Neuronal stem cells in the brain of adult vertebrates

Granagard administration prolongs the survival of human mesenchymal stem cells transplanted into a mouse model of multiple sclerosis

The clinical effect of human Mesenchymal stem cells (hMSCs) transplanted into EAE mice/MS patients is short lived due to poor survival of the transplanted cells. Since Granagard, a nanoformulation of pomegranate seed oil, extended the presence of Neuronal Stem cells transplanted into CJD mice brains, we tested whether this safe food supplement can also elongate the survival of hMSCs transplanted into EAE mice. Indeed, pathological studies 60 days post transplantation identified human cells only in brains of Granagard treated mice, concomitant with increased clinical activity. We conclude that Granagard may prolong the activity of stem cell transplantation in neurological diseases.

Modulation of gene expression on a transcriptome-wide level following human neural stem cell transplantation in aged mouse stroke brains

INTRODUCTION

Neural stem cell (NSC) transplantation offers great potential for treating ischemic stroke. Clinically, ischemia followed by reperfusion results in robust cerebrovascular injury that upregulates proinflammatory factors, disrupts neurovascular units, and causes brain cell death. NSCs possess multiple actions that can be exploited for reducing the severity of neurovascular injury. Our previous studies in young adult mice showed that human NSC transplantation during the subacute stage diminishes stroke pathophysiology and improves behavioral outcome.

METHODS

We employed a well-established and commonly used stroke model, middle cerebral artery occlusion with subsequent reperfusion (MCAO/R). Here, we assessed the outcomes of hNSC transplantation 48 h post-MCAO (24 h post-transplant) in aged mouse brains in response to stroke because aging is a crucial risk factor for cerebral ischemia. Next, we tested whether administration of the integrin α5β1 inhibitor, ATN-161, prior to hNSC transplantation further affects stoke outcome as compared with NSCs alone. RNA sequencing (RNA-seq) was used to assess the impact of hNSC transplantation on differentially expressed genes (DEGs) on a transcriptome-wide level.

RESULTS

Here, we report that hNSC-engrafted brains with or without ATN-161 showed significantly reduced infarct size, and attenuated the induction of proinflammatory factors and matrix metalloproteases. RNA-seq analysis revealed DEGs and molecular pathways by which hNSCs induce a beneficial post-stroke outcome in aged stroke brains. 811 genes were differentially expressed (651 downregulated and 160 upregulated) in hNSC-engrafted stroke brains. Functional pathway analysis identified enriched and depleted pathways in hNSC-engrafted aged mouse stroke brains. Depletion of pathways following hNSC-engraftment included signaling involving neuroinflammation, acute phase response, leukocyte extravasation, and phagosome formation. On the other hand, enrichment of pathways in hNSC-engrafted brains was associated with PPAR signaling, LXR/RXR activation, and inhibition of matrix metalloproteases. Hierarchical cluster analysis of DEGs in hNSC-engrafted brains indicate decreased expression of genes encoding TNF receptors, proinflammatory factors, apoptosis factors, adhesion and leukocyte extravasation, and Toll-like receptors.

CONCLUSIONS

Our study is the first to show global transcripts differentially expressed following hNSC transplantation in the subacute phase of stroke in aged mice. The outcome of our transcriptome study would be useful to develop new therapies ameliorating early-stage stroke injury.

Proverbs and Aphorisms in Neurorehabilitation: A Literature Review

Introduction: Brain plasticity is not limited to childhood or adolescence, as originally assumed, but continues into adulthood. Understanding this conceptual evolution about the nervous system, neuroscience and neurorehabilitation, researchers have left different proverbs and aphorisms derived of their investigations that are still used in university and postgraduate training. A proverb is defined as a phrase of popular origin traditionally repeated invariably, in which a moral thought, advice or teaching is expressed. On the other hand, an aphorism is understood as a brief and doctrinal phrase or sentence that is proposed as a rule in some science or art. The aim of this paper is to present a compilation of proverbs and aphorisms related to neuroscience and neurorehabilitation, classified chronologically, to illustrate the conceptual evolution about the brain and to improve our understanding about the management of neurological patients through the methods and techniques developed during the 19th, 20th and 21st centuries, as many therapies are based on them. Methods: A literature review was conducted based on the recommendations for Systematic Reviews guidelines for scoping reviews. A computerized search was conducted in the following electronic databases: CINAHL Medical Science, Medline through EBSCO, PubMed, Physiotherapy Evidence Database (PEDro) and Scopus, limiting the search to papers published until April 2021 in English and Spanish. Inverse searches were also carried out based on papers found in the databases. The following data were extracted: technique or approach; author; date of birth and death; proverbs and aphorisms; clinical interpretation. Results: Proverbs and aphorisms linked to authors such as Charles Edward Beevor (1854–1908), Heinrich Sebastian Frenkel (1860–1931), Rudolf Magnus (1873–1927), Nikolai Bernstein (1896–1966), Donald O. Hebb (1904–1985), Elwood Henneman (1915–1996), Wilder Graves Penfield (1891–1976), Humberto Augusto Maturana Romesín (1928), Edward Taub (1931), Janet Howard Carr (1933–2014), Roberta Barkworth Shepherd (1934), Brown & Hardman (1987), Jeffrey A. Kleim and Theresa A. Jones (2008) were compiled. Conclusion: Different authors have developed throughout history a series of proverbs and aphorisms related to neurosciences and neurorehabilitation that have helped to better our understanding of the nervous system and, therefore, in the management of the neurological patient through the methods and techniques developed throughout the 19th, 20th and 21st centuries.

Neural Stem Cells for Early Ischemic Stroke

Clinical treatments for ischemic stroke are limited. Neural stem cell (NSC) transplantation can be a promising therapy. Clinically, ischemia and subsequent reperfusion lead to extensive neurovascular injury that involves inflammation, disruption of the blood-brain barrier, and brain cell death. NSCs exhibit multiple potentially therapeutic actions against neurovascular injury. Currently, tissue plasminogen activator (tPA) is the only FDA-approved clot-dissolving agent. While tPA’s thrombolytic role within the vasculature is beneficial, tPA’s non-thrombolytic deleterious effects aggravates neurovascular injury, restricting the treatment time window (time-sensitive) and tPA eligibility. Thus, new strategies are needed to mitigate tPA’s detrimental effects and quickly mediate vascular repair after stroke. Up to date, clinical trials focus on the impact of stem cell therapy on neuro-restoration by delivering cells during the chronic stroke stage. Also, NSCs secrete factors that stimulate endogenous repair mechanisms for early-stage ischemic stroke. This review will present an integrated view of the preclinical perspectives of NSC transplantation as a promising treatment for neurovascular injury, with an emphasis on early-stage ischemic stroke. Further, this will highlight the impact of early sub-acute NSC delivery on improving short-term and long-term stroke outcomes.

Delay of gCJD aggravation in sick TgMHu2ME199K mice by combining NPC transplantation and Nano-PSO administration

gCJD is a fatal late-onset neurodegenerative disease linked to mutations in the PRNP gene. We have previously shown that transplantation of neural precursor cells (NPCs), or administration of a nanoformulation of pomegranate seed oil (Nano-PSO, GranaGard), into newborn asymptomatic TgMHu2ME199K mice modeling for E200K gCJD significantly delayed the advance of clinical disease. In the present study, we tested the individual and combined effects of both treatments in older and sick TgMHu2ME199K mice. We show that while transplantation of NPCs at both initial (140 days) and advance clinical states (230 days) arrested disease progression for about 30 days, after which scores rapidly climbed to those of untreated Tgs, administration of Nano-PSO to transplanted TgMHu2ME199K mice resulted in detention of disease advance for 60-80 days, followed by a slower disease progression thereafter. Pathological examinations demonstrated the combined treatment extended the survival of the transplanted NPCs, and also increased the generation of endogenous stem cells. Our results suggest that administration of Nano-PSO may increase the beneficial effects of NPCs transplantation.

Bacopa monnieri (L.) Wettst. Extract Improves Memory Performance via Promotion of Neurogenesis in the Hippocampal Dentate Gyrus of Adolescent Mice

Bacopa monnieri L. Wettst. (BM) is a botanical component of Ayurvedic medicines and of dietary supplements used worldwide for cognitive health and function. We previously reported that administration of BM alcoholic extract (BME) prevents trimethyltin (TMT)-induced cognitive deficits and hippocampal cell damage and promotes TMT-induced hippocampal neurogenesis. In this study, we demonstrate that administration of BME improves spatial working memory in adolescent (5-week- old) healthy mice but not adult (8-week-old) mice. Moreover, improved spatial working memory was retained even at 4 weeks after terminating 1-week treatment of adolescent mice. One-week BME treatment of adolescent mice significantly enhanced hippocampal BrdU incorporation and expression of genes involved in neurogenesis determined by RNAseq analysis. Cell death, as detected by histochemistry, appeared not to be significant. A significant increase in neurogenesis was observed in the dentate gyrus region 4 weeks after terminating 1-week treatment of adolescent mice with BME. Bacopaside I, an active component of BME, promoted the proliferation of neural progenitor cells in vitro in a concentration-dependent manner via the facilitation of the Akt and ERK1/2 signaling. These results suggest that BME enhances spatial working memory in healthy adolescent mice by promoting hippocampal neurogenesis and that the effects of BME are due, in significant amounts, to bacopaside I.

Adult Neurogenesis in the Context of Brain Repair and Functional Relevance

Urodeles and some fishes possess a remarkable capacity to regenerate their limbs/fins, a property that correlates with their additional ability to regenerate large areas of the brain and/or produce a variety of new neurons during adulthood. In contrast, neurogenesis in adult mammals is apparently restricted to two main regions, the subventricular zone of lateral ventricles and the subgranular zone of the hippocampus. There, astrocyte-like neural stem cells (NSCs) reside and derive into new neurons. Although it is becoming apparent that other brain regions carry out neurogenesis, in many cases, its functional significance is controversial, particularly, because very few putative NSCs capable of deriving into new neurons have been found. Hence, is renewal of certain neurons a requirement for a healthy brain? Are there specific physiological conditions that stimulate neurogenesis in a particular region? Does the complexity of the brain demand reduced neurogenesis? In this study, we review the production of new neurons in the vertebrate adult brain in the context of a possible functional relevance. In addition, we consider the intrinsic properties of potential cellular sources of new neurons, as well as the contribution of the milieu surrounding them to estimate the reparative capacity of the brain upon injury or a neurodegenerative condition. The conclusion of this review should bring into debate the potential and convenience of promoting neuronal regeneration in the adult human brain.

Tissue Engineering and Biomaterial Strategies to Elicit Endogenous Neuronal Replacement in the Brain

Neurogenesis in the postnatal mammalian brain is known to occur in the dentate gyrus of the hippocampus and the subventricular zone. These neurogenic niches serve as endogenous sources of neural precursor cells that could potentially replace neurons that have been lost or damaged throughout the brain. As an example, manipulation of the subventricular zone to augment neurogenesis has become a popular strategy for attempting to replace neurons that have been lost due to acute brain injury or neurodegenerative disease. In this review article, we describe current experimental strategies to enhance the regenerative potential of endogenous neural precursor cell sources by enhancing cell proliferation in neurogenic regions and/or redirecting migration, including pharmacological, biomaterial, and tissue engineering strategies. In particular, we discuss a novel replacement strategy based on exogenously biofabricated "living scaffolds" that could enhance and redirect endogenous neuroblast migration from the subventricular zone to specified regions throughout the brain. This approach utilizes the first implantable, biomimetic tissue-engineered rostral migratory stream, thereby leveraging the brain's natural mechanism for sustained neuronal replacement by replicating the structure and function of the native rostral migratory stream. Across all these strategies, we discuss several challenges that need to be overcome to successfully harness endogenous neural precursor cells to promote nervous system repair and functional restoration. With further development, the diverse and innovative tissue engineering and biomaterial strategies explored in this review have the potential to facilitate functional neuronal replacement to mitigate neurological and psychiatric symptoms caused by injury, developmental disorders, or neurodegenerative disease.

Neural stem cell therapy for neurovascular injury in Alzheimer's disease

Alzheimer's disease (AD), the most common form of dementia, is characterized by progressive neurodegeneration leading to severe cognitive decline and eventual death. AD pathophysiology is complex, but neurotoxic accumulation of amyloid-β (Aβ) and hyperphosphorylation of Tau are believed to be main drivers of neurodegeneration in AD. The formation and deposition of Aβ plaques occurs in the brain parenchyma as well as in the cerebral vasculature. Thus, proper blood-brain barrier (BBB) and cerebrovascular functioning are crucial for clearance of Aβ from the brain, and neurovascular dysfunction may be a critical component of AD development. Further, neuroinflammation and dysfunction of angiogenesis, neurogenesis, and neurorestorative capabilities play a role in AD pathophysiology. Currently, there is no effective treatment to prevent or restore loss of brain tissue and cognitive decline in patients with AD. Based on multifactorial and complex pathophysiological cascades in multiple Alzheimer's disease stages, effective AD therapies need to focus on targeting early AD pathology and preserving cerebrovascular function. Neural stem cells (NSCs) participate extensively in mammalian brain homeostasis and repair and exhibit pleiotropic intrinsic properties that likely make them attractive candidates for the treatment of AD. In the review, we summarize the current advances in knowledge regarding neurovascular aspects of AD-related neurodegeneration and discuss multiple actions of NSCs from preclinical studies of AD to evaluate their potential for future clinical treatment of AD.

Induction of typical and atypical neurogenesis in the adult substantia nigra after mouse embryonic stem cells transplantation

Neurogenesis in the substantia nigra (SN) has been a controversial issue. Here we report that neurogenesis can be induced in the adult rodent SN by transplantation of embryoid body cells (EBCs) derived from mouse embryonic stem cells. The detection of Sox2⁺ dividing (BrdU⁺) putative host neural precursor cells (NPCs) between 1 and 6 days post-transplantation (dpt) supported the neurogenic capacity of the adult SN. In agreement with the awakening of NPCs by EBCs, only host cells from implant-bearing SN were able to generate neurosphere-like aggregates in the presence of Egf and Fgf2. Later, at 15 dpt, a significant number of SN Dcx⁺ neuroblasts were detected. However, a continuous BrdU administration after transplantation showed that only a fraction (about 20-30%) of those host Dcx⁺ progeny derived from dividing cells and few BrdU⁺ cells, some of them NeuN⁺, survived up to 30 dpt. Unexpectedly, 25-30% of Dcx⁺ or Psa-Ncam⁺ cells at 15 dpt displayed astrocytic markers such as Gfap and S100b. Using a genetic lineage tracing strategy, we demonstrated that a large proportion of host Dcx⁺ and/or Tubb3⁺ neuroblasts originated from Gfap⁺ cells. Remarkably, new blood vessels formed in association with the neurogenic process that, when precluded, caused a reduction in neuroblast production. Accordingly, two proteins secreted by EBCs, Fgf2 and Vegf, were able to promote the emergence of Dcx⁺/Psa-Ncam⁺, Tubb3⁺ and NeuN⁺/BrdU⁺ cells in vivo in the absence of EBCs. We propose that the adult SN is a mostly silent neurogenic niche with the ability to generate new neurons by typical and atypical mechanisms.

Neural stem cell therapy for subacute and chronic ischemic stroke

Neural stem cells (NSCs) play vital roles in brain homeostasis and exhibit a broad repertoire of potentially therapeutic actions following neurovascular injury. One such injury is stroke, a worldwide leading cause of death and disability. Clinically, extensive injury from ischemic stroke results from ischemia-reperfusion (IR), which is accompanied by inflammation, blood-brain barrier (BBB) damage, neural cell death, and extensive tissue loss. Tissue plasminogen activator (tPA) is still the only US Food and Drug Administration-approved clot-lysing agent. Whereas the thrombolytic role of tPA within the vasculature is beneficial, the effects of tPA (in a non-thrombolytic role) within the brain parenchyma have been reported as harmful. Thus, new therapies are needed to reduce the deleterious side effects of tPA and quickly facilitate vascular repair following stroke. The Stroke Treatment Academic Industry Roundtable (STAIR) recommends that stroke therapies "focus on drugs/devices/treatments with multiple mechanisms of action and that target multiple pathways". Thus, based on multifactorial ischemic cascades in various stroke stages, effective stroke therapies need to focus on targeting and ameliorating early IR injury as well as facilitating angiogenesis, neurogenesis, and neurorestorative mechanisms following stroke. This review will discuss the preclinical perspectives of NSC transplantation as a promising treatment for neurovascular injury and will emphasize both the subacute and chronic phase of ischemic stroke.

Understanding the broad influence of sex hormones and sex differences in the brain

Sex hormones act throughout the entire brain of both males and females via both genomic and nongenomic receptors. Sex hormones can act through many cellular and molecular processes that alter structure and function of neural systems and influence behavior as well as providing neuroprotection. Within neurons, sex hormone receptors are found in nuclei and are also located near membranes, where they are associated with presynaptic terminals, mitochondria, spine apparatus, and postsynaptic densities. Sex hormone receptors also are found in glial cells. Hormonal regulation of a variety of signaling pathways as well as direct and indirect effects on gene expression induce spine synapses, up- or downregulate and alter the distribution of neurotransmitter receptors, and regulate neuropeptide expression and cholinergic and GABAergic activity as well as calcium sequestration and oxidative stress. Many neural and behavioral functions are affected, including mood, cognitive function, blood pressure regulation, motor coordination, pain, and opioid sensitivity. Subtle sex differences exist for many of these functions that are developmentally programmed by hormones and by not yet precisely defined genetic factors, including the mitochondrial genome. These sex differences and responses to sex hormones in brain regions, which influence functions not previously regarded as subject to such differences, indicate that we are entering a new era of our ability to understand and appreciate the diversity of gender-related behaviors and brain functions. © 2016 Wiley Periodicals, Inc.

Brain evolution by brain pathway duplication

Understanding the mechanisms of evolution of brain pathways for complex behaviours is still in its infancy. Making further advances requires a deeper understanding of brain homologies, novelties and analogies. It also requires an understanding of how adaptive genetic modifications lead to restructuring of the brain. Recent advances in genomic and molecular biology techniques applied to brain research have provided exciting insights into how complex behaviours are shaped by selection of novel brain pathways and functions of the nervous system. Here, we review and further develop some insights to a new hypothesis on one mechanism that may contribute to nervous system evolution, in particular by brain pathway duplication. Like gene duplication, we propose that whole brain pathways can duplicate and the duplicated pathway diverge to take on new functions. We suggest that one mechanism of brain pathway duplication could be through gene duplication, although other mechanisms are possible. We focus on brain pathways for vocal learning and spoken language in song-learning birds and humans as example systems. This view presents a new framework for future research in our understanding of brain evolution and novel behavioural traits.

Morphogenetic and Histogenetic Roles of the Temporal-Spatial Organization of Cell Proliferation in the Vertebrate Corticogenesis as Revealed by Inter-specific Analyses of the Optic Tectum Cortex Development

The central nervous system areas displaying the highest structural and functional complexity correspond to the so called cortices, i.e., concentric alternating neuronal and fibrous layers. Corticogenesis, i.e., the development of the cortical organization, depends on the temporal-spatial organization of several developmental events: (a) the duration of the proliferative phase of the neuroepithelium, (b) the relative duration of symmetric (expansive) versus asymmetric (neuronogenic) sub phases, (c) the spatial organization of each kind of cell division, (e) the time of determination and cell cycle exit and (f) the time of onset of the post-mitotic neuronal migration and (g) the time of onset of the neuronal structural and functional differentiation. The first five events depend on molecular mechanisms that perform a fine tuning of the proliferative activity. Changes in any of them significantly influence the cortical size or volume (tangential expansion and radial thickness), morphology, architecture and also impact on neuritogenesis and synaptogenesis affecting the cortical wiring. This paper integrates information, obtained in several species, on the developmental roles of cell proliferation in the development of the optic tectum (OT) cortex, a multilayered associative area of the dorsal (alar) midbrain. The present review (1) compiles relevant information on the temporal and spatial organization of cell proliferation in different species (fish, amphibians, birds, and mammals), (2) revises the main molecular events involved in the isthmic organizer (IsO) determination and localization, (3) describes how the patterning installed by IsO is translated into spatially organized neural stem cell proliferation (i.e., by means of growth factors, receptors, transcription factors, signaling pathways, etc.) and (4) describes the morpho- and histogenetic effect of a spatially organized cell proliferation in the above mentioned species. A brief section on the OT evolution is also included. This section considers how the differential operation of cell proliferation could explain differences among species.

Differential thyroid hormone sensitivity of fast cycling progenitors in the neurogenic niches of tadpoles and juvenile frogs

Adult neurogenesis occurs in neural stem cell (NSC) niches where slow cycling stem cells give rise to faster cycling progenitors. In the adult mouse NSC niche thyroid hormone, T3, and its receptor TRα act as a neurogenic switch promoting progenitor cell cycle completion and neuronal differentiation. Little is known about whether and how T3 controls proliferation of differentially cycling cells during xenopus neurogenesis. To address this question, we first used Sox3 as a marker of stem cell and progenitor populations and then applied pulse-chase EdU/IdU incorporation experiments to identify Sox3-expressing slow cycling (NSC) and fast cycling progenitor cells. We focused on the lateral ventricle of Xenopus laevis and two distinct stages of development: late embryonic development (pre-metamorphic) and juvenile frogs (post-metamorphic). These stages were selected for their relatively stable thyroid hormone availability, either side of the major dynamic phase represented by metamorphosis. TRα expression was found in both pre and post-metamorphic neurogenic regions. However, exogenous T3 treatment only increased proliferation of the fast cycling Sox3+ cell population in post-metamorphic juveniles, having no detectable effect on proliferation in pre-metamorphic tadpoles. We hypothesised that the resistance of proliferative cells to exogenous T3 in pre-metamorphic tadpoles could be related to T3 inactivation by the inactivating Deiodinase 3 enzyme. Expression of dio3 was widespread in the tadpole neurogenic niche, but not in the juvenile neurogenic niche. Use of a T3-reporter transgenic line showed that in juveniles, T3 had a direct transcriptional effect on rapid cycling progenitors. Thus, the fast cycling progenitor cells in the neurogenic niche of tadpoles and juvenile frogs respond differentially to T3 as a function of developmental stage.

Eva1 Maintains the Stem-like Character of Glioblastoma-Initiating Cells by Activating the Noncanonical NF-κB Signaling Pathway

Glioblastoma (GBM)-initiating cells (GIC) are a tumorigenic subpopulation that are resistant to radio- and chemotherapies and are the source of disease recurrence. Therefore, the identification and characterization of GIC-specific factors is critical toward the generation of effective GBM therapeutics. In this study, we investigated the role of epithelial V-like antigen 1 (Eva1, also known as myelin protein zero-like 2) in stemness and GBM tumorigenesis. Eva1 was prominently expressed in GICs in vitro and in stem cell marker (Sox2, CD15, CD49f)-expressing cells derived from human GBM tissues. Eva1 knockdown in GICs reduced their self-renewal and tumor-forming capabilities, whereas Eva1 overexpression enhanced these properties. Eva1 deficiency was also associated with decreased expression of stemness-related genes, indicating a requirement for Eva1 in maintaining GIC pluripotency. We further demonstrate that Eva1 induced GIC proliferation through the activation of the RelB-dependent noncanonical NF-κB pathway by recruiting TRAF2 to the cytoplasmic tail. Taken together, our findings highlight Eva1 as a novel regulator of GIC function and also provide new mechanistic insight into the role of noncanonical NF-κB activation in GIC, thus offering multiple potential therapeutic targets for preclinical investigation in GBM.

Ceacam1L Modulates STAT3 Signaling to Control the Proliferation of Glioblastoma-Initiating Cells

Glioblastoma-initiating cells (GIC) are a tumorigenic cell subpopulation resistant to radiotherapy and chemotherapy, and are a likely source of recurrence. However, the basis through which GICs are maintained has yet to be elucidated in detail. We herein demonstrated that the carcinoembryonic antigen-related cell adhesion molecule Ceacam1L acts as a crucial factor in GIC maintenance and tumorigenesis by activating c-Src/STAT3 signaling. Furthermore, we showed that monomers of the cytoplasmic domain of Ceacam1L bound to c-Src and STAT3 and induced their phosphorylation, whereas oligomerization of this domain ablated this function. Our results suggest that Ceacam1L-dependent adhesion between GIC and surrounding cells play an essential role in GIC maintenance and proliferation, as mediated by signals transmitted by monomeric forms of the Ceacam1L cytoplasmic domain.

Colitis induces enteric neurogenesis through a 5-HT4-dependent mechanism

BACKGROUND

The intestine is known to contain enteric neuronal progenitors, but their precise identity and the mechanisms that activate them remain unknown. Based on the evidence for the neurogenic role of serotonin (5-HT) in the postnatal gut and the observation of enteric neuronal hyperplasia in inflammatory bowel disease, we hypothesized that colitis induces a neurogenic response through 5-HT4 receptor signaling.

METHODS

We examined the effects of 5-HT4 agonism on colonic neurogenesis and gliogenesis in vitro and in vivo in adult mice using dextran sodium sulfate to experimentally induce colitis.

RESULTS

In vitro, 5-HT4 agonism led to increased neuronal proliferation and density. Induction of experimental colitis in vivo similarly resulted in increased numbers of myenteric neurons, and this was inhibited by 5-HT4 antagonism. Interestingly, both in vitro and in vivo, 5-HT4 signaling increased glial cell proliferation but did not increase glial cell numbers, leading us to hypothesize that glia may give rise to neurons. After induction of colitis in normal, Nestin-GFP and Sox2-GFP transgenic mice, it was revealed that multiple glial markers (Sox2, Nestin, and CD49b) became strongly expressed by enteric neurons. Immunoselected enteric glia were found to give rise to neurons in culture, and this was inhibited in the presence of 5-HT4 blockade. Finally, isolated glia gave rise to a neuronal network upon transplantation into aganglionic embryonic avian hindgut.

CONCLUSIONS

These results show that colitis promotes enteric neurogenesis in the adult colon through a serotonin-dependent mechanism that drives glial cells to transdifferentiate into neurons.

The proteome profiles of the olfactory bulb of juvenile, adult and aged rats - an ontogenetic study

Background

In this study, we searched for proteins that change their expression in the olfactory bulb (oB) of rats during ontogenesis. Up to now, protein expression differences in the developing animal are not fully understood. Our investigation focused on the question whether specific proteins exist which are only expressed during different development stages. This might lead to a better characterization of the microenvironment and to a better determination of factors and candidates that influence the differentiation of neuronal progenitor cells.

Results

After analyzing the samples by two-dimensional polyacrylamide gel electrophoresis (2DE) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), it could be shown that the number of expressed proteins differs depending on the developmental stages. Especially members of the functional classes, like proteins of biosynthesis, regulatory proteins and structural proteins, show the highest differential expression in the stages of development analyzed.

Conclusion

In this study, quantitative changes in the expression of proteins in the oB at different developmental stages (postnatal days (P) 7, 90 and 637) could be observed. Furthermore, the expression of many proteins was found at specific developmental stages. It was possible to identify these proteins which are involved in processes like support of cell migration and differentiation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12953-014-0058-x) contains supplementary material, which is available to authorized users.

Recognizing Resilience: Learning from the Effects of Stress on the Brain

As the central organ of stress and adaptation to stressors, the brain plays a pivotal role in behavioral and physiological responses that may lead to successful adaptation or to pathophysiology and mental and physical disease. In this context, resilience can be defined as "achieving a positive outcome in the face of adversity". Underlying this deceptively simple statement are several questions; first, to what extent is this ability limited to those environments that have shaped the individual or can it be more flexible; second, when in the life course does the brain develop capacity for flexibility for adapting positively to new challenges; and third, can such flexibility be instated in individuals where early life experiences have limited that capacity? Brain architecture continues to show plasticity throughout adult life and studies of gene expression and epigenetic regulation reveal a dynamic and ever-changing brain. The goal is to recognize those biological changes that underlie flexible adaptability, and to recognize gene pathways, epigenetic factors and structural changes that indicate lack of resilience leading to negative outcomes, particularly when the individual is challenged by new circumstances. Early life experiences determine individual differences in such capabilities via epigenetic pathways and laying down of brain architecture that determine the later capacity for flexible adaptation or the lack thereof. Reactivation of such plasticity in individuals lacking such resilience is a new challenge for research and practical application. Finally, sex differences in the plasticity of the brain are often overlooked and must be more fully investigated.

Sex, stress and the brain: interactive actions of hormones on the developing and adult brain

The brain is a target of steroid hormone actions that affect brain architecture, molecular and neurochemical processes, behavior and neuroprotection via both genomic and non-genomic actions. Estrogens have such effects throughout the brain and this article provides an historical and current view of how this new view has come about and how it has affected the study of sex differences, as well as other areas of neuroscience, including the effects of stress on the brain.

Neuroprotection for amyotrophic lateral sclerosis: role of stem cells, growth factors, and gene therapy

Various molecular mechanisms including apoptosis, inflammation, oxidative stress, mitochondrial dysfunction and excitotoxicity have been implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS), though the exact mechanisms have yet to be specified. Furthermore, the underlying restorative molecular mechanisms resulting in neuronal and/or non-neuronal regeneration have to be yet elucidated. Therapeutic agents targeting one or more of these mechanisms to combat either initiation or progression of the disease are under research. Novel treatments including stem cell therapy, growth factors, and gene therapy might prolong survival and delay progression of symptoms. Harnessing the regenerative potential of the central nervous system would be a novel approach for the treatment of motor neuron death resulting from ALS. Endogenous neural replacement, if augmented with administration of exogenous growth factors or with pharmaceuticals that increase the rate of neural progenitor formation, neural migration, and neural maturation could slow the rate of cell loss enough to result in clinical improvement. In this review, we discuss the impact of therapeutic treatment involving stem cell therapy, growth factors, gene therapy, and combination therapy on disease onset and progression of ALS. In addition, we summarize human clinical trials of stem cell therapy, growth factor therapy, and gene therapy in individuals with ALS.

Repeated paced mating promotes the arrival of more newborn neurons in the main and accessory olfactory bulbs of adult female rats

We have previously shown that the first-paced mating encounter increases the number of newborn cells in the granule cell layer (Gra; also known as internal cell layer, ICL) of the accessory olfactory bulb (AOB) in the adult female rat (Corona et al., 2011). In the present study we evaluated if repetition of the stimulus (paced mating) could increase the arrival of more newborn neurons in the olfactory bulb generated during the first session of paced sexual contact. Sexually naive female rats were bilaterally ovariectomized, hormonally supplemented with estradiol (E2) and progesterone (P) and randomly assigned to one of four groups: (1) without sexual contact, (2) one session of paced mating, (3) four sessions of paced mating, and (4) four sessions of non-paced mating. We also included a group of gonadally intact females. On the first day of the experiment, all females were i.p. injected with the marker of DNA synthesis bromodeoxyuridine and were killed 16 days later. Blood was collected at sacrifice to determine the plasma levels of E2 and P. The number of newborn neurons that arrived at the ICL of the AOB and the Gra of the main olfactory bulb (MOB) increased, relative to all other groups, only in the group that repeatedly mated under pacing conditions. No differences were found in E2 and P levels between supplemented groups indicating that our results are not influenced by changes in hormone concentrations. We suggest that repeated paced mating promotes the arrival of more newborn neurons in the AOB and MOB.

Transduction of neural precursor cells with TAT-heat shock protein 70 chaperone: therapeutic potential against ischemic stroke after intrastriatal and systemic transplantation

Novel therapeutic concepts against cerebral ischemia focus on cell-based therapies in order to overcome some of the side effects of thrombolytic therapy. However, cell-based therapies are hampered because of restricted understanding regarding optimal cell transplantation routes and due to low survival rates of grafted cells. We therefore transplanted adult green fluorescence protein positive neural precursor cells (NPCs) either intravenously (systemic) or intrastriatally (intracerebrally) 6 hours after stroke in mice. To enhance survival of NPCs, cells were in vitro protein-transduced with TAT-heat shock protein 70 (Hsp70) before transplantation followed by a systematic analysis of brain injury and underlying mechanisms depending on cell delivery routes. Transduction of NPCs with TAT-Hsp70 resulted in increased intracerebral numbers of grafted NPCs after intracerebral but not after systemic transplantation. Whereas systemic delivery of either native or transduced NPCs yielded sustained neuroprotection and induced neurological recovery, only TAT-Hsp70-transduced NPCs prevented secondary neuronal degeneration after intracerebral delivery that was associated with enhanced functional outcome. Furthermore, intracerebral transplantation of TAT-Hsp70-transduced NPCs enhanced postischemic neurogenesis and induced sustained high levels of brain-derived neurotrophic factor, glial cell line-derived neurotrophic factor, and vascular endothelial growth factor in vivo. Neuroprotection after intracerebral cell delivery correlated with the amount of surviving NPCs. On the contrary, systemic delivery of NPCs mediated acute neuroprotection via stabilization of the blood-brain-barrier, concomitant with reduced activation of matrix metalloprotease 9 and decreased formation of reactive oxygen species. Our findings imply two different mechanisms of action of intracerebrally and systemically transplanted NPCs, indicating that systemic NPC delivery might be more feasible for translational stroke concepts, lacking a need of in vitro manipulation of NPCs to induce long-term neuroprotection.

Interaction of hypoxia-inducible factor-1α and Notch signaling regulates medulloblastoma precursor proliferation and fate

Medulloblastoma (MDB) is the most common brain malignancy of childhood. It is currently thought that MDB arises from aberrantly functioning stem cells in the cerebellum that fail to maintain proper control of self-renewal. Additionally, it has been reported that MDB cells display higher endogenous Notch signaling activation, known to promote the survival and proliferation of neoplastic neural stem cells and to inhibit their differentiation. Although interaction between hypoxia-inducible factor-1α (HIF-1α) and Notch signaling is required to maintain normal neural precursors in an undifferentiated state, an interaction has not been identified in MDB. Here, we investigate whether hypoxia, through HIF-1α stabilization, modulates Notch1 signaling in primary MDB-derived cells. Our results indicate that MDB-derived precursor cells require hypoxic conditions for in vitro expansion, whereas acute exposure to 20% oxygen induces tumor cell differentiation and death through inhibition of Notch signaling. Importantly, stimulating Notch1 activation with its ligand Dll4 under hypoxic conditions leads to expansion of MDB-derived CD133(+) and nestin(+) precursors, suggesting a regulatory effect on stem cells. In contrast, MDB cells undergo neuronal differentiation when treated with γ-secretase inhibitor, which prevents Notch activation. These results suggest that hypoxia, by maintaining Notch1 in its active form, preserves MDB stem cell viability and expansion.

Transplantation of TAT-Bcl-xL-transduced neural precursor cells: long-term neuroprotection after stroke

Neural precursor cells (NPC) are an interesting tool in experimental stroke research, but their therapeutic potential is limited due to poor long-term survival. We therefore in vitro transduced subventricular zone-(SVZ)-derived NPC with the anti-apoptotic fusion protein TAT-Bcl-x(L) and analyzed NPC survival, differentiation, and post-stroke functional deficits after experimental ischemia in mice. Survival of TAT-Bcl-x(L)-transduced NPC, which were injected at day 7 post-stroke into the ischemic striatum, was significantly increased at 4 weeks after stroke. Increased survival of NPC was associated with reduced infarct injury and decreased post-stroke functional deficits. Animals grafted with TAT-Bcl-x(L)-transduced NPC showed an increased number of immature cells expressing the neuronal marker doublecortin. Since mature neuronal differentiation of NPC was not observed, reduced post-stroke injury cannot be attributed to enhanced neuronal regeneration, but rather to indirect by-stander effects of grafted NPC. In line with this, NPC-mediated neuroprotection of cortical neurons in vitro was associated with increased secretion of growth factors. Thus, in vitro transduction of cultivated NPC with TAT-Bcl-x(L) results in enhanced resistance of transplanted NPC followed by long-term neuroprotection and ameliorated functional deficits after transient focal cerebral ischemia in mice.

DeltaA mRNA and protein distribution in the zebrafish nervous system

Physical interaction between the transmembrane proteins Delta and Notch allows only a subset of neural precursors to become neurons, as well as regulating other aspects of neural development. To examine the localization of Delta protein during neural development, we generated an antibody specific to zebrafish Delta A (Dla). Here, we describe for the first time the subcellular localization of Dla protein in distinct puncta at cell cortex and/or membrane, supporting the function of Dla in direct cell-cell communication. In situ RNA hybridization and immunohistochemistry revealed dynamic, coordinated expression patterns of dla mRNA and Dla protein in the developing and adult zebrafish nervous system. Dla expression is mostly excluded from differentiated neurons and is maintained in putative precursor cells at least until larval stages. In the adult brain, dla mRNA and Dla protein are expressed in proliferative zones normally associated with stem cells.

Histone deacetylase inhibitors de-repress tyrosine hydroxylase expression in the olfactory bulb and rostral migratory stream

Most olfactory bulb (OB) interneurons are derived from neural stem cells in the subventricular zone (SVZ) and migrate to the OB via the rostral migratory stream (RMS). Mature dopaminergic interneurons in the OB glomerular layer are readily identified by their synaptic activity-dependent expression of tyrosine hydroxylase (TH). Paradoxically, TH is not expressed in neural progenitors migrating in the RMS, even though ambient GABA and glutamate depolarize these progenitors. In forebrain slice cultures prepared from transgenic mice containing a GFP reporter gene under the control of the Th 9kb upstream regulatory region, treatment with histone deacetylase (HDAC) inhibitors (either sodium butyrate, Trichostatin A or Scriptaid) induced Th-GFP expression specifically in the RMS independently of depolarizing conditions in the culture media. Th-GFP expression in the glomerular layer was also increased in slices treated with Trichostatin A, but this increased expression was dependent on depolarizing concentrations of KCl in the culture media. Th-GFP expression was also induced in the RMS in vivo by intra-peritoneal injections with either sodium butyrate or valproic acid. Quantitative RT-PCR analysis of neurosphere cultures confirmed that HDAC inhibitors de-repressed Th expression in SVZ-derived neural progenitors. Together, these findings suggest that HDAC function is critical for regulating Th expression levels in both neural progenitors and mature OB dopaminergic neurons. However, the differential responses to the combinatorial exposure of HDAC inhibitors and depolarizing culture conditions indicate that Th expression in mature OB neurons and neural progenitors in the RMS are regulated by distinct HDAC-mediated mechanisms.

Subtractive hybridization identifies genes differentially expressed by olfactory ensheathing cells and neural stem cells

The in vitro differentiation of embryonic stem cells into glia has received relatively limited attention to date when compared with the interest in the generation of neurons. We are interested in a particular glial phenotype, the aldynoglia, and their differentiation from multipotential neural precursors (MNP), since this type of glia can promote neuronal regeneration. We constructed cDNA libraries from cultures of purified olfactory ensheathing cells (OEC), an aldynoglia cell type, and MNP to perform subtractive hybridization. As a result, we isolated four genes from the OEC: one tenascin C (Tn-C) isoform, Insulin-like growth factor binding protein 5 (Igfbp-5), cytochrome oxidase subunit I (COX1) and a phosphodiesterase for cyclic nucleotides (CNPase). With the exception of CNPase, these genes are expressed more strongly in the OEC than in the MNP and moreover, the expression of all four is induced when MNP were exposed to OEC conditioned media. The data suggest a role for these genes in MNP differentiation, and their products appear to represent characteristic proteins of the aldynoglia phenotype.

Cell proliferation and death in the brain of active and hibernating frogs

'Binomial' cell proliferation and cell death have been studied in only a few non-mammalian vertebrates, such as fish. We thought it of interest to map cell proliferation/apoptosis in the brain of the frog (Rana esculenta L.) as this animal species undergoes, during the annual cycle, physiological events that could be associated with central nervous system damage. Therefore, we compared the active period and the deep underground hibernation of the frog. Using western blot analysis for proliferating cell nuclear antigen (PCNA), we revealed a positive 36 kDa band in all samples and found higher optical density values in the hibernating frogs than in active frogs. In both active and hibernating frogs, we found regional differences in PCNA-immunoreactive cells and terminal transferase dUTP nick-end labelling apoptotic cells in the ventricular zones and parenchyma areas of the main encephalon subdivisions. During the active period of the frogs, the highest concentration of PCNA-immunoreactive cells was found in the ventricle dorsal zone of the cerebral hemispheres but only some of the cells were apoptotic. By contrast, the tectal and cerebellar ventricular zones had a small or medium amount of PCNA-immunoreactive cells, respectively, and a higher number of apoptotic cells. During hibernation, an increased PCNA-immunoreactive cell number was observed in both the brain ventricles and parenchyma compared with active frogs. This increase was primarily evident in the lateral ventricles, a region known to be a proliferation 'hot spot'. Although differences existed among the brain areas, a general increase of apoptotic cell death was found in hibernating frogs, with the highest number of apoptotic cells being detected in the parenchyma of the cerebral hemispheres and optic tectum. In particular, the increased number of apoptotic cells in the hibernating frogs compared with active frogs in the parenchyma of these brain areas occurred when cell proliferation was higher in the corresponding ventricular zones. We suggest that the high number of dying cells found in the parenchymal regions of hibernating frogs might provide the stimulus for the ventricular zones to proliferate. Hibernating frogs could utilize an increased cell proliferation in the brain areas as a neuroprotective strategy to face cell death and the onset of neurological damages. Therefore, the hibernator promises to be a valuable model for studying the mechanisms naturally carried out by the central nervous system in order to adapt itself or survive adverse conditions.

Myelin-mediated inhibition of oligodendrocyte precursor differentiation can be overcome by pharmacological modulation of Fyn-RhoA and protein kinase C signalling

Failure of oligodendrocyte precursor cell (OPC) differentiation contributes significantly to failed myelin sheath regeneration (remyelination) in chronic demyelinating diseases. Although the reasons for this failure are not completely understood, several lines of evidence point to factors present following demyelination that specifically inhibit differentiation of cells capable of generating remyelinating oligodendrocytes. We have previously demonstrated that myelin debris generated by demyelination inhibits remyelination by inhibiting OPC differentiation and that the inhibitory effects are associated with myelin proteins. In the present study, we narrow down the spectrum of potential protein candidates by proteomic analysis of inhibitory protein fractions prepared by CM and HighQ column chromatography followed by BN/SDS/SDS–PAGE gel separation using Nano-HPLC-ESI-Q-TOF mass spectrometry. We show that the inhibitory effects on OPC differentiation mediated by myelin are regulated by Fyn-RhoA-ROCK signalling as well as by modulation of protein kinase C (PKC) signalling. We demonstrate that pharmacological or siRNA-mediated inhibition of RhoA-ROCK-II and/or PKC signalling can induce OPC differentiation in the presence of myelin. Our results, which provide a mechanistic link between myelin, a mediator of OPC differentiation inhibition associated with demyelinating pathologies and specific signalling pathways amenable to pharmacological manipulation, are therefore of significant potential value for future strategies aimed at enhancing CNS remyelination.

Behavior of hippocampal stem/progenitor cells following grafting into the injured aged hippocampus

Multipotent neural stem/progenitor cells (NSCs) from the embryonic hippocampus are potentially useful as donor cells to repopulate the degenerated regions of the aged hippocampus after stroke, epilepsy, or Alzheimer's disease. However, the efficacy of the NSC grafting strategy for repairing the injured aged hippocampus is unknown. To address this issue, we expanded FGF-2-responsive NSCs from the hippocampus of embryonic day 14 green fluorescent protein-expressing transgenic mice as neurospheres in vitro and grafted them into the hippocampus of 24-month-old F344 rats 4 days after CA3 region injury. Engraftment, migration, and neuronal/glial differentiation of cells derived from NSCs were analyzed 1 month after grafting. Differentiation of neurospheres in culture dishes or after placement on organotypic hippocampal slice cultures demonstrated that these cells had the ability to generate considerable numbers of neurons, astrocytes, and oligodendrocytes. Following grafting into the injured aged hippocampus, cells derived from neurospheres survived and dispersed, but exhibited no directed migration into degenerated or intact hippocampal cell layers. Phenotypic analyses of graft-derived cells revealed neuronal differentiation in 3%-5% of cells, astrocytic differentiation in 28% of cells, and oligodendrocytic differentiation in 6%-10% cells. The results demonstrate for the first time that NSCs derived from the fetal hippocampus survive and give rise to all three CNS phenotypes following transplantation into the injured aged hippocampus. However, grafted NSCs do not exhibit directed migration into lesioned areas or widespread neuronal differentiation, suggesting that direct grafting of primitive NSCs is not adequate for repair of the injured aged brain without priming the microenvironment.

In-tube transfection improves the efficiency of gene transfer in primary neuronal cultures

To facilitate genetic studies in primary neurons, we analyzed the efficiency of cationic lipid-mediated plasmid DNA transfection using adherent and acutely dissociated neuronal suspensions derived from embryonic mouse cortical tissue. Compared to transfections using adherent cultures, the in-tube procedure enhanced the delivery of a GFP reporter plasmid between four- to eightfold depending on the age of the harvested embryo. The procedure required relatively brief complex incubation times, and supported the transfection of cells expressing the neuronal markers NeuN and TuJ1 with improved uniformity in transfection events across the well surface. To demonstrate the utility of this approach in studying the genetic mechanisms controlling neuron development, we provide data regarding the role of the bZIP transcription factor c/EBP-beta in regulating neurite outgrowth. It is anticipated that this in vitro protocol will facilitate the identification of novel genes involved in both developmental and disease-relevant signaling pathways.

Myocyte enhancer factor 2C as a neurogenic and antiapoptotic transcription factor in murine embryonic stem cells

Cell-based therapies require a reliable source of cells that can be easily grown, undergo directed differentiation, and remain viable after transplantation. Here, we generated stably transformed murine ES (embryonic stem) cells that express a constitutively active form of myocyte enhancer factor 2C (MEF2CA). MEF2C has been implicated as a calcium-dependent transcription factor that enhances survival and affects synapse formation of neurons as well as differentiation of cardiomyocytes. We now report that expression of MEF2CA, both in vitro and in vivo, under regulation of the nestin enhancer effectively produces "neuronal" progenitor cells that differentiate into a virtually pure population of neurons. Histological, electrophysiological, and behavioral analyses demonstrate that MEF2C-directed neuronal progenitor cells transplanted into a mouse model of cerebral ischemia can successfully differentiate into functioning neurons and ameliorate stroke-induced behavioral deficits.

Neurogenesis after primary intracerebral hemorrhage in adult human brain

Neurogenesis occurs in discrete regions of normal brains of adult mammals including humans, and is induced in response to brain injury and neurodegenerative disease. Whether intracerebral hemorrhage can also induce neurogenesis in human brain is unknown. Specimens were obtained from patients with primary intracerebral hemorrhage undergoing surgical evacuation of an intracerebral hematoma, and evaluated by two-photon laser scanning confocal microscopy. We found that neural stem/progenitor cell-specific protein markers were expressed in cells located in the perihematomal regions of the basal ganglia and parietal lobe of the adult human brain after primary intracerebral hemorrhage (n=5). Cells in this region also expressed cell proliferation markers, which colocalized to the same cells that expressed neural stem/progenitor cell-specific proteins. Our data suggest that intracerebral hemorrhage induces neurogenesis in the adult human brain.

Direct-current electrical field guides neuronal stem/progenitor cell migration

Direct-current electrical fields (EFs) promote nerve growth and axon regeneration. We report here that at physiological strengths, EFs guide the migration of neuronal stem/progenitor cells (NSPCs) toward the cathode. EF-directed NSPC migration requires activation of N-methyl-d-aspartate receptors (NMDARs), which leads to an increased physical association of Rho GTPase Rac1-associated signals to the membrane NMDARs and the intracellular actin cytoskeleton. Thus, this study identifies the EF as a directional guidance cue in controlling NSPC migration and reveals a role of the NMDAR/Rac1/actin signal transduction pathway in mediating EF-induced NSPC migration. These results suggest that as a safe physical approach in clinical application, EFs may be developed as a practical therapeutic strategy for brain repair by directing NSPC migration to the injured brain regions to replace cell loss. Disclosure of potential conflicts of interest is found at the end of this article.

Stem cell myths

Stem cells, although difficult to define, hold great promise as tools for understanding development and as therapeutic agents. However, as with any new field, uncritical enthusiasm can outstrip reality. In this review, we have listed nine common myths that we believe affect our approach to evaluating stem cells for therapy. We suggest that careful consideration needs to be given to each of these issues when evaluating a particular cell for its use in therapy. Data need to be collected and reported for failed as well as successful experiments and a rigorous scientific approach taken to evaluate the undeniable promise of stem cell biology.

Production of neurospheres from CNS tissue

The relatively recent discovery of persistent adult neurogenesis has led to the experimental isolation and characterization of central nervous system neural stem cell populations. Protocols for in vitro analysis and expansion of neural stem cells are crucial for understanding their properties and defining characteristics. The methods described here allow for cell and molecular analysis of individual clones of cells--neurospheres--derived from neural stem/progenitor cells. Neurospheres can be cultivated from a variety of normal, genetically altered, or pathological tissue specimens, even with protracted postmortem intervals, for studies of mechanisms underlying neurogenesis, cell fate decisions, and cell differentiation. Neurosphere-forming cells hold great promise for the development of cell and molecular therapeutics for a variety of neurological diseases.

Temporal response of neural progenitor cells to disease onset and progression in amyotrophic lateral sclerosis-like transgenic mice

Regenerative medicine through neural stem cells (NSCs) or neural progenitor cells (NPCs) has been proposed as an alterative avenue for restoring neurological dysfunction in amyotrophic lateral sclerosis (ALS). It is critical to understand the organization and distribution of endogenous adult NPCs in response to motor neuron degeneration before regenerative medicine can be applied for ALS therapy. For this reason, we analyzed the temporal response of NPCs to motor neuron degeneration in the spinal cord and brain using nestin enhancer-driven LacZ reporter transgenic mice (pNes-Tg mice, control) and bi-transgenic mice containing both the nestin enhancer-driven LacZ reporter gene and mutant G93A-SOD1 gene (Bi-Tg mice). We observed an increase of NPCs in the dorsal horns of the spinal cord at the disease onset and progression stages in the Bi-Tg mice compared with that of age-matched pNes-Tg control mice. In contrast, an increase of NPCs in the ventral horns was detected at the disease progression stage. On the other hand, an increase of NPCs in the motor cortex at the disease-onset stage, but not at the disease progression stage, was detected. Furthermore, a decrease of NPCs in the lateral ventricle at the disease progression stage was observed, whereas no difference in the number of NPCs in the hippocampus was detected at the disease onset and progression stages. Some of the NPCs differentiate into neuron-like cells in response to motor neuron degeneration. The organization and distribution of endogenous adult NPCs in the ALS-like transgenic mice at the disease onset and progression stages provide fundamental bases for consideration of regenerative therapy of ALS by increasing de novo neurogenesis.

Adult neurogenesis and the memories of drug addiction

Evidence accumulated in the last decade indicating that psychoactive substances negatively influence neurogenesis in the adult hippocampus has provided new insights into the neurobiology of drug addiction. Using a variety of experimental approaches and treatments, drugs such as psychomotor stimulants, opioids, alcohol and psychedelic compounds have been shown to alter one or several aspects of adult neurogenesis, including the rate of progenitor proliferation, the survival of newly generated cells, and the maturation and acquisition of cellular phenotype. This evidence, though critical from a neurotoxicological standpoint, cannot be linked unambiguously to the process of drug dependence at this stage of research. Drug addiction is a complex recurrent process involving the acquisition and maintenance of drug taking, followed by detoxification, abstinence and eventual relapse to drug seeking. The specific contribution of adult hippocampal neurogenesis to each of these processes is yet to be determined. This notwithstanding, the suggested role of the hippocampus in the storage and retrieval of declarative and contextual memories on the one hand, and in the regulation of mood and affect on the other, provides a fertile ground for further exploring the mutual relationships between postnatal hippocampal neurogenesis and addictive behaviours.

Neuronal repair and replacement in spinal cord injury

Spinal cord injury (SCI) often induces loss of motor and/or sensory function below the level of injury. While deficits persist in complete lesions, partial lesions of the spinal cord can be followed by spontaneous functional recovery. In this review we address the mechanisms underlying spontaneous recovery in the adult CNS. We argue that the adult brain and spinal cord are able to spontaneously respond to SCI, and do so by (i) anatomically reorganizing axonal connections and (ii) generating new precursor cells. Knowledge of the endogenous recovery strategies should also provide the basis for the development of new therapeutic strategies for spinal cord injury. In this review we describe the processes of endogenous axonal repair and cell replacement in the injured spinal cord and discuss how transplantation of stem/progenitor cells could enhance these endogenous repair strategies.