Long-term Environmental Enrichment Research Articles

Long-term Environmental Enrichment Normalizes Schizophrenia-like Abnormalities and Promotes Hippocampal Slc6a4 Promoter Demethylation in Mice Submitted to a Two-hit Model

Here, we explored the impact of prolonged environmental enrichment (EE) on behavioral, neurochemical, and epigenetic changes in the serotonin transporter gene in mice subjected to a two-hit schizophrenia model. The methodology involved administering the viral mimetic PolyI:C to neonatal Swiss mice as a first hit during postnatal days (PND) 5–7, or a sterile saline solution as a control. At PND21, mice were randomly assigned either to standard environment (SE) or EE housing conditions. Between PND35-44, the PolyI:C-treated group was submitted to various unpredictable stressors, constituting the second hit. Behavioral assessments were conducted on PND70, immediately after the final EE exposure. Following the completion of behavioral assessments, we evaluated the expression of proteins in the hippocampus that are indicative of microglial activation, such as Iba-1, as well as related to neurogenesis, including doublecortin (Dcx). We also performed methylation analysis on the serotonin transporter gene (Slc6a4) to investigate alterations in serotonin signaling. The findings revealed that EE for 50 days mitigated sensorimotor gating deficits and working memory impairments in two-hit mice and enhanced their locomotor and exploratory behaviors. EE also normalized the overexpression of hippocampal Iba-1 and increased the expression of hippocampal Dcx. Additionally, we observed hippocampal demethylation of the Slc6a4 gene in the EE-exposed two-hit group, indicating epigenetic reprogramming. These results contribute to the growing body of evidence supporting the protective effects of long-term EE in counteracting behavioral disruptions caused by the two-hit schizophrenia model, pointing to enhanced neurogenesis, diminished microglial activation, and epigenetic modifications of serotonergic pathways as underlying mechanisms.

Long-term environmental enrichment is associated with better fornix microstructure in older adults.

Sustained environmental enrichment (EE) through a variety of leisure activities may decrease the risk of developing Alzheimer's disease. This cross-sectional cohort study investigated the association between long-term EE in young adulthood through middle life and microstructure of fiber tracts associated with the memory system in older adults. N = 201 cognitively unimpaired participants (≥ 60 years of age) from the DZNE-Longitudinal Cognitive Impairment and Dementia Study (DELCODE) baseline cohort were included. Two groups of participants with higher (n = 104) or lower (n = 97) long-term EE were identified, using the self-reported frequency of diverse physical, intellectual, and social leisure activities between the ages 13 to 65. White matter (WM) microstructure was measured by fractional anisotropy (FA) and mean diffusivity (MD) in the fornix, uncinate fasciculus, and parahippocampal cingulum using diffusion tensor imaging. Long-term EE groups (lower/higher) were compared with adjustment for potential confounders, such as education, crystallized intelligence, and socio-economic status. Reported participation in higher long-term EE was associated with greater fornix microstructure, as indicated by higher FA (standardized β = 0.117, p = 0.033) and lower MD (β = -0.147, p = 0.015). Greater fornix microstructure was indirectly associated (FA: unstandardized B = 0.619, p = 0.038; MD: B = -0.035, p = 0.026) with better memory function through higher long-term EE. No significant effects were found for the other WM tracts. Our findings suggest that sustained participation in a greater variety of leisure activities relates to preserved WM microstructure in the memory system in older adults. This could be facilitated by the multimodal stimulation associated with the engagement in a physically, intellectually, and socially enriched lifestyle. Longitudinal studies will be needed to support this assumption.

Long-term environmental enrichment overcomes depression, learning, and memory impairment in elderly CD-1 mice with maternal sleep deprivation exposure.

Early-life stress disrupts central nervous system development and increases the risk of neuropsychiatric disorder in offspring based on rodent studies. Maternal sleep deprivation (MSD) in rodents has also been associated with depression and cognitive decline in adult offspring. However, it is not known whether these issues persist into old age. Environmental enrichment is a non-pharmacological intervention with proven benefits in improving depression and cognitive impairment; however, it is unclear whether these benefits hold for aging mice following MSD exposure. The aim of this study was to explore the effects of MSD on depression and cognition in elderly offspring CD-1 mice and to determine whether long-term environmental enrichment could alleviate these effects by improving neuroinflammation and synaptic plasticity. The offspring mice subjected to MSD were randomly assigned to either a standard environment or an enriched environment. At 18 months of age, the forced swimming and tail suspension tests were used to evaluated depression-like behaviors, and the Morris water maze test was used to evaluate cognitive function. The expression levels of hippocampal proinflammatory cytokines and synaptic plasticity-associated proteins were also measured. MSD increased depression-like behaviors and impaired cognition function in aging CD-1 offspring mice. These effects were accompanied by upregulated interleukin (IL)-1β, IL-6, and tumor necrosis factor-α expression, and downregulated brain-derived neurotrophic factor, tyrosine kinase receptor B, postsynaptic density-95, and synaptophysin expression in the hippocampus. All of these changes were reversed by long-term exposure to an enriched environment. These findings suggest that MSD exerts long-term effects on the behaviors of offspring in mice, leading to depression and cognitive impairment in older age. Importantly, long-term environmental enrichment could counteract the behavior difficulties induced by MSD through improving hippocampal proinflammatory cytokines and synaptic plasticity-associated proteins.

Maternal separation increased memory function and anxiety without effects of environmental enrichment in male rats

Maternal separation is a detrimental postnatal influence, whereas environmental enrichment is a therapeutic and protective agent. It is unclear if long-term environmental enrichment can compensate for the effects of maternal separation stress on memory-related alterations. This study examined how environmental enrichment affected memory functions, anxiety level, Grin2a, Grin2b, BDNF, and cFos expressions in the maternally separated rats. There are seven groups in this study: control (C), maternal separation+standard cage (MS), maternal separation + enriched cage (MSE), enriched cage (E), the maternal separation that decapitated at postnatal 21 (MS21) and standard cage that decapitated at PN21 (C21) for hormone and gene expression analysis. The maternal separation procedure consisted of postnatal 21 days. Learning and memory performance were determined with the Morris water tank test; anxiety and locomotor activity were examined with the open field and elevated plus-maze test. The expression levels of genes were measured by the RT-PCR method. Blood corticosterone level was evaluated by the ELISA method. Results showed that MS increased memory performance, locomotor activity, and anxiety, but it did not change gene expression levels. An enriched environment did not change the memory performance, locomotor activity, and related gene expression levels. MSE group increased their memory performance, but the anxiety, locomotor activity, and gene expression level did not change. Grin2a, Grin2b, and BDNF gene expression and corticosterone levels increased in the MS21 group. Maternal separation increased memory performance, but it also increased anxiety. Environmental enrichment alone was insufficient to cause alterations in the memory performance.

Environmental enrichment improves declined cognition induced by prenatal inflammatory exposure in aged CD-1 mice: Role of NGPF2 and PSD-95.

Research suggests that prenatal inflammatory exposure could accelerate age-related cognitive decline that may be resulted from neuroinflammation and synaptic dysfunction during aging. Environmental enrichment (EE) may mitigate the cognitive and synaptic deficits. Neurite growth-promoting factor 2 (NGPF2) and postsynaptic density protein 95 (PSD-95) play critical roles in neuroinflammation and synaptic function, respectively. We examined whether this adversity and EE exposure can cause alterations in Ngpf2 and Psd-95 expression. In this study, CD-1 mice received intraperitoneal injection of lipopolysaccharide (50 μg/kg) or normal saline from gestational days 15-17. After weaning, half of the male offspring under each treatment were exposed to EE. The Morris water maze was used to assess spatial learning and memory at 3 and 15 months of age, whereas quantitative real-time polymerase chain reaction and Western blotting were used to measure hippocampal mRNA and protein levels of NGPF2 and PSD-95, respectively. Meanwhile, serum levels of IL-6, IL-1β, and TNF-α were determined by enzyme-linked immunosorbent assay. The results showed that aged mice exhibited poor spatial learning and memory ability, elevated NGPF2 mRNA and protein levels, and decreased PSD-95 mRNA and protein levels relative to their young counterparts during natural aging. Embryonic inflammatory exposure accelerated age-related changes in spatial cognition, and in Ngpf2 and Psd-95 expression. Additionally, the levels of Ngpf2 and Psd-95 products were significantly positively and negatively correlated with cognitive dysfunction, respectively, particularly in prenatal inflammation-exposed aged mice. Changes in serum levels of IL-6, IL-1β, and TNF-α reflective of systemic inflammation and their correlation with cognitive decline during accelerated aging were similar to those of hippocampal NGPF2. EE exposure could partially restore the accelerated decline in age-related cognitive function and in Psd-95 expression, especially in aged mice. Overall, the aggravated cognitive disabilities in aged mice may be related to the alterations in Ngpf2 and Psd-95 expression and in systemic state of inflammation due to prenatal inflammatory exposure, and long-term EE exposure may ameliorate this cognitive impairment by upregulating Psd-95 expression.

Long-Term Environmental Enrichment Relieves Dysfunctional Cognition and Synaptic Protein Levels Induced by Prenatal Inflammation in Older CD-1 Mice.

A mounting body of evidence suggests that prenatal inflammation may enhance the rate of age-associated cognitive decline and may involve aberrant amounts of synaptic proteins in the hippocampus, including synaptotagmin-1 (Syt1) and activity-regulated cytoskeleton-associated protein (Arc). However, little is known about the specific impact of adolescent environmental enrichment (EE) on age-associated cognitive decline and the changes in synaptic proteins caused by prenatal inflammation. In this study, CD-1 mice in late pregnancy were given intraperitoneal doses of lipopolysaccharide (LPS, 50 μg/kg) or normal saline. Offspring arising from LPS dams were divided into a LPS group and a LPS plus EE (LPS-E) group. The LPS-E mice were exposed to EE from 2 months of age until the end of the experiment (3 or 15 months old). The Morris water maze (MWM) was used to assess the spatial learning and memory capacities of experimental mice, while western blotting and RNA-scope were used to determine the expression levels of Arc and Syt1 in the hippocampus at the protein and mRNA levels, respectively. Analysis revealed that at 15 months of age, the control mice experienced a reduction in cognitive ability and elevated expression levels of Arc and Syt1 genes when compared to control mice at 3 months of age. The LPS-E group exhibited better cognition and lower protein and mRNA levels of Arc and Syt1 than mice in the LPS group of the same age. However, the enriched environment mitigated but did not counteract, the effects of prenatal inflammation on cognitive and synaptic proteins when tested at either 3 or 15 months of age. Our findings revealed that long-term environmental enrichment improved the expression levels of synaptic proteins in CD-1 mice and that this effect was linked to the dysfunctional cognition caused by prenatal inflammation; this process may also be involved in the reduction of hippocampal Arc and Syt1 gene expression.

MRI-derived brain age as a biomarker of ageing in rats: validation using a healthy lifestyle intervention

The difference between brain age predicted from MRI and chronological age (the so-called BrainAGE) has been proposed as an ageing biomarker. We analyse its cross-species potential by testing it on rats undergoing an ageing modulation intervention. Our rat brain age prediction model combined Gaussian process regression with a classifier and achieved a mean absolute error (MAE) of 4.87 weeks using cross-validation on a longitudinal dataset of 31 normal ageing rats. It was then tested on two groups of 24 rats (MAE = 9.89 weeks, correlation coefficient = 0.86): controls vs. a group under long-term environmental enrichment and dietary restriction (EEDR). Using a linear mixed-effects model, BrainAGE was found to increase more slowly with chronological age in EEDR rats (p=0.015 for the interaction term). Cox regression showed that older BrainAGE at 5 months was associated with higher mortality risk (p=0.03). Our findings suggest that lifestyle-related prevention approaches may help to slow down brain ageing in rodents and the potential of BrainAGE as a predictor of age-related health outcomes.

Sedentary Life and Reduced Mastication Impair Spatial Learning and Memory and Differentially Affect Dentate Gyrus Astrocyte Subtypes in the Aged Mice.

To explore the impact of reduced mastication and a sedentary lifestyle on spatial learning and memory in the aged mice, as well as on the morphology of astrocytes in the molecular layer of dentate gyrus (MolDG), different masticatory regimens were imposed. Control mice received a pellet-type hard diet, while the reduced masticatory activity group received a pellet diet followed by a powdered diet, and the masticatory rehabilitation group received a pellet diet, followed by powder diet and then a pellet again. To mimic sedentary or active lifestyles, mice were housed in an impoverished environment of standard cages or in an enriched environment. The Morris Water Maze (MWM) test showed that masticatory-deprived group, regardless of environment, was not able to learn and remember the hidden platform location, but masticatory rehabilitation combined with enriched environment recovered such disabilities. Microscopic three-dimensional reconstructions of 1,800 glial fibrillary acidic protein (GFAP)-immunolabeled astrocytes from the external third of the MolDG were generated using a stereological systematic and random sampling approach. Hierarchical cluster analysis allowed the characterization into two main groups of astrocytes with greater and lower morphological complexities, respectively, AST1 and AST2. When compared to compared to the hard diet group subjected to impoverished environment, deprived animals maintained in the same environment for 6 months showed remarkable shrinkage of astrocyte branches. However, the long-term environmental enrichment (18-month-old) applied to the deprived group reversed the shrinkage effect, with significant increase in the morphological complexity of AST1 and AST2, when in an impoverished or enriched environment. During housing under enriched environment, complexity of branches of AST1 and AST2 was reduced by the powder diet (pellet followed by powder regimes) in young but not in old mice, where it was reversed by pellet diet (pellet followed by powder and pellet regime again). The same was not true for mice housed under impoverished environment. Interestingly, we were unable to find any correlation between MWM data and astrocyte morphological changes. Our findings indicate that both young and aged mice subjected to environmental enrichment, and under normal or rehabilitated masticatory activity, preserve spatial learning and memory. Nonetheless, data suggest that an impoverished environment and reduced mastication synergize to aggravate age-related cognitive decline; however, the association with morphological diversity of AST1 and AST2 at the MolDG requires further investigation.

Neurovascular integrative effects of long-term environmental enrichment on chronic cerebral hypoperfusion rat model

Vascular dementia (VaD) is one of the most common types of dementia followed by Alzheimer's disease (AD). Recent studies showed that approximately 30 %–35 % of patients with AD at post-mortem exhibited vascular pathologies, which suggested that mixed dementia may be the most common type of dementia. Permanent bilateral common carotid artery occlusion (2VO) is a well-characterized method for investigating cognitive functions and the histopathological consequences of chronic cerebral hypoperfusion (CCH) in rats. In the present study, we investigated the effects of environmental enrichment (EE) on cognitive impairment after CCH, as well as the effects of CCH-induced neurovascular damage on cognitive function. Wistar rats were randomly allocated to a sham group, a 2VO group, and a 2VO + EE group. The 2VO procedure was performed at 12 weeks, while EE was performed for 8 weeks before and 6 weeks after 2VO. The effect of EE on cognitive functions in 2VO rats was investigated using the radial-arm maze and Morris Water Maze tests. Neurovascular integrity was assessed based on immunoreactivity for glial fibrillary acidic protein (GFAP), morphological changes in microvessels, and the expression of matrix metalloproteinase-9 (MMP-9) and zonula occludens-1 (ZO-1) in the motor cortex and hippocampus. EE ameliorated microvessel fragmentation by sustaining the tight junction through increases of ZO-1 expression after CCH, resulting in preserving the neurovascular unit. In summary, EE mitigated cognitive impairment by restoring neurovascular integrity. These findings suggest that EE can be a valuable and meaningful environmental intervention for patients with cognitive impairment.

Short-term but not long-term exposure to an enriched environment facilitates the extinction of aversive memory

Environmental enrichment (EE) has been used to investigate behavioral changes and neuroplasticity in brain in normal and pathological conditions. Besides, the EE has been used to understand the neurobehavioral systems involved in learning experiences, visual inputs, defensive responses, social interactions and memory. However, the required exposure duration to remove aversive memories remains lacking. Therefore, the purpose of the present study was to investigate the time-course effect of EE exposure on the extinction of aversive memory. Young adult male Wistar rats were exposed to two different EE protocols: short-term environmental enrichment (EE2 – animal kept under enriched conditions for two weeks) and long-term environmental enrichment (EE4 – animal kept under enriched conditions for four weeks). The contextual fear conditioning test was used to assess aversive memory. The both EE protocols provide changes in Zif-268 immunoreactivity in mesocorticolimbic areas such as CA1 and central amygdala; however, only short-term EE reduces the ZIF-268 immunoreactivity in VTA. Besides, both EE protocols also provide an increase in TH immunoreactivity in VTA and nucleus accumbens, but only the short-term EE modifies the TH immunoreactivity in CA1 and infralimbic region of the prefrontal cortex. The time-course effect of EE interferes differently on the extinction of aversive memory, being two weeks of exposure with EE sufficient to cause improvement in coping during aversive situations, favoring the extinction of conditioned fear memory.

Duration of Environmental Enrichment Determines Astrocyte Number and Cervical Lymph Node T Lymphocyte Proportions but Not the Microglial Number in Middle-Aged C57BL/6 Mice.

Environmental enrichment (EE) has been shown to modulate behavior and immunity. We recently reported that both short and long-term EE enhance baseline locomotion and alleviate depressive-like behavior, but only long-term EE affects locomotion adversely in a threatening environment and enhances anxiety-like behavior in middle-age mice. We have now investigated whether the observed changes in behavior after short- and long-term EE were associated with underlying immune changes. Hence, at the end of behavioral testing, mice were sacrificed, and brains and cervical lymph nodes were collected to investigate the differential effects of the duration of EE (short- and long-term) on the number of immunopositive glial cells in the dentate gyrus, CA1, CA2, and CA3 regions of the hippocampus and proportions of T cell subsets in the cervical lymph nodes using immunohistochemistry and flow cytometry, respectively. EE, regardless of duration, caused an increase in microglia number within the dentate gyrus, CA1 and CA3 hippocampal regions, but only long-term EE increased astrocytes number within the dentate gyrus and CA3 hippocampal regions. A significantly higher proportion of CD8+ naive T cells was observed after long-term EE vs. short-term EE. No significant differences were observed in the proportion of central memory and effector memory T cells or early activated CD25+ cells between any of the test groups. Our results suggest that EE, irrespective of duration, enhances the numbers of microglia, but long-term EE is required to modify astrocyte number and peripheral T cell proportions in middle-aged mice. Our findings provide new insights into the therapeutic effects of EE on various brain disorders, which may be at least partly mediated by glial and neuroimmune modulation.

Long-term environmental enrichment affects microglial morphology in middle age mice.

Aging is associated with increased central nervous system inflammation, in large part due to dysfunctional microglia. Environmental enrichment (EE) provides a model for studying the dynamics of lifestyle factors in the development of age-related neuroinflammation and microglial dysfunction. EE results in improvements in learning and memory, metabolism, and mental health in a variety of animal models. We recently reported that implementing EE in middle age promotes healthy aging. In the present study, we investigated whether EE influences microglial morphology, and whether EE is associated with changes in expression of microglial and neuroinflammatory markers. Inflammatory cytokines and MHC-II were reduced following 12-month EE in 10-month-old mice. Long-term EE for 7.5 months resulted in broad increases in Iba1 expression in hippocampus, hypothalamus, and amygdala detected by immunohistochemistry. Quantification of microglial morphology reveal both hypertrophy and ramification in these three brain regions, without increases in microglial cell density. These data indicate that long-term EE implemented in middle age results in a microglial state distinct from that of normal aging in standard laboratory housing, in specific brain regions, associated with reduced neuroinflammatory markers and improvement of systemic metabolism.

The effects of short-term and long-term environmental enrichment on locomotion, mood-like behavior, cognition and hippocampal gene expression

BackgroundEnvironmental enrichment (EE) has been shown to modulate behavior and hippocampal gene expression; however, the currently available literature does not explain the differential effects that may relate to the duration of EE. AimTo investigate the differential effects of short- and long-term EE on locomotion, anxiety-, depressive- and cognition-like behaviors, and hippocampal gene expression under physiological conditions. MethodsWe assigned either short-term or long-term intervention with respective controls to healthy C57BL/6 mice (n = 12–16/group). The short-term EE group received EE for four weeks starting at eight months of age, while the long-term EE group received EE for six months starting at three months of age. Differential effects of the duration of EE on various behaviors and hippocampal gene expression at nine months of age were measured using an established behavioral battery and high-throughput RT-qPCR, respectively. ResultsBoth short-term and long-term EE significantly enhanced locomotion in the home cage and reduced depressive-like behavior in the forced-swim test. Long-term EE, however, reduced locomotion in the open-field test. Additionally, short-term EE reduced the mean body weight and showed anxiolytic effects in the elevated-zero maze (EZM), while these effects were lost after long-term EE. There were no effects of either short-term or long-term EE on the expression of 43 hippocampal genes of interest tested at adjusted p < 0.05. ConclusionBoth short and long-term EE are equally beneficial for baseline locomotor activity and depressive-like behavior. However, long-term EE affects locomotion adversely in a threatening environment and is anxiogenic.

Implementation of environmental enrichment after middle age promotes healthy aging.

With increases in life expectancy, it is vital to understand the dynamics of aging, their interaction with lifestyle factors, and the connections to age-related disease processes. Our work on environmental enrichment (EE), a housing environment boosting mental health, has revealed a novel anticancer and anti-obesity phenotype mediated by a brain-fat axis: the hypothalamic-sympathoneural-adipocyte (HSA) axis in young animals. Here we investigated EE effects on healthspan and lifespan when initiated after middle age. Short-term EE for six weeks activated the HSA axis in 10-month-old mice. Long-term EE for twelve months reduced adiposity, improved glucose tolerance, decreased leptin levels, enhanced motor abilities, and inhibited anxiety. In addition to adipose remodeling, EE decreased age-related liver steatosis, reduced hepatic glucose production, and increased glucose uptake by liver and adipose tissue contributing to the improved glycemic control. The EE-induced liver modulation was associated with a suppression of protein kinase Cε. Moreover, EE down-regulated the expression of inflammatory genes in the brain, adipose, and liver. EE initiated at 18-month of age significantly improved glycemic control and showed a trend of positive impact on mean lifespan. These data suggest that EE induces metabolic and behavioral adaptations that are shared by factors known to increase healthspan and lifespan.

Lifelong environmental enrichment in the absence of exercise protects the brain from age-related cognitive decline

Environmental manipulations enhance neuroplasticity, with enrichment-induced cognitive improvements linked to increased expression of growth factors and enhanced hippocampal neurogenesis. Environmental enrichment (EE) is defined as the addition of social, physical and somatosensory stimulation into an animal's environment via larger group housing, extra objects and, often, running wheels. Previous studies from our laboratory report that physical activity is a potent memory enhancer but that long-term environmental stimulation can be as effective as exercise at ameliorating age-related memory decline. To assess the effects of EE, in the absence of exercise, rats were housed in continuous enriched conditions for 20 months and memory assessed at young, middle aged and aged timepoints. MRI scans were also performed at these timepoints to assess regional changes in grey matter and blood flow with age, and effects of EE upon these measures. Results show an age-related decline in recognition, spatial and working memory that was prevented by EE. A parallel reduction in βNGF in hippocampus, and cell proliferation in the dentate gyrus, was prevented by EE. Furthermore, EE attenuated an age-related increase in apoptosis and expression of pro-inflammatory markers IL-1β and CD68. Long-term EE induced region-specific changes in grey matter intensity and partially rescued age-related reductions in cerebral blood flow. This study demonstrates that sensory enrichment alone can ameliorate many features typical of the ageing brain, such as increases in apoptosis and pro-inflammatory markers. Furthermore, we provide novel data on enrichment-induced regional grey matter alterations and age-related changes in blood flow in the rat.This article is part of the Special Issue entitled “Neurobiology of Environmental Enrichment”.

A Method to Define the Effects of Environmental Enrichment on Colon Microbiome Biodiversity in a Mouse Colon Tumor Model.

Several recent studies have illustrated the beneficial effects of living in an enriched environment on improving human disease. In mice, environmental enrichment (EE) reduces tumorigenesis by activating the mouse immune system, or affects tumor bearing animal survival by stimulating the wound repair response, including improved microbiome diversity, in the tumor microenvironment. Provided here is a detailed procedure to assess the effects of environmental enrichment on the biodiversity of the microbiome in a mouse colon tumor model. Precautions regarding animal breeding and considerations for animal genotype and mouse colony integration are described, all of which ultimately affect microbial biodiversity. Heeding these precautions may allow more uniform microbiome transmission, and consequently will alleviate non-treatment dependent effects that can confound study findings. Further, in this procedure, microbiota changes are characterized using 16S rDNA sequencing of DNA isolated from stool collected from the distal colon following long-term environmental enrichment. Gut microbiota imbalance is associated with the pathogenesis of inflammatory bowel disease and colon cancer, but also of obesity and diabetes among others. Importantly, this protocol for EE and microbiome analysis can be utilized to study the role of microbiome pathogenesis across a variety of diseases where robust mouse models exist that can recapitulate human disease.

The Effect of Long-Term Environmental Enrichment in Chronic Cerebral Hypoperfusion-Induced Memory Impairment in Rats.

Vascular dementia (VaD) is the second most common cause of dementia. It occurs when the cerebral blood supply is reduced by disarrangement of the circulatory system. Environmental enrichment (EE) has been associated with cognitive improvement, motor function recovery, and anxiety relief with respect to various neurodegenerative diseases and emotional stress models. The purpose of this study was to determine whether long-term EE influenced cognitive impairment in a rat model of chronic hypoperfusion induced by permanent occlusion of bilateral common carotid arteries (BCCAo). The Y-maze and Morris water maze tests were performed to evaluate the rats' cognitive functions. Also, the protein expression of brain-derived neurotrophic factor (BDNF), phosphorylated cAMP-calcium response element binding protein (pCREB), and vascular endothelial growth factor (VEGF) were confirmed by Western blot. The microvessels and angiogenesis-associated proteins in the hippocampal region were investigated using immunohistochemistry. The VaD + EE group showed significantly better cognitive functions than the VaD group in both the Y-maze and MWM tests. In addition, the VaD + EE group showed significantly increased expression of BDNF, pCREB, and VEGF in the hippocampus compared to the VaD group. Rats in the VaD + EE group also had increased length of microvessels and VEGF expression in the hippocampus. These results suggest that long-term EE exerts neuroprotective effects against cognitive impairment induced by chronic cerebral hypoperfusion through the enhancement of BDNF, pCREB, and VEGF expression and indicate that EE may be a good nursing intervention in vascular dementia patients.

Effects of Long-Term Environmental Enrichment on Anxiety, Memory, Hippocampal Plasticity and Overall Brain Gene Expression in C57BL6 Mice.

There is ample evidence that physical activity exerts positive effects on a variety of brain functions by facilitating neuroprotective processes and influencing neuroplasticity. Accordingly, numerous studies have shown that continuous exercise can successfully diminish or prevent the pathology of neurodegenerative diseases such as Alzheimer’s disease in transgenic mouse models. However, the long-term effect of physical activity on brain health of aging wild-type (WT) mice has not yet been studied in detail. Here, we show that prolonged physical and cognitive stimulation, mediated by an enriched environment (EE) paradigm for a duration of 11 months, leads to reduced anxiety and improved spatial reference memory in C57BL6 WT mice. While the number of CA1 pyramidal neurons remained unchanged between standard housed (SH) and EE mice, the number of dentate gyrus (DG) neurons, as well as the CA1 and DG volume were significantly increased in EE mice. A whole-brain deep sequencing transcriptome analysis, carried out to better understand the molecular mechanisms underlying the observed effects, revealed an up-regulation of a variety of genes upon EE, mainly associated with synaptic plasticity and transcription regulation. The present findings corroborate the impact of continuous physical activity as a potential prospective route in the prevention of age-related cognitive decline and neurodegenerative disorders.

Alteration of Energy Metabolism and Antioxidative Processing in the Hippocampus of Rats Reared in Long-Term Environmental Enrichment

Environmental enrichment (EE) is a typical experimental method that promotes levels of novelty and complexity that enhance experience-dependent neuroplasticity and cognitive behavior function in laboratory animals. Early EE is associated with resilience in the face of later-life challenges. Since increased synaptic activity enhances endogenous neuronal antioxidant defenses, we hypothesized that long-term EE beginning at an early stage may alter the levels of oxidative stress. We investigated global protein expression and oxidative stress in hippocampal proteins from rats nurtured for a 6-month EE beginning in the prenatal period. The analysis of protein expression was carried out using 2-dimensional gel electrophoresis with matrix-associated laser desorption ionization time-of-flight mass spectrometry. Proteins with altered expression were involved in energy metabolism (phosphoglycerate mutase 1, α-enolase isoform 1, adenylate kinase 1, and triose phosphate isomerase) and antioxidant enzymes (superoxide dismutase 1, glutathione S-transferase ω type 1, peroxiredoxin 5, DJ-1, and glial maturation factor β). Using Western blot assays, some of the proteins with altered expression and NADPH oxidase 2 were confirmed to be decreased. Further confirmation was demonstrated with attenuated expression of 7,8-dihydro-8-oxo-deoxyguanine, a DNA oxidative stress marker, in the hippocampus of EE group rats. Our data demonstrate that a long-term EE program beginning in the prenatal and early postnatal phase of development modulates energy metabolism and reduced oxidant stress possibly through enhanced synaptic activity. We provide evidence that EE can be developed as a tool to protect the brain from oxidative stress-induced injury.

Environmental Enrichment Attenuates Traumatic Brain Injury: Induced Neuronal Hyperexcitability in Supragranular Layers of Sensory Cortex.

We have previously demonstrated that traumatic brain injury (TBI) induces significant long-term neuronal hyperexcitability in supragranular layers of sensory cortex, coupled with persistent sensory deficits. Hence, we aimed to investigate whether brain plasticity induced by environmental enrichment (EE) could attenuate abnormal neuronal and sensory function post-TBI. TBI (n = 22) and sham control (n = 21) animals were randomly assigned housing in either single or enriched conditions for 7-9 weeks. Then, in terminal experiments, extracellular recordings were obtained from barrel cortex neurons in response to whisker motion, including those mimicking motion in awake animals undertaking different tasks. Long-term EE exposure (6 weeks) attenuated TBI-induced hyperexcitability in layers 2-3, such that neuronal activity in TBI animals exposed to EE was restored to control levels. Little to no EE-induced changes in population neuronal responses occurred in input layer 4 and output layer 5. However, single-cell responses demonstrated EE-induced hypoexcitation in L4 post-TBI. EE was also able to fully ameliorate sensory hypersensitivity post-TBI, although it was not found to improve motor function. Long-term enrichment post-TBI induces changes at both the population and single-cell level in the sensory cortex, where EE may act to restore the excitation/inhibition balance in supragranular cortical layers.