Microglia regulation of synaptic plasticity and learning and memory

Spermidine attenuates microglial activation, neuroinflammation, and neuronal injury in rat model of vascular dementia

Spermidine has been implicated to provide beneficial effects on cognitive function in several model organisms as well as older adults with mild and moderate dementia. Nevertheless, the potential impact of spermidine on learning and memory deficits in vascular dementia (VaD) remains largely unknown. Here, bilateral common carotid artery occlusion (BCCAo) was applied to induce chronic cerebral hypoperfusion in rats. We demonstrated that spermidine therapy improved the spatial learning performance in model animals, accompanied with decreased cerebral histopathologic injury and increased restored myelin basic protein (MBP) expression. Moreover, spermidine suppressed abnormal microglia activation, inhibited the excessive generation of proinflammatory mediators, such as tumor necrosis factor (TNF)α and inducible nitric oxide synthase (iNOS), and increased the anti-inflammatory cytokine transforming growth factor (TGF)β expression in rodent brain following hypoperfusion. Our findings indicated that spermidine alleviated cognitive impairments of rats after VaD-like injury possibly via suppressing microglia-modulated neuroinflammation and neuronal injury. These data may shed light on understanding the pathogenesis of VaD and point to the promising value of spermidine supplementation for cognition improvement.

Exposure to malathion impairs learning and memory of zebrafish by disrupting cholinergic signal transmission, undermining synaptic plasticity, and aggravating neuronal apoptosis

The prevalence of organophosphorus pesticides, such as malathion, in water environments poses a severe threat to aquatic organisms. Although the brain is a potential target for malathion, little is known about its effect on cognitive functions in fish. In this study, we evaluated the effect of 4-week malathion exposure on the learning and memory of zebrafish using T-maze tasks. In addition to verifying the accumulation of malathion in the brain and its deleterious effects on blood-brain barrier integrity, the impacts of malathion on cholinergic signal transmission, synaptic plasticity, apoptosis, and oxidative stress were determined. Our results demonstrated that a 4-week malathion exposure resulted in typical learning and memory-deficit-like behaviors. Apart from inhibiting cholinergic signal transmission, synaptic plasticity was severely undermined by malathion (as evidenced by the disruption of BDNF/PI3K/AKT/CREB pathway, suppression of synaptophysins, and activation of microglia). Moreover, significantly higher levels of TUNEL fluorescence signals as well as apoptotic enzymes and genes probably induced by oxidative stress were detected in the brains of malathion-exposed zebrafish. Collectively, our results suggested that malathion at environmentally realistic levels can significantly undermine learning and memory of zebrafish by disrupting cholinergic signal transmission, impairing synaptic plasticity, and aggravating neuronal apoptosis via inducing oxidative stress.

Altered monocyte subpopulations and their association with autism spectrum disorder risk in children

OBJECTIVE

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by deficits in social communication, restricted interests, and repetitive behaviors. Emerging evidence suggests a link between immune dysregulation and ASD. This study investigates alterations in monocyte subpopulations and cytokine production in children with ASD and their potential associations with ASD risk and severity.

METHODS

Initially, the immune status of peripheral blood mononuclear cells was assessed in cohort-I of 96 typically developing (TD) children and 92 children diagnosed with ASD using flow cytometry. Subsequently, the secretion of cytokines IL-6 and IL-10 by monocytes was evaluated following stimulation with a leukocyte activation mixture and intracellular protein staining technique in cohort-II.

RESULTS

Children with ASD exhibited significantly higher levels of total monocytes, classical monocytes (CD14hi/CD16-), and non-classical monocytes (CD14low/CD16+) compared to TD children (p < 0.001). Elevated levels of classical monocytes (β: 0.395; 95 %CI: 0.260-0.530; p < 0.001) and non-classical monocytes (β: 0.629; 95 %CI: 0.516-0.742; p < 0.001) were significantly associated with ASD after adjusting for age, sex and body mass index. Furthermore, increased production of IL-6 by monocytes was observed in children with ASD (p = 0.001). Logistic regression analysis revealed that classical monocytes (OR: 1.104; 95 %CI: 1.062-1.147; p < 0.001), non-classical monocytes (OR: 2.913; 95 %CI: 2.130-3.986; p < 0.001) and IL-6 production by monocytes (OR: 1.306; 95 %CI: 1.096-1.557; p = 0.003) are risk factors for ASD. Spearman correlation analysis revealed a negative correlation between classical monocyte levels and adaptive behavior developmental quotient (DQ) (r = - 0.377; p = 0.001), fine motor DQ (r = - 0.329; p = 0.003) and personal-social DQ (r = - 0.247; p = 0.029) in children with ASD.

CONCLUSION

Elevated classical and non-classical monocytes are potential risk factors for ASD and may influence neurodevelopmental outcomes. Further research is needed to elucidate the precise mechanisms and therapeutic implications.

The "don't eat me" signal CD47 is associated with microglial phagocytosis defects and autism-like behaviors in 16p11.2 deletion mice

Various pathological characteristics of autism spectrum disorder (ASD) stem from abnormalities in brain resident immune cells, specifically microglia, to prune unnecessary synapses or neural connections during early development. Animal models of ASD exhibit an abundance of synapses in different brain regions, which is strongly linked to the appearance of ASD behaviors. Overexpression of CD47 on neurons acts as a "don't eat me" signal, safeguarding synapses from inappropriate pruning by microglia. Indeed, CD47 overexpression occurs in 16p11.2 deletion carriers, causing decreased synaptic phagocytosis and the manifestation of ASD characteristics. However, the role of CD47 in synaptic pruning impairment leading to ASD phenotypes in the 16p11.2 deletion mouse model is unclear. Moreover, whether blocking CD47 can alleviate ASD mice's behavioral deficits remains unknown. Here, we demonstrate a strong link between increased CD47 expression, decreased microglia phagocytosis capacity, and increased impairment in social novelty preference in the 16p11.2 deletion mice. The reduction in microglia phagocytosis caused a rise in excitatory synapses and transmission in the prefrontal cortex of 16p11.2 deletion mice. Importantly, blocking CD47 using a specific CD47 antibody or reducing CD47 expression using a specific short hairpin RNA (shRNA) enhanced the microglia phagocytosis and reduced excitatory transmission. Reduction in CD47 expression improved social novelty preference deficits in 16p11.2 mice. These findings demonstrate that CD47 is associated with the ASD phenotypes in the 16p11.2 deletion mice and could be a promising target for the development of treatment for ASD.

Integrating endocannabinoid signaling, CCK interneurons, and hippocampal circuit dynamics in behaving animals

The brain's endocannabinoid signaling system modulates a diverse range of physiological phenomena and is also involved in various psychiatric and neurological disorders. The basic components of the molecular machinery underlying endocannabinoid-mediated synaptic signaling have been known for decades. However, limitations associated with the short-lived nature of endocannabinoid lipid signals had made it challenging to determine the spatiotemporal specificity and dynamics of endocannabinoid signaling in vivo. Here, we discuss how novel technologies have recently enabled unprecedented insights into endocannabinoid signaling taking place at specific synapses in behaving animals. In this review, we primarily focus on cannabinoid-sensitive inhibition in the hippocampus in relation to place cell properties to illustrate the potential of these novel methodologies. In addition, we highlight implications of these approaches and insights for the unraveling of cannabinoid regulation of synapses in vivo in other brain circuits in both health and disease.

The roles of extracellular vesicles in mental disorders: information carriers, biomarkers, therapeutic agents

Mental disorders are complex conditions that encompass various symptoms and types, affecting approximately 1 in 8 people globally. They place a significant burden on both families and society as a whole. So far, the etiology of mental disorders remains poorly understood, making diagnosis and treatment particularly challenging. Extracellular vesicles (EVs) are nanoscale particles produced by cells and released into the extracellular space. They contain bioactive molecules including nucleotides, proteins, lipids, and metabolites, which can mediate intercellular communication and are involved in various physiological and pathological processes. Recent studies have shown that EVs are closely linked to mental disorders like schizophrenia, major depressive disorder, and bipolar disorder, playing a key role in their development, diagnosis, prognosis, and treatment. Therefore, based on recent research findings, this paper aims to describe the roles of EVs in mental disorders and summarize their potential applications in diagnosis and treatment, providing new ideas for the future clinical transformation and application of EVs.

Novel peptidomimetic compounds attenuate hypoxic-ischemic brain injury in neonatal rats

Hypoxic-ischemic (HI) brain injury is a common neurological problem in neonates. The postsynaptic density protein-95 (PSD-95) is an excitatory synaptic scaffolding protein that regulates synaptic function, and represents a potential therapeutic target to attenuate HI brain injury. Syn3 and d-Syn3 are novel high affinity cyclic peptides that bind the PDZ3 domain of PSD-95. We investigated the neuroprotective efficacy of Syn3 and d-Syn3 after exposure to HI in neonatal rodents. Postnatal (P) day-7 rats were treated with Syn3 and d-Syn3 at zero, 24, and 48-h after carotid artery ligation and 90-min of 8 % oxygen. Hemispheric volume atrophy and Iba-1 positive microglia were quantified by cresyl violet and immunohistochemical staining. Treatment with Syn3 and d-Syn3 reduced tissue volume loss by 47.0 % and 41.0 % in the male plus female, and by 42.1 % and 65.0 % in the male groups, respectively. Syn3 reduced tissue loss by 52.3 % in females. D-Syn3 reduced Iba-1 positive microglia/DAPI ratios in the pooled group, males, and females. Syn3 effects were observed in the pooled group and females. Changes in Iba-1 positive microglia/DAPI cellular ratios correlated directly with reduced hemispheric volume loss, suggesting that Syn3 and d-Syn3 provide neuroprotection in part by their effects on Iba-1 positive microglia. The pathogenic cis phosphorylated Thr231 in Tau (cis P-tau) is a marker of neuronal injury. Cis P-tau was induced in cortical cells of the placebo-treated pooled group, males and females after HI, and reduced by treatment with d-Syn3. Therefore, treatment with these peptidomimetic agents exert neuroprotective effects after exposure of neonatal subjects to HI related brain injury.

Inflammation, Anti-inflammatory Interventions, and Post-stroke Cognitive Impairment: a Systematic Review and Meta-analysis of Human and Animal Studies

The pathophysiology and treatment of post-stroke cognitive impairment (PSCI) are not clear. Stroke triggers an inflammatory response, which might affect synapse function and cognitive status. We performed a systematic review and meta-analysis to assess whether patients with PSCI have increased levels of inflammatory markers and whether anti-inflammatory interventions in animals decrease PSCI. We systematically searched PubMed, EMBASE, and PsychInfo for studies on stroke. For human studies, we determined the standardized mean difference (SMD) on the association between PSCI and markers of inflammation. For animal studies, we determined the SMD of post-stroke cognitive outcome after an anti-inflammatory intervention. Interventions were grouped based on proposed mechanism of action. In patients, the SMD of inflammatory markers for those with versus those without PSCI was 0.46 (95% CI 0.18; 0.76; I2 = 92%), and the correlation coefficient between level of inflammation and cognitive scores was - 0.25 (95% CI - 0.34; - 0.16; I2 = 75%). In animals, the SMD of cognition for those treated with versus those without anti-inflammatory interventions was 1.43 (95% CI 1.12; 1.74; I2 = 83%). The largest effect sizes in treated animals were for complement inhibition (SMD = 1.94 (95% CI 1.50; 2.37), I2 = 51%) and fingolimod (SMD = 2.1 (95% CI 0.75; 3.47), I2 = 81%). Inflammation is increased in stroke survivors with cognitive impairment and is negatively correlated with cognitive functioning. Anti-inflammatory interventions seem to improve cognitive functioning in animals. Complement inhibition and fingolimod are promising therapies on reducing PSCI.

E2F2 induces microglial activation and augments depressive-like behavior in mice by repressing PTPN6 transcription

Depression is the leading contributor to disability and suicide ideation. Informed by the insights from bioinformatics analyses, this study investigates the roles of E2F transcription factor 2 (E2F2) and protein tyrosine phosphatase non-receptor type 6 (PTPN6) in the activation of microglia and the manifestation of depressive-like behavior in mice. Chronic unpredictable mild stress was applied to induce a mouse model of depression, while a cellular model featuring microglia was established through exposure to lipopolysaccharide and adenosine triphosphate. E2F2 was upregulated whereas PTPN6 was downregulated in these models. Notably, E2F2 was found to bind to the PTPN6 promoter, thereby repressing its transcription. Various behavioral tests demonstrated that silencing of E2F2, accomplished via shRNA transfection, led to increased locomotor activity, heightened social interaction rates, enhanced sucrose preference, and reduced immobility time in response to stress stimuli in mice. Furthermore, E2F2 silencing effectively reduced expression of Iba1, a microglial activation marker, and decreased concentrations of pro-inflammatory cytokines both in vivo and in vitro. However, these mitigating effects were countered by additional PTPN6 silencing. In conclusion, this study investigation underscores the role of E2F2 in promoting inflammatory activation of microglia and exacerbating depressive-like behavior in mice by repressing PTPN6 transcription.

Modification of Neural Circuit Functions by Microglial P2Y6 Receptors in Health and Neurodegeneration

Neural circuits consisting of neurons and glial cells help to establish all functions of the CNS. Microglia, the resident immunocytes of the CNS, are endowed with UDP-sensitive P2Y6 receptors (P2Y6Rs) which regulate phagocytosis/pruning of excessive synapses during individual development and refine synapses in an activity-dependent manner during adulthood. In addition, this type of receptor plays a decisive role in primary (Alzheimer's disease, Parkinson's disease, neuropathic pain) and secondary (epilepsy, ischemic-, mechanical-, or irradiation-induced) neurodegeneration. A whole range of microglial cytokines controlled by P2Y6Rs, such as the interleukins IL-1β, IL-6, IL-8, and tumor necrosis factor-α (TNF-α), leads to neuroinflammation, resulting in neurodegeneration. Hence, small molecular antagonists of P2Y6Rs and genetic knockdown of this receptor provide feasible ways to alleviate inflammation-induced neurological disorders but might also interfere with the regulation of the synaptic circuitry. The present review aims at investigating this dual role of P2Y6Rs in microglia, both in shaping neural circuits by targeted phagocytosis and promoting neurodegenerative illnesses by fostering neuroinflammation through multiple transduction mechanisms.

Potential roles for microglia in drug addiction: Adolescent neurodevelopment and beyond

Adolescence is a sensitive period for development of addiction-relevant brain circuits, and it is also when people typically start experimenting with drugs. Unfortunately, such substance use may cause lasting impacts on the brain, and might increase vulnerability to later-life addictions. Microglia are the brain's immune cells, but their roles in shaping neural connectivity and synaptic plasticity, especially in developmental sensitive periods like adolescence, may also contribute to addiction-related phenomena. Here, we overview how drugs of abuse impact microglia, and propose that they may play poorly-understood, but important roles in addiction vulnerability and progression.

Urolithin A alleviates schizophrenic-like behaviors and cognitive impairment in rats through modulation of neuroinflammation, neurogenesis, and synaptic plasticity

Cognitive impairment in schizophrenia occurs in the early stages of the disease and is closely associated with prognosis. Alleviation of cognitive impairment in schizophrenia faces major challenges owing to the lack of preventive and therapeutic drugs that are novel and effective. Urolithin A (UA) is a gut microbial metabolite of ellagic acid that has demonstrated neuroprotective effects in multiple neurological disease models. Nonetheless, the neuromodulatory role of UA in schizophrenia is yet to be elucidated. Wistar rat pups were separated from their mothers for 24 h on postnatal days (PNDs) 9-10 to establish an early-life stress model. The pups were pretreated with UA at different administration times (2, 4, and 6 weeks) and doses (50, 100, and 150 mg/kg) from adolescence (PND29). Behavioral tests were performed after the end of the administration. Subsequently, hippocampal samples were collected for histopathological and molecular evaluations. Male offspring rats subjected to maternal separation exhibited increased sensitivity to prepulse inhibition and cognitive impairment, accompanied by severe neuroinflammation and impaired neurogenesis. However, UA attenuated maternal separation-induced prepulse inhibition deficits and cognitive impairments and restored hippocampal neurogenesis in a dose-dependent manner. Furthermore, UA pretreatment preserved dendritic spine density, synapses, and presynaptic vesicles. In addition, it exerted anti-inflammatory effects by inhibiting microglial activation and expression of the proinflammatory cytokines tumor necrosis factor-α, interleukin-6, and interleukin-1β. Potential mechanisms included upregulation of brain-derived neurotrophic factor protein expression and activation of the extracellular signal-regulated kinase signaling pathway. This study is the first preclinical evaluation of the effects of UA on cognitive impairment in schizophrenia. The findings suggest that changes in cognitive function linked to schizophrenia are driven by the interaction among neuroinflammation, neurogenesis, and synaptic plasticity and that UA has the potential to reverse these processes. These observations provide evidence for future clinical trials of UA as a dietary supplement for preventing schizophrenia.

Perimenopause promotes neuroinflammation in select hippocampal regions in a mouse model of Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder characterized by age-dependent amyloid beta (Aβ) aggregation and accumulation, neuroinflammation, and cognitive deficits. Significantly, there are prominent sex differences in the risk, onset, progression, and severity of AD, as well as response to therapies, with disease burden disproportionally affecting women. Although menopause onset (i.e., perimenopause) may be a critical transition stage for AD susceptibility in women, the role of early ovarian decline in initial disease pathology, particularly key neuroinflammatory processes, is not well understood. To study this, we developed a unique mouse model of perimenopausal AD by combining an accelerated ovarian failure (AOF) model of menopause induced by 4-vinylcyclohexene diepoxide (VCD) with the 5xFAD transgenic AD mouse model. To target early stages of disease progression, 5xFAD females were studied at a young age (∼4 months) and at the beginning stage of ovarian failure analogous to human perimenopause (termed "peri-AOF"), and compared to age-matched males. Assessment of neuropathology was performed by immunohistochemical labeling of Aβ as well as markers of astrocyte and microglia activity in the hippocampus, a brain region involved in learning and memory that is deleteriously impacted during AD. Our results show that genotype, AOF, and sex contributed to AD-like pathology. Aggregation of Aβ was heightened in female 5xFAD mice and further increased at peri-AOF, with hippocampal subregion specificity. Further, select increases in glial activation also paralleled Aβ pathology in distinct hippocampal subregions. However, cognitive function was not affected by peri-AOF. These findings align with the hypothesis that perimenopause constitutes a period of susceptibility for AD pathogenesis in women.

Glial Cells in Spinal Muscular Atrophy: Speculations on Non-Cell-Autonomous Mechanisms and Therapeutic Implications

Spinal muscular atrophy (SMA) is a neuromuscular disorder caused by homozygous deletions or mutations in the SMN1 gene, leading to progressive motor neuron degeneration. While SMA has been classically viewed as a motor neuron-autonomous disease, increasing evidence indicates a significant role of glial cells-astrocytes, microglia, oligodendrocytes, and Schwann cells-in the disease pathophysiology. Astrocytic dysfunction contributes to motor neuron vulnerability through impaired calcium homeostasis, disrupted synaptic integrity, and neurotrophic factor deficits. Microglia, through reactive gliosis and complement-mediated synaptic stripping, exacerbate neurodegeneration and neuroinflammation. Oligodendrocytes exhibit impaired differentiation and metabolic support, while Schwann cells display abnormalities in myelination, extracellular matrix composition, and neuromuscular junction maintenance, further compromising motor function. Dysregulation of pathways such as NF-κB, Notch, and JAK/STAT, alongside the upregulation of complement proteins and microRNAs, reinforces the non-cell-autonomous nature of SMA. Despite the advances in SMN-restorative therapies, they do not fully mitigate glial dysfunction. Targeting glial pathology, including modulation of reactive astrogliosis, microglial polarization, and myelination deficits, represents a critical avenue for therapeutic intervention. This review comprehensively examines the multifaceted roles of glial cells in SMA and highlights emerging glia-targeted strategies to enhance treatment efficacy and improve patient outcomes.

Extracellular vesicles lay the ground for neuronal plasticity by restoring mitochondrial function, cell metabolism and immune balance

Extracellular vesicles (EVs) convey complex signals between cells that can be used to promote neuronal plasticity and neurological recovery in brain disease models. These EV signals are multimodal and context-dependent, making them unique therapeutic principles. This review analyzes how EVs released from various cell sources control neuronal metabolic function, neuronal survival and plasticity. Preferential sites of EV communication in the brain are interfaces between pre- and postsynaptic neurons at synapses, between astrocytes and neurons at plasma membranes or tripartite synapses, between oligodendrocytes and neurons at axons, between microglial cells/macrophages and neurons, and between cerebral microvascular cells and neurons. At each of these interfaces, EVs support mitochondrial function and cell metabolism under physiological conditions and orchestrate neuronal survival and plasticity in response to brain injury. In the injured brain, the promotion of neuronal survival and plasticity by EVs is tightly linked with EV actions on mitochondrial function, cell metabolism, oxidative stress and immune responses. Via the stabilization of cell metabolism and immune balance, neuronal plasticity responses are activated and functional neurological recovery is induced. As such, EV lay the ground for neuronal plasticity.

Histone deacetylases: the critical enzymes for microglial activation involved in neuropathic pain

Neuropathic pain is a common health problem in clinical practice that can be caused by many different factors, including infection, ischemia, trauma, diabetes mellitus, nerve compression, autoimmune disorders, cancer, trigeminal neuralgia, and abuse of certain drugs. This type of pain can persistently affect patients for a long time, even after the rehabilitation of their damaged tissues. Researchers have identified the crucial role of microglial activation in the pathogenesis of neuropathic pain. Furthermore, emerging evidence has shown that the expression and/or activities of different histone deacetylases (HDACs) can modulate microglial function and neuropathic pain. In this review, we will summarize and discuss the functions and mechanisms of HDACs in microglial activation and neuropathic pain development. Additionally, we will also list the emerging HDAC inhibitors or activators that may contribute to therapeutic advancement in alleviating neuropathic pain.

Maintaining moderate levels of hypochlorous acid promotes neural stem cell proliferation and differentiation in the recovery phase of stroke

JOURNAL/nrgr/04.03/01300535-202503000-00029/figure1/v/2024-06-17T092413Z/r/image-tiff It has been shown clinically that continuous removal of ischemia/reperfusion-induced reactive oxygen species is not conducive to the recovery of late stroke. Indeed, previous studies have shown that excessive increases in hypochlorous acid after stroke can cause severe damage to brain tissue. Our previous studies have found that a small amount of hypochlorous acid still exists in the later stage of stroke, but its specific role and mechanism are currently unclear. To simulate stroke in vivo, a middle cerebral artery occlusion rat model was established, with an oxygen-glucose deprivation/reoxygenation model established in vitro to mimic stroke. We found that in the early stage (within 24 hours) of ischemic stroke, neutrophils produced a large amount of hypochlorous acid, while in the recovery phase (10 days after stroke), microglia were activated and produced a small amount of hypochlorous acid. Further, in acute stroke in rats, hypochlorous acid production was prevented using a hypochlorous acid scavenger, taurine, or myeloperoxidase inhibitor, 4-aminobenzoic acid hydrazide. Our results showed that high levels of hypochlorous acid (200 μM) induced neuronal apoptosis after oxygen/glucose deprivation/reoxygenation. However, in the recovery phase of the middle cerebral artery occlusion model, a moderate level of hypochlorous acid promoted the proliferation and differentiation of neural stem cells into neurons and astrocytes. This suggests that hypochlorous acid plays different roles at different phases of cerebral ischemia/reperfusion injury. Lower levels of hypochlorous acid (5 and 100 μM) promoted nuclear translocation of β-catenin. By transfection of single-site mutation plasmids, we found that hypochlorous acid induced chlorination of the β-catenin tyrosine 30 residue, which promoted nuclear translocation. Altogether, our study indicates that maintaining low levels of hypochlorous acid plays a key role in the recovery of neurological function.

Genome-wide association study reveals multiple loci for nociception and opioid consumption behaviors associated with heroin vulnerability in outbred rats

The increased prevalence of opioid use disorder (OUD) makes it imperative to disentangle the biological mechanisms contributing to individual differences in OUD vulnerability. OUD shows strong heritability, however genetic variants contributing to vulnerability remain poorly defined. We performed a genome-wide association study using over 850 male and female heterogeneous stock (HS) rats to identify genes underlying behaviors associated with OUD such as nociception, as well as heroin-taking, extinction and seeking behaviors. By using an animal model of OUD, we were able to identify genetic variants associated with distinct OUD behaviors while maintaining a uniform environment, an experimental design not easily achieved in humans. Furthermore, we used a novel non-linear network-based clustering approach to characterize rats based on OUD vulnerability to assess genetic variants associated with OUD susceptibility. Our findings confirm the heritability of several OUD-like behaviors, including OUD susceptibility. Additionally, several genetic variants associated with nociceptive threshold prior to heroin experience, heroin consumption, escalation of intake, and motivation to obtain heroin were identified. Tom1, a microglial component, was implicated for nociception. Several genes involved in dopaminergic signaling, neuroplasticity and substance use disorders, including Brwd1, Pcp4, Phb1l2 and Mmp15 were implicated for the heroin traits. Additionally, an OUD vulnerable phenotype was associated with genetic variants for consumption and break point, suggesting a specific genetic contribution for OUD-like traits contributing to vulnerability. Together, these findings identify novel genetic markers related to the susceptibility to OUD-relevant behaviors in HS rats.

Neuron-to-glia and glia-to-glia signaling directs critical period experience-dependent synapse pruning

Experience-dependent glial synapse pruning plays a pivotal role in sculpting brain circuit connectivity during early-life critical periods of development. Recent advances suggest a layered cascade of intercellular communication between neurons and glial phagocytes orchestrates this precise, targeted synapse elimination. We focus here on studies from the powerful Drosophila forward genetic model, with reference to complementary findings from mouse work. We present both neuron-to-glia and glia-to-glia intercellular signaling pathways directing experience-dependent glial synapse pruning. We discuss a putative hierarchy of secreted long-distance cues and cell surface short-distance cues that act to sequentially orchestrate glia activation, infiltration, target recognition, engulfment, and then phagocytosis for synapse pruning. Ligand-receptor partners mediating these stages in different contexts are discussed from recent Drosophila and mouse studies. Signaling cues include phospholipids, small neurotransmitters, insulin-like peptides, and proteins. Conserved receptors for these ligands are discussed, together with mechanisms where the receptor identity remains unknown. Potential mechanisms are proposed for the tight temporal-restriction of heightened experience-dependent glial synapse elimination during early-life critical periods, as well as potential means to re-open such plasticity at maturity.

Models developed to explain the effects of stress on brain and behavior

There is an integral relationship between stress, brain function and behavior. Over the year's extensive research has led to the development of various models to explain the intricate intersection between brain and stress. This chapter delves into some of the theoretical frameworks that explains the neurobiological and behavioral responses to stress using key models of stress such as the allostatic load model, which is the most common model that describes how chronic stress affect brain structure and function resulting in long-term changes in regions such as the hippocampus, amygdala, and prefrontal cortex which phenotypically express as cognitive impairments, emotional dysfunction seen in various forms of neurological disorder. The neuro-endocrine model, follows the glucocorticoid cascade hypothesis, that associates prolonged stress exposure to hippocampal damage and cognitive decline via alteration in the hypothalamic-pituitary-adrenal (HPA) axis and the overproduction of stress hormones like cortisol which can induce hippocampal atrophy, impair learning and memory, and promote depressive-like behaviors. The neurobiological stress model addresses the role of the hypothalamic-pituitary-adrenal (HPA) axis and stress-related neurotransmitters in shaping behavioral responses, emphasizing alterations in neuroplasticity and synaptic function. These models demonstrate how chronic stress can alter neural plasticity, neurotransmitter systems, and synaptic connectivity, affecting behavior and cognitive function. Hence by integrating molecular, neurobiological, and behavioral perspectives, these models offer a comprehensive understanding of how stress alters brain activity and behavior. The chapter further showcase how these models direct the development of medical interventions, shedding light on potential therapies that target the underlying molecular mechanisms of stress-induced brain changes.

Internalization of extracellular Tau oligomers in Alzheimer's disease

A key factor in the progression of Alzheimer's disease (AD) is internalization of extracellular Tau oligomers (ecTauOs) by neuroglial cells. Aberrant hyperphosphorylation of Tau results in their dissociation from microtubules and formation of toxic intracellular Tau oligomers (icTauOs). These are subsequently released to the extracellular space following neuronal dysfunction and death. Although receptor mediated internalization of these ecTauOs by other neurons, microglia and astrocytes can facilitate elimination, incomplete degradation thereof promotes inflammation, exacerbates pathologic spread and accelerates neurodegeneration. Targeting Tau oligomer degradation pathways, blocking internalization receptors, and mitigating neuroinflammation are proposed as therapeutic strategies to control Tau propagation and toxicity. This review highlights the urgent need for innovative approaches to prevent the spread of Tau pathology, emphasizing its implications for AD and related neurodegenerative diseases.

Microglial Regulation of Neural Networks in Neuropsychiatric Disorders

Microglia serve as vital innate immune cells in the central nervous system, playing crucial roles in the generation and development of brain neurons, as well as mediating a series of immune and inflammatory responses. The morphologic transitions of microglia are closely linked to their function. With the advent of single-cell sequencing technology, the diversity of microglial subtypes is increasingly recognized. The intricate interactions between microglia and neuronal networks have significant implications for psychiatric disorders and neurodegenerative diseases. A deeper investigation of microglia in neurologic diseases such as Alzheimer disease, depression, and epilepsy can provide valuable insights in understanding the pathogenesis of diseases and exploring novel therapeutic strategies, thereby addressing issues related to central nervous system disorders.

Phenotypic and Functional Alterations in Peripheral Blood Mononuclear Cell-Derived Microglia in a Primate Model of Chronic Alcohol Consumption

Alcohol-induced dysregulation of microglial activity is associated with neuroinflammation, cognitive decline, heightened risk for neurodegenerative diseases, alcohol dependence, and escalation of alcohol drinking. Given the challenge of longitudinally sampling primary microglia, we optimized an in vitro method to differentiate peripheral blood mononuclear cells (PBMC) from non-human primates (NHP) into microglia-like cells (induced-microglia; iMGL). The iMGLs displayed transcriptional profiles distinct from those of monocyte progenitors and closely resembling those of primary microglia. Notably, morphological features showed that differentiated iMGLs derived from NHPs with chronic alcohol consumption (CAC) possessed a more mature-like microglial morphology. Additionally, dysregulation in key inflammatory and regulatory markers alongside increased baseline phagocytic activity was observed in CAC-derived IMGLs in the resting state. Phenotypic and functional assessments following LPS stimulation indicated the presence of an immune-tolerant phenotype and enrichment of a CD86+ hyper-inflammatory subpopulation in iMGLs derived from ethanol-exposed animals. Collectively, these findings demonstrate that in vitro differentiation of PBMC offers a minimally invasive approach to studying the impact of CAC on microglial function revealing that CAC reshapes both functional and transcriptional profiles of microglia.

New insights into anti-depression effects of bioactive phytochemicals

Depression is one of the most common psychological disorders, and due to its high prevalence and mortality rates, it imposes a significant disease burden. Contemporary treatments for depression involve various synthetic drugs, which have limitations such as side effects, single targets, and slow onset of action. Unlike synthetic medications, phytochemicals offer the benefits of a multi-target and multi-pathway mode of treatment for depression. In this literature review, we describe the pharmacological actions, experimental models, and clinical trials of the antidepressant effects of various phytochemicals. Additionally, we summarize the potential mechanisms by which these phytochemicals prevent depression, including regulating neurotransmitters and their receptors, the HPA axis, inflammatory responses, managing oxidative stress, neuroplasticity, and the gut microbiome. Phytochemicals exert therapeutic effects through multiple pathways and targets, making traditional Chinese medicine (TCM) a promising adjunctive antidepressant for the prevention, alleviation, and treatment of depression. Therefore, this review aims to provide robust evidence for subsequent research into developing phytochemical resources as effective antidepressant agents.

Biological sex, microglial signaling pathways, and radiation exposure shape cortical proteomic profiles and behavior in mice

Patients receiving cranial radiation therapy experience tissue damage and cognitive deficits that severely decrease their quality of life. Experiments in rodent models show that these adverse neurological effects are in part due to functional changes in microglia, the resident immune cells of the central nervous system. Increasing evidence suggests that experimental manipulation of microglial signaling can regulate radiation-induced changes in the brain and behavior. Furthermore, many studies show sex-dependent neurological effects of radiation exposure. Despite this, few studies have used both males and females to explore how sex and microglial function interact to influence radiation effects on the brain. Here, we used a system levels approach to examine how deficiencies in purinergic and fractalkine signaling, two important microglial signaling pathways, impact brain proteomic and behavioral profiles in irradiated and control male and female mice. We performed a comprehensive analysis of the cortical proteomes from irradiated and control C57BL/6J, P2Y12-/-, and CX3CR1-/- mice of both sexes using multiple bioinformatics methods. We identified distinct proteins and biological processes, as well as behavioral profiles, regulated by sex, genotype, radiation exposure, and their interactions. Disrupting microglial signaling, had the greatest impact on proteomic expression, with CX3CR1-/- mice showing the most distinct proteomic profile characterized by upregulation of CX3CL1. Surprisingly, radiation exposure caused relatively smaller proteomic changes in glial and synaptic proteins, including Rgs10, Crybb1, C1qa, and Hexb. While we observed some radiation effects on locomotor behavior, biological sex as well as loss of P2Y12 and CX3CR1 signaling had a stronger influence on locomotor outcomes in our model. Lastly, loss of P2Y12 and CX3CR1 strongly regulated exploratory behaviors. Overall, our findings provide novel insights into the molecular pathways and proteins that are linked to P2Y12 and CX3CR1 signaling, biological sex, radiation exposure, and their interactions.

Microglial type I interferon signaling mediates chronic stress-induced synapse loss and social behavior deficits

Inflammation and synapse loss have been associated with deficits in social behavior and are involved in pathophysiology of many neuropsychiatric disorders. Synapse loss, characterized by reduction in dendritic spines can significantly disrupt synaptic connectivity and neural circuitry underlying social behavior. Chronic stress is known to induce loss of spines and dendrites in the prefrontal cortex (PFC), a brain region implicated in social behavior. However, the underlying mechanisms are not well understood. In the present study, we investigated the role of type I Interferon (IFN-I) signaling in chronic unpredictable stress (CUS)-induced synapse loss and behavior deficits in mice. We found increased expression of type I IFN receptor (IFNAR) in microglia following CUS. Conditional knockout of microglial IFNAR in adult mice rescued CUS-induced social behavior deficits and synapse loss. Bulk RNA sequencing data show that microglial IFNAR deletion attenuated CUS-mediated changes in the expression of genes such as Keratin 20 (Krt20), Claudin-5 (Cldn5) and Nuclear Receptor Subfamily 4 Group A Member 1 (Nr4a1) in the PFC. Cldn5 and Nr4a1 are known for their roles in synaptic plasticity. Krt20 is an intermediate filament protein responsible for the structural integrity of epithelial cells. The reduction in Krt20 following CUS presents a novel insight into the potential contribution of cytokeratin in stress-induced alterations in neuroplasticity. Overall, these results suggest that microglial IFNAR plays a critical role in regulating synaptic plasticity and social behavior deficits associated with chronic stress conditions.

Exosomal circRNAs: Deciphering the novel drug resistance roles in cancer therapy

Exosomal circular RNA (circRNAs) are pivotal in cancer biology, and tumor pathophysiology. These stable, non-coding RNAs encapsulated in exosomes participated in cancer progression, tumor growth, metastasis, drug sensitivity and the tumor microenvironment (TME). Their presence in bodily fluids positions them as potential non-invasive biomarkers, revealing the molecular dynamics of cancers. Research in exosomal circRNAs is reshaping our understanding of neoplastic intercellular communication. Exploiting the natural properties of exosomes for targeted drug delivery and disrupting circRNA-mediated pro-tumorigenic signaling can develop new treatment modalities. Therefore, ongoing exploration of exosomal circRNAs in cancer research is poised to revolutionize clinical management of cancer. This emerging field offers hope for significant breakthroughs in cancer care. This review underscores the critical role of exosomal circRNAs in cancer biology and drug resistance, highlighting their potential as non-invasive biomarkers and therapeutic targets that could transform the clinical management of cancer.

Intermittent Fasting Improves Social Interaction and Decreases Inflammatory Markers in Cortex and Hippocampus

Autism spectrum disorder (ASD) is a psychiatric condition characterized by reduced social interaction, anxiety, and stereotypic behaviors related to neuroinflammation and microglia activation. We demonstrated that maternal exposure to Western diet (cafeteria diet or CAF) induced microglia activation, systemic proinflammatory profile, and ASD-like behavior in the offspring. Here, we aimed to identify the effect of alternate day fasting (ADF) as a non-pharmacologic strategy to modulate neuroinflammation and ASD-like behavior in the offspring prenatally exposed to CAF diet. We found that ADF increased plasma beta-hydroxybutyrate (BHB) levels in the offspring exposed to control and CAF diets but not in the cortex (Cx) and hippocampus (Hpp). We observed that ADF increased the CD45 + cells in Cx of both groups; In control individuals, ADF promoted accumulation of CD206 + microglia cells in choroid plexus (CP) and increased in CD45 + macrophages cells and lymphocytes in the Cx. Gestational exposure to CAF diet promoted defective sociability in the offspring; ADF improved social interaction and increased microglia CD206 + in the Hpp and microglia complexity in the dentate gyrus. Additionally, ADF led to attenuation of the ER stress markers (Bip/ATF6/p-JNK) in the Cx and Hpp. Finally, biological modeling showed that fasting promotes higher microglia complexity in Cx, which is related to improvement in social interaction, whereas in dentate gyrus sociability is correlated with less microglia complexity. These data suggest a contribution of intermittent fasting as a physiological stimulus capable of modulating microglia phenotype and complexity in the brain, and social interaction in male mice.

Typical development of synaptic and neuronal properties can proceed without microglia in the cortex and thalamus

Brain-resident macrophages, microglia, have been proposed to have an active role in synaptic refinement and maturation, influencing plasticity and circuit-level connectivity. Here we show that several neurodevelopmental processes previously attributed to microglia can proceed without them. Using a genetically modified mouse that lacks microglia (Csf1r∆FIRE/∆FIRE), we find that intrinsic properties, synapse number and synaptic maturation are largely normal in the hippocampal CA1 region and somatosensory cortex at stages where microglia have been implicated. Seizure susceptibility and hippocampal-prefrontal cortex coherence in awake behaving animals, processes that are disrupted in mice deficient in microglia-enriched genes, are also normal. Similarly, eye-specific segregation of inputs into the lateral geniculate nucleus proceeds normally in the absence of microglia. Single-cell and single-nucleus transcriptomic analyses of neurons and astrocytes did not uncover any substantial perturbation caused by microglial absence. Thus, the brain possesses remarkable adaptability to execute developmental synaptic refinement, maturation and connectivity in the absence of microglia.

Microglial activation and hypothalamic structural plasticity in HFD obesity: insights from semaglutide and minocycline

High-fat diet (HFD)-induced microglial activation contributes to hypothalamic inflammation and obesity, but the mechanisms linking microglia to structural changes remain unclear. This study explored the role of microglia in impairing hypothalamic synaptic plasticity in diet-induced obesity mice and evaluated the therapeutic potential of semaglutide (Sema) and minocycline (MI). Six-week-old C57BL/6J mice were divided into low-fat diet and HFD groups. At week 30, the HFD-fed mice were treated daily with Sema or MI for six weeks. Confocal microscopy assessed hypothalamic dendritic spines, synaptic organization, and microglia-synapse interactions. We also analyzed microglial morphology, CD68/CD11b colocalization with Iba-1, synaptic marker expression, and phagocytosis-related pathways (C1q, C3, CD11b). BV2 microglia were used to examine the direct effects of Sema or MI on microglia and validate the in vivo findings. HFD feeding induced microglial activation, as indicated by increased colocalization of CD68 or synaptophysin and CD11b with Iba-1, along with elevated C1q, C3, and CD11b expression, signaling enhanced synaptic phagocytosis. This was accompanied by reduced hypothalamic dendritic spines, decreased synaptic marker expression, and disrupted excitatory/inhibitory synaptic organization in the melanocortin system, as well as impaired glucose metabolism, disrupted leptin-ghrelin balance, and increased food intake and body weight. Sema and MI treatments reversed the pathological changes of microglial activation and restored hypothalamic synaptic structure, although their effects on synaptic organization and metabolic outcomes differed. Our findings highlight the key role of microglial activation in hypothalamic synaptic impairment in diet-induced obesity models, with Sema and MI possibly offering distinct therapeutic pathways to mitigate these impairments.

Repetitive transcranial magnetic stimulation in Alzheimer's disease: effects on neural and synaptic rehabilitation

Alzheimer's disease is a neurodegenerative disease resulting from deficits in synaptic transmission and homeostasis. The Alzheimer's disease brain tends to be hyperexcitable and hypersynchronized, thereby causing neurodegeneration and ultimately disrupting the operational abilities in daily life, leaving patients incapacitated. Repetitive transcranial magnetic stimulation is a cost-effective, neuro-modulatory technique used for multiple neurological conditions. Over the past two decades, it has been widely used to predict cognitive decline; identify pathophysiological markers; promote neuroplasticity; and assess brain excitability, plasticity, and connectivity. It has also been applied to patients with dementia, because it can yield facilitatory effects on cognition and promote brain recovery after a neurological insult. However, its therapeutic effectiveness at the molecular and synaptic levels has not been elucidated because of a limited number of studies. This study aimed to characterize the neurobiological changes following repetitive transcranial magnetic stimulation treatment, evaluate its effects on synaptic plasticity, and identify the associated mechanisms. This review essentially focuses on changes in the pathology, amyloidogenesis, and clearance pathways, given that amyloid deposition is a major hypothesis in the pathogenesis of Alzheimer's disease. Apoptotic mechanisms associated with repetitive transcranial magnetic stimulation procedures and different pathways mediating gene transcription, which are closely related to the neural regeneration process, are also highlighted. Finally, we discuss the outcomes of animal studies in which neuroplasticity is modulated and assessed at the structural and functional levels by using repetitive transcranial magnetic stimulation, with the aim to highlight future directions for better clinical translations.

Transcranial near-infrared light promotes remyelination through AKT1/mTOR pathway to ameliorate postoperative neurocognitive disorder in aged mice

Postoperative neurocognitive disorder (PND) is a prevalent complication following surgery and anesthesia, characterized by progressive cognitive decline. The precise etiology of PND remains unknown, and effective targeted therapeutic strategies are lacking. Transcranial near-infrared light (tNIRL) has shown potential benefits for cognitive dysfunction diseases, but its effect on PND remains unclear. Our previous research indicated a close association between demyelination and PND. In other central nervous system (CNS) disorders, tNIRL has been demonstrated to facilitate remyelination in response to demyelination. In this study, we established the PND model in 18-month-old male C57BL/6 mice using isoflurane anesthesia combined with left common carotid artery exposure. Following surgery, PND-aged mice were subjected to daily 2.5-minute tNIRL treatment at 810 nm for three consecutive days. Subsequently, we observed that tNIRL significantly improved cognitive performance and reduced inflammatory cytokine levels in the hippocampus of PND mice. Furthermore, tNIRL increased the expression of oligodendrocyte transcription factor 2 (OLIG2) and myelin basic protein (MBP), promoting remyelination while enhancing synaptic function-associated proteins such as synaptophysin (SYP) and postsynaptic density protein 95 (PSD95). Further investigation revealed that tNIRL may activate the AKT1/mTOR pathway to facilitate remyelination in PND mice. These findings indicate that tNIRL is a novel non-invasive therapeutic approach for treating PND.

Remote photobiomodulation ameliorates behavioral and neuropathological outcomes in a rat model of repeated closed head injury

Repeated closed-head injuries (rCHI) from activities like contact sports, falls, military combat, and traffic accidents pose a serious risk due to their cumulative impact on the brain. Often, rCHI is not diagnosed until symptoms of irreversible brain damage appear, highlighting the need for preventive measures. This study assessed the prophylactic efficacy of remote photobiomodulation (PBM) targeted at the lungs against rCHI-induced brain injury and associated behavioral deficits. Utilizing the "Marmarou" weight-drop model, rCHI was induced in rats on days 0, 5, and 10. Remote PBM, employing an 808 nm continuous wave laser, was administered daily in 2-min sessions per lung side over 20 days. Behavioral deficits were assessed through three-chamber social interaction, forced swim, grip strength, open field, elevated plus maze, and Barnes maze tests. Immunofluorescence staining and 3D reconstruction evaluated neuronal damage, apoptosis, degeneration, and the morphology of microglia and astrocytes, as well as astrocyte and microglia-mediated excessive synapse elimination. Additionally, 16S rDNA amplicon sequencing analyzed changes in the lung microbiome following remote PBM treatment. Results demonstrated that remote PBM significantly improved depressive-like behaviors, motor dysfunction, and social interaction impairment while enhancing grip strength and reducing neuronal damage, apoptosis, and degeneration induced by rCHI. Analysis of lung microbiome changes revealed an enrichment of lipopolysaccharide (LPS) biosynthesis pathways, suggesting a potential link to neuroprotection. Furthermore, remote PBM mitigated hyperactivation of cortical microglia and astrocytes and significantly reduced excessive synaptic phagocytosis by these cells, highlighting its potential as a preventive strategy for rCHI with neuroprotective effects.

Minimal differences observed when comparing the morphological profiling of microglia obtained by confocal laser scanning and optical sectioning microscopy

Background

While widefield microscopy has long been constrained by out-of-focus scattering, advancements have generated a solution in the form of confocal laser scanning microscopy (cLSM) and optical sectioning microscopy using structured illumination (OSM). In this study, we aim to investigate, using microglia branching, if cLSM and OSM can produce images with comparable morphological characteristics.

Results

By imaging the somatosensory microglia from a tissue slice of a 3-week-old mouse and establishing morphological parameters that characterizes the microglial branching pattern, we were able to show that there is no difference in total length of the branch tree, number of branches, mean branch length and number of primary to terminal branches. We did find that area-based parameters such as mean occupied area and mean surveillance area were bigger in cLSM isolated microglia compared to OSM ones. Additionally, by investigating the difference in acquisition time between techniques and personal costs we were able to establish that the amortization could be made in 6.11 ± 2.93 years in the case of countries with a Human Development Index (HDI) = 7-9 and 7.06 ± 3.13 years, respectably, for countries with HDI < 7. As such, OSM systems seem a valid option if one just wants basic histological evaluation, and cLSM should be considered for groups that demand higher resolution or volumetric images.

The role of inhibitory immune checkpoint receptors in the pathogenesis of Alzheimer's disease

There is mounting evidence that microglial cells have a key role in the pathogenesis of Alzheimer's disease (AD). In AD pathology, microglial cells not only are unable to remove β-amyloid (Aβ) plaques and invading pathogens but also are involved in synaptic pruning, chronic neuroinflammation, and neuronal degeneration. Microglial cells possess many different inhibitory immune checkpoint receptors, such as PD-1, LILRB2-4, Siglecs, and SIRPα receptors, which can be targeted by diverse cell membrane-bound and soluble ligand proteins to suppress the functions of microglia. Interestingly, in the brains of AD patients there are elevated levels of many of the inhibitory ligands acting via these inhibitory checkpoint receptors. For instance, Aβ oligomers, ApoE4, and fibronectin are able to stimulate the LILRB2-4 receptors. Increased deposition of sialoglycans, e.g., gangliosides, inhibits microglial function via Siglec receptors. AD pathology augments the accumulation of senescent cells, which are known to possess a high level of PD-L1 proteins, and thus, they can evade immune surveillance. A decrease in the expression of SIRPα receptor in microglia and its ligand CD47 in neurons enhances the phagocytic pruning of synapses in AD brains. Moreover, cerebral neurons contain inhibitory checkpoint receptors which can inhibit axonal growth, reduce synaptic plasticity, and impair learning and memory. It seems that inappropriate inhibitory immune checkpoint signaling impairs the functions of microglia and neurons thus promoting AD pathogenesis. KEY MESSAGES: Microglial cells have a major role in the pathogenesis of AD. A decline in immune activity of microglia promotes AD pathology. Microglial cells and neurons contain diverse inhibitory immune checkpoint receptors. The level of ligands for inhibitory checkpoint receptors is increased in AD pathology. Impaired signaling of inhibitory immune checkpoint receptors promotes AD pathology.

Neuroglia in anxiety disorders

Anxiety disorders are some of the most prevalent in the world and are extraordinarily debilitating to many individuals, costing millions in disability. One of the most disabling is posttraumatic stress disorder (Snijders et al., 2020). Understanding the pathophysiology of these illnesses further and the cell types involved will allow better targeting of treatments. Glial cells, encompassing microglia, astrocytes, and oligodendrocytes, play critical roles in the pathophysiology of PTSD and other anxiety illnesses. Each of these cell types interacts with aspects of neuro-epigenetics, neuroimmune, and neuronal signaling and may contribute to the pathophysiology of anxiety illnesses. This chapter covers the literature on the role of glial cells in the neurobiology and pathology of anxiety disorders, more specifically PTSD. PTSD is one of the most debilitating anxiety disorders and one of the most complicated from a neurobiologic perspective. This chapter also features a discussion surrounding the current state of treatment and some of the hypothesized mechanisms for novel treatments including tetrahydrocannabidiol and 3,4-methylenedioxymethamphetamine. Finally, thoughts on the future directions for precision treatment and pharmacologic development with a focus on neuroglia are undertaken.

In vitro models for human neuroglia

Neuroglia are a heterogenous population of cells in the nervous system. In the central nervous system, this group is classified into astrocytes, oligodendrocytes, and microglia. Neuroglia in the peripheral nervous system are divided into Schwann cells and enteric glia. These groups of cells display considerable differences in their developmental origin, morphology, function, and regional abundance. Compared to animal models, human neuroglia differ in their transcriptomic profile, morphology, and function. Investigating the physiology of healthy or diseased human neuroglia in vivo is challenging due to the inaccessibility of the tissue. Therefore, researchers have developed numerous in vitro models attempting to replicate the natural tissue environment. Earlier models made use of postmortem, postsurgical, or fetal tissue to establish human neuroglial cells in vitro, either as a pure population of the desired cell type or as organotypic slice cultures. Advancements in human stem cell differentiation techniques have greatly enhanced the possibilities for creating in vitro models of human neuroglia. This chapter provides an overview of the current models used to study the functioning and development of human neuroglia in vitro, both in health and disease.

Unraveling the complexity of microglial responses in traumatic brain and spinal cord injury

Microglia, the resident innate immune cells of the central nervous system (CNS), play an important role in neuroimmune signaling, neuroprotection, and neuroinflammation. In the healthy CNS, microglia adopt a surveillant and antiinflammatory phenotype characterized by a ramified scanning morphology that maintains CNS homeostasis. In response to acquired insults, such as traumatic brain injury (TBI) or spinal cord injury (SCI), microglia undergo a dramatic morphologic and functional switch to that of a reactive state. This microglial switch is initially protective and supports the return of the injured tissue to a physiologic homeostatic state. However, there is now a significant body of evidence that both TBI and SCI can result in a chronic state of microglial activation, which contributes to neurodegeneration and impairments in long-term neurologic outcomes in humans and animal models. In this review, we discuss the complex role of microglia in the pathophysiology of TBI and SCI, and recent advancements in knowledge of microglial phenotypic states in the injured CNS. Furthermore, we highlight novel therapeutic strategies targeting chronic microglial responses in experimental models and discuss how they may ultimately be translated to the clinic for human brain and SCI.

Protective Effects of Mdivi-1 on Cognition Disturbance Following Sepsis in Mice via Alleviating Microglia Activation and Polarization

BACKGROUND

Neuroinflammation is one of the essential pathogeneses of cognitive damage suffering from sepsis-associated encephalopathy (SAE). Lots of evidences showed the microglia presented mitochondrial fragmentation during SAE. This study investigated the protective effects and novel mechanisms of inhibiting microglia mitochondrial fragmentation via mitochondrial division inhibitor 1 (Mdivi-1) on cognitive damage in SAE.

METHODS

The SAE model was performed by cecal ligation and puncture (CLP), and Mdivi-1 was administrated via intraperitoneal injection. Morris water maze was performed to assess cognitive function. Mitochondrial morphology was observed by electron microscope or MitoTracker staining. The qRT-PCR, immunofluorescence staining, and western blots were used to detect the inflammatory factors and protein content, respectively. Flow cytometry was used to detect the polarization of hippocampal microglia. Bioinformatics analysis was used to verify hypotheses.

RESULTS

Mdivi-1 administration alleviated sepsis-induced mitochondrial fragmentation, microglia activation, polarization, and cognitive damage. The mechanisms study showed neuroinflammation and oxidative stress were suppressed via NF-κB and Keap1/Nrf2/HO-1 pathways following Mdivi-1 administration; meanwhile, pyroptosis in microglia was reduced, which was associated with enhanced autophagosome formation via p62 elevation following Mdivi-1 administration.

CONCLUSION

Inhibition of microglia mitochondrial fragmentation is beneficial to SAE cognitive disturbance, the mechanisms are related to alleviating neuroinflammation, oxidative stress, and pyroptosis.

Progress of Chinese Medicine in Regulating Microglial Polarization against Alzheimer's Disease

Alzheimer's disease (AD), the predominant form of dementia, is a neurodegenerative disorder of the central nervous system (CNS) characterized by a subtle onset and a spectrum of cognitive and functional declines. The clinical manifestation of AD encompasses memory deficits, cognitive deterioration, and behavioral disturbances, culminating in a severe impairment of daily living skills. Despite its high prevalence, accounting for 60-70% of all dementia cases, there remains an absence of curative therapeutics. Microglia (MG), the resident immune cells of the CNS, exhibit a bifurcated role in AD pathogenesis. Functioning in a neuroprotective capacity, MGs express scavenger receptors, facilitating the clearance of [Formula: see text]-amyloid protein (A[Formula: see text]) and cellular debris. Conversely, aberrant activation of MGs can lead to the secretion of pro-inflammatory cytokines, thereby propagating neuroinflammatory responses that are detrimental to neuronal integrity. The dynamics of MG activation and the ensuing neuroinflammation are pivotal in the evolution of AD. Chinese medicine (CM), a treasure trove of traditional Chinese cultural practices, has demonstrated significant potential in the therapeutic management of AD. Over the past triennium, CM has garnered considerable research attention for its multifaceted approaches to AD, including the regulation of MG polarization. This review synthesizes current knowledge on the origins, polarization dynamics, and mechanistic interplay of MG with AD pathology. It further explores the nexus between MG polarization and cardinal pathological hallmarks of AD, such as A[Formula: see text] plaque deposition, hyperphosphorylation of tau, synaptic plasticity impairments, neuroinflammation, and brain-gut-axis dysregulation. The review also encapsulates the therapeutic strategies of CM, which encompass monomers, formulae, and acupuncture. These strategies modulate MG polarization in the context of AD treatment, thereby providing a robust theoretical framework in which to conduct future investigative endeavors in both the clinical and preclinical realms.

The Role of Endothelial L-PGDS in the Pro-Angiogenic and Anti-Inflammatory Effects of Low-Dose Alcohol Consumption

Light alcohol consumption (LAC) may reduce the incidence and improve the prognosis of ischemic stroke. Recently, we found that LAC promotes cerebral angiogenesis and inhibits early inflammation following ischemic stroke. In addition, LAC upregulates lipocalin-type prostaglandin D2 synthase (L-PGDS) in the brain. Thus, we determined the role of endothelial L-PGDS in the protective effect of LAC. In in vitro studies, chronic exposure to low-concentration ethanol upregulated L-PGDS and significantly increased the proliferation in cultured C57BL/6J mouse brain microvascular endothelial cells (MBMVECs). AT-56, a selective L-PGDS inhibitor, abolished low-concentration ethanol exposure-induced proliferation. In in vivo studies, 8-week gavage feeding with 0.7 g/kg/day ethanol, defined as LAC, promoted cerebral angiogenesis under physiological conditions and following ischemic stroke in male C57BL/6J mice. In addition, LAC inhibited the post-ischemic expression of adhesion molecules, neutrophil infiltration, and microglial activation. AT-56 and endothelial cell (EC)-specific L-PGDS conditional knockout did not significantly alter cerebral angiogenesis and post-ischemic inflammation in the control mice but eliminated the pro-angiogenic and anti-inflammatory effects of LAC. Furthermore, EC-specific L-PGDS conditional knockout alleviated the neuroprotective effect of LAC against cerebral ischemia/reperfusion injury. These findings suggest that endothelial L-PGDS may be crucial in the pro-angiogenic and anti-inflammatory effects of LAC against ischemic stroke.

Forget me not: The effect of doxycycline on human declarative memory

Investigations into neuroprotective drugs are in high demand for the treatment of neurodegenerative diseases, such as multiple sclerosis or Alzheimer's disease, but also psychiatric disorders, such as depression, trauma, and substance use. One potential drug class being investigated are tetracyclines impacting on a variety of neuroprotective mechanisms. At the same time, tetracyclines like doxycycline have been suggested to affect human fear and spatial memory as well as reducing declarative memory retention. Based on the assumed necessity for synaptic consolidation in hippocampus-dependent learning, we hypothesised declarative memory may be similarly impaired by doxycycline as fear and spatial memory. Therefore, in this study we investigate the potential diminishing effects of doxycycline on consolidation of declarative memory in healthy humans. Additionally, to test for effect specificity we assessed motor memory, sustained attention, and processing speed. We administered a neuropsychological test battery in three independent randomized placebo-controlled double-blind trials (RCTs), in which healthy young volunteers (total N = 252) either received a single oral dose doxycycline (200 mg, n = 126) or placebo (n = 126) in a between-subject design. We found no evidence for a detrimental effect of doxycycline on declarative memory; instead, doxycycline improved declarative learning (p-value=0.022, Cohen's d=0.15) and memory consolidation (p=0.040, d=0.26). Contrarily, doxycycline slightly reduced motor learning (p=0.001, d=0.10) but subtly strengthened long-term motor memory (p=0.001, d=0.10). These results suggest that doxycycline can improve declarative learning and memory without having long term negative effects on other cognitive domains in healthy humans. Our results give hope to further investigate doxycycline in neuroprotective treatment applications.

The Neuroimmune System and the Cerebellum

The recognition that there is an innate immune system of the brain, referred to as the neuroimmune system, that preforms many functions comparable to that of the peripheral immune system is a relatively new concept and much is yet to be learned. The main cellular components of the neuroimmune system are the glial cells of the brain, primarily microglia and astrocytes. These cell types preform many functions through secretion of signaling factors initially known as immune factors but referred to as neuroimmune factors when produced by cells of the brain. The immune functions of glial cells play critical roles in the healthy brain to maintain homeostasis that is essential for normal brain function, to establish cytoarchitecture of the brain during development, and, in pathological conditions, to minimize the detrimental effects of disease and injury and promote repair of brain structure and function. However, dysregulation of this system can occur resulting in actions that exacerbate or perpetuate the detrimental effects of disease or injury. The neuroimmune system extends throughout all brain regions, but attention to the cerebellar system has lagged that of other brain regions and information is limited on this topic. This article is meant to provide a brief introduction to the cellular and molecular components of the brain immune system, its functions, and what is known about its role in the cerebellum. The majority of this information comes from studies of animal models and pathological conditions, where upregulation of the system facilitates investigation of its actions.

An Amino Acids and Dipeptide Injection Inhibits the TNF-α/HMGB1 Inflammatory Signaling Pathway to Reduce Pyroptosis and M1 Microglial Polarization in POCD Mice: the Gut to the Brain

Peripheral surgery-induced neural inflammation is a key pathogenic mechanism of postoperative cognitive dysfunction (POCD). However, the mechanism underlying neuroinflammation and associated neural injury remains elusive. Surgery itself can lead to gut damage, and the occurrence of POCD is accompanied by high levels of TNF-α in the serum and blood‒brain barrier (BBB) damage. Reductions in stress, inflammation and protein loss have been emphasized as strategies for enhanced recovery after surgery (ERAS). We designed an amino acids and dipeptide (AAD) formula for injection that could provide intestinal protection during surgery. Through the intraoperative infusion of AAD based on the ERAS concept, we aimed to explore the effect of AAD injection on POCD and its underlying mechanism from the gut to the brain. Here, we observed that AAD injection ameliorated neural injury in POCD, in addition to restoring the function of the intestinal barrier and BBB. We also found that TNF-α levels decreased in the ileum, blood and hippocampus. Intestinal barrier protectors and TNF-α inhibitors also alleviated neural damage. AAD injection treatment decreased HMGB1 production, pyroptosis, and M1 microglial polarization and increased M2 polarization. In vitro, AAD injection protected the impaired gut barrier and decreased TNF-α production, alleviating damage to the BBB by stimulating cytokine transport in the body. HMGB1 and Caspase-1 inhibitors decreased pyroptosis and M1 microglial polarization and increased M2 polarization to protect TNF-α-stimulated microglia in vitro. Collectively, these findings suggest that the gut barrier-TNF-α-BBB-HMGB1-Caspase-1 inflammasome-pyroptosis-M1 microglia pathway is a novel mechanism of POCD related to the gut-brain axis and that intraoperative AAD infusion is a potential treatment for POCD.

Transcriptomic evidence of black soybean ethanolic extract and 2-aminobutyric acid in suppressing neuroinflammation and enhancing synaptic transmission

INTRODUCTION

Recently, the awareness of the beneficial utilization of natural bioactive compounds in treating neuroinflammation has gained particular attention. We aimed to understand the anti-neuroinflammatory effect of black soybeans (Glycine max (L.) Merr) ethanolic extract (BBEE) and its bioactive compound, 2-aminobutyric acid (2-AB), against LPS-induced SH-SY5Y cells.

METHOD

Cell viability and the optimum therapeutic dose were confirmed by MTT assay. We conducted a whole-transcriptomic analysis of BBEE and 2-AB in LPS-induced SH-SY5Y cells using microarray normalized with SST-RMA. DEGs were selected based on p-value < 0.05 and fold change > 2, and validated by RT-qPCR and immunocytochemical analyses.

RESULTS

We found that both BBEE and 2-AB down-regulated the expression of inflammatory cytokines IL6 and TNFA under LPS-induced conditions. This was also observed in the microarray data, showing downregulation of several inflammatory pathways, such as NF-kB, and IL6-JAK/STAT3-signaling pathways. In contrast, it upregulated the expression of CALML3, GRIN2, and GRIA2 gene expressions, which influence the AMPK and CAMK2 signaling pathways, indicating the potential of BBEE in neurotransmission and synaptic function. Also, immunofluorescence analysis revealed that 2-AB treatment significantly increased PSD-95 and Ca2+ levels, suggesting its effect on synaptic transmission essential for brain function.

CONCLUSION

Our findings suggest the potential anti-neuroinflammatory effects of BBEE and 2-AB, which may offer therapeutic and preventive benefits in mitigating neurological disorders. Given that BB is widely consumed in many Asian countries, our study may encourage its incorporation into the daily diet to slow inflammation-induced neurodegenerative disorders, reduce age-related cognitive decline, and enhance overall brain function.

Berberine modulates microglial polarization by activating TYROBP in Alzheimer's disease

BACKGROUND

Characterized by β-amyloid (Aβ) plaques, neurofibrillary tangles, and aberrant neuroinflammation in the brain, Alzheimer's disease (AD) is the most common neurodegenerative disease. Microglial polarization is a subtle mechanism which maintains immunological homeostasis and has emerged as a putative therapeutic to combat AD. Berberine (BBR) is a natural alkaloid compound with multiple pharmacological effects, and has shown considerable therapeutic potential against inflammatory disorders. However, BBR functions and underlying mechanisms in neuroinflammation remain unclear.

PURPOSE

To examine BBR pharmacological effects and mechanisms in neuroinflammation with a view to treating AD.

METHODS

BBR effects on cognitive performance in 5 × FAD mice were assessed using open field, Y-maze, and Morris Water Maze (MWM) tests. Neuroinflammation-related markers and Aβ pathology were examined in brain sections from mice. Transcriptomic analyses of hippocampus tissues were also conducted. Microglial BV2 cells were also used to verify potential BBR mechanisms in neuroinflammation and microglial polarization.

RESULTS

BBR improved cognitive performance, reduced amyloid pathology, and alleviated aberrant neuroinflammation in an AD mouse model. BBR induced microglial polarization to an M2-like phenotype, which was manifested by lowered and elevated proinflammatory and anti-inflammatory cytokine production, respectively, improved microglial uptake and Aβ clearance. Mechanistically, BBR directly interacted with TYROBP and promoted its activation by stabilizing TYROBP oligomerization. TYROBP knockdown aggravated M1-like polarization and pro-inflammatory gene expression in microglial cells in the presence of lipopolysaccharide (LPS)+Aβ, while blocked microglial M2-like polarization benefited from BBR administration.

CONCLUSIONS

BBR modulated neuroinflammation by regulating microglial polarization via TYROBP activation. Our study provided new insight into BBR pharmacological actions in regulating microglial homeostasis and combating AD.

Siglecs-mediated immune regulation in neurological disorders

The surfaces of various immune cells are rich in glycan chains, including the sialic-acid-binding immunoglobulin-like lectins (Siglecs) family. As an emerging glyco-immune checkpoint, Siglecs have the ability to bind and interact with various glycoproteins, thereby eliciting a series of downstream reactions to modulate the immune response. The impact of Siglecs has been extensively studied in tumor immunotherapy. However, research in neurological disorders and neurological diseases is very limited, and therapeutic options involving Siglecs need further exploration. Siglecs play a crucial role in the development, homeostasis, and repair processes of the nervous system, especially in degenerative diseases. This review summarizes studies on the immunomodulatory role mediated by Siglecs expressed on different immune cells in various neurological disorders, elucidates how dysregulated sialic acid contributes to several psychiatric disorders, and discusses the progress and limitations of research on the treatment of neurological disorders.

Potential key pathophysiological participant and treatment target in autism spectrum disorder: Microglia

Autism spectrum disorder (ASD) is a group of neurodevelopmental disorders characterized by social and communication deficits, as well as restricted or repetitive behaviors or interests. Although the etiology of ASD remains unclear, there is abundant evidence suggesting that microglial dysfunction is likely to be a significant factor in the pathophysiology of ASD. Microglia, the primary innate immune cells in the central nervous system (CNS), play a crucial role in brain development and homeostasis. Recently, numerous studies have shown that microglia in ASD models display various abnormalities including morphology, function, cellular interactions, genetic and epigenetic factors, as well as the expression of receptors, transcription factors, and cytokines. They impact normal neural development through various mechanisms contributing to ASD, such as neuroinflammation, and alterations in synaptic formation and pruning. The focus of this review is on recent studies regarding microglial abnormalities in ASD and their effects on the onset and progression of ASD at both cellular and molecular levels. It can provide insight into the specific contribution of microglia to ASD pathogenesis and help in designing potential therapeutic and preventative strategies targeting microglia.

Microglial depletion rescues spatial memory impairment caused by LPS administration in adult mice

Recent studies have highlighted the importance of microglia, the resident macrophages in the brain, in regulating cognitive functions such as learning and memory in both healthy and diseased states. However, there are conflicting results and the underlying mechanisms are not fully understood. In this study, we examined the effect of depleting adult microglia on spatial learning and memory under both physiological conditions and lipopolysaccharide (LPS)-induced neuroinflammation. Our results revealed that microglial depletion by PLX5622 caused mild spatial memory impairment in mice under physiological conditions; however, it prevented memory deficits induced by systemic LPS insult. Inactivating microglia through minocycline administration replicated the protective effect of microglial depletion on LPS-induced memory impairment. Furthermore, our study showed that PLX5622 treatment suppressed LPS-induced neuroinflammation, microglial activation, and synaptic dysfunction. These results strengthen the evidence for the involvement of microglial immunoactivation in LPS-induced synaptic and cognitive malfunctions. They also suggest that targeting microglia may be a potential approach to treating neuroinflammation-associated cognitive dysfunction seen in neurodegenerative diseases.

Oral administration of Porphyromonas gingivalis to mice with diet-induced obesity impairs cognitive function associated with microglial activation in the brain

Objective

Both periodontal disease and obesity are risk factors for dementia, but their links to 1brain function remain unclear. In this study, we examined the effects of oral infection with a periodontal pathogen on cognitive function in a mouse model of obesity, focusing on the roles of microglia.

Methods

To create a mouse model of diet-induced obesity and periodontitis, male C57BL/6 J mice were first fed a high-fat diet containing 60% lipid calories for 18 weeks, beginning at 12 weeks of age, to achieve diet-induced obesity. Then, Porphyromonas gingivalis administration in the oral cavity twice weekly for 6 weeks was performed to induce periodontitis in obese mice.

Results

Obese mice orally exposed to P. gingivalis showed cognitive impairment in the novel object recognition test. Increased expression levels of inflammatory cytokines (e.g. interleukin-1β and tumor necrosis factor-α) were observed in the hippocampus of P. gingivalis-treated obese mice. Immunohistochemical analysis revealed that microglia cell body size was increased in the hippocampus and prefrontal cortex of P. gingivalis-treated obese mice, indicating microglial activation. Furthermore, depletion of microglia by PLX3397, a colony-stimulating factor 1 receptor inhibitor, ameliorated cognitive dysfunction.

Conclusion

These results suggest that microglia mediate periodontal infection-induced cognitive dysfunction in obesity.