Background:Alzheimer's disease (AD) is characterized by early accumulation of amyloid-β (Aβ) plaques and tau pathology which precede overt neurodegeneration and cognitive decline. Detecting microstructural brain changes associated with Aβ deposition before the onset of atrophy is critical for early diagnosis and intervention. Objective:This study investigates whether diffusion kurtosis imaging (DKI) can detect early microstructural alterations in cortical and subcortical gray matter (GM) associated with Aβ pathology in individuals with mild cognitive impairment (MCI). Methods:Using DKI-derived metrics-mean kurtosis (MK) and mean diffusivity (MD) - we assessed cortical and subcortical microstructure in 67 participants (23 cognitively normal [CN], 44 MCI, including 29 Aβ-positive). Aβ burden was quantified using 11C-PiB PET imaging. Cortical atrophy, hippocampal volume, and white matter hyperintensities (WMH) were also evaluated. Results:Aβ-positive MCI patients exhibited significantly elevated cortical MK, particularly in the left lateral temporal lobe and right precuneus, compared to both CN and Aβ-negative MCI groups. MK positively correlated with Aβ burden in parietal and temporal cortices, even in the absence of cortical atrophy. In contrast, MD showed weaker and less consistent associations with Aβ and was more strongly influenced by age. No significant subcortical MK or MD differences were observed. Conclusion:Elevated MK in Aβ-positive MCI patients suggests that DKI can detect early microstructural changes associated with the presence of amyloid pathology before the onset of cortical atrophy. MK may serve as a promising non-invasive biomarker for identifying prodromal AD and monitoring disease progression.

Background:Alzheimer's disease (AD) is a continuum between normal health and dementia with a long preclinical phase, during which AD pathologies start to emerge, but where there are not yet any overt symptoms. The hallmark pathologies of AD are extracellular β-amyloid (Aβ) plaques and intra-neuronal neurofibrillary tangles (NFTs). Aβ deposition is present at the preclinical stage. Additionally, raised microglial activation is a key factor in AD. However, its exact timing and role is still unclear. This exploratory study investigated the prevalence of microglial activation and its association with Aβ deposition and memory impairment in preclinical AD. Methods:A total of 19 preclinical AD subjects with no cognitive complaints but abnormal Aβ deposition present on 11C-Pittsburgh Compound B (11C-PiB PET) and 10 healthy subjects with no cognitive complains or abnormal Aβ deposition on 11C-PiB PET underwent 11C-PK11195 PET (11C-PK). Additionally, the preclinical AD subjects underwent formal cognitive testing with sensitive memory tests, including the Rey Auditory Verbal Learning Test, the Rey Complex Figure Test, and the Face-Name Associative Memory Exam. Results:Microglial activation was raised in occipital and parietal cortices in preclinical AD subjects compared to healthy controls (p < 0.01). In the preclinical subjects there were significant positive correlations between Aβ load and microglial activation in parietal areas (p < 0.01). Finally, in the preclinical subjects, there were significant negative correlations between microglial activation and memory test performance in selected cortical areas (p < 0.01). Conclusion:Microglial activation was significantly raised in preclinical AD cases with no cognitive complaints and associated with impaired memory test performance. This suggests that microglial activation is present before overt clinical symptoms emerge and may be detrimental to cognition even at this early stage.

Background: Children of parents with schizophrenia (SZ) or bipolar disorder (BP) are at familial high risk (FHR) of developing severe mental illnesses. Based on findings in FHR populations and adults with SZ and BP, we hypothesized that children at FHR for schizophrenia (FHR-SZ) or bipolar disorder (FHR-BP) would show sex-specific differences in subcortical grey matter volume, particularly in the thalamus, amygdala, and hippocampus, compared with population-based controls (PBC). Methods: We examined eight major subcortical grey matter structures in 108 FHR-SZ, 69 FHR-BP, and 120 PBC children aged 11-12 years from the Danish High Risk and Resilience Study. Structural magnetic resonance imaging (MRI) was used to estimate subcortical volumes and R1, a measure of myelin, iron, water, and macromolecular content. Sex-specific group differences were tested across regions. Results: The thalamus and amygdala, but not hippocampus, showed sex-specific group differences in volume. FHR-SZ males showed smaller thalamic volumes than FHR-BP and PBC males, whereas FHR-BP females showed larger thalamic volumes compared with PBC females. FHR-BP males showed larger relative amygdala volumes (corrected for total brain volume) compared to PBC males. No significant differences were observed for subcortical R1. Conclusions: Children at FHR-SZ and FHR-BP exhibited sex-specific differences in subcortical brain volumes before the typical onset of SZ and BP. These differences may reflect early sex-specific neurodevelopmental correlates of familial risk and highlight the importance of modelling sex-specific effects in developmental neuropsychiatric research. Longitudinal studies are needed to determine how these volumetric differences evolve and whether they are associated with later clinical outcomes.

The vascular network in the brain delivers oxygen and nutrients to cells to maintain normal brain function. Substrate delivery depends on local cerebral blood flow (CBF) regulation and capillary transit-time distribution. Damage to capillaries and cells regulating capillary flow dynamics may impair blood flow control and increase capillary transit-time heterogeneity (CTH), limiting oxygen availability to areas of high metabolic demand. These changes are particularly important in the hippocampus, which has distinct vascular topography compared to cortex and plays a key role in cognition. Age-related vascular dysfunction often precedes cognitive impairment yet remains poorly understood in the hippocampus. Further studies are necessary to explore how vascular changes contribute to the development of Alzheimer's disease, where the hippocampus is one of the first areas affected. This study aims to investigate hippocampal capillary flow dynamics and oxygenation in aging. Imaging was performed with awake-restrained in vivo two-photon microscopy (TPM) and laser speckle contrast imaging (LSCI) through a chronic hippocampal cranial window in young and aged female mice. Steady state hippocampal hemodynamics were investigated using intravascularly (IV)-administered fluorescent dyes. CTH was estimated using an indicator dilution technique. IV partial pressure of oxygen (pO2) and tissue oxygen tension (PtO2) estimates were achieved using oxygen-sensitive dye injected IV and through a ventricular cannula, respectively. Pulsatility index (PI) was calculated from LSCI scatter patterns without contrast agents. A spatial learning and memory assay evaluated cognitive impairment. We will present an analysis of age-related changes in hippocampal microvascular hemodynamics. Preliminary data suggest capillary diameter estimates in aging mice appear less dynamic than in youth (Figure 1), while flow dynamics remain unchanged. Further analysis is expected to reveal changes in pO2 corresponding to altered capillary flow distributions to build on preliminary observations. Correlating vascular and behavioral changes will provide a broader understanding of age-induced cognitive changes.

BACKGROUND:Familial high risk (FHR) is the strongest predictor of developing schizophrenia (SZ) and bipolar disorder (BP). Children at FHR uniquely allow for the identification of early brain markers of vulnerability. Previous studies have often spanned wide age ranges and neglected sex differences, despite evidence of distinct sex-specific brain developmental trajectories. We investigated sex-specific group differences in brain morphometry among 11- to 12-year-old children at FHR-SZ or FHR-BP. METHODS:This study included 278 children from VIA 11 (the Danish High Risk and Resilience Study): 101 FHR-SZ (51 boys), 64 FHR-BP (32 boys), and 113 population-based control (PBC) (57 boys) children. Structural magnetic resonance imaging scans were acquired on 3T scanners at 2 sites. Brain volume, cortical volume, surface area, and cortical thickness were extracted using FreeSurfer. RESULTS:Significant group-by-sex interactions were observed for brain, cortical, and intracranial volume and surface area (η2 = 0.030-0.038, p = .006-.016). Boys at FHR-SZ exhibited smaller brain, cortical, and intracranial volume and surface area than PBC boys (Cohen's d = -0.677 to -0.489, p = .001-.015). Girls at FHR-BP had larger brain and cortical volumes than PBC girls (Cohen's d = 0.525 to 0.537, p = .017-.020). No significant differences were observed for cortical thickness (p > .210). CONCLUSIONS:Children at FHR-SZ and FHR-BP exhibited sex-specific morphometric differences, potentially reflecting sex-specific endophenotypic markers of risk. Given the smaller size of the FHR-BP group, these findings should be interpreted cautiously. Nevertheless, our findings underscore the importance of considering sex as a factor in neurodevelopmental psychiatric research. Longitudinal studies are needed to track how these neuroanatomical differences evolve over time and to evaluate their predictive value for transition to SZ or BP.

Oxygen availability in brain tissue is closely linked to local hemodynamics and even slight disturbances in the cerebral microcirculation may damage cells due to the brain's high energy demands. In addition to local cerebral blood flow, knowledge of the oxygen extraction fraction (OEF) is critical when assessing brain tissue oxygenation. A biophysical model that relates the brain's microvascular hemodynamics to OEF has previously been proposed. Here, we aimed to calibrate and compare this model with OEF measurements determined by [15O]-based positron emission tomography imaging (PET). Local brain hemodynamics were assessed in 68 healthy elderly individuals using dynamic susceptibility contrast magnetic resonance imaging (DSC-MRI). Average DSC-MRI-based mean transit time and capillary transit time heterogeneity were compared to PET OEF to calibrate the model parameters. The calibrated biophysical model produced OEF estimates in the range of PET OEF with a moderate correlation (r = 0.31, p = 0.009), albeit with a tendency to overestimate smaller PET OEF values and underestimate larger PET OEF values. We discuss the assumptions made when modeling oxygen transport in measurements of local hemodynamics and in [15O]-based tracer uptake, respectively, and propose that the biophysical model provides a valuable tool to link hemodynamic changes to oxygen uptake in the human brain.

In the last 20 years, there has been a revolution in our understanding of how blood flow is regulated in many tissues. Whereas it used to be thought that essentially all blood flow control occurred at the arteriole level, it is now recognized that control of capillary blood flow by contractile pericytes plays a key role both in regulating blood flow physiologically and in reducing it in clinically relevant pathological conditions. In this article, we compare and contrast how brain and cardiac pericytes regulate cerebral and coronary blood flow, focusing mainly on the pathological events of cerebral and cardiac ischaemia. The cerebral and coronary capillary beds differ dramatically in morphology, yet in both cases, pericyte-mediated capillary constriction plays a key role in restricting blood flow after ischaemia and possibly in other pathological conditions. We conclude with suggestions for therapeutic approaches to relaxing pericytes, which may prove useful in the long-term for reducing pericyte-induced ischaemia.

Normal brain function hinges on energy-intensive processes. Consequently, alterations to the brain's metabolic state are common hallmarks in several pathological conditions. Phosphorus Magnetic Resonance Spectroscopy (31P MRS) is a noninvasive method for measuring key markers of brain energy metabolism, including adenosine triphosphate (ATP), inorganic phosphate (Pi), and phosphocreatine (PCr), as well as markers for cell membrane phospholipid turnover, phosphomonoester (PME) and phosphodiester (PDE). Preclinical rodent 31P MRS has so far been done under anesthesia - with isoflurane being one of the most commonly used anesthetic agents. The use of isoflurane in 31P MRS is a concern, as anesthetics are known to affect neuronal activity and energy metabolism in the brain. Its use therefore comes with a risk of perturbing brain physiology. Awake mouse MRS avoids this and allows the effect of isoflurane to be quantified. Thus, we here compare mouse brain 31P MRS in awake MR-habituated mice and isoflurane anesthesia. We find that 31P metabolite levels differ between the awake state and isoflurane anesthesia in mice. Our findings show that low-dose isoflurane anesthesia reduces PCr levels in the mouse brain and is accompanied by decreases in intracellular pH and decreased PME levels.

Microvascular pulsatility in the brain is crucial for sustaining the delicate balance between the brain's metabolic demands and blood supply, as it affects nutrient exchange, waste removal and blood-brain barrier permeability. Abnormal pulsatility, associated with ageing or vascular risk factors, may impair the clearance of metabolic waste or contribute to conditions such as cerebral small vessel disease, ultimately leading to dementia and increasing the risk of stroke. In the present study, we introduce a new approach for robust full-field characterization of microvascular pulsatility and apply it to study cerebral perfusion and pulsatility across nearly the entire lifespan of awake and anaesthetized C57BL/6 mice. Our findings in awake animals reveal remarkably stable perfusion and pulsatility from 18 to 81 weeks, with pulsatility starting to change only in the final weeks of observation. In contrast, measurements taken under anaesthesia display a range of age-dependent and age-independent changes. We show that isoflurane affects the perfusion in an age-dependent manner, and both isoflurane and ketamine-xylazine, despite their distinct mechanisms, double the perfusion pulsatility and affect vascular diameter pulsatility in a complex manner, highlighting a previously overlooked detrimental effect of anaesthesia on assessing brain function. ### Competing Interest Statement The authors have declared no competing interest.

INTRODUCTION:Disturbances in microvascular flow dynamics are hypothesized to precede the symptomatic phase of Alzheimer's disease (AD). However, evidence in presymptomatic AD remains elusive, underscoring the need for therapies targeting these early vascular changes. METHODS:We employed a multimodal approach, combining in vivo optical imaging, molecular techniques, and ex vivo magnetic resonance imaging, to investigate early capillary dysfunction in C57BL/6-Tg(Thy1-APPSwDutIowa)BWevn/Mmjax (Tg-SwDI) mice without memory impairment. We also assessed the efficacy of carbonic anhydrase inhibitors (CAIs) in preventing capillary flow disturbances. RESULTS:Our study revealed capillary flow disturbances associated with alterations in capillary morphology, adhesion molecule expression, and amyloid beta (Aβ) load in 9- to 10-month-old Tg-SwDI mice without memory impairment. CAI treatment ameliorated these capillary flow disturbances, enhanced oxygen availability, and reduced Aβ load. DISCUSSION:These findings underscore the importance of capillary flow disturbances as early biomarkers in presymptomatic AD and highlight the potential of CAIs for preserving vascular integrity in the early stages of AD. HIGHLIGHTS:Uncovered early capillary dysfunction in a presymptomatic Alzheimer's disease (AD) mouse model. Evidence linking capillary stalls and capillary dysfunction with oxygen delivery issues in AD. Novel use of carbonic anhydrase inhibitors to prevent early capillary flow disturbances in AD.

BACKGROUND:Cerebral amyloid angiopathy (CAA) is a hallmark of Alzheimer's disease (AD), linked to adverse effects of emerging AD treatments. We explored the molecular effects of CAA in mouse brain and evaluated how these could be prevented by two repurposed United States Food and Drug Administration (FDA) approved treatments. METHODS:Brain proteomics was performed on the Tg-SwDI genetic mouse model carrying disease causing mutations and developing AD characteristic cognitive deficits and severe CAA. Cortical and hippocampal tissues from presymptomatic male and female mice were studied. RESULTS:We identify a core of dysregulated proteins across studies, including established markers of AD as well as proteins indicative of astrogliosis and negative regulators of synaptic stability and function. Two FDA approved, repurposed carbonic anhydrase inhibitors (CAIs), acetazolamide and methazolamide, were effective in preventing these molecular adaptations. DISCUSSION:The two drugs broadly prevent proteome adaptations to the detrimental genotype and retain glutamatergic synapse proteins significantly closer to wild-type levels. HIGHLIGHTS:The brain proteome changes of mice with CAA are mapped. Cortical and hippocampal tissues from presymptomatic male and female mice are studied. Markers of AD, astrogliosis, and synaptic stability are dysregulated. Two CAI are effective in preventing these protein changes.

Disturbances in cerebral oxygen delivery and utilization are increasingly recognized as key features, and potential contributors to, neuronal damage in multiple sclerosis (MS). We recently discovered microvascular changes, which are thought to limit oxygen extraction, in MS-related white matter (WM) lesions compared to unspecific WM lesions. It is unclear whether such microvascular changes antedate demyelinating changes in MS, or whether they are secondary to subsequent disease changes, such as inflammation, tissue edema, and blood-brain barrier break-down. Diffusion kurtosis imaging (DKI) is sensitive to early MS-related disease changes, including altered myelin integrity, cellularity, and edema detecting deviations from Gaussian diffusion that serve as indirect markers of tissue integrity. The purpose of this study was to examine whether regions with altered DKI metrics overlap with regions with microvascular changes in MS patients, and to compare microvascular changes with parallel DKI changes in both MS-related lesions and unrelated WM lesions to learn more about their microstructural correlates. In this cross-sectional study, we assessed microstructural damage in 54 MS patients and 26 non-diseased symptomatic controls (SC) using diffusion kurtosis imaging (DKI) and explored the relationship between these findings and microvascular flow patterns and oxygen delivery measured by dynamic susceptibility contrast-enhanced MRI (DSC-MRI). MRI at 3T included three-dimensional (3D) T2-weighted fluid-attenuated inversion recovery (T2-FLAIR), 3D magnetization-prepared 2 rapid acquisition gradient-echo (MP2RAGE), post-contrast 3D T1-weighted images, DSC-MRI, and DKI. White matter lesions (WMLs) were manually outlined as MS-characteristic T2-FLAIR lesions, MS contrast-enhancing lesions and nonspecific lesions T2-FLAIR lesions. DKI-derived structural parameters, mean kurtosis (MK) and mean diffusivity (MD), were extracted from lesion masks and normal-appearing white matter (NAWM) and correlated with DSC-derived vascular parameters mean transit time (MTT), and the distribution of capillary transit times (CTH). Finally, an extended flow-diffusion model of oxygen transport was employed to evaluate tissue oxygen availability based on local blood flow and microvascular flow patterns. After adjusting for age and sex, NAWM in MS showed higher MD (+2.4 %, p = 0.01) and lower MK (-2.8 %, p = 0.01) compared with SC without concurrent changes in perfusion or oxygenation. Unspecific T2-FLAIR lesions demonstrated higher MD relative to NAWM (+13 %, p < 0.001) and reduced MK (-6.7 %, p < 0.001), but no microvascular impairment. By contrast, MS T2-FLAIR lesions showed more pronounced structural alterations, with higher MD than unspecific lesions (+13 %, p = 0.01) and markedly reduced MK (-16 %, p = 0.02), accompanied by increased CTH (+31 %, p = 0.02) and prolonged MTT (+32 %, p = 0.02), consistent with impaired oxygen extraction despite preserved CBF. Our findings indicate that, microstructural alterations, as assessed by DKI, are detectable in normal-appearing tissue before microvascular disturbances become evident on GE-DSC MRI. In MS lesions, however, microvascular flow heterogeneity coexists with tissue degeneration, suggesting inefficient oxygen extraction as a likely contributor to lesion pathology. These results emphasize the need for longitudinal studies to determine the temporal relationship between impaired oxygen extraction and disease progression.

Abnormal cerebrovascular pulsatility is associated with white‐matter injury, blood–brain‐barrier leakage, and impaired glymphatic clearance, yet its extent in the microvasculature and aging dynamics remained obscured due to experimental and technical limitations. A multi‐modal approach for quantifying flow and diameter pulsatility in small cerebral vessels is developed and applied it longitudinally in male C57BL/6JRj mice from 18 to 81 weeks, both in awake and anesthetized conditions. In the awake state, mean perfusion and pulsatility indexes varied by <10%, indicating preserved hemodynamics until late life when arterial diameter pulsatility and venular caliber rose modestly. Anaesthesia radically changes the microvascular dynamics: isoflurane produces age‐dependent hyperemia, and both isoflurane and ketamine–xylazine double flow pulsatility and reshape diameter oscillations in drug‐specific ways. To complement the longitudinal data from males, a separate cross‐sectional comparison between sexes at 50–51 weeks of age is performed, which reveal significantly lower microvascular flow pulsatility in females despite no difference in mean perfusion. The results suggest that microvascular pulsatility remains stable during healthy aging yet can shift dramatically depending on the animal's condition, even if average cerebral perfusion is unchanged.

The locus coeruleus (LC) produces most of the brain’s noradrenaline (NA). Among its many roles, NA is often said to be neuroprotective and important for brain upkeep. For this reason, loss of LC integrity is thought to impact brain volume and microstructure as well as plasticity broadly. LC dysfunction is also a suspected driver in the development of neurodegenerative diseases. Nevertheless, the impact of LC dysfunction on the gross structure and microstructure of normal brains is not well-studied. We employed high-field ex vivo magnetic resonance imaging (MRI) to investigate brain volumetrics and microstructure in control (CON) mice and mice with LC ablation (LCA) at two ages, representing the developing brain and the fully matured brain. These whole-brain methods are known to be capable of detecting subtle morphological changes and brain microstructural remodeling. We found mice behavior consistent with histologically confirmed LC ablation. However, MRI showed no difference between CON and LCA groups with regard to brain size, relative regional volumes, or regional microstructural indices. Our findings suggest that LC-NA is not needed for postnatal brain maturation and growth in mice. Nor is it required for maintenance in the normal adult mouse brain, as no atrophy or microstructural aberration is detected after weeks of LC dysfunction. This adds clarity to the often-encountered notion that LC-NA is important for brain “trophic support” as it shows that such effects are likely most relevant to mechanisms related to brain plasticity and neuroprotection in the (pre)diseased brain.

APOE-epsilon 4 is a genetic risk factor for Alzheimer's disease (AD). AD is associated with reduced cerebral blood flow (CBF) and with microvascular changes that limit the transport of oxygen from blood into brain tissue: reduced microvascular cerebral blood volume and high relative transit time heterogeneity (RTH). Healthy APOE-epsilon 4 carriers reveal brain regions with elevated CBF compared with carriers of the common epsilon 3 allele. Such asymptomatic hyperemia may reflect microvascular dysfunction: a vascular disease entity characterized by suboptimal tissue oxygen uptake, rather than limited blood flow per se. Here, we used perfusion MRI to show that elevated regional CBF is accompanied by reduced capillary blood volume in healthy APOE-epsilon 4 carriers (carriers) aged 30-70 years compared with similarly aged APOE-epsilon 3 carriers (noncarriers). Younger carriers have elevated hippocampal RTH and more extreme RTH values throughout both white matter (WM) and cortical gray matter (GM) compared with noncarriers. Older carriers have reduced WM CBF and more extreme GM RTH values than noncarriers. Across all groups, lower WM and hippocampal RTH correlate with higher educational attainment, which is associated with lower AD risk. Three days of dietary nitrate supplementation increased carriers' WM CBF but caused older carriers to score worse on two of six aggregate neuropsychological scores. The intervention improved late recall in younger carriers and in noncarriers. The APOE-epsilon 4 gene is associated with microvascular changes that may impair tissue oxygen extraction. We speculate that vascular risk factor control is particularly important for APOE-epsilon 4 carriers' healthy aging.

Mitochondria are the main suppliers of energy for cells and their bioenergetic function is regulated by mitochondrial dynamics: the constant changes in mitochondria size, shape, and cristae morphology to secure cell homeostasis. Although changes in mitochondrial function are implicated in a wide range of diseases, our understanding is challenged by a lack of reliable ways to extract spatial features from the cristae, the detailed visualization of which requires electron microscopy (EM). Here, we present a semi-automatic method for the segmentation, 3D reconstruction, and shape analysis of mitochondria, cristae, and intracristal spaces based on 2D EM images of the murine hippocampus. We show that our method provides a more accurate characterization of mitochondrial ultrastructure in 3D than common 2D approaches and propose an operational index of mitochondria's internal organization. With an improved consistency of 3D shape analysis and a decrease in the workload needed for large-scale analysis, we speculate that this tool will help increase our understanding of mitochondrial dynamics in health and disease. We present a new method for the efficient segmentation and 3D shape analysis of mitochondrial inner components from FIBSEM images using multiplanar UNET and persistent homology.