Effects of voluntary exercise on structure and function of cortical microvasculature

Simple and Complex Wheel Running Effect on Depression, Memory, Neuroinflammation, and Neurogenesis in Alzheimer's Rat Model

INTRODUCTION

The aim of this study was to investigate 12 wk of simple and complex voluntary wheel running on Alzheimer's disease (AD), associated biomarkers, and behaviors.

METHODS

Sixty male Wistar rats were randomly divided into six groups: healthy control (Con-Sed), AD only (AD-Sed), simple wheel control (SWC), complex wheel control (CWC), simple wheel AD (SWAD), and complex wheel AD (CWAD). Novelty-suppressed feeding test and the Morris water maze test were used to evaluate depression and memory, respectively. Ki67 was measured in the hippocampus, whereas interleukin (IL)-1β and neural/glial antigen 2 (NG2) were measured in both the hippocampus and the prefrontal cortex. One-way ANOVA with Tukey's post hoc test was performed.

RESULTS

AD-Sed group had significantly lower spacial memory ( P < 0.001) compared with Con-Sed. Simple and complex wheel running attenuated these deficits in the SWAD and CWAD groups, respectively ( P < 0.001). Only the CWAD group had significantly improved novelty-suppressed feeding test time compared with AD-Sed ( P < 0.001), equivalent to the healthy wheel running groups. AD-Sed has significantly higher hippocampal concentrations of Ki67 ( P = 0.01) compared with the Con-Sed. Both SWAD and CWAD had significantly reduced Ki67 with similar concentrations compared with the SWC and CWC groups ( P > 0.05). AD-Sed animals also presented with significantly higher hippocampal and prefrontal cortex concentrations of IL-1β compared with Con-Sed ( P < 0.001). SWAD and CWAD had no effect in changing these concentrations. Complex wheel running significantly increased NG2 in the healthy control and AD models, whereas simple wheel running significantly increased NG2 in the AD model.

CONCLUSIONS

The results of our study suggest that complex wheel running might be more advantageous in promoting memory and neuroplasticity while reducing depression that is associated with AD.

Effects of voluntary and forced physical exercise on the retinal health of aging Wistar rats

Aging is accompanied by an increased prevalence of degenerative conditions, including those affecting ocular health, which significantly impact quality of life and increase the burden on healthcare systems. Among these, retinal aging is of particular concern due to its direct link to vision impairment, a leading cause of disability in the elderly. Vision loss in the aging population is associated with heightened risks of cognitive decline, social isolation, and morbidity. This study addresses the critical gap in our understanding of modifiable lifestyle factors, such as physical exercise, that may mitigate retinal aging and its related pathologies. We investigated the effects of different exercise regimens-voluntary (recreational-type) and forced (high-intensity)-on the retinal health of aging Wistar rats (18-month-old), serving as a model for studying the translational potential of exercise interventions in humans. Male Wistar rats were divided into four groups: a young control (3-month-old) for baseline comparison, an aged sedentary control, an aged group engaging in voluntary exercise via a running wheel in their cage, and an aged group subjected to forced exercise on a treadmill for six sessions of 20 min each per week. After a 6-month experimental period, we assessed retinal function via electroretinography (ERG), measured retinal thickness histologically, and analyzed protein expression changes relevant to oxidative stress, inflammation, and anti-aging mechanisms. Our findings reveal that voluntary exercise positively impacts retinal function and morphology, reducing oxidative stress and inflammation markers while enhancing anti-aging protein expression. In contrast, forced exercise showed diminished benefits. These insights underscore the importance of exercise intensity and preference in preserving retinal health during aging. The study highlights the potential of recreational physical activity as a non-invasive strategy to counteract retinal aging, advocating for further research into exercise regimens as preventative therapies for age-related ocular degenerations.

The Effects of Body Composition, Physical Fitness on Time of Useful Consciousness in Hypobaric Hypoxia

INTRODUCTION

Several previous studies have reported that hypoxia accidents of fighter pilots are rarer than gravity-induced loss of consciousness and spatial disorientation; however, the risk is greater. Therefore, this study aimed to investigate the relationship between physical fitness and body composition on time of useful consciousness (TUC) in hypobaric hypoxia.

MATERIALS AND METHODS

Body composition and physical fitness testing on human participants were performed; subsequently, they were exposed to hypobaric hypoxia at a simulated altitude of 25,000 ft. Cognitive testing of the participants was accomplished by having them perform arithmetic task tables until they stopped writing for a period exceeding 5 seconds, at which point, they were placed on 100% oxygen. TUC was measured from the time the participants removed their oxygen masks to the time when the oxygen masks were placed back on them. Pearson's correlation was used to determine the relationship between TUC and other variables, and multiple regression was performed to determine the independent variables that best explain the TUC.

RESULTS

TUC was positively correlated with the maximum oxygen uptake, stroke volume, arteriovenous oxygen difference, and endurance (sit-up and push-up). The maximum heart rate on the ground, high altitude, body fat mass, and percent body fat were negatively correlated with TUC. A regression analysis showed that 84.5% of the TUC can be explained by body composition and physical fitness.

CONCLUSIONS

Our results revealed that increased cardiorespiratory fitness and decreased body fat mass could significantly impact the TUC. Therefore, for Air Force pilots who are frequently at high altitudes and at risk for exposure to hypoxia, aerobic exercise is significant to hypoxia tolerance.

Aerobic exercise reverses aging-induced depth-dependent decline in cerebral microcirculation

Aging is a major risk factor for cognitive impairment. Aerobic exercise benefits brain function and may promote cognitive health in older adults. However, underlying biological mechanisms across cerebral gray and white matter are poorly understood. Selective vulnerability of the white matter to small vessel disease and a link between white matter health and cognitive function suggests a potential role for responses in deep cerebral microcirculation. Here, we tested whether aerobic exercise modulates cerebral microcirculatory changes induced by aging. To this end, we carried out a comprehensive quantitative examination of changes in cerebral microvascular physiology in cortical gray and subcortical white matter in mice (3-6 vs. 19-21 months old), and asked whether and how exercise may rescue age-induced deficits. In the sedentary group, aging caused a more severe decline in cerebral microvascular perfusion and oxygenation in deep (infragranular) cortical layers and subcortical white matter compared with superficial (supragranular) cortical layers. Five months of voluntary aerobic exercise partly renormalized microvascular perfusion and oxygenation in aged mice in a depth-dependent manner, and brought these spatial distributions closer to those of young adult sedentary mice. These microcirculatory effects were accompanied by an improvement in cognitive function. Our work demonstrates the selective vulnerability of the deep cortex and subcortical white matter to aging-induced decline in microcirculation, as well as the responsiveness of these regions to aerobic exercise.

Aerobic exercise reverses aging-induced depth-dependent decline in cerebral microcirculation

Aging is a major risk factor for cognitive impairment. Aerobic exercise benefits brain function and may promote cognitive health in older adults. However, underlying biological mechanisms across cerebral gray and white matter are poorly understood. Selective vulnerability of the white matter to small vessel disease and a link between white matter health and cognitive function suggests a potential role for responses in deep cerebral microcirculation. Here, we tested whether aerobic exercise modulates cerebral microcirculatory changes induced by aging. To this end, we carried out a comprehensive quantitative examination of changes in cerebral microvascular physiology in cortical gray and subcortical white matter in mice (3-6 vs. 19-21 months old), and asked whether and how exercise may rescue age-induced deficits. In the sedentary group, aging caused a more severe decline in cerebral microvascular perfusion and oxygenation in deep (infragranular) cortical layers and subcortical white matter compared with superficial (supragranular) cortical layers. Five months of voluntary aerobic exercise partly renormalized microvascular perfusion and oxygenation in aged mice in a depth-dependent manner, and brought these spatial distributions closer to those of young adult sedentary mice. These microcirculatory effects were accompanied by an improvement in cognitive function. Our work demonstrates the selective vulnerability of the deep cortex and subcortical white matter to aging-induced decline in microcirculation, as well as the responsiveness of these regions to aerobic exercise.

Brain microvascular damage linked to a moderate level of strain induced by controlled cortical impact

Cerebral blood vessels play an important role in brain metabolic activity in general and following traumatic brain injury (TBI) in particular. However, the extent to which TBI alters microvessel structure is not well understood. Specifically, how intracranial mechanical responses produced during impacts relate to vascular damage needs to be better studied. Therefore, the objective of this study was to investigate the biomechanical mechanisms and thresholds of brain microvascular injury. Detailed microvascular damage of mouse brain was quantified using Arterial Spin Labeling (ASL) magnetic resonance imaging (MRI) and ex vivo Serial Two-Photon Tomography (STPT) in seven mice that had undergone controlled cortical impact. Mechanical strains were investigated through finite element (FE) modeling of the mouse brain. We then compared the post-injury vessel density map with FE-predicted strain and found a moderate correlation between the vessel length density and the predicted peak maximum principal strains (MPS) (R² = 0.52). High MPS was observed at the impact regions with low vessel length density, supporting the mechanism of strain-triggered microvascular damage. Using logistic regression, the MPS corresponding to a 50% probability of injury was found to be 0.17. Given the literature reporting MPS of over 0.2 in the human brain for mild TBI/concussion cases, it is highly recommended to consider microvascular damage when investigating mild TBI/concussion in the future.

Microvascular Alterations in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder associated with continual decline in cognition and ability to perform routine functions such as remembering familiar places or understanding speech. For decades, amyloid beta (Aβ) was viewed as the driver of AD, triggering neurodegenerative processes such as inflammation and formation of neurofibrillary tangles (NFTs). This approach has not yielded therapeutics that cure the disease or significant improvements in long-term cognition through removal of plaques and Aβ oligomers. Some researchers propose alternate mechanisms that drive AD or act in conjunction with amyloid to promote neurodegeneration. This review summarizes the status of AD research and examines research directions including and beyond Aβ, such as tau, inflammation, and protein clearance mechanisms. The effect of aging on microvasculature is highlighted, including its contribution to reduced blood flow that impairs cognition. Microvascular alterations observed in AD are outlined, emphasizing imaging studies of capillary malfunction. The review concludes with a discussion of two therapies to protect tissue without directly targeting Aβ for removal: (1) administration of growth factors to promote vascular recovery in AD; (2) inhibiting activity of a calcium-permeable ion channels to reduce microglial activation and restore cerebral vascular function.

Sural Nerve Perfusion in Mice

Peripheral nerve function is metabolically demanding and nerve energy failure has been implicated in the onset and development of diabetic peripheral neuropathy and neuropathic pain conditions. Distal peripheral nerve oxygen supply relies on the distribution of red blood cells (RBCs) in just a few, nearby capillary-sized vessels and is therefore technically challenging to characterize. We developed an approach to characterize distal sural nerve hemodynamics in anesthetized, adult male mice using in vivo two-photon laser scanning microscopy. Our results show that RBC velocities in mouse sural nerve vessels are higher than those previously measured in mouse brain, and are sensitive to hindlimb temperatures. Nerve blood flow, measured as RBC flux, however, was similar to that of mouse brain and unaffected by local temperature. Power spectral density analysis of fluctuations in RBC velocities over short time intervals suggest that the technique is sufficiently sensitive and robust to detect subtle flow oscillations over time scales from 0.1 to tens of seconds. We conclude that in vivo two-photon laser scanning microscopy provides a suitable approach to study peripheral nerve hemodynamics in mice, and that local temperature control is important during such measurements.

Aerobic exercise increases sprouting angiogenesis in the male rat motor cortex

Exercise is beneficial to brain health, and historically, the advantageous effects of exercise on the brain have been attributed to neuronal plasticity. However, it has also become clear that the brain vascular system also exhibits plasticity in response to exercise. This plasticity occurs in areas involved in movement, such as the motor cortex. This experiment aimed to further characterize the effects of exercise on structural vascular plasticity in the male rat motor cortex, by specifically identifying whether features of angiogenesis, the growth of new capillaries, or changes in vessel diameter were present. Male rats in the exercise group engaged in a 5-week bout of voluntary wheel running, while a second group of rats remained sedentary. After the exercise regimen, vascular corrosion casts, resin replicas of the brain vasculature, were made for all animals and imaged using a scanning electron microscope. Results indicate sprouting angiogenesis was the primary form of structural vascular plasticity detected in the motor cortex under these aerobic exercise parameters. Additionally, exercised rats displayed a slight increase in capillary diameter and expanded endothelial cell nuclei diameters in this region.

The effects of voluntary running on cerebrovascular morphology and spatial short-term memory in a mouse model of amyloidosis

Physical activity has been correlated with a reduced risk of cognitive decline, including that associated with vascular dementia, mild cognitive impairment (MCI) and Alzheimer's disease (AD); recent literature suggests this may in part result from benefits to the cerebrovascular network. Using a transgenic (Tg) mouse model of AD, we evaluated the effect of running on cortical and hippocampal vascular morphology, cerebral amyloid angiopathy, amyloid plaque load, and spatial memory. TgCRND8 mice present with progressive amyloid pathology, advancing from the cortex to the hippocampus in a time-dependent manner. We postulated that the characteristic progression of pathology could lead to differential, time-dependent effects of physical activity on vascular morphology in these brain regions at 6 months of age. We used two-photon fluorescent microscopy and 3D vessel tracking to characterize vascular and amyloid pathology in sedentary TgCRND8 mice compared those who have a history of physical activity (unlimited access to a running wheel, from 3 to 6 months of age). In sedentary TgCRND8 mice, capillary density was found to be lower in the cortex and higher in the hippocampus compared to non-transgenic (nonTg) littermates. Capillary length, vessel branching, and non-capillary vessel tortuosity were also higher in the hippocampus of sedentary TgCRND8 compared to nonTg mice. Three months of voluntary running resulted in normalizing cortical and hippocampal microvascular morphology, with no significant difference between TgCRND8 and nonTg mice. The benefits of physical activity on cortical and hippocampal vasculature in 6-month old TgCRND8 mice were not paralleled by significant changes on parenchymal and cerebral amyloid pathology. Short-term spatial memory- as evaluated by performance in the Y-maze- was significantly improved in running compared to sedentary TgCRND8 mice. These results suggest that long-term voluntary running contributes to the maintenance of vascular morphology and spatial memory in TgCRND8 mice, even in the absence of an effect on amyloid pathology.

Wheel running for 26 weeks is associated with sustained vascular plasticity in the rat motor cortex

Vascular pathologies represent the leading causes of mortality worldwide. The nervous system has evolved mechanisms to compensate for the cerebral hypoxia caused by many of these conditions. Vessel dilation and growth of new vessels are two prominent responses to hypoxia, both of which play a critical role in maintaining cerebral homeostasis. One way to facilitate cerebrovascular plasticity, and develop neuroprotection against vascular pathologies, is through aerobic exercise. The present study explored the long-term consequences of aerobic exercise on vascular structure and function in the motor cortex. Rats were assigned to a sedentary condition or were provided access to running wheels for 26 weeks. Rats were then anesthetized, and angiograms were captured using spectral domain optical coherence tomography (SD-OCT) to explore cerebrovascular reactivity in response to altered oxygen and carbon dioxide status. Following this procedure, all rats were euthanized, and unbiased stereological quantification of blood vessel density was collected from sections of the primary motor cortex infused with India ink. Results demonstrated that chronic exercise increased capillary and arteriole surface area densities and enhanced arteriole reactivity in response to hypercapnia-hypoxia, as displayed by increased vasodilation within the motor cortex of exercised animals.

Voluntary exercise increases brain tissue oxygenation and spatially homogenizes oxygen delivery in a mouse model of Alzheimer's disease

Although vascular contributions to dementia and Alzheimer's disease (AD) are increasingly recognized, the potential brain oxygenation disruption associated with AD and whether preventive strategies to maintain tissue oxygenation are beneficial remain largely unknown. This study aimed to examine (1) whether brain oxygenation is compromised by the onset of AD and (2) how voluntary exercise modulates the influence of AD on brain oxygenation. In vivo 2-photon phosphorescence lifetime microscopy was used to investigate local changes of brain tissue oxygenation with the progression of AD and its modulation by exercise in the barrel cortex of awake transgenic AD mice. Our results show that cerebral tissue oxygen partial pressure (PO₂) decreased with the onset of AD. Reduced PO₂ was associated with the presence of small near-hypoxic areas, an increased oxygen extraction fraction, and reduced blood flow, observations that were all reverted by exercise. AD and age also increased the spatial heterogeneity of brain tissue oxygenation, which was normalized by exercise. Ex vivo staining also showed fewer amyloid-β (Aβ) deposits in the exercise group. Finally, we observed correlations between voluntary running distance and cerebral tissue oxygenation/blood flow, suggesting a dose-response relationship of exercise on the brain. Overall, this study suggests that compromised brain oxygenation is an indicator of the onset of AD, with the emergence of potential deleterious mechanisms associated with hypoxia. Furthermore, voluntary exercise enhanced the neurovascular oxygenation process, potentially offering a means to delay these changes.

Altered cerebral blood flow and cerebrovascular function after voluntary exercise in adult mice

The beneficial effects of physical exercise on brain health are well documented, yet how exercise modulates cerebrovascular function is not well understood. This study used continuous arterial spin labeling magnetic resonance imaging with a hypercapnic challenge to examine changes in cerebral blood flow and vascular function after voluntary exercise in healthy, adult mice. Thirty exercise mice and twenty-one control mice were imaged prior to the start of the exercise regime (at 12 weeks of age) and after 4 weeks of voluntary exercise. After the second in vivo imaging session, we performed high-resolution ex vivo anatomical brain imaging to correlate the structural brain changes with functional measures of flow and vascular reserve. We found that exercise resulted in increases in the normocapnic and hypercapnic blood flow in the hippocampus. Moreover, the change in normocapnic blood flow between pre-exercise and post-exercise was positively correlated to the hippocampal structure volume following exercise. There was no overall effect of voluntary exercise on blood flow in the motor cortex. Surprisingly, the hypercapnic hippocampal blood flow when measured prior to the start of exercise was predictive of subsequent exercise activity. Moreover, exercise was found to normalize this pre-existing difference in hypercapnic blood flow between mice.