Affective dysfunction in a mouse model of Rett syndrome: Therapeutic effects of environmental stimulation and physical activity

Adolescent treadmill exercise enhances hippocampal brain-derived neurotrophic factor (BDNF) expression and improves cognition in autism-modeled rats

Autism spectrum disorder (ASD) is a prevalent neurodevelopmental disorder characterized by repetitive behaviors and altered communication abilities. Exercise is a low-cost intervention that could improve cognitive function and improve brain plasticity mechanisms. Here, the valproic acid (VPA) model was utilized to induce ASD-like phenotypes in rodents. Animals were exercised on a treadmill and performance was evaluated on a cognitive flexibility task. Biomarkers related to exercise and plasticity regulation were quantified from the prefrontal cortex, hippocampus, and skeletal muscle. Exercised VPA animals had higher levels of hippocampal BDNF compared to sedentary VPA animals and upregulated antioxidant enzyme expression in skeletal muscle. Cognitive improvements were demonstrated in both sexes, but in different domains of cognitive flexibility. This research demonstrates the benefits of exercise and provides evidence that molecular responses to exercise occur in both the central nervous system and in the periphery. These results suggest that improving regulation of BDNF via exercise, even at low intensity, could provide better synaptic regulation and cognitive benefits for individuals with ASD.

Molecular insights into enriched environments and behavioral improvements in autism: a systematic review and meta-analysis

Aims

Autism is a multifaceted developmental disorder of the nervous system, that necessitates novel therapeutic approaches beyond traditional medications and psychosomatic therapy, such as appropriate sensory integration training. This systematic mapping review aims to synthesize existing knowledge on enriching environmental interventions as an alternative avenue for improving autism, guiding future research and practice.

Method

A comprehensive search using the terms ASD and Enriched Environment was conducted across PubMed, EMBASE, ISI, Cochrane, and OVID databases. Most of the literature included in this review was derived from animal model experiments, with a particular focus on assessing the effect of EE on autism-like behavior, along with related pathways and molecular mechanisms. Following extensive group discussion and screening, a total of 19 studies were included for analysis.

Results

Enriched environmental interventions exhibited the potential to induce both behavioral and biochemical changes, ameliorating autism-like behaviors in animal models. These improvements were attributed to the targeting of BDNF-related pathways, enhanced neurogenesis, and the regulation of glial inflammation.

Conclusion

This paper underscores the positive impact of enriched environmental interventions on autism through a review of existing literature. The findings contribute to a deeper understanding of the underlying brain mechanisms associated with this intervention.

Voluntary Running Improves Behavioral and Structural Abnormalities in a Mouse Model of CDKL5 Deficiency Disorder

Cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder (CDD) is a rare neurodevelopmental disease caused by mutations in the X-linked CDKL5 gene. CDD is characterized by a broad spectrum of clinical manifestations, including early-onset refractory epileptic seizures, intellectual disability, hypotonia, visual disturbances, and autism-like features. The Cdkl5 knockout (KO) mouse recapitulates several features of CDD, including autistic-like behavior, impaired learning and memory, and motor stereotypies. These behavioral alterations are accompanied by diminished neuronal maturation and survival, reduced dendritic branching and spine maturation, and marked microglia activation. There is currently no cure or effective treatment to ameliorate the symptoms of the disease. Aerobic exercise is known to exert multiple beneficial effects in the brain, not only by increasing neurogenesis, but also by improving motor and cognitive tasks. To date, no studies have analyzed the effect of physical exercise on the phenotype of a CDD mouse model. In view of the positive effects of voluntary running on the brain of mouse models of various human neurodevelopmental disorders, we sought to determine whether voluntary daily running, sustained over a month, could improve brain development and behavioral defects in Cdkl5 KO mice. Our study showed that long-term voluntary running improved the hyperlocomotion and impulsivity behaviors and memory performance of Cdkl5 KO mice. This is correlated with increased hippocampal neurogenesis, neuronal survival, spine maturation, and inhibition of microglia activation. These behavioral and structural improvements were associated with increased BDNF levels. Given the positive effects of BDNF on brain development and function, the present findings support the positive benefits of exercise as an adjuvant therapy for CDD.

Sex-dependent influence of postweaning environmental enrichment in Angelman syndrome model mice

INTRODUCTION

Angelman syndrome (AS) is a rare neurodevelopmental disorder caused by mutation or loss of UBE3A and marked by intellectual disability, ataxia, autism-like symptoms, and other atypical behaviors. One route to treatment may lie in the role that environment plays early in postnatal life. Environmental enrichment (EE) is one manipulation that has shown therapeutic potential in preclinical models of many brain disorders, including neurodevelopmental disorders. Here, we examined whether postweaning EE can rescue behavioral phenotypes in Ube3a maternal deletion mice (AS mice), and whether any improvements are sex-dependent.

METHODS

Male and female mice (C57BL/6J Ube3atm1Alb mice and wild-type (WT) littermates; ≥10 mice/group) were randomly assigned to standard housing (SH) or EE at weaning. EE had a larger footprint, a running wheel, and a variety of toys that promoted foraging, burrowing, and climbing. Following 6 weeks of EE, animals were submitted to a battery of tests that reliably elicit behavioral deficits in AS mice, including rotarod, open field, marble burying, and forced swim; weights were also monitored.

RESULTS

In male AS-EE mice, we found complete restoration of motor coordination, marble burying, and forced swim behavior to the level of WT-SH mice. We also observed a complete normalization of exploratory distance traveled in the open field, but we found no rescue of vertical behavior or center time. AS-EE mice also had weights comparable to WT-SH mice. Intriguingly, in the female AS-EE mice, we found a failure of EE to rescue the same behavioral deficits relative to female WT-SH mice.

CONCLUSIONS

Environmental enrichment is an effective route to correcting the most penetrant phenotypes in male AS mice but not female AS mice. This finding has important implications for the translatability of early behavioral intervention for AS patients, most importantly the potential dependency of treatment response on sex.

Motor training improves coordination and anxiety in symptomatic Mecp2-null mice despite impaired functional connectivity within the motor circuit

Rett syndrome (RTT) is a severe neurodevelopmental disorder caused by loss of function of the X-linked methyl-CpG–binding protein 2 (MECP2). Several case studies report that gross motor function can be improved in children with RTT through treadmill walking, but whether the MeCP2-deficient motor circuit can support actual motor learning remains unclear. We used two-photon calcium imaging to simultaneously observe layer (L) 2/3 and L5a excitatory neuronal activity in the motor cortex (M1) while mice adapted to changing speeds on a computerized running wheel. Despite circuit hypoactivity and weakened functional connectivity across L2/3 and L5a, the Mecp2-null circuit’s firing pattern evolved with improved performance over 2 weeks. Moreover, trained mice became less anxious and lived 20% longer than untrained mice. Because motor deficits and anxiety are core symptoms of RTT, which is not diagnosed until well after symptom onset, these results underscore the benefit of motor learning.

Neuroinflammation in autism spectrum disorders: Exercise as a "pharmacological" tool

The worldwide prevalence of ASD is around 1%. Although the pathogenesis of ASD is not entirely understood, it is recognized that a combination of genetic, epigenetics, environmental factors and immune system dysfunction can play an essential role in its development. It has been suggested that autism results from the central nervous system derangements due to low-grade chronic inflammatory reactions associated with the immune system activation. ASD individuals have increased microglial activation, density, and increased proinflammatory cytokines in the several brain regions. Autism has no available pharmacological treatments, however there are pedagogical and psychotherapeutic therapies, and pharmacological treatment, that help to control behavioral symptoms. Recent data indicate that exercise intervention programs may improve cognitive and behavioral symptoms in children with ASD. Exercise can also modify inflammatory profiles that will ameliorate associated metabolic disorders. This review highlights the involvement of neuroinflammation in ASD and the beneficial effects of physical exercise on managing ASD symptoms and associated comorbidities.

Rehabilitation therapies in Rett syndrome across the lifespan: A scoping review of human and animal studies

PURPOSE

To perform a scoping review of the evidence for therapeutic interventions to manage functional impairments associated with Rett syndrome (RTT) throughout the lifespan.

METHODS

MEDLINE, EMBASE, PsycINFO, CENTRAL, CINAHL, Scopus and Index to Chiropractic Literature were searched systematically up to December 2019. Two investigators independently reviewed all search results and extracted those that met the inclusion criteria. Human and animal model studies pertaining to therapies that increase functional ability or treat RTT-associated symptoms in all age groups were included. Relevant studies were grouped into intervention categories and rated using the Oxford Centre of Evidence Based Medicine Levels of Evidence. Demographics of participants, interventions, and outcomes were summarized.

RESULTS

Ninety-one articles representing 88 studies met the inclusion criteria, of which 80 were human clinical studies and eight were studies using animal models. Study designs were primarily case series and only six studies involved participants above the age of 40.

CONCLUSION

A small number of rigorously studied rehabilitation interventions have been published. Published studies aim to address a wide variety of functional impairments. Research regarding implementation of therapies for older patients with RTT is lacking and requires further exploration.

Environmental Enrichment Rescues Visually-Mediated Behavior in Ten-m3 Knockout Mice During an Early Critical Period

Environmental enrichment (EE) has been shown to promote neural plasticity. Its capacity to induce functional repair in models which exhibit profound sensory deficits due to aberrant axonal guidance has not been well-characterized. Ten-m3 knockout (KO) mice exhibit a highly-stereotyped miswiring of ipsilateral retinogeniculate axons and associated profound deficits in binocularly-mediated visual behavior. We determined whether, and when, EE can drive functional recovery by analyzing Ten-m3 KO and wildtype (WT) mice that were enriched for 6 weeks from adulthood, weaning or birth in comparison to standard-housed controls. EE initiated from birth, but not later, rescued the response of Ten-m3 KOs to the "looming" stimulus (expanding disc in dorsal visual field), suggesting improved visual function. EE can thus induce recovery of visual behavior, but only during an early developmentally-restricted time-window.

From Basic Visual Science to Neurodevelopmental Disorders: The Voyage of Environmental Enrichment-Like Stimulation

Genes and environmental stimuli cooperate in the regulation of brain development and formation of the adult neuronal architecture. Genetic alterations or exposure to perturbing environmental conditions, therefore, can lead to altered neural processes associated with neurodevelopmental disorders and brain disabilities. In this context, environmental enrichment emerged as a promising and noninvasive experimental treatment for favoring recovery of cognitive and sensory functions in different neurodevelopmental disorders. The aim of this review is to depict, mainly through the much explicative examples of amblyopia, Down syndrome, and Rett syndrome, the increasing interest in the potentialities and applications of enriched environment-like protocols in the field of neurodevelopmental disorders and the understanding of the molecular mechanisms underlying the beneficial effects of these protocols, which might lead to development of pharmacological interventions.

Treating Rett syndrome: from mouse models to human therapies

Rare diseases are very difficult to study mechanistically and to develop therapies for because of the scarcity of patients. Here, the rare neuro-metabolic disorder Rett syndrome (RTT) is discussed as a prototype for precision medicine, demonstrating how mouse models have led to an understanding of the development of symptoms. RTT is caused by mutations in the X-linked gene methyl-CpG-binding protein 2 (MECP2). Mecp2-mutant mice are being used in preclinical studies that target the MECP2 gene directly, or its downstream pathways. Importantly, this work may improve the health of RTT patients. Clinical presentation may vary widely among individuals based on their mutation, but also because of the degree of X chromosome inactivation and the presence of modifier genes. Because it is a complex disorder involving many organ systems, it is likely that recovery of RTT patients will involve a combination of treatments. Precision medicine is warranted to provide the best efficacy to individually treat RTT patients.

Gene-environment interactions informing therapeutic approaches to cognitive and affective disorders

Gene-environment interactions drive experience-dependent changes in the brain that alter cognition, emotion and behaviour. Positive engagement with the environment, through novel experience and physical activity, can improve brain function, although the mechanisms mediating such experience-dependent plasticity remain to be fully elucidated. In this article, we discuss the therapeutic value of environmental stimuli, exercise and environmental enrichment (EE), for cognitive and affective disorders, with implications for the understanding and treatment of depression and anxiety disorders. We demonstrate that environmental manipulations are potential therapeutic strategies for improving outcomes in these psychiatric disorders, including beneficial impacts on cognition. We discuss how EE and exercise are therapeutic environmental interventions impacting both affective and cognitive function. Serotonergic (5-HTergic) signaling is strongly implicated in the manifestation of psychiatric disorders and regulates cognitive and emotional processing that can underpin them. Thus, we focus on evidence implicating the serotonergic system in mediating gene-environment interactions to EE and exercise. Finally, we discuss robust gene-environment interactions associated with EE and exercise interventions, and their impacts on specific brain areas, particularly the hippocampus. We focus on potential mediators of this experience-dependent plasticity, including adult neurogenesis and brain-derived neurotrophic factor (BDNF). Furthermore, we explore molecular and cellular mechanisms of experience-dependent plasticity that potentially underlie the restoration of affective and cognitive phenotypes, thus identifying novel therapeutic targets. This article is part of the Special Issue entitled "Neurobiology of Environmental Enrichment".

Physical exercise as an epigenetic modulator of brain plasticity and cognition

A large amount of evidence has demonstrated the power of exercise to support cognitive function, the effects of which can last for considerable time. An emerging line of scientific evidence indicates that the effects of exercise are longer lasting than previously thought up to the point to affect future generations. The action of exercise on epigenetic regulation of gene expression seem central to building an "epigenetic memory" to influence long-term brain function and behavior. In this review article, we discuss new developments in the epigenetic field connecting exercise with changes in cognitive function, including DNA methylation, histone modifications and microRNAs (miRNAs). The understanding of how exercise promotes long-term cognitive effects is crucial for directing the power of exercise to reduce the burden of neurological and psychiatric disorders.

The roles of motor activity and environmental enrichment in intellectual disability

In people with intellectual disabilities, an enriched environment can stimulate the acquisition of motor skills and could partially repair neuronal impairment thanks to exploration and motor activity. A deficit in environmental and motor stimulation leads to low scores in intelligence tests and can cause serious motor skill problems. Although studies in humans do not give much evidence for explaining basic mechanisms of intellectual disability and for highlighting improvements due to enriched environmental stimulation, animal models have been valuable in the investigation of these conditions. Here, we discuss the role of environmental enrichment in four intellectual disabilities: Foetal Alcohol Spectrum Disorder (FASD), Down, Rett, and Fragile X syndromes.

Short-term environmental enrichment is sufficient to counter stress-induced anxiety and associated structural and molecular plasticity in basolateral amygdala

Moderate levels of anxiety enable individual animals to cope with stressors through avoidance, and could be an adaptive trait. However, repeated stress exacerbates anxiety to pathologically high levels. Dendritic remodeling in the basolateral amygdala is proposed to mediate potentiation of anxiety after stress. Similarly, modulation of brain-derived neurotrophic factor is thought to be important for the behavioral effects of stress. In the present study, we investigate if relatively short periods of environmental enrichment in adulthood can confer resilience against stress-induced anxiety and concomitant changes in neuronal arborisation and brain derived neurotrophic factor within basolateral amygdala. Two weeks of environmental enrichment countermanded the propensity of increased anxiety following chronic immobilization stress. Environmental enrichment concurrently reduced dendritic branching and spine density of projection neurons of the basolateral amygdala. Moreover, stress increased abundance of BDNF mRNA in the basolateral amygdala in agreement with the dendritic hypertrophy post-stress and role of BDNF in promoting dendritic arborisation. In contrast, environmental enrichment prevented stress-induced rise in the BDNF mRNA abundance. Gain in body weights and adrenal weights remained unaffected by exposure to environmental enrichment. These observations suggest that a short period of environmental enrichment can provide resilience against maladaptive effects of stress on hormonal, neuronal and molecular mediators of anxiogenesis.

Environmental and Pharmacological Manipulations Blunt the Stress Response of Zebrafish in a Similar Manner

Here we provide evidence that both pharmacological and environmental manipulations similarly blunt the cortisol release in response to an acute stressor in adult zebrafish. Different groups of fish were maintained isolated or group-housed in barren or enriched tanks, and then exposed or not to diazepam or fluoxetine. Acute stress increased cortisol levels in group-housed zebrafish maintained in barren environment. Single-housed zebrafish displayed a blunted cortisol response to stress. Environmental enrichment also blunted the stress response and this was observed in both isolated and group-housed fish. The same blunting effect was observed in zebrafish exposed to diazepam or fluoxetine. We highlighted environmental enrichment as an alternative and/or complimentary therapeutic for reducing stress and as a promoter of animal welfare.

Dimensional assessment of behavioral changes in the cuprizone short-term exposure model for psychosis

Recent clinical studies have suggested a role for immune/inflammatory responses in the pathophysiology of psychosis. However, a mechanistic understanding of this process and its application for drug discovery is underdeveloped. Here we assessed our recently developed cuprizone short-term exposure (CSE) mouse model across behavioral domains targeting neurocognitive and neuroaffective systems. We propose that the CSE model may be useful for understanding the mechanism associating inflammation and psychosis, with applications for drug discovery in that context.