Journal of Cerebral Blood Flow & Metabolism

BackgroundQuantitative cerebral blood flow (CBF) measured with [15O]water positron emission tomography (PET) is the reference standard for quantifying brain perfusion. However, clinical interpretation of individual CBF measurements is limited by the absence of large normative datasets accounting for physiological variability across the adult lifespan. Long-axial field-of-view PET enables high-sensitivity quantitative [15O]water perfusion imaging without arterial blood sampling, allowing normative characterization of cerebral perfusion at unprecedented scale. The aim of this study was to establish normative and covariate-adjusted models of cerebral blood flow across the adult lifespan using total-body [15O]water PET. MethodsQuantitative CBF measurements were obtained in 302 neurologically healthy adults (age 21-86 years) using total-body [15O]water PET. Linear mixed-effects models were used to evaluate the effects of age, sex, body mass index (BMI), and blood hemoglobin concentration on CBF and to generate normative prediction models across the adult lifespan. Between-subject and within-subject variability were estimated from repeated scans in a subset of participants (n=51). ResultsMean grey matter CBF was 46.1 mL/(min*dL), with substantial inter-individual variability but high within-subject reproducibility (intraclass correlation coefficients 0.78-0.89). Advancing age was associated with a decline in CBF of approximately 7% per decade (p_FDR < 10-12). Higher BMI was associated with lower CBF (approximately -6% per 10 kg/m2; p_FDR < 0.01). Women exhibited higher CBF than men (approximately 7.5%), but this difference was largely explained by lower blood hemoglobin concentration in women. Covariate-adjusted models were used to generate normative predictions and prediction intervals describing expected CBF across adulthood. ConclusionThis study establishes a normative database of quantitative cerebral blood flow across the adult lifespan using high-sensitivity [15O]water PET. Age, BMI, and hemoglobin are major determinants of inter-individual variability in CBF. The resulting generative models provide a quantitative reference framework for interpreting cerebral perfusion measurements and may enable automated detection of abnormal brain perfusion in clinical PET imaging.

Coronary artery disease increases risk of cognitive decline and stroke and is associated with white matter alterations. However, the biological basis of these changes remains unclear. Myelin content and iron deposition are crucial measures of white matter health and can be measured with quantitative MRI. This study investigated whether myelin and iron alterations occur in coronary artery disease, and their relationship with cognition. In this cross-sectional study, 46 individuals with coronary artery disease and 40 healthy controls aged > 50 years, with normal cognition underwent 3T MRI and cognitive assessments. Quantitative MRI metrics (susceptibility, magnetization transfer saturation, R2* and R1 relaxation rates) were calculated in the border zones between adjacent arterial territories (watershed regions) and in the areas outside these borders (non-watershed regions). Relative to controls, the coronary artery disease group showed lower myelin and higher iron content, as measured by lower magnetization transfer saturation and R1, and higher susceptibility specifically in watershed regions. Importantly, these microstructural alterations were associated with poorer cognitive performance in the coronary artery disease group with lower magnetization transfer and R1related to poorer global cognition and with higher magnetic susceptibility with poorer verbal memory. These findings suggest that coronary artery disease is associated with demyelination and iron deposition in white matter, most prominently in watershed regions, which are known for their susceptibility to stroke. The association of these microstructural alterations with cognition highlights the role of white matter as a key vulnerable region and a promising focus for future mechanistic and therapeutic studies.

BACKGROUNDSteno-occlusive diseases of the internal carotid artery (ICA) or middle cerebral artery (MCA) can lead to hemodynamic impairment, yet conventional imaging often fails to reflect metabolic dysfunction. Integrated positron emission tomography and magnetic resonance imaging (PET/MRI) allows simultaneous assessment of cerebral blood flow (CBF) and glucose metabolism. This study compared baseline perfusion and metabolic characteristics between patients receiving medical therapy or extracranial-intracranial (EC-IC) bypass surgery. METHODSThis retrospective study enrolled 34 patients with unilateral ICA/MCA stenosis or occlusion confirmed by digital subtraction angiography. All patients underwent 18F-FDG PET/MRI before treatment. Glucose metabolism was quantified using the cerebral metabolic rate of glucose (CMRGlu) from dynamic PET and the standard uptake value ratio (SUVR) from static PET. CBF was measured using three-dimensional arterial spin labeling with post-labeling delays of 2.0 and 2.5 seconds. Perfusion and metabolic parameters were compared across vascular territories. RESULTSBaseline clinical characteristics and long-term outcomes did not differ between groups (all P>0.05). Cerebral blood flow was similar across all arterial territories and post-labeling delays, with no hemispheric asymmetry detected (all P>0.05). In contrast, glucose metabolism was significantly lower in the surgical group, with reduced CMRGlu in the ischemic middle cerebral artery (23.58{+/-}7.46 vs 18.82{+/-}5.04mol/100g-1/min-1, P=0.037) and anterior cerebral artery territories (26.37{+/-}8.76 vs 20.71{+/-}5.78mol/100g-1/min-1, P=0.034). No differences were observed in the posterior cerebral artery or in SUVR across all regions (all P>0.05). CONCLUSIONSDespite similar perfusion profiles, the surgical group demonstrated lower glucose metabolism, suggesting that metabolic imaging may aid in identifying patients who could benefit from revascularization.

Background and PurposeSubarachnoid hemorrhage (SAH) triggers a complex immune response that critically influences early brain injury (EBI) and long-term outcomes. However, the precise spatiotemporal dynamics and heterogeneity of immune cell infiltration and microglial reprogramming remain poorly understood. We aimed to construct a high-resolution immune atlas to delineate cell states, lineage trajectories, and spatial niches following SAH. MethodsWe integrated single-cell RNA sequencing (scRNA-seq) of CD45+ immune cells with spatial transcriptomics (ST) in a murine endovascular perforation SAH model. Immune landscapes were profiled at 24 hours (acute phase) and 72 hours (subacute phase) post-injury, compared with sham controls. Advanced bioinformatics integrated transcriptional signatures with spatial localization to map macrophage, neutrophil, and microglial dynamics. ResultsOur atlas reveals a coordinated immune transition from acute inflammation to reparative processing. We identified five macrophage, four neutrophil, and eight microglial subsets with distinct spatiotemporal patterns. Notably, we discovered a SAH-specific inflammatory microglial population (MG_03; Spp1+/Lpl+) that clusters at the rupture site during the acute phase. This subset is transcriptionally distinct from disease-associated microglia (DAM) in other neurodegenerative conditions. Trajectory analysis suggests MG_03 acts as a signaling hub for immune recruitment before transitioning toward proliferative and reparative states (MG_06-08) that disperse into the parenchyma by 72 hours. ConclusionsThis study provides the first comprehensive spatiotemporal immune atlas of SAH, highlighting the distinct role of the Spp1+ MG_03 subpopulation in early injury sensing. These findings offer a roadmap for identifying precise therapeutic windows and targeting specific immune subsets to mitigate EBI. Graphical AbstractExperimental workflow for single-cell RNA sequencing (scRNA-seq) and spatial transcriptomics (ST) in a mouse SAH model induced by endovascular perforation. Brain tissue from the ipsilateral (injured) hemisphere was collected from sham and at 24 h and 72 h post-SAH. For scRNA-seq, CD45 immune cells were isolated prior to library preparation. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=124 SRC="FIGDIR/small/703421v1_ufig1.gif" ALT="Figure 1"> View larger version (39K): org.highwire.dtl.DTLVardef@4a1bc9org.highwire.dtl.DTLVardef@16664c4org.highwire.dtl.DTLVardef@1619725org.highwire.dtl.DTLVardef@a0d34_HPS_FORMAT_FIGEXP M_FIG C_FIG

With few exceptions, pathological progression in ischemic stroke is presumed to occur uniformly within the ischemic core region. These exceptions include edema formation, brain tissue [Na+] increase, and the qualitative visually-observed decrease of brain tissue [K+], [K+]br, all of which occur in peripheral regions of the ischemic core. We hypothesize that [K+]br within these peripheral regions are heterogeneous (with lower [K+]br in the peripheral compared to the central ischemic core) and are not associated with neuronal degradation. Permanent focal ischemia in 13 rats was produced for 2.5-5 h. Brain sections were quantitatively stained for K+ to assess [K+]br variations between the peripheral and central ischemic core. Regions within the cortical ribbon were used to explore differing rates of K+-depletion expressed as the slopes of [K+]br vs. time relations. Adjacent sections were observed for reflective change and stained for microtubule-associated protein 2 (MAP2) to identify the ischemic region and to relate neuronal pathology to [K+]br variations. The mean value of normal cortex (NC) [K+]br was 96 mEq/kg and of K+-depletion in all ischemic regions over time was 12.2 mEq/kg/h, consistent with measurements from other studies. Exaggerated K+-depletion occurred in 56% of the peripheral ischemic core regions classed as depleted peripheral ischemic core (ICp-DP) regions. These were clearly separated (p<0.001) from the non-depleted peripheral ischemic core (ICp-ND) regions. The normal cortex (NC) regions show stability of [K+]br with a slope near zero. However, the 13.6 mEq/kg/h slopes of the central ischemic core (ICc) and ICp-ND regions were similar (p=0.99) and showed a significant decrease over time. The 6.2 mEq/kg/h slope of the ICp-DP regions was significantly different from that of the ICc (p=0.010) and the ICp-ND (p=0.0071). This lower slope of the ICp-DP curve 2.5 h after stroke onset is due to the accelerated K+-efflux from 0 to 2.5 h, as its value at stroke onset must be [~]100 mEq/kg. However, these differential K+ losses were not reflected in the homogeneous peripheral ischemic core MAP2 immunoreactivity losses. Unlike [K+]br, there was no difference between the MAP2 immunoreactivity in K+-depleted and non-K+-depleted peripheral ischemic core regions (ICp-ND vs ICp-DP, ICp-ND vs ICp-DP, unpaired t-test, p=0.83, p=0.16, respectively). While confirming previous results of quantitative regional losses of [K+]br in the ischemic core, we show that K+ dynamics within the peripheral and the central ischemic core are heterogeneous and not related to MAP2-assessed neuronal structural integrity: the K+-depleted regions in the peripheral ischemic core regions are presumably closer to glymphatic system and other K+-efflux pathways. Such differing K+ dynamics at the edge of the ischemic core in the hyper-acute period in first hours after ischemic onset possibly relate to the spreading depolarization-mediated expansion of the infarct during the period of secondary brain injury. Peripheral ischemic core regions with less K+ might limit spreading depolarization initiation and propagation if there is insufficient K+ for depolarization to occur and make restoration of parenchymal membrane potential improbable even if the functionality of the Na+,K+-ATPase is restored. Further study of differing K+-dynamics within the ischemic core might lead to a better understanding of ischemic stroke pathophysiology.

Intracerebral haemorrhage (ICH) is a severe form of stroke with high morbidity and mortality rates. For survivors, acute haematoma expansion strongly determines neurological outcome. Although blood pressure reduction is widely investigated as a strategy to limit haematoma growth, the haemodynamic mechanisms regulating haemorrhage development remain poorly understood. Zebrafish provide a tractable in vivo model to study cerebrovascular biology and spontaneous ICH, yet the contribution of vascular regulation to haemorrhage onset and expansion has not been explored in this species. Here, we investigated whether pharmacological modulation of vascular dilation influences ICH development in zebrafish larvae. We first characterised vascular changes during the developmental window in which spontaneous ICH occurs and observed increased heart rate and progressive reductions in arterial diameter between 2 and 3 days post-fertilisation, suggesting increased vascular resistance. We then tested whether vasoconstriction promotes haemorrhage using angiotensin II, which induced systemic and cerebrovascular vasoconstriction but did not increase ICH incidence or haematoma size in two independent ICH models. In contrast, pharmacological vasodilation using sodium nitroprusside or isoproterenol significantly reduced haematoma size in a high-incidence model of atorvastatin-induced ICH. Live imaging of cerebral blood flow revealed that vasodilation was associated with the confinement of red blood cells around affected vessels rather than dispersing into the brain ventricles. Together, these findings indicate that vascular dilation modulates haemorrhage progression in zebrafish ICH and establish this model as a platform to investigate haemodynamic mechanisms regulating haematoma expansion.

BackgroundAdult hippocampal neurogenesis is markedly altered after cerebral ischemia. Although stroke increases the production of newborn neurons, many of these cells display aberrant morphological and positional features that impair their functional integration and contribute to long-term cognitive decline. Given the clinical heterogeneity of ischemic stroke and the persistent translational failures of preclinical approaches relying on single-model studies it remains unknown whether post-stroke neurogenic alterations are conserved across different experimental paradigms. This study aimed to define common and model-specific features of hippocampal neurogenesis across complementary focal ischemia models. MethodsWe performed a multi-center, multimodel analysis within the STROKE-IMPaCT consortium using permanent and transient middle cerebral artery occlusion (MCAO) paradigms (MCAO via ligation or cauterization under normoxic (dMCAO) or hypoxic conditions (dMCAO+Hypoxia); and filament-based tMCAO across six international sites. Brains from adult C57BL/6J mice were collected 3 days, 7 days, or 2 months after ischemia, sham, or naive conditions. Hippocampal cell proliferation (Ki67) and neuroblast density (DCX) were quantified, and the morphological maturation of newborn neurons was evaluated using high-resolution analyses of dendritic architecture and somatodendritic polarity. All analyses were performed blind to experimental group. ResultsAcross all stroke models, ischemia induced a robust bilateral increase in hippocampal cell proliferation, most pronounced at 3 days and still elevated at 7 days, with levels returning to baseline by 2 months. Neuroblast density was similarly increased at 7 days, particularly in the ipsilateral hippocampus, but normalized by 2 months. Despite recovery in cell number, long-term morphological analysis revealed a consistent reduction in apical dendrite length and a higher proportion of neurons exhibiting aberrant features including ectopic localization, multipolar or inverted polarity, and abnormal lateral growth across all models. These abnormalities were observed both when pooling data across sites and when analyzing each model or center individually. ConclusionsIschemia induces an early, transient increase in hippocampal neurogenesis across diverse stroke paradigms, but the newborn neurons generated after stroke consistently display maladaptive morphological features. These cross-model, cross-site abnormalities indicate that aberrant hippocampal neurogenesis represents a robust hallmark of post-stroke pathology within the investigated species, independent of ischemia type or surgical approach, despite known differences in the spatial distribution of primary injury across experimental stroke models. Our findings support the concept that maladaptive neurogenesis may contribute to chronic post-stroke cognitive impairment and underscore the need to consider the quality not only the quantity of newborn neurons when developing therapeutic strategies.

BackgroundFailure of cerebrovascular reserve is a fundamental determinant of ischemic vulnerability, yet the mechanisms by which vascular smooth muscle dysfunction compromises reserve and predisposes the brain to injury remain incompletely defined. We therefore tested whether a pathogenic smooth muscle mutation produces a baseline failure of cerebrovascular reserve sufficient to render the brain vulnerable to hypoperfusion, even in the absence of fixed arterial occlusion. MethodsWe examined cerebrovascular structure, hemodynamics, and reserve in a genetically defined mouse model of ACTA2-associated multisystemic smooth muscle dysfunction syndrome with systemic or brain-restricted expression of the mutant allele. Cerebral artery morphology was assessed using magnetic resonance angiography and black ink angiography. Vascular smooth muscle phenotype was evaluated by immunohistochemistry and proliferation assays. Blood pressure reactivity and cerebral blood flow (CBF) were measured simultaneously using femoral arterial catheterization and laser speckle flowmetry during vasoactive challenges and controlled hypotension. Cerebrovascular stress responses were tested using unilateral common carotid artery occlusion. Downstream brain effects were assessed by histology, resting state functional connectivity imaging, and behavioral testing. ResultsImpaired smooth muscle contractility drove rectification and narrowing of major cerebral arteries, downregulation of contractile markers, and increased vascular cell proliferation. These structural changes produced a distinct physiological phenotype: mutant mice exhibited blunted vasoreactivity, diminished spontaneous vasodynamic activity, and a downward shift in the blood pressure-CBF relationship across a wide range of arterial pressures, consistent with loss of cerebrovascular reserve. As a result, CBF was reduced at baseline and could not be maintained during hypotension or acute vascular stress. During carotid occlusion, mutant mice showed impaired compensatory perfusion, greater physiological instability, and worse behavioral outcomes. Chronic reserve failure coincided with white matter loss, reduced neuronal density, disrupted large-scale functional connectivity, and deficits in locomotion, anxiety-related behavior, and working memory. ConclusionsPathogenic smooth muscle dysfunction caused by ACTA2 mutation produces a baseline failure of cerebrovascular reserve that renders the brain vulnerable to hypoperfusion and stress-induced ischemic injury. These findings establish cerebrovascular reserve failure as a central physiological mechanism linking vascular dysfunction to end-organ brain injury and identify reserve preservation as a critical, potentially actionable determinant of brain health in hypotension-prone vascular disease. Clinical PerspectiveO_ST_ABSWhat Is New?C_ST_ABS- ACTA2 smooth muscle dysfunction produces baseline cerebrovascular reserve impairment, with reduced cerebral blood flow and a downward-shifted pressure-flow relationship in the absence of critical large-vessel occlusion. - Vascular tone dysregulation is coupled to end-organ brain injury, including white matter and neuronal loss, disrupted functional connectivity, and behavioral deficits. - The results support complementary disease mechanisms in ACTA2 vasculopathy: baseline reserve limitation and injury-provoked occlusive remodeling. Clinical Implications- Patients with ACTA2 vasculopathy may be vulnerable to ischemic brain injury during hypotension or systemic stress despite the absence of critical stenosis or occlusion on routine imaging. - Peri-procedural and acute-care management should emphasize preserving perfusion pressure and cerebrovascular reserve (e.g., during anesthesia, dehydration, or systemic illness). - More broadly, cerebrovascular reserve is a clinically relevant, potentially modifiable determinant of brain health in hypotension-prone vasculopathies and conditions characterized by impaired vascular reactivity.

Alzheimers disease (AD) is categorized as a neurodegenerative disease, but there is a growing recognition of the vascular components in AD pathophysiology. Reduction in cerebral perfusion is routinely observed in AD patients and preclinical models prior to overt clinical symptoms. However, there is a limited mechanistic understanding of the early neurovascular deficits in AD, and how these may ultimately contribute to pathology. Here, we investigated the mechanisms of early neurovascular dysfunction in AD by using 3-month-old 5xFAD mice, a familial mouse model of AD. Functional hyperemia--the increase in cerebral blood flow (CBF) in response to neuronal activity--is driven by inward rectifier K+ (Kir2.1)-mediated hyperpolarizing (electrical) signals and Ca2+-dependent nitric oxide production within the capillary endothelial cells (cECs). Electrical and Ca2+ signals are tightly coupled through cECs membrane potential, referred to as Electro-Calcium (E-Ca) coupling. We hypothesize that E-Ca uncoupling contributes to impaired functional hyperemia in 5xFAD mice and that these neurovascular deficits precede the neurodegeneration and cognitive decline. At three months of age, 5xFAD mice did not exhibit any impairment in spatial learning and memory, or neuronal density. However, whisker stimulation-induced functional hyperemia was significantly reduced in 5xFAD mice compared to controls. Functional hyperemia exhibited a bimodal response in controls--consisting of fast and slow phases--with the slow phase being significantly reduced in 5xFAD mice. To identify mechanisms underlying these deficits, we measured cortical neuronal and endothelial Ca2+ activity using in-vivo imaging. Neuronal Ca2+ activity was comparable between controls and 5xFAD mice, while cECs Ca2+ activity was significantly reduced in 5xFAD mice. Moreover, Kir2.1 channel blocker, barium (100 M) significantly suppressed cECs Ca2+ activity in controls, but not in 5xFAD mice, consistent with crippled E-Ca coupling. Despite these vascular functional impairments, capillary density was preserved in 5xFAD mice. TRPV4 channels are one of the major Ca2+ entry pathways in cECs and potentiate E-Ca coupling. cECs TRPV4 current density was significantly reduced in 5xFAD mice while Kir2.1 current density was unchanged, indicating that impaired TRPV4 function underlies the E-Ca uncoupling. In summary, early E-Ca uncoupling leads to impaired functional hyperemia in 5xFAD mice and may contribute to later neuronal and cognitive decline.

Cerebral small vessel disease (cSVD) is a leading cause of stroke and vascular cognitive impairment, yet the cellular mechanisms underlying microvascular dysfunction in human disease remain incompletely understood. In particular, the relationship between pericyte alterations and endothelial activation, two key features of blood-brain barrier dysfunction, remains unresolved. Here, we performed a quantitative single-vessel analysis of the human cortical microvasculature across increasing cSVD severity and ageing. Using multiplex immunohistochemistry combined with spectral unmixing and automated image analysis, we analysed 11,409 microvascular fragments from post-mortem brain tissue derived from 20 cases. Endothelial cells, pericytes, and endothelial activation were assessed using PECAM-1, PDGFR{beta}, and VCAM-1, respectively. Microvascular density and diameter differed between cortical grey matter and the underlying white matter, with white matter vessels being less dense and wider in controls. While vessel diameter remained stable across disease stages, microvascular density increased with cSVD severity and age in the white matter. At the molecular level, PDGFR{beta} signal decreased markedly with increasing cSVD severity, consistent with progressive pericyte loss. This reduction was observed in both grey and white matter and correlated with disease severity and age. Notably, intermediate disease groups displayed marked heterogeneity, with vessels exhibiting either preserved or near-complete pericyte coverage, suggesting a potentially bimodal transition. In parallel, endothelial markers PECAM-1 and VCAM-1 increased significantly with disease severity, reflecting endothelial activation. Unsupervised Gaussian mixture clustering of marker expression identified three vascular states characterised by (i) preserved pericytes with low endothelial activation, (ii) marked pericyte loss without endothelial activation, and (iii) combined pericyte depletion and endothelial activation. These clusters broadly aligned with clinical severity but revealed intermediate states not captured by post-mortem diagnosis alone. Together, these findings suggest that pericyte loss and endothelial activation are partially dissociated processes that occur in a sequential progression in human cSVD, supporting pericyte dysfunction as an early event and highlighting it as a potential therapeutic target in microvascular disease.

BackgroundCerebral small vessel disease (CSVD) is strongly linked to stroke and dementia risk, frequently predating clinical events for years to decades. Preventive efforts focus on treatment of modifiable vascular risk factors (VRF), but the complex changes in VRF over long periods in relation to CSVD burden remain unclear. Thus, we aimed to characterize life-long VRF trajectories in community-dwelling individuals and relate them to CSVD burden. MethodsFramingham Heart Study participants from the Original and Offspring cohorts with six or more repeated VRF assessments over their lifetime were eligible for the present study. Among those who underwent MRI imaging, CSVD burden was quantified by assigning one point each for cerebral microbleeds, covert infarcts, extensive white matter hyperintensities, cortical superficial siderosis, and high perivascular space burden (range: 0-5). VRF trajectories and trajectory-based clusters were then examined in relation to CSVD burden using functional regression analysis. ResultsOf 7,961 participants with longitudinal VRF measurements (mean baseline age 39.8 {+/-} 10 years, 45% men), 1,625 underwent MRI imaging after exclusions for other neurological conditions. In models that used individual VRF trajectories as covariates, systolic and diastolic blood pressure, pulse pressure, cigarettes per day and triglycerides were significantly associated with CSVD burden later in life. In a complementary analysis, we clustered VRF trajectories and then used each participants cluster assignment (rather than the raw trajectories) as the covariate; cluster assignments diverged early in life for systolic blood pressure and pulse pressure and were significantly associated with CSVD burden. ConclusionsIndividuals following high risk lifetime patterns of vascular risk factors have higher CSVD burden later in life. These results highlight the importance of primordial and primary prevention with sustained risk factor management across the lifespan to mitigate CSVD burden, a strong determinant of stroke and dementia risk.

Stroke is a leading cause of mortality and morbidity worldwide. MRI-visible perivascular spaces (PVS) are an emerging marker of cerebral small vessel disease and may have prognostic value in stroke. We investigated longitudinal changes in PVS volume and cluster count following ischaemic stroke. PVS volumes and cluster counts were compared between stroke survivors (n=124; 39 women; median [Q1, Q3] age=70 [62, 76] years) and healthy controls (n=39; 15 women; median age=69 [66, 72.5] years). MRI scans were acquired at 3 months, 12 months, and 36 months post-stroke. PVS were automatically segmented from T1-weighted MRI using a validated deep learning algorithm (nnU-Net). Generalised linear mixed-effects models were used to assess group differences and longitudinal changes in PVS, adjusting for baseline age, sex, total intracranial volume, and BMI. At the 12-month timepoint, no significant differences in PVS metrics were observed between stroke and control groups. However, at the 36-month timepoint we observed a significant brain-wide reduction in PVS volume (exp({beta})=0.93, 95%CI [0.87, 1], p=0.035) and cluster count (exp({beta})=0.92, 95%CI [0.85, 0.99], p=0.003) in the stroke group compared to control. Regionally, by 36 months, stroke patients demonstrated significant PVS reductions relative to controls in the frontal (PVS volume: exp({beta})=0.93, 95%CI [0.82, 0.99], p=0.032; PVS cluster counts: exp({beta})=0.91, 95%CI [0.83, 1], p=0.037) and parietal lobes (PVS volume: exp({beta})=0.93, 95%CI [0.85, 1.01], p=0.10; PVS cluster counts: exp({beta})=0.84, 95%CI [0.68, 1.08], p<0.001). These findings suggest that ischaemic stroke is associated with dynamic and regional changes in PVS volume and counts.

IntroductionThe ischaemic penumbra is the principal therapeutic target in acute ischaemic stroke (AIS). Although perfusion imaging enables identification of salvageable tissue, its availability is limited and iodinated contrast exposure carries risk. Validated blood-based biomarkers could serve as scalable surrogates for imaging-defined penumbra. ObjectiveWe conducted a systematic review and meta-analysis to assess the association between blood-based biomarkers reported in the literature and the ischaemic penumbra. MethodsWe searched Ovid MEDLINE, Embase (Ovid), PsycINFO (Ovid), and Web of Science until December 3, 2025, for studies involving human subjects with AIS aged over 18 years or animal subjects that reported the presence of infarct and ischaemic penumbra. The primary outcome was the difference in mean biomarker levels in subjects with and without ischaemic penumbrae as defined by the study authors. We used the QUADAS-2 tool to assess risk of bias. We calculated each biomarkers pooled standardized mean difference (SMD) and 95% CI where possible. Protein-protein interaction network (PPI) and pathway analyses were conducted in Cytoscape and the enrichR R package (PROSPERO: CRD42023453175). ResultsWe identified 11 studies (1765 human subjects and 8 nonhuman primates) that assessed 53 candidate blood-based biomarkers. Two studies had a low risk of bias, while nine had a risk of bias. A meta-analysis was conducted for seven biomarkers in humans from four studies. Of these, three biomarkers demonstrated significant association with penumbrae in humans: mid-regional pro-adrenomedullin (MR-proADM; SMD 0.80 [95% CI 0.49 to 1.10]), interleukin-10 (IL-10; SMD 1.94 [0.85 to 3.03]), and neuron-specific enolase (NSE; SMD -0.71 [-1.40 to -0.01]). However, substantial statistical heterogeneity was observed for several pooled biomarkers (I{superscript 2} >90%), limiting confidence in effect size precision. Amongst biomarkers where meta-analysis was not possible, 37 biomarkers showed significant association with presence of a penumbra. Oxygen radical absorbance capacity after perchloric acid treatment (ORACPCA; SMD 0.31 [0.01 to 0.60]) showed significant association with penumbra presence; 34 genes (e.g., STK26 r = 0.58, p = 0.003; MGA r = 0.58, p = 0.004; IL1B r = -0.59, p = 0.003; NUP98 r = -0.71, p < 0.001), circOGDH (r = 0.962, p = 0.002), and NT-proBNP (r = 0.199, p < 0.001) were significantly correlated with penumbra volume. PPI analysis identified IL-1{beta} as the most highly connected node (10 interactions), followed by IL-10 and HDAC1/HCAR2. Cdc42 was reported to be significantly associated with penumbrae in nonhuman primates, but there were insufficient data to calculate SMD. Pathway enrichment revealed positive associations with angiogenesis and IL-12 signalling, and negative associations with leukocyte migration, chemokine signalling, and platelet activation. ConclusionsCurrently reported biomarkers of ischaemic penumbra are not ready for clinical implementation. Although implicated pathways converge on inflammatory regulation, haemostasis, and cerebral perfusion, rigorous prospective validation is required before integration into prehospital or emergency triage workflows.

BackgroundStroke remains a leading cause of mortality worldwide. Ischemic stroke, caused by arterial occlusion, induces sensorimotor deficits and memory impairments. Excessive activity of the brain angiotensin II type 1 receptor (AT1R) is associated with hypertension and cerebral ischemia. Candesartan (CN), an AT1R blocker, improves cerebrovascular blood flow. Pomegranate (Punica granatum) is rich in polyphenolic antioxidants that reduce oxidative stress and inflammation, suggesting potential neuroprotective effects in cerebral ischemia. AimThis study compared the neuroprotective effects of CN administered alone or in combination with pomegranate (POM) in a rat model of cerebral ischemia induced by chronic unilateral carotid artery ligation. MethodsCerebral ischemia was induced by ligation of the right common carotid artery (RCCA) in adult rats. Animals were randomly assigned to four groups: sham control, untreated ischemic, ischemic treated with CN, and ischemic treated with CN + POM. Sensorimotor and cognitive functions were assessed 1-15 days post-surgery using beam balance (BB), beam walking (BW), modified sticky-tape (MST), novel object recognition (NOR), and the Morris water maze (MWM) tests. ResultsRCCA ligation induced marked sensorimotor deficits and memory impairments. Both CN monotherapy and CN + POM treatment equally restored sensorimotor function to sham-control levels, as demonstrated by BB, BW, and MST tests. In contrast, CN + POM treatment showed greater efficacy than CN alone in improving short-term recognition and spatial memory, as demonstrated by NOR and MWM performance. ConclusionCN effectively reverses ischemia-induced sensorimotor deficits, whereas the addition of POM confers specific and enhanced protection against cognitive impairment, indicating distinct mechanisms underlying sensorimotor and memory recovery after cerebral ischemia.

BackgroundWhile identifying high-risk carotid disease remains a significant clinical challenge, the specific role of carotid intraplaque hemorrhage (IPH) is poorly understood. Although IPH has been linked to white matter lesion (WML) burden, current assessments overlook the directional impact of plaque instability on the brain. This study sought to determine whether IPH is an independent driver of asymmetric WML pathology and evaluate if this phenotype can identify a high-risk demographic for TIA and stroke. MethodsThis multi-center retrospective study analyzed 264 participants (mean age 71.8 years) from the Canadian Atherosclerosis Imaging Network (2010-2015). Participants underwent 3T MRI to assess carotid IPH and WMLs. We quantified WMLs using a deep-learning pipeline to extract three biomarkers: volume (WML-ICV), intensity (WML-Intensity), and intensity ratio (WML-IR). The Asymmetry Index Measure (AIM) defined the inter-hemispheric log-ratio, while the association between IPH and AIM was examined using multivariable linear regression adjusted for age, sex, stenosis, and scanner manufacturer. A secondary composite outcome of TIA/stroke was analyzed via logistic regression to evaluate the interaction between IPH, age, and sex. ResultsWhile whole-brain WML burden did not significantly differ by IPH status (p > 0.60), IPH status was a robust independent predictor of hemispheric asymmetry (WML-ICV: p = 0.01; WML-Intensity, p = 0.01). Post-hoc analysis confirmed WML burden was significantly higher in IPH+ older males ([&ge;] 70 years) compared to younger cohorts (p < 0.04). This older male subgroup also demonstrated 4.57-fold higher adjusted odds of TIA/stroke (p = 0.02) compared to other demographic subgroups (all p > 0.87). ConclusionsCarotid IPH is independently associated with a rightward asymmetric WML phenotype not captured by global metrics. This imaging marker identifies a high-risk demographic of older males with a nearly five-fold increase in clinical events, suggesting that hemispheric-level analysis provides critical prognostic value for stroke risk stratification.

IntroductionNeuroinflammation is increasingly implicated in age-related cognitive decline, neurodegeneration and neuropsychiatric disorders. During systemic inflammation, microglia are rapidly activated, simultaneously changing their shape and releasing cytokines that perturb neuronal function. This change in glial morphology alters their intracellular diffusion properties and provides a potentially measurable signature of their activation state. Diffusion-weighted magnetic resonance spectroscopy (dMRS) shows promise in detecting these changes. Here, we combined IFN-{beta} challenge with dMRS to assess changes in metabolite diffusion in healthy young and older adults. We hypothesised that IFN-{beta} would increase diffusion of choline-containing compounds (tCho) but not N-acetylaspartate + N-acetylaspartylglutamate (tNAA), age would be associated with an increase in tCho diffusion and concentration, lower tNAA concentration and increased effects of IFN-{beta}. MethodsWe recruited 15 young (mean 25.2 {+/-} 5.1 years, 6 male) and 15 older (mean 62.6 {+/-} 4.1 years, 5 male) healthy volunteers, each tested twice, once after IFN-{beta} and once after placebo. Physiological and behavioural responses were recorded hourly, and blood samples taken at baseline, 4 and 6.5 hours post-injection. dMRS occurred at [~]4.5 hours at 3T, using a semi-LASER sequence with four diffusion weightings (b = 0 and 3 x 3500 s/mm{superscript 2}), in 4.5 cm3 VOIs in the left thalamus and corona radiata. Apparent Diffusion Coefficients (ADCs) of tCho, tNAA and creatine+phosphocreatine (tCr) were calculated from averaged spectra using custom MATLAB software. ResultsIFN-{beta} administration produced a significant increase in thalamic tCho diffusivity compared with placebo (t(28) = -2.15, p = 0.040), with no change in tNAA or tCr ADC, or tCho concentrations. IFN-{beta}-related increases in tCho ADC positively correlated with increases in circulating IL-6 (R{superscript 2} = 0.14, p = 0.040). Age-related effects were also evident during the placebo condition, with older participants showing lower thalamic tNAA diffusivity (t(27) = 2.86, p = 0.008), lower tNAA/tCr in both grey and white matter (grey: t(27) = 2.49, p = 0.023; white: t(27) = 2.94, p = 0.007), and higher white-matter tCho/tCr (t(27) = -2.23, p = 0.034). ConclusiondMRS detected IFN-{beta}-induced increases in thalamic tCho diffusivity corresponding with peripheral inflammation, supporting its sensitivity to acute inflammation-induced changes in glial morphology. Age-related differences in tNAA diffusion and concentrations further highlight metabolite-specific ageing effects. HighlightsO_LIdMRS detects increased thalamic total choline diffusivity following IFN-{beta}-induced inflammation. C_LIO_LIIFN-{beta}-related changes in total choline diffusivity are associated with peripheral IL-6 responses. C_LIO_LIAgeing is linked to reduced NAA diffusion and higher white-matter tCho/tCr C_LIO_LIdMRS is sensitive to inflammation- and age-related neurochemical changes in vivo. C_LI

BackgroundDynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) enables non-invasive characterization of carotid atherosclerotic plaque. PurposeTo evaluate the performance and reproducibility of a simplified DCE-MRI quantification method for carotid plaque assessment. MethodsT1-weighted black-blood DCE-MRI of the carotid arteries at 3T was performed at baseline and after six months in patients with mild-to-moderate atherosclerotic lesions in a pilot placebo-controlled randomized trial evaluating the effects of low-dose (0.5mg daily) colchicine therapy on carotid plaque volume. DCE-MRI signal intensity was measured in manually drawn regions of interest in the plaque core, remote non-atherosclerotic vessel wall, and skeletal muscle. Peak signal intensities were normalized to skeletal muscle signal in the same slice. ResultsIn patients (n=28, median [interquartile range] age 72 [64-74] years, 36% female, n=13/15 colchicine/placebo), normalized peak signal intensity was higher in the plaque core than in the remote vessel wall at both baseline (3.5 [2.3-4.1] vs 2.1 [1.7-2.5], p<0.001) and follow-up (3.2 [2.5-4.4] vs 2.0 [1.7-2.5], p<0.001). Measurements did not differ between baseline and follow-up for all patients (0.7{+/-}0.7 for plaque core, 0.6{+/-}0.4 for remote vessel wall, p>0.80 for both) nor between colchicine intervention and placebo control (p>0.35 for either region). ConclusionsNormalised peak signal intensity on DCE-MRI was consistently higher in the carotid plaque core than in the remote vessel wall, showed excellent reproducibility in both regions over six months, and was not altered by colchicine treatment. This simplified, muscle-normalised approach may facilitate future studies exploring DCE-MRI measures potentially related to plaque vulnerability.

In brain-heart interactions, several pathways have been proposed to mediate feedback loops between systems. Among these, cerebrovascular dynamics operate at their interface. However, how cardiovascular control, ventilation mechanisms, and cerebral autoregulation interact is not well characterized, especially in ageing and post-stroke conditions, where perfusion can be compromised. In a cohort of 57 elderly participants, including 30 stroke survivors, we investigated the relationship between cardiac sympathetic activity and both, cerebral blood flow regulation and ventilatory status. Sympathetic reflexes, assessed via cardiac sympathetic index (CSI) during sit-to-stand transitions, were preserved across all participants, with marginal group differences between stroke and non-stroke populations. However, among individuals with constrained ventilation, indexed by reduced end-tidal CO2 at baseline, we identified a more elevated CSI following postural change, scaling with the degree of CO2 dysregulation. Furthermore, transcranial Doppler measurements revealed exaggerated changes in mean flow velocity (MFV) within the right middle cerebral artery in most participants. These MFV shifts significantly correlated with the magnitude of cardiac sympathetic change under orthostatic stress, suggesting that CSI can capture maladaptive cerebrovascular responses. Together, these findings highlight a distinct cardiac-cerebrovascular crosstalk in elderly individuals, revealing patterns consistent with compensatory or maladaptive sympathetic overactivation under conditions of impaired cerebrovascular control.

Disturbances of neurovascular coupling (NVC) contribute to metabolic derailment and neurological symptoms associated with epilepsy. While postictal arterial constriction can be alleviated by inhibitors of voltage gated calcium channels (VGCCs), less is known regarding seizure-associated electrical signals in higher-order capillaries and their role in determining pericyte tone during seizures. Here we investigated electrical signaling within the ex vivo neurovascular unit (NVU) derived from rat and human brain tissue. We focused on electrical signal transduction between pericytes and endothelial cells and the potential role of VGCCs in vasomotion. Using dye coupling and paired patch-clamp recordings, we showed that morphologically heterogeneous groups of mid-capillary pericytes build a functional syncytium with endothelial cells. Coupling was asymmetric, allowing for directed propagation of electrical signals. Regardless of their morphology, mid-capillary pericytes responded with depolarization and constriction to metabotropic receptor (GPCR) activation (by thromboxane, norepinephrine and UDP-glucose). However, depolarization via the patch pipette induced neither Ca2+-influx nor constriction, suggesting lack of contribution of VGCCs to vasomotion. On inducing epileptiform activity, A2a adenosine receptors and inwardly rectifying potassium channels hyperpolarized the capillary syncytium, followed by repeated depolarizations due to seizure-associated potassium increase in the parenchyma. Thus, while mid-capillary pericytes are contractile, their tone does not rely on their membrane potential and VGCCs. However, syncytial coupling allows for transmission of seizure-associated hyper- and depolarizing signals to upstream feeding arterioles. Significance statementElectro-metabolic signaling is a mechanism, which couples neuronal metabolic activity to local blood flow, by generation and conduction of hyperpolarizing electrical signals in the vasculature. Repeated seizures are followed by postictal hypoperfusion, suggesting disturbances in this signaling mechanism. Due to the inaccessibility of mid capillary pericytes, little is known about how seizure-associated electrical signals modulate local capillary tone. O_LIRat and human mid-capillary pericytes are contractile and actively regulate capillary diameter upon GPCR activation. C_LIO_LIWhile GPCR-induced vasoconstriction is associated with depolarization of the pericytes, depolarization via the patch pipette induces neither constriction nor intracellular Ca2+ increases. C_LIO_LIDespite differences in their morphology, mesh and thin strand pericytes participate in a common electrical syncytium along with the capillary endothelial cells both in rat and in human tissue. C_LIO_LISignal transmission at electrical synapses between pericyte-pericyte and pericyte-endothelial cell pairs is asymmetric, suggesting a preferred direction of propagation of electrical signals. C_LIO_LIActivation of A2a adenosine receptors and Kir channels mediate capillary hyperpolarization prior to the onset of seizures, which is followed by seizure-associated depolarization due to extracellular potassium accumulation. C_LI

The role of the choroid plexus (CP) as the primary source of cerebrospinal fluid (CSF) remains controversial. Here, we used dynamic indirect D2O magnetic resonance imaging (MRI) at 9.4T to investigate whole-brain CSF dynamics in rats. Spin-echo echo-planar imaging (SE-EPI) was performed during intravenous D2O infusion with a temporal resolution of 10.69 s and an in-plane resolution of 150 x 150 {micro}m. An echo time of 150.0 ms was employed to effectively suppress signals from brain parenchyma, blood, and interstitial fluid, resulting in preferential visualization of CSF. The ambient and supracerebellar cisterns (AC+SC) exhibited the greatest signal attenuation, reaching 47.32 {+/-} 15.70% of baseline, whereas the lateral ventricles (LV1, LV2) showed smaller reductions (68.73 {+/-} 18.72%-72.64 {+/-} 15.07% of baseline). CSF production rates were quantified using a one-compartment perfusion model. Estimated secretion rates were 0.11 and 0.13 {micro}L/min in the lateral ventricles and 1.30 {micro}L/min in the AC+SC region, indicating a 5.42-fold higher CSF production outside the ventricles. These findings provide direct in vivo evidence that the lateral ventricles are not the primary site of CSF production. The proposed D2O-based dynamic SE-EPI approach is safe, non-invasive, cost-effective, and suitable for widespread application.