucose deprivation/recovery (OGD/R) cell model was constructed to simulate the pathological state of astrocytes in a TBI environment. The viability of astrocytes was measured by CCK-8, and the cytoskeleton changes were observed by Phalloidin- TRITC staining. The expressions of differentiation markers, Cx43 and phosphorylated Cx43 (P-Cx43) of A1/A2 astrocytes were detected by Western blot, and the complement C3 and S100A10 of A1/A2 astrocytes were detected by ELISA. The TBI rat model was established. The water content of brain tissue was measured by dry-wet specific gravity method, the pathological morphology of brain tissue in cortical injury area was observed by HE staining method, ROS was detected by fluorescence quantitative method, Cx43 expression was detected by immunohistochemistry method, and the differentiation markers of A1/A2 astrocytes were detected by immunofluorescence.

RESULTS

In the TBI environment, astrocytes showed decreased cell viability, blurred skeleton, and increased expression of Cx43. In TBI rats, the water content of brain tissue increased, the brain tissue in the cortex injury area was seriously damaged, ROS and Cx43 expression were significantly increased, and mainly distributed in A2 astrocytes. Remazolam can reverse the above results after the intervention.

CONCLUSION

Remazolam affects the phenotype and function of astrocytes to improve TBI via regulating Cx43, and plays a role in protecting the neurological function of TBI rats.

Control of astrocytic Ca2+ signaling by nitric oxide-dependent S-nitrosylation of Ca2+ homeostasis modulator 1 channels

BACKGROUND

Astrocytes Ca2+ signaling play a central role in the modulation of neuronal function. Activation of metabotropic glutamate receptors (mGluR) by glutamate released during an increase in synaptic activity triggers coordinated Ca2+ signals in astrocytes. Importantly, astrocytes express the Ca2+-dependent nitric oxide (NO)-synthetizing enzymes eNOS and nNOS, which might contribute to the Ca2+ signals by triggering Ca2+ influx or ATP release through the activation of connexin 43 (Cx43) hemichannels, pannexin-1 (Panx-1) channels or Ca2+ homeostasis modulator 1 (CALHM1) channels. Hence, we aim to evaluate the participation of NO in the astrocytic Ca2+ signaling initiated by stimulation of mGluR in primary cultures of astrocytes from rat brain cortex.

RESULTS

Astrocytes were stimulated with glutamate or t-ACPD and NO-dependent changes in [Ca2+]i and ATP release were evaluated. In addition, the activity of Cx43 hemichannels, Panx-1 channels and CALHM1 channels was also analyzed. The expression of Cx43, Panx-1 and CALHM1 in astrocytes was confirmed by immunofluorescence analysis and both glutamate and t-ACPD induced NO-mediated activation of CALHM1 channels via direct S-nitrosylation, which was further confirmed by assessing CALHM1-mediated current using the two-electrode voltage clamp technique in Xenopus oocytes. Pharmacological blockade or siRNA-mediated inhibition of CALHM1 expression revealed that the opening of these channels provides a pathway for ATP release and the subsequent purinergic receptor-dependent activation of Cx43 hemichannels and Panx-1 channels, which further contributes to the astrocytic Ca2+ signaling.

CONCLUSIONS

Our findings demonstrate that activation of CALHM1 channels through NO-mediated S-nitrosylation in astrocytes in vitro is critical for the generation of glutamate-initiated astrocytic Ca2+ signaling.

Long-range inhibitory neurons mediate cortical neurovascular coupling

To meet the high energy demands of brain function, cerebral blood flow (CBF) parallels changes in neuronal activity by a mechanism known as neurovascular coupling (NVC). However, which neurons play a role in mediating NVC is not well understood. Here, we identify in mice and humans a specific population of cortical GABAergic neurons that co-express neuronal nitric oxide synthase and tachykinin receptor 1 (Tacr1). Through whole-tissue clearing, we demonstrate that Tacr1 neurons extend local and long-range projections across functionally connected cortical areas. We show that whisker stimulation elicited Tacr1 neuron activity in the barrel cortex through feedforward excitatory pathways. Additionally, through optogenetic experiments, we demonstrate that Tacr1 neurons are instrumental in mediating CBF through the relaxation of mural cells in a similar fashion to whisker stimulation. Finally, by electron microscopy, we observe that Tacr1 processes contact astrocytic endfeet. These findings suggest that Tacr1 neurons integrate cortical activity to mediate NVC.

Blood-brain barrier biomarkers

The blood-brain barrier (BBB) is a dynamic interface that regulates the exchange of molecules and cells between the brain parenchyma and the peripheral blood. The BBB is mainly composed of endothelial cells, astrocytes and pericytes. The integrity of this structure is essential for maintaining brain and spinal cord homeostasis and protection from injury or disease. However, in various neurological disorders, such as traumatic brain injury, Alzheimer's disease, and multiple sclerosis, the BBB can become compromised thus allowing passage of molecules and cells in and out of the central nervous system parenchyma. These agents, however, can serve as biomarkers of BBB permeability and neuronal damage, and provide valuable information for diagnosis, prognosis and treatment. Herein, we provide an overview of the BBB and changes due to aging, and summarize current knowledge on biomarkers of BBB disruption and neurodegeneration, including permeability, cellular, molecular and imaging biomarkers. We also discuss the challenges and opportunities for developing a biomarker toolkit that can reliably assess the BBB in physiologic and pathophysiologic states.

Longitudinal alterations in brain perfusion and vascular reactivity in the zQ175DN mouse model of Huntington's disease

BACKGROUND

Huntington's disease (HD) is marked by a CAG-repeat expansion in the huntingtin gene that causes neuronal dysfunction and loss, affecting mainly the striatum and the cortex. Alterations in the neurovascular coupling system have been shown to lead to dysregulated energy supply to brain regions in several neurological diseases, including HD, which could potentially trigger the process of neurodegeneration. In particular, it has been observed in cross-sectional human HD studies that vascular alterations are associated to impaired cerebral blood flow (CBF). To assess whether whole-brain changes in CBF are present and follow a pattern of progression, we investigated both resting-state brain perfusion and vascular reactivity longitudinally in the zQ175DN mouse model of HD.

METHODS

Using pseudo-continuous arterial spin labelling (pCASL) MRI in the zQ175DN model of HD and age-matched wild-type (WT) mice, we assessed whole-brain, resting-state perfusion at 3, 6 and 9 and 13 months of age, and assessed hypercapnia-induced cerebrovascular reactivity (CVR), at 4.5, 6, 9 and 15 months of age.

RESULTS

We found increased perfusion in cortical regions of zQ175DN HET mice at 3 months of age, and a reduction of this anomaly at 6 and 9 months, ages at which behavioural deficits have been reported. On the other hand, under hypercapnia, CBF was reduced in zQ175DN HET mice as compared to the WT: for multiple brain regions at 6 months of age, for only somatosensory and retrosplenial cortices at 9 months of age, and brain-wide by 15 months. CVR impairments in cortical regions, the thalamus and globus pallidus were observed in zQ175DN HET mice at 9 months, with whole brain reactivity diminished at 15 months of age. Interestingly, blood vessel density was increased in the motor cortex at 3 months, while average vessel length was reduced in the lateral portion of the caudate putamen at 6 months of age.

CONCLUSION

Our findings reveal early cortical resting-state hyperperfusion and impaired CVR at ages that present motor anomalies in this HD model, suggesting that further characterization of brain perfusion alterations in animal models is warranted as a potential therapeutic target in HD.

The effects of CO2 levels and body temperature on brain interstitial pH alterations during the induction of hypoxic-ischemic encephalopathy in newborn pigs

Brain interstitial pH (pHbrain) alterations play a crucial role in the development of hypoxic-ischemic (HI) encephalopathy (HIE) caused by asphyxia in neonates. The newborn pig is one of the most suitable large animal models for studying HIE, however, compared to rats, experimental data on pHbrain alterations during HIE induction are limited. The major objective of the present study was thus to compare pHbrain changes during HIE development induced by experimental normocapnic hypoxia (H) or asphyxia (A), elicited with ventilation of a gas mixture containing 6%O2 or 6%O2/20%CO2, respectively for 20 min, under either normothermia (NT) or hypothermia (HT) (38.5 ± 0.5 °C or 33.5 ± 0.5 °C core temperature, respectively) in anesthetized piglets yielding four groups: H-NT, A-NT, H-HT, and A-HT. pHbrain changes during HI stress and the 60 min reoxygenation period were measured using a pH-selective microelectrode inserted into the parietal cortex through an open cranial window. In all groups, the pHbrain response to HI stress was acidosis, at the nadir pHbrain values dropped from the baseline of 7.27 ± 0.02 to H-NT:5.93 ± 0.30, A-NT:5.90 ± 0.52, H-HT:6.81 ± 0.27, and A-HT:6.27 ± 0.24 indicating that (1) H and A elicited similar, severe brain acidosis under NT greatly exceeding pH changes in arterial blood (pHa dropped to 7.24 ± 0.07 and 6.78 ± 0.03 from 7.52 ± 0.06 and 7.50 ± 0.05, respectively), and (2) HT ameliorated more the brain acidosis induced by H than by A. In all four groups, pHbrain was restored to baseline values without an alkalotic overshoot during the observed reoxygenation, Our findings suggest that under NT either H or A - both commonly employed HI stresses to elicit HIE in piglet models - would result in a similar acidotic pHbrain response without an alkalotic component either during the HI stress or the early reoxygenation period.

Spatiotemporal cerebral blood flow dynamics underlies emergence of the limbic-sensorimotor-association cortical gradient in human infancy

Infant cerebral blood flow (CBF) delivers nutrients and oxygen to fulfill brain energy consumption requirements for the fastest period of postnatal brain development across lifespan. However, organizing principle of whole-brain CBF dynamics during infancy remains obscure. Leveraging a unique cohort of 100+ infants with high-resolution arterial spin labeled MRI, we found the emergence of the cortical hierarchy revealed by highest-resolution infant CBF maps available to date. Infant CBF across cortical regions increased in a biphasic pattern with initial rapid and sequentially slower rate, with break-point ages increasing along the limbic-sensorimotor-association cortical gradient. Increases in CBF in sensorimotor cortices were associated with enhanced language and motor skills, and frontoparietal association cortices for cognitive skills. The study discovered emergence of the hierarchical limbic-sensorimotor-association cortical gradient in infancy, and offers standardized reference of infant brain CBF and insight into the physiological basis of cortical specialization and real-world infant developmental functioning.

Sleep loss impairs blood-brain barrier function: Cellular and molecular mechanisms

Sleep is a physiological process that preserves the integrity of the neuro-immune-endocrine network to maintain homeostasis. Sleep regulates the production and secretion of hormones, neurotransmitters, cytokines and other inflammatory mediators, both at the central nervous system (CNS) and at the periphery. Sleep promotes the removal of potentially toxic metabolites out of the brain through specialized systems such as the glymphatic system, as well as the expression of specific transporters in the blood-brain barrier. The blood-brain barrier maintains CNS homeostasis by selectively transporting metabolic substrates and nutrients into the brain, by regulating the efflux of metabolic waste products, and maintaining bidirectional communication between the periphery and the CNS. All those processes are disrupted during sleep loss. Brain endothelial cells express the blood-brain barrier phenotype, which arises after cell-to-cell interactions with mural cells, like pericytes, and after the release of soluble factors by astroglial endfeet. Astroglia, pericytes and brain endothelial cells respond differently to sleep loss; evidence has shown that sleep loss induces a chronic low-grade inflammatory state at the CNS, which is associated with blood-brain barrier dysfunction. In animal models, blood-brain barrier dysfunction is characterized by increased blood-brain barrier permeability, decreased tight junction protein expression and pericyte detachment from the capillary wall. Blood-brain barrier dysfunction may promote defects in brain clearance of potentially neurotoxic metabolites and byproducts of neural physiology, which may eventually contribute to neurodegenerative diseases. This chapter aims to describe the cellular and molecular mechanisms by which sleep loss modifies the function of the blood-brain barrier.

EEG and fNIRS datasets based on Stroop task during two weeks of high-altitude exposure in new immigrants

Maintaining sufficient cerebral oxygen metabolism is crucial for human survival, especially in challenging conditions such as high-altitudes. Human cognitive neural activity is sensitive to fluctuations in oxygen levels. However, there is a lack of publicly available datasets on human behavioural responses and cerebral dynamics assessments during the execution of conflicting tasks in natural hypoxic environments. We recruited 80 healthy new immigrant volunteers (males, aged 20 ± 2 years) and employed the Stroop cognitive conflict paradigm. After a two-week exposure to both high and low-altitudes, the behavioural performance, prefrontal oxygen levels, and electroencephalography (EEG) signals were recorded. Comparative analyses were conducted on the behavioural reaction times and accuracy during Stroop tasks, and statistical analyses of participants' prefrontal oxygen levels and EEG signals were performed. We anticipate that our open-access dataset will contribute to the development of monitoring devices and algorithms, designed specifically for measuring cerebral oxygen and EEG dynamics in populations exposed to extreme environments, particularly among individuals suffering from oxygen deficiency.

An interaction graph approach to gain new insights into mechanisms that modulate cerebrovascular tone

Mechanisms to modulate cerebrovascular tone are numerous, interconnected, and spatially dependent, increasing the complexity of experimental study design, interpretation of action-effect pathways, and mechanistic modelling. This difficulty is exacerbated when there is an incomplete understanding of these pathways. We propose interaction graphs to break down this complexity, while still maintaining a holistic view of mechanisms to modulate cerebrovascular tone. These graphs highlight the competing processes of neurovascular coupling, cerebral autoregulation, and cerebral reactivity. Subsequent analysis of these interaction graphs provides new insights and suggest potential directions for research on neurovascular coupling, modelling, and dementia.

Oxygen and the Spark of Human Brain Evolution: Complex Interactions of Metabolism and Cortical Expansion across Development and Evolution

Scientific theories on the functioning and dysfunction of the human brain require an understanding of its development-before and after birth and through maturation to adulthood-and its evolution. Here we bring together several accounts of human brain evolution by focusing on the central role of oxygen and brain metabolism. We argue that evolutionary expansion of human transmodal association cortices exceeded the capacity of oxygen delivery by the vascular system, which led these brain tissues to rely on nonoxidative glycolysis for additional energy supply. We draw a link between the resulting lower oxygen tension and its effect on cytoarchitecture, which we posit as a key driver of genetic developmental programs for the human brain-favoring lower intracortical myelination and the presence of biosynthetic materials for synapse turnover. Across biological and temporal scales, this protracted capacity for neural plasticity sets the conditions for cognitive flexibility and ongoing learning, supporting complex group dynamics and intergenerational learning that in turn enabled improved nutrition to fuel the metabolic costs of further cortical expansion. Our proposed model delineates explicit mechanistic links among metabolism, molecular and cellular brain heterogeneity, and behavior, which may lead toward a clearer understanding of brain development and its disorders.

Sustained release of vascular endothelial growth factor A and basic fibroblast growth factor from nanofiber membranes reduces oxygen/glucose deprivation-induced injury to neurovascular units

Upregulation of vascular endothelial growth factor A/basic fibroblast growth factor (VEGFA/bFGF) expression in the penumbra of cerebral ischemia can increase vascular volume, reduce lesion volume, and enhance neural cell proliferation and differentiation, thereby exerting neuroprotective effects. However, the beneficial effects of endogenous VEGFA/bFGF are limited as their expression is only transiently increased. In this study, we generated multilayered nanofiber membranes loaded with VEGFA/bFGF using layer-by-layer self-assembly and electrospinning techniques. We found that a membrane containing 10 layers had an ideal ultrastructure and could efficiently and stably release growth factors for more than 1 month. This 10-layered nanofiber membrane promoted brain microvascular endothelial cell tube formation and proliferation, inhibited neuronal apoptosis, upregulated the expression of tight junction proteins, and improved the viability of various cellular components of neurovascular units under conditions of oxygen/glucose deprivation. Furthermore, this nanofiber membrane decreased the expression of Janus kinase-2/signal transducer and activator of transcription-3 (JAK2/STAT3), Bax/Bcl-2, and cleaved caspase-3. Therefore, this nanofiber membrane exhibits a neuroprotective effect on oxygen/glucose-deprived neurovascular units by inhibiting the JAK2/STAT3 pathway.

Computational modeling of neuron-glia signaling interactions to unravel cellular and neural circuit functioning

Glial cells have been shown to be vital for various brain functions, including homeostasis, information processing, and cognition. Over the past 30 years, various signaling interactions between neuronal and glial cells have been shown to underlie these functions. This review summarizes the interactions, particularly between neurons and astrocytes, which are types of glial cells. Some of the interactions remain controversial in part due to the nature of experimental methods and preparations used. Based on the accumulated data, computational models of the neuron-astrocyte interactions have been developed to explain the complex functions of astrocytes in neural circuits and to test conflicting hypotheses. This review presents the most significant recent models, modeling methods and simulation tools for neuron-astrocyte interactions. In the future, we will especially need more experimental research on awake animals in vivo and new computational models of neuron-glia interactions to advance our understanding of cellular dynamics and the functioning of neural circuits in different brain regions.

Resting-State fMRI: Emerging Concepts for Future Clinical Application

Resting-state functional magnetic resonance imaging (rsfMRI) has been developed as a method of investigating spontaneous neural activity. Based on its low-frequency signal synchronization, rsfMRI has made it possible to identify multiple macroscopic structures termed resting-state networks (RSNs) on a single scan of less than 10 minutes. It is easy to implement even in clinical practice, in which assigning tasks to patients can be challenging. These advantages have accelerated the adoption and growth of rsfMRI. Recently, studies on the global rsfMRI signal have attracted increasing attention. Because it primarily arises from physiological events, less attention has hitherto been paid to the global signal than to the local network (i.e., RSN) component. However, the global signal is not a mere nuisance or a subsidiary component. On the contrary, it is quantitatively the dominant component that accounts for most of the variance in the rsfMRI signal throughout the brain and provides rich information on local hemodynamics that can serve as an individual-level diagnostic biomarker. Moreover, spatiotemporal analyses of the global signal have revealed that it is closely and fundamentally associated with the organization of RSNs, thus challenging the basic assumptions made in conventional rsfMRI analyses and views on RSNs. This review introduces new concepts emerging from rsfMRI spatiotemporal analyses focusing on the global signal and discusses how they may contribute to future clinical medicine. EVIDENCE LEVEL: 5 TECHNICAL EFFICACY: Stage 1.

Environmentally Relevant Concentrations of Tetrabromobisphenol A Exposure Impends Neurovascular Formation through Perturbing Mitochondrial Metabolism in Zebrafish Embryos and Human Primary Endothelial Cells

Tetrabromobisphenol A (TBBPA), the most extensively utilized brominated flame retardant, has raised growing concerns regarding its environmental and health risks. Neurovascular formation is essential for metabolically supporting neuronal networks. However, previous studies primarily concerned the neuronal injuries of TBBPA, its impact on the neurovascularture, and molecular mechanism, which are yet to be elucidated. In this study, 5, 30, 100, 300 μg/L of TBBPA were administered to Tg (fli1a: eGFP) zebrafish larvae at 2-72 h postfertilization (hpf). The findings revealed that TBBPA impaired cerebral and ocular angiogenesis in zebrafish. Metabolomics analysis showed that TBBPA-treated neuroendothelial cells exhibited disruption of the TCA cycle and the Warburg effect pathway. TBBPA induced a significant reduction in glycolysis and mitochondrial ATP production rates, accompanied by mitochondrial fragmentation and an increase in mitochondrial reactive oxygen species (mitoROS) production in neuroendothelial cells. The supplementation of alpha-ketoglutaric acid, a key metabolite of the TCA cycle, mitigated TBBPA-induced mitochondrial damage, reduced mitoROS production, and restored angiogenesis in zebrafish larvae. Our results suggested that TBBPA exposure impeded neurovascular injury via mitochondrial metabolic perturbation mediated by mitoROS signaling, providing novel insight into the neurovascular toxicity and mode of action of TBBPA.

[Blood-brain barrier breakdown and autoimmune cerebellar ataxia]

Autoimmune cerebellar ataxia is a disease entity that affects the cerebellum and is induced by autoimmune mechanisms. The disease is classified into several etiologies, including gluten ataxia, anti-glutamate decarboxylase (GAD) ataxia, paraneoplastic cerebellar degeneration, primary autoimmune cerebellar ataxia and postinfectious cerebellar ataxia. The autoimmune response in the periphery cross-reacts with similar antigens in the cerebellum due to molecular mimicry. Breakdown of the blood‒brain barrier (BBB) could potentially explain the vulnerability of the cerebellum during the development of autoimmune cerebellar ataxia, as it gives rise to the entry of pathogenic autoantibodies or lymphocytes into the cerebellum. In this review, the maintenance of the BBB under normal conditions and the molecular basis of BBB disruption under pathological conditions are highlighted. Next, the pathomechanism of BBB breakdown in each subtype of autoimmune cerebellar ataxia is discussed. We recently identified glucose-regulated protein (GRP) 78 antibodies in paraneoplastic cerebellar degeneration and Lambert-Eaton myasthenic syndrome, and GRP78 antibodies induced by cross-reactivity with tumors can disrupt the BBB and penetrate anti-P/Q type voltage-gated calcium channel (VGCC) antibodies into the cerebellum, thus leading to cerebellar ataxia in this disease.

Stimulus type and duration affect magnitude and evolution of flicker-induced hyperemia measured by laser speckle flowgraphy at the optic disc and peripapillary vessels

Neurovascular coupling is a vital mechanism employed by the cerebrovascular system, including the eye, to regulate blood flow in periods of neuronal activation. This study aims to investigate if laser speckle flowgraphy (LSFG) can detect coupling response elicited by flickering light stimuli and how variations in stimulus type and duration can affect the magnitude and evolution of blood flow in the optic nerve head (ONH) and peripapillary vessels. Healthy adults were exposed to two types of 10-Hz flicker stimuli: a photopic negative response-like stimulus (PhNR-S) or a visual evoked potential-like stimulus (VEP-S)-each presented in separate 10- and 60-s epochs. Both PhNR-S and VEP-S significantly increased ONH blood flow (p < 0.001) immediately after flicker cessation, with a trend of 60-s stimuli (PhNR-S = 11.6%; VEP-S = 10.4%) producing a larger response than 10-s stimuli (PhNR-S = 7.5%; VEP-S = 6.2%). Moreover, exposure to 60-s stimuli elicited a significantly prolonged ONH hyperemic response, especially with PhNR-S. Lastly, stimulation with either 60-s stimuli elicited a robust increase in blood flow within the peripapillary arterioles (p < 0.01) and venules (p < 0.01) as well. Flicker stimulation with common visual electrophysiology stimuli (PhNR-S and VEP-S) induced a demonstrable increase in ONH and peripapillary vessel blood flow, which varied with flicker duration. Our results validate that LSFG is a robust method to quantify flicker-induced hyperemic responses and to study neurovascular coupling in humans.

Serotonergic regulation of cortical neurovascular coupling and hemodynamics upon awakening from sleep in mice

Neurovascular coupling (NVC) is the functional hyperemia of the brain responding to local neuronal activity. It is mediated by astrocytes and affected by subcortical ascending pathways in the cortex that convey information, such as sensory stimuli and the animal condition. Here, we investigate the influence of the raphe serotonergic system, a subcortical ascending arousal system in animals, on the modulation of cortical NVC and cerebral blood flow (CBF). Raphe serotonergic neurons were optogenically activated for 30 s, which immediately awakened the mice from non-rapid eye movement sleep. This caused a biphasic cortical hemodynamic change: a transient increase for a few seconds immediately after photostimulation onset, followed by a large progressive decrease during the stimulation period. Serotonergic neuron activation increased intracellular Ca2+ levels in cortical pyramidal neurons and astrocytes, demonstrating its effect on the NVC components. Pharmacological inhibition of cortical neuronal firing activity and astrocyte metabolic activity had small hypovolemic effects on serotonin-induced biphasic CBF changes, while blocking 5-HT1B receptors expressed primarily in cerebral vasculature attenuated the decreasing CBF phase. This suggests that serotonergic neuron activation leading to animal awakening could allow the NVC to exert a hyperemic function during a biphasic CBF response, with a predominant decrease in the cortex.

Neurovascular coupling impairment as a mechanism for cognitive deficits in COVID-19

Components that comprise our brain parenchymal and cerebrovascular structures provide a homeostatic environment for proper neuronal function to ensure normal cognition. Cerebral insults (e.g. ischaemia, microbleeds and infection) alter cellular structures and physiologic processes within the neurovascular unit and contribute to cognitive dysfunction. COVID-19 has posed significant complications during acute and convalescent stages in multiple organ systems, including the brain. Cognitive impairment is a prevalent complication in COVID-19 patients, irrespective of severity of acute SARS-CoV-2 infection. Moreover, overwhelming evidence from in vitro, preclinical and clinical studies has reported SARS-CoV-2-induced pathologies in components of the neurovascular unit that are associated with cognitive impairment. Neurovascular unit disruption alters the neurovascular coupling response, a critical mechanism that regulates cerebromicrovascular blood flow to meet the energetic demands of locally active neurons. Normal cognitive processing is achieved through the neurovascular coupling response and involves the coordinated action of brain parenchymal cells (i.e. neurons and glia) and cerebrovascular cell types (i.e. endothelia, smooth muscle cells and pericytes). However, current work on COVID-19-induced cognitive impairment has yet to investigate disruption of neurovascular coupling as a causal factor. Hence, in this review, we aim to describe SARS-CoV-2's effects on the neurovascular unit and how they can impact neurovascular coupling and contribute to cognitive decline in acute and convalescent stages of the disease. Additionally, we explore potential therapeutic interventions to mitigate COVID-19-induced cognitive impairment. Given the great impact of cognitive impairment associated with COVID-19 on both individuals and public health, the necessity for a coordinated effort from fundamental scientific research to clinical application becomes imperative. This integrated endeavour is crucial for mitigating the cognitive deficits induced by COVID-19 and its subsequent burden in this especially vulnerable population.

Oxidative Stress and Cerebral Vascular Tone: The Role of Reactive Oxygen and Nitrogen Species

The brain's unique characteristics make it exceptionally susceptible to oxidative stress, which arises from an imbalance between reactive oxygen species (ROS) production, reactive nitrogen species (RNS) production, and antioxidant defense mechanisms. This review explores the factors contributing to the brain's vascular tone's vulnerability in the presence of oxidative damage, which can be of clinical interest in critically ill patients or those presenting acute brain injuries. The brain's high metabolic rate and inefficient electron transport chain in mitochondria lead to significant ROS generation. Moreover, non-replicating neuronal cells and low repair capacity increase susceptibility to oxidative insult. ROS can influence cerebral vascular tone and permeability, potentially impacting cerebral autoregulation. Different ROS species, including superoxide and hydrogen peroxide, exhibit vasodilatory or vasoconstrictive effects on cerebral blood vessels. RNS, particularly NO and peroxynitrite, also exert vasoactive effects. This review further investigates the neuroprotective effects of antioxidants, including superoxide dismutase (SOD), vitamin C, vitamin E, and the glutathione redox system. Various studies suggest that these antioxidants could be used as adjunct therapies to protect the cerebral vascular tone under conditions of high oxidative stress. Nevertheless, more extensive research is required to comprehensively grasp the relationship between oxidative stress and cerebrovascular tone, and explore the potential benefits of antioxidants as adjunctive therapies in critical illnesses and acute brain injuries.