Telencephalon Organoids Derived from an Individual with ADHD Show Altered Neurodevelopment of Early Cortical Layer Structure.

Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder that occurs in early childhood and can persist to adulthood. It can affect many aspects of a patient's daily life, so it is necessary to explore the mechanism and pathological alterations. For this purpose, we applied induced pluripotent stem cell (iPSC)-derived telencephalon organoids to recapitulate the alterations occurring in the early cerebral cortex of ADHD patients. We found that telencephalon organoids of ADHD showed less growth of layer structures than control-derived organoids. On day 35 of differentiation, the thinner cortex layer structures of ADHD-derived organoids contained more neurons than those of control-derived organoids. Furthermore, ADHD-derived organoids showed a decrease in cell proliferation during development from day 35 to 56. On day 56 of differentiation, there was a significant difference in the proportion of symmetric and asymmetric cell division between the ADHD and control groups. In addition, we observed increased cell apoptosis in ADHD during early development. These results show alterations in the characteristics of neural stem cells and the formation of layer structures, which might indicate key roles in the pathogenesis of ADHD. Our organoids exhibit the cortical developmental alterations observed in neuroimaging studies, providing an experimental foundation for understanding the pathological mechanisms of ADHD.

Transcriptomic Crosstalk between Gliomas and Telencephalic Neural Stem and Progenitor Cells for Defining Heterogeneity and Targeted Signaling Pathways.

Recent studies have begun to reveal surprising levels of cell diversity in the human brain, both in adults and during development. Distinctive cellular phenotypes point to complex molecular profiles, cellular hierarchies and signaling pathways in neural stem cells, progenitor cells, neuronal and glial cells. Several recent reports have suggested that neural stem and progenitor cell types found in the developing and adult brain share several properties and phenotypes with cells from brain primary tumors, such as gliomas. This transcriptomic crosstalk may help us to better understand the cell hierarchies and signaling pathways in both gliomas and the normal brain, and, by clarifying the phenotypes of cells at the origin of the tumor, to therapeutically address their most relevant signaling pathways.

Diversity and function of motile ciliated cell types within ependymal lineages of the zebrafish brain.

Motile cilia defects impair cerebrospinal fluid (CSF) flow and can cause brain and spine disorders. The development of ciliated cells, their impact on CSF flow, and their function in brain and axial morphogenesis are not fully understood. We have characterized motile ciliated cells within the zebrafish brain ventricles. We show that the ventricles undergo restructuring through development, involving a transition from mono- to multiciliated cells (MCCs) driven by gmnc. MCCs co-exist with monociliated cells and generate directional flow patterns. These ciliated cells have different developmental origins and are genetically heterogenous with respect to expression of the Foxj1 family of ciliary master regulators. Finally, we show that cilia loss from the tela choroida and choroid plexus or global perturbation of multiciliation does not affect overall brain or spine morphogenesis but results in enlarged ventricles. Our findings establish that motile ciliated cells are generated by complementary and sequential transcriptional programs to support ventricular development.

Neuron-Radial Glial Cell Communication via BMP/Id1 Signaling Is Key to Long-Term Maintenance of the Regenerative Capacity of the Adult Zebrafish Telencephalon.

The central nervous system of adult zebrafish displays an extraordinary neurogenic and regenerative capacity. In the zebrafish adult brain, this regenerative capacity relies on neural stem cells (NSCs) and the careful management of the NSC pool. However, the mechanisms controlling NSC pool maintenance are not yet fully understood. Recently, Bone Morphogenetic Proteins (BMPs) and their downstream effector Id1 (Inhibitor of differentiation 1) were suggested to act as key players in NSC maintenance under constitutive and regenerative conditions. Here, we further investigated the role of BMP/Id1 signaling in these processes, using different genetic and pharmacological approaches. Our data show that BMPs are mainly expressed by neurons in the adult telencephalon, while id1 is expressed in NSCs, suggesting a neuron-NSC communication via the BMP/Id1 signaling axis. Furthermore, manipulation of BMP signaling by conditionally inducing or repressing BMP signaling via heat-shock, lead to an increase or a decrease of id1 expression in the NSCs, respectively. Induction of id1 was followed by an increase in the number of quiescent NSCs, while knocking down id1 expression caused an increase in NSC proliferation. In agreement, genetic ablation of id1 function lead to increased proliferation of NSCs, followed by depletion of the stem cell pool with concomitant failure to heal injuries in repeatedly injured mutant telencephala. Moreover, pharmacological inhibition of BMP and Notch signaling suggests that the two signaling systems cooperate and converge onto the transcriptional regulator her4.1. Interestingly, brain injury lead to a depletion of NSCs in animals lacking BMP/Id1 signaling despite an intact Notch pathway. Taken together, our data demonstrate how neurons feedback on NSC proliferation and that BMP1/Id1 signaling acts as a safeguard of the NSC pool under regenerative conditions.

Developmental Differences Between the Limbic and Neocortical Telencephalic Wall: An Intrasubject Slice-Matched 3 T MRI-Histological Correlative Study in Humans.

The purpose of the study was to investigate the interrelation of the signal intensities and thicknesses of the transient developmental zones in the cingulate and neocortical telencephalic wall, using T2-weighted 3 T-magnetic resonance imaging (MRI) and histological scans from the same brain hemisphere. The study encompassed 24 postmortem fetal brains (15-35 postconceptional weeks, PCW). The measurements were performed using Fiji and NDP.view2. We found that T2w MR signal-intensity curves show a specific regional and developmental stage profile already at 15 PCW. The MRI-histological correlation reveals that the subventricular-intermediate zone (SVZ-IZ) contributes the most to the regional differences in the MRI-profile and zone thicknesses, growing by a factor of 2.01 in the cingulate, and 1.78 in the neocortical wall. The interrelations of zone or wall thicknesses, obtained by both methods, disclose a different rate and extent of shrinkage per region (highest in neocortical subplate and SVZ-IZ) and stage (highest in the early second half of fetal development), distorting the zones' proportion in histological sections. This intrasubject, slice-matched, 3 T correlative MRI-histological study provides important information about regional development of the cortical wall, critical for the design of MRI criteria for prenatal brain monitoring and early detection of cortical or other brain pathologies in human fetuses.

Loss-of-function of p53 isoform Δ113p53 accelerates brain aging in zebrafish.

Reactive oxygen species (ROS) stress has been demonstrated as potentially critical for induction and maintenance of cellular senescence, and been considered as a contributing factor in aging and in various neurological disorders including Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS). In response to low-level ROS stress, the expression of Δ133p53, a human p53 isoform, is upregulated to promote cell survival and protect cells from senescence by enhancing the expression of antioxidant genes. In normal conditions, the basal expression of Δ133p53 prevents human fibroblasts, T lymphocytes, and astrocytes from replicative senescence. It has been also found that brain tissues from AD and ALS patients showed decreased Δ133p53 expression. However, it is uncharacterized if Δ133p53 plays a role in brain aging. Here, we report that zebrafish Δ113p53, an ortholog of human Δ133p53, mainly expressed in some of the radial glial cells along the telencephalon ventricular zone in a full-length p53-dependent manner. EDU-labeling and cell lineage tracing showed that Δ113p53-positive cells underwent cell proliferation to contribute to the neuron renewal process. Importantly, Δ113p53M/M mutant telencephalon possessed less proliferation cells and more senescent cells compared to wild-type (WT) zebrafish telencephalon since 9-months old, which was associated with decreased antioxidant genes expression and increased level of ROS in the mutant telencephalon. More interestingly, unlike the mutant fish at 5-months old with cognition ability, Δ113p53M/M zebrafish, but not WT zebrafish, lost their learning and memory ability at 19-months old. The results demonstrate that Δ113p53 protects the brain from aging by its antioxidant function. Our finding provides evidence at the organism level to show that depletion of Δ113p53/Δ133p53 may result in long-term ROS stress, and finally lead to age-related diseases, such as AD and ALS in humans.

Isoliquiritin exert protective effect on telencephalon infarction injury by regulating multi-pathways in zebrafish model of ischemic stroke.

BACKGROUND: Ischemic stroke is a multifactorial disease contributing to mortality and neurological dysfunction. Isoliquiritin (ISL) has been reported to possess a series of pharmacological activities including antioxidant, anti-inflammatory, antifungal, anti-depression, anti-neurotoxicity and pro-angiogenesis activities but whether it can be used for ischemic stroke treatment remains unknown. PURPOSE: The goal of this study is to explore its therapeutic effect on ischemic stroke and demonstrated the potential mechanism of ISL in zebrafish model. METHODS: Using the photothrombotic-induced adult zebrafish model of ischemic stroke, we visualized the telencephalon (Tel) and optic tectum (OT) infarction injury at 24 h post-light exposure for 30 min by TTC and H&E staining. The effect of ISL on neurological deficits was analyzed during open tank swimming by video tracking. The antioxidant activity against ischemia injury was quantified by SOD, GSH-Px and MDA assay. Transcriptome analysis of zebrafish Tel revealed how ISL regulating gene expression to exert protective effect, which were also been validated by real-time quantitative PCR assays. RESULTS: We found for the first time that the Tel tissue was the first damaged site of the whole brain and it showed more sensitivity to the brain ischemic damage compared to the OT. ISL reduced the rate of Tel injury, ameliorated neurological deficits as well as counteracted oxidative damages by increasing SOD, GSH-Px and decreasing MDA activity. GO enrichment demonstrated that ISL protected membrane and membrane function as well as initiate immune regulation in the stress response after ischemia. KEGG pathway analysis pointed out that immune-related pathways, apoptosis as well as necroptosis pathways were more involved in the protective mechanism of ISL. Furthermore, the log2 fold change in expression pattern of 25 genes detected by qRT-PCR was consistent with that by RNA-seq. CONCLUSIONS: Tel was highly sensitive to the brain ischemia injury in zebrafish model of ischemic stroke. ISL significantly exerted protective effect on Tel injury, neurological deficits and oxidative damages. ISL could regulate a variety of genes related to immune, apoptosis and necrosis pathways against complex cascade reaction after ischemia. These findings enriched the study of ISL, making it a novel multi-target agent for ischemic stroke treatment.

Mechanical Brain Injury Increases Cells' Production of Cystathionine ß-Synthase and Glutamine Synthetase, but Reduces Pax2 Expression in the Telencephalon of Juvenile Chum Salmon, Oncorhynchus keta.

The considerable post-traumatic brain recovery in fishes makes them a useful model for studying the mechanisms that provide reparative neurogenesis, which is poorly represented in mammals. After a mechanical injury to the telencephalon in adult fish, lost neurons are actively replaced due to the proliferative activity of neuroepithelial cells and radial glia in the neurogenic periventricular zone. However, it is not enough clear which signaling mechanisms are involved in the activation of adult neural stem cells (aNSC) after the injury (reactive proliferation) and in the production of new neurons (regenerative neurogenesis) from progenitor cells (NPC). In juvenile Pacific salmon, the predominant type of NSCs in the telencephalon are neuroepithelial cells corresponding to embryonic NSCs. Expression of glutamine synthetase (GS), a NSC molecular marker, was detected in the neuroepithelial cells of the pallium and subpallium of juvenile chum salmon, Oncorhynchus keta. At 3 days after a traumatic brain injury (TBI) in juvenile chum salmon, the GS expression was detected in the radial glia corresponding to aNSC in the pallium and subpallium. The maximum density of distribution of GS+ radial glia was found in the dorsal pallial region. Hydrogen sulfide (H2S) is a proneurogenic factor that reduces oxidative stress and excitotoxicity effects, along with the increased GS production in the brain cells of juvenile chum salmon. In the fish brain, H2S producing by cystathionine ß-synthase in neurogenic zones may be involved in maintaining the microenvironment that provides optimal conditions for the functioning of neurogenic niches during constitutive neurogenesis. After injury, H2S can determine cell survivability, providing a neuroprotective effect in the area of injury and reducing the process of glutamate excitotoxicity, acting as a signaling molecule involved in changing the neurogenic environment, which leads to the reactivation of neurogenic niches and cell regeneration programs. The results of studies on the control of the expression of regulatory Sonic Hedgehog genes (Shh) and the transcription factors Paired Box2 (Pax2) regulated by them are still insufficient. A comparative analysis of Pax2 expression in the telencephalon of intact chum salmon showed the presence of constitutive patterns of Pax2 expression in neurogenic areas and non-neurogenic parenchymal zones of the pallium and subpallium. After mechanical injury, the patterns of Pax2 expression changed, and the amount of Pax2+ decreased (p < 0.05) in lateral (Dl), medial (Dm) zones of the pallium, and the lateral zone (Vl) of the subpallium compared to the control. We believe that the decrease in the expression of Pax2 may be caused by the inhibitory effect of the Pax6 transcription factor, whose expression in the juvenile salmon brain increases upon injury.

Tetrabromobisphenol A Disturbs Brain Development in Both Thyroid Hormone-Dependent and -Independent Manners in Xenopus laevis.

Although tetrabromobisphenol A (TBBPA) has been well proven to disturb TH signaling in both in vitro and in vivo assays, it is still unclear whether TBBPA can affect brain development due to TH signaling disruption. Here, we employed the T3-induced Xenopus metamorphosis assay (TIXMA) and the spontaneous metamorphosis assay to address this issue. In the TIXMA, 5-500 nmol/L TBBPA affected T3-induced TH-response gene expression and T3-induced brain development (brain morphological changes, cell proliferation, and neurodifferentiation) at premetamorphic stages in a complicated biphasic concentration-response manner. Notably, 500 nmol/L TBBPA treatment alone exerted a stimulatory effect on tadpole growth and brain development at these stages, in parallel with a lack of TH signaling activation, suggesting the involvement of other signaling pathways. As expected, at the metamorphic climax, we observed inhibitory effects of 50-500 nmol/L TBBPA on metamorphic development and brain development, which was in agreement with the antagonistic effects of higher concentrations on T3-induced brain development at premetamorphic stages. Taken together, all results demonstrate that TBBPA can disturb TH signaling and subsequently interfere with TH-dependent brain development in Xenopus; meanwhile, other signaling pathways besides TH signaling could be involved in this process. Our study improves the understanding of the effects of TBBPA on vertebrate brain development.

The role of lipids in ependymal development and the modulation of adult neural stem cell function during aging and disease.

Within the adult mammalian central nervous system, the ventricular-subventricular zone (V-SVZ) lining the lateral ventricles houses neural stem cells (NSCs) that continue to produce neurons throughout life. Developmentally, the V-SVZ neurogenic niche arises during corticogenesis following the terminal differentiation of telencephalic radial glial cells (RGCs) into either adult neural stem cells (aNSCs) or ependymal cells. In mice, these two cellular populations form rosettes during the late embryonic and early postnatal period, with ependymal cells surrounding aNSCs. These aNSCs and ependymal cells serve a number of key purposes, including the generation of neurons throughout life (aNSCs), and acting as a barrier between the CSF and the parenchyma and promoting CSF bulk flow (ependymal cells). Interestingly, the development of this neurogenic niche, as well as its ongoing function, has been shown to be reliant on different aspects of lipid biology. In this review we discuss the developmental origins of the rodent V-SVZ neurogenic niche, and highlight research which has implicated a role for lipids in the physiology of this part of the brain. We also discuss the role of lipids in the maintenance of the V-SVZ niche, and discuss new research which has suggested that alterations to lipid biology could contribute to ependymal cell dysfunction in aging and disease.

Prenatal alcohol exposure is a leading cause of interneuronopathy in humans.

Alcohol affects multiple neurotransmitter systems, notably the GABAergic system and has been recognised for a long time as particularly damaging during critical stages of brain development. Nevertheless, data from the literature are most often derived from animal or in vitro models. In order to study the production, migration and cortical density disturbances of GABAergic interneurons upon prenatal alcohol exposure, we performed immunohistochemical studies by means of the proliferation marker Ki67, GABA and calretinin antibodies in the frontal cortical plate of 17 foetal and infant brains antenatally exposed to alcohol, aged 15 weeks' gestation to 22 postnatal months and in the ganglionic eminences and the subventricular zone of the dorsal telencephalon until their regression, i.e., 34 weeks' gestation. Results were compared with those obtained in 17 control brains aged 14 weeks of gestation to 35 postnatal months. We also focused on interneuron vascular migration along the cortical microvessels by confocal microscopy with double immunolabellings using Glut1, GABA and calretinin. Semi-quantitative and quantitative analyses of GABAergic and calretininergic interneuron density allowed us to identify an insufficient and delayed production of GABAergic interneurons in the ganglionic eminences during the two first trimesters of the pregnancy and a delayed incorporation into the laminar structures of the frontal cortex. Moreover, a mispositioning of GABAergic and calretininergic interneurons persisted throughout the foetal life, these cells being located in the deep layers instead of the superficial layers II and III. Moreover, vascular migration of calretininergic interneurons within the cortical plate was impaired, as reflected by low numbers of interneurons observed close to the cortical perforating vessel walls that may in part explain their abnormal intracortical distribution. Our results are globally concordant with those previously obtained in mouse models, in which alcohol has been shown to induce an interneuronopathy by affecting interneuron density and positioning within the cortical plate, and which could account for the neurological disabilities observed in children with foetal alcohol disorder spectrum.

Adult neuronal regeneration in the telencephalon of the killifish Aphaniops hormuzensis.

The potential of central nervous system regeneration was evaluated for the first time in the injured brain of the old world killifish Aphaniops hormuzensis. The histomorphological organization in the regeneration procedure was evaluated using the hematoxylin and eosin (H&E) staining and the bromodeoxyuridine (BrdU) immunohistochemistry technique. The histological tissue sections were sampled daily for 10 days. Based on the H&E staining, a large gliosis reaction was detected along with vacuolization and telencephalon deformation on 1-day post-lesion (dpl). The vacuolated zone declined fast and the telencephalon hemisphere recovered on 3 dpl. The symptoms of injured telencephalon nervous tissue were resolved within 7 dpl in both genders. In the BrdU test of the control group, BrdU-labeled cells were observed in the ventricular zone (VZ), pallium (Pa), and lateral pallium (LPa). On 1 dpl, the BrdU+ cells accumulated in the VZ, Pa, and LPa (located near the injury area). From 3 dpl onwards, the BrdU+ cells were reduced in the telencephalic VZ, Pa, and LPa. Based on the BrdU+ results, the adult brain in A. hormuzensis possesses a remarkable capacity for neuronal regeneration. By taking into account the high neural regeneration potency of A. hormuzensis and its relatively short lifespan, it could be concluded that besides the currently known models, the members of aphaniid fishes could probably be valuable animals to study the regeneration phenomenon in the vertebrates.

DOT1L promotes progenitor proliferation and primes neuronal layer identity in the developing cerebral cortex.

Cortical development is controlled by transcriptional programs, which are orchestrated by transcription factors. Yet, stable inheritance of spatio-temporal activity of factors influencing cell fate and localization in different layers is only partly understood. Here we find that deletion of Dot1l in the murine telencephalon leads to cortical layering defects, indicating DOT1L activity and chromatin methylation at H3K79 impact on the cell cycle, and influence transcriptional programs conferring upper layer identity in early progenitors. Specifically, DOT1L prevents premature differentiation by increasing expression of genes that regulate asymmetric cell division (Vangl2, Cenpj). Loss of DOT1L results in reduced numbers of progenitors expressing genes including SoxB1 gene family members. Loss of DOT1L also leads to altered cortical distribution of deep layer neurons that express either TBR1, CTIP2 or SOX5, and less activation of transcriptional programs that are characteristic for upper layer neurons (Satb2, Pou3f3, Cux2, SoxC family members). Data from three different mouse models suggest that DOT1L balances transcriptional programs necessary for proper neuronal composition and distribution in the six cortical layers. Furthermore, because loss of DOT1L in the pre-neurogenic phase of development impairs specifically generation of SATB2-expressing upper layer neurons, our data suggest that DOT1L primes upper layer identity in cortical progenitors.

Glia maturation factor beta is required for reactive gliosis after traumatic brain injury in zebrafish.

Gliosis is a hallmark of neural pathology that occurs after most forms of central nervous system (CNS) injuries including traumatic brain injury (TBI). Identification of genes that control gliosis may provide novel treatment targets for patients with diverse CNS injuries. Glia maturation factor beta (GMFB) is crucial in brain development and stress response. In the present study, GMFB was found to be widely expressed in adult zebrafish telencephalon. A gmfb mutant zebrafish was created using CRISPR/cas9. In the uninjured zebrafish telencephalon, glial fibrillary acidic protein (GFAP) fibers in gmfb mutants were disorganized and shorter than wild type zebrafish. After TBI, transformation of quiescent type I radial glial cells (RGC) to proliferative type II RGCs was significantly suppressed in the gmfb mutant. RGC proliferation and hypertrophy post-TBI was reduced in gmfb mutants, indicating that reactive gliosis was attenuated. TBI-induced acute inflammation was also found to be alleviated in the gmfb mutant. Morphological changes also suggest attenuation of microglial reactive gliosis. In a mouse model of TBI, GMFB expression was increased around the injury site. These GMFB+ cells were identified as astrocytes and microglia. Taken together, the data suggests that GMFB is not only required for normal development of GFAP fibers in the zebrafish telencephalon, but also promotes reactive gliosis after TBI. Our findings provide novel information to help better understand the reactive gliosis process following TBI.

Hypoxia-Induced Neuroinflammation and Learning-Memory Impairments in Adult Zebrafish Are Suppressed by Glucosamine.

This study investigated changes in neuroinflammation and cognitive function in adult zebrafish exposed to acute hypoxia and protective effects of glucosamine (GlcN) against hypoxia-induced brain damage. The survival rate of zebrafish following exposure to hypoxia was improved by GlcN pretreatment. Moreover, hypoxia-induced upregulation of neuroglobin, NOS2α, glial fibrillary acidic protein, and S100ß in zebrafish was suppressed by GlcN. Hypoxia stimulated cell proliferation in the telencephalic ventral domain and in cerebellum subregions. GlcN decreased the number of bromodeoxyuridine (BrdU)-positive cells in the telencephalon region, but not in cerebellum regions. Transient motor neuron defects, assessed by measuring the locomotor and exploratory activity of zebrafish exposed to hypoxia recovered quickly. GlcN did not affect hypoxia-induced motor activity changes. In passive avoidance tests, hypoxia impaired learning and memory ability, deficits that were rescued by GlcN. A learning stimulus increased the nuclear translocation of phosphorylated cAMP response element binding protein (p-CREB), an effect that was greatly inhibited by hypoxia. GlcN restored nuclear p-CREB after a learning trial in hypoxia-exposed zebrafish. The neurotransmitters, γ-aminobutyric acid and glutamate, were increased after hypoxia in the zebrafish brain, and GlcN further increased their levels. In contrast, acetylcholine levels were reduced by hypoxia and restored by GlcN. Acetylcholinesterase inhibitor physostigmine partially reversed the impaired learning and memory of hypoxic zebrafish. This study represents the first examination of the molecular mechanisms underlying hypoxia-induced memory and learning defects in a zebrafish model. Our results further suggest that GlcN-associated hexosamine metabolic pathway could be an important therapeutic target for hypoxic brain damage.

Modeling consequences of prolonged strong unpredictable stress in zebrafish: Complex effects on behavior and physiology.

Chronic stress is the major pathogenetic factor of human anxiety and depression. Zebrafish (Danio rerio) have become a novel popular model species for neuroscience research and CNS drug discovery. The utility of zebrafish for mimicking human affective disorders is also rapidly growing. Here, we present a new zebrafish model of clinically relevant, prolonged unpredictable strong chronic stress (PUCS). The 5-week PUCS induced overt anxiety-like and motor retardation-like behaviors in adult zebrafish, also elevating whole-body cortisol and proinflammatory cytokines - interleukins IL-1ß and IL-6. PUCS also elevated whole-body levels of the anti-inflammatory cytokine IL-10 and increased the density of dendritic spines in zebrafish telencephalic neurons. Chronic treatment of fish with an antidepressant fluoxetine (0.1mg/L for 8days) normalized their behavioral and endocrine phenotypes, as well as corrected stress-elevated IL-1ß and IL-6 levels, similar to clinical and rodent data. The CNS expression of the bdnf gene, the two genes of its receptors (trkB, p75), and the gfap gene of glia biomarker, the glial fibrillary acidic protein, was unaltered in all three groups. However, PUCS elevated whole-body BDNF levels and the telencephalic dendritic spine density (which were corrected by fluoxetine), thereby somewhat differing from the effects of chronic stress in rodents. Together, these findings support zebrafish as a useful in-vivo model of chronic stress, also calling for further cross-species studies of both shared/overlapping and distinct neurobiological responses to chronic stress.

Neuronal expression of brain derived neurotrophic factor in the injured telencephalon of adult zebrafish.

The reparative ability of the central nervous system varies widely in the animal kingdom. In the mammalian brain, the regenerative mechanisms are very limited and newly formed neurons do not survive longer, probably due to a non-suitable local environment. On the opposite, fish can repair the brain after injury, with fast and complete recovery of damaged area. The brain of zebrafish, a teleost fish widely used as vertebrate model, also possesses high regenerative properties after injury. Taking advantage of this relevant model, the aim of the present study was to investigate the role of brain-derived neurotrophic factor (BDNF) in the regenerative ability of adult brain, after stab wound telencephalic injury. BDNF is involved in many brain functions and plays key roles in the repair process after traumatic brain lesions. It has been reported that BDNF strengthens the proliferative activity of neuronal precursor cells, facilitates the neuronal migration toward injured areas, and shows survival properties due to its anti-apoptotic effects. BDNF mRNA levels, assessed by quantitative PCR and in situ hybridization at 1, 4, 7, and 15 days after the lesion, were increased in the damaged telencephalon, mostly suddenly after the lesion. Double staining using in situ hybridization and immunocytochemistry revealed that BDNF mRNA was restricted to cells identified as mature neurons. BDNF mRNA expressing neurons mostly increased in the area around the lesion, showing a peak 1 day after the lesion. Taken together, these results highlight the role of BDNF in brain repair processes and reinforce the value of zebrafish for the study of regenerative neurogenesis.

Critical appraisal of pathology transmission in the α-synuclein fibril model of Lewy body disorders.

Lewy body disorders are characterized by the emergence of α-synucleinopathy in many parts of the central and peripheral nervous systems, including in the telencephalon. Dense α-synuclein+ pathology appears in regio inferior of the hippocampus in both Parkinson's disease and dementia with Lewy bodies and may disturb cognitive function. The preformed α-synuclein fibril model of Parkinson's disease is growing in use, given its potential for seeding the self-propagating spread of α-synucleinopathy throughout the mammalian brain. Although it is often assumed that the spread occurs through neuroanatomical connections, this is generally not examined vis-à-vis the uptake and transport of tract-tracers infused at precisely the same stereotaxic coordinates. As the neuronal connections of the hippocampus are historically well defined, we examined the first-order spread of α-synucleinopathy three months following fibril infusions centered in the mouse regio inferior (CA2+CA3), and contrasted this to retrograde and anterograde transport of the established tract-tracers FluoroGold and biotinylated dextran amines (BDA). Massive hippocampal α-synucleinopathy was insufficient to elicit memory deficits or loss of cells and synaptic markers in this model of early disease processes. However, dense α-synuclein+ inclusions in the fascia dentata were negatively correlated with memory capacity. A modest compensatory increase in synaptophysin was evident in the stratum radiatum of cornu Ammonis in fibril-infused animals, and synaptophysin expression correlated inversely with memory function in fibril but not PBS-infused mice. No changes in synapsin I/II expression were observed. The spread of α-synucleinopathy was somewhat, but not entirely consistent with FluoroGold and BDA axonal transport, suggesting that variables other than innervation density also contribute to the materialization of α-synucleinopathy. For example, layer II entorhinal neurons of the perforant pathway exhibited somal α-synuclein+ inclusions as well as retrogradely labeled FluoroGold+ somata. However, some afferent brain regions displayed dense retrograde FluoroGold label and no α-synuclein+ inclusions (e.g. medial septum/diagonal band), supporting the selective vulnerability hypothesis. The pattern of inclusions on the contralateral side was consistent with specific spread through commissural connections (e.g. stratum pyramidale of CA3), but again, not all commissural projections exhibited α-synucleinopathy (e.g. hilar mossy cells). The topographical extent of inclusions is displayed here in high-resolution images that afford viewers a rich opportunity to dissect the potential spread of pathology through neural circuitry. Finally, the results of this expository study were leveraged to highlight the challenges and limitations of working with preformed α-synuclein fibrils.

Somatic Mutations Activating the mTOR Pathway in Dorsal Telencephalic Progenitors Cause a Continuum of Cortical Dysplasias.

Focal cortical dysplasia (FCD) and hemimegalencephaly (HME) are epileptogenic neurodevelopmental malformations caused by mutations in mTOR pathway genes. Deep sequencing of these genes in FCD/HME brain tissue identified an etiology in 27 of 66 cases (41%). Radiographically indistinguishable lesions are caused by somatic activating mutations in AKT3, MTOR, and PIK3CA and germline loss-of-function mutations in DEPDC5, NPRL2, and TSC1/2, including TSC2 mutations in isolated HME demonstrating a "two-hit" model. Mutations in the same gene cause a disease continuum from FCD to HME to bilateral brain overgrowth, reflecting the progenitor cell and developmental time when the mutation occurred. Single-cell sequencing demonstrated mTOR activation in neurons in all lesions. Conditional Pik3ca activation in the mouse cortex showed that mTOR activation in excitatory neurons and glia, but not interneurons, is sufficient for abnormal cortical overgrowth. These data suggest that mTOR activation in dorsal telencephalic progenitors, in some cases specifically the excitatory neuron lineage, causes cortical dysplasia.

Main lesions in the central nervous system of dogs due to Leishmania infantum infection.

BACKGROUND: Canine visceral leishmaniasis (CVL) is endemic in São Luís Maranhão/Brazil and it leads a varied clinical picture, including neurological signs. RESULTS: Histopathological evaluation showed that 14 dogs exhibited pathological alterations in at least one of the analyzed areas. Of these, mononuclear inflammatory reaction was the most frequent, although other lesions, such as hemorrhage, chromatolysis and gliosis were also observed. The presence of L. infantum amastigotes was confirmed in eight dogs, identified in four regions: telencephalon, hippocampus, thalamus and caudal colliculus, but only one presented neurological signs. Polymerase chain reaction results detected the DNA of the parasite in 11 samples from seven dogs. The positive areas were the telencephalon, thalamus, hippocampus, cerebellum, caudal and rostral colliculus. CONCLUSION: These results reveal that during canine visceral leishmaniasis, the central nervous system may display some alterations, without necessarily exhibiting clinical neurological manifestations. In addition, the L. infantum parasite has the ability to cross the blood brain barrier and penetrate the central nervous system.