Differential effects and rates of normal aging in cerebellum and hippocampus

Microglial colonization routes and their impacts on cellular diversity

Microglia are the resident immune cells of the central nervous system. Unlike other glial cells-such as astrocytes and oligodendrocytes-which originate from neural stem cells alongside neurons, microglia derive from erythromyeloid progenitors that emerge in the yolk sac during early embryonic development. Once they reach the brain, microglia expand their population through proliferation during development. A growing body of research has revealed that microglia play diverse roles throughout life, both in physiological and pathological contexts. With recent advancements in single-cell transcriptomics, it has become increasingly evident that microglia exhibit substantial heterogeneity in their gene expression patterns. While various functions and subtypes of microglia are being uncovered, the mechanisms underlying their diversity remain largely unknown. Two key hypotheses may explain how microglial diversity arises. One possibility is that their diversity is influenced by the different colonization routes they take before settling in the brain. Alternatively, microglia may acquire distinct properties in response to their local environment. This review explores both possibilities, with a particular focus on the first hypothesis, drawing on recent findings that highlight the multiple routes microglia utilize to colonize the brain. It discusses how these processes contribute to the establishment of microglial diversity during brain development.

Involvement of ROS signal in aging and regulation of brain functions

Reactive oxygen species (ROS) are redox-signaling molecules involved in aging and lifestyle-related diseases. In the brain, in addition to the production of ROS as byproducts of metabolism, expression of ROS synthases has recently been demonstrated, suggesting possible involvement of ROS in various brain functions. This review highlights current knowledge on the relationship between ROS and brain functions, including their contribution to age-related decline in synaptic plasticity and cognitive function. While most studies demonstrate either the positive or negative effects of ROS on synaptic plasticity, the dual effects of ROS at individual synapses have been demonstrated recently in the mouse cerebellum. Furthermore, the cooperative interaction between these two effects determines the direction of synaptic plasticity. It is anticipated that further elucidation of both the positive and negative effects of ROS on brain function will lead to the development of more effective therapeutic strategies with fewer side effects for ROS-related brain dysfunction.

Icariin maintaining TMEM119-positive microglial population improves hippocampus-associated memory in senescent mice in relation to R-3-hydroxybutyric acid metabolism

ETHNOPHARMACOLOGICAL RELEVANCE

Epimedium Tourn. ex L. is a traditional Chinese medicine used for thousands of years in China to treat forgetfulness. Icariin is a principal component of the genus Epimedium.

AIM OF THE STUDY

The metabolic mechanism of icariin treating forgetfulness is explored.

MATERIALS AND METHODS

A D-galactose-induced senescent mouse model was employed. The cognitive performance of mice was assessed in the fear conditioning test. Hippocampal pathology was assessed in the immunohistochemistry assay. Plasma metabolome was analyzed using GC-MS method, and the differential metabolites were further identified by UPLC-MS/MS or GC-MS method. The liver function, including ALT and AST, was assessed by enzyme reaction. Icariin was administered intraperitoneally at 50 and 100 mg/kg. Mice were administered five consecutive days per week for 8 weeks.

RESULTS

Icariin treatment improved hippocampus-related fear memory but not amygdala-related memory, whereas Pexidartinib (PLX3397), a microglial scavenger, did not. Icariin treatment maintained the TMEM119-positive microglial population and decreased the accumulation of the senescent biomarker p16 in the dorsal hippocampus in senescent mouse brains, whereas PLX3397 did not. Notably, p16 in the CA2 subregion significantly decreased in icariin-treated mice than the other hippocampal subregions. The senescent mice exhibited the circulating metabolic characteristics of mild ketoacidosis, active tricarboxylic acid (TCA) cycle, lactic acidosis, hyperglycemia, active detoxification, active cis-oleic acid metabolism, and inhibitory GABA shut. R-3-Hydroxybutyric acid primarily produced in the liver was selectively and robustly decreased by icariin treatment, which was not observed with PLX3397 treatment. The TCA cycle was rescued in senescent mice by icariin treatment. Icariin also protected liver function (plasma ALT) in D-gal-induced senescent mice.

CONCLUSIONS

Icariin may protect mouse hippocampal cognition from D-gal-induced senescence by protecting microglial homeostasis, and facilitating the utilization of R-3-hydroxybutyric acid is one of the underpins.

Astrocytes in aging

The mammalian nervous system is impacted by aging. Aging alters brain architecture, is associated with molecular damage, and can manifest with cognitive and motor deficits that diminish the quality of life. Astrocytes are glial cells of the CNS that regulate the development, function, and repair of neural circuits during development and adulthood; however, their functions in aging are less understood. Astrocytes change their transcriptome during aging, with astrocytes in areas such as the cerebellum, the hypothalamus, and white matter-rich regions being the most affected. While numerous studies describe astrocyte transcriptional changes in aging, many questions still remain. For example, how is astrocyte function altered by transcriptional changes that occur during aging? What are the mechanisms promoting astrocyte aged states? How do aged astrocytes impact brain function? This review discusses features of aged astrocytes and their potential triggers and proposes ways in which they may impact brain function and health span.

The modulatory role of bone morphogenetic protein signaling in cerebellar synaptic plasticity

Bone morphogenetic proteins (BMPs), regulators of bone formation, have been implicated in embryogenesis and morphogenesis of various tissues and organs. BMP signaling plays a role in the formation of appropriate synaptic connections and development of normal neural circuits in the brain. However, physiological roles of BMP signaling in postnatal neural functions, including synaptic plasticity, remain largely unknown. Long-term depression (LTD) of synaptic transmission at parallel fiber (PF)-Purkinje cell (PC) synapses in the cerebellum has been suggested one neuronal mechanism underlying cerebellar functions. Here, we explored the contribution of BMP signaling to the induction of mouse cerebellar LTD. We first demonstrated that BMP2 and/or 4 were expressed in GABAergic neurons in mature networks of the cerebellar cortex. mRNA encoding BMP receptor type 1B (Bmpr1b) was expressed in the PC layer. Exogenous application of noggin, a BMP ligand inhibitor, suppressed the induction of cerebellar LTD by conjunctive stimulation, which caused normal LTD under control condition. Furthermore, mice deficient in BMPR1B exhibited attenuation of the extent of LTD induction, whereas they showed normal excitatory synaptic transmission at PF-PC synapses. These results suggest that after postnatal development, BMP signaling activated by BMPR1B, expressed in the PC layer, plays a crucial role in the facilitation of cerebellar LTD, leading to the modulation of cerebellar functions and behaviors.

A single dose of glycogen phosphorylase inhibitor improves cognitive functions of aged mice and affects the concentrations of metabolites in the brain

Inhibition of glycogen phosphorylase (Pyg) - a regulatory enzyme of glycogen phosphorolysis - influences memory formation in rodents. We have previously shown that 2-week intraperitoneal administration of a Pyg inhibitor BAY U6751 stimulated the "rejuvenation" of the hippocampal proteome and dendritic spines morphology and improved cognitive skills of old mice. Given the tedious nature of daily intraperitoneal drug administration, in this study we investigated whether a single dose of BAY U6751 could induce enduring behavioral effects. Obtained results support the efficacy of such treatment in significantly improving the cognitive performance of 20-22-month-old mice. Metabolomic analysis of alterations observed in the hippocampus, cerebellum, and cortex reveal that the inhibition of glycogen phosphorolysis impacts not only glucose metabolism but also various other metabolic processes.

Cerebello-Hippocampal Interactions in the Human Brain: A New Pathway for Insights Into Aging

The cerebellum is recognized as being important for optimal behavioral performance across task domains, including motor function, cognition, and affect. Decades of work have highlighted cerebello-thalamo-cortical circuits, from both structural and functional perspectives. However, these circuits of interest have been primarily (though not exclusively) focused on targets in the cerebral cortex. In addition to these cortical connections, the circuit linking the cerebellum and hippocampus is of particular interest. Recently, there has been an increased interest in this circuit, thanks in large part to novel findings in the animal literature demonstrating that neuronal firing in the cerebellum impacts that in the hippocampus. Work in the human brain has provided evidence for interactions between the cerebellum and hippocampus, though primarily this has been in the context of spatial navigation. Given the role of both regions in cognition and aging, and emerging evidence indicating that the cerebellum is impacted in age-related neurodegenerative disease such as Alzheimer's, I propose that further attention to this circuit is warranted. Here, I provide an overview of cerebello-hippocampal interactions in animal models and from human imaging and outline the possible utility of further investigations to improve our understanding of aging and age-related cognitive decline.

Climbing Fiber Activation Induced by Footshock in the Cerebellar Vermis Lobule IV/V of Freely Moving Mice

Parallel fibers (PFs) in the cerebellar cortex are involved in a series of coordinated responses in the fear conditioning paradigm induced by footshock. However, whether footshock can activate cerebellar climbing fibers (CFs) remains unclear. In this study, we recorded calcium (Ca2+) activity in CFs by optical fiber photometry in the cerebellar vermis lobule IV/V of freely moving mice with footshock stimulation. We found that the activation of CFs in the lobule IV/V was highly correlated with footshock stimulation but not with the sound stimulation used as a control. This result suggests that afferent information from CFs might be associated with the motor initiation of fear-related behaviors or fear emotion itself. Thus, our results suggest that a characteristic CF signal in the cerebellar cortex might be related to fear processing or footshock-related behaviors (such as startle responses or pain sensation).

Consensus Paper: Cerebellum and Ageing

Given the key roles of the cerebellum in motor, cognitive, and affective operations and given the decline of brain functions with aging, cerebellar circuitry is attracting the attention of the scientific community. The cerebellum plays a key role in timing aspects of both motor and cognitive operations, including for complex tasks such as spatial navigation. Anatomically, the cerebellum is connected with the basal ganglia via disynaptic loops, and it receives inputs from nearly every region in the cerebral cortex. The current leading hypothesis is that the cerebellum builds internal models and facilitates automatic behaviors through multiple interactions with the cerebral cortex, basal ganglia and spinal cord. The cerebellum undergoes structural and functional changes with aging, being involved in mobility frailty and related cognitive impairment as observed in the physio-cognitive decline syndrome (PCDS) affecting older, functionally-preserved adults who show slowness and/or weakness. Reductions in cerebellar volume accompany aging and are at least correlated with cognitive decline. There is a strongly negative correlation between cerebellar volume and age in cross-sectional studies, often mirrored by a reduced performance in motor tasks. Still, predictive motor timing scores remain stable over various age groups despite marked cerebellar atrophy. The cerebello-frontal network could play a significant role in processing speed and impaired cerebellar function due to aging might be compensated by increasing frontal activity to optimize processing speed in the elderly. For cognitive operations, decreased functional connectivity of the default mode network (DMN) is correlated with lower performances. Neuroimaging studies highlight that the cerebellum might be involved in the cognitive decline occurring in Alzheimer's disease (AD), independently of contributions of the cerebral cortex. Grey matter volume loss in AD is distinct from that seen in normal aging, occurring initially in cerebellar posterior lobe regions, and is associated with neuronal, synaptic and beta-amyloid neuropathology. Regarding depression, structural imaging studies have identified a relationship between depressive symptoms and cerebellar gray matter volume. In particular, major depressive disorder (MDD) and higher depressive symptom burden are associated with smaller gray matter volumes in the total cerebellum as well as the posterior cerebellum, vermis, and posterior Crus I. From the genetic/epigenetic standpoint, prominent DNA methylation changes in the cerebellum with aging are both in the form of hypo- and hyper-methylation, and the presumably increased/decreased expression of certain genes might impact on motor coordination. Training influences motor skills and lifelong practice might contribute to structural maintenance of the cerebellum in old age, reducing loss of grey matter volume and therefore contributing to the maintenance of cerebellar reserve. Non-invasive cerebellar stimulation techniques are increasingly being applied to enhance cerebellar functions related to motor, cognitive, and affective operations. They might enhance cerebellar reserve in the elderly. In conclusion, macroscopic and microscopic changes occur in the cerebellum during the lifespan, with changes in structural and functional connectivity with both the cerebral cortex and basal ganglia. With the aging of the population and the impact of aging on quality of life, the panel of experts considers that there is a huge need to clarify how the effects of aging on the cerebellar circuitry modify specific motor, cognitive, and affective operations both in normal subjects and in brain disorders such as AD or MDD, with the goal of preventing symptoms or improving the motor, cognitive, and affective symptoms.

Cerebellum Purkinje cell vulnerability in aged rats with memory impairment

The cerebellum is involved in higher order cognitive function and is susceptible to age-related atrophy. However, limited evidence has directly examined the cerebellum's role in cognitive aging. To interrogate potential substrates of the relationship between cerebellar structure and memory in aging, here we target the Purkinje cells (PCs). The sole output neurons of the cerebellum, PC loss and/or degeneration underlie a variety of behavioral abnormalities. Using a rat model of normal cognitive aging, we immunostained sections through the cerebellum for the PC-specific protein, calbindin-D28k. Although morphometric quantification revealed no significant difference in total PC number as a function of age or cognitive status, regional cell number was a more robust correlate of memory performance in the young cerebellum than in aged animals. Parallel biochemical analysis of PC-specific protein levels in whole cerebellum additionally revealed that calbindin-D28k and Purkinje cell protein-2 (pcp-2) levels were lower selectively in aged rats with spatial memory impairment compared to both young animals and aged rats with intact memory. These results suggest that cognitive aging is associated with cerebellum vulnerability, potentially reflecting disruption of the cerebellum-medial temporal lobe network.

Biology of cognitive aging across species

Aging is associated with cognitive decline, which can critically affect quality of life. Examining the biology of cognitive aging across species will lead to a better understanding of the fundamental mechanisms involved in this process, and identify potential interventions that could help to improve cognitive function in aging individuals. This minireview aimed to explore the mechanisms and processes involved in cognitive aging across a range of species, from flies to rodents, and covers topics, such as the role of reactive oxygen species and autophagy/mitophagy in cognitive aging. Overall, this literature provides a comprehensive overview of the biology of cognitive aging across species, highlighting the latest research findings and identifying potential avenues for future research. Geriatr Gerontol Int 2024; 24: 15-24.

Cerebellum and Aging: Update and Challenges

The cerebellum plays a vital role in the aging process. With the aging of the cerebellum, there is a decline in balance and motor function, particularly fine motor skills, and an increased risk of falling. However, in recent years, numerous studies have revealed that the cerebellum has several roles besides balance and fine motor skills, such as cognitive function and memory. It also plays a role in many neurodegenerative diseases. Interestingly, the cerebellum ages more rapidly than other brain regions, including the hippocampus. With increasing studies reporting that the cerebellum has a more prominent and interconnected role in the brain, it is essential to understand why aging affects it more, leading to solutions to help curb the accelerated decline. Here, we summarize the cerebellum's function and look at how it ages at the cellular, molecular, and functional levels. Additionally, we explore the the effects of alcoholism on the aging cerebellum as well as the role of the cerebellum in diseases such as Alzheimer's, Parkinson's, and Multiple Sclerosis.

Dietary Marine Oils Selectively Decrease Obesogenic Diet-Derived Carbonylation in Proteins Involved in ATP Homeostasis and Glutamate Metabolism in the Rat Cerebellum

The regular intake of diets high in saturated fat and sugars increases oxidative stress and has been linked to cognitive decline and premature brain aging. The cerebellum is highly vulnerable to oxidative stress and thus, obesogenic diets might be particularly detrimental to this tissue. However, the precise molecular mechanisms behind obesity-related brain damage are still not clear. Since protein carbonylation, a biomarker of oxidative stress, influences protein functions and is involved in metabolic control, the current investigation addressed the effect of long-term high-fat and high-sucrose diet intake on the cerebellum of Sprague-Dawley rats by deciphering the changes caused in the carbonylated proteome. The antioxidant effects of fish oil supplementation on cerebellar carbonylated proteins were also investigated. Lipid peroxidation products and carbonylated proteins were identified and quantified using immunoassays and 2D-LC-MS/MS in the cerebellum. After 21 weeks of nutritional intervention, the obesogenic diet selectively increased carbonylation of the proteins that participate in ATP homeostasis and glutamate metabolism in the cerebellum. Moreover, the data demonstrated that fish oil supplementation restrained carbonylation of the main protein targets oxidatively damaged by the obesogenic diet, and additionally protected against carbonylation of several other proteins involved in amino acid biosynthesis and neurotransmission. Therefore, dietary interventions with fish oils could help the cerebellum to be more resilient to oxidative damage. The results could shed some light on the effect of high-fat and high-sucrose diets on redox homeostasis in the cerebellum and boost the development of antioxidant-based nutritional interventions to improve cerebellum health.

Dysphagia following cerebellar stroke: analyzing the contribution of the cerebellum to swallowing function

Swallowing is essential for human health, and the cerebellum is crucial for motor movement regulation. Cerebellar strokes may cause dysphagia, but their exact effects remain unexplored in swallowing function. Therefore, the aim of this study was to analyze the precise clinical characteristics of the oral and pharyngeal phases of swallowing after cerebellar stroke and to critically discuss the cerebellum's contribution to swallowing. The study involved 34 participants with cerebellar strokes, gathered through convenience sampling. Neurologists diagnosed isolated strokes, and a speech and language pathologist examined swallowing ability using the Mann Assessment of Swallowing Ability. The study found that 52.9% of people experienced dysphagia after a cerebellar stroke. Dysphagia was significantly associated with a higher risk of aspiration. Age was also significantly correlated with dysphagia. No significant correlation was found between swallowing ability and sex. In conclusion, this study suggests isolated cerebellar stroke can adversely affect the motor and non-motor aspects of swallowing and cause severe dysphagia and aspiration risk. Thus, early diagnosis and timely management of dysphagia following a cerebellar stroke can help prevent serious consequences.

Assessing cognitive decline in the aging brain: lessons from rodent and human studies

As life expectancy continues to increase worldwide, age-related dysfunction will largely impact our societies in the future. Aging is well established to promote the deterioration of cognitive function and is the primary risk factor for the development of prevalent neurological disorders. Even in the absence of dementia, age-related cognitive decline impacts specific types of memories and brain structures in humans and animal models. Despite this, preclinical and clinical studies that investigate age-related changes in brain physiology often use largely different methods, which hinders the translational potential of findings. This review seeks to integrate what is known about age-related changes in the brain with analogue cognitive tests used in humans and rodent studies, ranging from "pen and paper" tests to virtual-reality-based paradigms. Finally, we draw parallels between the behavior paradigms used in research compared to the enrollment into clinical trials that aim to study age-related cognitive decline.

Sex- and age-dependent contribution of System xc- to cognitive, sensory, and social behaviors revealed by comprehensive behavioral analyses of System xc- null mice

Background

System xc- (Sxc-) is an important heteromeric amino acid cystine/glutamate exchanger that plays a pivotal role in the CNS by importing cystine into cells while exporting glutamate. Although certain behaviors have been identified as altered in Sxc- null mutant mice, our understanding of the comprehensive impact of Sxc- on behavior remains incomplete.

Methods

To address this gap, we compared motor, sensory and social behaviors of male and female mice in mice null for Sxc- (SLC7A11sut/sut) with wildtype littermates (SLC7A11+/+) in a comprehensive and systematic manner to determine effects of genotype, sex, age, and their potential interactions.

Results

Motor performance was not affected by loss of Sxc- in both males and females, although it was impacted negatively by age. Motor learning was specifically disrupted in female mice lacking Sxc- at both 2 and 6 months of age. Further, female SLC7A11sut/sut mice at both ages exhibited impaired sociability, but normal spatial and recognition memory, as well as sensorimotor gating. Finally, pronounced open-space anxiety was displayed by female SLC7A11sut/sut when they were young. In contrast, young SLC7A11sut/sut male mice demonstrated normal sociability, delayed spatial learning, increased open-space anxiety and heightened sensitivity to noise. As they aged, anxiety and noise sensitivity abated but hyperactivity emerged.

Discussion

We find that the behavioral phenotypes of female SLC7A11sut/sut are similar to those observed in mouse models of autism spectrum disorder, while behaviors of male SLC7A11sut/sut resemble those seen in mouse models of attention deficit hyperactivity disorder. These results underscore the need for further investigation of SLC7A11 in neurodevelopment. By expanding our understanding of the potential involvement of Sxc-, we may gain additional insights into the mechanisms underlying complex neurodevelopmental conditions.

Effects of pyrethroids on the cerebellum and related mechanisms: a narrative review

Pyrethroids (PYRs) are a group of synthetic organic chemicals that mimic natural pyrethrins. Due to their low toxicity and persistence in mammals, they are widely used today. PYRs exhibit higher lipophilicity than other insecticides, which allows them to easily penetrate the blood-brain barrier and directly induce toxic effects on the central nervous system. Several studies have shown that the cerebellum appears to be one of the regions with the largest changes in biomarkers. The cerebellum, which is extremely responsive to PYRs, functions as a crucial region for storing motor learning memories. Exposure to low doses of various types of PYRs during rat development resulted in diverse long-term effects on motor activity and coordination functions. Reduced motor activity may result from developmental exposure to PYRs in rats, as indicated by delayed cerebellar morphogenesis and maturation. PYRs also caused adverse histopathological and biochemical changes in the cerebellum of mothers and their offspring. By some studies, PYRs may affect granule cells and Purkinje cells, causing damage to cerebellar structures. Destruction of cerebellar structures and morphological defects in Purkinje cells are known to be directly related to functional impairment of motor coordination. Although numerous data support that PYRs cause damage to cerebellar structures, function and development, the mechanisms are not completely understood and require further in-depth studies. This paper reviews the available evidence on the relationship between the use of PYRs and cerebellar damage and discusses the mechanisms of PYRs.

Purkinje-cell-specific DNA repair-deficient mice reveal that dietary restriction protects neurons by cell-intrinsic preservation of genomic health

Dietary restriction (DR) is a universal anti-aging intervention, which reduces age-related nervous system pathologies and neurological decline. The degree to which the neuroprotective effect of DR operates by attenuating cell intrinsic degradative processes rather than influencing non-cell autonomous factors such as glial and vascular health or systemic inflammatory status is incompletely understood. Following up on our finding that DR has a remarkably large beneficial effect on nervous system pathology in whole-body DNA repair-deficient progeroid mice, we show here that DR also exerts strong neuroprotection in mouse models in which a single neuronal cell type, i.e., cerebellar Purkinje cells, experience genotoxic stress and consequent premature aging-like dysfunction. Purkinje cell specific hypomorphic and knock-out ERCC1 mice on DR retained 40 and 25% more neurons, respectively, with equal protection against P53 activation, and alike results from whole-body ERCC1-deficient mice. Our findings show that DR strongly reduces Purkinje cell death in our Purkinje cell-specific accelerated aging mouse model, indicating that DR protects Purkinje cells from intrinsic DNA-damage-driven neurodegeneration.

The landscape of aging

Aging is characterized by a progressive deterioration of physiological integrity, leading to impaired functional ability and ultimately increased susceptibility to death. It is a major risk factor for chronic human diseases, including cardiovascular disease, diabetes, neurological degeneration, and cancer. Therefore, the growing emphasis on "healthy aging" raises a series of important questions in life and social sciences. In recent years, there has been unprecedented progress in aging research, particularly the discovery that the rate of aging is at least partly controlled by evolutionarily conserved genetic pathways and biological processes. In an attempt to bring full-fledged understanding to both the aging process and age-associated diseases, we review the descriptive, conceptual, and interventive aspects of the landscape of aging composed of a number of layers at the cellular, tissue, organ, organ system, and organismal levels.

Dynamic 5-Hydroxymethylcytosine Change: Implication for Aging of Non-Human Primate Brain

Profiling of 5-hydroxymethylcytosine (5hmC) in the brain regions of rhesus monkey at different ages reveals accumulation and tissue-specific patterns of 5hmC with aging. Region-specific differentially hydroxymethylated regions (DhMRs) are involved in neuronal functions and signal transduction. These data suggest that 5hmC may be a key regulator of gene transcription in neurodevelopment and thus a potential candidate for the epigenetic clock. Importantly, non-human primates are the ideal animal models for investigation of human aging and diseases not only because they are more genetically similar to humans but also epigenetically.

Deficits in Cerebellum-Dependent Learning and Cerebellar Morphology in Male and Female BTBR Autism Model Mice

Recently, there has been increased interest in the role of the cerebellum in autism spectrum disorder (ASD). To better understand the pathophysiological role of the cerebellum in ASD, it is necessary to have a variety of mouse models that have face validity for cerebellar disruption in humans. Here, we add to the literature on the cerebellum in mouse models of autism with the characterization of the cerebellum in the idiopathic BTBR T + Itpr3tf/J (BTBR) inbred mouse strain, which has behavioral phenotypes that are reminiscent of ASD in patients. When we examined both male and female BTBR mice in comparison to C57BL/6J (C57) controls, we noted that both sexes of BTBR mice showed motor coordination deficits characteristic of cerebellar dysfunction, but only the male mice showed differences in delay eyeblink conditioning, a cerebellum-dependent learning task that is known to be disrupted in ASD patients. Both male and female BTBR mice showed considerable expansion of, and abnormal foliation in, the cerebellum vermis—including a significant expansion of specific lobules in the anterior cerebellum. In addition, we found a slight but significant decrease in Purkinje cell density in both male and female BTBR mice, irrespective of the lobule. Finally, there was a marked reduction of Purkinje cell dendritic spine density in both male and female BTBR mice. These findings suggest that, for the most part, the BTBR mouse model phenocopies many of the characteristics of the subpopulation of ASD patients that have a hypertrophic cerebellum. We discuss the significance of strain differences in the cerebellum as well as the importance of this first effort to identify both similarities and differences between male and female BTBR mice with regard to the cerebellum.

The association of reproductive stage with lobular cerebellar network connectivity across female adulthood

Sex-specific differences in the aging cerebellum may be related to hormone changes with menopause. We evaluated the association between reproductive stage and lobular cerebellar network connectivity using data from the Cambridge Centre for Ageing and Neuroscience repository. We used raw structural and resting state neuroimaging data and information regarding age, sex, and menopause-related variables. Crus I and II and Lobules V and VI were our cerebellar seeds of interest. We characterized reproductive stage using the Stages of Reproductive Aging Workshop criteria. Results show that postmenopausal females have lower cerebello-striatal and cerebello-cortical connectivity, particularly in frontal regions, along with lower connectivity within the cerebellum, compared to reproductive females. Postmenopausal females also exhibit greater connectivity in some brain areas as well. Differences begin to emerge across transitional stages of menopause. Further, results reveal sex-specific differences in connectivity between female reproductive groups and age-matched male control groups. This suggests that menopause may be associated with cerebellar network connectivity in aging females, and sex differences in the aging brain may be related to this biological process.

Brain Region- and Age-Dependent 5-Hydroxymethylcytosine Activity in the Non-Human Primate

Because of the difficulty in collecting fresh brains of humans at different ages, it remains unknown how epigenetic regulation occurs in the primate brains during aging. In the present study, we examined the genomic distribution of 5hmC, an indicator of DNA methylation, in the brain regions of non-human primates (rhesus monkey) at the ages of 2 (juvenile), 8 (young adult), and 17 (old) years. We found that genomic 5hmC distribution was accumulated in the monkey brain as age increased and displayed unique patterns in the cerebellum and striatum in an age-dependent manner. We also observed a correlation between differentially hydroxymethylated regions (DhMRs) and genes that contribute to brain region-related functions and diseases. Our studies revealed, for the first time, the brain-region and age-dependent 5hmC modifications in the non-human primate and the association of these 5hmC modifications with brain region-specific function and potentially aging-related brain diseases.

Don't forget the little brain: A framework for incorporating the cerebellum into the understanding of cognitive aging

With the rapidly growing population of older adults, an improved understanding of brain and cognitive aging is critical, given the impacts on health, independence, and quality of life. To this point, we have a well-developed literature on the cortical contributions to cognition in advanced age. However, while this work has been foundational for our understanding of brain and behavior in older adults, subcortical contributions, particularly those from the cerebellum, have not been integrated into these models and frameworks. Incorporating the cerebellum into models of cognitive aging is an important step for moving the field forward. There has also been recent interest in this structure in Alzheimer's dementia, indicating that such work may be beneficial to our understanding of neurodegenerative disease. Here, I provide an updated overview of the cerebellum in advanced age and propose that it serves as a critical source of scaffolding or reserve for cortical function. Age-related impacts on cerebellar function further impact cortical processing, perhaps resulting in many of the activation patterns commonly seen in aging.

Differential Abnormality in Functional Connectivity Density in Preclinical and Early-Stage Alzheimer's Disease

Background

Both subjective cognitive decline (SCD) and amnestic mild cognitive impairment (aMCI) have a high risk of progression to Alzheimer's disease (AD). While most of the available evidence described changes in functional connectivity (FC) in SCD and aMCI, there was no confirmation of changes in functional connectivity density (FCD) that have not been confirmed. Therefore, the purpose of this study was to investigate the specific alterations in resting-state FCD in SCD and aMCI and further assess the extent to which these changes can distinguish the preclinical and early-stage AD.

Methods

A total of 57 patients with SCD, 59 patients with aMCI, and 78 healthy controls (HC) were included. The global FCD, local FCD, and long-range FCD were calculated for each voxel to identify brain regions with significant FCD alterations. The brain regions with abnormal FCD were then used as regions of interest for FC analysis. In addition, we calculated correlations between neuroimaging alterations and cognitive function and performed receiver-operating characteristic analyses to assess the diagnostic effect of the FCD and FC alterations on SCD and aMCI.

Results

FCD mapping revealed significantly increased global FCD in the left parahippocampal gyrus (PHG.L) and increased long-range FCD in the left hippocampus for patients with SCD when compared to HCs. However, when compared to SCD, patients with aMCI showed significantly decreased global FCD and long-range FCD in the PHG.L. The follow-up FC analysis further revealed significant variations between the PHG.L and the occipital lobe in patients with SCD and aMCI. In addition, patients with SCD also presented significant changes in FC between the left hippocampus, the left cerebellum anterior lobe, and the inferior temporal gyrus. Moreover, changes in abnormal indicators in the SCD and aMCI groups were significantly associated with cognitive function. Finally, combining FCD and FC abnormalities allowed for a more precise differentiation of the clinical stages.

Conclusion

To our knowledge, this study is the first to investigate specific alterations in FCD and FC for both patients with SCD and aMCI and confirms differential abnormalities that can serve as potential imaging markers for preclinical and early-stage Alzheimer's disease (AD). Also, it adds a new dimension of understanding to the diagnosis of SCD and aMCI as well as the evaluation of disease progression.

Principles of brain aging: Status and challenges of modeling human molecular changes in mice

Due to the extension of human life expectancy, the prevalence of cognitive impairment is rising in the older portion of society. Developing new strategies to delay or attenuate cognitive decline is vital. For this purpose, it is imperative to understand the cellular and molecular events at the basis of brain aging. While several organs are directly accessible to molecular analysis through biopsies, the brain constitutes a notable exception. Most of the molecular studies are performed on postmortem tissues, where cell death and tissue damage have already occurred. Hence, the study of the molecular aspects of cognitive decline largely relies on animal models and in particular on small mammals such as mice. What have we learned from these models? Do these animals recapitulate the changes observed in humans? What should we expect from future mouse studies? In this review we answer these questions by summarizing the state of the research that has addressed cognitive decline in mice from several perspectives, including genetic manipulation and omics strategies. We conclude that, while extremely valuable, mouse models have limitations that can be addressed by the optimal design of future studies and by ensuring that results are cross-validated in the human context.

Phagocytic microglia in development: Are they what they eat?

Microglia, the innate immune cells of the brain, are indispensable for proper brain development. As professional phagocytes, microglia engulf other cells within distinct developmental niches to sculpt the architecture of the brain. Here, I highlight the age-, brain region-, and substrate-dependent diversity of developmental phagocytosis, and pose the idea that phagocytosis may, in turn, drive changes in microglia phenotype. Ultimately, phagocytosis might be just as important for shaping microglia function as it is for shaping the brain.

Design-based stereological study of the guinea-pig (Cavia porcellus) cerebellum

Guinea pigs have proved useful as experimental animal models in studying cerebellar anatomical and structural alterations in human neurological disease; however, they are also currently acquiring increasing veterinary interest as companion animals. The morphometric features of the normal cerebellum in guinea pigs have not been previously investigated using stereology. The objective of the present work was to establish normal volumetric and quantitative stereological parameters for cerebellar tissues in guinea pigs, by means of unbiased design-based stereology. Cerebellar total volume, gray and white matter volume fractions, molecular and granular layers volume fractions, cerebellar surface area, Purkinje cellular and nuclear volumes, and the Purkinje cell total count were stereologically estimated. For this purpose, cerebellar hemispheres from six adult male guinea pigs were employed. Isotropic, uniform random sections were obtained by applying the orientator method, and subsequently processed for light microscopy. The cerebellar total volume, the white and grey matter volume fractions, and the molecular and granular layer volumes were estimated using the Cavalieri's principle and the point counting system. The cerebellar surface area was estimated through the use of test lines; Purkinje cellular and nuclear volumes were analysed using the nucleator technique, whereas the Purkinje cell total count was obtained by means of the optical disector technique. The mean ± standard deviation total volume of a guinea-pig cerebellar hemisphere was 0.11 ± 0.01 cm³ . The mean volumetric proportions occupied by the gray and white matters were, respectively, 78.0 ± 2.6% and 22.0 ± 2.6%, whereas their mean absolute volumes were found to be 0.21 ± 0.02 cm³ and 0.059 ± 0.006 cm³ . The volumes of the molecular and granular layers were estimated at 112.4 ± 20.6 mm³ and 104.4 ± 7.3 mm³ , whereas their mean thicknesses were calculated to be 0.184 ± 0.020 mm and 0.17 ± 0.02 mm. The molecular and granular layers accounted for 40.7 ± 3.9% and 37.4 ± 1.8% of total cerebellar volume respectively. The surface area of the cerebellum measured 611.4 ± 96.8 mm² . Purkinje cells with a cellular volume of 3210.1 µm³ and with a nuclear volume of 470.9 µm³ had a higher incidence of occurrence. The mean total number of Purkinje cells for a cerebellar hemisphere was calculated to be 253,090 ± 34,754. The morphometric data emerging from the present study provide a set of reference data which might prove valuable as basic anatomical contribution for practical applications in veterinary neurology.

Early loss of cerebellar Purkinje cells in human and a transgenic mouse model of Alzheimer's disease

BACKGROUND

The cerebellum's involvement in AD has been under-appreciated by historically labeling as a normal control in AD research.

METHODS

We determined the involvement of the cerebellum in AD progression. Postmortem human and APPswe/PSEN1dE9 mice cerebellums were used to assess the cerebellar Purkinje cells (PC) by immunohistochemistry. The locomotor and spatial cognitive functions were assessed in 4- to 5-month-old APPswe/PSEN1dE9 mice. Aβ plaque and APP processing were determined in APPswe/PSEN1dE9 mice at different age groups by immunohistochemistry and Western blot.

RESULTS

We observed loss of cerebellar PC in mild cognitive impairment and AD patients compared with cognitively normal controls. A strong trend towards PC loss was found in AD mice as early as 5 months. Impairment of balance beam and rotorod performance, but no spatial learning and memory dysfunction was observed in AD mice at 4-5 months. Aβ plaque in the cerebral cortex was evidenced in AD mice at 2 months and dramatically increased at 6 months. Less and smaller Aβ plaques were observed in the cerebellum than in the cerebrum of AD mice. Similar intracellular APP staining was observed in the cerebellum and cerebrum of AD mice at 2 to 10 months. Similar expression of full-length APP and C-terminal fragments were indicated in the cerebrum and cerebellum of AD mice during aging.

DISCUSSION

Our study in post-mortem human brains and transgenic AD mice provided neuropathological and functional evidence that cerebellar dysfunction may occur at the early stage of AD and likely independent of Aβ plaque.

Unlike dietary restriction, rapamycin fails to extend lifespan and reduce transcription stress in progeroid DNA repair-deficient mice

Dietary restriction (DR) and rapamycin extend healthspan and life span across multiple species. We have recently shown that DR in progeroid DNA repair‐deficient mice dramatically extended healthspan and trippled life span. Here, we show that rapamycin, while significantly lowering mTOR signaling, failed to improve life span nor healthspan of DNA repair‐deficient Ercc1^∆/− mice, contrary to DR tested in parallel. Rapamycin interventions focusing on dosage, gender, and timing all were unable to alter life span. Even genetically modifying mTOR signaling failed to increase life span of DNA repair‐deficient mice. The absence of effects by rapamycin on P53 in brain and transcription stress in liver is in sharp contrast with results obtained by DR, and appoints reducing DNA damage and transcription stress as an important mode of action of DR, lacking by rapamycin. Together, this indicates that mTOR inhibition does not mediate the beneficial effects of DR in progeroid mice, revealing that DR and rapamycin strongly differ in their modes of action.

Improving Accuracy of Brainstem MRI Volumetry: Effects of Age and Sex, and Normalization Strategies

Background: Brainstem-mediated functions are impaired in neurodegenerative diseases and aging. Atrophy can be visualized by MRI. This study investigates extrinsic sources of brainstem volume variability, intrinsic sources of anatomical variability, and the influence of age and sex on the brainstem volumes in healthy subjects. We aimed to develop efficient normalization strategies to reduce the effects of intrinsic anatomic variability on brainstem volumetry.

Methods: Brainstem segmentation was performed from MPRAGE data using our deep-learning-based brainstem segmentation algorithm MD-GRU. The extrinsic variability of brainstem volume assessments across scanners and protocols was investigated in two groups comprising 11 (median age 33.3 years, 7 women) and 22 healthy subjects (median age 27.6 years, 50% women) scanned twice and compared using Dice scores. Intrinsic anatomical inter-individual variability and age and sex effects on brainstem volumes were assessed in segmentations of 110 healthy subjects (median age 30.9 years, range 18–72 years, 53.6% women) acquired on 1.5T (45%) and 3T (55%) scanners. The association between brainstem volumes and predefined anatomical covariates was studied using Pearson correlations. Anatomical variables with associations of |r| > 0.30 as well as the variables age and sex were used to construct normalization models using backward selection. The effect of the resulting normalization models was assessed by % relative standard deviation reduction and by comparing the inter-individual variability of the normalized brainstem volumes to the non-normalized values using paired t- tests with Bonferroni correction.

Results: The extrinsic variability of brainstem volumetry across different field strengths and imaging protocols was low (Dice scores > 0.94). Mean inter-individual variability/SD of total brainstem volumes was 9.8%/7.36. A normalization based on either total intracranial volume (TICV), TICV and age, or v-scale significantly reduced the inter-individual variability of total brainstem volumes compared to non-normalized volumes and similarly reduced the relative standard deviation by about 35%.

Conclusion: The extrinsic variability of the novel brainstem segmentation method MD-GRU across different scanners and imaging protocols is very low. Anatomic inter-individual variability of brainstem volumes is substantial. This study presents efficient normalization models for variability reduction in brainstem volumetry in healthy subjects.

Plastic changes to dendritic spines in the cerebellar and prefrontal cortices underlie the decline in motor coordination and working memory during successful aging

Old age is the last stage of life and by taking a multidimensional view of aging, Neuroscientists have been able to characterize pathological or successful aging. Psychomotor and cognitive performance are recognized as two major domains of successful aging, with a loss of motor coordination and working memory deficits two of the most characteristic features of elderly people. Dendritic spines in both the cerebellar and prefrontal cortices diminish in aging, yet the plastic changes in dendritic spines have not been related to behavioral performance neither the changes in the cerebellar or prefrontal cortices. As such, motor coordination and visuospatial working memory (vsWM) was evaluated here in aged, 22-month-old rats, calculating the density of spines and the proportion of the different types of spines. These animals performed erratically and slowly in a motor coordination-related paradigm, and the vsWM was resolved deficiently. Spine density was reduced in aged animals, and the proportional density of each of the spine types studied diminished in both the brain regions studied. The loss of dendritic spines and particularly, the changes in the proportional density of the different spine types could underlie, at least in part, the behavioral deficits observed during aging. To our knowledge, this is the first study of the plastic changes in different dendritic spine types that might underlie the behavioral alterations in motor and cognitive abilities associated with aging. Further neurochemical and molecular studies will help better understand the functional significance of the plastic changes to dendritic spines in both successful and pathological aging.

Cerebellar network organization across the human menstrual cycle

The cerebellum contains the vast majority of neurons in the brain and houses distinct functional networks that constitute at least two homotopic maps of cerebral networks. It is also a major site of sex steroid hormone action. While the functional organization of the human cerebellum has been characterized, the influence of sex steroid hormones on intrinsic cerebellar network dynamics has yet to be established. Here we investigated the extent to which endogenous fluctuations in estradiol and progesterone alter functional cerebellar networks at rest in a woman densely sampled over a complete menstrual cycle (30 consecutive days). Edgewise regression analysis revealed robust negative associations between progesterone and cerebellar coherence. Graph theory metrics probed sex hormones' influence on topological brain states, revealing relationships between sex hormones and within-network integration in Ventral Attention, Dorsal Attention, and SomatoMotor Networks. Together these results suggest that the intrinsic dynamics of the cerebellum are intimately tied to day-by-day changes in sex hormones.

BDNF signaling during the lifetime of dendritic spines

Dendritic spines are tiny membrane specialization forming the postsynaptic part of most excitatory synapses. They have been suggested to play a crucial role in regulating synaptic transmission during development and in adult learning processes. Changes in their number, size, and shape are correlated with processes of structural synaptic plasticity and learning and memory and also with neurodegenerative diseases, when spines are lost. Thus, their alterations can correlate with neuronal homeostasis, but also with dysfunction in several neurological disorders characterized by cognitive impairment. Therefore, it is important to understand how different stages in the life of a dendritic spine, including formation, maturation, and plasticity, are strictly regulated. In this context, brain-derived neurotrophic factor (BDNF), belonging to the NGF-neurotrophin family, is among the most intensively investigated molecule. This review would like to report the current knowledge regarding the role of BDNF in regulating dendritic spine number, structure, and plasticity concentrating especially on its signaling via its two often functionally antagonistic receptors, TrkB and p75NTR. In addition, we point out a series of open points in which, while the role of BDNF signaling is extremely likely conclusive, evidence is still missing.

Global and age-related neuroanatomical abnormalities in a Pax6-deficient mouse model of aniridia suggests a role for Pax6 in adult structural neuroplasticity

PAX6 encodes a highly conserved transcription factor necessary for normal development of the eyes and central nervous system. Heterozygous loss-of-function mutations in PAX6 cause the disorder aniridia in humans and the Small eye trait in mice. Aniridia is a congenital and progressive disorder known for ocular phenotypes; however, recently, consequences of PAX6 haploinsufficiency in the brains of aniridia patients have been identified. These findings span structural and functional abnormalities, including deficits in cognitive and sensory processing. Furthermore, some of these abnormalities are accelerated as aniridia patients age. Although some functional abnormalities may be explained by structural changes, variability of results remain, and the effects of PAX6 heterozygous loss-of-function mutations on neuroanatomy, particularly with regard to aging, have yet to be resolved. Our study used high-resolution magnetic resonance imaging (MRI) and histology to investigate structural consequences of such mutations in the adult brain of our aniridia mouse model, Small eye Neuherberg allele (Pax6SeyNeu/+), at two adult age groups. Using both MRI and histology enables a direct comparison with human studies, while providing higher resolution for detection of more subtle changes. We show volumetric changes in major brain regions of the the Pax6SeyNeu/+ mouse compared to wild-type including genotype- and age-related olfactory bulb differences, age-related cerebellum differences, and genotype-related eye differences. We also show alterations in thickness of major interhemispheric commissures, particularly those anteriorly located within the brain including the optic chiasm, corpus callosum, and anterior commissure. Together, these genotype and age related changes to brain volumes and structures suggest a global decrease in adult brain structural plasticity in our Pax6SeyNeu/+ mice.

Innate sensing of mechanical properties of brain tissue by microglia

External organic or inorganic objects (foreign bodies) that are inadvertently or purposefully placed in the human or animal tissues can trigger local tissue responses that aim at the elimination and/or segregation of foreign bodies from the tissue. The foreign body response (FBR) may have major implications for neurodegeneration associated with the formation of aberrant protein-based aggregates or plaques. The distinct physical features of the plaques, including high rigidity and varying surface properties, may trigger microglial mechanosensing of the plaque as a foreign body. The microglial FBR may have a dual function by promoting and/or suppressing the plaque driven neurodegeneration. Microglial contact with the plaque may trigger inflammatory activation of microglia and support microglia-driven neuronal damage. Conversely, persistent microglial activation may trigger the formation of a microglia-supported cell barrier that segregates and compacts the plaques thus preventing further plaque-induced damage to healthy neurons.

Moderate intensity intermittent exercise upregulates neurotrophic and neuroprotective genes expression and inhibits Purkinje cell loss in the cerebellum of ovariectomized rats

Decreases in estrogen levels due to menopause or ovariectomy may disrupt cerebellar motor functions. This study aimed at investigating the effects of Moderate Intensity Intermittent Exercise (MIEx) on the cerebellum of ovariectomized rats by analyzing neurotrophic and neuroprotective markers, as well as cerebellar motor functions. Thirty-two female Sprague Dawley rats were divided into four groups, i.e. Sham and ovariectomy (Ovx) of non-MIEx (NMIEx) groups, and Sham and Ovx with MIEx groups. MIEx was performed 5 days a week on treadmill for 6 weeks. Motor functions were assessed using rotarod, footprint, open field, and wire hanging tests. Real-time polymerase chain reaction was performed to determine messenger RNA (mRNA) expressions of Pgc-1α, BDNF, synaptophysin, Bcl-2, and Bax. Unbiased stereology was used to estimate the total number of cerebellar Purkinje cells. The Ovx MIEx group had higher Pgc-1α and Bcl-2 mRNA expressions, and number of Purkinje cells, but lower Bax mRNA expression than the Ovx NMIEx group. All motor functions of MIEx groups were better than the Sham and Ovx groups without MIEx. Motor functions on rotarod task, OFT, and FPT correlated significantly with the mRNAs expression of Bcl-2, Bax, BDNF, synaptophysin, Pgc-1α, and the number of cerebellar Purkinje cells in ovariectomized rats. MIEx improves cerebellar neurotrophic and neuroprotective markers, as well as motor functions of ovariectomized rats.

Surgical Trauma Exacerbates Cognitive Deficits and Neuroinflammation in Aged Rats: The Role of CX3CL1-CX3CR1 Signaling

Age is the most prominent risk factor for the development of postoperative cognitive dysfunction. The present study investigated the role of CX3CL1-CX3CR1 signaling in age-related differences in surgery-induced cognitive deficits and neuroinflammation. Adult and aged male Sprague-Dawley rats were subjected to partial hepatectomy or partial hepatectomy with intracerebroventricular infusion of CX3CL1. On postoperative days 3, 7, and 14, the rats were subjected to an open field test and the Morris water maze test. Hippocampal interleukin-1β, CX3CL1, CX3CR1, brain derived neurotrophic factor (BDNF), ionized calcium-binding adapter molecule 1 (Iba-1), and Arginase-1 (Arg1) levels were measured. Age exacerbated cognitive impairment and increased neuroinflammation following surgery. Surgery-induced decreases in CX3CL1 and CX3CR1 proteins were accompanied by increased microglial activation, as indicated by increased Iba-1 expression. Corresponding decline in Arg1 and BDNF levels were observed. Treatment with CX3CL1 decreased proinflammatory cytokines expression, increased BDNF and Arg1 levels in the brain, and enhanced behavioral recovery. The surgery-induced decreases in CX3CL1 and CX3CR1 expression exacerbated postoperative cognitive deficits and exaggerated neuroinflammatory responses in this rodent model. Treatment with CX3CL1 attenuated these effects, at least partly by inhibiting microglial activation, decreasing the associated production of proinflammatory cytokines, and enhancing BDNF expression.

New advances regarding adaptation of the vestibulo-ocular reflex

This is a review summarizing the development of vestibulo-ocular reflex (VOR) adaptation behavior with relevance to rehabilitation over the last 10 years and examines VOR adaptation using head-on-body rotations, specifically the influence of training target contrast, position and velocity error signal, active vs. passive head rotations, and sinusoidal vs. head impulse rotations. This review discusses optimization of the single VOR adaptation training session, consolidation between repeated training sessions, and dynamic incremental VOR adaptation. Also considered are the effects of aging and the roles of the efferent vestibular system, cerebellum, and otoliths on angular VOR adaptation. Finally, this review examines VOR adaptation findings in studies using whole body rotations.

Role of Microglia in Ataxias

Microglia, the resident macrophages of the central nervous system, critically influence neural function during development and in adulthood. Microglia are also profoundly sensitive to insults to the brain to which they respond with process of activation that includes spectrum of changes in morphology, function, and gene expression. Ataxias are a class of neurodegenerative diseases characterized by motor discoordination and predominant cerebellar involvement. In case of inherited forms of ataxia, mutant proteins are expressed throughout the brain and it is unclear why cerebellum is particularly vulnerable. Recent studies demonstrated that cerebellar microglia have a uniquely hyper-vigilant immune phenotype compared to microglia from other brain regions. These findings may indicate that microglia actively contribute to cerebellar vulnerability in ataxias. Here we review current knowledge about cerebellar microglia, their activation, and their role in the pathogenesis of ataxias. In addition, we briefly review advantages and disadvantages of several experimental approaches available to study microglia.

The Aging Astrocyte Transcriptome from Multiple Regions of the Mouse Brain

Aging brains undergo cognitive decline, associated with decreased neuronal synapse number and function and altered metabolism. Astrocytes regulate neuronal synapse formation and function in development and adulthood, but whether these properties change during aging, contributing to neuronal dysfunction, is unknown. We addressed this by generating aged and adult astrocyte transcriptomes from multiple mouse brain regions. These data provide a comprehensive RNA-seq database of adult and aged astrocyte gene expression, available online as a resource. We identify astrocyte genes altered by aging across brain regions and regionally unique aging changes. Aging astrocytes show minimal alteration of homeostatic and neurotransmission-regulating genes. However, aging astrocytes upregulate genes that eliminate synapses and partially resemble reactive astrocytes. We further identified heterogeneous expression of synapse-regulating genes between astrocytes from different cortical regions. We find that alterations to astrocytes in aging create an environment permissive to synapse elimination and neuronal damage, potentially contributing to aging-associated cognitive decline.

Impaired cerebellar plasticity and eye-blink conditioning in calpain-1 knock-out mice

Calpain-1 and calpain-2 are involved in the regulation of several signaling pathways and neuronal functions in the brain. Our recent studies indicate that calpain-1 is required for hippocampal synaptic plasticity, including long-term depression (LTD) and long-term potentiation (LTP) in field CA1. However, little is known regarding the contributions of calpain-1 to cerebellar synaptic plasticity. Low frequency stimulation (LFS, 5 Hz, 5 min)-induced LTP at parallel fibers to Purkinje cell synapses was markedly impaired in cerebellar slices from calpain-1 knock-out (KO) mice. Application of a selective calpain-2 inhibitor enhanced LFS-induced LTP in both wild-type (WT) and calpain-1 KO mice. Three protocols were used to induce LTD at these synapses: LFS (1 Hz, 15 min), perfusion with high potassium and glutamate (K-Glu) or dihydroxyphenylglycine (DHPG), a mGluR1 agonist. All three forms of LTD were impaired in calpain-1 KO mice. DHPG application stimulated calpain-1 but not calpain-2 in cerebellar slices, and DHPG-induced LTD impairment was reversed by application of a protein phosphatase 2A (PP2A) inhibitor, okadaic acid. As in hippocampus, BDNF induced calpain-1 activation and PH domain and Leucine-rich repeat Protein Phosphatase 1/suprachiasmatic nucleus oscillatory protein (PHLPP1/SCOP) degradation followed by extracellular signal-regulated kinase (ERK) activation, as well as calpain-2 activation leading to degradation of phosphatase and tensin homolog deleted on chromosome ten (PTEN) in cerebellar slices. The role of calpain-1 in associative learning was evaluated in the delay eyeblink conditioning (EBC). Calpain-1 KO mice exhibited significant learning impairment in EBC during the first 2 days of acquisition training. However, after 5 days of training, the percentage of conditioned responses (CRs) between calpain-1 KO and WT mice was identical. Both calpain-1 KO and WT mice exhibited typical extinction patterns. Our results indicate that calpain-1 plays critical roles in multiple forms of synaptic plasticity and associative learning in both hippocampus and cerebellum.

Genomics: New Light on Alzheimer's Disease Research

Alzheimer's disease (AD) is a progressive neurodegenerative disease that represents a major cause of death in many countries. AD is characterized by profound memory loss, disruptions in thinking and reasoning, and changes in personality and behavior followed by malfunctions in various bodily systems. Although AD was first identified over 100 years ago, and tremendous efforts have been made to cure the disease, the precise mechanisms underlying the onset of AD remain unclear. The recent development of next-generation sequencing tools and bioinformatics has enabled us to investigate the role of genetics in the pathogenesis of AD. In this review, we discuss novel discoveries in this area, including the results of genome-wide association studies (GWAS) that have implicated a number of novel genes as risk factors, as well as the identification of epigenetic regulators strongly associated with the onset and progression of AD. We also review how genetic risk factors may interact with age-associated, progressive decreases in cognitive function in patients with AD.

The Effects of Light and Moderate Intensity Exercise on the Femoral Bone and Cerebellum of d-Galactose-Exposed Rats

Aging causes the degeneration of organs of the locomotor system, including the cerebellum and bones. Exercise may reverse this deterioration. d-galactose has been frequently used in rodents to accelerate aging. The present study aimed at investigating the effects of exercise on cerebellar and serum growth factors, motor activity, and the number of bone cells of the femoral head of d-galactose-treated rats. Twenty-four male Wistar rats were divided randomly into four groups, that is, three treated groups injected with 300 mg/(mL·kg) body weight (bw) d-galactose solution daily for 4 weeks, and a control group injected with normal saline. Following the 4-week administration of d-galactose solution, two of the treated groups performed light- (45% VO₂max) and moderate- (55% VO₂max) intensity exercise, by running on a treadmill 4 × a week for 4 weeks. Locomotor activity was examined in rotarod and open field tests. The cerebellar and serum Insulin-like Growth Factor 1 (IGF-1) and Brain-Derived Neurotrophic Factor (BDNF) levels were measured using enzyme-linked immunosorbent assay (ELISA). The number of osteoblasts and osteoclasts of femoral head was estimated using unbiased stereological methods. It was found that the number of osteoclasts was higher in the d-galactose-treated group than the normal control and moderate-intensity exercise groups. No significant difference between groups was found in the rotarod and open field test performance, IGF-1 and BDNF levels, as well as number of osteoblasts. In conclusion, a 4-week administration of high-dosed-galactose caused the increase of the number of osteoclasts. A subsequent 4-week moderate-intensity exercise reversed this increase to the normal level.

Cannabinoid 1 receptor signaling on GABAergic neurons influences astrocytes in the ageing brain

Astrocytes, key regulators of brain homeostasis, interact with neighboring glial cells, neurons and the vasculature through complex processes involving different signaling pathways. It is not entirely clear how these interactions change in the ageing brain and which factors influence astrocyte ageing. Here, we investigate the role of endocannabinoid signaling, because it is an important modulator of neuron and astrocyte functions, as well as brain ageing. We demonstrate that mice with a specific deletion of CB1 receptors on GABAergic neurons (GABA-Cnr1-/- mice), which show a phenotype of accelerated brain ageing, affects age-related changes in the morphology of astrocytes in the hippocampus. Thus, GABA-Cnr1-/- mice showed a much more pronounced age-related and layer-specific increase in GFAP-positive areas in the hippocampus compared to wild-type animals. The number of astrocytes, in contrast, was similar between the two genotypes. Astrocytes in the hippocampus of old GABA-Cnr1-/- mice also showed a different morphology with enhanced GFAP-positive process branching and a less polarized intrahippocampal distribution. Furthermore, astrocytic TNFα levels were higher in GABA-Cnr1-/- mice, indicating that these morphological changes were accompanied by a more pro-inflammatory function. These findings demonstrate that the disruption of endocannabinoid signaling on GABAergic neurons is accompanied by functional changes in astrocyte activity, which are relevant to brain ageing.

Epigenetic regulation of brain region-specific microglia clearance activity

The rapid elimination of dying neurons and nonfunctional synapses in the brain is carried out by microglia, the resident myeloid cells of the brain. Here we show that microglia clearance activity in the adult brain is regionally regulated and depends on the rate of neuronal attrition. Cerebellar, but not striatal or cortical, microglia exhibited high levels of basal clearance activity, which correlated with an elevated degree of cerebellar neuronal attrition. Exposing forebrain microglia to apoptotic cells activated gene-expression programs supporting clearance activity. We provide evidence that the polycomb repressive complex 2 (PRC2) epigenetically restricts the expression of genes that support clearance activity in striatal and cortical microglia. Loss of PRC2 leads to aberrant activation of a microglia clearance phenotype, which triggers changes in neuronal morphology and behavior. Our data highlight a key role of epigenetic mechanisms in preventing microglia-induced neuronal alterations that are frequently associated with neurodegenerative and psychiatric diseases.

The Age-Related Perfusion Pattern Measured With Arterial Spin Labeling MRI in Healthy Subjects

Aim: To analyze age-related cerebral blood flow (CBF) using arterial spin labeling (ASL) MRI in healthy subjects with multivariate principal component analysis (PCA). Methods: 50 healthy subjects (mean age 45.8 ± 18.5 years, range 21-85) had 3D structural MRI and pseudo-continuous ASL MRI at resting state. The relationship between CBF and age was examined with voxel-based univariate analysis using multiple regression and two-sample t-test (median age 41.8 years as a cut-off). An age-related CBF pattern was identified using multivariate PCA. Results: Age correlated negatively with CBF especially anteriorly and in the cerebellum. After adjusting by global value, CBF was relatively decreased with aging in certain regions and relatively increased in others. The age-related CBF pattern showed relative reductions in frontal and parietal areas and cerebellum, and covarying increases in temporal and occipital areas. Subject scores of this pattern correlated negatively with age (R2 = 0.588; P < 0.001) and discriminated between the older and younger subgroups (P < 0.001). Conclusion: A distinct age-related CBF pattern can be identified with multivariate PCA using ASL MRI.