Treadmill exercise suppressed stress-induced dendritic spine elimination in mouse barrel cortex and improved working memory via BDNF/TrkB pathway

Physical exercise regulates microglia in health and disease

There is a well-established link between physical activity and brain health. As such, the effectiveness of physical exercise as a therapeutic strategy has been explored in a variety of neurological contexts. To determine the extent to which physical exercise could be most beneficial under different circumstances, studies are needed to uncover the underlying mechanisms behind the benefits of physical activity. Interest has grown in understanding how physical activity can regulate microglia, the resident immune cells of the central nervous system. Microglia are key mediators of neuroinflammatory processes and play a role in maintaining brain homeostasis in healthy and pathological settings. Here, we explore the evidence suggesting that physical activity has the potential to regulate microglia activity in various animal models. We emphasize key areas where future research could contribute to uncovering the therapeutic benefits of engaging in physical exercise.

Treadmill Exercise Reshapes Cortical Astrocytic and Neuronal Activity to Improve Motor Learning Deficits Under Chronic Alcohol Exposure

Alcohol abuse induces various neurological disorders including motor learning deficits, possibly by affecting neuronal and astrocytic activity. Physical exercise is one effective approach to remediate synaptic loss and motor deficits as shown by our previous works. In this study, we unrevealed the role of exercise training in the recovery of cortical neuronal and astrocytic functions. Using a chronic alcohol injection mouse model, we found the hyperreactivity of astrocytes along with dendritic spine loss plus lower neuronal activity in the primary motor cortex. Persistent treadmill exercise training, on the other hand, improved neural spine formation and inhibited reactive astrocytes, alleviating motor learning deficits induced by alcohol exposure. These data collectively support the potency of endurance exercise in the rehabilitation of motor functions under alcohol abuse.

Treadmill exercise training inhibits morphine CPP by reversing morphine effects on GABA neurotransmission in D2-MSNs of the accumbens-pallidal pathway in male mice

Relapse is a major challenge in the treatment of drug addiction, and exercise has been shown to decrease relapse to drug seeking in animal models. However, the neural circuitry mechanisms by which exercise inhibits morphine relapse remain unclear. In this study, we report that 4-week treadmill training prevented morphine conditioned place preference (CPP) expression during abstinence by acting through the nucleus accumbens (NAc)-ventral pallidum (VP) pathway. We found that neuronal excitability was reduced in D2-dopamine receptor-expressing medium spiny neurons (D2-MSNs) following repeated exposure to morphine and forced abstinence. Enhancing the excitability of NAc D2-MSNs via treadmill training decreased the expression of morphine CPP. We also found that the effects of treadmill training were mediated by decreasing enkephalin levels and that restoring opioid modulation of GABA neurotransmission in the VP, which increased neurotransmitter release from NAc D2-MSNs to VP, decreased morphine CPP. Our findings suggest the inhibitory effect of exercise on morphine CPP is mediated by reversing morphine-induced neuroadaptations in the NAc-to-VP pathway.

Low-intensity transcranial ultrasound stimulation improves memory in vascular dementia by enhancing neuronal activity and promoting spine formation

Memory is closely associated with neuronal activity and dendritic spine formation. Low-intensity transcranial ultrasound stimulation (TUS) improves the memory of individuals with vascular dementia (VD). However, it is unclear whether neuronal activity and dendritic spine formation under ultrasound stimulation are involved in memory improvement in VD. In this study, we found that seven days of TUS improved memory in VD model while simultaneously increasing pyramidal neuron activity, promoting dendritic spine formation, and reducing dendritic spine elimination. These effects lasted for 7 days but disappeared on 14 d after TUS. Neuronal activity and dendritic spine formation strongly corresponded to improvements in memory behavior over time. In addition, we also found that the memory, neuronal activity and dendritic spine of VD mice cannot be restored again by TUS of 7 days after 28 d. Collectively, these findings suggest that TUS increases neuronal activity and promotes dendritic spine formation and is thus important for improving memory in patients with VD.

Making Sense of Psychedelics in the CNS

For centuries, ancient lineages have consumed psychedelic compounds from natural sources. In the modern era, scientists have since harnessed the power of computational tools, cellular assays, and behavioral metrics to study how these compounds instigate changes on molecular, cellular, circuit-wide, and system levels. Here, we provide a brief history of psychedelics and their use in science, medicine, and culture. We then outline current techniques for studying psychedelics from a pharmacological perspective. Finally, we address known gaps in the field and potential avenues of further research to broaden our collective understanding of physiological changes induced by psychedelics, the limits of their therapeutic capabilities, and how researchers can improve and inform treatments that are rapidly becoming accessible worldwide.

Visualization analysis of exercise intervention on Alzheimer disease based on bibliometrics: Trends, hotspots and topics

BACKGROUND

As the challenges of an aging society continue to escalate, Alzheimer disease (AD) has emerged as a significant health, social, and public concern, garnering substantial attention. Exercise, as a safe, effective, and cost-efficient approach with the potential to mitigate brain aging, has garnered considerable interest. Nevertheless, there has been a limited research investigating the current trends, hotspots, and topics of exercise on AD.

METHODS

The literature spanning from 2013 to 2022 was obtained from the Web of Science database, and CiteSpace VI was employed to conduct an analysis encompassing fundamental data, keywords, and co-citation analysis.

RESULTS

A total of 9372 publications were included in the analysis. The annual number of publications has exhibited a gradual increase. The United States and China made significant contributions, with England showing higher citation rates and greater academic influence. The Journal of Alzheimers Disease, Neurosciences Neurology, Liu-Ambrose, Teresa represents the most published journal, discipline, and author, respectively. The research trends can be summarized as exploring functional changes and potential mechanisms related to exercise impact on AD. The hotspots in the research include the intersection of AD and diabetes mellitus, as well as the underlying effects induced by exercise. The topics of interest revolve around the application of emerging technologies in the context of exercise and AD.

CONCLUSION

This bibliometric analysis has identified relevant trends, hotspots, and topics within the exercise intervention on AD. It offers a comprehensive overview that can equip researchers with valuable insights for future exploration and assist scholars in charting research trajectories in related domains.

Neurological, Behavioral, and Pathophysiological Characterization of the Co-Occurrence of Substance Use and HIV: A Narrative Review

Combined antiretroviral therapy (cART) has greatly reduced the severity of HIV-associated neurocognitive disorders in people living with HIV (PLWH); however, PLWH are more likely than the general population to use drugs and suffer from substance use disorders (SUDs) and to exhibit risky behaviors that promote HIV transmission and other infections. Dopamine-boosting psychostimulants such as cocaine and methamphetamine are some of the most widely used substances among PLWH. Chronic use of these substances disrupts brain function, structure, and cognition. PLWH with SUD have poor health outcomes driven by complex interactions between biological, neurocognitive, and social factors. Here we review the effects of comorbid HIV and psychostimulant use disorders by discussing the distinct and common effects of HIV and chronic cocaine and methamphetamine use on behavioral and neurological impairments using evidence from rodent models of HIV-associated neurocognitive impairments (Tat or gp120 protein expression) and clinical studies. We also provide a biopsychosocial perspective by discussing behavioral impairment in differentially impacted social groups and proposing interventions at both patient and population levels.

Microglia in Alzheimer's disease: pathogenesis, mechanisms, and therapeutic potentials

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by protein aggregation in the brain. Recent studies have revealed the critical role of microglia in AD pathogenesis. This review provides a comprehensive summary of the current understanding of microglial involvement in AD, focusing on genetic determinants, phenotypic state, phagocytic capacity, neuroinflammatory response, and impact on synaptic plasticity and neuronal regulation. Furthermore, recent developments in drug discovery targeting microglia in AD are reviewed, highlighting potential avenues for therapeutic intervention. This review emphasizes the essential role of microglia in AD and provides insights into potential treatments.

Treadmill exercise modulates the medial prefrontal-amygdala neural circuit to improve the resilience against chronic restraint stress

Aerobic exercise effectively ameliorates mental disorders including anxiety and depression. Current findings mainly attribute its neural mechanism to the improvement of adult neurogenesis, while leaving the possible circuitry mechanism unclear. In the current study, we identify the overexcitation of the medial prefrontal cortex (mPFC) to basolateral amygdala (BLA) pathway under chronic restraint stress (CRS), and 14-day treadmill exercise selectively reverses such abnormalities. Using chemogenetic approaches, we find that the mPFC-BLA circuit is necessary for preventing anxiety-like behaviors in CRS mice. These results collectively suggest a neural circuitry mechanism by which exercise training improves the resilience against environmental stress.

Modulation effects of low-intensity transcranial ultrasound stimulation on the neuronal firing activity and synaptic plasticity of mice

Low-intensity transcranial ultrasound stimulation (TUS) has been effective in modulating several neurological and psychiatric disorders. However, how TUS modulates neuronal firing activity and synaptic plasticity remains unclear. Thus, we behaviorally tested the whisker-dependent novel object discrimination ability in mice after ultrasound stimulation and examined the cortical neuronal firing activity and synaptic plasticity in awake mice after ultrasound stimulation by two-photon fluorescence imaging. The current study presented the following results: (1) TUS could significantly improve the whisker-dependent new object discrimination ability of mice, suggesting that their learning and memory abilities were significantly enhanced; (2) TUS significantly enhanced neuronal firing activity; and (3) TUS increased the growth rate of dendritic spines in the barrel cortex, but did not promote the extinction of dendritic spines, resulting in enhanced synaptic plasticity. The above results indicate that TUS can improve the learning and memory ability of mice and enhance the neuronal firing activity and synaptic plasticity that are closely related to it. This study provides a research basis for the application of ultrasound stimulation in the treatment of learning- and memory-related diseases.

Novel approaches to increase synaptic resilience as potential treatments for Alzheimer's disease

A significant proportion of brains with Alzheimer's disease pathology are obtained from patients that were cognitively normal, suggesting that differences within the brains of these individuals made them resilient to the disease. Here, we describe recent approaches that specifically increase synaptic resilience, as loss of synapses is considered to be the first change in the brains of Alzheimer's patients. We start by discussing studies showing benefit from increased expression of neurotrophic factors and protective genes. Methods that effectively make dendritic spines stronger, specifically by acting through actin network proteins, scaffolding proteins and inhibition of phosphatases are described next. Importantly, the therapeutic strategies presented in this review tackle Alzheimer's disease not by targeting plaques and tangles, but instead by making synapses resilient to the pathology associated with Alzheimer's disease, which has tremendous potential.

Molecular mechanisms of exercise intervention in alleviating the symptoms of autism spectrum disorder: Targeting the structural alterations of synapse

Autism spectrum disorder (ASD) is a complex and heterogeneous neurodevelopmental disorder characterized by stereotyped behaviors, specific interests, and impaired social and communication skills. Synapses are fundamental structures for transmitting information between neurons. It has been reported that synaptic deficits, such as the increased or decreased density of synapses, may contribute to the onset of ASD, which affects the synaptic function and neuronal circuits. Therefore, targeting the recovery of the synaptic normal structure and function may be a promising therapeutic strategy to alleviate ASD symptoms. Exercise intervention has been shown to regulate the structural plasticity of synapses and improve ASD symptoms, but the underlying molecular mechanisms require further exploration. In this review, we highlight the characteristics of synaptic structural alterations in the context of ASD and the beneficial effects of an exercise intervention on improving ASD symptoms. Finally, we explore the possible molecular mechanisms of improving ASD symptoms through exercise intervention from the perspective of regulating synaptic structural plasticity, which contributes to further optimizing the related strategies of exercise intervention promoting ASD rehabilitation in future.

Physical exercise modulates the microglial complement pathway in mice to relieve cortical circuitry deficits induced by mutant human TDP-43

The aggregation of TAR DNA binding protein 43 kDa (TDP-43) is related to different neurodegenerative diseases, which leads to microglial activation and neuronal loss. The molecular mechanism driving neuronal death by reactive microglia, however, has not been completely resolved. In this study, we generated a mouse model by overexpressing mutant human TDP-43 (M337V) in the primary motor cortex, leading to prominent motor-learning deficits. In vivo 2-photon imaging shows an active approach of microglia toward parvalbumin interneurons, resulting in disrupted cortical excitatory-inhibitory balance. Proteomics studies suggest that activation of the complement pathway induces microglial activity. To develop an early interventional strategy, treadmill exercise successfully prevents the deterioration of motor dysfunction under enhanced adipocytic release of clusterin to block the complement pathway. These results demonstrate a previously unrecognized pathway by which TDP-43 induces cortical deficits and provide additional insights for the mechanistic explanation of exercise training in disease intervention.

Physical exercise mediates a cortical FMRP-mTOR pathway to improve resilience against chronic stress in adolescent mice

Aerobic exercise effectively relieves anxiety disorders via modulating neurogenesis and neural activity. The molecular mechanism of exercise-mediated anxiolysis, however, remains incomplete. On a chronic restrain stress (CRS) model in adolescent mice, we showed that 14-day treadmill exercise profoundly maintained normal neural activity and axonal myelination in the medial prefrontal cortex (mPFC), in association with the prevention of anxiety-like behaviors. Further interrogation of molecular mechanisms revealed the activation of the mechanistic target of the rapamycin (mTOR) pathway within mPFC under exercise training. At the upstream of mTOR, exercise-mediated brain RNA methylation inhibited the expression of Fragile X mental retardation protein (FMRP) to activate the mTOR pathway. In summary, treadmill exercise modulates an FMRP-mTOR pathway to maintain cortical neural activity and axonal myelination, contributing to improved stress resilience. These results extended our understanding of the molecular substrate of exercise-mediated anxiolytic effect during adolescent period.

Effect of combination fluoxetine and exercise on prefrontal BDNF, anxiety-like behavior and fear extinction in a female rat model of post-traumatic stress disorder (PTSD): a comparison with male animals

Despite significant differences between men and women in the symptoms of PTSD and the response to therapeutic interventions, most PTSD studies have been done on male subjects. Continuing our previous study in male rats, this study aimed at better understanding the effect of a combination therapy of exercise with fluoxetine on female PTSD rats. The results were then compared with our past findings in male animals. Female adult Wistar rats subjected to PTSD were treated with moderate treadmill exercise or fluoxetine, or a combination of both. PTSD was induced by the single prolonged stress (SPS) model. Elevated plus-maze (EPM), serum and prefrontal BDNF, and fear extinctions were evaluated. The results showed that exercise plus fluoxetine decreased anxiety-like behavior, improved fear extinction, and increased BDNF changes in female rats. The effects of exercise alone were comparable with those of combination therapy except that combination therapy was more effective on OAT (open arm entry). The majority of results in female rats, except for those of prefrontal BDNF, 4th extinction, and OAT, were similar to those of male rats as shown in our previous study. According to our findings, exercise as a safe and cost-effective intervention can be considered as a complementary efficient option for PTSD treatment in both sexes. To achieve better treatment outcomes in PTSD patient, considering sex differences is recommended.

Running from Stress: Neurobiological Mechanisms of Exercise-Induced Stress Resilience

Chronic stress, even stress of a moderate intensity related to daily life, is widely acknowledged to be a predisposing or precipitating factor in neuropsychiatric diseases. There is a clear relationship between disturbances induced by stressful stimuli, especially long-lasting stimuli, and cognitive deficits in rodent models of affective disorders. Regular physical activity has a positive effect on the central nervous system (CNS) functions, contributes to an improvement in mood and of cognitive abilities (including memory and learning), and is correlated with an increase in the expression of the neurotrophic factors and markers of synaptic plasticity as well as a reduction in the inflammatory factors. Studies published so far show that the energy challenge caused by physical exercise can affect the CNS by improving cellular bioenergetics, stimulating the processes responsible for the removal of damaged organelles and molecules, and attenuating inflammation processes. Regular physical activity brings another important benefit: increased stress robustness. The evidence from animal studies is that a sedentary lifestyle is associated with stress vulnerability, whereas a physically active lifestyle is associated with stress resilience. Here, we have performed a comprehensive PubMed Search Strategy for accomplishing an exhaustive literature review. In this review, we discuss the findings from experimental studies on the molecular and neurobiological mechanisms underlying the impact of exercise on brain resilience. A thorough understanding of the mechanisms underlying the neuroprotective potential of preconditioning exercise and of the role of exercise in stress resilience, among other things, may open further options for prevention and therapy in the treatment of CNS diseases.

Physical Exercise Prevented Stress-Induced Anxiety via Improving Brain RNA Methylation

Physical exercise is effective in alleviating mental disorders by improving synaptic transmission; however, the link between body endurance training and neural adaptation has not yet been completely resolved. In this study, the authors investigated the role of RNA N⁶ -methyladenosine (m6A), an emerging epigenetic mechanism, in improved resilience against chronic restraint stress. A combination of molecular, behavioral, and in vivo recording data demonstrates exercise-mediated restoration of m6A in the mouse medial prefrontal cortex, whose activity is potentiated to exert anxiolytic effects. Furthermore, it is revealed that hepatic biosynthesis of one methyl donor is necessary for exercise to improve brain RNA m6A to counteract environmental stress. This novel liver-brain axis provides an explanation for brain network changes upon exercise training and provides new insights into the diagnosis and treatment of anxiety disorders.

Dysregulated cortical synaptic plasticity under methyl-CpG binding protein 2 deficiency and its implication in motor impairments

Caused by the mutation of methyl-CpG binding protein 2 (MeCP2), Rett syndrome leads to a battery of severe neural dysfunctions including the regression of motor coordination and motor learning. Current understanding has revealed the motor cortex as the critical region mediating voluntary movement. In this review article, we will summarize major findings from human patients and animal models regarding the cortical synaptic plasticity under the regulation of MeCP2. We will also discuss how mutation of MeCP2 leads to the disruption of cortical circuitry homeostasis to cause motor deficits. Lastly, potential values of physical exercise and neuromodulation approaches to recover neural plasticity and motor function will be evaluated. All of this evidence may help to accelerate timely diagnosis and effective interventions for Rett syndrome patients.

Four weeks of light-intensity exercise enhances empathic behavior in mice: The possible involvement of BDNF

Empathy is one of the essential functions of mammals for maintaining relationships with others. Physical activity contributes to enhancing empathic attitude and behavior; however, it is remained to cover the effective intensity of exercise on mammal empathy. Here, we tested the effects of light-intensity exercise, which has beneficial effects on expressing neurotrophic factors in the brain, on empathic behavior. Eight-week-old male C57BL/6 mice were subjected to forced wheel running at light-intensity (7.0 m/min, 30 min/day, 5 days/week) for 4 weeks. Then, all mice were subjected to helping behavior to evaluate their empathic behavior. The insular cortex was collected for analyzing the expressions of mRNA and miRNA. Four weeks of light-intensity exercise enhanced helping behavior. Exercised mice exhibited higher Bdnf gene expressions in the insular cortex than sedentary mice. In addition, there was a significant positive correlation between mRNA levels of Fndc5 and Bdnf in the insular cortex. Based on miRNA sequencing, 26 out of 51 miRNAs were significantly upregulated, and 25 out of 51 miRNAs were significantly downregulated in the insular cortex of mice with exercise. There were significant correlations between 11 out of 51 miRNAs and helping behavior; miR-486a-3p, which relates to FNDC5 expression, was contained. These results imply that miR-486a-3p/Fndc5/Bdnf pathway in the insular cortex would be a possible target for treating empathy.

Moderate-intensity continuous training and high-intensity interval training improve cognition, and BDNF levels of middle-aged overweight men

The prevalence of overweight and obesity is increasing worldwide, which has been associated with poor cognitive outcomes. Participating in regular physical exercise may also improve cognition, and levels of brain-derived neurotrophic factor (BDNF), but the optimal exercise prescription remains to be elucidated. The purpose of the present study is to compare the effects of moderate intensity continuous training (MICT) and high intensity interval training (HIIT) on cognition, and serum BDNF levels in middle-aged and overweight men. Twenty-five sedentary, overweight men participated in the 8-week training intervention. Subjects were randomized into MICT (n = 12) or HIIT (n = 13) and performed exercise sessions 3x/week for 8-weeks. Cognitive function, and serum BDNF levels were assessed pre- and post-intervention. Statistical analysis was carried out using the Graph Pad Prism 7.0, and the level of significance was set at 5%. Significant improvements were observed in cognitive test scores, and BDNF levels in MICT and HIIT groups (p < 0.05). There were no significant differences in cognitive function between MICT and HIIT. The present study implicates that 8 weeks of MICT or HIIT may be a very useful non-pharmacological treatment option to improve cognitive function, and BDNF levels in middle-aged overweight men.

Effect of treadmill exercise on serum corticosterone, serum and hippocampal BDNF, hippocampal apoptosis and anxiety behavior in an ovariectomized rat model of post-traumatic stress disorder (PTSD)

There is a sex difference in vulnerability to PTSD and in response to therapeutic interventions. Since relation between gonadal hormones and PTSD has been revealed, this study aimed to understand the severity of PTSD-induced impairments after ovarian hormone deficiency and the influence of exercise on PTSD accompanied by ovarian hormone deficiency. Female adult Wistar rats were subjected to ovariectomy, PTSD, or combination ovariectomy plus PTSD. Twenty days after ovariectomy, PTSD was induced by single prolonged stress (SPS) model. The exercise started 14 days after SPS and continued for 4 weeks. Thirty minutes moderate treadmill exercise was planned for 5 days per week. On day 65, after assessing rats using the elevated plus-maze (EPM) test, corticosterone, BDNF, and apoptotic markers were tested. p < 0.05 was considered as significant level. The results showed that ovariectomy worsened the effect of SPS on hippocampal BDNF and led to greater increase in serum corticosterone and hippocampal caspase 3 and BAX in SPS rats. Also, ovariectomy exacerbated anxiety-like behavior in SPS rats. Exercise improved the alterations of hippocampal BDNF, corticosterone, caspase 3, and BAX in SPS ovariectomized rats. However, exercise had no statistically significant effect on anxiety-like behavior in this group. According to the results, exercise is effective to attenuate SPS-induced impairments in molecular and cellular responses even when the condition becomes more complicated due to ovarian hormone deficiency. However, exercise alone cannot help to improve behavior impairments in PTSD combined with an ovarian hormone deficiency. Therefore, exercise could likely be considered as a complementary intervention to strengthen other treatments.

Physical Exercise Exerts Neuroprotective Effect on Memory Impairment by Mitigate the Decline of Striatum Catecholamine and Spine Density in a Vascular Dementia Rat Model

OBJECTIVE

The present study aims to investigate the underlying neurochemical mechanism of physical exercise on striatum synapsis and memory function in vascular dementia model.

METHODS

32 Sprague-Dawley (SD) rats were randomly divided into 4 groups: control group (C group, n = 6), vascular dementia group (Vascular dementia group, n = 7), physical exercise and vascular dementia group (Exe-VD group, n = 6), physical exercise and black group (Exe group, n = 6). 4 weeks of voluntary wheel running were used as pre-exercise training. Vascular dementia model was established by bilateral common carotid arteries occlusion (BCCAo) for 1 week. Passive avoidance test (PAT) were used to test memory function. The level of striatum catecholamine in the microdialysate were detected by enzyme linked immunosorbent assy (ELISA). Golgi staining was used to analyze striatum neuronal spine density.

RESULTS

Behavioral data indicated that 4 weeks of physical exercise ameliorated memory impairment in vascular dementia model. Striatum catecholamine level significantly decreased in VD group when compared with C group (P < .001). But this phenomenon can be rescue by physical exercise (P < .001). In addition, compared with C group, neuronal spine density significantly decreased in VD group (P < .01), but 4 weeks of physical exercise can rescue this phenomenon (P < .05).

CONCLUSION

4 weeks of physical exercise improves memory function by mitigate the decline of striatum catecholamine and spine density in VD model.

The effect of URB597, exercise or their combination on the performance of 6-OHDA mouse model of Parkinson disease in the elevated plus maze, tail suspension test and step-down task

Parkinson disease (PD) is a progressive neurodegenerative disorder that is often accompanied by motor and psychiatric symptoms. Various approaches have been proposed for the treatment of PD. Here, we investigated the effect of a low dose of fatty acid amide hydrolase inhibitor URB597 (as an enhancer of endocannabinoid anandamide levels), exercise or their combination on some behavior alterations in PD mice lesioned by 6-hydroxydopamine (6-OHDA). The impact of swimming exercise (5×/week for 4 weeks) and URB597 (0.1 mg/kg, 2×/week for 4 weeks) on the anxiety-related behavior (elevated plus maze; EPM), depression-related behavior (tail suspension test; TST), and passive avoidance memory (step-down task) was examined in the sham and male NMRI mouse of PD model. The results show that URB597 prevented memory deficits and elicited antidepressant- and anxiolytic-like effects but did not affect hypolocomotion in the PD mice. However, URB597 did not have a significant effect on the performance of the sham mice in the performed tests. Moreover, swimming training abolished depressive- and anxiogenic-like behaviors and increased locomotion without affecting memory deficits in the PD mice. Meanwhile, swimming decreased immobility time and increased locomotion in the sham mice. Furthermore, URB597 in association with swimming training prevented all deficits induced in the PD mice, while this combination impaired memory and produced the positive effects on depression- and anxiety-related behaviors and locomotion of the sham mice. It is concluded that although URB597 or exercise alone had positive effects on most behavioral tests, their combination improved all parameters in the PD mice.

Dendritic Spines: Mediators of Cognitive Resilience in Aging and Alzheimer's Disease

Cognitive resilience is often defined as the ability to remain cognitively normal in the face of insults to the brain. These insults can include disease pathology, such as plaques and tangles associated with Alzheimer's disease, stroke, traumatic brain injury, or other lesions. Factors such as physical or mental activity and genetics may contribute to cognitive resilience, but the neurobiological underpinnings remain ill-defined. Emerging evidence suggests that dendritic spine structural plasticity is one plausible mechanism. In this review, we highlight the basic structure and function of dendritic spines and discuss how spine density and morphology change in aging and Alzheimer's disease. We note evidence that spine plasticity mediates resilience to stress, and we tackle dendritic spines in the context of cognitive resilience to Alzheimer's disease. Finally, we examine how lifestyle and genetic factors may influence dendritic spine plasticity to promote cognitive resilience before discussing evidence for actin regulatory kinases as therapeutic targets for Alzheimer's disease.

Running exercise protects spinophilin-immunoreactive puncta and neurons in the medial prefrontal cortex of APP/PS1 transgenic mice

The medial prefrontal cortex (mPFC) is thought to be closely associated with emotional processes, decision making, and memory. Previous studies have identified the prefrontal cortex as one of the most vulnerable brain regions in Alzheimer's disease (AD). Running exercise has widely been recognized as a simple and effective method of physical activity that enhances brain function and slows the progression of AD. However, the effect of exercise on the mPFC of AD is unclear. To address these issues, we investigated the effects of 4 months of exercise on the numbers of spinophilin-immunoreactive puncta and neurons in the mPFC of 12-month-old APPswe/PSEN1dE9 (APP/PS1) transgenic AD model mice using stereological methods. The spatial learning and memory abilities of mice were tested using the Morris water maze. Four months of running exercise delayed declines in spatial learning and memory abilities. The stereological results showed significantly lower numbers of spinophilin-immunoreactive puncta and neurons in the mPFC of APP/PS1 mice than in the wild-type control group. The numbers of spinophilin-immunoreactive puncta and neurons in the mPFC of running APP/PS1 mice were significantly greater than those in the APP/PS1 control mice. In addition, running-induced improvements in spatial learning and memory were significantly associated with running-induced increases in spinophilin-immunoreactive puncta and neurons numbers in the mPFC. Running exercise could delay the loss of spinophilin-immunoreactive puncta and neurons in the mPFC of APP/PS1 mice. This finding might provide an important structural basis for exercise-induced improvements in the spatial learning and memory abilities of individuals with AD.

Microglia regulation of synaptic plasticity and learning and memory

Microglia are the resident macrophages of the central nervous system. Microglia possess varied morphologies and functions. Under normal physiological conditions, microglia mainly exist in a resting state and constantly monitor their microenvironment and survey neuronal and synaptic activity. Through the C1q, C3 and CR3 “Eat Me” and CD47 and SIRPα “Don’t Eat Me” complement pathways, as well as other pathways such as CX3CR1 signaling, resting microglia regulate synaptic pruning, a process crucial for the promotion of synapse formation and the regulation of neuronal activity and synaptic plasticity. By mediating synaptic pruning, resting microglia play an important role in the regulation of experience-dependent plasticity in the barrel cortex and visual cortex after whisker removal or monocular deprivation, and also in the regulation of learning and memory, including the modulation of memory strength, forgetfulness, and memory quality. As a response to brain injury, infection or neuroinflammation, microglia become activated and increase in number. Activated microglia change to an amoeboid shape, migrate to sites of inflammation and secrete proteins such as cytokines, chemokines and reactive oxygen species. These molecules released by microglia can lead to synaptic plasticity and learning and memory deficits associated with aging, Alzheimer’s disease, traumatic brain injury, HIV-associated neurocognitive disorder, and other neurological or mental disorders such as autism, depression and post-traumatic stress disorder. With a focus mainly on recently published literature, here we reviewed the studies investigating the role of resting microglia in synaptic plasticity and learning and memory, as well as how activated microglia modulate disease-related plasticity and learning and memory deficits. By summarizing the function of microglia in these processes, we aim to provide an overview of microglia regulation of synaptic plasticity and learning and memory, and to discuss the possibility of microglia manipulation as a therapeutic to ameliorate cognitive deficits associated with aging, Alzheimer’s disease, traumatic brain injury, HIV-associated neurocognitive disorder, and mental disorders.

Stress induces microglia-associated synaptic circuit alterations in the dorsomedial prefrontal cortex

The mammalian dorsomedial prefrontal cortex (dmPFC) receives diverse inputs and plays important roles in adaptive behavior and cognitive flexibility. Stress, a major risk factor for many psychiatric disorders, compromises the structure and function of multiple brain regions and circuits. Here we show that 7-day restraint stress impairs reversal learning in the 4-choice odor discrimination test, a decision-making task requiring an intact dmPFC. In vivo two-photon imaging further reveals that stress increases dmPFC dendritic spine elimination, particularly those of the mushroom morphology, without affecting spine formation. In addition, stress alters dmPFC microglial branching complexity and elevates their terminal process dynamics. In stressed mice, dmPFC microglia contact dendrites more frequently, and dendritic spines with microglial contact are prone to elimination. In summary, our work suggests that stress-induced changes in glial-synapse interaction contributes to synaptic loss in dmPFC, resulting in neuronal circuit deficits and impaired cognitive flexibility.

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Restraint stress impairs cognitive flexibility in adolescent mice.

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Stress leads to synapse loss on pyramidal neurons in the dorsomedial prefrontal cortex.

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Stress decreases microglial complexity but increases their terminal dynamics and contacts with dendritic spines.

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Dendritic spines contacted by microglial processes are more prone to elimination.

Neuromodulation-Based Stem Cell Therapy in Brain Repair: Recent Advances and Future Perspectives

Stem cell transplantation holds a promising future for central nervous system repair. Current challenges, however, include spatially and temporally defined cell differentiation and maturation, plus the integration of transplanted neural cells into host circuits. Here we discuss the potential advantages of neuromodulation-based stem cell therapy, which can improve the viability and proliferation of stem cells, guide migration to the repair site, orchestrate the differentiation process, and promote the integration of neural circuitry for functional rehabilitation. All these advantages of neuromodulation make it one potentially valuable tool for further improving the efficiency of stem cell transplantation.

Voluntary exercise ameliorates synaptic pruning deficits in sleep-deprived adolescent mice

Adolescence is a critical period for brain development and adequate sleep during this period is essential for physical function and mental health. Emerging evidence has detailed the neurological impacts of sleep insufficiency on adolescents, as was unveiled by our previous study, microglia, one of the crucial contributors to synaptic pruning, is functionally disrupted by lack of sleep. Here, we provided evidence featuring the protective effect and the underlying mechanisms of voluntary exercise (VE) on microglial functions in an adolescent 72 h sleep deprivation (SD) model. We identified that the aberrant hippocampal neuronal activity and impaired short-term memory performance in sleep-deprived mice were prevented by 11 days of VE. VE significantly normalized the SD-induced dendritic spine increment and maintained the microglial phagocytic ability in sleep-deprived mice. Moreover, we found that the amendment of the noradrenergic signal in the central nervous system may explain the preventative effects of VE on the abnormalities of microglial and neuronal functions caused by SD. These data suggested that VE may confer protection to the microglia-mediated synaptic pruning in the sleep-deprived adolescent brains. Therefore, physical exercise could be a beneficial health practice for the adolescents that copes the adverse influence of inevitable sleep insufficiency.

Experience and activity-dependent control of glucocorticoid receptors during the stress response in large-scale brain networks

The diversity of actions of the glucocorticoid stress hormones among individuals and within organs, tissues and cells is shaped by age, gender, genetics, metabolism, and the quantity of exposure. However, such factors cannot explain the heterogeneity of responses in the brain within cells of the same lineage, or similar tissue environment, or in the same individual. Here, we argue that the stress response is continuously updated by synchronized neural activity on large-scale brain networks. This occurs at the molecular, cellular and behavioral levels by crosstalk communication between activity-dependent and glucocorticoid signaling pathways, which updates the diversity of responses based on prior experience. Such a Bayesian process determines adaptation to the demands of the body and external world. We propose a framework for understanding how the diversity of glucocorticoid actions throughout brain networks is essential for supporting optimal health, while its disruption may contribute to the pathophysiology of stress-related disorders, such as major depression, and resistance to therapeutic treatments.

An analog of psychedelics restores functional neural circuits disrupted by unpredictable stress

Psychological stress affects a wide spectrum of brain functions and poses risks for many mental disorders. However, effective therapeutics to alleviate or revert its deleterious effects are lacking. A recently synthesized psychedelic analog tabernanthalog (TBG) has demonstrated anti-addictive and antidepressant potential. Whether TBG can rescue stress-induced affective, sensory, and cognitive deficits, and how it may achieve such effects by modulating neural circuits, remain unknown. Here we show that in mice exposed to unpredictable mild stress (UMS), administration of a single dose of TBG decreases their anxiety level and rescues deficits in sensory processing as well as in cognitive flexibility. Post-stress TBG treatment promotes the regrowth of excitatory neuron dendritic spines lost during UMS, decreases the baseline neuronal activity, and enhances whisking-modulation of neuronal activity in the somatosensory cortex. Moreover, calcium imaging in head-fixed mice performing a whisker-dependent texture discrimination task shows that novel textures elicit responses from a greater proportion of neurons in the somatosensory cortex than do familiar textures. Such differential response is diminished by UMS and is restored by TBG. Together, our study reveals the effects of UMS on cortical neuronal circuit activity patterns and demonstrate that TBG combats the detrimental effects of stress by modulating basal and stimulus-dependent neural activity in cortical networks.

Probiotics Exert Protective Effect against Sepsis-Induced Cognitive Impairment by Reversing Gut Microbiota Abnormalities

Recent evidence has revealed that probiotics could affect neurodevelopment and cognitive function via regulating gut microbiota. However, the role of probiotics in sepsis-associated encephalopathy (SAE) remained unclear. This study was conducted to assess the effects and therapeutic mechanisms of probiotic Clostridium butyricum (Cb) against SAE in mice. The SAE model mouse was induced by cecal ligation and puncture (CLP) and was given by intragastric administration with Cb for 1 month. A series of behavioral tests, including neurological severity score, tail suspension test, and elevated maze test, were used to assess cognitive impairment. Nissl staining and Fluoro-Jade C (FJC) staining were used to assess neuronal injury. Microglia activation, the release of neuroinflammatory cytokines, and the levels of ionized calcium-binding adapter molecule 1 (Iba-1) and brain-derived neurotrophic factor (BDNF) in the brain were determined. The compositions of the gut microbiota were detected by 16S rRNA sequencing. Our results revealed that Cb significantly attenuated cognitive impairment and neuronal damage. Moreover, Cb significantly inhibited excessive activation of microglia, decreased Iba-1 level, and increased BDNF level in the SAE mice. In addition, Cb improved gut microbiota dysbiosis of SAE mice. These findings revealed that Cb exerted anti-inflammatory effects and improved cognitive impairment in SAE mice, and their neuroprotective mechanisms might be mediated by regulating gut microbiota.

Characterization of blood-derived exosomal proteins after exercise

Objective

To assess changes in plasma exosome levels and protein content in mice after long-term exercise.

Methods

We subjected 9-month-old adult C57BL/6J mice to daily treadmill running exercise for 4 weeks prior to the isolation of blood-derived exosomes. Exosomal proteins were identified using mass spectrometry.

Results

Extracellular bodies were successfully isolated from mouse blood. Protein levels were altered in blood-derived exosomes after chronic treadmill exercise. Levels of the secretagogue secretogranin 2 were markedly elevated in exercise-induced exosomes.

Conclusion

Our data suggest that levels of secretogranin 2 were increased in mouse exosomes following chronic treadmill exercise. We conclude that exercise increases exocrine secretion of secretogranin 2.

Ginsenoside Rd reverses cognitive deficits by modulating BDNF-dependent CREB pathway in chronic restraint stress mice

Cognitive impairment has been widely recognized as a common symptom of chronic stress. Ginsenoside Rd (GRd), the major active compound in Panax ginseng, was previously reported in various neurological researches. However, little research is available regarding on the effect of GRd on cognitive improvement in mice subjected to chronic stress. In the present study, we investigated the neuroprotective effects of GRd in chronic restraint stress (CRS)-induced cognitive deficits and explored the potential mechanism in male C57BL/6J mice. Our results demonstrated that oral administration of GRd for 28 days markedly increased the spontaneous alternation in Y-maze and the relative discrimination index in novel object or location recognition tests following CRS. Additionally, GRd treatment considerably increased the antioxidant enzymes activities in the hippocampus. The expression levels of hippocampus and serum inflammation factors in the CRS groups were also counter-regulated by GRd treatment. Meanwhile, GRd treatment could reverse CRS-induced the decrease in phosphorylated phosphoinositide 3-kinase (PI3K), camp-reflecting element binding protein (CREB), brain-derived neurotrophic factor (BDNF) and tyrosine kinase B (TrkB) expression in the hippocampus. These findings provided evidences that GRd improves cognitive impairment in CRS mice by mitigating oxidative stress and inflammation, while upregulating the hippocampal BDNF-mediated CREB signaling pathway.

Pro-inflammatory cytokines serve as communicating molecules between the liver and brain for hepatic encephalopathy pathogenesis and Lycium barbarum polysaccharides protection

ETHNOPHARMACOLOGICAL RELEVANCE

Gogi berry is a traditional food supplement and medical herbal which has been widely used in Eastern Asian countries. Lycium barbarum polysaccharides (LBP) are the major active components of Gogi berry and have been proved to possess a lot of biological activities.

AIM OF THE STUDY

We aimed to delineate the protective effect and mechanism of LBP on hepatic encephalopathy (HE).

MATERIALS AND METHODS

We investigated the protective mechanism of LBP in a thioacetamide (TAA, intraperitoneally injected, 400 mg/kg) induced acute HE mice model. Key phenotypes of clinical HE were phenocopied in the mice model, including high mortality, severe hepatic histology injury, increased hepatic oxidative stress, apoptosis, enhanced circulating levels of pro-inflammatory cytokines and ammonia, suppressed tryptophan hydroxylase activity, and deficits in locomotor activity.

RESULTS

The pathological alterations were effectively ameliorated by the oral administration with LBP (5 mg/kg, oral gavage, everyday), which were mediated by regulating MAPK pathways in both the liver and brain. Knockout of pro-inflammatory cytokines TNF-α or IL-6 effectively ameliorated impaired mice locomotor activity and MAPK activation in the brain. In an in vitro TNF-α-, IL-6-, or ammonia-induced microglia damaged cell model, cell injuries were evidently protected by the co-administration with LBP (50 μg/ml).

CONCLUSION

LBP ameliorated the hepatic/brain injuries and impaired locomotor activities in a HE mice model. Pro-inflammatory cytokines may serve as communicating molecules linking the liver and brain for the HE pathogenesis, partly through MAPK regulation.

Exercise effects on brain and behavior in healthy mice, Alzheimer's disease and Parkinson's disease model-A systematic review and meta-analysis

This systematic review and meta-analysis examines how exercise modifies brain and behavior in healthy mice, dementia (D) and Parkinson disease (PD) models. A search was performed on the Medline and Scopus electronic databases (2008-2019). Search terms were "mice", "brain", "treadmill", "exercise", "physical exercise". In the total, 430 were found but only 103 were included. Animals n = 1,172; exercised 4-8 weeks (Range 24 h to 32 weeks), 60 min/day (Range 8-120 min per day), and 10/12 m/min (Range 0.2 m/min to 36 m/min). Hippocampus, cerebral cortex, striatum and whole brain were more frequently investigated. Exercise improved learning and memory. Meta-analysis showed that exercise increased: cerebral BDNF in health (n = 150; z = 5.8, CI 3.43-12.05; p < 0.001 I2 = 94.3 %), D (n = 124; z = 4.18, CI = 2.22-9.12; p < 0.001; I2 = 93.7 %) and PD (n = 16 z = 4.26, CI 5.03-48.73 p < 0.001 I2 = 94.8 %). TrkB improved in health (n = 84 z = 5.49, CI 3.8-17.73 p < 0.001, I2 = 0.000) and PD (n = 22; z = 3.1, CI = 2.58-67.3, p < 0.002 I2 = 93.8 %). Neurogenesis increased in health (n = 68; z = 7.08, CI 5.65-21.25 p < 0.001; I2 17.58) and D model (n = 116; z = 4.18, CI 2.22-9.12 p < 0.001 I2 93.7 %). Exercise augmented amyloid clearance (n = 166; z = 7.51 CI = 4.86-14.85, p < 0.001 I2 = 58.72) and reduced amyloid plaques in D models (n = 49; z = 4.65, CI = 3.94-15.3 p < 0.001 I2 = 0.000). In conclusion, exercise improved brain and behavior, neurogenesis in healthy and dementia models, reduced toxicity and cerebral amyloid. Evidence regarding inflammation, oxidative stress and energy metabolism were scarce. Studies examining acute vs chronic exercise, extreme training and the durability of exercise benefit were rare. Vascular or glucose metabolism changes were seldom reported.

Physical Activity Reduces Epilepsy Incidence: a Retrospective Cohort Study in Swedish Cross-Country Skiers and an Experimental Study in Seizure-Prone Synapsin II Knockout Mice

BACKGROUND

Epilepsy patients commonly exercise less than the general population. Animal studies indicate beneficial effects of physical activity in established epilepsy, while its effect on the development is currently less known.

METHODS

Here, we investigated the incidence of epilepsy during 20 years in a cohort of participants from the long-distance Swedish cross-country ski race Vasaloppet (n = 197,685) and compared it to the incidence of non-participating-matched controls included in the Swedish population register (n = 197,684). Individuals diagnosed with diseases such as stroke and epilepsy before entering the race were excluded from both groups. Experimentally, we also determined how physical activity could affect the development of epilepsy in epilepsy-prone synapsin II knockout mice (SynIIKO), with and without free access to a running wheel.

RESULTS

We identified up to 40-50% lower incidence of epilepsy in the Vasaloppet participants of all ages before retirement. A lower incidence of epilepsy in Vasaloppet participants was seen regardless of gender, education and occupation level compared to controls. The participants included both elite and recreational skiers, and in a previous survey, they have reported a higher exercise rate than the general Swedish population. Sub-analyses revealed a significantly lower incidence of epilepsy in participants with a faster compared to slower finishing time. Dividing participants according to specified epilepsy diagnoses revealed 40-50% decrease in focal and unspecified epilepsy, respectively, but no differences in generalized epilepsy. Voluntary exercise in seizure-prone SynIIKO mice for 1 month before predicted epilepsy development decreased seizure manifestation from > 70 to 40%. Brain tissue analyses following 1 month of exercise showed increased hippocampal neurogenesis (DCX-positive cells), while microglial (Iba1) and astrocytic activation (GFAP), neuronal Map2, brain-derived neurotrophic factor and its receptor tyrosine receptor kinase B intensity were unaltered. Continued exercise for additionally 2 months after predicted seizure onset in SynIIKO mice resulted in a 5-fold reduction in seizure manifestation (from 90 to 20%), while 2 months of exercise initiated at the time of predicted seizure development gave no seizure relief, suggesting exercise-induced anti-epileptogenic rather than anti-convulsive effect.

CONCLUSION

The clinical study and the experimental findings in mice indicate that physical activity may prevent or delay the development of epilepsy.

Corticosterone-mediated microglia activation affects dendritic spine plasticity and motor learning functions in minimal hepatic encephalopathy

Minimal hepatic encephalopathy (MHE) is characterized as cognitive deficits including memory and learning dysfunctions after liver injuries or hepatic diseases. Our understandings of neurological mechanisms of MHE-associated cognitive syndromes, however, are far from complete. In the current study we generated a mouse MHE model by repetitive administrations of thioacetamide (TAA), which induced hyperammonemia plus elevated proinflammatory cytokines in both the general circulation and motor cortex. MHE mice presented prominent motor learning deficits, which were associated with excess dendritic spine pruning in the motor cortex under 2-photon in vivo microscopy. The pharmaceutical blockade of glucocorticoid receptor or suppression of its biosynthesis further rescued motor learning deficits and synaptic protein loss. Moreover, MHE mice presented microglial activation, which can be alleviated after glucocorticoid pathway inhibition. In sum, our data demonstrates corticosterone-induced microglial activation, synaptic over-pruning and motor learning impairments in MHE, providing new insights for MHE pathogenesis and potential targets of clinical interventions.

Exercise and substance abuse

Exercise intervention has long been used as one adjunctive treatment for drug abuse. Both animal studies and human trials suggest that exercise training effectively prevents addiction formation, suppresses drug-seeking behaviors, and ceases addictions. Moreover, exercise improves both mental and cognitive deficits that commonly occur during drug withdrawal. Those observations are supported by neurobiological studies in which exercise training modulates several neural networks including the dopaminergic reward system, and regulates neurogenesis and spinogenesis that affect cognitive behaviors and mental health. In sum, exercise training is a safe and effective way to relieve substance abuse, although both intervention guideline and biomarkers warrants further investigation.

Exercise, spinogenesis and cognitive functions

Exercise training improves mental and cognitive functions by enhancing neurogenesis and neuroprotection. Recent studies suggest the facilitation of spinogenesis across different brain regions including hippocampus and cerebral cortex by physical activity. In this article we will summarize major findings for exercise effects on synaptogenesis and spinogenesis, in order to provide mechanisms for exercise intervention of both psychiatric diseases and neurodegenerative disorders. We will also revisit major findings for molecular mechanism governing exercise-related spinogenesis, and will discuss the screening for novel factors, or exerkines, whose levels are correlated with endurance training and affect neural plasticity. We believe that further studies focusing on the molecular mechanism of exercise-mediate spinogenesis should benefit the optimization of exercise therapy in clinics and the evaluation of treatment efficiency using specific biomarkers.

Influence of MLC901 Alone and with Moderate Exercise on Pain Response Concurrent Due to Stress of Male Mice

Background:

Physical exercise is known to have a positive effect on pain responses induced by stress, while chronic stress causes a negative effect on cognitive abilities. Depending on the type, duration, and intensity of the stressor, it can induce analgesia or hyperalgesia. Furthermore, the beneficial effects of traditional Chinese medicine MLC901 on stress processes have been reported. Here, the effects of MLC901 and moderate physical activity on pain response in restraint-stressed mice was investigated.

Materials and Methods:

Male NMRI mice were used in this study and were restrained in plexiglass mesh restrainers for induction of chronic restraint stress. Treadmill exercise was carried out for moderated exercise, 5 days/week for 4 weeks. MLC901 was intraperitoneally administered in the experimental groups. The pain response of the adult NMRI mice was detected via the hot-plate test.

Results:

It was showed that intraperitoneal administration of MLC901 dose (0.4 but not 0.1 and 0.2 mg/kg; once/2 days; for 25 days) resulted in the decreased percentage of time in the hot plate, indicating hyperalgesia. Moreover, restraint stress for 3 but not 6 and 9 hours/day elicit hyperalgesia in mice. The data showed that subthreshold dose of MLC901 (0.1 mg/kg) reduced hyperalgesia in 3-day stressed mice. Moderate treadmill running (10 meters/min for 30 min/day, 5 days/ week) potentiated the effect of 6 and 9 days on pain (induced hyperalgesia) that was blocked by MLC901 (0.1 mg/kg).

Conclusion:

Our findings indicated that subthreshold dose of MLC901 alone or when it associated with moderate exercise decreased hyperalgesia induced by stress, indicating the protective effect of MLC901.

Exercise training improves motor skill learning via selective activation of mTOR

Physical exercise improves learning and memory, but little in vivo evidence has been provided to illustrate the molecular mechanisms. Here, we show that chronic treadmill exercise activates the mechanistic target of rapamycin (mTOR) pathway in mouse motor cortex. Both ex vivo and in vivo recordings suggest that mTOR activation leads to potentiated postsynaptic excitation and enhanced neuronal activity of layer 5 pyramidal neurons after exercise, in association with increased oligodendrogenesis and axonal myelination. Exercise training also increases dendritic spine formation and motor learning. Together, exercise activates mTOR pathway, which is necessary for spinogenesis, neuronal activation, and axonal myelination leading to improved motor learning. This model provides new insights for neural network adaptations through exercises and supports the intervention of cognitive deficits using exercise training.

Ginsenoside Rb1 pretreatment reverses hippocampal changes in BDNF/TrkB mRNA and protein in rats subjected to acute immobilization stress

Purpose

Episodes of acute emotional or physical stress can have significant adverse effects on the hippocampus. Ginsenoside Rb1, the most predominant ginsenoside present in Panax species, has been reported to show a neuroprotective effect. The purpose of this study was to investigate the influence of ginsenoside Rb1 on plasma corticosterone (CORT) and adrenocorticotropic hormone (ACTH) levels and hippocampal brain-derived neurotrophic factor (BDNF) and tyrosine kinase B (TrkB) levels in rats subjected to acute immobilization stress.

Methods

Wistar rats were divided into controls treated with saline only (N), rats exposed to stress only (M), and rats pretreated with Rb1 (40 mg.kg (−1)) thirty minutes prior to stress exposure (R). In the model, animals were restrained in a plastic immobilizer for 2 h of acute immobilization stress at room temperature. ELISA was used to determine plasma levels of CORT and ACTH. The effect of Rb1 pretreatment on the expression of BDNF and TrkB was determined by immunofluorescence, real-time PCR, and Western blotting analysis.

Results

The R group showed significantly increased plasma CORT and ACTH levels compared to the N and M groups. Acute stress stimulation suppressed BDNF and TrkB protein and mRNA expression in the hippocampus; otherwise, Rb1 pretreatment reversed the decreases.

Conclusion

The results from this study demonstrate that Rb1 pretreatment reverses the decreases in hippocampal BDNF/TrkB and increases the plasma levels of CORT and ACTH, indicating a potential neuroprotective effect of Rb1 against acute stress.

Persistence of learning-induced synapses depends on neurotrophic priming of glucocorticoid receptors

Signal transduction upon activation of receptor tyrosine kinases by neurotrophins and nuclear receptors by glucocorticoids is essential for homeostasis. Phosphorylation (PO₄) is one way these receptors communicate with one another to support homeostatic reactions in learning and memory. Using a newly developed glucocorticoid receptor (GR)-PO₄–deficient knock-in mouse, we show that consolidation of learning-induced neuroplasticity depends on both GR-PO₄ and neurotrophic signaling. Cross-talk between these pathways affects experience-dependent neuroplasticity and behavior, extending previous implications of neurotrophic priming of glucocorticoid response for adaptive plasticity to chronic stress and antidepressant response. Therefore, a disruption of cross-talk between these pathways by, for example, the misalignment of circadian glucocorticoid release and experience-dependent neurotrophic signaling may contribute to the pathophysiology of stress-related disorders.

Stress can either promote or impair learning and memory. Such opposing effects depend on whether synapses persist or decay after learning. Maintenance of new synapses formed at the time of learning upon neuronal network activation depends on the stress hormone-activated glucocorticoid receptor (GR) and neurotrophic factor release. Whether and how concurrent GR and neurotrophin signaling integrate to modulate synaptic plasticity and learning is not fully understood. Here, we show that deletion of the neurotrophin brain-derived neurotrophic factor (BDNF)–dependent GR-phosphorylation (PO₄) sites impairs long-term memory retention and maintenance of newly formed postsynaptic dendritic spines in the mouse cortex after motor skills training. Chronic stress and the BDNF polymorphism Val66Met disrupt the BDNF-dependent GR-PO₄ pathway necessary for preserving training-induced spines and previously acquired memories. Conversely, enrichment living promotes spine formation but fails to salvage training-related spines in mice lacking BDNF-dependent GR-PO₄ sites, suggesting it is essential for spine consolidation and memory retention. Mechanistically, spine maturation and persistence in the motor cortex depend on synaptic mobilization of the glutamate receptor subunit A1 (GluA1) mediated by GR-PO₄. Together, these findings indicate that regulation of GR-PO₄ via activity-dependent BDNF signaling is important for the formation and maintenance of learning-dependent synapses. They also define a signaling mechanism underlying these effects.

Effects of physical exercise and stress on hippocampal CA1 and dentate gyrus synaptic transmission and long-term potentiation in adolescent and adult Wistar rats

It is commonly recognized that physical exercise positively affects several CNS regions and improves cognitive abilities. For example, exercise is associated with an increase in neurogenesis and facilitation of long-term potentiation in the hippocampus. Conversely, animal models for depression are associated with a decrease in neurogenesis and a reduction of long-term potentiation in the hippocampus. Although exercise could be a viable option in the treatment of some forms of depression, the mechanisms responsible for such improvements have not been elucidated. In this study, we examine hippocampal function using electrophysiological field recordings in CA1 and dentate gyrus to study baseline synaptic transmission and long-term potentiation in adolescent and adult rats prenatally exposed to the glucocorticoid dexamethasone. One group of animals was allowed to run voluntarily for 10 or 21 days using an exercise wheel before the experiments, and the control group was prevented from running (i.e. the exercise wheel was locked). In adult saline-exposed animals, exercise was associated with increased long-term potentiation in the dentate gyrus. Unexpectedly, in dexamethasone-exposed animals, dentate gyrus long-term potentiation was facilitated, whereas long-term potentiation in CA1 was unaffected by prenatal dexamethasone or by 10 or 21 days of voluntary running. Irrespective of age, prenatal dexamethasone and running had limited effects on synaptic transmission and presynaptic release in CA1 and dentate gyrus. In summary, running facilitates dentate gyrus long-term potentiation in adult animals that resembles the effects of prenatal dexamethasone.

Neuroprotective effects of exercise in rodent models of memory deficit and Alzheimer's

Alzheimer's disease (AD) is a fastest growing neurodegenerative condition with no standard treatment. There are growing evidence about the beneficial effects of exercise in brain health promotion and slowing the cognitive decline. The aim of this study was to review the protective mechanisms of treadmill exercise in different models of rodent memory deficits. Online literature database, including PubMed-Medline, Scopus, Google scholar were searched from 2003 till 2017. Original article with English language were chosen according to following key words in the title: (exercise OR physical activity) AND (memory OR learning). Ninety studies were finally included in the qualitative synthesis. The results of these studies showed the protective effects of exercise on AD induced neurodegerative and neuroinflammatory process. Neuroperotective effects of exercise on the hippocampus seem to be increasing in immediate-early gene c-Fos expression in dentate gyrus; enhancing the Wnt3 expression and inhibiting glycogen synthase kinase-3β expression; increasing the 5-bro-mo-2'-deoxyridine-positive and doublecortin-positive cells (dentate gyrus); increasing the level of astrocytes glial fibrillary acidic protein and decrease in S100B protein, increasing in blood brain barrier integrity; prevention of oxidative stress injury, inducing morphological changes in astrocytes in the stratum radiatum of cornu ammonis 1(CA1) area; increase in cell proliferation and suppress apoptosis in dentate gyrus; increase in brain-derived neurotrophic factor and tropomyosin receptor kinase B expressions; enhancing the glycogen levels and normalizing the monocarboxylate transporter 2 expression.

Protective and therapeutic effects of exercise on stress-induced memory impairment

The objective of this paper was to systematically evaluate the potential preventive and therapeutic effects of exercise in attenuating stress-induced memory impairment. A systematic review was employed, searching PubMed, PsychInfo, Sports Discus and Google Scholar databases. For eligibility, studies had to be published in English, employ an experimental design, have the acute or chronic bout of exercise occur prior to, during or after the stressor, implement a psychophysiological stressor, and have an assessment of memory function occurring after the stressor. In total, 23 studies were evaluated, all of which were conducted among animal models. All 23 studies employed a chronic exercise protocol and a chronic stress protocol. Eight studies evaluated a preventive model, three employed a concurrent model, ten studies employed a therapeutic model, and two studies evaluated both a preventive and therapeutic model within the same study. Among the eight studies employing a preventive model, all eight demonstrated that the stress regimen impaired memory function. In all eight of these studies, when exercise occurred prior to the stressor, exercise attenuated the stress-induced memory impairment effect. Among the ten studies employing a therapeutic model, one study showed that the stress protocol enhanced memory function, one showed that the stress protocol did not influence memory, and eight demonstrated that the stress regimen impaired memory function. Among the eight studies showing that the stress protocol impaired memory function, all eight studies demonstrated that exercise, after the stressor, attenuated stress-induced memory impairment. Within animal models, chronic stress is associated with memory impairment and chronic exercise has both a preventive and therapeutic effect in attenuating stress-induced memory impairment. Additional experimental work in human studies is needed. Such work should also examine acute exercise and stress protocols.

Physical Exercise Enhances Neuroplasticity and Delays Alzheimer's Disease

Accumulating evidence indicates that exercise can improve learning and memory as well as attenuate neurodegeneration, including Alzheimer's disease (AD). In addition to improving neuroplasticity by altering the synaptic structure and function in various brain regions, exercise also modulates systems like angiogenesis and glial activation that are known to support neuroplasticity. Moreover, exercise helps to maintain a cerebral microenvironment that facilitates synaptic plasticity by enhancing the clearance of Aβ, one of the main culprits of AD pathogenesis. The purpose of this review is to highlight the positive impacts of exercise on promoting neuroplasticity. Possible mechanisms involved in exercise-modulated neuroplasticity are also discussed. Undoubtedly, more studies are needed to design an optimal personalized exercise protocol for enhancing brain function.