Cerebral blood flow in normal aging adults: cardiovascular determinants, clinical implications, and aerobic fitness

Association of Arterial Stiffness Index and Brain Structure in the UK Biobank: A 10-Year Retrospective Analysis

Arterial stiffening and changes in brain structure both occur with normal aging and can be exacerbated via acquired health conditions. While cross-sectional associations exist, the longitudinal relationship between arterial stiffness and brain structure remains unclear. In this study, we investigated 1) associations between baseline arterial stiffness index (ASI) and brain structure (global and regional grey matter volumes (GMV), white matter hyperintensities (WMH)) 10-years post-baseline (10.4±0.8 years) and 2) associations between the 10-year change in ASI from baseline and brain structure 10-years post-baseline in 650 healthy middle- to older-aged adults (53.4±7.5 years) from the UK Biobank. We observed significant associations between baseline ASI and GMV (p<0.001) and WMH (p=0.0036) 10-years post-baseline. No significant associations between 10-year change in ASI and brain structure (global GMV p=0.24; WMH volume p=0.87) were observed. There were significant associations of baseline ASI in 2 of 60 regional brain volumes analyzed (right posterior superior temporal gyrus p=0.001; left superior lateral occipital cortex p<0.001). Strong associations with baseline ASI, but not changes in ASI over 10-years, suggest arterial stiffness at the entry point of older adulthood is more impactful on brain structure 10-years later compared to age-related stiffening. Based on these associations, we suggest clinical monitoring and potential intervention for reducing arterial stiffness should occur in midlife to reduce vascular contributions to structural changes in the brain, supporting a healthy trajectory of brain aging. Our findings also support use of ASI as a surrogate for gold standard measures in showing overall relationships between arterial stiffness and brain structure.

Blood brain barrier dysfunction in healthy aging and dementia: Why, how, what for?

The blood brain barrier (BBB) is an indispensable structure that maintains the central nervous system (CNS) microenvironment for a correct neuronal function. It is composed by highly specialized microvessels, surrounded by astrocytes, pericytes, neurons and microglia cells, which tightly control the influx and efflux of substances to the brain parenchyma. During aging, the BBB becomes impaired, and it may contribute to the development of neurodegenerative and neurological disorders including Alzheimer's disease and other dementias. Restoring the BBB can be a strategy to prevent disease onset and development, reducing the symptoms of these conditions. This work critically reviews the major mechanisms underlying BBB breakdown in healthy and unhealthy aging, as well as biomarkers and methodologies that accurately assess its impairment. Complementarily, potential therapeutic targets are discussed as new strategies to restore the normal function of the BBB in aging.

Aging drives cerebrovascular network remodeling and functional changes in the mouse brain

Aging is frequently associated with compromised cerebrovasculature and pericytes. However, we do not know how normal aging differentially impacts vascular structure and function in different brain areas. Here we utilize mesoscale microscopy methods and in vivo imaging to determine detailed changes in aged murine cerebrovascular networks. Whole-brain vascular tracing shows an overall ~10% decrease in vascular length and branching density with ~7% increase in vascular radii in aged brains. Light sheet imaging with 3D immunolabeling reveals increased arteriole tortuosity of aged brains. Notably, vasculature and pericyte densities show selective and significant reductions in the deep cortical layers, hippocampal network, and basal forebrain areas. We find increased blood extravasation, implying compromised blood-brain barrier function in aged brains. Moreover, in vivo imaging in awake mice demonstrates reduced baseline and on-demand blood oxygenation despite relatively intact neurovascular coupling. Collectively, we uncover regional vulnerabilities of cerebrovascular network and physiological changes that can mediate cognitive decline in normal aging.

Preliminary investigations into human neurofluid transport using multiple novel non-contrast MRI methods

We discuss two potential non-invasive MRI methods to study phenomena related to subarachnoid cerebrospinal fluid (CSF) motion and perivascular fluid transport, and their association with sleep and aging. We apply diffusion-based intravoxel incoherent motion (IVIM) imaging to evaluate pseudodiffusion coefficient, D*, or CSF movement across large spaces like the subarachnoid space (SAS). We also performed perfusion-based multi-echo, Hadamard encoded arterial spin labeling (ASL) to evaluate whole brain cortical cerebral blood flow (CBF) and trans-endothelial exchange (Tex) of water from the vasculature into the perivascular space and parenchyma. Both methods were used in young adults (N = 9, 6 F, 23 ± 3 years old) in the setting of sleep and sleep deprivation. To study aging, 10 older adults (6 F, 67 ± 3 years old) were imaged after a night of normal sleep and compared with the young adults. D* in SAS was significantly (p < 0.05) reduced with sleep deprivation (0.016 ± 0.001 mm2/s) compared to normal sleep (0.018 ± 0.001 mm2/s) and marginally reduced with aging (0.017 ± 0.001 mm2/s, p = 0.029). Cortical CBF and Tex were unchanged with sleep deprivation but significantly lower in older adults (37 ± 3 ml/100 g/min, 578 ± 61 ms) than in young adults (42 ± 2 ml/100 g/min, 696 ± 62 ms). IVIM was sensitive to sleep physiology and aging, and multi-echo, multi-delay ASL was sensitive to aging.

Spontaneous cerebrovascular reactivity at rest in older adults with and without mild cognitive impairment and memory deficits

Background

Older adults with mild cognitive impairment (MCI) exhibit deficits in cerebrovascular reactivity (CVR), suggesting CVR is a biomarker for vascular contributions to MCI. This study examined if spontaneous CVR is associated with MCI and memory impairment.

Methods

161 older adults free of dementia or major neurological/psychiatric disorders were recruited. Participants underwent clinical interviews, cognitive testing, venipuncture for Alzheimer's biomarkers, and brain MRI. Spontaneous CVR was quantified during 5 minutes of rest.

Results

Whole brain CVR was negatively associated with age, but not MCI. Lower CVR in the parahippocampal gyrus (PHG) was found in participants with MCI and was linked to worse memory performance on memory tests. Results remained significant after adjusting for Alzheimer's biomarkers and vascular risk factors.

Conclusion

Spontaneous CVR deficits in the PHG are observed in older adults with MCI and memory impairment, indicating medial temporal microvascular dysfunction's role in cognitive decline.

Age-Related Decline in Blood-Brain Barrier Function is More Pronounced in Males than Females in Parietal and Temporal Regions

The blood-brain barrier (BBB) plays a pivotal role in protecting the central nervous system (CNS), shielding it from potential harmful entities. A natural decline of BBB function with aging has been reported in both animal and human studies, which may contribute to cognitive decline and neurodegenerative disorders. Limited data also suggest that being female may be associated with protective effects on BBB function. Here we investigated age and sex-dependent trajectories of perfusion and BBB water exchange rate (kw) across the lifespan in 186 cognitively normal participants spanning the ages of 8 to 92 years old, using a non-invasive diffusion prepared pseudo-continuous arterial spin labeling (DP-pCASL) MRI technique. We found that the pattern of BBB kw decline with aging varies across brain regions. Moreover, results from our DP-pCASL technique revealed a remarkable decline in BBB kw beginning in the early 60s, which was more pronounced in males. In addition, we observed sex differences in parietal and temporal regions. Our findings provide in vivo results demonstrating sex differences in the decline of BBB function with aging, which may serve as a foundation for future investigations into perfusion and BBB function in neurodegenerative and other brain disorders.

Peripheral vascular dysfunction and the aging brain

Aging is the greatest non-modifiable risk factor for most diseases, including cardiovascular diseases (CVD), which remain the leading cause of mortality worldwide. Robust evidence indicates that CVD are a strong determinant for reduced brain health and all-cause dementia with advancing age. CVD are also closely linked with peripheral and cerebral vascular dysfunction, common contributors to the development and progression of all types of dementia, that are largely driven by excessive levels of oxidative stress (e.g., reactive oxygen species [ROS]). Emerging evidence suggests that several fundamental aging mechanisms (e.g., "hallmarks" of aging), including chronic low-grade inflammation, mitochondrial dysfunction, cellular senescence and deregulated nutrient sensing contribute to excessive ROS production and are common to both peripheral and cerebral vascular dysfunction. Therefore, targeting these mechanisms to reduce ROS-related oxidative stress and improve peripheral and/or cerebral vascular function may be a promising strategy to reduce dementia risk with aging. Investigating how certain lifestyle strategies (e.g., aerobic exercise and diet modulation) and/or select pharmacological agents (natural and synthetic) intersect with aging "hallmarks" to promote peripheral and/or cerebral vascular health represent a viable option for reducing dementia risk with aging. Therefore, the primary purpose of this review is to explore mechanistic links among peripheral vascular dysfunction, cerebral vascular dysfunction, and reduced brain health with aging. Such insight and assessments of non-invasive measures of peripheral and cerebral vascular health with aging might provide a new approach for assessing dementia risk in older adults.

Evaluation of the correlation between cerebral hemodynamics and blood pressure by comparative analysis of variation in cerebral blood flow in hypertensive versus normotensive individuals: A systematic review and meta-analysis

Current understanding of the cerebral vascular response to variations in blood pressure (BP) among individuals with hypertension is limited. The aim of this meta-analysis was to determine the correlation between hypertension, risk of stroke, and cerebral blood flow (CBF). We reviewed studies published between 2000 and 2023 from PubMed, Google Scholar, and Science Direct that compared mean CBF in normotensive (NTN) and hypertensive (HTN) patients. A random effects model was used to construct the risk ratio (RR), 95% confidence interval (CI), forest plot, and inverse variance weighting. Additionally, a mixed-effects meta-regression was employed to examine the impact of study-specific patient variables. This meta-analysis included eight prospective cross-sectional studies published from 2002 to 2023. It revealed a significant average difference in the standard mean CBF of -0.45 (95% CI -0.60 to -0.30, I2 = 69%, P < 0.00001), distinguishing NTN from HTN subjects. A RR of 0.90 (95% CI 0.63 to 1.30, I2 = 89%, P = 0.04) indicated a significant decrease in CBF among individuals with hypertension. We found a statistically significant relationship between changes in diastolic and systolic BPs and the mean CBF (R -0.81, P = 0.001 and R = -0.90, P = 0.005, respectively). Our research demonstrates a strong relationship between elevated BP and reduced CBF, with hypertension reducing CBF compared to NTN individuals, by increasing cerebrovascular resistance.

Brain atrophy, reduced cerebral perfusion, arterial stiffening, and wall thickening with aging coincide with stimulus-specific changes in fMRI-BOLD responses

The aim of this study was to investigate how aging affects blood flow and structure of the brain. It was hypothesized older individuals would have lower gray matter volume (GMV), resting cerebral blood flow (CBF0), and depressed responses to isometabolic and neurometabolic stimuli. In addition, increased carotid-femoral pulse-wave velocity (PWV), carotid intima-media thickness (IMT), and decreased brachial flow-mediated dilation (FMD) would be associated with lower CBF0, cerebrovascular reactivity (CVR), and GMV. Brain scans (magnetic resonance imaging) and cardiovascular examinations were conducted in young (age = 24 ± 3 yr, range = 22-28 yr; n = 13) and old (age = 71 ± 4 yr; range = 67-82 yr, n = 14) participants, and CBF0, CVR [isometabolic % blood oxygen level-dependent (BOLD) in response to a breath hold (BH)], brain activation patterns during a working memory task (neurometabolic %BOLD response to N-back trial), GMV, PWV, IMT, and FMD were measured. CBF0 and to a lesser extent CVRBH were lower in the old group (P ≤ 0.050); however, the increase in the %BOLD response to the memory task was not blunted (P ≥ 0.2867). Age-related differential activation patterns during the working memory task were characterized by disinhibition of the default mode network in the old group (P < 0.0001). Linear regression analyses revealed PWV, and IMT were negatively correlated with CBF0, CVRBH, and GMV across age groups, but within the old group alone only the relationships between PWV-CVRBH and IMT-GMV remained significant (P ≤ 0.0183). These findings suggest the impacts of age on cerebral %BOLD responses are stimulus specific, brain aging involves alterations in cerebrovascular and possibly neurocognitive control, and arterial stiffening and wall thickening may serve a role in cerebrovascular aging.NEW & NOTEWORTHY Cerebral perfusion was lower in old versus young adults. %Blood oxygen level-dependent (BOLD) responses to an isometabolic stimulus and gray matter volume were decreased in old versus young adults and associated with arterial stiffening and wall thickening. The increased %BOLD response to a neurometabolic stimulus appeared unaffected by age; however, the old group displayed disinhibition of the default mode network during the stimulus. Thus, age-related alterations in cerebral %BOLD responses were stimulus specific and related to arterial remodeling.

Proteomics of mouse brain endothelium uncovers dysregulation of vesicular transport pathways during aging

Age-related decline in brain endothelial cell (BEC) function contributes critically to neurological disease. Comprehensive atlases of the BEC transcriptome have become available, but results from proteomic profiling are lacking. To gain insights into endothelial pathways affected by aging, we developed a magnetic-activated cell sorting-based mouse BEC enrichment protocol compatible with proteomics and resolved the profiles of protein abundance changes during aging. Unsupervised cluster analysis revealed a segregation of age-related protein dynamics with biological functions, including a downregulation of vesicle-mediated transport. We found a dysregulation of key regulators of endocytosis and receptor recycling (most prominently Arf6), macropinocytosis and lysosomal degradation. In gene deletion and overexpression experiments, Arf6 affected endocytosis pathways in endothelial cells. Our approach uncovered changes not picked up by transcriptomic studies, such as accumulation of vesicle cargo and receptor ligands, including Apoe. Proteomic analysis of BECs from Apoe-deficient mice revealed a signature of accelerated aging. Our findings provide a resource for analysing BEC function during aging.

Intensive Blood Pressure Control After Endovascular Thrombectomy for Acute Ischemic Stroke: a Systematic Review and Meta-Analysis

BACKGROUND AND PURPOSE

Optimal clinical outcome with successful recanalization from endovascular thrombectomy (EVT) requires optimal blood pressure (BP) management. We aimed to evaluate the efficacy and safety of the intensive BP target (< 140 mm Hg) versus the standard BP target (< 180 mm Hg) after EVT for acute ischemic stroke.

METHODS

We conducted a systematic review and meta-analysis synthesizing evidence from randomized controlled trials (RCTs) obtained from PubMed, Embase Cochrane, Scopus, and WOS until September 7th, 2023. We used the fixed-effect model to report dichotomous outcomes using risk ratio (RR) and continuous outcomes using mean difference (MD), with a 95% confidence interval (CI).

PROSPERO ID

CRD42023463206.

RESULTS

We included four RCTs with 1559 patients. There was no difference between intensive BP and standard BP targets regarding the National Institutes of Health Stroke Scale (NIHSS) change after 24 h [MD: 0.44 with 95% CI (0.0, 0.87), P = 0.05]. However, the intensive BP target was significantly associated with a decreased risk of excellent neurological recovery (mRS ≤ 1) [RR: 0.87 with 95% CI (0.76, 0.99), P = 0.03], functional independence (mRS ≤ 2) [RR: 0.81 with 95% CI (0.73, 0.90), P = 0.0001] and independent ambulation (mRS ≤ 3) [RR: 0.85 with 95% CI (0.79, 0.92), P < 0.0001].

CONCLUSIONS

An intensive BP target after EVT is associated with worse neurological recovery and significantly decreased rates of functional independence and independent ambulation compared to the standard BP target. Therefore, the intensive BP target should be avoided after EVT for acute ischemic stroke.

Cerebrovascular adaptations to habitual resistance exercise with aging

Resistance training (RT) is associated with improved metabolism, bone density, muscular strength, and lower risk of osteoporosis, sarcopenia, and cardiovascular disease. Although RT imparts many physiological benefits, cerebrovascular adaptations to chronic RT are not well defined. Participation in RT is associated with greater resting peripheral arterial diameters, improved endothelial function, and general cardiovascular health, whereas simultaneously linked to reductions in central arterial compliance. Rapid blood pressure fluctuations during resistance exercise, combined with reduced arterial compliance, could lead to cerebral microvasculature damage and subsequent cerebral hypoperfusion. Reductions in cerebral blood flow (CBF) accompany normal aging, where chronic reductions in CBF are associated with changes in brain structure and function, and increased risk of neurodegeneration. It remains unclear whether reductions in arterial compliance with RT relate to subclinical cerebrovascular pathology, or if such adaptations require interpretation in the context of RT specifically. The purpose of this narrative review is to synthesize literature pertaining to cerebrovascular adaptations to RT at different stages of the life span. This review also aims to identify gaps in the current understanding of the long-term impacts of RT on cerebral hemodynamics and provide a mechanistic rationale for these adaptations as they relate to aging, cerebral vasculature, and overall brain health.

Age-related loss of Notch3 underlies brain vascular contractility deficiencies, glymphatic dysfunction, and neurodegeneration in mice

Vascular aging affects multiple organ systems, including the brain, where it can lead to vascular dementia. However, a concrete understanding of how aging specifically affects the brain vasculature, along with molecular readouts, remains vastly incomplete. Here, we demonstrate that aging is associated with a marked decline in Notch3 signaling in both murine and human brain vessels. To clarify the consequences of Notch3 loss in the brain vasculature, we used single-cell transcriptomics and found that Notch3 inactivation alters regulation of calcium and contractile function and promotes a notable increase in extracellular matrix. These alterations adversely impact vascular reactivity, manifesting as dilation, tortuosity, microaneurysms, and decreased cerebral blood flow, as observed by MRI. Combined, these vascular impairments hinder glymphatic flow and result in buildup of glycosaminoglycans within the brain parenchyma. Remarkably, this phenomenon mirrors a key pathological feature found in brains of patients with CADASIL, a hereditary vascular dementia associated with NOTCH3 missense mutations. Additionally, single-cell RNA sequencing of the neuronal compartment in aging Notch3-null mice unveiled patterns reminiscent of those observed in neurodegenerative diseases. These findings offer direct evidence that age-related NOTCH3 deficiencies trigger a progressive decline in vascular function, subsequently affecting glymphatic flow and culminating in neurodegeneration.

C-kit controls blood-brain barrier permeability by regulating caveolae-mediated transcytosis after chronic cerebral hypoperfusion

Blood-brain barrier (BBB) dysfunction plays a pivotal role in the pathology of chronic cerebral hypoperfusion (CCH)-related neurodegenerative diseases. Continuous endothelial cells (EC) that line the blood vessels of the brain are important components of the BBB to strictly control the flow of substances and maintain the homeostatic environment of the brain. However, the molecular mechanisms from the perspective of EC-induced BBB dysfunction after CCH are largely unknown. In this study, the BBB function was assessed using immunostaining and transmission electron microscopy. The EC dysfunction profile was screened by using EC enrichment followed by RNA sequencing. After identified the key EC dysfunction factor, C-kit, we used the C-kit inhibition drug (imatinib) and C-kit down-regulation method (AAV-BR1-C-kit shRNA) to verify the role of C-kit on BBB integrity and EC transcytosis after CCH. Furthermore, we also activated C-kit with stem cell factor (SCF) to observe the effects of C-kit on BBB following CCH. We explored that macromolecular proteins entered the brain mainly through EC transcytosis after CCH and caused neuronal loss. Additionally, we identified receptor tyrosine kinase C-kit as a key EC dysfunction molecule. Furthermore, the pharmacological inhibition of C-kit with imatinib counteracted BBB leakage by reducing caveolae-mediated transcytosis. Moreover, treatment with AAV-BR1-C-kit shRNA, which targets brain EC to inhibit C-kit expression, also ameliorated BBB leakage by reducing caveolae-mediated transcytosis. Furthermore, the SCF increased the permeability of the BBB by actively increasing caveolae-mediated transcytosis. This study provides evidence that C-kit is a key BBB permeability regulator through caveolae-mediated transcytosis in EC after CCH.

Mitochondrial malfunction and atrophy of astrocytes in the aged human cerebral cortex

How aging affects cells of the human brain active milieu remains largely unknown. Here, we analyze astrocytes and neurons in the neocortical tissue of younger (22-50 years) and older (51-72 years) adults. Aging decreases the amount of reduced mitochondrial cytochromes in astrocytes but not neurons. The protein-to-lipid ratio decreases in astrocytes and increases in neurons. Aged astrocytes show morphological atrophy quantified by the decreased length of branches, decreased volume fraction of leaflets, and shrinkage of the anatomical domain. Atrophy correlates with the loss of gap junction coupling between astrocytes and increased input resistance. Aging is accompanied by the upregulation of glial fibrillary acidic protein (GFAP) and downregulation of membrane-cytoskeleton linker ezrin associated with leaflets. No significant changes in neuronal excitability or spontaneous inhibitory postsynaptic signaling is observed. Thus, brain aging is associated with the impaired morphological presence and mitochondrial malfunction of cortical astrocytes, but not neurons.

Mean Arterial Pressure and Cerebral Hemodynamics Across The Lifespan: A Cross-Sectional Study From Human Connectome Project-Aging

BACKGROUND

Cerebral perfusion is directly affected by systemic blood pressure, which has been shown to be negatively correlated with cerebral blood flow (CBF). The impact of aging on these effects is not fully understood.

PURPOSE

To determine whether the relationship between mean arterial pressure (MAP) and cerebral hemodynamics persists throughout the lifespan.

STUDY TYPE

Retrospective, cross-sectional study.

POPULATION

Six hundred and sixty-nine participants from the Human Connectome Project-Aging ranging between 36 and 100+ years and without a major neurological disorder.

FIELD STRENGTH/SEQUENCE

Imaging data was acquired at 3.0 Tesla using a 32-channel head coil. CBF and arterial transit time (ATT) were measured by multi-delay pseudo-continuous arterial spin labeling.

ASSESSMENT

The relationships between cerebral hemodynamic parameters and MAP were evaluated globally in gray and white matter and regionally using surface-based analysis in the whole group, separately within different age groups (young: <60 years; younger-old: 60-79 years; oldest-old: ≥80 years).

STATISTICAL TESTS

Chi-squared, Kruskal-Wallis, ANOVA, Spearman rank correlation and linear regression models. The general linear model setup in FreeSurfer was used for surface-based analyses. P < 0.05 was considered significant.

RESULTS

Globally, there was a significant negative correlation between MAP and CBF in both gray (ρ = -0.275) and white matter (ρ = -0.117). This association was most prominent in the younger-old [gray matter CBF (β = -0.271); white matter CBF (β = -0.241)]. In surface-based analyses, CBF exhibited a widespread significant negative association with MAP throughout the brain, whereas a limited number of regions showed significant prolongation in ATT with higher MAP. The associations between regional CBF and MAP in the younger-old showed a different topographic pattern in comparison to young subjects.

DATA CONCLUSION

These observations further emphasize the importance of cardiovascular health in mid-to-late adulthood for healthy brain aging. The differences in the topographic pattern with aging indicate a spatially heterogeneous relationship between high blood pressure and CBF.

LEVEL OF EVIDENCE

3 TECHNICAL EFFICACY STAGE: 3.

Heritability of cerebral blood flow in adolescent and young adult twins: an arterial spin labeling perfusion imaging study

Blood perfusion is a fundamental physiological property of all organs and is closely linked to brain metabolism. Genetic factors were reported to have important influences on cerebral blood flow. However, the profile of genetic contributions to cerebral blood flow in adolescents or young adults was underexplored. In this study, we recruited a sample of 65 pairs of same-sex adolescent or young adult twins undergoing resting arterial spin labeling imaging to conduct heritability analyses. Our findings indicate that genetic factors modestly affect cerebral blood flow in adolescents or young adults in the territories of left anterior cerebral artery and right posterior cerebral artery, with the primary contribution being to the frontal regions, cingulate gyrus, and striatum, suggesting a profile of genetic contributions to specific brain regions. Notably, the regions in the left hemisphere demonstrate the highest heritability in most regions examined. These results expand our knowledge of the genetic basis of cerebral blood flow in the developing brain and emphasize the importance of regional analysis in understanding the heritability of cerebral blood flow. Such insights may contribute to our understanding of the underlying genetic mechanism of brain functions and altered cerebral blood flow observed in youths with brain disorders.

Identification and quantification of (poly)phenol and methylxanthine metabolites in human cerebrospinal fluid: evidence of their ability to cross the BBB

Increasing evidence suggests that dietary (poly)phenols and methylxanthines have neuroprotective effects; however, little is known about whether they can cross the blood-brain barrier (BBB) and exert direct effects on the brain. We investigated the presence of (poly)phenol and methylxanthine metabolites in plasma and cerebrospinal fluid (CSF) from 90 individuals at risk of dementia using liquid chromatography-mass spectrometry and predicted their mechanism of transport across the BBB using in silico modelling techniques. A total of 123 and 127 metabolites were detected in CSF and plasma, respectively. In silico analysis suggests that 5 of the 20 metabolites quantified in CSF can cross the BBB by passive diffusion, while at least 9 metabolites require the aid of cell transporters to cross the BBB. Our results showed that (poly)phenols and methylxanthines are bioavailable, can cross the BBB via passive diffusion or transport carriers, and can reach brain tissues to exert neuroprotective effects.

Cerebral arterial flow dynamics during systole and diastole phases in young and older healthy adults

BACKGROUND

Since arterial flow is the leading actor in neuro-fluids flow dynamics, it might be interesting to assess whether it is meaningful to study the arterial flow waveform in more detail and whether this provides new important information. Few studies have focused on determining the influence of heart rate variation over time on the arterial flow curve. Therefore, this study aimed to evaluate cerebral arterial flow waveforms at extracranial and intracranial compartments in young and elderly healthy adults, also considering systole and diastole phases.

METHODS

Cine phase-contrast magnetic resonance imaging (CINE-PC MRI) was performed on twenty-eight healthy young volunteers (HYV) and twenty healthy elderly volunteers (HEV) to measure arterial blood flows at the extracranial and intracranial planes. A semi-automated protocol using MATLAB scripts was implemented to identify the main representative points in the arterial flow waveforms. Representative arterial profiles were estimated for each group. Moreover, the effects of age and sex on flow times, amplitude-related parameters, and parameters related to systole and diastole phases were evaluated at the extracranial and intracranial compartments. Student's t-test or Wilcoxon's test (depending on the normality of the distribution) was used to detect significant differences.

RESULTS

In HYVs, significant differences were observed between extracranial and intracranial levels in parameters related to the AP1 amplitude. Besides the detected differences in pulsatility index (extracranial: 0.92 ± 0.20 vs. 1.28 ± 0.33; intracranial: 0.79 ± 0.15 vs. 1.14 ± 0.18, p < .001) and average flow (715 ± 136 vs. 607 ± 125 ml/min, p = .008) between HYV and HEV, differences in the amplitude value of the arterial flow profile feature points were also noted. Contrary to systole duration (HYV: 360 ± 29 ms; HEV: 364 ± 47 ms), diastole duration presented higher inter-individual variability in both populations (HYV: 472 ± 145 ms; HEV: 456 ± 106 ms). Our results also showed that, with age, it is mainly the diastolic phase that changes. Although no significant differences in duration were observed between the two populations, the mean flow value in the diastolic phase was significantly lower in HEV (extracranial: 628 ± 128 vs. 457 ± 111 ml/min; intracranial: 599 ± 121 vs. 473 ± 100 ml/min, p < .001). No significant differences were observed in the arterial flow parameters evaluated between females and males in either HYV or HEV.

CONCLUSION

Our study provides a novel contribution on the influence of the cardiac cycle phases on cerebral arterial flow. The main contribution in this study concerns the identification of age-related alterations in cerebral blood flow, which occur mainly during the diastolic phase. Specifically, we observed that mean flow significantly decreases with age during diastole, whereas mean flow during systole is consistent.

Geometric versus Hemodynamic Indexes for Rupture-Destined Aneurysms: A Retrospective Cohort and a Repeated-Measures Study

INTRODUCTION

A proper stratification of intracranial aneurysms is critical in identifying rupture-destined aneurysms and unruptured intracranial aneurysms. We aimed to determine the utility of geometric and hemodynamic indexes in differentiating two types of aneurysms and to examine the characteristics of natural evolutionary changes of unruptured aneurysms.

METHODS

Rupture-destined aneurysm refers to an aneurysm that undergoes subsequent aneurysmal subarachnoid hemorrhage (SAH). On the other hand, an unruptured intracranial aneurysm is characterized by an aneurysm that does not experience rupture during serial time-of-flight magnetic resonance angiography (TOF-MRA). In addition to geometric indexes, signal intensity gradient (SIG), an in vivo approximated wall shear stress from TOF-MRA, was measured in aneurysms. The difference between the maximum and minimum values of SIG in an aneurysm compared to parent arterial values was designated as the delta-SIG ratio.

RESULTS

This study analyzed 20 rupture-destined aneurysms in 20 patients and 45 unruptured intracranial aneurysms in 41 patients with follow-up TOF-MRA. While geometric indexes did not show differences between the two groups, the delta-SIG ratio was higher in the rupture-destined aneurysms (1.5 ± 0.6 vs. 1.1 ± 0.3, p = 0.032). The delta-SIG ratio showed a higher area under the receiver operating characteristic curve for SAH than the size ratio (0.72 [95% CI, 0.58-0.87] vs. 0.56 [95% CI, 0.41-0.72], p = 0.033). The longitudinal re-examination of TOF-MRA in the unruptured intracranial aneurysms revealed evidence of aneurysmal growth, while concurrently exhibiting hemodynamic stability.

CONCLUSION

The delta-SIG ratio showed higher discriminatory results between the two groups compared to geometric indexes. Aneurysmal rupture risk should be assessed by considering both geometric and hemodynamic information. This study was registered on ClinicalTrials.gov (NCT05450939).

Gut microbiome association with brain imaging markers, APOE genotype, calcium and vegetable intakes, and obesity in healthy aging adults

Introduction

Advanced age is a significant factor in changes to brain physiology and cognitive functions. Recent research has highlighted the critical role of the gut microbiome in modulating brain functions during aging, which can be influenced by various factors such as apolipoprotein E (APOE) genetic variance, body mass index (BMI), diabetes, and dietary intake. However, the associations between the gut microbiome and these factors, as well as brain structural, vascular, and metabolic imaging markers, have not been well explored.

Methods

We recruited 30 community dwelling older adults between age 55-85 in Kentucky. We collected the medical history from the electronic health record as well as the Dietary Screener Questionnaire. We performed APOE genotyping with an oral swab, gut microbiome analysis using metagenomics sequencing, and brain structural, vascular, and metabolic imaging using MRI.

Results

Individuals with APOE e2 and APOE e4 genotypes had distinct microbiota composition, and higher level of pro-inflammatory microbiota were associated higher BMI and diabetes. In contrast, calcium- and vegetable-rich diets were associated with microbiota that produced short chain fatty acids leading to an anti-inflammatory state. We also found that important gut microbial butyrate producers were correlated with the volume of the thalamus and corpus callosum, which are regions of the brain responsible for relaying and processing information. Additionally, putative proinflammatory species were negatively correlated with GABA production, an inhibitory neurotransmitter. Furthermore, we observed that the relative abundance of bacteria from the family Eggerthellaceae, equol producers, was correlated with white matter integrity in tracts connecting the brain regions related to language, memory, and learning.

Discussion

These findings highlight the importance of gut microbiome association with brain health in aging population and could have important implications aimed at optimizing healthy brain aging through precision prebiotic, probiotic or dietary interventions.

Global effects of aging on the hemodynamic response function in the human brain

In functional magnetic resonance imaging, the hemodynamic response function (HRF) is a transient, stereotypical response to local changes in cerebral hemodynamics and oxygen metabolism due to briefly (< 4 s) evoked neural activity. Accordingly, the HRF is often used as an impulse response with the assumption of linearity in data analysis. In cognitive aging studies, it has been very common to interpret differences in brain activation as age-related changes in neural activity. Contrary to this assumption, however, evidence has accrued that normal aging may also significantly affect the vasculature, thereby affecting cerebral hemodynamics and metabolism, confounding interpretation of fMRI aging studies. In this study, use was made of a multisensory stimulus to evoke the HRF in ~ 87% of cerebral cortex in cognitively intact adults with ages ranging from 22-75 years. The stimulus evokes both positive and negative HRFs, which were characterized using model-free parameters in native-space coordinates. Results showed significant age trends in HRF parameter distributions in terms of both amplitudes (e.g., peak amplitude and CNR) and temporal dynamics (e.g., full-width-at-half-maximum). This work sets the stage for using HRF methods as a biomarker for age-related pathology.

Influence of end-tidal CO2 on cerebral blood flow during orthostatic stress in controls and adults with myalgic encephalomyelitis/chronic fatigue syndrome

Brain perfusion is sensitive to changes in CO2 levels (CO2 reactivity). Previously, we showed a pathological cerebral blood flow (CBF) reduction in the majority of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) patients during orthostatic stress. Limited data are available on the relation between CO2 and CBF changes in ME/CFS patients. Therefore, we studied this relation between ME/CFS patients and healthy controls (HC) during tilt testing. In this retrospective study, supine and end-tilt CBF, as measured by extracranial Doppler flow, were compared with PET CO2 data in female patients either with a normal heart rate and blood pressure (HR/BP) response or with postural orthostatic tachycardia syndrome (POTS), and in HC. Five hundred thirty-five female ME/CFS patients and 34 HC were included. Both in supine position and at end-tilt, there was a significant relation between CBF and PET CO2 in patients (p < 0.0001), without differences between patients with a normal HR/BP response and with POTS. The relations between the %CBF change and the PET CO2 reduction were both significant in patients and HC (p < 0.0001 and p = 0.0012, respectively). In a multiple regression analysis, the patient/HC status and PET CO2 predicted CBF. The contribution of the PET CO2 to CBF changes was limited, with low adjusted R2 values. In female ME/CFS patients, CO2 reactivity, as measured during orthostatic stress testing, is similar to that of HC and is independent of the type of hemodynamic abnormality. However, the influence of CO2 changes on CBF changes is modest in female ME/CFS patients.

Preliminary cross-sectional investigations into the human glymphatic system using multiple novel non-contrast MRI methods

We discuss two potential non-invasive MRI methods to cross-sectionally study two distinct facets of the glymphatic system and its association with sleep and aging. We apply diffusion-based intravoxel incoherent motion (IVIM) imaging to evaluate pseudodiffusion coefficient, D * , or cerebrospinal fluid (CSF) movement across large spaces like the subarachnoid space (SAS). We also performed perfusion-based multi-echo, Hadamard encoded multi-delay arterial spin labeling (ASL) to evaluate whole brain cortical cerebral blood flow (CBF) and transendothelial exchange (Tex) of water from the vasculature into the perivascular space and parenchyma. Both methods were used in young adults (N=9, 6F, 23±3 years old) in the setting of sleep and sleep deprivation. To study aging, 10 older adults, (6F, 67±3 years old) were imaged after a night of normal sleep only and compared with the young adults. D * in SAS was significantly (p<0.05) lesser after sleep deprivation (0.014±0.001 mm2/s) than after normal sleep (0.016±0.001 mm2/s), but was unchanged with aging. Cortical CBF and Tex on the other hand, were unchanged after sleep deprivation but were significantly lower in older adults (37±3 ml/100g/min, 476±66 ms) than young adults (42±2 ml/100g/min, 624±66 ms). IVIM was thus, sensitive to sleep physiology and multi-echo, multi-delay ASL was sensitive to aging.

Faster Walking Speeds Require Greater Activity from the Primary Motor Cortex in Older Adults Compared to Younger Adults

Gait speed declines with age and slower walking speeds are associated with poor health outcomes. Understanding why we do not walk faster as we age, despite being able to, has implications for rehabilitation. Changes in regional oxygenated haemoglobin (HbO2) across the frontal lobe were monitored using functional near infrared spectroscopy in 17 young and 18 older adults while they walked on a treadmill for 5 min, alternating between 30 s of walking at a preferred and fast (120% preferred) speed. Gait was quantified using a triaxial accelerometer (lower back). Differences between task (preferred/fast) and group (young/old) and associations between regional HbO2 and gait were evaluated. Paired tests indicated increased HbO2 in the supplementary motor area (right) and primary motor cortex (left and right) in older adults when walking fast (p < 0.006). HbO2 did not significantly change in the young when walking fast, despite both groups modulating gait. When evaluating the effect of age (linear mixed effects model), greater increases in HbO2 were observed for older adults when walking fast (prefrontal cortex, premotor cortex, supplementary motor area and primary motor cortex) compared to young adults. In older adults, increased step length and reduced step length variability were associated with larger increases in HbO2 across multiple regions when walking fast. Walking fast required increased activation of motor regions in older adults, which may serve as a therapeutic target for rehabilitation. Widespread increases in HbO2 across the frontal cortex highlight that walking fast represents a resource-intensive task as we age.

Brain perfusion, cognition, and plasma Alzheimer's biomarkers in moyamoya disease

INTRODUCTION

Because growing interest has been focusing on cerebral blood flow (CBF) to predict, prevent, and treat Alzheimer's disease (AD), it is important to clarify the role of CBF in AD pathology and cognitive decline.

METHODS

In a moyamoya disease (MMD) cohort, we examined CBF, specific cognitive domains, and plasma AD biomarkers, as well as correlations among these variables.

RESULTS

CBF was significantly reduced in newly diagnosed MMD patients, while plasma phosphorylated tau181 was elevated and positively correlated with hypoperfusion accumulation. MMD patients scored significantly lower than controls in multiple cognitive tests. Revascularization increased CBF to the recipient brain territories as well as cognitive performance but produced no significant change in AD biomarker levels.

DISCUSSION

These data suggest a link between accumulated reductions in CBF and cognitive decline, as well as a possible role of AD-like pathological burden. Further studies in MMD will provide opportunities to explore new treatment strategies.

Lipopolysaccharide-Induced Delirium-like Behaviour in a Rat Model of Chronic Cerebral Hypoperfusion Is Associated with Increased Indoleamine 2,3-Dioxygenase Expression and Endotoxin Tolerance

Indoleamine 2,3-dioxygenase (IDO) and the tryptophan-kynurenine pathway (TRP-KP) are upregulated in ageing and could be implicated in the pathogenesis of delirium. This study evaluated the role of IDO/KP in lipopolysaccharide (LPS)-induced delirium in an animal model of chronic cerebral hypoperfusion (CCH), a proposed model for delirium. CCH was induced by a permanent bilateral common carotid artery ligation (BCCAL) in Sprague Dawley rats to trigger chronic neuroinflammation-induced neurodegeneration. Eight weeks after permanent BCCAL, the rats were treated with a single systemic LPS. The rats were divided into three groups: (1) post-BCCAL rats treated with intraperitoneal (i.p.) saline, (2) post-BCCAL rats treated with i.p. LPS 100 μg/kg, and (3) sham-operated rats treated with i.p. LPS 100 μg/kg. Each group consisted of 10 male rats. To elucidate the LPS-induced delirium-like behaviour, natural and learned behaviour changes were assessed by a buried food test (BFT), open field test (OFT), and Y-maze test at 0, 24-, 48-, and 72 h after LPS treatment. Serum was collected after each session of behavioural assessment. The rats were euthanised after the last serum collection, and the hippocampi and cerebral cortex were collected. The TRP-KP neuroactive metabolites were measured in both serum and brain tissues using ELISA. Our data show that LPS treatment in CCH rats was associated with acute, transient, and fluctuated deficits in natural and learned behaviour, consistent with features of delirium. These behaviour deficits were mild compared to the sham-operated rats, which exhibited robust behaviour impairments. Additionally, heightened hippocampal IDO expression in the LPS-treated CCH rats was associated with reduced serum KP activity together with a decrease in the hippocampal quinolinic acid (QA) expression compared to the sham-operated rats, suggested for the presence of endotoxin tolerance through the immunomodulatory activity of IDO in the brain. These data provide new insight into the underlying mechanisms of delirium, and future studies should further explore the role of IDO modulation and its therapeutic potential in delirium.

The multifactorial nature of healthy brain ageing: Brain changes, functional decline and protective factors

As the global population faces a progressive shift towards a higher median age, understanding the mechanisms underlying healthy brain ageing has become of paramount importance for the preservation of cognitive abilities. The first part of the present review aims to provide a comprehensive look at the anatomical changes the healthy brain endures with advanced age, while also summarizing up to date findings on modifiable risk factors to support a healthy ageing process. Subsequently, we describe the typical cognitive profile displayed by healthy older adults, conceptualizing the well-established age-related decline as an impairment of four main cognitive factors and relating them to their neural substrate previously described; different cognitive trajectories displayed by typical Alzheimer's Disease patients and successful agers with a high cognitive reserve are discussed. Finally, potential effective interventions and protective strategies to promote cognitive reserve and defer cognitive decline are reviewed and proposed.

Age-dependent dysfunction of the cerebrovascular system in the zebrafish telencephalon

The brain is an essential organ that controls various biological activities via the nervous system. The cerebral blood vessels supply oxygen and nutrients to neuronal cells and carry away waste products, which is essential in maintaining brain functions. Aging affects cerebral vascular function and decreases brain function. However, the physiological process of age-dependent cerebral vascular dysfunction is not fully understood. In this study, we examined aging effects on cerebral vascular patterning, vascular function, and learning ability in adult zebrafish. We found that the tortuosity of the blood vessels was increased, and the blood flow rate was reduced with aging in the zebrafish dorsal telencephalon. Moreover, we found cerebral blood flow positively correlated with learning ability in middle-old-aged zebrafish, as in aged humans. In addition, we also found that the elastin fiber decreased in the middle-old-aged fish brain vessel, suggesting a possible molecular mechanism underlying vessel dysfunction. Therefore, adult zebrafish may serve as a useful model for studying the aging-dependent decline in vascular function and human diseases such as vascular dementia.

Changes in white matter functional networks across late adulthood

Introduction

The aging brain is characterized by decreases in not only neuronal density but also reductions in myelinated white matter (WM) fibers that provide the essential foundation for communication between cortical regions. Age-related degeneration of WM has been previously characterized by histopathology as well as T2 FLAIR and diffusion MRI. Recent studies have consistently shown that BOLD (blood oxygenation level dependent) effects in WM are robustly detectable, are modulated by neural activities, and thus represent a complementary window into the functional organization of the brain. However, there have been no previous systematic studies of whether or how WM BOLD signals vary with normal aging. We therefore performed a comprehensive quantification of WM BOLD signals across scales to evaluate their potential as indicators of functional changes that arise with aging.

Methods

By using spatial independent component analysis (ICA) of BOLD signals acquired in a resting state, WM voxels were grouped into spatially distinct functional units. The functional connectivities (FCs) within and among those units were measured and their relationships with aging were assessed. On a larger spatial scale, a graph was reconstructed based on the pair-wise connectivities among units, modeling the WM as a complex network and producing a set of graph-theoretical metrics.

Results

The spectral powers that reflect the intensities of BOLD signals were found to be significantly affected by aging across more than half of the WM units. The functional connectivities (FCs) within and among those units were found to decrease significantly with aging. We observed a widespread reduction of graph-theoretical metrics, suggesting a decrease in the ability to exchange information between remote WM regions with aging.

Discussion

Our findings converge to support the notion that WM BOLD signals in specific regions, and their interactions with other regions, have the potential to serve as imaging markers of aging.

Dynamic Volumetric Imaging of Mouse Cerebral Blood Vessels In Vivo with an Ultralong Anti-Diffracting Beam

Volumetric imaging of a mouse brain in vivo with one-photon and two-photon ultralong anti-diffracting (UAD) beam illumination was performed. The three-dimensional (3D) structure of blood vessels in the mouse brain were mapped to a two-dimensional (2D) image. The speed of volumetric imaging was significantly improved due to the long focal length of the UAD beam. Comparing one-photon and two-photon UAD beam volumetric imaging, we found that the imaging depth of two-photon volumetric imaging (80 μm) is better than that of one-photon volumetric imaging (60 μm), and the signal-to-background ratio (SBR) of two-photon volumetric imaging is two times that of one-photon volumetric imaging. Therefore, we used two-photon UAD volumetric imaging to perform dynamic volumetric imaging of mouse brain blood vessels in vivo, and obtained the blood flow velocity.

Possible molecular mechanisms underlying the development of atherosclerosis in cancer survivors

Cancer survivors undergone treatment face an increased risk of developing atherosclerotic cardiovascular disease (CVD), yet the underlying mechanisms remain elusive. Recent studies have revealed that chemotherapy can drive senescent cancer cells to acquire a proliferative phenotype known as senescence-associated stemness (SAS). These SAS cells exhibit enhanced growth and resistance to cancer treatment, thereby contributing to disease progression. Endothelial cell (EC) senescence has been implicated in atherosclerosis and cancer, including among cancer survivors. Treatment modalities for cancer can induce EC senescence, leading to the development of SAS phenotype and subsequent atherosclerosis in cancer survivors. Consequently, targeting senescent ECs displaying the SAS phenotype hold promise as a therapeutic approach for managing atherosclerotic CVD in this population. This review aims to provide a mechanistic understanding of SAS induction in ECs and its contribution to atherosclerosis among cancer survivors. We delve into the mechanisms underlying EC senescence in response to disturbed flow and ionizing radiation, which play pivotal role in atherosclerosis and cancer. Key pathways, including p90RSK/TERF2IP, TGFβR1/SMAD, and BH4 signaling are explored as potential targets for cancer treatment. By comprehending the similarities and distinctions between different types of senescence and the associated pathways, we can pave the way for targeted interventions aim at enhancing the cardiovascular health of this vulnerable population. The insights gained from this review may facilitate the development of novel therapeutic strategies for managing atherosclerotic CVD in cancer survivors.

Aging drives cerebrovascular network remodeling and functional changes in the mouse brain

Aging is the largest risk factor for neurodegenerative disorders, and commonly associated with compromised cerebrovasculature and pericytes. However, we do not know how normal aging differentially impacts the vascular structure and function in different brain areas. Here we utilize mesoscale microscopy methods (serial two-photon tomography and light sheet microscopy) and in vivo imaging (wide field optical spectroscopy and two-photon imaging) to determine detailed changes in aged cerebrovascular networks. Whole-brain vascular tracing showed an overall ~10% decrease in vascular length and branching density, and light sheet imaging with 3D immunolabeling revealed increased arteriole tortuosity in aged brains. Vasculature and pericyte densities showed significant reductions in the deep cortical layers, hippocampal network, and basal forebrain areas. Moreover, in vivo imaging in awake mice identified delays in neurovascular coupling and disrupted blood oxygenation. Collectively, we uncover regional vulnerabilities of cerebrovascular network and physiological changes that can mediate cognitive decline in normal aging.

Large-Scale Network Connectivity and Cognitive Function Changes After Exercise Training in Older Adults with Intact Cognition and Mild Cognitive Impairment

Background

Despite growing evidence regarding the association between exercise training (ET) and functional brain network connectivity, little is known about the effects of ET on large-scale within- and between-network functional connectivity (FC) of core brain networks.

Objective

We investigated the effects of ET on within- and between-network functional connectivity of the default mode network (DMN), frontoparietal network (FPN), and salience network (SAL) in older adults with intact cognition (CN) and older adults diagnosed with mild cognitive impairment (MCI). The association between ET-induced changes in FC and cognitive performance was examined.

Methods

33 older adults (78.0±7.0 years; 16 MCI and 17 CN) participated in this study. Before and after a 12-week walking ET intervention, participants underwent a graded exercise test, Controlled Oral Word Association Test (COWAT), Rey Auditory Verbal Learning Test (RAVLT), a narrative memory test (logical memory; LM), and a resting-state fMRI scan. We examined the within (_W) and between (_B) network connectivity of the DMN, FPN, and SAL. We used linear regression to examine associations between ET-related changes in network connectivity and cognitive function.

Results

There were significant improvements in cardiorespiratory fitness, COWAT, RAVLT, and LM after ET across participants. Significant increases in DMN_W and SAL_W, and DMN-FPN_B, DMN-SAL_B, and FPN-SAL_B were observed after ET. Greater SAL_W and FPN-SAL_B were associated with enhanced LM immediate recall performance after ET in both groups.

Conclusion

Increased within- and between-network connectivity following ET may subserve improvements in memory performance in older individuals with intact cognition and with MCI due to Alzheimer's disease.

Normative Cerebral Hemodynamics in Middle-aged and Older Adults Using 4D Flow MRI: Initial Analysis of Vascular Aging

Background Characterizing cerebrovascular hemodynamics in older adults is important for identifying disease and understanding normal neurovascular aging. Four-dimensional (4D) flow MRI allows for a comprehensive assessment of cerebral hemodynamics in a single acquisition. Purpose To establish reference intracranial blood flow and pulsatility index values in a large cross-sectional sample of middle-aged (45-65 years) and older (>65 years) adults and characterize the effect of age and sex on blood flow and pulsatility. Materials and Methods In this retrospective study, patients aged 45-93 years (cognitively unimpaired) underwent cranial 4D flow MRI between March 2010 and March 2020. Blood flow rates and pulsatility indexes from 13 major arteries and four venous sinuses and total cerebral blood flow were collected. Intraobserver and interobserver reproducibility of flow and pulsatility measures was assessed in 30 patients. Descriptive statistics (mean ± SD) of blood flow and pulsatility were tabulated for the entire group and by age and sex. Multiple linear regression and linear mixed-effects models were used to assess the effect of age and sex on total cerebral blood flow and vessel-specific flow and pulsatility, respectively. Results There were 759 patients (mean age, 65 years ± 8 [SD]; 506 female patients) analyzed. For intra- and interobserver reproducibility, median intraclass correlation coefficients were greater than 0.90 for flow and pulsatility measures across all vessels. Regression coefficients β ± standard error from multiple linear regression showed a 4 mL/min decrease in total cerebral blood flow each year (age β = -3.94 mL/min per year ± 0.44; P < .001). Mixed effects showed a 1 mL/min average annual decrease in blood flow (age β = -0.95 mL/min per year ± 0.16; P < .001) and 0.01 arbitrary unit (au) average annual increase in pulsatility over all vessels (age β = 0.011 au per year ± 0.001; P < .001). No evidence of sex differences was observed for flow (β = -1.60 mL/min per male patient ± 1.77; P = .37), but pulsatility was higher in female patients (sex β = -0.018 au per male patient ± 0.008; P = .02). Conclusion Normal reference values for blood flow and pulsatility obtained using four-dimensional flow MRI showed correlations with age. © RSNA, 2023 Supplemental material is available for this article. See also the editorial by Steinman in this issue.

Effects of 12-week Tai Chi program on physical function, depression, and quality of life among cognitively impaired older adults: a feasibility study

BACKGROUND

Older adults with cognitive decline need physical activity for maintaining brain health and mitigating cognitive decline. Tai Chi is a safe and gentle aerobic exercise and has been recommended for people with various health conditions to improve their physical functioning, well-being, and quality of life (QoL). This study aimed to determine the feasibility of a 12-week program of Tai Chi for memory (TCM) among older adults with mild cognitive impairment (MCI) or dementia; and to determine the pilot effects of TCM on physical functioning, depression, and health-related QoL.

METHODS

A quasi-experimental design was used with two groups: MCI and dementia. The feasibility of the 12-week TCM program was assessed after it finished in terms of its acceptability, demand, implementation, practicality, adaptation, integration, expansion, and limited-efficacy testing. Other health-related outcomes, physical functioning, depression, and health-related QoL were measured before and after the TCM program. Outcome measures consist of a digital hand dynamometer for grip strength, the standard sit-and-reach test, the one-leg-standing balance test, timed up and go (TUG) test, the Korean version of the Geriatric Depression Scale, and the 12-item Short Form survey (SF-12). Paired and independent t-tests were used to compare the effects of TCM within and between groups.

RESULTS

The TCM program was completed by 41 participants with MCI (n = 21) or dementia (n = 20), and its accepted feasibility was assessed. After TCM, the MCI group exhibited significant enhancements in right-hand grip strength (t = - 2.13, p = .04) and physical-health-related QoL (t = - 2.27, p = .03). TUG scores improved in both groups (MCI, t = 3.96 p = .001; dementia, t = 2.54 p = .02). The adopted form of the TCM program was effectively and safely applied to those with various levels of cognitive impairment. The program was well accepted by the participants with a mean attendance rate of 87%. No adverse events were reported during the program.

CONCLUSION

TCM has the potential to improve physical functioning and QoL. Since there was no comparison group to control for confounding factors and low statistical power in the present study, further studies are warranted with a stronger design that includes longer follow-up periods. This protocol was retrospectively registered on Dec 1, 2022 (NCT05629650) at ClinicalTrials.gov.

The association of executive functions and physical fitness with cognitive-motor multitasking in a street crossing scenario

Age-related decline in cognitive-motor multitasking performance has been attributed to declines in executive functions and physical fitness (motor coordinative fitness and cardiovascular fitness). It has been suggested that those cognitive and physical resources strongly depend on lifestyle factors such as long-term regular physical activity and cognitive engagement. Although research suggests that there is covariation between components of executive functions and physical fitness, the interdependence between these components for cognitive-motor multitasking performance is not yet clear. The aim of the study was to examine the contribution and interrelationship between executive functions, motor coordinative fitness, and cardiovascular fitness on street crossing while multitasking. We used the more ecologically valid scenario to obtain results that might be directly transferable to daily life situation. Data from 50 healthy older adults (65-75 years, 17 females, recruited in two different cities in Germany) were analyzed. Participants' executive functions (composite score including six tests), motor coordinative fitness (composite score including five tests), and cardiovascular fitness (spiroergometry), as well as their street crossing performance while multitasking were assessed. Street crossing was tested under single-task (crossing a two-line road), and multitask conditions (crossing a two-line road while typing numbers on a keypad as simulation of mobile phone use). Street crossing performance was assessed by use of cognitive outcomes (typing, crossing failures) and motor outcomes (stay time, crossing speed). Linear mixed-effects models showed beneficial main effects of executive functions for typing (p = 0.004) and crossing failures (p = 0.023), and a beneficial main effect of motor coordinative fitness for stay time (p = 0.043). Commonality analysis revealed that the proportion of variance commonly explained by executive functions, motor coordinative fitness, and cardiovascular fitness was small for all street crossing outcomes. For typing and crossing failures (cognitive outcomes), the results further showed a higher relative contribution of executive functions compared to motor coordinative fitness and cardiovascular fitness. For stay time (motor outcome), the results correspondingly revealed a higher relative contribution of motor coordinative fitness compared to executive functions and cardiovascular fitness. The findings suggest that during cognitive-motor multitasking in everyday life, task performance is determined by the components of executive functions and physical fitness related to the specific task demands. Since multitasking in everyday life includes cognitive and motor tasks, it seems to be important to maintain both executive functions and physical fitness for independent living up to old age.

Effect of Baduanjin exercise on cerebral blood flow and cognitive frailty in the community older adults with cognitive frailty: A randomized controlled trial

Objectives

Regular Baduanjin exercise training has been shown to be beneficial to the physical and cognitive health of older adults, but the underlying mechanisms remain to be investigated. This study examined the influence of Baduanjin on cerebral hemodynamics in community-dwelling older adults with cognitive frailty.

Design

Randomized controlled trial.

Methods

A total of 102 eligible participants were randomly allocated into the Baduanjin exercise intervention group (BEG) or usual physical activity control group (CG) for 24 weeks. Cerebral hemodynamic parameters of bilateral middle/anterior cerebral artery and basilar artery, cognitive ability and physical frailty were assessed using Transcranial Doppler (TCD), Montreal Cognitive Assessment (MoCA) and Edmonton Frailty Scale (EFS) at baseline and 24 weeks post-intervention.

Results

After 24 weeks intervention, the changes in peak systolic velocity (PSV), mean blood flow velocity (MBFV), and end diastolic velocity (EDV) in the right middle cerebral artery and basilar artery were better in the BEG than in the CG; the increase in MoCA scores and the decrease in EFS scores were significantly higher in the BEG than in the CG. Moreover, the interaction of exercise and time on those variables showed obvious significance.

Conclusions

The 24 weeks Baduanjin exercise training had a positive beneficial effect on cerebral blood flow in community-dwelling older adults with cognitive frailty. This may be a potential mechanism by which Baduanjin exercise improves the cognitive frailty in older adults.

Trial registration

Chinese Clinical Trial Registry, ChiCTR1800020341.

Date of registration

December 25, 2018, http://www.chictr.org.cn/showproj.aspx?proj=29846.

Modifiable risk factors of dementia linked to excitation-inhibition imbalance

Recent evidence identifies 12 potentially modifiable risk factors for dementia to which 40% of dementia cases are attributed. While the recognition of these risk factors has paved the way for the development of new prevention measures, the link between these risk factors and the underlying pathophysiology of dementia is yet not well understood. A growing number of recent clinical and preclinical studies support a role of Excitation-Inhibition (E-I) imbalance in the pathophysiology of dementia. In this review, we aim to propose a conceptual model on the links between the modifiable risk factors and the E-I imbalance in dementia. This model, which aims to address the current gap in the literature, is based on 12 mediating common mechanisms: the hypothalamic-pituitary-adrenal (HPA) axis dysfunction, neuroinflammation, oxidative stress, mitochondrial dysfunction, cerebral hypo-perfusion, blood-brain barrier (BBB) dysfunction, beta-amyloid deposition, elevated homocysteine level, impaired neurogenesis, tau tangles, GABAergic dysfunction, and glutamatergic dysfunction. We believe this model serves as a framework for future studies in this field and facilitates future research on dementia prevention, discovery of new biomarkers, and developing new interventions.

Neurovascular correlates of retinal microvascular caliber in adolescent bipolar disorder

BACKGROUND

The connection between vascular and brain metrics is well-studied in older adults, but neglected in youth and in psychiatric populations at increased cardiovascular risk. We therefore examined the association of retinal vascular caliber with cerebral blood flow (CBF) in adolescents with and without bipolar disorder (BD).

METHODS

Ninety-four adolescents (n = 48 BD, n = 46 controls) completed retinal fundus imaging, yielding estimates of arteriolar and venular diameter. Arterial spin labelling MRI was performed to measure CBF. We tested for associations between retinal vascular caliber and CBF in regions of interest; anterior cingulate cortex (ACC), middle frontal gyrus, and hippocampus in BD and controls separately. Complementary voxel-wise analyses were also performed.

RESULTS

In the BD group, higher arteriovenous ratio (AVR) was associated with greater ACC CBF (β = 0.34, p_uncorrected = 0.02), after controlling for age, sex, and BMI, however this finding did not survive correction for multiple comparisons. The control group did not show any associations (β = 0.13, p_uncorrected = 0.40). Voxel-wise analyses within the BD group detected a significant positive association between AVR and regional CBF in two distinct clusters: i) left hippocampus (p < 0.0001); ii) right middle temporal gyrus (p = 0.04).

LIMITATIONS

Limited sample size; young, medically healthy sample limits signal detection; cross-sectional design.

CONCLUSION

This study reveals that higher AVR is associated with higher regional CBF in adolescents with BD. Present findings advance understanding of potential neurofunctional mechanisms linking retinal vascular caliber with psychiatric diagnoses. This proof-of-concept study was designed to generate initial insights to guide future studies focusing on the vascular-brain connection in youth and in psychiatry.

Effects of preventive interventions on neuroimaging biomarkers in subjects at-risk to develop Alzheimer's disease: A systematic review

Alzheimer's Disease (AD) is a multifactorial and complex neurodegenerative disorder. Some modifiable risk factors have been associated with an increased risk of appearance of the disease and/or cognitive decline. Preventive clinical trials aiming at reducing one or combined risk factors have been implemented and their potential effects assessed on cognitive trajectories and on AD biomarkers. However, the effect of interventions on surrogate markers, in particular imaging biomarkers, remains poorly understood. We conducted a review of the literature and analyzed 43 interventional studies that included physical exercise, nutrition, cognitive training or multidomain interventions, and assessed various brain imaging biomarkers, to determine the effects of preventive interventions on imaging biomarkers for subjects at-risk to develop AD. Deciphering the global and regional brain effect of each and combined interventions will help to better understand the interplay relationship between multimodal interventions, cognition, surrogate brain markers, and to better design primary and secondary outcomes for future preventive clinical trials. Those studies were pondered using generally-admitted quality criteria to reveal that interventions may affect the brain of patients with cognitive impairment rather than those without cognitive impairment thus indicating that particular care should be taken when selecting individuals for interventions. Additionally, a majority of the studies concurred on the effect of the interventions and particularly onto the frontal brain areas.

Aerobic exercise training reduces cerebrovascular impedance in older adults: a 1-year randomized controlled trial

Older adults have higher cerebrovascular impedance than young individuals which may contribute to chronic brain hypoperfusion. Besides, middle-aged athletes exhibit lower cerebrovascular impedance than their sedentary peers. We examined whether aerobic exercise training (AET) reduces cerebrovascular impedance in sedentary older adults. We conducted a proof-of-concept trial that randomized 73 older adults to 1 yr of AET (n = 36) or stretching and toning (SAT, n = 37) interventions. Cerebrovascular impedance was estimated from simultaneous recordings of carotid artery pressure (CAP) via applanation tonometry and cerebral blood flow velocity (CBFV) in the middle cerebral artery via transcranial Doppler using transfer function analysis. Fifty-six participants completed 1-yr interventions, and 41 of those completed cerebrovascular impedance measurements. AET group showed a significant increase in V̇o2peak after the intervention [estimated marginal mean (95% confidence interval); from 22.8 (21.6 to 24.1) to 24.9 (23.6 to 26.2) mL·kg-1·cm-1, P < 0.001], but not SAT [from 21.7 (20.5 to 22.9) to 22.3 (21.1 to 23.7) mL·kg-1·cm-1, P = 0.114]. Coherence between changes in CBFV and CAP was >0.90 in the frequency range of 0.78-3.12 Hz. The averaged cerebrovascular impedance modulus (Z) in this frequency range decreased after 1-yr AET [from 1.05 (0.96 to 1.14) to 0.95 (0.92 to 1.06) mmHg·s·cm-1, P = 0.023], but not SAT [from 0.96 (0.87 to 1.04) to 1.01 (0.92 to 1.10) mmHg·s·cm-1, P = 0.138]. Reductions in Z were correlated positively with reductions in carotid pulse pressure (r = 0.628, P = 0.004) and inversely with mean CBFV (r = -0.563, P = 0.012) in the AET group. One-year AET reduces cerebrovascular impedance in older adults, which may benefit brain perfusion.NEW & NOTEWORTHY Estimation of cerebrovascular impedance is essential for understanding dynamic cerebral blood flow regulation. This randomized controlled trial demonstrated that aerobic exercise training reduced cerebrovascular impedance in older adults, which may benefit brain perfusion.

Cerebral blood flow predicts multiple demand network activity and fluid intelligence across the adult lifespan

The preservation of cognitive function in old age is a public health priority. Cerebral hypoperfusion is a hallmark of dementia but its impact on maintaining cognitive ability across the lifespan is less clear. We investigated the relationship between baseline cerebral blood flow (CBF) and blood oxygenation level-dependent (BOLD) response during a fluid reasoning task in a population-based adult lifespan cohort. As age differences in CBF could lead to non-neuronal contributions to the BOLD signal, we introduced commonality analysis to neuroimaging to dissociate performance-related CBF effects from the physiological confounding effects of CBF on the BOLD response. Accounting for CBF, we confirmed that performance- and age-related differences in BOLD responses in the multiple-demand network were implicated in fluid reasoning. Age differences in CBF explained not only performance-related BOLD responses but also performance-independent BOLD responses. Our results suggest that CBF is important for maintaining cognitive function, while its non-neuronal contributions to BOLD signals reflect an age-related confound. Maintaining perfusion into old age may serve to support brain function and preserve cognitive performance.

Cerebral Blood Flow Alterations and Obesity: A Systematic Review and Meta-Analysis

Background: Reduction in cerebral blood flow (CBF) plays an essential role in the cognitive impairment and dementia in obesity. However, current conclusions regarding CBF changes in patients with obesity are inconsistent. Objective: A systematic review and meta-analysis was performed to evaluate the relationship between obesity and CBF alterations. Methods: We systematically screened published cross-sectional and longitudinal studies focusing on the differences in CBF between obese and normal-weight individuals. Eighteen studies including 24,866 participants, of which seven articles reported longitudinal results, were evaluated in the present study. Results: The results of the meta-analysis showed that in cross-sectional studies, body mass index (BMI) was negatively associated with CBF (β= –0.31, 95% confidence interval [CI]: –0.44, –0.19). Moreover, this systematic review demonstrated that obese individuals showed global and regional reductions in the CBF and increased CBF in diverse functional areas of the frontal lobe, including the prefrontal cortex, left frontal superior orbital, right frontal mid-orbital cortex, and left premotor superior frontal gyrus. Conclusion: Our findings suggest that BMI, rather than waist circumference and waist-to-hip ratio, is inversely associated with CBF in cross-sectional studies. The CBF of obese individuals showed global and regional reductions, including the frontal lobe, temporal and parietal lobes, cerebellum, hippocampus, and thalamus.

Acute inorganic nitrate intake increases regional insulin action in the brain: Results of a double-blind, randomized, controlled cross-over trial with abdominally obese men

AIMS

Improving brain insulin sensitivity may be a promising approach in the prevention and treatment of metabolic and cognitive diseases. Our aim was to investigate acute effects of inorganic nitrate on regional cerebral blood flow (CBF) responses to intranasal insulin in abdominally obese men.

METHODS

Eighteen apparently healthy men, aged 18-60 years and with a waist circumference ≥ 102 cm, participated in a randomized, double-blind, placebo-controlled cross-over trial. The study consisted of two test days separated by at least one week. Men received in random order a drink providing 10 mmol (i.e., 625 mg nitrate) potassium nitrate or an isomolar placebo drink with potassium chloride. Brain insulin action was assessed 120-150 min after the drinks by quantifying acute effects of nasal insulin on regional CBF using arterial spin labeling Magnetic Resonance Imaging. Glucose and insulin concentrations were measured at regular intervals, while blood pressure was determined fasted and at 240 min.

RESULTS

Inorganic nitrate intake increased regional insulin action in five brain clusters. The two largest clusters were located in the right temporal lobe (ΔCBF: 7.0 ± 3.8 mL/100 g/min, volume: 5296 mm³, P < 0.001; and ΔCBF: 6.5 ± 4.3 mL/100 g/min, volume: 3592 mm³, P < 0.001), while two other cortical clusters were part of the right frontal (ΔCBF: 9.0 ± 6.0 mL/100 g/min, volume: 1096 mm³, P = 0.007) and the left parietal lobe (ΔCBF: 6.1 ± 4.3 mL/100 g/min, volume: 1024 mm³, P = 0.012). One subcortical cluster was located in the striatum (ΔCBF: 5.9 ± 3.2 mL/100 g/min, volume: 1792 mm³, P < 0.001). No effects of nitrate were observed on CBF before administration. Following nitrate intake, circulating nitrate plus nitrite concentrations increased over time (P = 0.003), but insulin and glucose concentrations and blood pressure did not change.

CONCLUSION

Acute inorganic nitrate intake may improve regional brain insulin action in abdominally obese men. These regions are involved in the regulation of different metabolic and cognitive processes. The trial was registered on January 6th, 2021 at ClinicalTrials.gov as NCT04700241.

Implementation of exercise countermeasures during spaceflight and microgravity analogue studies: Developing countermeasure protocols for bedrest in older adults (BROA)

Significant progress has been made in the development of countermeasures to attenuate the negative consequences of prolonged exposure to microgravity on astronauts’ bodies. Deconditioning of several organ systems during flight includes losses to cardiorespiratory fitness, muscle mass, bone density and strength. Similar deconditioning also occurs during prolonged bedrest; any protracted time immobile or inactive, especially for unwell older adults (e.g., confined to hospital beds), can lead to similar detrimental health consequences. Due to limitations in physiological research in space, the six-degree head-down tilt bedrest protocol was developed as ground-based analogue to spaceflight. A variety of exercise countermeasures have been tested as interventions to limit detrimental changes and physiological deconditioning of the musculoskeletal and cardiovascular systems. The Canadian Institutes of Health Research and the Canadian Space Agency recently provided funding for research focused on Understanding the Health Impact of Inactivity to study the efficacy of exercise countermeasures in a 14-day randomized clinical trial of six-degree head-down tilt bedrest study in older adults aged 55–65 years old (BROA). Here we will describe the development of a multi-modality countermeasure protocol for the BROA campaign that includes upper- and lower-body resistance exercise and head-down tilt cycle ergometry (high-intensity interval and continuous aerobic exercise training). We provide reasoning for the choice of these modalities following review of the latest available information on exercise as a countermeasure for inactivity and spaceflight-related deconditioning. In summary, this paper sets out to review up-to-date exercise countermeasure research from spaceflight and head-down bedrest studies, whilst providing support for the proposed research countermeasure protocols developed for the bedrest study in older adults.

Quantification of hypoxic regions distant from occlusions in cerebral penetrating arteriole trees

The microvasculature plays a key role in oxygen transport in the mammalian brain. Despite the close coupling between cerebral vascular geometry and local oxygen demand, recent experiments have reported that microvascular occlusions can lead to unexpected distant tissue hypoxia and infarction. To better understand the spatial correlation between the hypoxic regions and the occlusion sites, we used both in vivo experiments and in silico simulations to investigate the effects of occlusions in cerebral penetrating arteriole trees on tissue hypoxia. In a rat model of microembolisation, 25 μm microspheres were injected through the carotid artery to occlude penetrating arterioles. In representative models of human cortical columns, the penetrating arterioles were occluded by simulating the transport of microspheres of the same size and the oxygen transport was simulated using a Green’s function method. The locations of microspheres and hypoxic regions were segmented, and two novel distance analyses were implemented to study their spatial correlation. The distant hypoxic regions were found to be present in both experiments and simulations, and mainly due to the hypoperfusion in the region downstream of the occlusion site. Furthermore, a reasonable agreement for the spatial correlation between hypoxic regions and occlusion sites is shown between experiments and simulations, which indicates the good applicability of in silico models in understanding the response of cerebral blood flow and oxygen transport to microemboli.

The brain function depends on the continuous oxygen supply through the bloodstream inside the microvasculature. Occlusions in the microvascular network will disturb the oxygen delivery in the brain and result in hypoxic tissues that can lead to infarction and cognitive dysfunction. To aid in understanding the formation of hypoxic tissues caused by micro-occlusions in the penetrating arteriole trees, we use rodent experiments and simulations of human vascular networks to study the spatial correlations between the hypoxic regions and the occlusion locations. Our results suggest that hypoxic regions can form distally from the occlusion site, which agrees with the previous observations in the rat brain. These distant hypoxic regions are primarily due to the lack of blood flow in the brain tissues downstream of the occlusion. Moreover, a reasonable agreement of the spatial relationship is found between the experiments and the simulations, which indicates the applicability of in silico models to study the effects of microemboli on the brain tissue.

Orthostatic intolerance: a handicap of aging or physical deconditioning?

Despite several studies that have been investigated physical inactivity and age-related effects on orthostatic tolerance, impaired hemodynamics and postural balance responses to orthostatic stress are incorrectly attributed to aging or sedentarism alone. The isolated effects from aging and sedentarism should be investigated through comparative studies between senior athletes and age-matched controls, and physical activity assessments on aging follow-up studies. On the other hand, bed rest and space flight studies mimic accelerated physical inactivity or disuse, which is not the same physiological decline provoked by aging alone. Thus, the elementary question is: could orthostatic intolerance be attributed to aging or physical inactivity? The main purpose of this review is to provide an overview of possible mechanisms underlying orthostatic tolerance contrasting the paradigm of aging and/or physical inactivity. The key points of this review are the following: (1) to counterpoint all relevant literature on physiological aspects of orthostatic tolerance; (2) to explore the mechanistic aspects underneath the cerebrovascular, cardiorespiratory, and postural determinants of orthostatic tolerance; and (3) examine non-pharmacological interventions with the potential to counterbalance the physical inactivity and aging effects. To date, the orthostatic intolerance cannot be attributed exclusively with aging since physical inactivity plays an important role in postural balance, neurovascular and cardiorespiratory responses to orthostatic stress. These physiological determinates should be interpreted within an integrative approach of orthostatic tolerance, that considers the interdependence between physiological systems in a closed-loop model. Based on this multisystem approach, acute and chronic countermeasures may combat aging and sedentarism effects on orthostatic tolerance.

Time course recovery of cerebral blood velocity metrics post aerobic exercise: A systematic review

Currently, the standard approach for restricting exercise prior to cerebrovascular data collection varies widely between 6-24 hours. This universally employed practice is a conservative approach to safeguard physiological alterations that could potentially confound one's study design. Therefore, the purpose of this systematic review was to amalgamate the literature that examines the extent and duration cerebrovascular function is impacted following aerobic exercise measured via transcranial Doppler ultrasound. Further, an exploratory aim was to scrutinize and discuss common biases/limitations in the previous studies to help guide future investigations. Search strategies were developed and imported into PubMed, SPORTDiscus, and Medline databases. A total of 595 records were screened and 35 articles met the inclusion criteria in this review, which included assessments of basic cerebrovascular metrics (n=35), dynamic cerebral autoregulation (dCA; n=9), neurovascular coupling (NVC; n=2); and/or cerebrovascular reactivity (CVR-CO₂; n=1) following acute bouts of aerobic exercise. Across all studies, it was found NVC was impacted for 1-hour, basic cerebrovascular parameters and CVR-CO₂ parameters 2-hours, and dCA metrics 6-hours post-exercise. Therefore, future studies can provide participants with these evidence-based time restrictions, regarding the minimum time to abstain from exercise prior to data collection. However, it should be noted, other physiological mechanisms could still be altered (e.g., metabolic, hormonal, and/or autonomic influences), despite cerebrovascular function returning to baseline levels. Thus, future investigations should seek to control for as many physiological influences when employing cerebrovascular assessments, immediately following these time restraints. The main limitations/biases were lack of female participants, cardiorespiratory fitness, and consideration for vessel diameter.

Effects of 4-month running exercise on the spatial learning ability and white matter volume and microvessels of middle-aged female and male rats

Age-related degeneration of microvessels is known to occur in white matter, and exercise training can enhance brain function and promote cerebral blood flow. However, the effects of exercise training on microvessels in aged white matter are unknown. Forty-one middle-aged male and female Sprague-Dawley rats were randomly divided into a sedentary group and an exercised group. The rats in the exercised group were made to run on treadmills for 4 months. The spatial learning capacities of all groups were then assessed with the Morris water maze. White matter and its microvessels were investigated using immunohistological techniques and stereological methods. In the exercised group, females but not males, showed improved performance over time in the Morris water maze. In females but not males, the exercised rats showed significantly increased white matter volume compared with that of sedentary rats. The total length of microvessels in the white matter in the exercised group was significantly increased compared with that in the sedentary group in both males and females, but the total volume and total surface area of microvessels in the white matter did not differ significantly between the sedentary and exercised rats. Regular treadmill exercise had protective effects on spatial learning capacity, white matter volume, and the total length of microvessels in the white matter in middle-aged female rats and on the total length of microvessels in the white matter in middle-aged male rats. The results obtained might increase our understanding of the mechanisms by which exercise delays brain aging.