A critical period for social experience-dependent oligodendrocyte maturation and myelination

The Fragile X Messenger Ribonucleoprotein 1 Regulates the Morphology and Maturation of Human and Rat Oligodendrocytes

The Fragile X Messenger Ribonucleoprotein (FMRP) is an RNA binding protein that regulates the translation of multiple mRNAs and is expressed by neurons and glia in the mammalian brain. Loss of FMRP leads to fragile X syndrome (FXS), a common inherited form of intellectual disability and autism. While most research has been focusing on the neuronal contribution to FXS pathophysiology, the role of glia, particularly oligodendrocytes, is largely unknown. FXS individuals are characterized by white matter changes, which imply impairments in oligodendrocyte differentiation and myelination. We hypothesized that FMRP regulates oligodendrocyte maturation and myelination during postnatal development. Using a combination of human pluripotent stem cell-derived oligodendrocytes and an Fmr1 knockout rat model, we studied the role of FMRP on mammalian oligodendrocyte development. We found that the loss of FMRP leads to shared defects in oligodendrocyte morphology in both rat and human systems in vitro, which persist in the presence of FMRP-expressing axons in chimeric engraftment models. Our findings point to species-conserved, cell-autonomous defects during oligodendrocyte maturation in FXS.

Oligodendroglia Are Primed for Antigen Presentation in Response to Chronic Stress-Induced Microglial-Derived Inflammation

Chronic stress is a major contributor to the development of major depressive disorder, one of the leading causes of disability worldwide. Using a model of repeated social defeat stress in mice, we and others have reported that neuroinflammation plays a dynamic role in the development of behavioral deficits consistent with social avoidance and impaired reward responses. Animals susceptible to the model also exhibit hypomyelination in the medial prefrontal cortex, indicative of changes in the differentiation pathway of cells of the oligodendroglial lineage (OLN). We computationally confirmed the presence of immune oligodendrocytes, a population of OLN cells, which express immune markers and myelination deficits. In the current study, we report that microglia are necessary to induce expression of antigen presentation markers (and other immune markers) on oligodendroglia. We further associate the appearance of these markers with changes in the OLN and confirm that microglial changes precede OLN changes. Using co-cultures of microglia and OLN, we show that under inflammatory conditions the processes of phagocytosis and expression of MHCII are linked, suggesting potential priming for antigen presentation by OLN cells. Our findings provide insights into the nature of these OLN cells with immune capabilities, their obligatory interaction with microglia, and identify them as a potential cellular contributor to the pathological manifestations of psychosocial stress.

Revisiting the Pathogenesis of X-Linked Adrenoleukodystrophy

BACKGROUND

X-ALD is a white matter (WM) disease caused by mutations in the ABCD1 gene encoding the transporter of very-long-chain fatty acids (VLCFAs) into peroxisomes. Strikingly, the same ABCD1 mutation causes either devastating brain inflammatory demyelination during childhood or, more often, progressive spinal cord axonopathy starting in middle-aged adults. The accumulation of undegraded VLCFA in glial cell membranes and myelin has long been thought to be the central mechanism of X-ALD.

METHODS

This review discusses studies in mouse and drosophila models that have modified our views of X-ALD pathogenesis.

RESULTS

In the Abcd1 knockout (KO) mouse that mimics the spinal cord disease, the late manifestations of axonopathy are rapidly reversed by ABCD1 gene transfer into spinal cord oligodendrocytes (OLs). In a peroxin-5 KO mouse model, the selective impairment of peroxisomal biogenesis in OLs achieves an almost perfect phenocopy of cerebral ALD. A drosophila knockout model revealed that VLCFA accumulation in glial myelinating cells causes the production of a toxic lipid able to poison axons and activate inflammatory cells. Other mouse models showed the critical role of OLs in providing energy substrates to axons. In addition, studies on microglial changing substates have improved our understanding of neuroinflammation.

CONCLUSIONS

Animal models supporting a primary role of OLs and axonal pathology and a secondary role of microglia allow us to revisit of X-ALD mechanisms. Beyond ABCD1 mutations, pathogenesis depends on unidentified contributors, such as genetic background, cell-specific epigenomics, potential environmental triggers, and stochasticity of crosstalk between multiple cell types among billions of glial cells and neurons.

Activity-driven myelin sheath growth is mediated by mGluR5

Myelination by oligodendrocytes in the central nervous system is influenced by neuronal activity, but the molecular mechanisms by which this occurs have remained unclear. Here we employed pharmacological, genetic, functional imaging and optogenetic-stimulation approaches in zebrafish to assess activity-regulated myelination in vivo. Pharmacological inhibition and activation of metabotropic glutamate receptor 5 (mGluR5) impaired and promoted myelin sheath elongation, respectively, during development, without otherwise affecting the oligodendrocyte lineage. Correspondingly, mGluR5 loss-of-function mutants exhibit impaired myelin growth, while oligodendrocyte-specific mGluR5 gain of function promoted sheath elongation. Functional imaging and optogenetic-stimulation studies revealed that mGluR5 mediates activity-driven high-amplitude Ca2+ transients in myelin. Furthermore, we found that long-term stimulation of neuronal activity drives myelin sheath elongation in an mGluR5-dependent manner. Together these data identify mGluR5 as a mediator of the influence of neuronal activity on myelination by oligodendrocytes in vivo, opening up opportunities to assess the functional relevance of activity-regulated myelination.

Social housing conditions, hierarchical status and testing order affect behavioral test outcomes of male C57BL6/J mice

Male mice are frequently used for behavioral neuroscience research, but outcomes of behavioral tests are often variable across studies, contributing to poor reproducibility. Social housing conditions, social hierarchical status and within-cage order of testing are factors that likely influence behavioral outcomes, but it is unknown to what extent and if these factors interact. For this purpose, behavior of socially and individually housed male C57BL6/J mice was studied upon subjection to the open field test, the elevated plus-maze test and the three-chamber social test. In socially housed animals, effects of social hierarchical status and within-cage testing order were evaluated. We show that the differences in behavior outcomes between individually and socially housed mice depend on the social hierarchical status and the test order of the socially housed mice. Careful consideration of these factors in the design, analysis and interpretation of behavioral experiments with socially housed mice can lead to more precise results and more reliable research outcomes.

The complex effects of miR-146a in the pathogenesis of Alzheimer's disease

Alzheimer's disease is a neurodegenerative disorder characterized by cognitive dysfunction and behavioral abnormalities. Neuroinflammatory plaques formed through the extracellular deposition of amyloid-β proteins, as well as neurofibrillary tangles formed by the intracellular deposition of hyperphosphorylated tau proteins, comprise two typical pathological features of Alzheimer's disease. Besides symptomatic treatment, there are no effective therapies for delaying Alzheimer's disease progression. MicroRNAs (miR) are small, non-coding RNAs that negatively regulate gene expression at the transcriptional and translational levels and play important roles in multiple physiological and pathological processes. Indeed, miR-146a, a NF-κB-regulated gene, has been extensively implicated in the development of Alzheimer's disease through several pathways. Research has demonstrated substantial dysregulation of miR-146a both during the initial phases and throughout the progression of this disorder. MiR-146a is believed to reduce amyloid-β deposition and tau protein hyperphosphorylation through the TLR/IRAK1/TRAF6 pathway; however, there is also evidence supporting that it can promote these processes through many other pathways, thus exacerbating the pathological manifestations of Alzheimer's disease. It has been widely reported that miR-146a mediates synaptic dysfunction, mitochondrial dysfunction, and neuronal death by targeting mRNAs encoding synaptic-related proteins, mitochondrial-related proteins, and membrane proteins, as well as other mRNAs. Regarding the impact on glial cells, miR-146a also exhibits differential effects. On one hand, it causes widespread and sustained inflammation through certain pathways, while on the other hand, it can reverse the polarization of astrocytes and microglia, alleviate neuroinflammation, and promote oligodendrocyte progenitor cell differentiation, thus maintaining the normal function of the myelin sheath and exerting a protective effect on neurons. In this review, we provide a comprehensive analysis of the involvement of miR-146a in the pathogenesis of Alzheimer's disease. We aim to elucidate the relationship between miR-146a and the key pathological manifestations of Alzheimer's disease, such as amyloid-β deposition, tau protein hyperphosphorylation, neuronal death, mitochondrial dysfunction, synaptic dysfunction, and glial cell dysfunction, as well as summarize recent relevant studies that have highlighted the potential of miR-146a as a clinical diagnostic marker and therapeutic target for Alzheimer's disease.

Perturbations of CB1 receptor signalling during adolescence impair cortical myelination in female rats

The constant increase in cannabis use among adolescents raises concerns about its potential neurobehavioral effects. Adolescence is a critical period for brain development, involving significant changes in grey and white matter. Grey matter decreases as the brain undergoes synaptic pruning, while white matter increases due to myelination. Cannabis use during this developmental window, particularly its active ingredient delta-9-tetrahydrocannabinol (THC), may disrupt these processes, increasing the risk of developing psychiatric disorders later in life. While the impact of THC on grey matter has been explored, the specific role of CB1 receptors as well as the effect of THC exposure in adolescent myelination remain unclear. This study investigates how CB1 receptor blockade and THC exposure during adolescence affect myelination in the prefrontal cortex of female rats. Blocking CB1 receptors during adolescence hindered myelination in the prefrontal cortex. Behaviourally, this disruption in myelin formation was associated with increased risk-taking behaviour. Notably, our data suggest that alterations in the AKT/Hippo/YAP signalling pathway may play a crucial role in mediating these effects. Supporting the involvement of the endocannabinoid system in cortical myelination during adolescence, we found that administering exogenous THC impaired myelin formation only when given during early to mid-adolescence. Moreover, when a more intensive THC exposure protocol was applied during this developmental period, the effects on myelination were long-lasting and persisted into adulthood. Overall, these data support a role for CB1 receptors in shaping cortical myelination in adolescent female rats and show that adolescent exposure to THC might adversely impact this developmental process.

Time- and sex-dependent effects of juvenile social isolation on mouse brain morphology

During early life stages, social isolation disrupts the proper brain growth and brain circuit formation, which is associated with the risk of mental disorders and cognitive deficits in adulthood. Nevertheless, the impact of juvenile social isolation on brain development, particularly regarding variations across age and sex, remains poorly understood. Here, we investigate the effects of social isolation stress (SIS) during early (3-5 weeks old) or late (5-7 weeks old) juvenile period on brain morphology in adult male and female mice using ultra high-field MRI (11.7 T). We found that both early and late SIS in female mice led to volumetric increases in multiple brain regions, such as the medial prefrontal cortex (mPFC) and hippocampus. Correlation tractography revealed that the fiber tracts in the right corpus callosum and right amygdala were positively correlated with SIS in female mice. In male mice, early SIS resulted in small volumetric increases in the isocortex, whereas late SIS led to reductions in the isocortex and hypothalamus. Furthermore, early SIS caused a negative correlation, while late SIS exhibited a positive correlation, with fiber tracts in the corpus callosum and amygdala in male mice. Using a Random Forest classifier, we achieved effective discrimination between socially isolated and control conditions in the brain volume of female mice, with the limbic areas playing a key role in the model's accuracy. Finally, we discovered that SIS led to context fear generalization in a sex-dependent manner. Our findings highlight the importance of considering both the time- and sex-dependent effects of juvenile SIS on brain development and emotional processing, providing new insights into its long-term consequences.

Microbiome's effect on white matter in autism

Autism spectrum disorder (ASD) is characterized by deficits in social communication and restricted, repetitive behavioral patterns. Although other physiological presentations in individuals with ASD are heterogeneous, neuroimaging studies have consistently revealed a developmental pattern of initial white matter hypermyelination followed by reduced myelination compared with typically developing peers. Multiple studies have demonstrated that core ASD symptoms, including impairments in social skills, language acquisition, learning capabilities, motor performance, and sensory processing, correlate significantly with white matter dysregulation measured through diffusion tensor imaging (DTI). Longitudinal studies have shown that decreased gut microbiome diversity, particularly reductions in beneficial bacteria such as Bifidobacterium and Lactobacillus, correlates with symptom severity. Emerging mechanistic evidence suggests bidirectional relationships between microbiome composition and white matter development, both directly through metabolites like short-chain fatty acids (SCFAs) that regulate oligodendrocyte function and subsequent myelination, and indirectly through modulation of neuroinflammatory pathways. By integrating molecular-level gut physiology findings with macro-level brain imaging data, we may identify novel therapeutic approaches targeting the gut-brain axis in ASD management.

Development of the rodent prefrontal cortex: circuit formation, plasticity, and impacts of early life stress

The prefrontal cortex (PFC), located at the anterior region of the cerebral cortex, is a multimodal association cortex essential for higher-order brain functions, including decision-making, attentional control, memory processing, and regulation of social behavior. Structural, circuit-level, and functional abnormalities in the PFC are often associated with neurodevelopmental disorders. Here, we review recent findings on the postnatal development of the PFC, with a particular emphasis on rodent studies, to elucidate how its structural and circuit properties are established during critical developmental windows and how these processes influence adult behaviors. Recent evidence also highlights the lasting effects of early life stress on the PFC structure, connectivity, and function. We explore potential mechanisms underlying these stress-induced alterations, with a focus on epigenetic regulation and its implications for PFC maturation and neurodevelopmental disorders. By integrating these insights, this review provides an overview of the developmental processes shaping the PFC and their implications for brain health and disease.

The crosstalk between CNS resident glial cells and peripheral immune cells is critical for age-dependent demyelination and subsequent remyelination

White-matter diseases like multiple sclerosis begin in young adulthood. Aging, being a risk factor, contributes to the progression of these diseases and makes neurological disabilities worsen. Aging causes white matter alteration due to myelin loss, axonal degeneration, and hyperintensities, resulting in cognitive impairment and neurological disorders. Aging also negatively affects central nervous system resident glial cells and peripheral immune cells, contributing to myelin degeneration and diminished myelin renewal process. Restoration of myelin failure with aging accelerates the progression of cognitive decline. This review will mainly focus on how age-related altered functions of glial and peripheral cells will affect myelin sheath alteration and myelin restoration. This understanding can give us insights into the underlying mechanisms of demyelination and failure of remyelination with aging concerning altered glial and peripheral immune cell function and their crosstalk. Also, we will explain the therapeutic strategies to enhance the remyelination process of an aging brain to improve the cognitive health of an aging person.

Genetic overlap between multi-site chronic pain and cognition: a large-scale genome-wide cross-trait analysis

Background

Different studies have consistently demonstrated a positive correlation between chronic pain and cognitive changes. This study aimed to explore the genetic factors underlying the relationship between chronic pain and cognitive traits, and to investigate whether an inherent causal connection exists between them.

Method

The genetic contributions of chronic multi-site pain and eight cognitive traits were investigated based on Genome-wide association studies (GWAS) data. Linkage disequilibrium score regression (LDSC) was employed to assess the genetic correlations between each pair of traits. The shared genetic components of these traits were investigated by identifying single nucleotide polymorphisms (SNPs) with pleiotropic effects using the Cross Phenotype Association (CPASSOC) method. Furthermore, enrichment analysis and transcriptome-wide association studies (TWAS) were performed to characterize the significant associations between genetic traits. The latent causal variable model (LCV) was employed to explore the potential causal relationship between both traits.

Results

A significant negative genetic correlation was found between chronic pain and several cognitive functions, particularly intelligence (rg = -0. 11, p = 7.77 × 10-64). CPASSOC identified 150 pleiotropic loci. A co-localization analysis was conducted, which identified 20 loci exhibiting pleiotropic effects at the same genomic position. The LCV analysis indicated no causal relationship between both traits.

Conclusion

The present work contributed to an enhanced understanding of the complex genetic interplay between cognitive function and chronic pain.

GABAergic neuron-to-glioma synapses in diffuse midline gliomas

High-grade gliomas (HGGs) are the leading cause of brain cancer-related death. HGGs include clinically, anatomically and molecularly distinct subtypes that stratify into diffuse midline gliomas (DMGs), such as H3K27M-altered diffuse intrinsic pontine glioma, and hemispheric HGGs, such as IDH wild-type glioblastoma. Neuronal activity drives glioma progression through paracrine signalling1,2 and neuron-to-glioma synapses3-6. Glutamatergic AMPA receptor-dependent synapses between neurons and glioma cells have been demonstrated in paediatric3 and adult4 high-grade gliomas, and early work has suggested heterogeneous glioma GABAergic responses7. However, neuron-to-glioma synapses mediated by neurotransmitters other than glutamate remain understudied. Using whole-cell patch-clamp electrophysiology, in vivo optogenetics and patient-derived orthotopic xenograft models, we identified functional, tumour-promoting GABAergic neuron-to-glioma synapses mediated by GABAA receptors in DMGs. GABAergic input has a depolarizing effect on DMG cells due to NKCC1 chloride transporter function and consequently elevated intracellular chloride concentration in DMG malignant cells. As membrane depolarization increases glioma proliferation3,6, we found that the activity of GABAergic interneurons promotes DMG proliferation in vivo. The benzodiazepine lorazepam enhances GABA-mediated signalling, increases glioma proliferation and growth, and shortens survival in DMG patient-derived orthotopic xenograft models. By contrast, only minimal depolarizing GABAergic currents were found in hemispheric HGGs and lorazepam did not influence the growth rate of hemispheric glioblastoma xenografts. Together, these findings uncover growth-promoting GABAergic synaptic communication between GABAergic neurons and H3K27M-altered DMG cells, underscoring a tumour subtype-specific mechanism of brain cancer neurophysiology.

An increased copy number of glycine decarboxylase (GLDC) associated with psychosis reduces extracellular glycine and impairs NMDA receptor function

Glycine is an obligatory co-agonist at excitatory NMDA receptors in the brain, especially in the dentate gyrus, which has been postulated to be crucial for the development of psychotic associations and memories with psychotic content. Drugs modulating glycine levels are in clinical development for improving cognition in schizophrenia. However, the functional relevance of the regulation of glycine metabolism by endogenous enzymes is unclear. Using a chromosome-engineered allelic series in mice, we report that a triplication of the gene encoding the glycine-catabolizing enzyme glycine decarboxylase (GLDC) - as found on a small supernumerary marker chromosome in patients with psychosis - reduces extracellular glycine levels as determined by optical fluorescence resonance energy transfer (FRET) in dentate gyrus (DG) and suppresses long-term potentiation (LTP) in mPP-DG synapses but not in CA3-CA1 synapses, reduces the activity of biochemical pathways implicated in schizophrenia and mitochondrial bioenergetics, and displays deficits in schizophrenia-like behaviors which are in part known to be dependent on the activity of the dentate gyrus, e.g., prepulse inhibition, startle habituation, latent inhibition, working memory, sociability and social preference. Our results demonstrate that Gldc negatively regulates long-term synaptic plasticity in the dentate gyrus in mice, suggesting that an increase in GLDC copy number possibly contributes to the development of psychosis in humans.

Oligodendrocytes in Alzheimer's disease pathophysiology

Our understanding of Alzheimer's disease (AD) has transformed from a purely neuronal perspective to one that acknowledges the involvement of glial cells. Despite remarkable progress in unraveling the biology of microglia, astrocytes and vascular elements, the exploration of oligodendrocytes in AD is still in its early stages. Contrary to the traditional notion of oligodendrocytes as passive bystanders in AD pathology, emerging evidence indicates their active participation in and reaction to amyloid and tau pathology. Oligodendrocytes undergo a functional transition to a disease-associated state, engaging in immune modulation, stress responses and cellular survival. Far from being inert players, they appear to serve a dual role in AD pathogenesis, potentially offering defense mechanisms against pathology while also contributing to disease progression. This Review explores recent advancements in understanding the roles of oligodendrocytes and their myelin sheaths in the context of AD, shedding light on their complex interactions within the disease pathology.

Multivariate Links Between the Developmental Timing of Adversity Exposure and White Matter Tract Connectivity in Adulthood

BACKGROUND

Early-life adversity is pervasive worldwide and represents a potent risk factor for increased mental health burden across the lifespan. However, there is substantial individual heterogeneity in associations between adversity exposure, neurobiological changes, and mental health problems. Accounting for key features of adversity such as the developmental timing of exposure may clarify associations between adversity, neurodevelopment, and mental health.

METHODS

In the current study, we leveraged sparse canonical correlation analysis to characterize modes of covariation between adversity exposure across development and the connectivity of white matter tracts throughout the brain in a sample of 107 adults.

RESULTS

We found that adversity exposure during preschool age and middle childhood (ages 4-5 and 8 years in particular) were consistently linked across diffusion metrics with alterations in white matter tract connectivity. Whereas tracts supporting sensorimotor functions showed higher connectivity with higher preschool-age and middle childhood adversity exposure, tracts supporting cortico-cortical communication showed lower connectivity. Furthermore, latent patterns of tract connectivity associated with adversity experienced across preschool age and middle childhood (ages 3-8) were associated with posttraumatic stress symptoms in adulthood.

CONCLUSIONS

Our findings underscore that adversity exposure may differentially affect white matter in a function- and developmental timing-specific manner and suggest that adversity experienced from ages 3 to 8 years may shape the development of white matter tracts across the brain in ways that are relevant for mental health in adulthood.

The role of social isolation stress in escalated aggression in rodent models

Anti-social behavior and violence are major public health concerns. Globally, violence contributes to more than 1.6 million deaths each year. Previous studies have reported that social rejection or neglect exacerbates aggression. In rodent models, social isolation stress is used to demonstrate the adverse effects of social deprivation on physiological, endocrinological, immunological, and behavioral parameters, including aggressive behavior. This review summarizes recent rodent studies on the effect of social isolation stress during different developmental periods on aggressive behavior and the underlying neural mechanisms. Social isolation during adulthood affects the levels of neurosteroids and neuropeptides and increases aggressive behavior. These changes are ethologically relevant for the adaptation to changes in local environmental conditions in the natural habitats. Chronic deprivation of social interaction after weaning, especially during the juvenile to adolescent periods, leads to the disruption of the development of appropriate social behavior and the maladaptive escalation of aggressive behavior. The understanding of neurobiological mechanisms underlying social isolation-induced escalated aggression will aid in the development of therapeutic interventions for escalated aggression.

Role of immature choroid plexus in the pathology of model mice and human iPSC-derived organoids with autism spectrum disorder

During gestation, the choroid plexus (ChP) produces protein-rich cerebrospinal fluid and matures prior to brain development. It is assumed that ChP dysfunction has a profound effect on developmental neuropsychiatric disorders, such as autism spectrum disorder (ASD). However, the mechanisms linking immature ChP to the onset of ASD remain unclear. Here, we find that ChP-specific CAMDI-knockout mice develop an immature ChP alongside decreased multiciliogenesis and expression of differentiation marker genes following disruption of the cerebrospinal fluid barrier. These mice exhibit ASD-like behaviors, including anxiety and impaired socialization. Additionally, the administration of metformin, an FDA-approved drug, before the social critical period achieves ChP maturation and restores social behaviors. Furthermore, both the ASD model mice and organoids derived from patients with ASD developed an immature ChP. These results propose the involvement of an immature ChP in the pathogenesis of ASD and suggest the targeting of functional maturation of the ChP as a therapeutic strategy for ASD.

A critical period for paired-housing-dependent autistic-like behaviors attenuation in a prenatal valproic acid-induced male mouse model of autism

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by impairments in social communication and the presence of restrictive and repetitive behaviors. Investigating the etiological process and identifying an appropriate therapeutic target remain as formidable challenges to overcome ASD due to numerous risk factors and complex symptoms associated with the disorder. Recent studies have indicated that early rehabilitative intervention can alleviate the symptoms of individuals with ASD. However, there remain unsolved issues of behavioral intervention such as the appropriate time and types of therapies. In this study, we employed a mouse model prenatally exposed to valproic acid to establish a validated ASD mouse model and We found that paired-housing with control mice for 4 week after weaning palliated sociability deficits, anxiety and repetitive behaviors in this model of ASD-like behaviors, while paired-housing with their ASD littermate did not produce this effects. Furthermore, by evaluating different time window of paired-housing, we found that paired-housing during postnatal day 21 (P21) to P35, but not P21 to P28 or P35 to P49 or P28 to P35, is a critical period for the influence of paired-housing on autistic-like behaviors. Finally, paired-housing with control mice improved the impaired GABA system in this model of ASD. So our study demonstrates the therapeutic potential of environmental intervention during a critical period in the treatment of ASD.

The connecting brain in context: How adolescent plasticity supports learning and development

Puberty initiates significant neurobiological changes that amplify adolescents' responsiveness to their environment, facilitating neural adaptation through processes like synaptic pruning, myelination, and neuronal reorganization. This heightened neuroplasticity, combined with their burgeoning social curiosity and appetite for risk, propels adolescents to explore diverse new environments and forge social bonds. Such exploration can accelerate experiential learning and the formation of social networks as adolescents prepare for adult independence. This review examines the complex interplay between adolescent neuroplasticity, environmental influences, and learning processes, synthesizing findings from recent studies that illustrate how factors such as social interactions, school environments, and neighborhood contexts influence both the transient activation and enduring organization of the developing brain. We advocate for incorporating social interaction into adolescent-tailored interventions, leveraging their social plasticity to optimize learning and development during this critical phase. Going forward, we discuss the importance of longitudinal studies that employ multimodal approaches to characterize the dynamic interactions between development and environment, highlighting recent advancements in quantifying environmental impacts in studies of developmental neuroscience. Ultimately, this paper provides an updated synopsis of adolescent neuroplasticity and the environment, underscoring the potential for environmental enrichment programs to support healthy brain development and resilience at this critical development stage.

Social isolation during adolescence differentially affects spatial learning in adult male and female mice

Social isolation is a risk factor for cognitive impairment. Adolescents may be particularly vulnerable to these effects, because they are in a critical period of development marked by significant physical, hormonal, and social changes. However, it is unclear if the effects of social isolation on learning and memory are similar in both sexes or if they persist into adulthood after a period of recovery. We socially isolated male and female 129Sv/Ev mice throughout adolescence (postnatal days 29-56), provided a 2-week resocialization recovery period, and then tested spatial learning and cognitive flexibility in the active place avoidance task. After behavioral testing, mice were injected with 5'-bromo-2'-deoxyuridine (BrdU) so that lasting effects of social isolation on cell proliferation in the dentate gyrus could be examined. Tissue was also stained for doublecortin (DCX). We found that in males, isolation led to a modest impairment in the rate of initial spatial learning, whereas in females, initial learning was unaffected. However, when the location of the shock zone was switched during the conflict variant of the task, cognitive flexibility was impaired in females only. Similarly, social isolation reduced cell proliferation and the number of immature neurons in the ventral dentate gyrus only in females. Together, these findings indicate that social isolation during adolescence differentially impairs spatial processing in males and females, with effects that persist into adulthood.

Impacts of adverse childhood experiences on individuals with autism spectrum disorder

Individuals with autism spectrum disorder (ASD) are more likely to experience adverse childhood experiences (ACEs) compared with typically developing (TD) individuals, which predisposes them to an elevated risk of mental health issues. This review elucidates the profound impact of ACEs on individuals with ASD by synthesizing findings from a plethora of epidemiologic and biological studies, encompassing genetics, epigenetics, and neuroimaging. Despite the limited number of studies explicitly focusing on this intersection, the extant literature consistently demonstrates that ASD individuals are disproportionately affected by ACEs, leading to significant deterioration in mental health and brain function. Furthermore, the nature and extent of the effects of ACEs appear to diverge between ASD and TD populations, underscoring the necessity for tailored clinical and research approaches. Understanding these complex and intertwined interactions is imperative for advancing both clinical practice and research, with the goal of mitigating the adverse outcomes associated with ACEs in ASD individuals.

A novel quadrant spatial assay reveals environmental preference in mouse spontaneous and parental behaviors

Environmental factors have well-documented impacts on brain development and mental health. Therefore, it is crucial to employ a reliable assay system to assess the spatial preference of model animals. In this study, we introduced an unbiased quadrant chamber assay system and discovered that parental pup-gathering behavior takes place in a very efficient manner. Furthermore, we found that test mice exhibited preferences for specific environments in both spontaneous and parental pup-gathering behavior contexts. Notably, the spatial preferences of autism spectrum disorder model animals were initially suppressed but later equalized during the spontaneous behavior assay, accompanied by increased time spent in the preferred chamber. In conclusion, our novel quadrant chamber assay system provides an ideal platform for investigating the spatial preference of mice, offering potential applications in studying environmental impacts and exploring neurodevelopmental and psychiatric disorder models.

Discovering functional interactions among schizophrenia-risk genes by combining behavioral genetics with cell biology

Despite much progress in identifying risk genes for polygenic brain disorders, their core pathogenic mechanisms remain poorly understood. In particular, functions of many proteins encoded by schizophrenia risk genes appear diverse and unrelated, complicating the efforts to establish the causal relationship between genes and behavior. Using various mouse lines, recent studies indicate that alterations of parvalbumin-positive (PV+) GABAergic interneurons can lead to schizophrenia-like behavior. PV+ interneurons display fast spiking and contribute to excitation-inhibition balance and network oscillations via feedback and feedforward inhibition. Here, we first summarize different lines of genetically modified mice that display motor, cognitive, emotional, and social impairments used to model schizophrenia and related mental disorders. We highlight ten genes, encoding either a nuclear, cytosolic, or membrane protein. Next, we discuss their functional relationship in regulating fast spiking and other aspects of PV+ interneurons and in the context of other domains of schizophrenia. Future investigations combining behavioral genetics and cell biology should elucidate functional relationships among risk genes to identify the core pathogenic mechanisms underlying polygenic brain disorders.

Effects of adolescent alcohol exposure on oligodendrocyte lineage cells and myelination in mice: Age and subregion differences

Adolescence is an important phase for the structural and functional development of the brain. The immaturity of adolescent brain development is associated with high susceptibility to exogenous disturbances, including alcohol. In this study, the acquisition of conditioned place preference (CPP) in adolescent mice by alcohol (2 g/kg) and the parvalbumin-positive interneurons (PV+ interneurons), oligodendrocyte lineage cells (OPCs), and myelination in the medial prefrontal cortex (mPFC) were assessed. We aim to determine the age- and subregional-specificity of the effects of alcohol. Alcohol (2 g/kg) was injected intraperitoneally on even days, and saline was injected intraperitoneally on odd days. The control group received a continuous intraperitoneal injection with saline. Differences in alcohol-induced CPP acquisition were assessed, followed by immunohistochemical staining. The results showed a pronounced CPP acquisition in 4- and 5-week-old mice. In the mPFC, there were reduced PV+ interneurons and OPCs in 3-week-old mice and reduced oligodendrocyte numbers in 4-week-old mice. The 5-week-old mice showed impaired myelination and a decrease in the number of PV+ interneurons, mature oligodendrocytes, and OPCs in the mPFC. Since the alterations in 5-week-old mice are more pronounced, we further explored the mPFC-associated subregional-specificity. In the alcohol-exposed mice, the oligodendrocyte numbers were decreased in the anterior cingulate cortex (ACC), PV+ interneuron numbers were declined in the prelimbic cortex (PL), and the number of oligodendrocytes, PV+ interneurons, and OPCs was also decreased with impaired myelination in the infralimbic cortex (IL). Our data suggest that adolescent alcohol exposure notably affected the acquisition of CPP, myelin formation, and the counts of PV+ interneurons, mature oligodendrocytes, and OPCs in the mPFC in 5-week-old mice. Also, the IL subregion was the worst-affected subregion of the mPFC in alcohol-exposed 5-week-old mice. It reveals that the effects of alcohol on adolescence and its mPFC myelination show obvious age- and subregional-specificity.

A meta-analysis of the effects of early life stress on the prefrontal cortex transcriptome suggests long-term effects on myelin

Background

Early life stress (ELS) refers to exposure to negative childhood experiences, such as neglect, disaster, and physical, mental, or emotional abuse. ELS can permanently alter the brain, leading to cognitive impairment, increased sensitivity to future stressors, and mental health risks. The prefrontal cortex (PFC) is a key brain region implicated in the effects of ELS.

Methods

To better understand the effects of ELS on the PFC, we ran a meta-analysis of publicly available transcriptional profiling datasets. We identified five datasets (GSE89692, GSE116416, GSE14720, GSE153043, GSE124387) that characterized the long-term effects of multi-day postnatal ELS paradigms (maternal separation, limited nesting/bedding) in male and female laboratory rodents (rats, mice). The outcome variable was gene expression in the PFC later in adulthood as measured by microarray or RNA-Seq. To conduct the meta-analysis, preprocessed gene expression data were extracted from the Gemma database. Following quality control, the final sample size was n=89: n=42 controls & n=47 ELS: GSE116416 n=23 (no outliers); GSE116416 n=44 (2 outliers); GSE14720 n=7 (no outliers); GSE153043 n=9 (1 outlier), and GSE124387 n=6 (no outliers). Differential expression was calculated using the limma pipeline followed by an empirical Bayes correction. For each gene, a random effects meta-analysis model was then fit to the ELS vs. Control effect sizes (Log2 Fold Changes) from each study.

Results

Our meta-analysis yielded stable estimates for 11,885 genes, identifying five genes with differential expression following ELS (false discovery rate< 0.05): transforming growth factor alpha ( Tgfa ), IQ motif containing GTPase activating protein 3 ( Iqgap3 ), collagen, type XI, alpha 1 ( Col11a1 ), claudin 11 ( Cldn11 ) and myelin associated glycoprotein ( Mag ), all of which were downregulated. Broadly, gene sets associated with oligodendrocyte differentiation, myelination, and brain development were downregulated following ELS. In contrast, genes previously shown to be upregulated in Major Depressive Disorder patients were upregulated following ELS.

Conclusion

These findings suggest that ELS during critical periods of development may produce long-term effects on the efficiency of transmission in the PFC and drive changes in gene expression similar to those underlying depression.

Early postnatal whisker deprivation cross-modally modulates prefrontal cortex myelination and leads to social novelty deficit

Sensory experience affects not only the corresponding primary sensory cortex, but also synaptic and neural circuit functions in other brain regions in a cross-modal manner. However, it remains unclear whether oligodendrocyte (OL) generation and myelination can also undergo cross-modal modulation. Here, we report that while early life short-term whisker deprivation from birth significantly reduces in the number of mature of OLs and the degree of myelination in the primary somatosensory cortex(S1) at postnatal day 14 (P14), it also simultaneously affects the primary visual cortex (V1), but not the medial prefrontal cortex (mPFC) with a similar reduction. Interestingly, when mice were subjected to long-term early whisker deprivation from birth (P0) to P35, they exhibited dramatically impaired myelination and a deduced number of differentiated OLs in regions including the S1, V1, and mPFC, as detected at P60. Meanwhile, the process complexity of OL precursor cells (OPCs) was also rduced, as detected in the mPFC. However, when whisker deprivation occurred during the mid-late postnatal period (P35 to P50), myelination was unaffected in both V1 and mPFC brain regions at P60. In addition to impaired OL and myelin development in the mPFC, long-term early whisker-deprived mice also showed deficits in social novelty, accompanied by abnormal activation of c-Fos in the mPFC. Thus, our results reveal a novel form of cross-modal modulation of myelination by sensory experience that can lead to abnormalities in social behavioral, suggesting a possible similar mechanism underlying brain pathological conditions that suffer from both sensory and social behavioral deficits, such as autism spectrum disorders.

Mitigating the Effects of Maternal Loss on Harbour Seal Pups in Captive Care

Stranded newborn "orphan" harbour seal pups entering captive care are often maintained for some weeks in isolation, mainly as a precaution against the spread of infection. However, this practice raises concerns for the welfare and normal socialisation of pups, who normally spend their first post-natal weeks close to their mothers and other seals. The present study recorded and described the behaviour of six paired orphan pups in rehabilitation up to about five weeks of age, provided with free access to water and haul-out areas. The occurrences of resting, following, nosing and body contacts, and aquatic play were recorded and compared qualitatively and quantitatively with the same behaviours of free-living pups with their mothers. The pups entered the water every day, although more often from about 2.5 weeks of age. They displayed to each other the same behaviours that free-living pups display to their mothers, although they engaged in relatively more physical contact, body nosing, and aquatic play. The study has shown that orphan pups maintained in pairs with free water access can act reciprocally as mother substitutes, thereby promoting species-typical primary socialisation and welfare during their early days of captive care.

Single nucleus RNA-sequencing reveals transcriptional synchrony across different relationships

As relationships mature, partners share common goals, improve their ability to work together, and experience coordinated emotions. However, the neural underpinnings responsible for this unique, pair-specific experience remain largely unexplored. Here, we used single nucleus RNA-sequencing to examine the transcriptional landscape of the nucleus accumbens (NAc) in socially monogamous prairie voles in peer or mating-based relationships. We show that, regardless of pairing type, prairie voles exhibit transcriptional synchrony with a partner. Further, we identify genes expressed in oligodendrocyte progenitor cells that are synchronized between partners, correlated with dyadic behavior, and sensitive to partner separation. Together, our data indicate that the pair-specific social environment profoundly shapes transcription in the NAc. This provides a potential biological mechanism by which shared social experience reinforces and strengthens relationships.

Oligodendrocytes use postsynaptic proteins to coordinate myelin formation on axons of distinct neurotransmitter classes

Axon myelination can tune neuronal circuits through placement and modulation of different patterns of myelin sheaths on distinct types of axons. How myelin formation is coordinated on distinct axon classes remains largely unknown. Recent work indicates neuronal activity and vesicle release promote myelin formation, and myelin-producing oligodendrocytes express canonical postsynaptic factors that potentially facilitate oligodendrocyte-axon interaction for myelin ensheathment. Here, we examined whether the inhibitory postsynaptic scaffold protein Gephyrin (Gphn) mediates selective myelination of specific axon classes in the larval zebrafish. Consistent with this possibility, Gphn was enriched in myelin on GABAergic and glycinergic axons. Strikingly, in gphnb deficient larvae, myelin sheaths were longer specifically on GABAergic axons, and the frequency of myelin placement shifted toward glutamatergic axons at the expense of GABAergic axons. Collectively, our results indicate that oligodendrocytes use postsynaptic machinery to coordinate myelin formation in an axon identity-dependent manner.

Pan-ErbB inhibition impairs cognition via disrupting myelination and aerobic glycolysis in oligodendrocytes

White matter (WM) abnormalities are an emerging feature of schizophrenia, yet the underlying pathophysiological mechanisms are largely unknown. Disruption of ErbB signaling, which is essential for peripheral myelination, has been genetically associated with schizophrenia and WM lesions in schizophrenic patients. However, the roles of ErbB signaling in oligodendrocytes remain elusive. Here, we used an in vivo pan-ErbB inhibition strategy and demonstrated the functions of endogenous ErbB receptors in oligodendrocytes. Through analyses of the cellular, histological, biochemical, behavioral, and electrophysiological differences in mice with manipulated ErbB activities in oligodendrocytes at different differentiation stages, we found that ErbB signaling regulates myelination and aerobic glycolysis in oligodendrocytes, and both functions are required for working memory. ErbB inhibition in oligodendrocytes at early differentiation stages induces hypomyelination by suppressing the myelinating capacity of newly formed oligodendrocytes. In contrast, ErbB inhibition in mature oligodendrocytes alters neither myelination nor oligodendrocyte numbers, but accelerates axonal conduction decline under energy stress. Mechanistically, ErbB inhibition attenuates K-Ras activities, leading to the reduced expression of lactate dehydrogenase A that promotes aerobic glycolysis in mature oligodendrocytes. Supplementation of L-lactate restores axonal conduction and working memory capacity that are suppressed by ErbB inhibition in mature oligodendrocytes. These findings emphasize the indispensable roles of ErbB signaling in WM integrity and function and provide insights into the multifaceted contributions of WM abnormalities to cognitive impairment.

Glial Cell Development and Function in the Zebrafish Central Nervous System

Over the past decades the zebrafish has emerged as an excellent model organism with which to study the biology of all glial cell types in nervous system development, plasticity, and regeneration. In this review, which builds on the earlier work by Lyons and Talbot in 2015, we will summarize how the relative ease to manipulate the zebrafish genome and its suitability for intravital imaging have helped understand principles of glial cell biology with a focus on oligodendrocytes, microglia, and astrocytes. We will highlight recent findings on the diverse properties and functions of these glial cell types in the central nervous system and discuss open questions and future directions of the field.

Quantifying myelin density in the feline auditory cortex

The cerebral cortex comprises many distinct regions that differ in structure, function, and patterns of connectivity. Current approaches to parcellating these regions often take advantage of functional neuroimaging approaches that can identify regions involved in a particular process with reasonable spatial resolution. However, neuroanatomical biomarkers are also very useful in identifying distinct cortical regions either in addition to, or in place of functional measures. For example, differences in myelin density are thought to relate to functional differences between regions, are sensitive to individual patterns of experience, and have been shown to vary across functional hierarchies in a predictable manner. Accordingly, the current study provides quantitative stereological estimates of myelin density for each of the 13 regions that make up the feline auditory cortex. We demonstrate that significant differences can be observed between auditory cortical regions, with the highest myelin density observed in the regions that comprise the auditory core (i.e., the primary auditory cortex and anterior auditory field). Moreover, our myeloarchitectonic map suggests that myelin density varies in a hierarchical fashion that conforms to the traditional model of spatial organization in auditory cortex. Taken together, these results establish myelin as a useful biomarker for parcellating auditory cortical regions, and provide detailed estimates against which other, less invasive methods of quantifying cortical myelination may be compared.

Neonatal hypoxia-ischemia alters the events governing the hippocampal critical period of postnatal synaptic plasticity leading to deficits in working memory in mice

Postnatal critical periods of synaptic plasticity (CPsp) are characterized by profound neural network refinement, which is shaped by synaptic activity and sculpted by maturation of the GABAergic network. Even after therapeutic hypothermia (TH), neonatal hypoxia-ischemia (HI) impairs two triggers for the initiation of the CPsp in the hippocampus: i) PSA-NCAM developmental decline and ii) parvalbumin (PV) + interneuron (IN) maturation. Thus, we investigated whether neonatal HI despite TH disturbs other events governing the onset, consolidation and closure of the postnatal CPsp in the hippocampus. We induced cerebral HI in P10 C57BL6 mice with right carotid ligation and 45 m of hypoxia (FiO2 = 0.08), followed by normothermia (36 °C, NT) or TH (31 °C) for 4 h with anesthesia-exposed shams as controls. ELISA, immunoblotting and immunohistochemistry were performed at 24 h (P11), 5 days (P15), 8 days (P18) and 30 days (P40) after HI injury. We specifically assessed: i) BDNF levels and TrkB activation, controlling the CPsp, ii) Otx2 and NPTX2 immunoreactivity (IR), engaging CPsp onset and iii) NogoR1, Lynx1 IR, PNN formation and myelination (MBP) mediating CPsp closure. Pups aged to P40 also received a battery of tests assessing working memory. Here, we documented deficits in hippocampal BDNF levels and TrkB activation at P18 in response to neonatal HI even with TH. Neonatal HI impaired in the CA1 the developmental increase in PV, Otx2, and NPTX2 between P11 and P18, the colocalization of Otx2 and PV at P18 and P40, the accumulation of NPTX2 in PV+ dendrites at P18 and P40, and the expression of NogoR at P40. Furthermore, neonatal HI decreased BDNF and impaired PNN development and myelination (MBP) at P40. Most of these abnormalities were insensitive to TH and correlated with memory deficits. Neonatal HI appears to disrupt many of the molecular and structural events initiating and consolidating the postnatal hippocampal CPsp, perhaps due to the early and delayed deficits in TrkB activation leading to memory deficits.

Proteomic evidence of depression-associated astrocytic dysfunction in the human male olfactory bulb

The olfactory bulb (OB), a major structure of the limbic system, has been understudied in human investigations of psychopathologies such as depression. To explore more directly the molecular features of the OB in depression, a global comparative proteome analysis was carried out with human post-mortem OB samples from 11 males having suffered from depression and 12 healthy controls. We identified 188 differentially abundant proteins (with adjusted p < 0.05) between depressed cases and controls. Gene ontology and gene enrichment analyses suggested that these proteins are involved in biological processes including the complement and coagulation cascades. Cell type enrichment analysis displayed a significant reduction in several canonical astrocytic proteins in OBs from depressed patients. Furthermore, using RNA-fluorescence in-situ hybridization, we observed a decrease in the percentage of ALDH1L1+ cells expressing canonical astrocytic markers including ALDOC, NFIA, GJA1 (connexin 43) and SLC1A3 (EAAT1). These results are consistent with previous reports of downregulated astrocytic marker expression in other brain regions in depressed patients. We also conducted a comparative phosphoproteomic analysis of OB samples and found a dysregulation of proteins involved in neuronal and astrocytic functions. To determine whether OB astrocytic abnormalities is specific to humans, we also performed proteomics on the OB of socially defeated male mice, a commonly used model of depression. Cell-type specific analysis revealed that in socially defeated animals, the most striking OB protein alterations were associated with oligodendrocyte-lineage cells rather than with astrocytes, highlighting an important species difference. Overall, this study further highlights cerebral astrocytic abnormalities as a consistent feature of depression in humans.

Developing forebrain synapses are uniquely vulnerable to sleep loss

Sleep is an essential behavior that supports lifelong brain health and cognition. Neuronal synapses are a major target for restorative sleep function and a locus of dysfunction in response to sleep deprivation (SD). Synapse density is highly dynamic during development, becoming stabilized with maturation to adulthood, suggesting sleep exerts distinct synaptic functions between development and adulthood. Importantly, problems with sleep are common in neurodevelopmental disorders including autism spectrum disorder (ASD). Moreover, early life sleep disruption in animal models causes long-lasting changes in adult behavior. Divergent plasticity engaged during sleep necessarily implies that developing and adult synapses will show differential vulnerability to SD. To investigate distinct sleep functions and mechanisms of vulnerability to SD across development, we systematically examined the behavioral and molecular responses to acute SD between juvenile (P21 to P28), adolescent (P42 to P49), and adult (P70 to P100) mice of both sexes. Compared to adults, juveniles lack robust adaptations to SD, precipitating cognitive deficits in the novel object recognition task. Subcellular fractionation, combined with proteome and phosphoproteome analysis revealed the developing synapse is profoundly vulnerable to SD, whereas adults exhibit comparative resilience. SD in juveniles, and not older mice, aberrantly drives induction of synapse potentiation, synaptogenesis, and expression of perineuronal nets. Our analysis further reveals the developing synapse as a putative node of convergence between vulnerability to SD and ASD genetic risk. Together, our systematic analysis supports a distinct developmental function of sleep and reveals how sleep disruption impacts key aspects of brain development, providing insights for ASD susceptibility.

Neuron-Glial Interactions: Implications for Plasticity, Behavior, and Cognition

The traditional view of glial cells as mere supportive tissue has shifted, due to advances in technology and theoretical conceptualization, to include a diversity of other functions, such as regulation of complex behaviors. Astrocytes, the most abundant glial cells in the central nervous system (CNS), have been shown to modulate synaptic functions through gliotransmitter-mediated neurotransmitter reuptake, influencing neuronal signaling and behavioral functions. Contemporary studies further highlight astrocytes' involvement in complex cognitive functions. For instance, inhibiting astrocytes in the hippocampus can lead to memory deficits, suggesting their integral role in memory processes. Moreover, astrocytic calcium activity and astrocyte-neuron metabolic coupling have been linked to changes in synaptic strength and learning. Microglia, another type of glial cell, also extend beyond their supportive roles, contributing to learning and memory processes, with microglial reductions impacting these functions in a developmentally dependent manner. Oligodendrocytes, traditionally thought to have limited roles postdevelopment, are now recognized for their activity-dependent modulation of myelination and plasticity, thus influencing behavioral responses. Recent advancements in technology and computational modeling have expanded our understanding of glial functions, particularly how astrocytes influence neuronal circuits and behaviors. This review underscores the importance of glial cells in CNS functions and the need for further research to unravel the complexities of neuron-glia interactions, the impact of these interactions on brain functions, and potential implications for neurological diseases.

Oligodendrocytes: Myelination, Plasticity, and Axonal Support

The myelination of axons has evolved to enable fast and efficient transduction of electrical signals in the vertebrate nervous system. Acting as an electric insulator, the myelin sheath is a multilamellar membrane structure around axonal segments generated by the spiral wrapping and subsequent compaction of oligodendroglial plasma membranes. These oligodendrocytes are metabolically active and remain functionally connected to the subjacent axon via cytoplasmic-rich myelinic channels for movement of metabolites and macromolecules to and from the internodal periaxonal space under the myelin sheath. Increasing evidence indicates that oligodendrocyte numbers, specifically in the forebrain, and myelin as a dynamic cellular compartment can both respond to physiological demands, collectively referred to as adaptive myelination. This review summarizes our current understanding of how myelin is generated, how its function is dynamically regulated, and how oligodendrocytes support the long-term integrity of myelinated axons.

Neural adaptation to changes in self-voice during puberty

The human voice is a potent social signal and a distinctive marker of individual identity. As individuals go through puberty, their voices undergo acoustic changes, setting them apart from others. In this article, we propose that hormonal fluctuations in conjunction with morphological vocal tract changes during puberty establish a sensitive developmental phase that affects the monitoring of the adolescent voice and, specifically, self-other distinction. Furthermore, the protracted maturation of brain regions responsible for voice processing, coupled with the dynamically evolving social environment of adolescents, likely disrupts a clear differentiation of the self-voice from others' voices. This socioneuroendocrine framework offers a holistic understanding of voice monitoring during adolescence.

Dysregulated miR-124 mediates impaired social memory behavior caused by paternal early social isolation

Early social isolation (SI) leads to various abnormalities in emotion and behavior during adulthood. However, the negative impact of SI on offspring remains unclear. This study has discovered that paternal early SI causes social memory deficits and anxiety-like behavior in F1 young adult mice, with alterations of myelin and synapses in the medial prefrontal cortex (mPFC). The 2-week SI in the F1 progeny exacerbates social memory impairment and hypomyelination in the mPFC. Furthermore, the down-regulation of miR-124, a key inhibitor of myelinogenesis, or over-expression of its target gene Nr4a1 in the mPFC of the F1 mice improves social interaction ability and enhances oligodendrocyte maturation and myelin formation. Mechanistically, elevated levels of miR-124 in the sperm of paternal SI mice are transmitted epigenetically to offspring, altering the expression levels of miR-124/Nr4a1/glucocorticoid receptors in mPFC oligodendrocytes. This, in turn, impedes the establishment of myelinogenesis-dependent social behavior. This study unveils a novel mechanism through which miR-124 mediates the intergenerational effects of early isolation stress, ultimately impairing the establishment of social behavior and neurodevelopment.

Axonal neurotransmitter release in the regulation of myelination

Myelination of axons is a key determinant of fast action potential propagation, axonal health and circuit function. Previously considered a static structure, it is now clear that myelin is dynamically regulated in response to neuronal activity in the central nervous system (CNS). However, how activity-dependent signals are conveyed to oligodendrocytes remains unclear. Here, we review the potential mechanisms by which neurons could communicate changing activity levels to myelin, with a focus on the accumulating body of evidence to support activity-dependent vesicular signalling directly onto myelin sheaths. We discuss recent in vivo findings of activity-dependent fusion of neurotransmitter vesicles from non-synaptic axonal sites, and how modulation of this vesicular fusion regulates the stability and growth of myelin sheaths. We also consider the potential mechanisms by which myelin could sense and respond to axon-derived signals to initiate remodelling, and the relevance of these adaptations for circuit function. We propose that axonal vesicular signalling represents an important and underappreciated mode of communication by which neurons can transmit activity-regulated signals to myelinating oligodendrocytes and, potentially, more broadly to other cell types in the CNS.

Korean Red Ginseng and Rb1 restore altered social interaction, gene expressions in the medial prefrontal cortex, and gut metabolites under post-weaning social isolation in mice

Background

Post-weaning social isolation (SI) reduces sociability, gene expressions including myelin genes in the medial prefrontal cortex (mPFC), and alters microbiome compositions in rodent models. Korean Red Ginseng (KRG) and its major ginsenoside Rb1 have been reported to affect myelin formation and gut metabolites. However, their effects under post-weaning SI have not been investigated. This study investigated the effects of KRG and Rb1 on sociability, gene expressions in the mPFC, and gut metabolites under post-weaning SI.

Methods

C57BL/6J mice were administered with water or KRG (150, 400 mg/kg) or Rb1 (0.1 mg/kg) under SI or regular environment (RE) for 2 weeks during the post-weaning period (P21-P35). After this period, mice underwent a sociability test, and then brains and ceca were collected for qPCR/immunohistochemistry and non-targeted metabolomics, respectively.

Results

SI reduced sociability compared to RE; however, KRG (400 mg/kg) and Rb1 significantly restored sociability under SI. In the mPFC, expressions of genes related to myelin, neurotransmitter, and oxidative stress were significantly reduced in mice under SI compared to RE conditions. Under SI, KRG and Rb1 recovered the altered expressions of several genes in the mPFC. In gut metabolomics, 313 metabolites were identified as significant among 3027 detected metabolites. Among the significantly changed metabolites in SI, some were recovered by KRG or Rb1, including metabolites related to stress axis, inflammation, and DNA damage.

Conclusion

Altered sociability, gene expression levels in the mPFC, and gut metabolites induced by two weeks of post-weaning SI were at least partially recovered by KRG and Rb1.

Revisiting adolescence as a sensitive period for sociocultural processing

Waves of research and public discourse have characterized adolescence as periods of developmental risk and opportunity. Underlying this discussion is the recognition that adolescence is a period of major biological and social transition when experience may have an outsized effect on development. This article updates and expands upon prior work suggesting that adolescence may be a sensitive period for sociocultural processing specifically. By integrating evidence from developmental psychology and neuroscience, we identify how trajectories of social and neurobiological development may relate to adolescents' ability to adapt to and learn from their social environments. However, we also highlight gaps in the literature, including challenges in attributing developmental change to adolescent experiences. We discuss the importance of better understanding variability in biology (e.g., pubertal development) and cultural environments, as well as distinguishing between sensitive periods and periods of heightened sensitivity. Finally, we look toward future directions and translational implications of this research.

Nrg1 intracellular signaling regulates the development of interhemispheric callosal axons in mice

Schizophrenia is associated with altered cortical circuitry. Although the schizophrenia risk gene NRG1 is known to affect the wiring of inhibitory interneurons, its role in excitatory neurons and axonal development is unclear. Here, we investigated the role of Nrg1 in the development of the corpus callosum, the major interhemispheric connection formed by cortical excitatory neurons. We found that deletion of Nrg1 impaired callosal axon development in vivo. Experiments in vitro and in vivo demonstrated that Nrg1 is cell-autonomously required for axonal outgrowth and that intracellular signaling of Nrg1 is sufficient to promote axonal development in cortical neurons and specifically in callosal axons. Furthermore, our data suggest that Nrg1 signaling regulates the expression of Growth Associated Protein 43, a key regulator of axonal growth. In conclusion, our study demonstrates that NRG1 is involved in the formation of interhemispheric callosal connections and provides a novel perspective on the relevance of NRG1 in excitatory neurons and in the etiology of schizophrenia.

Clemastine improves emotional and social deficits in adolescent social isolation mice by reversing demyelination

Adolescence is a critical period for social experience-dependent oligodendrocyte maturation and myelination. Adolescent stress predisposes to cause irreversible changes in brain structure and function with lasting effects on adulthood or beyond. However, the molecular mechanisms linking adolescent social isolation stress with emotional and social competence remain largely unknown. In our study, we found that social isolation during adolescence leads to anxiety-like behaviors, depression-like behaviors, impaired social memory and altered patterns of social ultrasonic vocalizations in mice. In addition, adolescent social isolation stress induces demyelination in the prefrontal cortex and hippocampus of mice, with decreased myelin-related gene expression and disrupted myelin structure. More importantly, clemastine was sufficient to rescue the impairment of emotional and social memory by promoting remyelination. These findings reveal the demyelination mechanism of emotional and social deficits caused by social isolation stress in adolescence, and provides potential therapeutic targets for treating stress-related mental disorders.

KARS Mutations Impair Brain Myelination by Inducing Oligodendrocyte Deficiency: One Potential Mechanism and Improvement by Melatonin

It is very crucial to investigate key molecules that are involved in myelination to gain an understanding of brain development and injury. We have reported for the first time that pathogenic variants p.R477H and p.P505S in KARS, which encodes lysyl-tRNA synthetase (LysRS), cause leukoencephalopathy with progressive cognitive impairment in humans. The role and action mechanisms of KARS in brain myelination during development are unknown. Here, we first generated Kars knock-in mouse models through the CRISPR-Cas9 system. Kars knock-in mice displayed significant cognitive deficits. These mice also showed significantly reduced myelin density and content, as well as significantly decreased myelin thickness during development. In addition, Kars mutations significantly induced oligodendrocyte differentiation arrest and reduction in the brain white matter of mice. Mechanically, oligodendrocytes' significantly imbalanced expression of differentiation regulators and increased capase-3-mediated apoptosis were observed in the brain white matter of Kars knock-in mice. Furthermore, Kars mutations significantly reduced the aminoacylation and steady-state level of mitochondrial tRNALys and decreased the protein expression of subunits of oxidative phosphorylation complexes in the brain white matter. Kars knock-in mice showed decreased activity of complex IV and significantly reduced ATP production and increased reactive oxygen species in the brain white matter. Significantly increased percentages of abnormal mitochondria and mitochondrion area were observed in the oligodendrocytes of Kars knock-in mouse brain. Finally, melatonin (a mitochondrion protectant) significantly attenuated mitochondrion and oligodendrocyte deficiency in the brain white matter of KarsR504H/P532S mice. The mice treated with melatonin also showed significantly restored myelination and cognitive function. Our study first establishes Kars knock-in mammal models of leukoencephalopathy and cognitive impairment and indicates important roles of KARS in the regulation of mitochondria, oligodendrocyte differentiation and survival, and myelination during brain development and application prospects of melatonin in KARS (or even aaRS)-related diseases.

Dynamics of mature myelin

Myelin, which is produced by oligodendrocytes, insulates axons to facilitate rapid and efficient action potential propagation in the central nervous system. Traditionally viewed as a stable structure, myelin is now known to undergo dynamic modulation throughout life. This Review examines these dynamics, focusing on two key aspects: (1) the turnover of myelin, involving not only the renewal of constituents but the continuous wholesale replacement of myelin membranes; and (2) the structural remodeling of pre-existing, mature myelin, a newly discovered form of neural plasticity that can be stimulated by external factors, including neuronal activity, behavioral experience and injury. We explore the mechanisms regulating these dynamics and speculate that myelin remodeling could be driven by an asymmetry in myelin turnover or reactivation of pathways involved in myelin formation. Finally, we outline how myelin remodeling could have profound impacts on neural function, serving as an integral component of behavioral adaptation.

How childhood social isolation causes social dysfunction: deprivation or mismatch?

There is a major gap in our understanding of how childhood social isolation causes adult social dysfunction. To stimulate future developmental mechanistic studies, we present two conceptual models which highlight that isolation can disrupt developmental events that are concurrent (social deprivation model) or subsequent (developmental mismatch model) to adverse experience.

Environmental Deprivation Effects on Myelin Ultrastructure in Huntington Disease and Wildtype Mice

Environmental deprivation can have deleterious effects on adaptive myelination and oligodendroglia function. Early stage Huntington disease (HD) is characterised by white-matter myelin abnormalities in both humans and animal models. However, whether deprived environments exacerbate myelin-related pathological features of HD is not clearly understood. Here, we investigated the impact of deprivation and social isolation on ultrastructural features of myelin in the corpus callosum of the YAC128 mouse model of HD and wildtype (WT) mice using transmission electron microscopy. HD pathology on its own leads to increased representation of altered myelin features, such as thinner sheaths and compromised morphology. Interestingly, deprivation mirrors these effects in WT mice but does not greatly exacerbate the already aberrant myelin in HD mice, indicating a disease-related floor effect in the latter animals. These novel findings indicate that environmental deprivation causes abnormalities in myelin ultrastructure in the otherwise healthy corpus callosum of wild-type mice but has distinct effects on HD mice, where compromised myelin integrity is manifest from early stages of the disease.