Human neuroblasts migrate to the olfactory bulb via a lateral ventricular extension

From mice to mind: Strategies and progress in translating neuroregeneration

Decisions about what experimental therapies are advanced to clinical trials are based almost exclusively on findings in preclinical animal studies. Over the past 30 years, animal models have forecast the success of hundreds of neuroprotective pharmacological therapies for stroke, Alzheimer׳s disease, spinal cord injury, traumatic brain injury and amyotrophic lateral sclerosis. Yet almost without exception, all have failed. Rapid advances in stem cell technologies have raised new hopes that these neurological diseases may one day be treatable. Still, how can neuroregenerative therapies be translated into clinical realities if available animal models are such poor surrogates of human disease? To address this question we discuss human and rodent neurogenesis, evaluate mechanisms of action for cellular therapies and describe progress in translating neuroregeneration to date. We conclude that not only are appropriate animal models critical to the development of safe and effective therapies, but that the multiple mechanisms of stem cell-mediated therapies may be particularly well suited to the mechanistically diverse nature of central nervous system diseases in mice and man.

Long Non-Coding RNA Expression during Aging in the Human Subependymal Zone

The human subependymal zone (SEZ) is debatably a source of newly born neurons throughout life and neurogenesis is a multi-step process requiring distinct transcripts during cell proliferation and early neuronal maturation, along with orchestrated changes in gene expression during cell state/fate transitions. Furthermore, it is becoming increasingly clear that the majority of our genome that results in production of non-protein-coding RNAs plays vital roles in the evolution, development, adaptation, and region-specific function of the human brain. We predicted that some transcripts expressed in the SEZ may be unique to this specialized brain region, and that a comprehensive transcriptomic analysis of this region would aid in defining expression changes during neuronal birth and growth in adult humans. Here, we used deep RNA sequencing of human SEZ tissue during adulthood and aging to characterize the transcriptional landscape with a particular emphasis on long non-coding RNAs (lncRNAs). The data show predicted age-related changes in mRNAs encoding proliferation, progenitor, and inflammatory proteins as well as a unique subset of lncRNAs that are highly expressed in the human SEZ, many of which have unknown functions. Our results suggest the existence of robust proliferative and neuronal differentiation potential in the adult human SEZ and lay the foundation for understanding the involvement of lncRNAs in postnatal neurogenesis and potentially associated neurodevelopmental diseases that emerge after birth.

Insulin and IGF receptor signalling in neural-stem-cell homeostasis

Neural stem cells (NSCs) are found in two regions in the adult brain: the subgranular zone (SGZ) in the hippocampal dentate gyrus and the subventricular zone (SVZ) adjacent to the lateral ventricles. Similarly to other somatic stem cells, adult NSCs are found within specialized niches that are organized to facilitate NSC self-renewal. Alterations in stem-cell homeostasis can contribute to the consequences of neurodegenerative diseases, healthy ageing and tissue repair after damage. Insulin and the insulin-like growth factors (IGFs) function in stem-cell homeostasis across species. Studies in the mammalian central nervous system support essential roles for IGF and/or insulin signalling in NSC self-renewal, neurogenesis, cognition and sensory function through distinct ligand-receptor interactions. IGF-II is of particular interest as a result of its production by the choroid plexus and presence in cerebrospinal fluid (CSF). CSF regulates and supports the development, division and migration of cells in the adult brain and is required for NSC maintenance. In this Review, we discuss emerging data on the functions of IGF-II and IGF and/or insulin receptor signalling in the context of NSC regulation in the SVZ and SGZ. We also propose a model for IGF-II in which the choroid plexus is a major component of the NSC niche.

The evidence for increased L1 activity in the site of human adult brain neurogenesis

Retroelement activity is a common source of polymorphisms in human genome. The mechanism whereby retroelements contribute to the intraindividual genetic heterogeneity by inserting into the DNA of somatic cells is gaining increasing attention. Brain tissues are suspected to accumulate genetic heterogeneity as a result of the retroelements somatic activity. This study aims to expand our understanding of the role retroelements play in generating somatic mosaicism of neural tissues. Whole-genome Alu and L1 profiling of genomic DNA extracted from the cerebellum, frontal cortex, subventricular zone, dentate gyrus, and the myocardium revealed hundreds of somatic insertions in each of the analyzed tissues. Interestingly, the highest concentration of such insertions was detected in the dentate gyrus—the hotspot of adult neurogenesis. Insertions of retroelements and their activity could produce genetically diverse neuronal subsets, which can be involved in hippocampal-dependent learning and memory.

Neural stem cells in Parkinson's disease: a role for neurogenesis defects in onset and progression

Parkinson's disease (PD) is the second most common neurodegenerative disorder, leading to a variety of motor and non-motor symptoms. Interestingly, non-motor symptoms often appear a decade or more before the first signs of motor symptoms. Some of these non-motor symptoms are remarkably similar to those observed in cases of impaired neurogenesis and several PD-related genes have been shown to play a role in embryonic or adult neurogenesis. Indeed, animal models deficient in Nurr1, Pitx3, SNCA and PINK1 display deregulated embryonic neurogenesis and LRRK2 and VPS35 have been implicated in neuronal development-related processes such as Wnt/β-catenin signaling and neurite outgrowth. Moreover, adult neurogenesis is affected in both PD patients and PD animal models and is regulated by dopamine and dopaminergic (DA) receptors, by chronic neuroinflammation, such as that observed in PD, and by differential expression of wild-type or mutant forms of PD-related genes. Indeed, an increasing number of in vivo studies demonstrate a role for SNCA and LRRK2 in adult neurogenesis and in the generation and maintenance of DA neurons. Finally, the roles of PD-related genes, SNCA, LRRK2, VPS35, Parkin, PINK1 and DJ-1 have been studied in NSCs, progenitor cells and induced pluripotent stem cells, demonstrating a role for some of these genes in stem/progenitor cell proliferation and maintenance. Together, these studies strongly suggest a link between deregulated neurogenesis and the onset and progression of PD and present strong evidence that, in addition to a neurodegenerative disorder, PD can also be regarded as a developmental disorder.

Adult neurogenesis in humans- common and unique traits in mammals

New neurons generated in the adult brain have been shown in rodents to mediate specific functions, including neural plasticity. This Essay discusses recent work on human adult neurogenesis, examining how it compares to that in other mammals.

New neurons are continuously generated in specific regions in the adult brain. Studies in rodents have demonstrated that adult-born neurons have specific functional features and mediate neural plasticity. Data on the extent and dynamics of adult neurogenesis in adult humans are starting to emerge, and there are clear similarities and differences compared to other mammals. Why do these differences arise? And what do they mean?

The Neuropathology of Huntington's Disease

The basal ganglia are a highly interconnected set of subcortical nuclei and major atrophy in one or more regions may have major effects on other regions of the brain. Therefore, the striatum which is preferentially degenerated and receives projections from the entire cortex also affects the regions to which it targets, especially the globus pallidus and substantia nigra pars reticulata. Additionally, the cerebral cortex is itself severely affected as are many other regions of the brain, especially in more advanced cases. The cell loss in the basal ganglia and the cerebral cortex is extensive. The most important new findings in Huntington's disease pathology is the highly variable nature of the degeneration in the brain. Most interestingly, this variable pattern of pathology appears to reflect the highly variable symptomatology of cases with Huntington's disease even among cases possessing the same number of CAG repeats.

Regulation of subventricular zone-derived cells migration in the adult brain

The subventricular zone of the lateral ventricles (SVZ) is the largest source of neural stem cells (NSCs) in the adult mammalian brain. Newly generated neuroblasts from the SVZ form cellular chains that migrate through the rostral migratory stream (RMS) into the olfactory bulb (OB), where they become mature neurons. Migration through the RMS is a highly regulated process of intrinsic and extrinsic factors, orchestrated to achieve direction and integration of neuroblasts into OB circuitry. These factors include internal cytoskeletal and volume regulators, extracellular matrix proteins, and chemoattractant and chemorepellent proteins. All these molecules direct the cells away from the SVZ, through the RMS, and into the OB guaranteeing their correct integration. Following brain injury, some neuroblasts escape the RMS and migrate into the lesion site to participate in regeneration, a phenomenon that is also observed with brain tumors. This review focuses on factors that regulate the migration of SVZ precursor cells in the healthy and pathologic brain. A better understanding of the factors that control the movement of newly generated cells may be crucial for improving the use of NSC-replacement therapy for specific neurological diseases.

Subventricular zone progenitors in time and space: generating neuronal diversity

The adult mammalian brain harbors a population of cells around their lateral ventricles capable of giving rise to new neurons throughout life. The so-called subventricular zone (SVZ) is a heterogeneous germinative niche in regard to the neuronal types it generates. SVZ progenitors give rise to different olfactory bulb (OB) interneuron types in accordance to their position along the ventricles. Here, I review data showing the difference between progenitors located along different parts of the SVZ axes and ages. I also discuss possible mechanisms for the origin of this diversity.

Role of NG2 expressing cells in addiction: a new approach for an old problem

Neuron-glial antigen 2 (NG2) is a proteoglycan expressed predominantly in oligodendrocyte progenitor cells (OPCs). NG2-expressing OPCs (NG2-OPCs) are self-renewing cells that are widely distributed in the gray and white matter areas of the central nervous system. NG2-OPCs can mature into premyelinating oligodendrocytes and myelinating oligodendroglia which serve as the primary source of myelin in the brain. This review characterizes NG2-OPCs in brain structure and function, conceptualizes the role of NG2-OPCs in brain regions associated with negative reinforcement and relapse to drug seeking and discusses how NG2-OPCs are regulated by neuromodulators linked to motivational withdrawal. We hope to provide the readers with an overview of the role of NG2-OPCs in brain structure and function in the context of negative affect state in substance abuse disorders and to integrate our current understanding of the physiological significance of the NG2-OPCs in the adult brain.

Developmental regulation of human cortex transcription and its clinical relevance at single base resolution

Transcriptome analysis of human brain provides fundamental insight about development and disease, but largely relies on existing annotation. We sequenced transcriptomes of 72 prefrontal cortex samples across six life stages, and identified 50,650 differentially expression regions (DERs) associated with developmental and aging, agnostic of annotation. While many DERs annotated to non-exonic sequence (41.1%), most were similarly regulated in cytosolic mRNA extracted from independent samples. The DERs were developmentally conserved across 16 brain regions and within the developing mouse cortex, and were expressed in diverse cell and tissue types. The DERs were further enriched for active chromatin marks and clinical risk for neurodevelopmental disorders like schizophrenia. Lastly, we demonstrate quantitatively that these DERs associate with a changing neuronal phenotype related to differentiation and maturation. These data highlight conserved molecular signatures of transcriptional dynamics across brain development, some potential clinical relevance and the incomplete annotation of the human brain transcriptome.

Organization and cellular arrangement of two neurogenic regions in the adult ferret (Mustela putorius furo) brain

In the adult mammalian brain, two neurogenic regions have been characterized, the subventricular zone (SVZ) of the lateral ventricle (LV) and the subgranular zone (SGZ) of the dentate gyrus (DG). Despite remarkable knowledge of rodents, the detailed arrangement of neurogenic regions in most mammals is poorly understood. In this study, we used immunohistochemistry and cell type-specific antibodies to investigate the organization of two germinal regions in the adult ferret, which belongs to the order Carnivora and is widely used as a model animal with a gyrencephalic brain. From the SVZ to the olfactory bulb, doublecortin-positive cells tended to organize in chain-like clusters, which are surrounded by a meshwork of astrocytes. This structure is homologous to the rostral migratory stream (RMS) described in other species. Different from rodents, the horizontal limb of the RMS emerges directly from the LV, and the anterior region of the LV extends rostrally and reached the olfactory bulb. In the DG, glial fibrillary acidic protein-positive cells with long radial processes as well as doublecortin-positive cells are oriented in the SGZ. In both regions, doublecortin-positive cells showed characteristic morphology and were positive for polysialylated-neural cell adhesion molecule, beta-III tubulin, and lamin B1 (intense staining). Proliferating cells were detected in both regions using antibodies against proliferating cell nuclear antigen and phospho-histone H3. These observations demonstrate that the two neurogenic regions in ferrets have a similar cellular composition as those of other mammalian species despite anatomical differences in the brain.

Differential expression of doublecortin and microglial markers in the rat brain following fractionated irradiation

Ionizing radiation induces altered brain tissue homeostasis and can lead to morphological and functional deficits. In this study, adult male Wistar rats received whole-body exposure with fractionated doses of gamma rays (a total dose of 5 Gy) and were investigated 30 and 60 days later. Immunohistochemistry and confocal microscopy were used to determine proliferation rate of cells residing or derived from the forebrain anterior subventricular zone (SVZa) and microglia distributed along and/or adjacent to subventricular zone-olfactory bulb axis. Cell counting was performed in four anatomical parts along the well-defined pathway, known as the rostral migratory stream (RMS) represented by the SVZa, vertical arm, elbow and horizontal arm of the RMS. Different spatiotemporal distribution pattern of cell proliferation was seen up to 60 days after irradiation through the migratory pathway. A population of neuroblasts underwent less evident changes up to 60 days after treatment. Fractionated exposure led to decline or loss of resting as well as reactive forms of microglia until 60 days after irradiation. Results showed that altered expression of the SVZa derived cells and ultimative decrease of microglia may contribute to development of radiation-induced late effects.

Regulation and function of adult neurogenesis: from genes to cognition

Adult neurogenesis in the hippocampus is a notable process due not only to its uniqueness and potential impact on cognition but also to its localized vertical integration of different scales of neuroscience, ranging from molecular and cellular biology to behavior. This review summarizes the recent research regarding the process of adult neurogenesis from these different perspectives, with particular emphasis on the differentiation and development of new neurons, the regulation of the process by extrinsic and intrinsic factors, and their ultimate function in the hippocampus circuit. Arising from a local neural stem cell population, new neurons progress through several stages of maturation, ultimately integrating into the adult dentate gyrus network. The increased appreciation of the full neurogenesis process, from genes and cells to behavior and cognition, makes neurogenesis both a unique case study for how scales in neuroscience can link together and suggests neurogenesis as a potential target for therapeutic intervention for a number of disorders.

Microglial proliferation in the brain of chronic alcoholics with hepatic encephalopathy

Hepatic encephalopathy (HE) is a common complication of chronic alcoholism and patients show neurological symptoms ranging from mild cognitive dysfunction to coma and death. The HE brain is characterized by glial changes, including microglial activation, but the exact pathogenesis of HE is poorly understood. During a study investigating cell proliferation in the subventricular zone of chronic alcoholics, a single case with widespread proliferation throughout their adjacent grey and white matter was noted. This case also had concomitant HE raising the possibility that glial proliferation might be a pathological feature of the disease. In order to explore this possibility fixed postmortem human brain tissue from chronic alcoholics with cirrhosis and HE (n = 9), alcoholics without HE (n = 4) and controls (n = 4) were examined using immunohistochemistry and cytokine assays. In total, 4/9 HE cases had PCNA- and a second proliferative marker, Ki-67-positive cells throughout their brain and these cells co-stained with the microglial marker, Iba1. These cases were termed 'proliferative HE' (pHE). The microglia in pHEs displayed an activated morphology with hypertrophied cell bodies and short, thickened processes. In contrast, the microglia in white matter regions of the non-proliferative HE cases were less activated and appeared dystrophic. pHEs were also characterized by higher interleukin-6 levels and a slightly higher neuronal density . These findings suggest that microglial proliferation may form part of an early neuroprotective response in HE that ultimately fails to halt the course of the disease because underlying etiological factors such as high cerebral ammonia and systemic inflammation remain.

Generation of neuronal progenitor cells in response to tumors in the human brain

Data from transgenic mouse models show that neuronal progenitor cells (NPCs) migrate toward experimental brain tumors and modulate the course of pathology. However, the pathways whereby NPCs are attracted to CNS neoplasms are not fully understood and it is unexplored if NPCs migrate toward brain tumors (high-grade astrocytomas) in humans. We analyzed the tumor-parenchyma interface of neurosurgical resections for the presence of (NPCs) and distinguished these physiological cells from the tumor mass. We observed that polysialic acid neural cell adhesion molecule-positive NPCs accumulate at the border of high-grade astrocytomas and display a marker profile consistent with immature migratory NPCs. Importantly, these high-grade astrocytoma-associated NPCs did not carry genetic aberrations that are indicative of the tumor. Additionally, we observed NPCs accumulating in CNS metastases. These metastatic tumors are distinguished from neural cells by defined sets of markers. Transplanting murine glioma cells embedded in a cell-impermeable hollow fiber capsule into the brains of nestin-gfp reporter mice showed that diffusible factors are sufficient to induce a neurogenic reaction. In vitro, vascular endothelial growth factor (VEGF) secreted from glioma cells increases the migratory and proliferative behavior of adult human brain-derived neural stem and progenitor cells via stimulation of VEGF receptor-2 (VEGFR-2). In vivo, inhibiting VEGFR-2 signaling with a function-blocking antibody led to a reduction in NPC migration toward tumors. Overall, our data reveal a mechanism by which NPCs are attracted to CNS tumors and suggest that NPCs accumulate in human high-grade astrocytomas.

Differentiation of rhesus adipose stem cells into dopaminergic neurons

LIM homeobox transcription factor 1a (Lmx1a) has the capacity to initiate the development program of neuronal cells and promote the differentiation of embryonic stem cells into dopaminergic neurons. In this study, rhesus adipose stem cells were infected with recombinant adenovirus carrying the Lmx1a gene and co-cultured with embryonic rat neural stem cells. Cell differentiation was induced using sonic hedgehog and fibroblast growth factor-8. Immunofluorescence staining showed that cells were positive for neuron-specific enolase and β-tubulin III. Reverse transcription-PCR results demonstrated that rhesus adipose stem cells were not only positive for neuron-specific enolase and β-tubulin III, but also positive for the dopaminergic neuron marker, tyrosine hydroxylase, neurofilament, glial cell line-derived neurotrophic factor family receptor α2 and nuclear receptor related factor 1. The number of Lmx1a gene-infected cells expressing the dopaminergic neuron marker was substantially greater than the number of cells not infected with Lmx1α gene. These results suggest that Lmx1a-mediated regulation combined with the strategy of co-culture with neural stem cells can robustly promote the differentiation of rhesus adipose stem cells into dopaminergic neurons.

Treatment with UDP-glucose, GDNF, and memantine promotes SVZ and white matter self-repair by endogenous glial progenitor cells in neonatal rats with ischemic PVL

Periventricular leukomalacia (PVL) is one of the foremost neurological conditions leading to long-term abnormalities in premature infants. Since it is difficult to prevent initiation of this damage in utero, promoting the innate regenerative potential of the brain after birth may provide a more feasible, prospective therapy for PVL. Treatment with UDP-glucose (UDPG), an endogenous agonist of G protein-coupled receptor 17 (GPR17) that may enhance endogenous self-repair potentiality, glial cell line-derived neurotrophic factor (GDNF), a neurotrophic factor associated with the growth and survival of nerve cells, and memantine, a noncompetitive antagonist of N-methyl-d-aspartate (NMDA) receptors that block ischemia-induced glutamate signal transduction, has been reported to achieve functional, neurological improvement in neonatal rats with PVL. The aim of the present study was to further explore whether UDPG, GDNF and/or memantine could promote corresponding self-repair of the subventricular zone (SVZ) and white matter (WM) in neonatal rats with ischemia-induced PVL. SVZ or WM tissue samples and cultured glial progenitor cells derived from a 5 day-old neonatal rat model of PVL were utilized for studying response to UDPG, GDNF and memantine in vivo and in vitro, respectively. Labeling with 5'-bromo-2'-deoxyuridine and immunofluorescent cell lineage markers after hypoxia-ischemia or oxygen-glucose deprivation (OGD) revealed that UDPG, GDNF and memantine each significantly increased glial progenitor cells and preoligodendrocytes (preOLs), as well as more differentiated immature and mature oligodendrocyte (OL), in both the SVZ and WM in vivo or in vitro. SVZ and WM glial cell apoptosis was also significantly reduced by UDPG, GDNF or memantine, both in vivo and in vitro. These results indicated that UDPG, GDNF or memantine may promote endogenous self-repair by stimulating proliferation of glial progenitor cells derived from both the SVZ and WM, activating their differentiation into more mature OLs, and raising the survival rate of these newly generated glial cells in neonatal rats with ischemic PVL.

Signals that regulate the oncogenic fate of neural stem cells and progenitors

Brain tumors have frequently been associated with a neural stem cell (NSC) origin and contain stem-like tumor cells, so-called brain tumor stem cells (BTSCs) that share many features with normal NSCs. A stem cell state of BTSCs confers resistance to radiotherapy and treatment with alkylating agents. It is also a hallmark of aggressive brain tumors and is maintained by transcriptional networks that are also active in embryonic stem cells. Advances in reprogramming of somatic cells into induced pluripotent stem (iPS) cells have further identified genes that drive stemness. In this review, we will highlight the possible drivers of stemness in medulloblastoma and glioma, the most frequent types of primary malignant brain cancer in children and adults, respectively. Signals that drive expansion of developmentally defined neural precursor cells are also active in corresponding brain tumors. Transcriptomal subgroups of human medulloblastoma and glioma match features of NSCs but also more restricted progenitors. Lessons from genetically-engineered mouse (GEM) models show that temporally and regionally defined NSCs can give rise to distinct subgroups of medulloblastoma and glioma. We will further discuss how acquisition of stem cell features may drive brain tumorigenesis from a non-NSC origin. Genetic alterations, signaling pathways, and therapy-induced changes in the tumor microenvironment can drive reprogramming networks and induce stemness in brain tumors. Finally, we propose a model where dysregulation of microRNAs (miRNAs) that normally provide barriers against reprogramming plays an integral role in promoting stemness in brain tumors.

Neurogenesis and inflammation after ischemic stroke: what is known and where we go from here

This review covers the pathogenesis of ischemic stroke and future directions regarding therapeutic options after injury. Ischemic stroke is a devastating disease process affecting millions of people worldwide every year. The mechanisms underlying the pathophysiology of stroke are not fully understood but there is increasing evidence demonstrating the contribution of inflammation to the drastic changes after cerebral ischemia. This inflammation not only immediately affects the infarcted tissue but also causes long-term damage in the ischemic penumbra. Furthermore, the interaction between inflammation and subsequent neurogenesis is not well understood but the close relationship between these two processes has garnered significant interest in the last decade or so. Current approved therapy for stroke involving pharmacological thrombolysis is limited in its efficacy and new treatment strategies need to be investigated. Research aimed at new therapies is largely about transplantation of neural stem cells and using endogenous progenitor cells to promote brain repair. By understanding the interaction between inflammation and neurogenesis, new potential therapies could be developed to further establish brain repair mechanisms.

Buyang Huanwu Decoction regulates neural stem cell behavior in ischemic brain

The traditional Chinese medicine Buyang Huanwu Decoction has been shown to improve the neu-rological function of patients with stroke. However, the precise mechanisms underlying its effect remain poorly understood. In this study, we established a rat model of cerebral ischemia by middle cerebral artery occlusion and intragastrically administered 5 g/kg Buyang Huanwu Decoction, once per day, for 1, 7, 14 and 28 days after cerebral ischemia. Immunohistochemical staining revealed a number of cells positive for the neural stem cell marker nestin in the cerebral cortex, the subven-tricular zone and the ipsilateral hippocampal dentate gyrus in rat models of cerebral ischemia. Buyang Huanwu Decoction significantly increased the number of cells positive for 5-bromodeoxyuridine (BrdU), a cell proliferation-related marker, microtubule-associated protein-2, a marker of neuronal differentiation, and growth-associated protein 43, a marker of synaptic plasticity in the ischemic rat cerebral regions. The number of positive cells peaked at 14 and 28 days after intragastric administration of Buyang Huanwu Decoction. These findings suggest that Buyang Huanwu Decoction can promote the proliferation and differentiation of neural stem cells and hance synaptic plasticity in ischemic rat brain tissue.

Cell based therapies in Parkinson's Disease

Parkinson’s disease (PD) is the second most common neurodegenerative disorder after Alzheimer’s disease. It is characterized by bradykinesia, hypokinesia/ akinesia, rigidity, tremor, and postural instability, caused by dopaminergic (DA) striatal denervation. The prevalence of PD increases from 50 years of age with steep rise after age 60 years. Current treatment of PD relies heavily on replacing lost dopamine either with its precursor L-dopa or dopamine agonists (ropinirole, pramipexole, bromocriptine, lisuride etc). Other pharmacological measures like catechol-O-methyltrasferase (COMT) inhibitors like entacopone, telcapone and monoamine oxidase B (MAO-B) inhibitors like selegiline and rasagiline are also useful, while L-dopa remains the gold standard in the treatment of PD. Emerging therapies are focusing on cell based therapeutics derived from various sources.

Olfactory neuroblastoma and olfactory ventricle. A case report

A case of dumbbell nasal and intracerebral olfactory neuroblastoma (ONB) related to possible seeding through an "olfactory ventricle" in the olfactory bulb and nerve is reported. This anatomic variant was recognized at operation for the first time: it consists of a hollow cavity within the olfactory bulb and nerve which may be connected to the subventricular zone of the frontal horn of the lateral ventricle. Better scrutiny of this structure is necessary in view of its possible interference with the course and diffusion of ONBs.

Adult neurogenesis and its role in neuropsychiatric disease, brain repair and normal brain function

Neural stem/progenitor cells (NSPCs) in the mammalian brain retain the ability to generate new neurones throughout life in discrete brain regions, through a process called adult neurogenesis. Adult neurogenesis, a dramatic form of adult brain circuitry plasticity, has been implicated in physiological brain function and appears to be of pivotal importance for certain forms of learning and memory. In addition, failing or altered neurogenesis has been associated with a variety of brain diseases such as major depression, epilepsy and age-related cognitive decline. Here we review recent advances in our understanding of the basic biology underlying the neurogenic process in the adult brain, focusing on mechanisms that regulate quiescence, proliferation and differentiation of NSPCs. In addition, we discuss how neurogenesis influences normal brain function, and in particular its role in memory formation, as well as its contribution to neuropsychiatric diseases. Finally, we evaluate the potential of targeting endogenous NSPCs for brain repair.

Proliferation in the Alzheimer hippocampus is due to microglia, not astroglia, and occurs at sites of amyloid deposition

Microglia and astrocytes contribute to Alzheimer's disease (AD) etiology and may mediate early neuroinflammatory responses. Despite their possible role in disease progression and despite the fact that they can respond to amyloid deposition in model systems, little is known about whether astro- or microglia can undergo proliferation in AD and whether this is related to the clinical symptoms or to local neuropathological changes. Previously, proliferation was found to be increased in glia-rich regions of the presenile hippocampus. Since their phenotype was unknown, we here used two novel triple-immunohistochemical protocols to study proliferation in astro- or microglia in relation to amyloid pathology. We selected different age-matched cohorts to study whether proliferative changes relate to clinical severity or to neuropathological changes. Proliferating cells were found across the hippocampus but never in mature neurons or astrocytes. Almost all proliferating cells were colabeled with Iba1+, indicating that particularly microglia contribute to proliferation in AD. Proliferating Iba1+ cells was specifically seen within the borders of amyloid plaques, indicative of an active involvement in, or response to, plaque accumulation. Thus, consistent with animal studies, proliferation in the AD hippocampus is due to microglia, occurs in close proximity of plaque pathology, and may contribute to the neuroinflammation common in AD.

Evidence of adult neurogenesis in non-human primates and human

Adult neurogenesis in rodents has been extensively studied. Here, we briefly summarize the studies of adult neurogenesis based on non-human primate brains and human postmortem brain samples in recent decades. The differences between rodent, primate and human neurogenesis are discussed. We conclude that these differences may contribute to distinct physiological roles and the self-repair mechanisms in the brain across species.

Prospects for engineering neurons from local neocortical cell populations as cell-mediated therapy for neurological disorders

There is little cell replacement following neurological injury, limiting the regenerative response of the CNS. Progress in understanding the biology of neural stem cells has raised interest in using stem cells for replacing neurons lost to injury or to disease. Stem cell therapy may also have a role in rebuilding deficient neural circuitry underlying mood disorders, epilepsy, and pain modulation among other roles. In vitro expansion of stem cells with directed differentiation prior to transplantation is one approach to stem cell therapy. Emerging evidence suggests that it may be possible to convert in vivo endogenous neural cells to a neuronal fate directly, providing an alternative strategy for stem cell therapy to the CNS. This review assesses the evidence for engineering a subtype-specific neuronal fate of endogenous neural cells in the cerebral cortex as a function of initial cell lineage, reactive response to injury, conversion factors, and environmental context. We conclude with a discussion of some of the challenges that must be overcome to move this alternative in vivo engineered conversion process toward becoming a viable therapeutic option.

Endogenous neurogenesis following ischaemic brain injury: insights for therapeutic strategies

Ischaemic stroke is among the most common yet most intractable types of central nervous system (CNS) injury in the adult human population. In the acute stages of disease, neurons in the ischaemic lesion rapidly die and other neuronal populations in the ischaemic penumbra are vulnerable to secondary injury. Multiple parallel approaches are being investigated to develop neuroprotective, reparative and regenerative strategies for the treatment of stroke. Accumulating evidence indicates that cerebral ischaemia initiates an endogenous regenerative response within the adult brain that potentiates adult neurogenesis from populations of neural stem and progenitor cells. A major research focus has been to understand the cellular and molecular mechanisms that underlie the potentiation of adult neurogenesis and to appreciate how interventions designed to modulate these processes could enhance neural regeneration in the post-ischaemic brain. In this review, we highlight recent advances over the last 5 years that help unravel the cellular and molecular mechanisms that potentiate endogenous neurogenesis following cerebral ischaemia and are dissecting the functional importance of this regenerative mechanism following brain injury. This article is part of a Directed Issue entitled: Regenerative Medicine: the challenge of translation.

Adult neurogenesis: bridging the gap between mice and humans

Neural stem/progenitor cells (NSPCs) generate new neurons in the mammalian brain throughout life. Over the past two decades, substantial progress has been made in deciphering the cellular and molecular mechanisms underlying adult neurogenesis and in understanding the role played by new neurons in brain function in animal models of health and disease. By contrast, knowledge regarding the extent and relevance of neurogenesis in the adult human brain remains scant. Here we review new concepts about how new neurons shape adult brain circuits, discuss fundamental, unanswered questions about stem cell-associated neural plasticity, and illustrate how the gap between the animal-based basic research and current efforts to analyze life-long neuronal development of the human brain may be overcome by using novel experimental strategies.

Tangential migratory pathways of subpallial origin in the embryonic telencephalon of sharks: evolutionary implications

Tangential neuronal migration occurs along different axes from the axis demarcated by radial glia and it is thought to have evolved as a mechanism to increase the diversity of cell types in brain areas, which in turn resulted in increased complexity of functional networks. In the telencephalon of amniotes, different embryonic tangential pathways have been characterized. However, little is known about the exact routes of migrations in basal vertebrates. Cartilaginous fishes occupy a key phylogenetic position to assess the ancestral condition of vertebrate brain organization. In order to identify putative subpallial-derived tangential migratory pathways in the telencephalon of sharks, we performed a detailed analysis of the distribution pattern of GAD and Dlx2, two reliable markers of tangentially migrating interneurons of subpallial origin in the developing forebrain. We propose the existence of five tangential routes directed toward different telencephalic regions. We conclude that four of the five routes might have emerged in the common ancestor of jawed vertebrates. We have paid special attention to the characterization of the proposed migratory pathway directed towards the olfactory bulbs. Our results suggest that it may be equivalent to the "rostral migratory stream" of mammals and led us to propose a hypothesis about its evolution. The analysis of the final destinations of two other streams allowed us to identify the putative dorsal and medial pallium of sharks, the regions from which the neocortex and hippocampus might have, respectively, evolved. Derived features were also reported and served to explain some distinctive traits in the morphology of the telencephalon of cartilaginous fishes.

In vivo models of brain tumors: roles of genetically engineered mouse models in understanding tumor biology and use in preclinical studies

Although our knowledge of the biology of brain tumors has increased tremendously over the past decade, progress in treatment of these deadly diseases remains modest. Developing in vivo models that faithfully mirror human diseases is essential for the validation of new therapeutic approaches. Genetically engineered mouse models (GEMMs) provide elaborate temporally and genetically controlled systems to investigate the cellular origins of brain tumors and gene function in tumorigenesis. Furthermore, they can prove to be valuable tools for testing targeted therapies. In this review, we discuss GEMMs of brain tumors, focusing on gliomas and medulloblastomas. We describe how they provide critical insights into the molecular and cellular events involved in the initiation and maintenance of brain tumors, and illustrate their use in preclinical drug testing.

Adult hippocampal neurogenesis in Parkinson's disease: impact on neuronal survival and plasticity

In Parkinson's disease (PD) and other synucleinopathies, chronic neurodegeneration occurs within different areas of the central nervous system leading to progressive motor and nonmotor symptoms. The symptomatic treatment options that are currently available do not slow or halt disease progression. This highlights the need of a better understanding of disease mechanisms and disease models. The generation of newborn neurons in the adult hippocampus and in the subventricular zone/olfactory bulb system is affected by many different regulators and possibly involved in memory processing, depression, and olfaction, symptoms which commonly occur in PD. The pathology of the adult neurogenic niches in human PD patients is still mostly elusive, but different preclinical models have shown profound alterations of adult neurogenesis. Alterations in stem cell proliferation, differentiation, and survival as well as neurite outgrowth and spine formation have been related to different aspects in PD pathogenesis. Therefore, neurogenesis in the adult brain provides an ideal model to study disease mechanisms and compounds. In addition, adult newborn neurons have been proposed as a source of endogenous repair. Herein, we review current knowledge about the adult neurogenic niches in PD and highlight areas of future research.

Desvenlafaxine may accelerate neuronal maturation in the dentate gyri of adult male rats

Adult hippocampal neurogenesis has been linked to the effects of anti-depressant drugs on behavior in rodent models of depression. To explore this link further, we tested whether the serotonin-norepinephrine reuptake inhibitor (SNRI) venlafaxine impacted adult hippocampal neurogenesis differently than its primary active SNRI metabolite desvenlafaxine. Adult male Long Evans rats (n = 5-6 per group) were fed vehicle, venlafaxine (0.5 or 5 mg) or desvenlafaxine (0.5 or 5 mg) twice daily for 16 days. Beginning the third day of drug treatment, the rats were given a daily bromodeoxyuridine (BrdU; 50 mg/kg) injection for 5 days to label dividing cells and then perfused 2 weeks after the first BrdU injection to confirm total new hippocampal cell numbers and their phenotypes. The high desvenlafaxine dose increased total new BrdU+ cell number and appeared to accelerate neuronal maturation because fewer BrdU+ cells expressed maturing neuronal phenotypes and more expressed mature neuronal phenotypes in the dentate gyri of these versus vehicle-treated rats. While net neurogenesis was not increased in the dentate gyri of rats treated with the high desvenlafaxine dose, significantly more mature neurons were detected. Our data expand the body of literature showing that antidepressants impact adult neurogenesis by stimulating NPC proliferation and perhaps the survival of neuronal progeny and by showing that a high dose of the SNRI antidepressant desvenlafaxine, but neither a high nor low venlafaxine dose, may also accelerate neuronal maturation in the adult rat hippocampus. These data support the hypothesis that hippocampal neurogenesis may indeed serve as a biomarker of depression and the effects of antidepressant treatment, and may be informative for developing novel fast-acting antidepressant strategies.

Sialic acids in the brain: gangliosides and polysialic acid in nervous system development, stability, disease, and regeneration

Every cell in nature carries a rich surface coat of glycans, its glycocalyx, which constitutes the cell's interface with its environment. In eukaryotes, the glycocalyx is composed of glycolipids, glycoproteins, and proteoglycans, the compositions of which vary among different tissues and cell types. Many of the linear and branched glycans on cell surface glycoproteins and glycolipids of vertebrates are terminated with sialic acids, nine-carbon sugars with a carboxylic acid, a glycerol side-chain, and an N-acyl group that, along with their display at the outmost end of cell surface glycans, provide for varied molecular interactions. Among their functions, sialic acids regulate cell-cell interactions, modulate the activities of their glycoprotein and glycolipid scaffolds as well as other cell surface molecules, and are receptors for pathogens and toxins. In the brain, two families of sialoglycans are of particular interest: gangliosides and polysialic acid. Gangliosides, sialylated glycosphingolipids, are the most abundant sialoglycans of nerve cells. Mouse genetic studies and human disorders of ganglioside metabolism implicate gangliosides in axon-myelin interactions, axon stability, axon regeneration, and the modulation of nerve cell excitability. Polysialic acid is a unique homopolymer that reaches >90 sialic acid residues attached to select glycoproteins, especially the neural cell adhesion molecule in the brain. Molecular, cellular, and genetic studies implicate polysialic acid in the control of cell-cell and cell-matrix interactions, intermolecular interactions at cell surfaces, and interactions with other molecules in the cellular environment. Polysialic acid is essential for appropriate brain development, and polymorphisms in the human genes responsible for polysialic acid biosynthesis are associated with psychiatric disorders including schizophrenia, autism, and bipolar disorder. Polysialic acid also appears to play a role in adult brain plasticity, including regeneration. Together, vertebrate brain sialoglycans are key regulatory components that contribute to proper development, maintenance, and health of the nervous system.

The cockayne syndrome B protein is essential for neuronal differentiation and neuritogenesis

Cockayne syndrome (CS) is a progressive developmental and neurodegenerative disorder resulting in premature death at childhood and cells derived from CS patients display DNA repair and transcriptional defects. CS is caused by mutations in csa and csb genes, and patients with csb mutation are more prevalent. A hallmark feature of CSB patients is neurodegeneration but the precise molecular cause for this defect remains enigmatic. Further, it is not clear whether the neurodegenerative condition is due to loss of CSB-mediated functions in adult neurogenesis. In this study, we examined the role of CSB in neurogenesis by using the human neural progenitor cells that have self-renewal and differentiation capabilities. In this model system, stable CSB knockdown dramatically reduced the differentiation potential of human neural progenitor cells revealing a key role for CSB in neurogenesis. Neurite outgrowth, a characteristic feature of differentiated neurons, was also greatly abolished in CSB-suppressed cells. In corroboration with this, expression of MAP2 (microtubule-associated protein 2), a crucial player in neuritogenesis, was also impaired in CSB-suppressed cells. Consistent with reduced MAP2 expression in CSB-depleted neural cells, tandem affinity purification and chromatin immunoprecipitation studies revealed a potential role for CSB in the assembly of transcription complex on MAP2 promoter. Altogether, our data led us to conclude that CSB has a crucial role in coordinated regulation of transcription and chromatin remodeling activities that are required during neurogenesis.

Distinct and separable roles for EZH2 in neurogenic astroglia

The epigenetic mechanisms that enable specialized astrocytes to retain neurogenic competence throughout adult life are still poorly understood. Here we show that astrocytes that serve as neural stem cells (NSCs) in the adult mouse subventricular zone (SVZ) express the histone methyltransferase EZH2. This Polycomb repressive factor is required for neurogenesis independent of its role in SVZ NSC proliferation, as Ink4a/Arf-deficiency in Ezh2-deleted SVZ NSCs rescues cell proliferation, but neurogenesis remains defective. Olig2 is a direct target of EZH2, and repression of this bHLH transcription factor is critical for neuronal differentiation. Furthermore, Ezh2 prevents the inappropriate activation of genes associated with non-SVZ neuronal subtypes. In the human brain, SVZ cells including local astroglia also express EZH2, correlating with postnatal neurogenesis. Thus, EZH2 is an epigenetic regulator that distinguishes neurogenic SVZ astrocytes, orchestrating distinct and separable aspects of adult stem cell biology, which has important implications for regenerative medicine and oncogenesis.

DOI:http://dx.doi.org/10.7554/eLife.02439.001

In addition to the billions of nerve cells called neurons, the brain and spinal cord also contain star-shaped cells called astrocytes. At first it was thought that all astrocytes were the same, but it later became clear that there are several different types of astrocytes that perform different functions. Most neurons are formed in the embryo, but some astrocytes that are found deep within the brain can act as ‘neurogenic stem cells’ and continue to produce new neurons during adult life. However, it was not clear how these neurogenic astrocytes were different from other astrocytes.

Now Hwang et al. have found that neurogenic astrocytes contain a protein called EZH2 that is not found in other types of astrocyte in the adult brain. Researchers already knew that this protein, which acts to help keep DNA tightly packed inside the nucleus and to keep genes switched off, was important for brain development. EZH2 was also known to prevent stem cells from prematurely turning into specialized cell types. But, surprisingly, Hwang et al. found that EZH2 has two distinct roles in neurogenic astrocytes: it allows them to multiply to make more astrocytes, and it also helps guide astrocytes into becoming neurons. Hwang et al. showed that different sets of genes were involved in these two roles.

DOI:http://dx.doi.org/10.7554/eLife.02439.002

Adult neurogenesis: mechanisms and functional significance

New neurons are generated throughout life in distinct regions of the mammalian brain. This process, called adult neurogenesis, has been implicated in physiological brain function, and failing or altered neurogenesis has been associated with a number of neuropsychiatric diseases. Here, we provide an overview of the mechanisms governing the neurogenic process in the adult brain and describe how new neurons may contribute to brain function in health and disease.

Stem cells in neuroinjury and neurodegenerative disorders: challenges and future neurotherapeutic prospects

The prevalence of neurodegenerative diseases and neural injury disorders is increasing worldwide. Research is now focusing on improving current neurogenesis techniques including neural stem cell therapy and other biochemical drug-based approaches to ameliorate these disorders. Unfortunately, we are still facing many obstacles that are rendering current neurotherapies ineffective in clinical trials for reasons that are yet to be discovered. That is why we should start by fully understanding the complex mechanisms of neurogenesis and the factors that affect it, or else, all our suggested therapies would fail since they would not be targeting the essence of the neurological disorder but rather the symptoms. One possible paradigm shift is to switch from neuroprotectant therapies towards neurodegeneration/neurorestorative approaches. In addition, other and our laboratories are increasingly focusing on combining the use of pharmacological agents (such as Rho-associated kinase (ROCK) inhibitors or other growth factors (such as brain-derived neurotrophic factor (BDNF)) and stem cell treatment to enhance the survivability and/or differentiation capacity of transplanted stem cells in neurotrauma or other neurodegeneration animal models. Ongoing stem cell research is surely on the verge of a breakthrough of multiple effective therapeutic options for neurodegenerative disorders. Once, we fully comprehend the process of neurogenesis and its components, we will fully be capable of manipulating and utilizing it. In this work, we discuss the current knowledge of neuroregenerative therapies and their associated challenges.

Neurogenic and non-neurogenic functions of endogenous neural stem cells

Adult neurogenesis is a lifelong process that occurs in two main neurogenic niches of the brain, namely in the subventricular zone (SVZ) of the lateral ventricles and in the subgranular zone (SGZ) of the dentate gyrus (DG) in the hippocampus. In the 1960s, studies on adult neurogenesis have been hampered by the lack of established phenotypic markers. The precise tracing of neural stem/progenitor cells (NPCs) was therefore, not properly feasible. After the (partial) identification of those markers, it was the lack of specific tools that hindered a proper experimental elimination and tracing of those cells to demonstrate their terminal fate and commitment. Nowadays, irradiation, cytotoxic drugs as well as genetic tracing/ablation procedures have moved the field forward and increased our understanding of neurogenesis processes in both physiological and pathological conditions. Newly formed NPC progeny from the SVZ can replace granule cells in the olfactory bulbs of rodents, thus contributing to orchestrate sophisticated odor behavior. SGZ-derived new granule cells, instead, integrate within the DG where they play an essential role in memory functions. Furthermore, converging evidence claim that endogenous NPCs not only exert neurogenic functions, but might also have non-neurogenic homeostatic functions by the release of different types of neuroprotective molecules. Remarkably, these non-neurogenic homeostatic functions seem to be necessary, both in healthy and diseased conditions, for example for preventing or limiting tissue damage. In this review, we will discuss the neurogenic and the non-neurogenic functions of adult NPCs both in physiological and pathological conditions.

The effect of spaceflight on mouse olfactory bulb volume, neurogenesis, and cell death indicates the protective effect of novel environment

Space missions necessitate physiological and psychological adaptations to environmental factors not present on Earth, some of which present significant risks for the central nervous system (CNS) of crewmembers. One CNS region of interest is the adult olfactory bulb (OB), as OB structure and function are sensitive to environmental- and experience-induced regulation. It is currently unknown how the OB is altered by spaceflight. In this study, we evaluated OB volume and neurogenesis in mice shortly after a 13-day flight on Space Shuttle Atlantis [Space Transport System (STS)-135] relative to two groups of control mice maintained on Earth. Mice housed on Earth in animal enclosure modules that mimicked the conditions onboard STS-135 (AEM-Ground mice) had greater OB volume relative to mice maintained in standard housing on Earth (Vivarium mice), particularly in the granule (GCL) and glomerular (GL) cell layers. AEM-Ground mice also had more OB neuroblasts and fewer apoptotic cells relative to Vivarium mice. However, the AEM-induced increase in OB volume and neurogenesis was not seen in STS-135 mice (AEM-Flight mice), suggesting that spaceflight may have negated the positive effects of the AEM. In fact, when OB volume of AEM-Flight mice was considered, there was a greater density of apoptotic cells relative to AEM-Ground mice. Our findings suggest that factors present during spaceflight have opposing effects on OB size and neurogenesis, and provide insight into potential strategies to preserve OB structure and function during future space missions.

Reduced olfactory bulb volume in adults with a history of childhood maltreatment

The human olfactory bulb (OB) is the first relay station of the olfactory pathway and may have the potential for postnatal neurogenesis in early childhood. In animals, chronic stress affects the OB and olfactory functioning. For humans, it has been shown that major depressive disorder is accompanied by reduced OB volume and reduced olfactory function. However, it is not clear if major stress in childhood development also affects olfactory functioning and OB volume in humans. OB volume was measured and olfactory function was tested in 17 depressive patients with and 10 without a history of severe childhood maltreatment (CM). CM patients exhibited a significantly reduced olfactory threshold and identification ability. The OB volume of the CM patients was significantly reduced to 80% of the non-CM patients. In conclusion, postnatal neurogenesis might be by reduced in CM, which may affect olfactory function of the brain in later life. Alternatively, a reduced OB volume may enhance psychological vulnerability in the presence of adverse childhood conditions although other areas not analyzed in this study may also be involved.

Ventriculomegaly associated with ependymal gliosis and declines in barrier integrity in the aging human and mouse brain

Age-associated ventriculomegaly is typically attributed to neurodegeneration; however, additional factors might initiate or contribute to progressive ventricular expansion. By directly linking postmortem human MRI sequences with histological features of periventricular tissue, we show that substantial lateral ventricle surface gliosis is associated with ventriculomegaly. To examine whether loss of ependymal cell coverage resulting in ventricle surface glial scarring can lead directly to ventricle enlargement independent of any other injury or degenerative loss, we modeled in mice the glial scarring found along the lateral ventricle surface in aged humans. Neuraminidase, which cleaves glycosidic linkages of apical adherens junction proteins, was administered intracerebroventricularly to denude areas of ependymal cells. Substantial ependymal cell loss resulted in reactive gliosis rather than stem cell-mediated regenerative repair of the ventricle lining, and the gliotic regions showed morphologic and phenotypic characteristics similar to those found in aged humans. Increased levels of aquaporin-4, indicative of edema, observed in regions of periventricular gliosis in human tissue were also replicated in our mouse model. 3D modeling together with volume measurements revealed that mice with ventricle surface scarring developed expanded ventricles, independent of neurodegeneration. Through a comprehensive, comparative analysis of the lateral ventricles and associated periventricular tissue in aged humans and mouse, followed by modeling of surface gliosis in mice, we have demonstrated a direct link between lateral ventricle surface gliosis and ventricle enlargement. These studies highlight the importance of maintaining an intact ependymal cell lining throughout aging.

Regenerative medicine in Alzheimer's disease

Identifying novel, effective therapeutics for Alzheimer's disease (AD) is one of the major unmet medical needs for the coming decade. Because the current paradigm for developing and testing disease-modifying AD therapies is protracted and likely to be even longer, with the shift toward earlier intervention in preclinical AD, it is an open issue whether we can develop, test, and widely deploy a novel therapy in time to help the current at-risk generation if we continue to follow the standard paradigms of discovery and drug development. There is an imperative need to find safe and effective preventive measures that can be distributed rapidly to stem the coming wave of AD that will potentially engulf the next generation. We can define regenerative medicine broadly as approaches that use stem cell-based therapies or approaches that seek to modulate inherent neurogenesis. Neurogenesis, although most active during prenatal development, has been shown to continue in several small parts of the brain, including the hippocampus and the subventricular zone, suggesting its potential to reverse cognitive deficits. If AD pathology affects neurogenesis, then it follows that conditions that stimulate endogenous neurogenesis (eg, environmental stimuli, physical activity, trophic factors, cytokines, and drugs) may help to promote the regenerative and recovery process. Herein, we review the complex logistics of potentially implementing neurogenesis-based therapeutic strategies for the treatment of AD.

Existence of a potential neurogenic system in the adult human brain

Background

Prevailingly, adult mammalian neurogenesis is thought to occur in discrete, separate locations known as neurogenic niches that are best characterized in the subgranular zone (SGZ) of the dentate gyrus and in the subventricular zone (SVZ). The existence of adult human neurogenic niches is controversial.

Methods

The existence of neurogenic niches was investigated with neurogenesis marker immunostaining in histologically normal human brains obtained from autopsies. Twenty-eight adult temporal lobes, specimens from limbic structures and the hypothalamus of one newborn and one adult were examined.

Results

The neural stem cell marker nestin stained circumventricular organ cells and the immature neuronal marker doublecortin (DCX) stained hypothalamic and limbic structures adjacent to circumventricular organs; both markers stained a continuous structure running from the hypothalamus to the hippocampus. The cell proliferation marker Ki-67 was detected predominately in structures that form the septo-hypothalamic continuum. Nestin-expressing cells were located in the fimbria-fornix at the insertion of the choroid plexus; ependymal cells in this structure expressed the putative neural stem cell marker CD133. From the choroidal fissure in the temporal lobe, a nestin-positive cell layer spread throughout the SVZ and subpial zone. In the subpial zone, a branch of this layer reached the hippocampal sulcus and ended in the SGZ (principally in the newborn) and in the subiculum (principally in the adults). Another branch of the nestin-positive cell layer in the subpial zone returned to the optic chiasm. DCX staining was detected in the periventricular and middle hypothalamus and more densely from the mammillary body to the subiculum through the fimbria-fornix, thus running through the principal neuronal pathway from the hippocampus to the hypothalamus. The column of the fornix forms part of this pathway and appears to coincide with the zone previously identified as the human rostral migratory stream. Partial co-labeling with DCX and the neuronal marker βIII-tubulin was also observed.

Conclusions

Collectively, these findings suggest the existence of an adult human neurogenic system that rises from the circumventricular organs and follows, at minimum, the circuitry of the hypothalamus and limbic system.

Flow induced by ependymal cilia dominates near-wall cerebrospinal fluid dynamics in the lateral ventricles

While there is growing experimental evidence that cerebrospinal fluid (CSF) flow induced by the beating of ependymal cilia is an important factor for neuronal guidance, the respective contribution of vascular pulsation-driven macroscale oscillatory CSF flow remains unclear. This work uses computational fluid dynamics to elucidate the interplay between macroscale and cilia-induced CSF flows and their relative impact on near-wall dynamics. Physiological macroscale CSF dynamics are simulated in the ventricular space using subject-specific anatomy, wall motion and choroid plexus pulsations derived from magnetic resonance imaging. Near-wall flow is quantified in two subdomains selected from the right lateral ventricle, for which dynamic boundary conditions are extracted from the macroscale simulations. When cilia are neglected, CSF pulsation leads to periodic flow reversals along the ventricular surface, resulting in close to zero time-averaged force on the ventricle wall. The cilia promote more aligned wall shear stresses that are on average two orders of magnitude larger compared with those produced by macroscopic pulsatile flow. These findings indicate that CSF flow-mediated neuronal guidance is likely to be dominated by the action of the ependymal cilia in the lateral ventricles, whereas CSF dynamics in the centre regions of the ventricles is driven predominantly by wall motion and choroid plexus pulsation.