Neuroblast Proliferation Research Articles

Disrupted migration and proliferation of neuroblasts after postnatal administration of angiogenesis inhibitor

In adult rodents, neuroblasts originating from the subventricular zone migrate tangentially through the rostral migratory stream (RMS) toward the olfactory bulb where they differentiate into interneurons. Neuroblasts in the RMS migrate in chains for a long distance along specifically arranged blood vessels which promote their migration. Although blood vessels in the neurogenic region of the forebrain are present early in development, their rearrangement into this specific pattern takes place during the first postnatal weeks. Here we examined the relevance of this rearrangement to the migration-guiding “scaffold” for the neurogenic processes in the RMS such as cell migration and proliferation. To disturb the reorganization of blood vessels, endostatin – an inhibitor of angiogenesis, was administered systemically to rat pups during the first postnatal week. Ten days or three months later, the arrangement of blood vessels, migration and proliferation of cells in the RMS were assessed. As we expected, the inhibition of angiogenesis disrupted rearrangement of blood vessels in the RMS. The rearrangement’s failure resulted in a strong disruption of the mode and direction of neuroblast migration. Chain migration failed and neuroblasts migrated out of the RMS. The inhibition caused a slight increase in the number of proliferating cells in the RMS. The consequences were more obvious ten days after the inhibition of angiogenesis, although they persisted partly into adulthood. Altogether, here we show that the process of rearrangement of blood vessels in the RMS during the early postal period is crucial to ensure the regular course of postnatal neurogenesis.

Effects of p21 on adult hippocampal neuronal development after irradiation

Inhibition of hippocampal neurogenesis is implicated in neurocognitive impairment after cranial irradiation. We recently demonstrated that disruption of neuronal development after DNA damage was regulated by p53. The cyclin-dependent kinase inhibitor 1 or p21, a downstream effector p53, mediates cell cycle arrest in response to DNA damage. There is evidence that p21 negatively regulates proliferation of neural progenitors (NPCs). Here we characterized the effects of p21 on disruption of neuronal development in the hippocampal dentate gyrus after irradiation. We irradiated young adult mice wild type (+/+) or knockout (−/−) of the Cdkn1a (p21) gene, and used different bromodeoxyuridine (BrdU) paradigms for cell fate mapping. The acute apoptotic response of NPCs in the subgranular zone of the dentate gyrus was independent of p21 after irradiation. In nonirradiated mice, p21 knockout resulted in an increase in neuroblast proliferation and neurogenesis. At 9 weeks after 5Gy, NPCs in the subgranular zone demonstrated increased p21 expression. Loss of newborn type-1 cells and disruption of hippocampal neurogenesis was evident at 9 weeks after irradiation, and these effects were independent of p21 genotype status. Within the developmental milestones of NPCs, irradiation resulted in loss of early intermediate NPCs (type-2a cells) in wild-type mice, whereas the principal effect of irradiation with p21 loss was culling of proliferating late intermediate (type-2b cells) and neuroblasts. These results suggest that p21 exerts differential effects on cell fate of NPCs after irradiation. p21 may serve to protect proliferating late NPCs but does not alter the ultimate inhibition of new neuron production after DNA damage.

Abstract SY28-02: A phosphorylation switch regulating proliferation and differentiation in Xenopus development and neuroblastoma

Abstract Neuroblastoma is associated with stalling of normal differentiation, resulting in excessive proliferation of neuroblastic precursors. Here we show that Xenopus frog embryos can be used as a rapid and versatile model to investigate the molecular regulation of proliferation versus differentiation of neuroblasts and what may go wrong with this in neuroblastoma. We find that CDK-dependent phosphorylation of the transcriptional master regulator ASCL1 plays a critical role in controlling the balance between cell proliferation and differentiation in embryonic neuroblasts and in neuroblastoma, and can be modulated to reactivate differentiation of neuroblastoma cells. ASCL1 is a master regulator proneural transcription factor that controls the balance between proliferation and differentiation of neuroblasts and is expressed transiently during formation of noradrenergic neurons arising from the neural crest. Embryos of the frog Xenopus laevis provide a versatile, rapid, and inexpensive system to study the role of ASCL1 phosphorylation by cyclin-dependent kinases in restraining neuronal differentiation. We found that enhanced cyclin-dependent kinase activity or elevated MYCN levels are sufficient to lock neuroblasts into a noradrenergic precursor-like state by multisite phosphorylation of ASCL1 protein. Conversely, preventing phosphorylation of ASCL1 can potentiate neuronal differentiation even in the face of proproliferative cues. Thus, the in vivo use of Xenopus as a model organism led us to the hypothesis that neuroblastoma arises from neuroblasts that fail to undergo the normal developmental program of differentiation due to precocious phosphorylation of ASCL1. We have gone on to test this hypothesis directly in neuroblastoma cells. We show that ASCL1 is phosphorylated by cyclin-dependent kinases and that phospho-ASCL1 supports the proproliferative program in neuroblastoma cells. However, preventing CDK-dependent phosphorylation of ASCL1 results in changes in the genome-wide transcriptional program of neuroblastoma cells, leading to suppression of proproliferative targets and simultaneous activation of genes that drive cell cycle exit and differentiation. Mechanistically, ASCL1 ChIPSeq reveals enhanced binding of un(der)phosphorylated ASCL1 at sites associated with prodifferentiation targets. Moreover, PHOX protein binding at key downstream regulatory elements is also modulated by ASCL1 phosphorylation. Finally, we also show that chemical CDK inhibition is sufficient to drive differentiation of neuroblastoma cells in a manner dependent on endogenous ASCL1. Therefore, we conclude that CDK-dependent phosphorylation of ASCL1 acts as a critical fulcrum controlling the balance between proliferation and differentiation in Xenopus and in human cells, and thus offers a novel therapeutic opportunity for neuroblastoma. Citation Format: Anna Philpott, Fahad Ali, Luke Wylie, Daniel Marcos Corchado, Igor Chernukhin, Evangelia Papachristou, Tatiana Papkovskaia, Liam Lee, Christopher Weekes, Tom Hiscock, Clive D'Santos, Suzanne Turner, Jason Carroll. A phosphorylation switch regulating proliferation and differentiation in Xenopus development and neuroblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr SY28-02.

Drosophila nucleostemin 3 is required to maintain larval neuroblast proliferation

Stem cells must maintain proliferation during tissue development, repair and homeostasis, yet avoid tumor formation. In Drosophila, neural stem cells (neuroblasts) maintain proliferation during embryonic and larval development and terminate cell cycle during metamorphosis. An important question for understanding how tissues are generated and maintained is: what regulates stem cell proliferation versus differentiation? We performed a genetic screen which identified nucleostemin 3 (ns3) as a gene required to maintain neuroblast proliferation. ns3 is evolutionarily conserved with yeast and human Lsg1, which encode putative GTPases and are essential for organism growth and viability. We found NS3 is cytoplasmic and it is required to retain the cell cycle repressor Prospero in neuroblast cytoplasm via a Ran-independent pathway. NS3 is also required for proper neuroblast cell polarity and asymmetric cell division. Structure-function analysis further shows that the GTP-binding domain and acidic domain are required for NS3 function in neuroblast proliferation. We conclude NS3 has novel roles in regulating neuroblast cell polarity and proliferation.

Reactive Neuroblastosis in Huntington's Disease: A Putative Therapeutic Target for Striatal Regeneration in the Adult Brain.

The cellular and molecular mechanisms underlying the reciprocal relationship between adult neurogenesis, cognitive and motor functions have been an important focus of investigation in the establishment of effective neural replacement therapies for neurodegenerative disorders. While neuronal loss, reactive gliosis and defects in the self-repair capacity have extensively been characterized in neurodegenerative disorders, the transient excess production of neuroblasts detected in the adult striatum of animal models of Huntington’s disease (HD) and in post-mortem brain of HD patients, has only marginally been addressed. This abnormal cellular response in the striatum appears to originate from the selective proliferation and ectopic migration of neuroblasts derived from the subventricular zone (SVZ). Based on and in line with the term “reactive astrogliosis”, we propose to name the observed cellular event “reactive neuroblastosis”. Although, the functional relevance of reactive neuroblastosis is unknown, we speculate that this process may provide support for the tissue regeneration in compensating the structural and physiological functions of the striatum in lieu of aging or of the neurodegenerative process. Thus, in this review article, we comprehend different possibilities for the regulation of striatal neurogenesis, neuroblastosis and their functional relevance in the context of HD.

Regulation of neuroblast proliferation by surface glia in the Drosophila larval brain

Despite the importance of precisely regulating stem cell division, the molecular basis for this control is still elusive. Here, we show that surface glia in the developing Drosophila brain play essential roles in regulating the proliferation of neural stem cells, neuroblasts (NBs). We found that two classes of extracellular factors, Dally-like (Dlp), a heparan sulfate proteoglycan, and Glass bottom boat (Gbb), a BMP homologue, are required for proper NB proliferation. Interestingly, Dlp expressed in perineural glia (PG), the most outer layer of the surface glia, is responsible for NB proliferation. Consistent with this finding, functional ablation of PG using a dominant-negative form of dynamin showed that PG has an instructive role in regulating NB proliferation. Gbb acts not only as an autocrine proliferation factor in NBs but also as a paracrine survival signal in the PG. We propose that bidirectional communication between NBs and glia through TGF-β signaling influences mutual development of these two cell types. We also discuss the possibility that PG and NBs communicate via direct membrane contact or transcytotic transport of membrane components. Thus, our study shows that the surface glia acts not only as a simple structural insulator but also a dynamic regulator of brain development.

Layer-specific lipid signatures in the human subventricular zone demonstrated by imaging mass spectrometry

The subventricular zone is a key site of adult neurogenesis and is also implicated in neurodegenerative diseases and brain cancers. In the subventricular zone, cell proliferation, migration and differentiation of nascent stem cells and neuroblasts are regulated at least in part by lipids. The human subventricular zone is distinctly layered and each layer contains discrete cell types that support the processes of neuroblast migration and neurogenesis. We set out to determine the lipid signatures of each subventricular layer in the adult human brain (n = 4). We utilised matrix-assisted laser desorption/ionisation (MALDI) imaging mass spectrometry and liquid chromatography-mass spectrometry to characterise the lipidome of the subventricular zone, with histology and microscopy used for identifying anatomical landmarks. Our findings showed that the subventricular zone was rich in sphingomyelins and phosphatidylserines but deficient in phosphatidylethanolamines. The ependymal layer had an abundance of phosphatidylinositols, whereas the myelin layer was rich in sulfatides and triglycerides. The hypocellular layer showed enrichment of sphingomyelins. No discrete lipid signature was seen in the astrocytic ribbon. The biochemical functions of these lipid classes are consistent with the localisation we observed within the SVZ. Our study may, therefore, shed new light on the role of lipids in the regulation of adult neurogenesis.

Syngeneic Transplantation of Olfactory Ectomesenchymal Stem Cells Restores Learning and Memory Abilities in a Rat Model of Global Cerebral Ischemia

Stem cells are considered as promising tools to repair diverse tissue injuries. Among the different stem cell types, the “olfactory ectomesenchymal stem cells” (OE-MSCs) located in the adult olfactory mucosa stand as one of the best candidates. Here, we evaluated if OE-MSC grafts could decrease memory impairments due to ischemic injury. OE-MSCs were collected from syngeneic F344 rats. After a two-step global cerebral ischemia, inducing hippocampal lesions, learning abilities were evaluated using an olfactory associative discrimination task. Cells were grafted into the hippocampus 5 weeks after injury and animal's learning abilities reassessed. Rats were then sacrificed and the brains collected for immunohistochemical analyses. We observed significant impairments in learning and memory abilities following ischemia. However, 4 weeks after OE-MSC grafts, animals displayed learning and memory performances similar to those of controls, while sham rats did not improve them. Immunohistochemical analyses revealed that grafts promoted neuroblast and glial cell proliferation, which could permit to restore cognitive functions. These results demonstrated, for the first time, that syngeneic transplantations of OE-MSCs in rats can restore cognitive abilities impaired after brain injuries and provide support for the development of clinical studies based on grafts of OE-MSCs in amnesic patients following brain injuries.

Morphological alterations induced by the exposure to TiO2 nanoparticles in primary cortical neuron cultures and in the brain of rats.

Nowadays, nanoparticles (NPs) of titanium dioxide (TiO2) are abundantly produced. TiO2 NPs are present in various food products, in paints, cosmetics, sunscreens and toothpastes. However, the toxicity of TiO2 NPs on the central nervous system has been poorly investigated until now. The aim of this study was to evaluate the toxicity of TiO2 NPs on the central nervous system in vitro and in vivo. In cell cultures derived from embryonic cortical brain of rats, a significant decrease in neuroblasts was observed after 24 to 96 h of incubation with TiO2 NPs (5 to 20 μg/ml). This phenomenon resulted from an inhibition of neuroblast proliferation and a concomitant increase in apoptosis. In the same time, a gliosis, characterized by an increase in proliferation of astrocytes and the hypertrophy of microglial cells, occurred. The phagocytosis of TiO2 NPs by microgliocytes was also observed. In vivo, after intraperitoneal injection, the TiO2 NPs reached the brain through the blood brain barrier and the nanoparticles promoted various histological injuries such as cellular lysis, neuronal apoptosis, and inflammation. A reduction of astrocyte population was observed in some brain area such as plexiform zone, cerebellum and subependymal area. An oxidative stress was also detected by immunohistochemistry in neurons of hippocampus, cerebellum and in subependymal area. In conclusion, our study demonstrated clearly the toxic impact of TiO2 NPs on rat brain and neuronal cells and pointed about not yet referenced toxicity impacts of TiO2 such as the reduction of neuroblast proliferation both in vitro and in vivo.

Moesin is involved in polarity maintenance and cortical remodeling during asymmetric cell division.

An intact actomyosin network is essential for anchoring polarity proteins to the cell cortex and maintaining cell size asymmetry during asymmetric cell division of Drosophila neuroblasts (NBs). However, the mechanisms that control changes in actomyosin dynamics during asymmetric cell division remain unclear. We find that the actin-binding protein, Moesin, is essential for NB proliferation and mitotic progression in the developing brain. During metaphase, phosphorylated Moesin (p-Moesin) is enriched at the apical cortex, and loss of Moesin leads to defects in apical polarity maintenance and cortical stability. This asymmetric distribution of p-Moesin is determined by components of the apical polarity complex and Slik kinase. During later stages of mitosis, p-Moesin localization shifts more basally, contributing to asymmetric cortical extension and myosin basal furrow positioning. Our findings reveal Moesin as a novel apical polarity protein that drives cortical remodeling of dividing NBs, which is essential for polarity maintenance and initial establishment of cell size asymmetry.

Ultrasound-Mediated Kallidinogenase-Loaded Microbubble Targeted Therapy for Acute Cerebral Infarction

The neuroprotective effects of kallidinogenase against acute cerebral infarction have been demonstrated, and the use of microbubbles has been suggested as a therapeutic mechanism for drug delivery. This study was designed to investigate the optimal parameters for preparing kallidinogenase-loaded microbubbles (KLMs) and to evaluate the effects of KLM-targeted therapy on neurogenesis and angiogenesis following experimental acute cerebral infarction in rats. KLMs were prepared by mechanical shaking. Male Wistar rats were randomly divided into an ultrasound-mediated KLM-treated group and 4 control groups. Treatments were administered via daily tail vein injection on 6 consecutive days, starting at 24 hours after middle cerebral artery occlusion (MCAO). The ultrasound-treated groups were subjected to a 2-MHz pulse of ultrasonic irradiation on the lateral skull of the ischemic side for 10 minutes during injection. Cell proliferation was examined using a 5-bromo-2-deoxyuridine assay. Infarct volume and neurological function were evaluated on days 3 and 7 after MCAO. The ultrasound-mediated KLM and kallidinogenase treatments significantly increased the numbers of doublecortin-immunoreactive cells in the subventricular zone (SVZ) and laminin+ cells in the peri-infarction region on day 7 after MCAO, compared with the other 3 groups (all P <.05). The neurological function scores of the ultrasound-mediated KLM-treated group were significantly better than those of rats treated with kallidinogenase alone or with the other treatments (all P <.05). Treatment with the ultrasound-mediated KLMs promoted the proliferation of SVZ neuroblasts and vascular regeneration, which contributed to functional improvement after stroke. These findings provide a novel therapy for ischemic stroke.

Scalloped a member of the Hippo tumor suppressor pathway controls mushroom body size in Drosophila brain by non-canonical regulation of neuroblast proliferation

Cell proliferation, growth and survival are three different basic processes which converge at determining a fundamental property –the size of an organism. Scalloped (Sd) is the first characterised transcriptional partner to Yorkie (Yki), the downstream effector of the Hippo pathway which is a highly potential and evolutionarily conserved regulator of organ size. Here we have studied the hypomorphic effect of sd on the development of Mushroom Bodies (MBs) in Drosophila brain. We show that, sd non-function results in an increase in the size of MBs. We demonstrate that, sd regulation on MB size operates through multiple routes. Sd expressed in the differentiated MB neurons, imposes non-cell autonomous repression on the proliferation of MB precursor cells, and Sd expression in the MB neuroblasts (NB) cell autonomously represses mushroom body neuroblast (MBNB) proliferation. Further Sd in Kenyon cells (KCs) imparts a cell autonomous restriction on their growth. Our findings are distinctive because, while the classical sd loss of function phenotypes in eye, wing and lymph gland are reported as loss of tissue or reduced organ size, the present study shows that, Sd inactivation in the developing MB, promotes precursor cell proliferation and results in an increase in the organ size.

Drebrin E regulates neuroblast proliferation and chain migration in the adult brain.

F-actin-binding protein drebrin has two major isoforms: drebrin A and drebrin E. Drebrin A is the major isoform in the adult brain and is highly concentrated in dendritic spines, regulating spine morphology and synaptic plasticity. Conversely, drebrin E is the major isoform in the embryonic brain and regulates neuronal morphological differentiation, but it is also expressed in neurogenic regions of the adult brain. The subventricular zone (SVZ) is one of the brain regions where adult neurogenesis occurs. Neuroblasts migrate to the olfactory bulb (OB) and integrate into existing neuronal networks, after which drebrin expression changes from E to A, suggesting that drebrin E plays a specific role in neuroblasts in the adult brain. Therefore, to understand the role of drebrin E in the adult brain, we immunohistochemically analyzed adult neurogenesis using drebrin-null-mutant (DXKO) mice. In DXKO mice, the number of neuroblasts and cell proliferation decreased, although cell death remained unchanged. These results suggest that drebrin E regulates cell proliferation in the adult SVZ. Surprisingly, the decreased number of neuroblasts in the SVZ did not result in less neurons in the OB. This was because the survival rate of newly generated neurons in the OB increased in DXKO mice. Additionally, when neuroblasts reached the OB, the change in the migratory pathway from tangential to radial was partly disturbed in DXKO mice. These results suggest that drebrin E is involved in a chain migration of neuroblasts.

Eyeless uncouples mushroom body neuroblast proliferation from dietary amino acids in Drosophila.

Cell proliferation is coupled with nutrient availability. If nutrients become limited, proliferation ceases, because growth factor and/or PI3-kinase activity levels become attenuated. Here, we report an exception to this generality within a subpopulation of Drosophila neural stem cells (neuroblasts). We find that most neuroblasts enter and exit cell cycle in a nutrient-dependent manner that is reversible and regulated by PI3-kinase. However, a small subset, the mushroom body neuroblasts, which generate neurons important for memory and learning, divide independent of dietary nutrient conditions and PI3-kinase activity. This nutrient-independent proliferation is regulated by Eyeless, a Pax-6 orthologue, expressed in mushroom body neuroblasts. When Eyeless is knocked down, mushroom body neuroblasts exit cell cycle when nutrients are withdrawn. Conversely, when Eyeless is ectopically expressed, some non-mushroom body neuroblasts divide independent of dietary nutrient conditions. Therefore, Eyeless uncouples MB neuroblast proliferation from nutrient availability, allowing preferential neurogenesis in brain subregions during nutrient poor conditions.

Abstract 1940: Prenatal stress increases malignancy of neuroblastoma tumors in TH-MYCN animal model

Abstract Neuroblastoma (NB) is a pediatric malignancy arising due to defects in sympathetic neuron differentiation. NB is a heterogeneous disease, with phenotypes ranging from spontaneously regressing to highly aggressive, incurable tumors. This clinical variability cannot be explained solely by genetic aberrations. Even in families with hereditary NB the penetrance of the disease is incomplete and the same genetic mutation often results in tumors with phenotypes varying from differentiating ganglioneuromas to undifferentiated, highly aggressive NBs. Thus, other, perhaps non-genetic factors can contribute to the disease development and modify its phenotype. Strikingly, the two factors promoting de-differentiation of NB cells and their malignant phenotype, hypoxia and glucocorticoids, are elevated in the fetus during maternal stress, suggesting a role for prenatal stress in NB tumorigenesis. Previously, using TH-MYCN mice as a model of aggressive NB, we have shown that an increase in maternal corticosterone levels during pregnancy attained by inserting slow release pellets resulted in increased tumor frequency in TH-MYCN offspring. The goal of the current study was to determine the effect of prenatal stress on NB metastasis. To this end, pregnant mice carrying TH-MYCN hemizygous offspring were subjected to chronic stress at embryonic days 10-17, the time of sympathetic neuroblast proliferation and differentiation. Two established stress paradigms were used - chronic unpredictable stress, in which mice were subjected daily to various stressors, and chronic cold stress comprising of daily 30 min exposure to cold. The phenotypes of the disease and its dissemination were compared between offspring of control and stressed mothers. The offspring from both prenatally stressed groups presented with more malignant disease, as manifested by the presence of advanced lung metastases disseminating from small primary tumors (&amp;lt;200 mm3). This phenotype was associated with increased mortality in prenatally-stressed TH-MYCN offspring (p&amp;lt;0.01). In contrast, no advanced lung metastases and no disease-related deaths were observed in TH-MYCN offspring of control mothers despite the presence of large primary tumors (&amp;gt;1,000 mm3). Although not common, lung metastases occur preferentially in NB patients with MYCN amplification and are associated with significantly worse prognosis, as compared to patients with metastatic disease, but no pulmonary involvement (14 vs 43% 3-year event-free survival, respectively). Thus, the profound pulmonary dissemination observed in prenatally-stressed TH-MYCN mice mimics one of the most malignant NB phenotypes observed in human disease. Altogether, our data implicate maternal stress during pregnancy as a potential environmental factor modifying the effects of genetic aberrations and promoting malignant phenotype of NB. Citation Format: Sung Hyeok Hong, Larissa Wietlisbach, Susana Galli, Akanksha Mahajan, Shiya Zhu, Jason Tilan, Yichien Lee, Olga Rodriguez, Chris Albanese, Joanna Kitlinska. Prenatal stress increases malignancy of neuroblastoma tumors in TH-MYCN animal model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1940. doi:10.1158/1538-7445.AM2017-1940

Adult neurogenesis – accent on subgranular and subventricular zone in mammals

Tillrecently was assumed that neural cells stop dividing in early postnatal period of life, but last two decades large ammount ofresearches on that field proved contrary. There are evidences confirming existance of adult neurogenesis in most mammalian species, including humans.This process occurs spontaneouslyin physiological termsin two germinal brain regionscontaining neural stem cells; in subgranular zone of hippocampal dentate gyrus and subventricular zone of lateral ventricule.Neural stem cells in this germinal regions posses higher proliferative and differential capacity toward new future neurons, astrocytes and oligidendrocytes than neural stem cells from other regions in nervous system. Proliferative and regenerative power of this two niches has important role in brain adjustment to exterior stimuli during life which is called neuroplasticity. Germinal niches in brain are specific microenvironment in which close interaction of specific proneurogenic factors and resident neural stem cells and blood vessels form strictly controled conditions providing neuroblast and glioblast proliferation, differentiation, migration andmaturation and also survival and integration of newly created neuron or glial cell in existing brain sinaptic cirtuits. In case of harming this and other germinal brain centers different psichoneurologic disorders occur. Better understanding of germinal microenvironment function in human brainopens a new possibilities in neuroscience for creating a therapy based on adult neurogenesis manipulation through creating neurons “de novo”.

Postischemic fish oil treatment confers task-dependent memory recovery

A series of our previous studies demonstrated that fish oil (FO), equivalent to 300mg/kg docosahexahenoic acid (DHA), facilitates memory recovery after transient, global cerebral ischemia (TGCI) in the aversive radial maze (AvRM). The present study sought to address two main issues: (i) whether the memory-protective effect of FO that has been observed in the AvRM can be replicated in the passive avoidance test (PAT) and object location test (OLT) and (ii) whether FO at doses that are lower than those used previously can also prevent TGCI-induced memory loss. In Experiment 1, naive rats were trained in the PAT, subjected to TGCI (4-vessel occlusion model), and tested for retrograde memory performance 8 and 15days after ischemia. Fish oil (300mg/kg/day DHA) was given orally for 8days. The first dose was delivered 4h postischemia. In Experiment 2, the rats were subjected to TGCI, treated with the same FO regimen, and then trained and tested in the OLT. In Experiment 3, the rats were trained in the AvRM, subjected to TGCI, administered FO (100, 200, and 300mg/kg DHA), and tested for memory performance up to 3weeks after TGCI. At the end of the behavioral tests, the brains were examined for neurodegeneration and neuroblast proliferation. All of the behavioral tests (PAT, OLT, and AvRM) were sensitive to ischemia, but only the AvRM was able to detect the memory-protective effect of FO. Ischemia-induced neurodegeneration and neuroblast proliferation were unaffected by FO treatment. These results suggest that (i) the beneficial effect of FO on memory recovery after TGCI is task-dependent, (ii) doses of FO<300mg/kg DHA can protect memory function in the radial maze, and (iii) cognitive recovery occurs in the absence of neuronal rescue and/or hippocampal neurogenesis.

Neuroprotective and regenerative roles of intranasal Wnt-3a administration after focal ischemic stroke in mice

Wnt signaling is a conserved pathway involved in expansion of neural progenitors and lineage specification during development. However, the role of Wnt signaling in the post-stroke brain has not been well-elucidated. We hypothesized that Wnt-3a would play an important role for neurogenesis and brain repair. Adult male mice were subjected to a focal ischemic stroke targeting the sensorimotor cortex. Mice that received Wnt-3a (2 µg/kg/day, 1 h after stroke and once a day for the next 2 days, intranasal delivery) had reduced infarct volume compared to stroke controls. Wnt-3a intranasal treatment of seven days upregulated the expression of brain-derived growth factor (BDNF), increased the proliferation and migration of neuroblasts from the subventricular zone (SVZ), resulting in increased numbers of newly formed neurons and endothelial cells in the peri-infarct zone. Both the molecular and cellular effects of Wnt-3a were blocked by the Wnt specific inhibitors XAV-939 or Dkk-1. In functional assays, Wnt-3a treatment enhanced the local cerebral blood flow (LCBF) in the peri-infarct, as well as improved sensorimotor functions in a battery of behavioral tests. Together, our data demonstrates that the Wnt-3a signaling can act as a dual neuroprotective and regenerative factor for the treatment of ischemic stroke.

Adenosine A2A receptor and ERK-driven impulsivity potentiates hippocampal neuroblast proliferation

Dampened adenosine A2A receptor (A2AR) function has been implicated in addiction through enhancement of goal-directed behaviors. However, the contribution of the A2AR to the control of impulsive reward seeking remains unknown. Using mice that were exposed to differential reward of low rate (DRL) schedules during Pavlovian-conditioning, second-order schedule discrimination, and the 5-choice serial reaction time task (5-CSRTT), we demonstrate that deficits of A2AR function promote impulsive responses. Antagonism of the A2AR lowered ERK1 and ERK2 phosphorylation in the dorsal hippocampus (dHip) and potentiated impulsivity during Pavlovian-conditioning and the 5-CSRTT. Remarkably, inhibition of ERK1 and ERK2 phosphorylation by U0126 in the dHip prior to Pavlovian-conditioning exacerbated impulsive reward seeking. Moreover, we found decreased A2AR expression, and reduced ERK1 and ERK2 phosphorylation in the dHip of equilibrative nucleoside transporter type 1 (ENT1–/–) null mice, which displayed exacerbated impulsivity. To determine whether impulsive response behavior is associated with hippocampal neuroblast development, we investigated expression of BrdU+ and doublecortin (DCX+) following 5-CSRTT testing. These studies revealed that impulsive behavior driven by inhibition of the A2AR is accompanied by increased neuroblast proliferation in the hippocampus.

Stroke alters behavior of human skin-derived neural progenitors after transplantation adjacent to neurogenic area in rat brain

BackgroundIntracerebral transplantation of human induced pluripotent stem cells (iPSCs) can ameliorate behavioral deficits in animal models of stroke. How the ischemic lesion affects the survival of the transplanted cells, their proliferation, migration, differentiation, and function is only partly understood.MethodsHere we have assessed the influence of the stroke-induced injury on grafts of human skin iPSCs-derived long-term neuroepithelial-like stem cells using transplantation into the rostral migratory stream (RMS), adjacent to the neurogenic subventricular zone, in adult rats as a model system.ResultsWe show that the occurrence of an ischemic lesion, induced by middle cerebral artery occlusion, in the striatum close to the transplant does not alter the survival, proliferation, or generation of neuroblasts or mature neurons or astrocytes from the grafted progenitors. In contrast, the migration and axonal projection patterns of the transplanted cells are markedly influenced. In the intact brain, the grafted cells send many fibers to the main olfactory bulb through the RMS and a few of them migrate in the same direction, reaching the first one third of this pathway. In the stroke-injured brain, on the other hand, the grafted cells only migrate toward the ischemic lesion and virtually no axonal outgrowth is observed in the RMS.ConclusionsOur findings indicate that signals released from the stroke-injured area regulate the migration of and fiber outgrowth from grafted human skin-derived neural progenitors and overcome the influence on these cellular properties exerted by the neurogenic area/RMS in the intact brain.