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

The Subventricular Zone: A Key Player in Human Neocortical Development

One of the main characteristics of the developing brain is that all neurons and the majority of macroglia originate first in the ventricular zone (VZ), next to the lumen of the cerebral ventricles, and later on in a secondary germinal area above the VZ, the subventricular zone (SVZ). The SVZ is a transient compartment mitotically active in humans for several gestational months. It serves as a major source of cortical projection neurons as well as an additional source of glial cells and potentially some interneuron subpopulations. The SVZ is subdivided into the smaller inner (iSVZ) and the expanded outer SVZ (oSVZ). The enlargement of the SVZ and, in particular, the emergence of the oSVZ are evolutionary adaptations that were critical to the expansion and unique cellular composition of the primate cerebral cortex. In this review, we discuss the cell types and organization of the human SVZ during the first half of the 40 weeks of gestation that comprise intrauterine development. We focus on this period as it is when the bulk of neurogenesis in the human cerebral cortex takes place. We consider how the survival and fate of SVZ cells depend on environmental influences, by analyzing the results from in vitro experiments with human cortical progenitor cells. This in vitro model is a powerful tool to better understand human neocortex formation and the etiology of neurodevelopmental disorders, which in turn will facilitate the design of targeted preventive and/or therapeutic strategies.

Human adult neurogenesis across the ages: An immunohistochemical study

AIMS

Neurogenesis in the postnatal human brain occurs in two neurogenic niches; the subventricular zone (SVZ) in the wall of the lateral ventricles and the subgranular zone (SGZ) of the hippocampus. The extent to which this physiological process continues into adulthood is an area of ongoing research. This study aimed to characterize markers of cell proliferation and assess the efficacy of antibodies used to identify neurogenesis in both neurogenic niches of the human brain.

METHODS

Cell proliferation and neurogenesis were simultaneously examined in the SVZ and SGZ of 23 individuals aged 0.2-59 years, using immunohistochemistry and immunofluorescence in combination with unbiased stereology.

RESULTS

There was a marked decline in proliferating cells in both neurogenic niches in early infancy with levels reaching those seen in the adjacent parenchyma by 4 and 1 year of age, in the SVZ and SGZ, respectively. Furthermore, the phenotype of these proliferating cells in both niches changed with age. In infants, proliferating cells co-expressed neural progenitor (epidermal growth factor receptor), immature neuronal (doublecortin and beta III tubulin) and oligodendrocytic (Olig2) markers. However, after 3 years of age, microglia were the only proliferating cells found in either niche or in the adjacent parenchyma.

CONCLUSIONS

This study demonstrates a marked decline in neurogenesis in both neurogenic niches in early childhood, and that the sparse proliferating cells in the adult brain are largely microglia.

Decline in Proliferation and Immature Neuron Markers in the Human Subependymal Zone during Aging: Relationship to EGF- and FGF-Related Transcripts

Neuroblasts exist within the human subependymal zone (SEZ); however, it is debated to what extent neurogenesis changes during normal aging. It is also unknown how precursor proliferation may correlate with the generation of neuronal and glial cells or how expression of growth factors and receptors may change throughout the adult lifespan. We found evidence of dividing cells in the human SEZ (n D 50) in conjunction with a dramatic age-related decline (21-103 years) of mRNAs indicative of proliferating cells (Ki67) and immature neurons (doublecortin). Microglia mRNA (ionized calcium-binding adapter molecule 1) increased during aging, whereas transcript levels of stem/precursor cells (glial fibrillary acidic protein delta and achaete-scute homolog 1), astrocytes (vimentin and pan-glial fibrillary acidic protein), and oligodendrocytes (oligodendrocyte lineage transcription factor 2) remained stable. Epidermal growth factor receptor (EGFR) and fibroblast growth factor 2 (FGF2) mRNAs increased throughout adulthood, while transforming growth factor alpha (TGFα), EGF, Erb-B2 receptor tyrosine kinase 4 (ErbB4) and FGF receptor 1 (FGFR1) mRNAs were unchanged across adulthood. Cell proliferation mRNA positively correlated with FGFR1 transcripts. Immature neuron and oligodendrocyte marker expression positively correlated with TGFα and ErbB4 mRNAs, whilst astrocyte transcripts positively correlated with EGF, FGF2, and FGFR1 mRNAs. Microglia mRNA positively correlated with EGF and FGF2 expression. Our findings indicate that neurogenesis in the human SEZ continues well into adulthood, although proliferation and neuronal differentiation may decline across adulthood. We suggest that mRNA expression of EGF- and FGF-related family members do not become limited during aging and may modulate neuronal and glial fate determination in the SEZ throughout human life.

Development and aging of a brain neural stem cell niche

In the anterior forebrain, along the lateral wall of the lateral ventricles, a neurogenic stem cell niche is found in a region referred to as the ventricular-subventricular zone (V-SVZ). In rodents, robust V-SVZ neurogenesis provides new neurons to the olfactory bulb throughout adulthood; however, with increasing age stem cell numbers are reduced and neurogenic capacity is significantly diminished, but new olfactory bulb neurons continue to be produced even in old age. Humans, in contrast, show little to no new neurogenesis after two years of age and whether V-SVZ neural stem cells persist in the adult human brain remains unclear. Here, we review functional and organizational differences in the V-SVZ stem cell niche of mice and humans, and examine how aging affects the V-SVZ niche and its associated functions.

Prenatal Alcohol Exposure Affects Progenitor Cell Numbers in Olfactory Bulbs and Dentate Gyrus of Vervet Monkeys

Fetal alcohol exposure (FAE) alters hippocampal cell numbers in rodents and primates, and this may be due, in part, to a reduction in the number or migration of neuronal progenitor cells. The olfactory bulb exhibits substantial postnatal cellular proliferation and a rapid turnover of newly formed cells in the rostral migratory pathway, while production and migration of postnatal neurons into the dentate gyrus may be more complex. The relatively small size of the olfactory bulb, compared to the hippocampus, potentially makes this structure ideal for a rapid analysis. This study used the St. Kitts vervet monkey (Chlorocebus sabeus) to (1) investigate the normal developmental sequence of post-natal proliferation in the olfactory bulb and dentate gyrus and (2) determine the effects of naturalistic prenatal ethanol exposure on proliferation at three different ages (neonate, five months and two years). Using design-based stereology, we found an age-related decrease of actively proliferating cells in the olfactory bulb and dentate gyrus for both control and FAE groups. Furthermore, at the neonatal time point, the FAE group had fewer actively proliferating cells as compared to the control group. These data are unique with respect to fetal ethanol effects on progenitor proliferation in the primate brain and suggest that the olfactory bulb may be a useful structure for studies of cellular proliferation.

Demyelination-Induced Inflammation Attracts Newly Born Neurons to the White Matter

There is compelling evidence that microglial activation negatively impacts neurogenesis. However, microglia have also been shown to promote recruitment of newly born neurons to injured areas of the gray matter. In the present study, we explored whether demyelination-triggered inflammation alters the process of neurogenesis in the white matter. A 2-μl solution of 0.04 % ethidium bromide was stereotaxically injected into the corpus callosum of adult male rats. Brain inflammation was dampened by daily injections of progesterone (5 mg/kg, s.c.) for 14 days. Control rats received oil (s.c.). Newly born neurons (DCX and Tbr2), microglia (Iba-1), astrocytes (vimentin or GFAP), oligodendrocyte progenitor cells (OPCs; NG2), and mature oligodendrocytes (CC-1) were monitored in the vicinity of demyelination site using immunofluorescent staining. Western blot was used to explore microglial polarization using M1 (iNOS) and M2 (arginase-1) markers. Focal demyelination elicited strong microglial and astroglial activation and reduced the number of OPCs at the site of demyelination. This inflammatory response was associated with enhanced number of newly born neurons in the white matter and the subventricular zone (SVZ). A proportion of newly born neurons within the white matter showed features of OPCs. Interestingly, blunting brain inflammation led to reduced neurogenesis around the demyelination area and in the SVZ. These data suggest that the white matter inflammation creates a conducive environment for the recruitment of newly born neurons. The fact that a sizable fraction of these newly born neurons adopt OPC features suggests that they could contribute to the remyelination process.

Influence of glioblastoma contact with the lateral ventricle on survival: a meta-analysis

The ventricular-subventricular zone (V-SVZ), which lies in the walls of the lateral ventricles (LV), is the largest neurogenic niche within the adult brain. Whether radiographic contact with the LV influences survival in glioblastoma (GBM) patients remains unclear. We assimilated and analyzed published data comparing survival in GBM patients with (LV+GBM) and without (LV-GBM) radiographic LV contact. PubMed, EMBASE, and Cochrane electronic databases were searched. Fifteen studies with survival data on LV+GBM and LV-GBM patients were identified. Their Kaplan-Meier survival curves were digitized and pooled for generation of median overall (OS) and progression free (PFS) survivals and log-rank hazard ratios (HRs). The log-rank and reported multivariate HRs after accounting for the common predictors of GBM survival were analyzed separately by meta-analyses. The calculated median survivals (months) from pooled data were 12.95 and 16.58 (OS), and 4.54 and 6.25 (PFS) for LV+GBMs and LV-GBMs, respectively, with an overall log-rank HRs of 1.335 [1.204-1.513] (OS) and 1.387 [1.225-1.602] (PFS). Meta-analysis of log-rank HRs resulted in summary HRs of 1.58 [1.35-1.85] (OS, 10 studies) and 1.41 [1.22-1.64] (PFS, 5 studies). Meta-analysis of multivariate HRs resulted in summary HRs of 1.35 [1.14-1.58] (OS, 6 studies) and 1.64 [0.88-3.05] (PFS, 3 studies). Patients with GBM contacting the LV have lower survival. This effect may be independent of the common predictors of GBM survival, suggesting a clinical influence of V-SVZ contact on GBM biology.

Telencephalic-olfactory bulb ventricle wall organization in Austrolebias charrua: Cytoarchitecture, proliferation dynamics, neurogenesis and migration

Adult neurogenesis participates in fish olfaction sensitivity in response to environmental challenges. Therefore, we investigated if several populations of stem/progenitor cells that are retained in the olfactory bulbs (OB) may constitute different neurogenic niches that support growth and functional demands. By electron microscopy and combination cell proliferation and lineage markers, we found that the telencephalic ventricle wall (VW) at OB level of Austrolebias charrua fish presents three neurogenic niches (transitional 1, medial 2 and ventral 3). The main cellular types described in other vertebrate neurogenic niches were identified (transient amplifying cells, stem cells and migrating neuroblasts). However, elongated vimentin/BLBP+ radial glia were the predominant cells in transitional and ventral zones. Use of halogenated thymidine analogs chloro- and iodo-deoxyuridine administered at different experimental times showed that both regions have the highest cell proliferation and migration rates. Zone 1 migration was toward the OB and telencephalon, whereas in zone 3, migration was directed toward the OB rostral portion constituting the equivalent of the mammal rostral migratory band. Medial zone (MZ) has fewer proliferating non-migrant cells that are the putative stem cells as indicated by short and long proliferation assays as well as cell lineage markers. Sparse migration observed suggests MZ may collaborate with VW growth. Scanning electron microscopy evidenced that the whole VW has only monociliated cells with remarkable differences in cilium length among regions. In OB there are monociliated cells with dwarf cilium whereas ventral telencephalon shows long cilium. Summarizing, we identified three neurogenic niches that might serve different functional purposes.

Stem Cell-Mediated Regeneration of the Adult Brain

Acute or chronic injury of the adult mammalian brain is often associated with persistent functional deficits as its potential for regeneration and capacity to rebuild lost neural structures is limited. However, the discovery that neural stem cells (NSCs) persist throughout life in discrete regions of the brain, novel approaches to induce the formation of neuronal and glial cells, and recently developed strategies to generate tissue for exogenous cell replacement strategies opened novel perspectives how to regenerate the adult brain. Here, we will review recently developed approaches for brain repair and discuss future perspectives that may eventually allow for developing novel treatment strategies in acute and chronic brain injury.

Myeloperoxidase Inhibition Increases Neurogenesis after Ischemic Stroke

The relationship between inflammation and neurogenesis in stroke is currently not well understood. Focal ischemia enhances cell proliferation and neurogenesis in the neurogenic regions, including the subventricular zone (SVZ), dentate gyrus, as well as the non-neurogenic striatum, and cortex in the ischemic hemisphere. Myeloperoxidase (MPO) is a potent oxidizing enzyme secreted during inflammation by activated leukocytes, and its enzymatic activity is highly elevated after stroke. In this study, we investigated whether the inhibition of MPO activity by a specific irreversible inhibitor, 4-aminobenzoic acid hydrazide (ABAH) (MPO^-/- mice) can increase neurogenesis after transient middle cerebral artery occlusion in mice. ABAH administration increased the number of proliferating bromodeoxyuridine (BrdU)-positive cells expressing markers for neural stems cells, astrocytes, neuroprogenitor cells (Nestin), and neuroblasts (doublecortin) in the ischemic SVZ, anterior SVZ, striatum, and cortex. MPO inhibition also increased levels of brain-derived neurotrophic factor, phosphorylation of cAMP response element-binding protein (Ser133), acetylated H3, and NeuN to promote neurogenesis in the ischemic SVZ. ABAH treatment also increased chemokine CXC receptor 4 expression in the ischemic SVZ. MPO-deficient mice treated with vehicle or ABAH both showed similar effects on the number of BrdU⁺ cells in the ischemic hemisphere, demonstrating that ABAH is specific to MPO. Taken together, our results underscore a detrimental role of MPO activity to postischemia neurogenesis and that a strategy to inhibit MPO activity can increase cell proliferation and improve neurogenesis after ischemic stroke.

Traumatic Brain Injury Activation of the Adult Subventricular Zone Neurogenic Niche

Traumatic brain injury (TBI) is common in both civilian and military life, placing a large burden on survivors and society. However, with the recognition of neural stem cells in adult mammals, including humans, came the possibility to harness these cells for repair of damaged brain, whereas previously this was thought to be impossible. In this review, we focus on the rodent adult subventricular zone (SVZ), an important neurogenic niche within the mature brain in which neural stem cells continue to reside. We review how the SVZ is perturbed following various animal TBI models with regards to cell proliferation, emigration, survival, and differentiation, and we review specific molecules involved in these processes. Together, this information suggests next steps in attempting to translate knowledge from TBI animal models into human therapies for TBI.

Effect of thrombin preconditioning on migration of subventricular zone-derived cells after intracerebral hemorrhage in rats

OBJECTIVE

To investigate the effect of thrombin preconditioning (TPC) on the intracerebral hemorrhage (ICH)-induced proliferation, migration, and function of subventriclular zone (SVZ) cells and to find new strategies that enhance endogenous neurogenesis after ICH.

METHODS

Male Sprague-Dawley rats were randomly divided into 3 groups (ICH, TPC, and control group). Rats of each group were randomly divided into 5 subgroups (3-d, 7-d, 14-d, 21-d, and 28-d subgroup). ICH was caused by intrastrial stereotactic administration of collagenase type IV. Brdu was used to label newborn SVZ cells. Organotypic brain slices were cultured to dynamically observe the migration of SVZ cells at living brain tissue. Migration of Dil-labeled SVZ cells in living brain slices was traced by time-lapse microscopy. To assess whether SVZ cells migrating to injured striatum had the ability to form synapses with other cells, brain slices from each group were double immunolabeled with Brdu and synapsin I.

RESULTS

The number of Brdu-positive cells markedly increased in the ipsilateral SVZ and striatum 3 days after TPC, peaked at 14 days (P < 0.01), continued to 21 days, and then gradually decreased at 28 days with significant difference compared to the ICH group at each time point (P < 0.01). Migration of Dil-labeled SVZ cells in brain slices in each group was observed and imaged during a 12-h period. Dil-labeled SVZ cells in the TPC group were observed to migrate laterally toward striatum with time with a faster velocity compared to the ICH group (P < 0.01). Our study also demonstrated that TPC induced strong colocalization of Brdu and synapsin I in the ipsilateral striatum between 3 and 28 days after injury.TPC made colocalization of Brdu and synapsin I appear earlier and continue for a longer time compared to the ICH group.

CONCLUSIONS

Our results demonstrated that TPC could promote proliferation, migration, and function of SVZ cells after ICH, which may provide a new idea for enhancing endogenous neurogenesis and developing new therapeutic strategies against ICH-induced brain injury.

Neural stem cell heterogeneity through time and space in the ventricular-subventricular zone

BACKGROUND

The origin and classification of neural stem cells (NSCs) has been a subject of intense investigation for the past two decades. Efforts to categorize NSCs based on their location, function and expression have established that these cells are a heterogeneous pool in both the embryonic and adult brain. The discovery and additional characterization of adult NSCs has introduced the possibility of using these cells as a source for neuronal and glial replacement following injury or disease. To understand how one could manipulate NSC developmental programs for therapeutic use, additional work is needed to elucidate how NSCs are programmed and how signals during development are interpreted to determine cell fate.

OBJECTIVE

This review describes the identification, classification and characterization of NSCs within the large neurogenic niche of the ventricular-subventricular zone (V-SVZ).

METHODS

A literature search was conducted using Pubmed including the keywords "ventricular-subventricular zone," "neural stem cell," "heterogeneity," "identity" and/or "single cell" to find relevant manuscripts to include within the review. A special focus was placed on more recent findings using single-cell level analyses on neural stem cells within their niche(s).

RESULTS

This review discusses over 20 research articles detailing findings on V-SVZ NSC heterogeneity, over 25 articles describing fate determinants of NSCs, and focuses on 8 recent publications using distinct single-cell analyses of neural stem cells including flow cytometry and RNA-seq. Additionally, over 60 manuscripts highlighting the markers expressed on cells within the NSC lineage are included in a chart divided by cell type.

CONCLUSIONS

Investigation of NSC heterogeneity and fate decisions is ongoing. Thus far, much research has been conducted in mice however, findings in human and other mammalian species are also discussed here. Implications of NSC heterogeneity established in the embryo for the properties of NSCs in the adult brain are explored, including how these cells may be redirected after injury or genetic manipulation.

[Cellular replacement strategies and adult neurogenesis in idiopathic Parkinson's disease]

Parkinson's disease (PD) is the most common age-related movement disorder and characterized by slowly progressive neurodegeneration resulting in motor symptoms, such as bradykinesia, rigidity, tremor and postural instability. Moreover, non-motor symptoms, such as hyposmia, anxiety and depression reduce the quality of life in PD. Motor symptoms are associated with a distinct striatal dopaminergic deficit resulting from axonal dysfunction and neuronal loss in the substantia nigra (SN). Recent progress in stem cell technology allows the optimization of cellular transplantation strategies in order to alleviate the motor deficit, which potentially leads to a reactivation of this therapeutic strategy. Besides neurodegenerative processes impaired adult neurogenesis and consequentially reduced endogenous cellular plasticity may play an important role in PD. This article discusses the notion that non-motor symptoms in PD may partly be explained by reduced adult neurogenesis in the olfactory bulb and hippocampus.

Cell migration in the developing rodent olfactory system

The components of the nervous system are assembled in development by the process of cell migration. Although the principles of cell migration are conserved throughout the brain, different subsystems may predominantly utilize specific migratory mechanisms, or may display unusual features during migration. Examining these subsystems offers not only the potential for insights into the development of the system, but may also help in understanding disorders arising from aberrant cell migration. The olfactory system is an ancient sensory circuit that is essential for the survival and reproduction of a species. The organization of this circuit displays many evolutionarily conserved features in vertebrates, including molecular mechanisms and complex migratory pathways. In this review, we describe the elaborate migrations that populate each component of the olfactory system in rodents and compare them with those described in the well-studied neocortex. Understanding how the components of the olfactory system are assembled will not only shed light on the etiology of olfactory and sexual disorders, but will also offer insights into how conserved migratory mechanisms may have shaped the evolution of the brain.

Neurogenesis and Gliogenesis in Nervous System Plasticity and Repair

The brain constantly changes to store memories and adapt to new conditions. One type of plasticity that has gained increasing interest during the last years is the generation of new cells. The generation of both new neurons and glial cells contributes to neural plasticity and to some neural repair. There are substantial differences between mammalian species with regard to the extent of and mechanisms behind cell exchange in neural plasticity. Both neurogenesis and gliogenesis have several specific features in humans, which may contribute to the unique plasticity of the human brain.

Asiatic Acid Prevents the Deleterious Effects of Valproic Acid on Cognition and Hippocampal Cell Proliferation and Survival

Valproic acid (VPA) is commonly prescribed as an anticonvulsant and mood stabilizer used in the treatment of epilepsy and bipolar disorder. A recent study has demonstrated that VPA reduces histone deacetylase (HDAC) activity, an action which is believed to contribute to the effects of VPA on neural stem cell proliferation and differentiation which may explain the cognitive impairments produced in rodents and patients. Asiatic acid is a triterpenoid derived from the medicinal plant Centella asiatica. Our previous study has shown that Asiatic acid improves working spatial memory and increases cell proliferation in the sub granular zone of the hippocampal dentate gyrus. In the present study we investigate the effects of Asiatic acid in preventing the memory and cellular effects of VPA. Male Spraque-Dawley rats were orally administered Asiatic acid (30 mg/kg/day) for 28 days, while VPA-treated animals received injections of VPA (300 mg/kg) twice a day from Day 15 to Day 28 for 14 days. Spatial memory was determined using the novel object location (NOL) test and hippocampal cell proliferation and survival was quantified by immuostaining for Ki-67 and Bromodeoxyuridine (BrdU), respectively. The results showed that VPA-treated animals were unable to discriminate between objects in familiar and novel locations. Moreover, VPA significantly reduced numbers of Ki-67 and BrdU positive cells. These results indicate that VPA treatment caused impairments of spatial working memory, cell proliferation and survival in the subgranular zone (SGZ) of the hippocampal dentate gyrus (DG). However, these abnormalities were restored to control levels by co-treatment with Asiatic acid. These data demonstrate that Asiatic acid could prevent the spatial memory and neurogenesis impairments caused by VPA.

Prox1 Is Required for Oligodendrocyte Cell Identity in Adult Neural Stem Cells of the Subventricular Zone

Adult neural stem cells with the ability to generate neurons and glia cells are active throughout life in both the dentate gyrus (DG) and the subventricular zone (SVZ). Differentiation of adult neural stem cells is induced by cell fate determinants like the transcription factor Prox1. Evidence has been provided for a function of Prox1 as an inducer of neuronal differentiation within the DG. We now show that within the SVZ Prox1 induces differentiation into oligodendrocytes. Moreover, we find that loss of Prox1 expression in vivo reduces cell migration into the corpus callosum, where the few Prox1 deficient SVZ-derived remaining cells fail to differentiate into oligodendrocytes. Thus, our work uncovers a novel function of Prox1 as a fate determinant for oligodendrocytes in the adult mammalian brain. These data indicate that the neurogenic and oligodendrogliogenic lineages in the two adult neurogenic niches exhibit a distinct requirement for Prox1, being important for neurogenesis in the DG but being indispensable for oligodendrogliogenesis in the SVZ. Stem Cells 2016;34:2115-2129.

Control of adult neurogenesis by programmed cell death in the mammalian brain

The presence of neural stem cells (NSCs) and the production of new neurons in the adult brain have received great attention from scientists and the public because of implications to brain plasticity and their potential use for treating currently incurable brain diseases. Adult neurogenesis is controlled at multiple levels, including proliferation, differentiation, migration, and programmed cell death (PCD). Among these, PCD is the last and most prominent process for regulating the final number of mature neurons integrated into neural circuits. PCD can be classified into apoptosis, necrosis, and autophagic cell death and emerging evidence suggests that all three may be important modes of cell death in neural stem/progenitor cells. However, the molecular mechanisms that regulate PCD and thereby impact the intricate balance between self-renewal, proliferation, and differentiation during adult neurogenesis are not well understood. In this comprehensive review, we focus on the extent, mechanism, and biological significance of PCD for the control of adult neurogenesis in the mammalian brain. The role of intrinsic and extrinsic factors in the regulation of PCD at the molecular and systems levels is also discussed. Adult neurogenesis is a dynamic process, and the signals for differentiation, proliferation, and death of neural progenitor/stem cells are closely interrelated. A better understanding of how adult neurogenesis is influenced by PCD will help lead to important insights relevant to brain health and diseases.

Lifestyle Shapes the Dialogue between Environment, Microglia, and Adult Neurogenesis

Lifestyle modulates brain function. Diet, stress levels, and physical exercise among other factors influence the "brain cognitive reserve", that is, the capacity of the brain to maintain a normal function when confronting neurodegenerative diseases, injury, and/or aging. This cognitive reserve relays on several cellular and molecular elements that contribute to brain plasticity allowing adaptive responses to cognitive demands, and one of its key components is the hippocampal neurogenic reserve. Hippocampal neural stem cells give rise to new neurons that integrate into the local circuitry and contribute to hippocampal functions such as memory and learning. Importantly, adult hippocampal neurogenesis is well-known to be modulated by the demands of the environment and lifestyle factors. Diet, stress, and physical exercise directly act on neural stem cells and/or their progeny, but, in addition, they may also indirectly affect neurogenesis by acting on microglia. Microglia, the guardians of the brain, rapidly sense changes in the brain milieu, and it has been recently shown that their function is affected by lifestyle factors. However, few studies have analyzed the modulatory effect of microglia on adult neurogenesis in these conditions. Here, we review the current knowledge about the dialogue maintained between microglia and the hippocampal neurogenic cascade. Understanding how the communication between microglia and hippocampal neurogenesis is affected by lifestyle choices is crucial to maintain the brain cognitive reserve and prevent the maladaptive responses that emerge during disease or injury through adulthood and aging.

Implications of irradiating the subventricular zone stem cell niche

Radiation therapy is a standard treatment for brain tumor patients. However, it comes with side effects, such as neurological deficits. While likely multi-factorial, the effect may in part be associated with the impact of radiation on the neurogenic niches. In the adult mammalian brain, the neurogenic niches are localized in the subventricular zone (SVZ) of the lateral ventricles and the dentate gyrus of the hippocampus, where the neural stem cells (NSCs) reside. Several reports showed that radiation produces a drastic decrease in the proliferative capacity of these regions, which is related to functional decline. In particular, radiation to the SVZ led to a reduced long-term olfactory memory and a reduced capacity to respond to brain damage in animal models, as well as compromised tumor outcomes in patients. By contrast, other studies in humans suggested that increased radiation dose to the SVZ may be associated with longer progression-free survival in patients with high-grade glioma. In this review, we summarize the cellular and functional effects of irradiating the SVZ niche. In particular, we review the pros and cons of using radiation during brain tumor treatment, discussing the complex relationship between radiation dose to the SVZ and both tumor control and toxicity.

Role of the Retinoblastoma protein, Rb, during adult neurogenesis in the olfactory bulb

Adult neural stem cells (aNSCs) are relatively quiescent populations that give rise to distinct neuronal subtypes throughout life, yet, at a very low rate and restricted differentiation potential. Thus, identifying the molecular mechanisms that control their cellular expansion is critical for regeneration after brain injury. Loss of the Retinoblastoma protein, Rb, leads to several defects in cell cycle as well as neuronal differentiation and migration during brain development. Here, we investigated the role of Rb during adult neurogenesis in the olfactory bulb (OB) by inducing its temporal deletion in aNSCs and progenitors. Loss of Rb was associated with increased proliferation of adult progenitors in the subventricular zone (SVZ) and the rostral migratory stream (RMS) but did not alter self-renewal of aNSCs or neuroblasts subsequent migration and terminal differentiation. Hence, one month after their birth, Rb-null neuroblasts were able to differentiate into distinct subtypes of GABAergic OB interneurons but were gradually lost after 3 months. Similarly, Rb controlled aNSCs/progenitors proliferation in vitro without affecting their differentiation capacity. This enhanced SVZ/OB neurogenesis associated with loss of Rb was only transient and negatively affected by increased apoptosis indicating a critical requirement for Rb in the long-term survival of adult-born OB interneurons.

Neural Substrate Expansion for the Restoration of Brain Function

Restoring neurological and cognitive function in individuals who have suffered brain damage is one of the principal objectives of modern translational neuroscience. Electrical stimulation approaches, such as deep-brain stimulation, have achieved the most clinical success, but they ultimately may be limited by the computational capacity of the residual cerebral circuitry. An alternative strategy is brain substrate expansion, in which the computational capacity of the brain is augmented through the addition of new processing units and the reconstitution of network connectivity. This latter approach has been explored to some degree using both biological and electronic means but thus far has not demonstrated the ability to reestablish the function of large-scale neuronal networks. In this review, we contend that fulfilling the potential of brain substrate expansion will require a significant shift from current methods that emphasize direct manipulations of the brain (e.g., injections of cellular suspensions and the implantation of multi-electrode arrays) to the generation of more sophisticated neural tissues and neural-electric hybrids in vitro that are subsequently transplanted into the brain. Drawing from neural tissue engineering, stem cell biology, and neural interface technologies, this strategy makes greater use of the manifold techniques available in the laboratory to create biocompatible constructs that recapitulate brain architecture and thus are more easily recognized and utilized by brain networks.

Exosomes as Novel Regulators of Adult Neurogenic Niches

Adult neurogenesis has been convincingly demonstrated in two regions of the mammalian brain: the sub-granular zone (SGZ) of the dentate gyrus (DG) in the hippocampus, and the sub-ventricular zone (SVZ) of the lateral ventricles (LV). SGZ newborn neurons are destined to the granular cell layer (GCL) of the DG, while new neurons from the SVZ neurons migrate rostrally into the olfactory bulb (OB). The process of adult neurogenesis persists throughout life and is supported by a pool of neural stem cells (NSCs), which reside in a unique and specialized microenvironment known as "neurogenic niche". Neurogenic niches are structured by a complex organization of different cell types, including the NSC-neuron lineage, glial cells and vascular cells. Thus, cell-to-cell communication plays a key role in the dynamic modulation of homeostasis and plasticity of the adult neurogenic process. Specific cell-cell contacts and extracellular signals originated locally provide the necessary support and regulate the balance between self-renewal and differentiation of NSCs. Furthermore, extracellular signals originated at distant locations, including other brain regions or systemic organs, may reach the niche through the cerebrospinal fluid (CSF) or the vasculature and influence its nature. The role of several secreted molecules, such as cytokines, growth factors, neurotransmitters, and hormones, in the biology of adult NSCs, has been systematically addressed. Interestingly, in addition to these well-recognized signals, a novel type of intercellular messengers has been identified recently: the extracellular vesicles (EVs). EVs, and particularly exosomes, are implicated in the transfer of mRNAs, microRNAs (miRNAs), proteins and lipids between cells and thus are able to modify the function of recipient cells. Exosomes appear to play a significant role in different stem cell niches such as the mesenchymal stem cell niche, cancer stem cell niche and pre-metastatic niche; however, their roles in adult neurogenic niches remain virtually unexplored. This review focuses on the current knowledge regarding the functional relationship between cellular and extracellular components of the adult SVZ and SGZ neurogenic niches, and the growing evidence that supports the potential role of exosomes in the physiology and pathology of adult neurogenesis.

Induction of Neurorestoration From Endogenous Stem Cells

Neural stem cells (NSCs) persist in the subventricular zone lining the ventricles of the adult brain. The resident stem/progenitor cells can be stimulated in vivo by neurotrophic factors, hematopoietic growth factors, magnetic stimulation, and/or physical exercise. In both animals and humans, the differentiation and survival of neurons arising from the subventricular zone may also be regulated by the trophic factors. Since stem/progenitor cells present in the adult brain and the production of new neurons occurs at specific sites, there is a possibility for the treatment of incurable neurological diseases. It might be feasible to induce neurogenesis, which would be particularly efficacious in the treatment of striatal neurodegenerative conditions such as Huntington's disease, as well as cerebrovascular diseases such as ischemic stroke and cerebral palsy, conditions that are widely seen in the clinics. Understanding of the molecular control of endogenous NSC activation and progenitor cell mobilization will likely provide many new opportunities as therapeutic strategies. In this review, we focus on endogenous stem/progenitor cell activation that occurs in response to exogenous factors including neurotrophic factors, hematopoietic growth factors, magnetic stimulation, and an enriched environment. Taken together, these findings suggest the possibility that functional brain repair through induced neurorestoration from endogenous stem cells may soon be a clinical reality.

Cholinergic Circuit Control of Postnatal Neurogenesis

New neuron addition via continued neurogenesis in the postnatal/adult mammalian brain presents a distinct form of nervous system plasticity. During embryonic development, precise temporal and spatial patterns of neurogenesis are necessary to create the nervous system architecture. Similar between embryonic and postnatal stages, neurogenic proliferation is regulated by neural stem cell (NSC)-intrinsic mechanisms layered upon cues from their local microenvironmental niche. Following developmental assembly, it remains relatively unclear what may be the key driving forces that sustain continued production of neurons in the postnatal/adult brain. Recent experimental evidence suggests that patterned activity from specific neural circuits can also directly govern postnatal/adult neurogenesis. Here, we review experimental findings that revealed cholinergic modulation, and how patterns of neuronal activity and acetylcholine release may differentially or synergistically activate downstream signaling in NSCs. Higher-order excitatory and inhibitory inputs regulating cholinergic neuron firing, and their implications in neurogenesis control are also considered.

A Novel Cell Therapy Method for Recovering after Brain Stroke in Rats

BACKGROUND

Nowadays, stroke leads to a significant part of the adult mortality and morbidity and also it could result in some neurological deficits in the patients' lives. Cell therapy has opened a new approach to treat the brain ischemia and reduce its terrible effects on the patients' lives. There are several articles which show that the cell therapy could be beneficial for treating brain stroke. In this study, we have planned to present a new cell therapy method for stroke by administration of Mesenchymal stem cells and differentiated neural stem cells without astrocytes.

METHOD AND MATERIALS

The Mesenchymal stem cells were isolated from tibia and femur of a 250~300 g rat and they were cultured in DMEM/F12, 10% fetal bovine serum, 1% Pen/Strep. Neural stem cells were isolated from 14 days rat embryo ganglion eminence and were cultured in NSA media containing Neurobasal, 2% B27, bFGF 10 ng/ml and EGF 20 ng/ml after 5 days they formed some neurospheres. The isolated neural stem cells were differentiated to neural lineages by adding 5% fetal bovine serum to their culture media. After 48 hours the astrocytes were depleted by using MACS kit.

RESULTS

The group that received Mesenchymal stem cells systemically and differentiated neural stem cells without astrocytes had the best neurological outcomes and the least infarct volume and apoptosis. It could be understood that this cell therapy method might cause almost full recovery after brain stoke.

CONCLUSION

Using combination cell therapy with Mesenchymal stem cells and differentiated neural stem cells with removed astrocyte could provide a novel method for curing brain stroke.

The Role of the Microenvironmental Niche in Declining Stem-Cell Functions Associated with Biological Aging

Aging is strongly correlated with decreases in neurogenesis, the process by which neural stem and progenitor cells proliferate and differentiate into new neurons. In addition to stem-cell-intrinsic factors that change within the aging stem-cell pool, recent evidence emphasizes new roles for systemic and microenvironmental factors in modulating the neurogenic niche. This article focuses on new insights gained through the use of heterochronic parabiosis models, in which an old mouse and a young circulatory system are joined. By studying the brains of both young and old mice, researchers are beginning to uncover circulating proneurogenic "youthful" factors and "aging" factors that decrease stem-cell activity and neurogenesis. Ultimately, the identification of factors that influence stem-cell aging may lead to strategies that slow or even reverse age-related decreases in neural-stem-cell (NSC) function and neurogenesis.

Interneurons in the human olfactory system in Alzheimer's disease

The principal olfactory structures display Alzheimer's disease (AD) related pathology at early stages of the disease. Consequently, olfactory deficits are among the earliest symptoms. Reliable olfactory tests for accurate clinical diagnosis are rarely made. In addition, neuropathological analysis postmortem of olfactory structures is often not made. Therefore, the relationship between the clinical features and the underlying pathology is poorly defined. Traditionally, research into Alzheimer's disease has focused on the degeneration of cortical temporal projection neurons and cholinergic neurons. Recent evidence has demonstrated the neurodegeneration of interneuron populations in AD. This review provides an updated overview of the pathological involvement of interneuron populations in the human olfactory system in Alzheimer's disease.

Neurogenesis following Stroke Affecting the Adult Brain

A bulk of experimental evidence supports the idea that the stroke-damaged adult brain makes an attempt to repair itself by producing new neurons also in areas where neurogenesis does not normally occur (e.g., the striatum and cerebral cortex). Knowledge about mechanisms regulating the different steps of neurogenesis after stroke is rapidly increasing but still incomplete. The functional consequences of stroke-induced neurogenesis and the level of integration of the new neurons into existing neural circuitries are poorly understood. To have a substantial impact on the recovery after stroke, this potential mechanism for self-repair needs to be enhanced, primarily by increasing the survival and differentiation of the generated neuroblasts. Moreover, for efficient repair, optimization of neurogenesis most likely needs to be combined with promotion of other endogenous neuroregenerative responses (e.g., protection and sprouting of remaining mature neurons, transplantation of neural stem/progenitor cells [NSPC]-derived neurons and glia cells, and modulation of inflammation).

Effects of Asiatic Acid on Spatial Working Memory and Cell Proliferation in the Adult Rat Hippocampus

Asiatic acid is a pentacyclic triterpene from Centella asiatica. Previous studies have reported that asiatic acid exhibits antioxidant and neuroprotective activities in cell culture. It also prevents memory deficits in animal models. The objective of this study was to investigate the relationship between spatial working memory and changes in cell proliferation within the hippocampus after administration of asiatic acid to male Spraque-Dawley rats. Control rats received vehicle (propylene glycol) while treated rats received asiatic acid (30 mg/kg) orally for 14 or 28 days. Spatial memory was determined using the novel object location (NOL) test. In animals administered asiatic acid for both 14 and 28 days, the number of Ki-67 positive cells in the subgranular zone of the dentate gyrus was significantly higher than in control animals. This was associated with a significant increase in their ability to discriminate between novel and familiar object locations in a novel object discrimination task, a hippocampus-dependent spatial memory test. Administration of asiatic acid also significantly increased doublecortin (DCX) and Notch1 protein levels in the hippocampus. These findings demonstrate that asiatic acid treatment may be a potent cognitive enhancer which improves hippocampal-dependent spatial memory, likely by increasing hippocampal neurogenesis.

Role of a Burr Hole and Calvarial Bone Marrow-Derived Stem Cells in the Ischemic Rat Brain: A Possible Mechanism for the Efficacy of Multiple Burr Hole Surgery in Moyamoya Disease

Objective

This study investigates the role of a burr hole and calvarial bone marrow-derived stem cells (BMSCs) in a transient ischemic brain injury model in the rat and postulates a possible mechanism for the efficacy of multiple cranial burr hole (MCBH) surgery in moyamoya disease (MMD).

Methods

Twenty Sprague-Dawley rats (250 g, male) were divided into four groups : normal control group (n=5), burr hole group (n=5), ischemia group (n=5), and ischemia+burr hole group (n=5). Focal ischemia was induced by the transient middle cerebral artery occlusion (MCAO). At one week after the ischemic injury, a 2 mm-sized cranial burr hole with small cortical incision was made on the ipsilateral (left) parietal area. Bromodeoxyuridine (BrdU, 50 mg/kg) was injected intraperitoneally, 2 times a day for 6 days after the burr hole trephination. At one week after the burr hole trephination, brains were harvested. Immunohistochemical stainings for BrdU, CD34, VEGF, and Doublecortin and Nestin were done.

Results

In the ischemia+burr hole group, BrdU (+), CD34 (+), and Doublecortin (+) cells were found in the cortical incision site below the burr hole. A number of cells with Nestin (+) or VEGF (+) were found in the cerebral parenchyma around the cortical incision site. In the other groups, BrdU (+), CD34 (+), Doublecortin (+), and Nestin (+) cells were not detected in the corresponding area. These findings suggest that BrdU (+) and CD34 (+) cells are bone marrow-derived stem cells, which may be derived from the calvarial bone marrow through the burr hole. The existence of CD34 (+) and VEGF (+) cells indicates increased angiogenesis, while the existence of Doublecortin (+), Nestin (+) cells indicates increased neurogenesis.

Conclusion

Based on these findings, the BMSCs through burr holes seem to play an important role for the therapeutic effect of the MCBH surgery in MMD.

Current Neurogenic and Neuroprotective Strategies to Prevent and Treat Neurodegenerative and Neuropsychiatric Disorders

The adult central nervous system is commonly known to have a very limited regenerative capacity. The presence of functional stem cells in the brain can therefore be seen as a paradox, since in other organs these are known to counterbalance cell loss derived from pathological conditions. This fact has therefore raised the possibility to stimulate neural stem cell differentiation and proliferation or survival by either stem cell replacement therapy or direct administration of neurotrophic factors or other proneurogenic molecules, which in turn has also originated regenerative medicine for the treatment of otherwise incurable neurodegenerative and neuropsychiatric disorders that take a huge toll on society. This may be facilitated by the fact that many of these disorders converge on similar pathophysiological pathways: excitotoxicity, oxidative stress, neuroinflammation, mitochondrial failure, excessive intracellular calcium and apoptosis. This review will therefore focus on the most promising achievements in promoting neuroprotection and neuroregeneration reported to date.

Adding a spatial dimension to postnatal ventricular-subventricular zone neurogenesis

Neurogenesis does not stop abruptly at birth, but persists in specific brain regions throughout life. The neural stem cells (NSCs) located in the largest germinal region of the forebrain, the ventricular-subventricular zone (V-SVZ), replenish olfactory neurons throughout life. However, V-SVZ NSCs are heterogeneous: they have different embryonic origins and give rise to distinct neuronal subtypes depending on their location. In this Review, we discuss how this spatial heterogeneity arises, how it affects NSC biology, and why its consideration in future studies is crucial for understanding general principles guiding NSC self-renewal, differentiation and specification.

Lateralized differences in olfactory function and olfactory bulb volume relate to nasal septum deviation

One of the most common reasons for partial nasal obstruction is nasal septal deviation (NSD). The effect of a partial lateralized nasal obstruction on olfactory bulb (OB) volume remains unclear. Thus, the aim of this study was to investigate the side differences in olfactory function and OB in patients with serious NSD. Sixty-five volunteers were included: 22 patients with serious right NSD and 43 patients with left NSD. The patients' mean age was 22 years. All participants received volumetric magnetic resonance imaging scans of the entire brain and detailed lateralized olfactory tests. The majority of the patients exhibited an overall decreased olfactory function (as judged for the better nostril: functional anosmia in 3%, hyposmia in 72%, normosmia in 25%), which seems to be mostly due to the overall severe changes in nasal anatomy. As expected, olfactory function was significantly lower at the narrower side as indicated for odor thresholds, odor discrimination, and odor identification (P ≤ 0.005). When correlating relative scores and volumes (wider minus narrower side), a significantly positive correlation between the relative measures emerged for OB volume and odor identification, odor discrimination, and odor thresholds. Our study clearly highlights that septal deviation results in decreased olfactory function at the narrower side.

Stem cell niche irradiation in glioblastoma: providing a ray of hope?

Glioblastomas are organized hierarchically with a small number of glioblastoma stem cells that have unique self-renewal capacity and multilineage potency. The subventricular zone (SVZ) constitutes the largest neural stem cell niche in the adult human brain; it may also act as a reservoir of glioblastoma stem cells that can initiate, promote or repopulate a tumor. Incidental irradiation of SVZ has been shown to potentially influence outcomes suggesting that aggressively targeting the stem cell niche may offer a ray of hope in glioblastoma. The following review provides a summary of the experimental evidence supporting the origin and location of the putative glioblastoma stem cell in the SVZ, and offers a critical appraisal of the growing body of clinical evidence correlating SVZ dosimetry with outcomes in glioblastoma.

Adult Neurogenesis in Humans

Adult neurogenesis appears very well conserved among mammals. It was, however, not until recently that quantitative data on the extent of this process became available in humans, largely because of methodological challenges to study this process in man. There is substantial hippocampal neurogenesis in adult humans, but humans appear unique among mammals in that there is no detectable olfactory bulb neurogenesis but continuous addition of new neurons in the striatum.

Antisense oligonucleotides in therapy for neurodegenerative disorders

Antisense oligonucleotides are synthetic single stranded strings of nucleic acids that bind to RNA and thereby alter or reduce expression of the target RNA. They can not only reduce expression of mutant proteins by breakdown of the targeted transcript, but also restore protein expression or modify proteins through interference with pre-mRNA splicing. There has been a recent revival of interest in the use of antisense oligonucleotides to treat several neurodegenerative disorders using different approaches to prevent disease onset or halt disease progression and the first clinical trials for spinal muscular atrophy and amyotrophic lateral sclerosis showing promising results. For these trials, intrathecal delivery is being used but direct infusion into the brain ventricles and several methods of passing the blood brain barrier after peripheral administration are also under investigation.

New neurons for injured brains? The emergence of new genetic model organisms to study brain regeneration

Neuronal circuits in the adult brain have long been viewed as static and stable. However, research in the past 20 years has shown that specialized regions of the adult brain, which harbor adult neural stem cells, continue to produce new neurons in a wide range of species. Brain plasticity is also observed after injury. Depending on the extent and permissive environment of neurogenic regions, different organisms show great variability in their capacity to replace lost neurons by endogenous neurogenesis. In Zebrafish and Drosophila, the formation of new neurons from progenitor cells in the adult brain was only discovered recently. Here, we compare properties of adult neural stem cells, their niches and regenerative responses from mammals to flies. Current models of brain injury have revealed that specific injury-induced genetic programs and comparison of neuronal fitness are implicated in brain repair. We highlight the potential of these recently implemented models of brain regeneration to identify novel regulators of stem cell activation and regenerative neurogenesis.

Increased doublecortin (DCX) expression and incidence of DCX-immunoreactive multipolar cells in the subventricular zone-olfactory bulb system of suicides

Postmortem studies have confirmed the occurrence of adult hippocampal neurogenesis in humans and implicated this process in antidepressant response, yet neurogenesis in other regions remains to be examined in the context of depression. Here we assess the extent of subventricular zone-olfactory bulb (SVZ-OB) neurogenesis in adult humans having died by suicide. Protein expression of proliferative and neurogenic markers Sox2, proliferating cell nuclear antigen, and doublecortin (DCX) were examined in postmortem SVZ and OB samples from depressed suicides and matched sudden-death controls. In the SVZ, DCX-immunoreactive (IR) cells displayed phenotypes typical of progenitors, whereas in the olfactory tract (OT), they were multipolar with variable size and morphologies suggestive of differentiating cells. DCX expression was significantly increased in the OB of suicides, whereas SVZ DCX expression was higher among unmedicated, but not antidepressant-treated, suicides. Although very few DCX-IR cells were present in the control OT, they were considerably more common in suicides and correlated with OB DCX levels. Suicides also displayed higher DCX-IR process volumes. These results support the notion that OB neurogenesis is minimal in adult humans. They further raise the possibility that the differentiation and migration of SVZ-derived neuroblasts may be altered in unmedicated suicides, leading to an accumulation of ectopically differentiating cells in the OT. Normal SVZ DCX expression among suicides receiving antidepressants suggests a potentially novel mode of action of antidepressant medication. Given the modest group sizes and rarity of DCX-IR cells assessed here, a larger-scale characterization will be required before firm conclusions can be made regarding the identity of these cells.

Stem cells, mitochondria and aging

Decline in metabolism and regenerative potential of tissues are common characteristics of aging. Regeneration is maintained by somatic stem cells (SSCs), which require tightly controlled energy metabolism and genomic integrity for their homeostasis. Recent data indicate that mitochondrial dysfunction may compromise this homeostasis, and thereby contribute to tissue degeneration and aging. Progeroid Mutator mouse, accumulating random mtDNA point mutations in their SSCs, showed disturbed SSC homeostasis, emphasizing the importance of mtDNA integrity for stem cells. The mechanism involved changes in cellular redox-environment, including subtle increase in reactive oxygen species (H₂O₂and superoxide anion), which did not cause oxidative damage, but disrupted SSC function. Mitochondrial metabolism appears therefore to be an important regulator of SSC fate determination, and defects in it in SSCs may underlie premature aging. Here we review the current knowledge of mitochondrial contribution to SSC dysfunction and aging. This article is part of a Special Issue entitled: Mitochondrial Dysfunction in Aging.

Characterization of neural stem cells and their progeny in the sensory circumventricular organs of adult mouse

Although evidence has accumulated that neurogenesis and gliogenesis occur in the subventricular zone (SVZ) and subgranular zone (SGZ) of adult mammalian brains, recent studies indicate the presence of neural stem cells (NSCs) in adult brains, particularly the circumventricular regions. In the present study, we aimed to determine characterization of NSCs and their progenitor cells in the sensory circumventricular organs (CVOs), including organum vasculosum of the lamina terminalis, subfornical organ, and area postrema of adult mouse. There were two types of NSCs: tanycyte-like ependymal cells and astrocyte-like cells. Astrocyte-like NSCs proliferated slowly and oligodendrocyte progenitor cells (OPCs) and neural progenitor cells (NPCs) actively divided. Molecular marker protein expression of NSCs and their progenitor cells were similar to those reported in the SVZ and SGZ, except that astrocyte-like NSCs expressed S100β. These circumventricular NSCs possessed the capacity to give rise to oligodendrocytes and sparse numbers of neurons and astrocytes in the sensory CVOs and adjacent brain regions. The inhibition of vascular endothelial growth factor (VEGF) signaling by using a VEGF receptor-associated tyrosine kinase inhibitor AZD2171 largely suppressed basal proliferation of OPCs. A single systemic administration of lipopolysaccharide attenuated proliferation of OPCs and induced remarkable proliferation of microglia. The present study indicates that sensory circumventricular NSCs provide new neurons and glial cells in the sensory CVOs and adjacent brain regions.