Short-Term Environmental Enrichment is a Stronger Modulator of Brain Glial Cells and Cervical Lymph Node T Cell Subtypes than Exercise or Combined Exercise and Enrichment.

Physical exercise (PE) and environmental enrichment (EE) can modulate immunity. However, the differential effects of short-term PE, EE, and PE + EE on neuroimmune mechanisms during normal aging has not been elucidated. Hence, a cohort of 3-, 8-, and 13-month-old immunologically unchallenged C57BL/6 wild-type mice were randomly assigned to either Control, PE, EE, or PE + EE groups and provided with either no treatment, a running wheel, a variety of plastic and wooden objects alone or in combination with a running wheel for seven weeks, respectively. Immunohistochemistry and 8-color flow cytometry were used to determine the numbers of dentate gyrus glial cells, and the proportions of CD4+ and CD8+ T cell numbers and their subsets from cervical lymph nodes, respectively. An increase in the number of IBA1+ microglia in the dentate gyrus at 5 and 10 months was observed after EE, while PE and PE + EE increased it only at 10 months. No change in astroglia number in comparison to controls were observed in any of the treatment groups. Also, all treatments induced significant differences in the proportion of specific T cell subsets, i.e., CD4+ and CD8+ T naïve (TN), central memory (TCM), and effector memory (TEM) cells. Our results suggest that in the short-term, EE is a stronger modulator of microglial and peripheral T cell subset numbers than PE and PE + EE, and the combination of short-term PE and EE has no additive effects.

Short-term environmental enrichment, and not physical exercise, alleviate cognitive decline and anxiety from middle age onwards without affecting hippocampal gene expression.

Physical exercise (PE) and environmental enrichment (EE) have consistently been shown to modulate behavior and neurobiological mechanisms. The current literature lacks evidence to confirm the relationship between PE and EE, if any, and whether short-term treatment with PE, EE, or PE+EE could be considered to correct age-related behavioral deficits. Three-, 8-, and 13-month-old C57BL/6 mice were assigned to either PE, EE, or PE+EE treatment groups (n = 12-16/group) for 4 weeks before behavioral testing and were compared to controls. Differential effects of the treatments on various behaviors and hippocampal gene expression were measured using an established behavioral battery and high-throughput qPCR respectively. Short-term EE enhanced locomotor activity at 9 and 14 months of age, whereas the combination of PE and EE reduced locomotor activity in the home cage at 14 months. Short-term EE also was found to reverse the age-related increase in anxiety at 9 months and spatial memory deficits at 14 months of age. Conversely, short-term PE induced spatial learning impairment and depressive-like behavior at four months but showed no effects in 9- and 14-month-old mice. PE and PE+EE, but not EE, modified the expression of several hippocampal genes at 9 months of age compared with control mice. In conclusion, short-term EE may help to alleviate age-related cognitive decline and increase in anxiety, without altering hippocampal gene expression. On the contrary, PE is detrimental at a young age for both affective-like behaviors and spatial learning and memory but showed no effects at middle and late middle age despite hippocampal gene expression alterations.

TNF signaling via TNF receptors does not mediate the effects of short-term exercise on cognition, anxiety and depressive-like behaviors in middle-aged mice.

BACKGROUND: We recently reported that tumor necrosis factor (TNF) signaling via the TNFR1 and TNFR2 receptors mediates the effects of long-term exercise on locomotion, cognition and anxiety, but not depressive-like behavior. We now investigated whether the TNF signaling via its receptors also mediates the effects of short-term exercise on cognition, anxiety and depressive-like behaviors. METHODS: Thirteen-month-old C57BL/6 (WT), TNF-/-, TNFR1-/-, and TNFR2-/- mice were provided with 4 weeks of voluntary wheel running followed by behavioral testing using an established behavioral battery. Each genotype had a respective non-exercise control. RESULTS: There was no interaction between genotype and exercise in any of the tests but the main effect of genotype, and not exercise, were found to be significant in the open field (OF), forced-swim test (FST) and Barnes maze (BM). In the OF, the control and exercise TNFR2-/- mice spent significantly less time in the inner zone than mice in the control and exercise WT and TNF-/- cohorts. In the FST, control and exercise WT mice showed significantly higher immobility time than their control and exercise TNF-/-, TNFR1-/- and TNFR2-/- cohorts. In the BM, the latency to escape over 4 days of training was significantly higher in all KO groups compared to WT, irrespective of exercise. Also, the latency to escape to the original location during the probe trial was higher for control and exercise WT compared to corresponding TNFR1-/- mice. In contrast, the latency to escape to the new location was lower for control and exercise WT compared to control and exercise TNFR1-/- and TNFR2-/- mice. The latency to escape to the new location in exercise groups was longer compared to control within all genotypes. CONCLUSION: While TNF signaling via the TNF receptors mediates cognition, anxiety and depressive-like behaviors independently, it does not mediate the effects of short-term exercise on these behaviors in middle-aged mice.

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.

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.

Ceasing exercise induces depression-like, anxiety-like, and impaired cognitive-like behaviours and altered hippocampal gene expression.

BACKGROUND: Regular exercise can reduce depression-, anxiety-, and impaired cognitive-like behaviours, and upregulate hippocampal genes associated with neuroplasticity. However, the effects of ceasing exercise on depression-, anxiety-, and cognitive-like behaviours, and hippocampal gene expression remain unknown. METHODS: 12-week-old C57BL/6 mice (n = 12-16/group) were randomised to six months of exercise (exercise (EXC)), four months of exercise then two months of no exercise (exercise-cessation (EC)), or no-exercise control (CONT) until aged nine months. Depression-, anxiety-, and cognitive-like behaviours were tested with the forced swim test, open field and elevated zero maze, Y-maze, and Barnes maze. The expression of 75 hippocampal genes were investigated by high-throughput quantitative polymerase chain reaction (qPCR). RESULTS: Exercise cessation increased depression- and anxiety-like behaviours, and impaired spatial learning and cognitive flexibility compared to CONT and EXC mice. 10/75 hippocampal genes were differentially expressed in EC mice, including increased expression of neurogenesis associated genes (Ntrk1), and reduced expression of immune (Il10, Gfap) and monoamine related genes (Htr1a) compared to CONT mice. Altered expression of nine genes including increased Slc6a4 and reduced Sirt1 expression were shown in EC mice compared to EXC mice. CONCLUSIONS: Exercise cessation increased depression- and anxiety-like behaviours and impaired some cognition-like behaviours with altered neurogenic, monoaminergic, and immune hippocampal gene expression consistent with the pathogenesis of depression and related anxiety described by the neurogenic, monoaminergic, and immune hypotheses of depression. Mice and humans share mammalian physiology, so these findings could be relevant to humans. These results require replication and possibly translation into high-quality pilot clinical trials.

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

BACKGROUND: Environmental 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. AIM: To 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. METHODS: We 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. RESULTS: Both 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. CONCLUSION: Both 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.

TNF signalling via the TNF receptors mediates the effects of exercise on cognition-like behaviours.

BACKGROUND: Altered TNF levels are associated with cognitive impairment in depression, schizophrenia, bipolar disorder, and Alzheimer's disease (AD). Exercise improves cognition-like behaviours, reduces the expression of tumour necrosis factor alpha (TNF), and increases expression of the soluble TNF receptors soluble TNFR1 (sTNFR1) and sTNFR2. We suggest TNF and its receptors are involved in cognitive function and dysfunction, and investigate whether exercise mediates its effects on cognitive function via TNF and its receptors. METHODS: We utilised C57BL/6, TNF-/-, TNFR1-/-, and TNFR2-/- mice to compare exercise to non-exercise control groups to investigate whether exercise exerts its effects on various types of cognition-like behaviours via TNF and its receptors. RESULTS: Recognition memory improved with exercise in WT mice, was impaired in TNFR1-/- exercise mice, showed non-significant impairment with exercise in TNF-/- mice, and no changes in TNFR2-/- mice. In spatial learning there were exercise related improvements in WT mice, non-significant but meaningful impairments evident in TNFR1-/- exercise mice, modest improvement in TNF-/- exercise mice, and potentially meaningful non-significant improvements in TNFR2-/- exercise mice. Moreover, WT and TNFR2-/- mice displayed noteworthy non-significant improvements in spatial memory, whereas TNFR1-/- exercise mice demonstrated non-significant spatial memory impairment. Exercise did not alter cognitive flexibility in any strain. DISCUSSION: TNF receptor signalling via the TNFR1 and TNFR2 appears to mediate the effects of exercise on cognitive-like behaviours. The potential for exercise to regulate human TNF and TNF signalling and cognitive dysfunction needs investigation under inflammatory conditions including depression and neuropsychiatric disorders.

Exercise related anxiety-like behaviours are mediated by TNF receptor signaling, but not depression-like behaviours.

Depression can involve disrupted pro-inflammatory TNF signaling via the TNF receptors TNFR1 and TNFR2, or the soluble TNF receptors sTNFR1 and sTNFR2. However, exercise might attenuate pro-inflammatory signaling in depression and related anxiety. We hypothesized that six months voluntary wheel running exercise would improve depression-like and anxiety-like behaviours in WT and TNFR1-/- mice, but not in TNF-/- and TNFR2-/- mice compared to their respective control mice. METHODS: We investigated the effects of six months voluntary wheel running exercise on open field (OF) and elevated zero maze (EZM) anxiety-like behaviours, and forced swim test (FST) depression-like behaviours in control and exercise WT, TNF-/-, TNFR1-/-, and TNFR2-/- mice with two-way ANOVAs. RESULTS: Exercise reduced of anxiety-like behaviours in TNFR2-/- exercise mice compared to their respective controls. Compared to WT control mice, WT exercise mice displayed significantly reduced EZM anxiety-like behaviours. There were no exercise related changes in FST immobility time. Between-strains analyses found WT control and exercise mice displayed reduced EZM anxiety-like behaviours compared to TNF-/- and TNFR1-/- control and exercise mice, and WT exercise mice displayed reduced anxiety-like behavior compared to TNFR2-/- exercise mice. DISCUSSION: Exercise associated TNFR1 and TNFR2 signaling in concert in WT exercise mice mediated reductions in aspects of anxiety-like behaviours. These findings are consistent with the current view that imbalances in TNF signaling are involved in disrupted affect. Additional studies are needed to further explore the roles of exercise related TNFR1 and TNFR2 signaling in anxiety-like and depression-like behaviours.

The effects of aerobic exercise on depression-like, anxiety-like, and cognition-like behaviours over the healthy adult lifespan of C57BL/6 mice.

Preclinical studies have demonstrated exercise improves various types of behaviours such as anxiety-like, depression-like, and cognition-like behaviours. However, these findings were largely conducted in studies utilising short-term exercise protocols, and the effects of lifetime exercise on these behaviours remain unknown. This study investigates the behavioural effects of lifetime exercise in normal healthy ageing C57BL/6 mice over the adult lifespan. 12 week-old C57BL/6 mice were randomly assigned to voluntary wheel running or non-exercise (control) groups. Exercise commenced at aged 3 months and behaviours were assessed in young adult (Y), early middle age (M), and old (O) mice (n=11-17/group). The open field and elevated zero maze examined anxiety-like behaviours, depression-like behaviours were quantified with the forced swim test, and the Y maze and Barnes maze investigated cognition-like behaviours. The effects of lifetime exercise were not simply an extension of the effects of chronic exercise on anxiety-like, depression-like, and cognition-like behaviours. Exercise tended to reduce overt anxiety-like behaviours with ageing, and improved recognition memory and spatial learning in M mice as was expected. However, exercise also increased anxiety behaviours including greater freezing behaviour that extended spatial learning latencies in Y female mice in particular, while reduced distances travelled contributed to longer spatial memory and cognitive flexibility latencies in Y and O mice. Lifetime exercise may increase neurogenesis-associated anxiety. This could be an evolutionary conserved adaptation that nevertheless has adverse impacts on cognition-like function, with particularly pronounced effects in Y female mice with intact sex hormones. These issues require careful investigation in future rodent studies.

Epigenetic alterations following early postnatal stress: a review on novel aetiological mechanisms of common psychiatric disorders.

Stressor exposure during early life has the potential to increase an individual's susceptibility to a number of neuropsychiatric conditions such as mood and anxiety disorders and schizophrenia in adulthood. This occurs in part due to the dysfunctional stress axis that persists following early adversity impairing stress responsivity across life. The mechanisms underlying the prolonged nature of this vulnerability remain to be established. Alterations in the epigenetic signature of genes involved in stress responsivity may represent one of the neurobiological mechanisms. The overall aim of this review is to provide current evidence demonstrating changes in the epigenetic signature of candidate gene(s) in response to early environmental adversity. More specifically, this review analyses the epigenetic signatures of postnatal adversity such as childhood abuse or maltreatment and later-life psychopathology in human and animal models of early life stress. The results of this review shows that focus to date has been on genes involved in the regulation of hypothalamic-pituitary-adrenal (HPA) axis and its correlation to subsequent neurobiology, for example, the role of glucocorticoid receptor gene. However, epigenetic changes in other candidate genes such as brain-derived neurotrophic factor (BDNF) and serotonin transporter are also implicated in early life stress (ELS) and susceptibility to adult psychiatric disorders. DNA methylation is the predominantly studied epigenetic mark followed by histone modifications specifically acetylation and methylation. Further, these epigenetic changes are cell/tissue-specific in regulating expression of genes, providing potential biomarkers for understanding the trajectory of early stress-induced susceptibility to adult psychiatric disorders.

Effects of centrally administered etanercept on behavior, microglia, and astrocytes in mice following a peripheral immune challenge.

Peripheral cytokines affect central nervous system (CNS) function, manifesting in symptoms of anxiety and cognitive decline. Although the peripheral blockage of tumor necrosis factor (TNF)-α has been effective in alleviating depression and rheumatoid arthritis, it is yet unknown whether central blockade of TNF-α is beneficial for immune-challenged CNS function. This study investigated the effects of central etanercept administration following a peripheral immune challenge on anxiety-like and cognition-like behaviors and microglia and astrocyte numbers. Twelve-week-old C57BL/6 mice (n=40) were treated with either LPS or saline administered peripherally 24 h before being treated with either etanercept or artificial CSF (aCSF) by intracerebroventricular injection. Mice underwent behavioral analyses for locomotion, memory, and anxiety-like behavior 24 h post-etanercept/aCSF treatment, and tissue was collected to estimate the numbers of hippocampal microglia and astrocytes. Following peripheral immune challenge with LPS, mice showed increased anxiety-like behavior, which was significantly improved following treatment with etanercept (two-way ANOVA: Interaction: F(1,30)=0.60, P=0.44; Saline/LPS challenge: F(1,30)=23.92, P<0.0001, etanercept vs aCSF: F(1,30)=11.09, P=0.0023). For cognition, a significant interaction effect found by two-way ANOVA (Interaction: F(1,20)=4.96, P=0.037, Saline/LPS challenge: F(1,20)=4.966, P=0.31, aCSF/etanercept treatment: F(1,20)=0.06, P=0.80) and post-hoc analysis revealed a significant decrease in cognition in LPS-aCSF compared with Sal-aCSF mice (P=0.038), but no significant difference was noted between LPS-aCSF and LPS-Etan mice (P>0.9). A significant reduction in the number of microglia within the hippocampus of these mice was noted (two-way ANOVA: Interaction: F(1,15)=11.41, P=0.0041; Saline/LPS challenge: F(1,15)=50.13, P<0.0001, etanercept vs aCSF: F(1,15)=3.36, P=0.08). Centrally administered etanercept improved anxiety-like behavior but not spatial memory under a peripheral immune challenge and was associated with a decrease in the hippocampal microglia numbers. This suggests that etanercept recovers anxiety-like behavior possibly mediated by a reduction of TNF-α-related central inflammation.