Spatial learning and psychomotor performance of C57BL/6 mice: age sensitivity and reliability of individual differences

Small extracellular vesicles from young plasma reverse age-related functional declines by improving mitochondrial energy metabolism

Recent investigations into heterochronic parabiosis have unveiled robust rejuvenating effects of young blood on aged tissues. However, the specific rejuvenating mechanisms remain incompletely elucidated. Here we demonstrate that small extracellular vesicles (sEVs) from the plasma of young mice counteract pre-existing aging at molecular, mitochondrial, cellular and physiological levels. Intravenous injection of young sEVs into aged mice extends their lifespan, mitigates senescent phenotypes and ameliorates age-associated functional declines in multiple tissues. Quantitative proteomic analyses identified substantial alterations in the proteomes of aged tissues after young sEV treatment, and these changes are closely associated with metabolic processes. Mechanistic investigations reveal that young sEVs stimulate PGC-1α expression in vitro and in vivo through their miRNA cargoes, thereby improving mitochondrial functions and mitigating mitochondrial deficits in aged tissues. Overall, this study demonstrates that young sEVs reverse degenerative changes and age-related dysfunction, at least in part, by stimulating PGC-1α expression and enhancing mitochondrial energy metabolism.

Transplanting old organs promotes senescence in young recipients

In clinical organ transplantation, donor and recipient ages may differ substantially. Old donor organs accumulate senescent cells that have the capacity to induce senescence in naïve cells. We hypothesized that the engraftment of old organs may induce senescence in younger recipients, promoting age-related pathologies. When performing isogeneic cardiac transplants between age-mismatched C57BL/6 old donor (18 months) mice and young and middle-aged C57BL/6 (3- or 12- month-old) recipients , we observed augmented frequencies of senescent cells in draining lymph nodes, adipose tissue, livers, and hindlimb muscles 30 days after transplantation. These observations went along with compromised physical performance and impaired spatial learning and memory abilities. Systemic levels of the senescence-associated secretory phenotype factors, including mitochondrial DNA (mt-DNA), were elevated in recipients. Of mechanistic relevance, injections of mt-DNA phenocopied effects of age-mismatched organ transplantation on accelerating aging. Single treatment of old donor animals with senolytics prior to transplantation attenuated mt-DNA release and improved physical capacities in young recipients. Collectively, we show that transplanting older organs induces senescence in transplant recipients, resulting in compromised physical and cognitive capacities. Depleting senescent cells with senolytics, in turn, represents a promising approach to improve outcomes of older organs.

Post-Anesthesia Cognitive Dysfunction in Mice Is Associated with an Age-Related Increase in Neuronal Intracellular [Ca2+]-Neuroprotective Effect of Reducing Intracellular [Ca2+]: In Vivo and In Vitro Studies

Background: Postoperative cognitive dysfunction (POCD) is a common disorder after general anesthesia in elderly patients, the precise mechanisms of which remain unclear. Methods: We investigated the effect of isoflurane with or without dantrolene pretreatment on intracellular calcium concentration ([Ca2+]i), reactive oxygen species (ROS) production, cellular lactate dehydrogenase (LDH) leak, calpain activity, and cognitive function using the Morris water maze test of young (3 months), middle-aged (12-13 months), and aged (24-25 months) C57BL6/J mice. Results: Aged cortical and hippocampal neurons showed chronically elevated [Ca2+]i compared to young neurons. Furthermore, aged hippocampal neurons exhibited higher ROS production, increased LDH leak, and elevated calpain activity. Exposure to isoflurane exacerbated these markers in aged neurons, contributing to increased cognitive deficits in aged mice. Dantrolene pretreatment reduced [Ca2+]i for all age groups and prevented or significantly mitigated the effects of isoflurane on [Ca2+]i, ROS production, LDH leak, and calpain activity in aged neurons. Dantrolene also normalized or improved age-associated cognitive deficits and mitigated the cognitive deficits caused by isoflurane. Conclusions: These findings suggest that isoflurane-induced cytotoxicity and cognitive decline in aging are linked to disruptions in neuronal intracellular processes, highlighting the reduction of [Ca2+]i as a potential therapeutic intervention.

Age-related decline in cognitive flexibility is associated with the levels of hippocampal neurogenesis

Aging is associated with impairments in learning, memory, and cognitive flexibility, as well as a gradual decline in hippocampal neurogenesis. We investigated the performance of 6-and 14-month-old mice (considered mature adult and late middle age, respectively) in learning and memory tasks based on the Morris water maze (MWM) and determined their levels of preceding and current neurogenesis. While both age groups successfully performed in the spatial version of MWM (sMWM), the older mice were less efficient compared to the younger mice when presented with modified versions of the MWM that required a reassessment of the previously acquired experience. This was detected in the reversal version of MWM (rMWM) and was particularly evident in the context discrimination MWM (cdMWM), a novel task that required integrating various distal cues, local cues, and altered contexts and adjusting previously used search strategies. Older mice were impaired in several metrics that characterize rMWM and cdMWM, however, they showed improvement and narrowed the performance gap with the younger mice after additional training. Furthermore, we analyzed the adult-born mature and immature neurons in the hippocampal dentate gyrus and found a significant correlation between neurogenesis levels in individual mice and their performance in the tasks demanding cognitive flexibility. These results provide a detailed description of the age-related changes in learning and memory and underscore the importance of hippocampal neurogenesis in supporting cognitive flexibility.

Exercise may alleviate age-related spatial memory impairment by rescuing β-adrenergic receptor dysregulation via both G protein-dependent and β-arrestin-dependent mechanisms in rat hippocampus

Hippocampal-dependent memory abilities including spatial memory decline with age. Exercise improves memory decline in aging brain, but, the precise mechanisms are still unknown. Learning and memory are recently hypothesized to be mediated by a β-arrestin (βArr)-dependent β-adrenergic pathway. Hence, we examined the effect of 8 weeks of treadmill exercise on hippocampal expression of β-adrenergic receptors (β-ARs; members of the G protein-coupled receptor family), and βArrs as well as spatial learning and memory in aged male rats to determine whether β-AR/βArr pathway could be involved in age-related memory decline. A total of 24 young (3-month-old) and aged (18-month-old) male Wistar rats were divided into young control, aged sedentary, and aged + exercise (n = 8 for each). Western blot for β1- and β2-ARs as well as βArr1 and βArr2 was performed. Spatial learning and memory were evaluated with the Morris water maze. The results showed significant up-regulation of β1-ARs as well as significant down-regulation of β2-AR and βArrs (βArr1 and βArr2) in the hippocampus of aged rats. Spatial memory, but not spatial learning, was impaired in aging, and treadmill exercise improved it. Notably, the improvement in spatial memory was accompanied by amelioration of β-ARs dysregulation and increase in βArr2 levels after exercise. There was a negative association between the expression of βArr2 and β1-AR, but not β2-AR, such that an increase in βArr2 by exercise was associated with reduced β1-AR expression, suggesting βArr2 may contribute to posttranslational down-regulation of β1-ARs. These data suggest that both G protein-dependent and β-arrestin-dependent β-AR pathways may regulate spatial learning and memory in aging brain.

Sex differences in neurobehavioral consequences of methamphetamine exposure in adult mice

RATIONALE

Recreational and medical use of stimulants is increasing, and their use may increase susceptibility to aging and promote neurobehavioral impairments. The long-term consequences of these psychostimulants and how they interact with age have not been fully studied.

OBJECTIVES

Our study investigated whether chronic exposure to the prototypical psychostimulant, methamphetamine (METH), at doses designed to emulate human therapeutic dosing, would confer a pro-oxidizing redox shift promoting long-lasting neurobehavioral impairments.

METHODS

Groups of 4-month-old male and female C57BL/6 J mice were administered non-contingent intraperitoneal injections of either saline or METH (1.4 mg/kg) twice a day for 4 weeks. Mice were randomly assigned to one experimental group: (i) short-term cognitive assessments (at 5 months), (ii) long-term cognitive assessments (at 9.5 months), and (ii) longitudinal motor assessments (at 5, 7, and 9 months). Brain regions were assessed for oxidative stress and markers of neurotoxicity after behavior testing.

RESULTS

Chronic METH exposure induced short-term effects on associative memory, gait speed, dopamine (DA) signaling, astrogliosis in females, and spatial learning and memory, balance, DA signaling, and excitotoxicity in males. There were no long-term effects of chronic METH on cognition; however, it decreased markers of excitotoxicity in the striatum and exacerbated age-associated motor impairments in males.

CONCLUSION

In conclusion, cognitive and motor functions were differentially and sex-dependently affected by METH exposure, and oxidative stress did not seem to play a role in the observed behavioral outcomes. Future studies are necessary to continue exploring the long-term neurobehavioral consequences of drug use in both sexes and the relationship between aging and drugs.

A Neuroscience Primer for Integrating Geroscience With the Neurobiology of Aging

Neuroscience has a rich history of studies focusing on neurobiology of aging. However, much of the aging studies in neuroscience occur outside of the gerosciences. The goal of this primer is 2-fold: first, to briefly highlight some of the history of aging neurobiology and second, to introduce to geroscientists the broad spectrum of methodological approaches neuroscientists use to study the neurobiology of aging. This primer is accompanied by a corresponding geroscience primer, as well as a perspective on the current challenges and triumphs of the current divide across these 2 fields. This series of manuscripts is intended to foster enhanced collaborations between neuroscientists and geroscientists with the intent of strengthening the field of cognitive aging through inclusion of parameters from both areas of expertise.

Systemic GLP-1R agonist treatment reverses mouse glial and neurovascular cell transcriptomic aging signatures in a genome-wide manner

Pharmacological reversal of brain aging is a long-sought yet challenging strategy for the prevention and treatment of age-related neurodegeneration, due to the diverse cell types and complex cellular pathways impacted by the aging process. Here, we report the genome-wide reversal of transcriptomic aging signatures in multiple major brain cell types, including glial and mural cells, by systemic glucagon-like peptide-1 receptor (GLP-1R) agonist (GLP-1RA) treatment. The age-related expression changes reversed by GLP-1RA encompass both shared and cell type-specific functional pathways that are implicated in aging and neurodegeneration. Concomitantly, Alzheimer's disease (AD)-associated transcriptomic signature in microglia that arises from aging is reduced. These results show the feasibility of reversing brain aging by pharmacological means, provide mechanistic insights into the neurological benefits of GLP-1RAs, and imply that GLP-1R agonism may be a generally applicable pharmacological intervention for patients at risk of age-related neurodegeneration.

Thioredoxin interacting protein regulates age-associated neuroinflammation

Immune system hypersensitivity is believed to contribute to mental frailty in the elderly. Solid evidence indicates NOD-like receptor pyrin domain containing-3 (NLRP3)-inflammasome activation intimately connects aging-associated chronic inflammation (inflammaging) to senile cognitive decline. Thioredoxin interacting protein (TXNIP), an inducible protein involved in oxidative stress, is essential for NLRP3 inflammasome activity. This study aims to find whether TXNIP/NLRP3 inflammasome pathway is involved in senile dementia. According to our studies on sex-matched mice, TXNIP was significantly upregulated in aged animals, paralleled by the NLRP3-inflammasome over-activity leading to enhanced caspase-1 cleavage and IL-1β maturation, in both sexes. This was closely associated with depletion of the anti-aging and cognition enhancing protein klotho, in aged males. Txnip knockout reversed age-related NLRP3-hyperactivity and enhanced thioredoxin (TRX) levels. Further, TXNIP inhibition along with verapamil replicated TXNIP/NLRP3-inflammasome downregulation in aged animals, with FOXO-1 and mTOR upregulation. These alterations concurred with substantial improvements in both cognitive and sensorimotor abilities. Together, these findings substantiate the pivotal role of TXNIP to drive inflammaging in parallel with klotho depletion and functional decline, and delineate thioredoxin system as a potential target to decelerate senile dementia.

Enhanced synaptic properties of the prefrontal cortex and hippocampus after learning a spatial working memory task in adult male mice

Working memory (WM) is the ability to hold on-line and manipulate information. The prefrontal cortex (PFC) is a key brain region involved in WM, while the hippocampus is also involved, particularly, in spatial WM. Although several studies have investigated the neuronal substrates of WM in trained animals, the effects and the mechanisms underlying learning WM tasks have not been explored. In our study, we investigated the effects of learning WM tasks in mice on the function of PFC and hippocampus, by training mice in the delayed alternation task for 9 days (adaptive group). This group was compared to naïve mice (which stayed in their homecage) and mice trained in the alternation procedure only (non-adaptive). Following training, a cohort of mice (Experiment A) was tested in the left-right discrimination task and the reversal learning task, while another cohort (Experiment B) was tested in the attention set-shifting task (AST). The adaptive group performed significantly better in the reversal learning task (Experiment A) and AST (Experiment B), compared to non-adaptive and naïve groups. At the end of the behavioral experiments in Experiment A, field excitatory post-synaptic potential (fEPSP) recordings were performed in PFC and hippocampal brain slices. The adaptive group had enhanced the long-term potentiation (LTP) in the PFC, compared to the other groups. In the hippocampus, both the adaptive and the non-adaptive groups exhibited increased fEPSP compared to the naïve group, but no differences in LTP. In Experiment B, the dendritic spine density was measured, which, in the PFC, was found increased in the adaptive group, compared to the non-adaptive and naïve groups. In the hippocampus, there was an increase in mature dendritic spine density in the adaptive group, compared to the other two groups. Our results indicate a role for LTP and dendritic spine density in learning WM tasks.

Dietary fish hydrolysate supplementation containing n-3 LC-PUFAs and peptides prevents short-term memory and stress response deficits in aged mice

Brain aging is characterized by a decline in cognitive functions, which can lead to the development of neurodegenerative pathologies. Age-related spatial learning and memory deficits are associated with a chronic low-grade inflammation. Anxiety disorders and stress response alterations, occurring for a part of the elderly, have also been linked to an increased neuroinflammation and thus, an accelerated cognitive decline. Nutrition is an innovative strategy to prevent age-related cognitive impairments. Among the nutrients, n-3 long chain polyunsaturated fatty acids (LC-PUFAs) and low molecular weight peptides from proteins, especially those from marine resources, are good candidates for their immunomodulatory, anxiolytic and neuroprotective properties. The aim of this study is to determine the combined effect of n-3 LC-PUFAs and low molecular weight peptides on cognitive functions, and their mechanism of action. We are the first to show that a dietary supplementation with a fish hydrolysate containing n-3 LC-PUFAs and low molecular weight peptides prevented the age-related spatial short-term memory deficits and modulated navigation strategies adopted during spatial learning. In addition, the fish hydrolysate displayed anxiolytic activities with the reduction of anxiety-like behaviour in aged mice, restored the plasmatic corticosterone levels similar to adult animals following an acute stress and modulated the hypothalamic stress response. These effects on behaviour can be explained by the immunomodulatory and neuroprotective properties of the fish hydrolysate that limited microgliosis in vivo, decreased LPS-induced expression of pro-inflammatory cytokines and increased the expression of growth factors such as BDNF and NGF in vitro. Thus, n-3 LC-PUFAs and low molecular weight peptides contained in the fish hydrolysate can play an important role in the limitation of neuroinflammation and stress response alterations during aging and represent a potential strategy for the prevention of age-related cognitive decline.

C57BL/6 mice as a preclinical model to study age-related cognitive deficits: Executive functions impairment and inter-individual differences

OBJECTIVES

The aim of this study was to characterize age-related deficits of mice using different behavioral endpoints, with a focus on executive function and performance heterogeneity.

METHODS

2 month-old and 18 month-old C57BL/6J mice were tested in the novelty-based spatial preference Y-maze test and in sequential tasks in the Morris water maze test (reference memory, reversal learning and working memory), before being evaluated for motor skills in the activity meter and accelerating rotarod tests.

RESULTS

Aged mice displayed an almost normal acquisition in the water maze test, however, difficulties were observed in ability to perform reversal learning and working memory tasks. A marked heterogeneity characterized the performances of aged mice in both Morris water maze and Y-maze tests. Good and poor performers were observed in aged mice although the number of these mice varied depending on the cognitive parameter considered.

CONCLUSION

Aged mice display deficits in executive function and working memory, with varying severity between individual subjects, something that is also observed in other older animals and humans. Taking into account the heterogeneity in aged subjects within the experimental design of studies evaluating pharmacological treatments represents a promising way to improve the translational value of preclinical studies. In future studies, preselection of poor performers administered with cognitive enhancers and use of good performers as controls is suggested so that all cohorts of aged mice show similar physical and motor characteristics.

Effects of aging on the motor, cognitive and affective behaviors, neuroimmune responses and hippocampal gene expression

The known effects of aging on the brain and behavior include impaired cognition, increases in anxiety and depressive-like behaviors, and reduced locomotor activity. Environmental exposures and interventions also influence brain functions during aging. We investigated the effects of normal aging under controlled environmental conditions and in the absence of external interventions on locomotor activity, cognition, anxiety and depressive-like behaviors, immune function and hippocampal gene expression in C57BL/6 mice. Healthy mice at 4, 9, and 14 months of age underwent behavioral testing using an established behavioral battery, followed by cellular and molecular analysis using flow cytometry, immunohistochemistry, and quantitative PCR. We found that 14-month-old mice showed significantly reduced baseline locomotion, increased anxiety, and impaired spatial memory compared to younger counterparts. However, no significant differences were observed for depressive-like behavior in the forced-swim test. Microglia numbers in the dentate gyrus, as well as CD8+ memory T cells increased towards late middle age. Aging processes exerted a significant effect on the expression of 43 genes of interest in the hippocampus. We conclude that aging is associated with specific changes in locomotor activity, cognition, anxiety-like behaviors, neuroimmune responses and hippocampal gene expression.

Impaired Spatial Learning and Memory in Middle-Aged Mice with Kindling-Induced Spontaneous Recurrent Seizures

Temporal lobe epilepsy is the most common and often drug-resistant type of epilepsy in the adult and aging populations and has great diversity in etiology, electro-clinical manifestations, and comorbidities. Kindling through repeated brief stimulation of limbic structures is a commonly used model of temporal lobe epilepsy. Particularly, extended kindling can induce spontaneous recurrent seizures in several animal species. However, kindling studies in middle-aged, aging, or aged animals remain scarce, and currently, little is known about kindling-induced behavioral changes in middle-aged/aging animals. We therefore attempted to provide more information in this area using a mouse model of extended hippocampal kindling. We conducted experiments in middle-aged mice (C57BL/6, male, 12-14 months of age) to model new-onset epilepsy in adult/aging populations. Mice experienced twice daily hippocampal stimulations or handling manipulations for 60-70 days and then underwent continuous electroencephalogram (EEG)-video monitoring to detect spontaneous recurrent seizures. Extended kindled mice consistently exhibited spontaneous recurrent seizures with mean incidences of 6-7 events per day, and these seizures featured EEG discharges and corresponding convulsions. The handling control mice showed neither seizure nor aberrant EEG activity. The two groups of mice underwent the Morris water maze test of spatial learning and memory 1-2 weeks after termination of the kindling stimulation or handling manipulation. During visible platform trials, the kindled mice took a longer distance and required more time than the control mice to find the platform. During hidden platform trials, the kindled mice showed no improvement over 5-day trials in finding the platform whereas the control mice improved significantly. During probe tests in which the hidden platform was removed, the kindled mice spent less time than the controls searching in the correct platform location. There were no significant differences between the kindled and control mice with respect to swim speed or total locomotor activity in an open-field test. Together, these observations indicate that the extended kindled mice with spontaneous recurrent seizures are impaired in spatial learning and memory as assessed by the Morris water maze test. We postulate that the extended hippocampal kindling in middle-aged mice may help explore epileptogenic mechanisms and comorbidities potentially relevant to new-onset temporal lobe epilepsy in adult and aging patients. Limitations and confounds of our present experiments are discussed to improve future examinations of epileptic comorbidities in extended kindled mice.

Conclusions from a behavioral aging study on male and female F2 hybrid mice on age-related behavior, buoyancy in water-based tests, and an ethical method to assess lifespan

Due to strain-specific behavioral idiosyncrasies, inbred mouse strains are suboptimal research models for behavioral aging studies. The aim of this study is to determine age-related behavioral changes of F2 hybrid C57BL/6NxBALB/c male and female mice. Lifespan was followed (n_males=48, n_females=51) and cohorts of mature adult (7 months), middle-aged (15 months), and old mice (22 months of age; n=7-12 per group) were assessed regarding open-field activity, exploration, passive avoidance learning/memory, and depressive-like behavior. We found that both males and females demonstrated decreased exploratory behavior with age, while memory and depressive-like behavior were maintained. Females exhibited enhanced depressive-like behavior compared to males; however, a correlation between fat mass and swimming activity in the test directly accounted for 30-46% of this behavioral sex difference. In addition, we suggest a method to qualitatively estimate natural lifespan from survival analyses in which animals with signs of pain or severe disease are euthanized. This is, to our knowledge, the first behavioral study to consider both sex and aging in hybrid mice. We here define decreased exploratory behavior as a conserved hallmark of aging independent of sex, highlight the effect of buoyancy in water tests, and provide a method to assay lifespan with reduced animal suffering.

Deficits in Social Behavior Precede Cognitive Decline in Middle-Aged Mice

An extensive literature details deterioration of multiple brain functions, especially memory and learning, during aging in humans and in rodents. In contrast, the decline of social functions is less well understood. It is presently not clear whether age-dependent deficits observed in social behavior mainly reflect the disruption of social networks activity or are simply secondary to a more general impairment of cognitive and executive functions in older individuals. To address this issue, we carried out a battery of behavioral tasks exploring different brain functions in young (3 months) and middle-aged wild-type mice (9 months). Consistent with previous reports, our results show no obvious differences between these two groups in most of the domains investigated including learning and memory. Surprisingly, in social tasks, middle-aged animals showed significantly reduced levels of interactions when exposed to a new juvenile mouse. In the absence of overt cognitive decline, our findings suggest that social impairments may precede the disruption of other brain functions and argue for a selective vulnerability of social circuits during aging.

Young and aged TLR4 deficient mice show sex-dependent enhancements in spatial memory and alterations in interleukin-1 related genes

Toll-like receptor-4 (TLR4) is a transmembrane receptor that initiates an immune response following a bacterial infection or host derived molecules associated with cellular distress. Beyond triggering inflammation, TLR4 has been implicated in modulating behavioral and cognitive processes in a physiologically normal state, as young adult TLR4 deficient mice show learning enhancements in select tasks. Currently unknown is whether these benefits are present in both sexes and persist with aging. The present study evaluated spatial memory, anxiety-like behavior, and central levels of pro- and anti-inflammatory molecules in young (4-5 months) and aged (18-19 months) TLR4 deficient (TLR4-/-) and wild-type (WT) male and female mice. Results confirmed that TLR4-/- mice show enhanced spatial memory compared to WT mice. These effects were age- and sex-specific, as memory retention was superior in the TLR4-/- young males and aged females. While TLR4-/- mice showed age-related changes in behavior, these changes were attenuated relative to aged WT mice. Further, aged TLR4-/- mice showed differential expression of molecules involved in interleukin (IL)-1 signaling in the hippocampus. For instance, aged TLR4-/- females showed heightened expression of IL-1 receptor antagonist (IL-1ra) and the IL-1 accessory proteins AcP and AcPb. Collectively, these data provide the initial evidence that TLR4 deficiency enhances cognitive function and modulates the inflammatory profile of the hippocampus in a sex- and age-dependent manner.

BubR1 Insufficiency Impairs Affective Behavior and Memory Function in Mice

PURPOSE

Although aging causes functional declines in cognition, the molecular mechanism underlying these declines remains largely unknown. Recently, the spindle checkpoint kinase budding uninhibited by benzimidazole-related 1 (BubR1) has emerged as a key determinant for age-related pathology in various tissues including brain. However, the neurobehavioral impact of BubR1 has not been explored. In this study, we investigated the role of BubR1 in behavioral function.

METHODS

To investigate the neurobiological functions of BubR1 in vivo, we utilized transgenic mice harboring BubR1 hypomorphic alleles (BubR1H/H mice), which produce low amounts of BubR1 protein, as well as mice that have specific knockdown of BubR1 in the adult dentate gyrus. To assess anxiety-like behavior, the above groups were subjected to the elevated plus maze and the light-dark test, in addition to utilizing the tail-suspension and forced-swim test to determine depression-like behavior. We used novel object recognition to test for memory-related function.

RESULTS

We found that BubR1H/H mice display several behavioral deficits when compared to wild-type littermates, including increased anxiety in the elevated-plus maze test, depression-like behavior in the tail suspension test, as well as impaired memory function in the novel object recognition test. Similar to BubR1H/H mice, knockdown of BubR1 within the adult dentate gyrus led to increased anxiety-like behavior as well as depression-like behavior, and impaired memory function.

CONCLUSION

Our study demonstrates a requirement of BubR1 in maintaining proper affective and memory-related behavioral function. These results suggest that a decline in BubR1 levels with advanced age may be a crucial contributor to age-related hippocampal dysfunction.

Visualizing BDNF Transcript Usage During Sound-Induced Memory Linked Plasticity

Activity-dependent BDNF (brain-derived neurotrophic factor) expression is hypothesized to be a cue for the context-specificity of memory formation. So far, activity-dependent BDNF cannot be explicitly monitored independently of basal BDNF levels. We used the BLEV (BDNF-live-exon-visualization) reporter mouse to specifically detect activity-dependent usage of Bdnf exon-IV and -VI promoters through bi-cistronic co-expression of CFP and YFP, respectively. Enriching acoustic stimuli led to improved peripheral and central auditory brainstem responses, increased Schaffer collateral LTP, and enhanced performance in the Morris water maze. Within the brainstem, neuronal activity was increased and accompanied by a trend for higher expression levels of Bdnf exon-IV-CFP and exon-VI-YFP transcripts. In the hippocampus BDNF transcripts were clearly increased parallel to changes in parvalbumin expression and were localized to specific neurons and capillaries. Severe acoustic trauma, in contrast, elevated neither Bdnf transcript levels, nor auditory responses, parvalbumin or LTP. Together, this suggests that critical sensory input is essential for recruitment of activity-dependent auditory-specific BDNF expression that may shape network adaptation.

Discrete Pools of Oligomeric Amyloid-β Track with Spatial Learning Deficits in a Mouse Model of Alzheimer Amyloidosis

Despite increasing appreciation that oligomeric amyloid-β (Aβ) may contribute to cognitive decline of Alzheimer disease, defining the most critical forms has been thwarted by the changeable nature of these aggregates and the varying methods used for detection. Herein, using a broad approach, we quantified Aβ oligomers during the evolution of cognitive deficits in an aggressive model of Aβ amyloidosis. Amyloid precursor protein/tetracycline transactivator mice underwent behavioral testing at 3, 6, 9, and 12 months of age to evaluate spatial learning and memory, followed by histologic assessment of amyloid burden and biochemical characterization of oligomeric Aβ species. Transgenic mice displayed progressive impairments in acquisition and immediate recall of the trained platform location. Biochemical analysis of cortical extracts from behaviorally tested mice revealed distinct age-dependent patterns of accumulation in multiple oligomeric species. Dot blot analysis demonstrated that nonfibrillar Aβ oligomers were highly soluble and extracted into a fraction enriched for extracellular proteins, whereas prefibrillar species required high-detergent conditions to retrieve, consistent with membrane localization. Low-detergent extracts tested by 82E1 enzyme-linked immunosorbent assay confirmed the presence of bona fide Aβ oligomers, whereas immunoprecipitation-Western blotting using high-detergent extracts revealed a variety of SDS-stable low-n species. These findings show that different Aβ oligomers vary in solubility, consistent with distinct localization, and identify nonfibrillar Aβ oligomer-positive aggregates as tracking most closely with cognitive decline in this model.

Mechanisms of Hippocampal Aging and the Potential for Rejuvenation

The past two decades have seen remarkable progress in our understanding of the multifactorial drivers of hippocampal aging and cognitive decline. Recent findings have also raised the possibility of functional rejuvenation in the aged hippocampus. In this review, we aim to synthesize the mechanisms that drive hippocampal aging and evaluate critically the potential for rejuvenation. We discuss the functional changes in synaptic plasticity and regenerative potential of the aged hippocampus, followed by mechanisms of microglia aging, and assess the cross talk between these proaging processes. We then examine proyouth interventions that demonstrate significant promise in reversing age-related impairments in the hippocampus and, finally, attempt to look ahead toward novel therapeutics for brain aging.

HIV-1 Vpr disrupts mitochondria axonal transport and accelerates neuronal aging

Disruption of mitochondria axonal transport, essential for the maintenance of synaptic and neuronal integrity and function, has been identified in neurodegenerative diseases. Whether HIV-1 viral proteins affect mitochondria axonal transport is unknown, albeit HIV-associated neurocognitive disorders occur in around half of the patients living with HIV. Therefore, we sought to examine the effect of HIV-1 viral protein R (Vpr) on mitochondria axonal transport. Using mice primary neuronal cultures, we demonstrated that 4-day Vpr treatment reduced the ratio of moving mitochondria associated with (i) less energy (ATP) supply, (ii) reduction in Miro-1 and (iii) increase of α-synuclein which led to loss of microtubule stability as demonstrated by inconsecutive distribution of acetylated α-tubulin along the axons. Interestingly, the effect of Vpr on mitochondria axonal transport was partially restored in the presence of bongkrekic acid, a compound that negatively affected the Vpr-adenine nucleotide translocator (ANT) interaction and totally restored the ATP level in neurons. This indicated Vpr impaired mitochondria axonal transport partially related to its interaction with ANT. The above effect of Vpr was similar to the data obtained from hippocampal tissues isolated from 18-month-old aging mice compared to 5-month-old mice. In accord with previous clinical findings that HIV infection prematurely ages the brain and increases the susceptibility to HAND, we found that Vpr induced aging markers in neurons. Thus, we concluded that instead of causing cell death, low concentration of HIV-1 Vpr altered neuronal function related with inhibition of mitochondria axonal transport which might contribute to the accelerated neuronal aging.

Cognitive deficit in hippocampal-dependent tasks in Werner syndrome mouse model

Mammalian aging is often characterized by metabolic disturbances, cognitive declines and DNA repairs deficiency, but the underlying molecular mechanisms are still not well understood. Alterations in DNA repair can significantly exacerbate aging. Mammalian neuronal cells which accumulate unrepaired DNA damage over time could potentially lead to brain functions disorders. Focusing on the ATP-dependent RecQ-type DNA helicase, an enzyme involved in repair of double strand DNA, a mouse model of Werner syndrome (WS) had been proposed as a model of accelerated aging. Until now, no study has investigated the impact of this premature aging syndrome on learning and memory. Spatial memory and cognitive flexibility are particularly affected by the aging process in both men and rodents. Studies have shown that aged mice exhibited similar performance than young adult mice on non-hippocampus dependent memory whereas their performances were decreased in hippocampus-dependent tasks. In this study, we have submitted 3, 5 and 8 month-old WS mice to several behavioral paradigms to evaluate hippocampus-dependent (spatial object location, Morris water maze and fear conditioning) and non hippocampus-dependent (object recognition) memories. No effect on the locomotion activity and anxiety level has been observed in adult WS mice. Interestingly, the 8 month-old WS mice exhibit long-term memory impairment similar to aged mice, suggesting that adult WS mice do develop some aspects of cognitive aging.

Tart cherry supplementation improves working memory, hippocampal inflammation, and autophagy in aged rats

High consumption of fruits and vegetables has been associated with reduced risk of debilitating diseases and improved cognition in aged populations. These beneficial effects have been attributed to the phytochemicals found in fruits and vegetables, which have previously been shown to be anti-inflammatory and modulate autophagy. Tart cherries contain a variety of potentially beneficial phytochemicals; however, little research has been done to investigate the effects of tart cherry on the aging brain. Therefore, the purpose of this study was to determine if tart cherry supplementation can improve cognitive and motor function of aged rats via modulation of inflammation and autophagy in the brain. Thirty 19-month-old male Fischer 344 rats were weight-matched and assigned to receive either a control diet or a diet supplemented with 2 % Montmorency tart cherry. After 6 weeks on the diet, rats were given a battery of behavioral tests to assess for strength, stamina, balance, and coordination, as well as learning and working memory. Although no significant effects were observed on tests of motor performance, tart cherry improved working memory of aged rats. Following behavioral testing, the hippocampus was collected for western/densitometric analysis of inflammatory (GFAP, NOX-2, and COX-2) and autophagy (phosphorylated mTOR, Beclin 1, and p62/SQSTM) markers. Tart cherry supplementation significantly reduced inflammatory markers and improved autophagy function. Daily consumption of tart cherry reduced age-associated inflammation and promoted protein/cellular homeostasis in the hippocampus, along with improvements in working memory. Therefore, addition of tart cherry to the diet may promote healthy aging and/or delay the onset of neurodegenerative diseases.

Molecular and cellular aspects of age-related cognitive decline and Alzheimer's disease

As the population of people aged 60 or older continues to rise, it has become increasingly important to understand the molecular basis underlying age-related cognitive decline. In fact, a better understanding of aging biology will help us identify ways to maintain high levels of cognitive functioning throughout the aging process. Many cellular and molecular aspects of brain aging are shared with other organ systems; however, certain age-related changes are unique to the nervous system due to its structural, cellular and molecular complexity. Importantly, the brain appears to show differential changes throughout the aging process, with certain regions (e.g. frontal and temporal regions) being more vulnerable than others (e.g. brain stem). Within the medial temporal lobe, the hippocampus is especially susceptible to age-related changes. The important role of the hippocampus in age-related cognitive decline and in vulnerability to disease processes such as Alzheimer's disease has prompted this review, which will focus on the complexity of changes that characterize aging, and on the molecular connections that exist between normal aging and Alzheimer's disease. Finally, it will discuss behavioral interventions and emerging insights for promoting healthy cognitive aging.

Dietary Polyphenol Supplementation Prevents Alterations of Spatial Navigation in Middle-Aged Mice

Spatial learning and memory deficits associated with hippocampal synaptic plasticity impairments are commonly observed during aging. Besides, the beneficial role of dietary polyphenols has been suggested as potential functional food candidates to prevent this memory decline. Indeed, polyphenols could potentiate the signaling pathways of synaptic plasticity underlying learning and memory. In this study, spatial learning deficits of middle-aged mice were first highlighted and characterized according to their navigation patterns in the Morris water maze task. An eight-week polyphenol-enriched diet, containing a polyphenol-rich extract from grape and blueberry (PEGB; from the Neurophenols Consortium) with high contents of flavonoids, stilbenes and phenolic acids, was then successful in reversing these age-induced effects. The use of spatial strategies was indeed delayed with aging whereas a polyphenol supplementation could promote the occurrence of spatial strategies. These behavioral results were associated with neurobiological changes: while the expression of hippocampal calmodulin kinase II (CaMKII) mRNA levels was reduced in middle-aged animals, the polyphenol-enriched diet could rescue them. Besides, an increased expression of nerve growth neurotrophic factor (NGF) mRNA levels was also observed in supplemented adult and middle-aged mice. Thus these data suggest that supplementation with polyphenols could be an efficient nutritional way to prevent age-induced cognitive decline.

Luteinizing hormone downregulation but not estrogen replacement improves ovariectomy-associated cognition and spine density loss independently of treatment onset timing

Age-related changes in reproductive hormone levels are a well-known risk factor for the development of cognitive dysfunction and dementia in women. We and others have shown an important contribution of gonadotropins in this process. Lowering serum gonadotropin levels is able to rescue cognitive function in Alzheimer's disease and menopause models, but whether this is time-dependent and the exact mechanism through which gonadotropins regulate cognitive function is unknown. We show that pharmacologically lowering serum levels of luteinizing hormone lead to cognitive improvement immediately after ovariectomy and with a 4month interval after ovariectomy, when the benefits of 17β-estradiol are known to disappear in rodents. Importantly, we show that these improvements are associated with spine density changes at both time points. These findings suggest a role of luteinizing hormone in learning and memory and neuroplasticity processes as well as provide an alternative therapeutic strategy of menopause associated cognitive loss.

Curcumin Mimics the Neurocognitive and Anti-Inflammatory Effects of Caloric Restriction in a Mouse Model of Midlife Obesity

Dietary curcumin was studied for its potential to decrease adiposity and reverse obesity- associated cognitive impairment in a mouse model of midlife sedentary obesity. We hypothesized that curcumin intake, by decreasing adiposity, would improve cognitive function in a manner comparable to caloric restriction (CR), a weight loss regimen. 15-month-old male C57BL/6 mice were assigned in groups to receive the following dietary regimens for 12 weeks: (i) a base diet (Ain93M) fed ad libitum (AL), (ii) the base diet restricted to 70% of ad libitum (CR) or (iii) the base diet containing curcumin fed AL (1000 mg/kg diet, CURAL). Blood markers of inflammation, interleukin 6 (IL-6) and C-reactive protein (CRP), as well as an indicator of redox stress (GSH: GSSG ratio), were determined at different time points during the treatments, and visceral and subcutaneous adipose tissue were measured upon completion of the experiment. After 8 weeks of dietary treatment, the mice were tested for spatial cognition (Morris water maze) and cognitive flexibility (discriminated active avoidance). The CR group showed significant weight loss and reduced adiposity, whereas CURAL mice had stable weight throughout the experiment, consumed more food than the AL group, with no reduction of adiposity. However, both CR and CURAL groups took fewer trials than AL to reach criterion during the reversal sessions of the active avoidance task, suggesting an improvement in cognitive flexibility. The AL mice had higher levels of CRP compared to CURAL and CR, and GSH as well as the GSH: GSSG ratio were increased during curcumin intake, suggesting a reducing shift in the redox state. The results suggest that, independent of their effects on adiposity; dietary curcumin and caloric restriction have positive effects on frontal cortical functions that could be linked to anti-inflammatory or antioxidant actions.

Comparative Approaches to Understanding the Relation Between Aging and Physical Function

Despite dedicated efforts to identify interventions to delay aging, most promising interventions yielding dramatic life-span extension in animal models of aging are often ineffective when translated to clinical trials. This may be due to differences in primary outcomes between species and difficulties in determining the optimal clinical trial paradigms for translation. Measures of physical function, including brief standardized testing batteries, are currently being proposed as biomarkers of aging in humans, are predictive of adverse health events, disability, and mortality, and are commonly used as functional outcomes for clinical trials. Motor outcomes are now being incorporated into preclinical testing, a positive step toward enhancing our ability to translate aging interventions to clinical trials. To further these efforts, we begin a discussion of physical function and disability assessment across species, with special emphasis on mice, rats, monkeys, and man. By understanding how physical function is assessed in humans, we can tailor measurements in animals to better model those outcomes to establish effective, standardized translational functional assessments with aging.

Coenzyme Q10 and α-tocopherol reversed age-associated functional impairments in mice

The purpose of this study was to determine if intake of the antioxidants coenzyme Q10 (CoQ10) or α-tocopherol (Toc), either alone or in combination, could ameliorate cognitive and psychomotor impairments of aged mice, as well as reduce oxidative burden in tissues. For a period of 10 weeks, male C57BL/6J mice (3 or 18 months) were fed either a control diet, or one of three diets supplemented with Toc, CoQ10 or their combination, and were tested for cognitive and psychomotor functions. Old mice on the Toc or Toc/CoQ10 diets showed improved coordinated running performance. Mice on the diet containing Toc/CoQ10 demonstrated improved performance in the discriminated avoidance task. CoQ10 and Toc alone also resulted in improved performance, albeit to a lesser degree. Protein damage was decreased especially when the mice received Toc+CoQ10 combination. Overall, these results suggest that, Toc and CoQ supplementation can ameliorate age-related impairment and reduce protein oxidation. Moreover, concurrent supplementation of CoQ10 and Toc may be more effective than either antioxidant alone.

Intravenous ascorbate improves spatial memory in middle-aged APP/PSEN1 and wild type mice

The present study investigated the effects of a single intravenous (i.v.) dose of Vitamin C (ascorbate, ASC) on spatial memory in APP/PSEN1 mice, an Alzheimer's disease model. First, we confirmed the uptake time course in ASC-depleted gulo (-/-) mice, which cannot synthesize ASC. Differential tissue uptake was seen based on ASC transporter distribution. Liver (SVCT1 and SVCT2) ASC was elevated at 30, 60 and 120 min post-treatment (125 mg/kg, i.v.), whereas spleen (SVCT2) ASC increased at 60 and 120 min. There was no detectable change in cortical (SVCT2 at choroid plexus, and neurons) ASC within the 2-h interval, although the cortex preferentially retained ASC. APP/PSEN1 and wild type (WT) mice at three ages (3, 9, or 20 months) were treated with ASC (125 mg/kg, i.v.) or saline 45 min before testing on the Modified Y-maze, a two-trial task of spatial memory. Memory declined with age and ASC treatment improved performance in 9-month-old APP/PSEN1 and WT mice. APP/PSEN1 mice displayed no behavioral impairment relative to WT controls. Although dopamine and metabolite DOPAC decreased in the nucleus accumbens with age, and improved spatial memory was correlated with increased dopamine in saline treated mice, acute ASC treatment did not alter monoamine levels in the nucleus accumbens. These data show that the Modified Y-maze is sensitive to age-related deficits, but not additional memory deficits due to amyloid pathology in APP/PSEN1 mice. They also suggest improvements in short-term spatial memory were not due to changes in the neuropathological features of AD or monoamine signaling.

Battery of behavioral tests in mice that models age-associated changes in human motor function

Motor function in humans can be characterized with tests of locomotion, strength, balance, and endurance. The aim of our project was to establish an analogous test battery to assess motor function in mice. Male C57BL/6 mice were studied at 3 (n = 87), 20 (n = 48) and 26 (n = 43) months of age. Tests assessed locomotion, strength, balance/coordination, and endurance capacity in mice. Motor function was reduced in the older groups of mice for the locomotion, strength, and endurance subdomains (p < 0.001). As indicated with a summary score, motor function declined by 7.4 % from 3 to 20 months and by 13.5 % from 20 to 26 months. Based on comparison with previously published data in humans, the magnitude and relative time course of changes were similar in mice and humans in each subdomain except balance/coordination. Power calculations confirmed that the age-associated differences depicted by several of the individual tests and domain summary scores would be sufficient to assess the efficacy of interventions aimed at prevention or treatment of motor dysfunction with aging. The current study describes a mouse model that characterizes age-associated changes in clinically relevant domains of motor function and indicates that the preclinical model can be used to test strategies to attenuate age-associated declines in motor function.

Coenzyme Q(10) supplementation reverses age-related impairments in spatial learning and lowers protein oxidation

Coenzyme Q10 (CoQ) is widely available as a dietary supplement and remains under consideration as a treatment for age-associated neurodegenerative conditions. However, no studies have determined if supplementation, initiated relatively late in life, could have beneficial effects on mild functional impairments associated with normal brain aging. Accordingly, the current study assessed the effect of CoQ intake in older mice for which cognitive and psychomotor impairments were already evident. Separate groups of young (3.5 months) and relatively old mice (17.5 months) were fed a control diet or a diet supplemented with low (0.72 mg/g) or high (2.81 mg/g) concentrations of CoQ for 15 weeks. After 6 weeks, the mice were given tests for spatial learning (Morris water maze), spontaneous locomotor activity, motor coordination, and startle reflex. Age-related impairments in cognitive and psychomotor functions were evident in the 17.5-month-old mice fed the control diet, and the low-CoQ diet failed to affect any aspect of the impaired performance. However, in the Morris water maze test, old mice on the high-CoQ diet swam to the safe platform with greater efficiency than the mice on the control diet. The old mice supplemented with the high-CoQ diet did not show improvement when spatial performance was measured using probe trials and failed to show improvement in other tests of behavioral performance. Protein oxidative damage was decreased in the mitochondria from the heart, liver, and skeletal muscle of the high-CoQ-supplemented mice and, to some extent, in the brain mitochondria. Contrasting with the deleterious effect of long-term CoQ supplementation initiated during young adulthood previously published, this study suggests that CoQ improves spatial learning and attenuates oxidative damage when administered in relatively high doses and delayed until early senescence, after age-related declines have occurred. Thus, in individuals with age-associated symptoms of cognitive decline, high-CoQ intake may be beneficial.

Aging in the cerebellum and hippocampus and associated behaviors over the adult life span of CB6F1 mice

In the present study we examined the effects of normal aging in the hippocampus and cerebellum, as well as behaviors associated with these substrates. A total of 67 CB6F1 hybrid mice were tested at one of five ages (4, 8, 12, 18 or 25 months) on the context pre-exposure facilitation effect (CPFE) modification of fear conditioning, rotorod, Barnes maze, acoustic startle, Morris water maze (MWM) and 500-ms trace eyeblink classical conditioning (EBCC). Behavioral tasks were chosen to increase the ability to detect age-related changes in learning, as trace EBCC is considered a more difficult paradigm (compared to delay EBCC) and the CPFE has been found to be more sensitive to hippocampus insults than standard contextual fear conditioning. To assess the effects of age on the brain, hippocampus volume was calculated and unbiased stereology was used to estimate the number of Purkinje neurons in the cerebellar cortex. A significant, age-related loss of Purkinje neurons was found-beginning at 12 months of age-and hippocampus volume remained stable over the adult life span. Age-related impairment was found, beginning at 12-18 months in the rotorod, and mice with fewer Purkinje neurons showed greater impairment in this task. CB6F1 mice retained auditory acuity across the life span and mice aged 25 months showed significant age-related impairment in the EBCC task; however, deficits were not associated with the loss of Purkinje neurons. Although the CPFE task is considered more sensitive to hippocampus insult, no age-related impairment was found. Spatial memory retention was impaired in the Barnes maze at 25 months, but no significant deficits were seen in the MWM. These results support the finding of differential aging in the hippocampus and cerebellum.

Longitudinal behavioral changes in the APP/PS1 transgenic Alzheimer's disease model

The APP/PS1 double transgenic mouse is an Alzheimer's Disease-like model. However, cognitive deficits measured at one age do not necessarily indicate age-related progressions. Further, results of the most widely used behavioral assessment, water maze performance, are generally limited to 1-2 endpoints. Here, male APP/PS1 and noncarrier wildtypes (n=11/group) were assessed at 7-15 months of age for water maze, open field, and motor coordination performance. Body weights and motor coordination were comparable for both groups throughout. Beginning at approximately 9 months of age, the transgenic group exhibited hypoactivity in the open field which continued throughout. Latency to locate the platform and swim path length were longer in the transgenic group; however, these appeared to be more related to increased floating and thigmotactic behavior and only partially related to a cognitive impairment. Age-related decrements in performance were not substantial; however, substantial plaque numbers were measured in six representative 16-month-old transgenic mice. The stability of water maze performance may be related to the longitudinal testing and repetitive experience, which previous research has demonstrated can confer beneficial effects on behavior and plaque deposition in transgenic Alzheimer's Disease models [1]. These results emphasize the importance of measuring multiple water maze endpoints and demonstrate the feasibility of longitudinal assessments in this model.

Age sensitivity of behavioral tests and brain substrates of normal aging in mice

Knowledge of age sensitivity, the capacity of a behavioral test to reliably detect age-related changes, has utility in the design of experiments to elucidate processes of normal aging. We review the application of these tests in studies of normal aging and compare and contrast the age sensitivity of the Barnes maze, eyeblink classical conditioning, fear conditioning, Morris water maze, and rotorod. These tests have all been implemented to assess normal age-related changes in learning and memory in rodents, which generalize in many cases to age-related changes in learning and memory in all mammals, including humans. Behavioral assessments are a valuable means to measure functional outcomes of neuroscientific studies of aging. Highlighted in this review are the attributes and limitations of these measures in mice in the context of age sensitivity and processes of brain aging. Attributes of these tests include reliability and validity as assessments of learning and memory, well-defined neural substrates, and sensitivity to neural and pharmacological manipulations and disruptions. These tests engage the hippocampus and/or the cerebellum, two structures centrally involved in learning and memory that undergo functional and anatomical changes in normal aging. A test that is less well represented in studies of normal aging, the context pre-exposure facilitation effect (CPFE) in fear conditioning, is described as a method to increase sensitivity of contextual fear conditioning to changes in the hippocampus. Recommendations for increasing the age sensitivity of all measures of normal aging in mice are included, as well as a discussion of the potential of the under-studied CPFE to advance understanding of subtle hippocampus-mediated phenomena.

Prolonged intake of coenzyme Q10 impairs cognitive functions in mice

Coenzyme Q(10) (CoQ(10)) is widely consumed as a dietary supplement to enhance bioenergetic capacity and to ameliorate the debilitative effects of the aging process or certain pathological conditions. Our main purpose in this study was to determine whether CoQ(10) intake does indeed attenuate the age-associated losses in motor, sensory, and cognitive functions or decrease the rate of mortality in mice. Mice were fed a control nonpurified diet or that diet containing 0.68 mg/g (low dosage) or 2.6 mg/g (high dosage) CoQ(10), starting at 4 mo of age, and were tested for sensory, motor, and cognitive function at 7, 15, and 25 mo of age. Amounts of the ubiquinols CoQ(9)H(2) and CoQ(10)H(2) measured in a parallel study were augmented in the cerebral cortex but not in any other region of the brain. Intake of the low-CoQ(10) diet did not affect age-associated decrements in muscle strength, balance, coordinated running, or learning/memory, whereas intake at the higher amount increased spontaneous activity, worsened the age-related losses in acuity to auditory and shock stimuli, and impaired the spatial learning/memory of old mice. The CoQ(10) diets did not affect survivorship of mice through 25 mo of age. Our results suggest that prolonged intake of CoQ(10) in low amounts has no discernable impact on cognitive and motor functions whereas intake at higher amounts exacerbates cognitive and sensory impairments encountered in old mice. These findings do not support the notion that CoQ(10) is a fitness-enhancing or an "antiaging" substance under normal physiological conditions.

Dissociation of functional status from accrual of CML and RAGE in the aged mouse brain

The objectives of this study were: (i) to identify regions of the aged mouse brain in which advanced glycation end-products (AGEs) were increased, and (ii) assess the functional significance of AGEs by determining the extent to which they could predict age-related brain dysfunction. Densitometric analyses of immunoblots for N epsilon-(carboxymethyl)lysine (CML), a predominant AGE, and receptor for AGE (RAGE), were performed in different brain regions of mice aged 8 or 25 months. The 25-month-old mice were tested for ability to perform on tests of cognitive and psychomotor function prior to assessment of CML or RAGE, to determine if immunostaining results could predict functional impairment among the older mice. The amounts of CML increased with age in cortex, hippocampus, striatum, and midbrain, but were unchanged in the brainstem and cerebellum. Increases in RAGE were evident in all brain regions but the hippocampus, and were not linked to increased amounts of CML. Different statistical approaches each failed to reveal any strong association between the degree of age-related functional impairment among individual mice and amounts of CML or RAGE in any particular region of the brain. The findings from this study suggest that accrual of CML and expression of RAGE in different brain regions are time-related phenomena that do not account for individual differences in brain aging or cognitive decline.

Profiling psychomotor and cognitive aging in four-way cross mice

In part due to their genetic uniformity and stable characteristics, inbred rodents or their F1 progeny are frequently used to study brain aging. However, it is recognized that focus on a single genotype could lead to generalizations about brain aging that might not apply to the species as a whole, or to the human population. As a potential alternative to uniform genotypes, genetically heterogeneous (HET) mice, produced by a four-way cross, were tested in the current study to determine if they exhibit age-related declines in cognitive and psychomotor function similar to other rodent models of brain aging. Young (4 months) and older (23 months) CB6F1 × C3D2F1 mice were administered a variety of tests for cognitive, psychomotor, and sensory/reflexive capacities. Spontaneous locomotion, rearing, and ability to turn in an alley all decreased with age, as did behavioral measures sensitive to muscle strength, balance, and motor coordination. Although no effect of age was found for either startle response amplitude or reaction time to shock stimuli, the old mice reacted with less force to low intensity auditory stimuli. When tested on a spatial swim maze task, the old mice learned less efficiently, exhibited poorer retention after a 66-h delay, and demonstrated greater difficulty learning a new spatial location. In addition, the older mice were less able to learn the platform location when it was identified by a local visual cue. Because there was a significant correlation between spatial and cued discrimination performance in the old mice, it is possible that age-related spatial maze learning deficits could involve visual or motor impairments. Variation among individuals increased with age for most tests of psychomotor function, as well as for spatial swim performance, suggesting that four-way cross mice may be appropriate models of individualized brain aging. However, the analysis of spatial maze learning deficits in older CB6F1 × C3D2F1 mice may have limited applicability in the study of brain aging, because of a confounding with visually cued performance deficits.