Cerebral cortex lesions decrease the number of bromodeoxyuridine-positive subventricular zone cells in mice

Polycomb Protein Eed is Required for Neurogenesis and Cortical Injury Activation in the Subventricular Zone

The postnatal subventricular zone (SVZ) harbors neural stem cells (NSCs) that exhibit robust neurogenesis. However, the epigenetic mechanisms that maintain NSCs and regulate neurogenesis remain unclear. We report that label-retaining SVZ NSCs express Eed, the core component of Polycomb repressive complex 2. In vivo and in vitro conditional knockout and knockdown show Eed is necessary for maintaining NSC proliferation, neurogenesis and neurosphere formation. We discovered that Eed functions to maintain p21 protein levels in NSCs by repressing Gata6 transcription. Both Gata6 overexpression and p21 knockdown reduced neurogenesis, while Gata6 knockdown or p21 overexpression partially rescued neurogenesis after Eed loss. Furthermore, genetic deletion of Eed impaired injury induced SVZ proliferation and emigration. These data reveal a novel epigenetic regulated pathway and suggest an essential role for Eed in SVZ homeostasis and injury.

A new function for Prokineticin 2: Recruitment of SVZ-derived neuroblasts to the injured cortex in a mouse model of traumatic brain injury

Traumatic brain injury is an important cause of global morbidity and mortality. After an initial injury, there is a cascade of cellular and molecular events that ultimately lead to cell death. Therapies aim to both counteract these mechanisms and replenish the lost cell population in order to improve recovery. The adult mammal brain has at least two neurogenic regions that maintain physiological functions: the subgranular zone of the dentate gyrus in the hippocampus, which produces neurons that integrate locally, and the subventricular zone (SVZ) adjacent to the lateral ventricles, which produces neuroblasts that migrate through the rostral migratory stream (RMS) to the olfactory bulbs. Brain injuries, as well as neurodegenerative diseases, induce the SVZ to respond by increasing cell proliferation and migration to the injured areas. Here we report that cells migrate from the SVZ and RMS to the injured cortex after traumatic brain injury in mice, and that the physiological RMS migration is not impaired. We also show that Prokineticin 2 (PROK2), a chemokine important for the olfactory bulb neurogenesis, expressed exclusively by cortical microglia in the cortex as early as 24 h after injury. We then show that administration of a PROK2 receptor antagonist decreases the number of SVZ cells that reach the injured cortex, while injection of recombinant PROK2 into the cortex of uninjured mice attracts SVZ cells. We also demonstrate that cells expressing PROK2 in vitro directionally attract SVZ cells. These data suggest that PROK2 could be utilized in regeneration efforts for the acutely injured mammalian cortex.

Olfactory function in an excitotoxic model for secondary neuronal degeneration: Role of dopaminergic interneurons

Secondary neuronal degeneration (SND) occurring in Traumatic brain injury (TBI) consists in downstream destructive events affecting cells that were not or only marginally affected by the initial wound, further increasing the effects of the primary injury. Glutamate excitotoxicity is hypothesized to play an important role in SND. TBI is a common cause of olfactory dysfunction that may be spontaneous and partially recovered. The role of the glutamate excitotoxicity in the TBI-induced olfactory dysfunction is still unknown. We investigated the effects of excitotoxicity induced by bilateral N-Methyl-D-Aspartate (NMDA) OB administration in the olfactory function, OB volumes, and subventricular zone (SVZ) and OB neurogenesis in rats. NMDA OB administration induced a decrease in the number of correct choices in the olfactory discrimination tests one week after lesions (p<0.01), and a spontaneous recovery of the olfactory deficit two weeks after lesions (p<0.05). A lack of correlation between OB volumes and olfactory function was observed. An increase in SVZ neurogenesis (Ki67+ cells, PSANCAM+ cells (p<0.01) associated with an increase in OB glomerular dopaminergic immunostaining (p<0.05) were related to olfactory function recovery. The present results show that changes in OB volumes cannot explain the recovery of the olfactory function and suggest a relevant role for dopaminergic OB interneurons in the pathophysiology of recovery of loss of smell in TBI.

Traumatic Brain Injury Activation of the Adult Subventricular Zone Neurogenic Niche

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

Maturation-dependent response of neurogenesis after traumatic brain injury in children

OBJECT

Traumatic brain injury (TBI) is the leading cause of acquired disability in children, yet innate repair mechanisms are incompletely understood. Given data from animal studies documenting neurogenesis in response to trauma and other insults, the authors investigated whether similar responses could be found in children of different ages after TBI.

METHODS

Immunohistochemistry was used to label doublecortin (DCX), a protein expressed by immature migrating neuroblasts (newborn neurons), in specimens from patients ranging in age from 3 weeks to 10 years who had died either after TBI or from other causes. Doublecortin-positive (DCX+) cells were examined in the subventricular zone (SVZ) and periventricular white matter (PWM) and were quantified within the granule cell layer (GCL) and subgranular zone (SGZ) of the dentate gyrus to determine if age and/or injury affect the number of DCX+ cells in these regions.

RESULTS

The DCX+ cells decreased in the SVZ as patient age increased and were found in abundance around a focal subacute infarct in a 1-month-old non-TBI patient, but were scarce in all other patients regardless of age or history of trauma. The DCX+ cells in the PWM and dentate gyrus demonstrated a migratory morphology and did not co-localize with markers for astrocytes, microglia, or macrophages. In addition, there were significantly more DCX+ cells in the GCL and SGZ of the dentate gyrus in children younger than 1 year old than in older children. The density of immature migrating neuroblasts in infants (under 1 year of age) was significantly greater than in young children (2-6 years of age, p = 0.006) and older children (7-10 years of age, p = 0.007).

CONCLUSIONS

The main variable influencing the number of migrating neuroblasts observed in the SVZ, PWM, and hippocampus was patient age. Trauma had no discernible effect on the number of migrating neuroblasts in this cohort of patients in whom death typically occurred within hours to days after TBI.

Cortical contusion injury disrupts olfactory bulb neurogenesis in adult mice

Background

Experimental brain trauma activates quiescent neural stem cells (NSCs) to increase neuronal progenitor cell proliferation in the adult rodent brain. Previous studies have shown focal brain contusion in the form of a unilateral controlled cortical impact (CCI) stimulates NSCs to bilaterally increase neurogenesis in the adult hippocampus.

Results

In this study we clarified the bi-lateral effects of a unilateral CCI on proliferation in the subventricular zone (SVZ) NSC niche and on neurogenesis in the olfactory bulb of adult mice. By varying the depth of impact from 1 mm to 2 mm depth, we show CCI to the left somatosensory cortex resulted in graded changes in mouse behavior and cellular pathology in the forebrain. As expected, contusion to the sensorimotor cortex resulted in motor coordination deficits in adult mice. During the first 3 days after injury, CCI increased proliferation in the impacted cortex, deeper striatum and SVZ of the forebrain ipsilateral to the CCI. In each of these regions proliferation was increased with increasing injury severity. At 30 days post-procedure, CCI resulted in a significant reduction in neurogenesis in the olfactory bulb ipsilateral to the CCI. Olfactory avoidance testing indicated disruptions in olfactory bulb neurogenesis were associated with impaired olfactory discrimination in mice post-injury.

Conclusion

The data demonstrate a focal cortical contusion injury to the left somatosensory cortex disrupts SVZ-olfactory bulb neurogenesis and impairs olfactory discrimination and motor coordination in adult mice.

Determinants of central nervous system adult neurogenesis are sex, hormones, mouse strain, age, and brain region

Multiple sclerosis is a sexually dimorphic (SD) disease that causes oligodendrocyte death, but SD of glial cells is poorly studied. Here, we analyze SD of neural progenitors in 6-8 weeks and 6-8 months normal C57BL/6, SJL/J, and BALB/c mice in the subventricular zone (SVZ), dorsolateral horn (DLC), corpus callosum (CC), and parenchyma. With a short 2-h bromodeoxyuridine (BrdU) pulse, no gender and strain differences are present at 6-8 weeks. At 6-8 months, the number of BrdU(+) cells decreases twofold in each sex, strain, and region, indicating that a common aging mechanism regulates BrdU incorporation. Strikingly, 2× more BrdU(+) cells are found in all brain regions in 6-8 months C57BL/6 females versus males, no gender differences in 6-8 months SJL/J, and fewer BrdU(+) cells in females versus males in BALB/cs. The number of BrdU(+) cells modestly fluctuates throughout the estrous cycle in C57BL/6 and SJLs. Castration causes a dramatic increase in BrdU(+) cells in SVZ and DLC. These findings indicate that testosterone is a major regulator of adult neural proliferation. At 6-8 months, the ratio of PDGFRα(+) cells in the CC to BrdU(+) cells in the DLC of both strains, sexes, estrous cycle, and castrated mice was essentially the same, suggesting that BrdU(+) cells in the DLC differentiate into CC oligodendrocytes. The ratio of TUNEL(+) to BrdU(+) cells does not match proliferation, indicating that these events are differentially regulated. Differential regulation of these two processes leads to the variation in glial numbers between gender and strain. Explanations of neural proliferation based upon data from one sex or strain may be very misleading.

Potentials of endogenous neural stem cells in cortical repair

In the last few decades great thrust has been put in the area of regenerative neurobiology research to combat brain injuries and neurodegenerative diseases. The recent discovery of neurogenic niches in the adult brain has led researchers to study how to mobilize these cells to orchestrate an endogenous repair mechanism. The brain can minimize injury-induced damage by means of an immediate glial response and by initiating repair mechanisms that involve the generation and mobilization of new neurons to the site of injury where they can integrate into the existing circuit. This review highlights the current status of research in this field. Here, we discuss the changes that take place in the neurogenic milieu following injury. We will focus, in particular, on the cellular and molecular controls that lead to increased proliferation in the Sub ventricular Zone (SVZ) as well as neurogenesis. We will also concentrate on how these cellular and molecular mechanisms influence the migration of new cells to the affected area and their differentiation into neuronal/glial lineage that initiate the repair mechanism. Next, we will discuss some of the different factors that limit/retard the repair process and highlight future lines of research that can help to overcome these limitations. A clear understanding of the underlying molecular mechanisms and physiological changes following brain damage and the subsequent endogenous repair should help us develop better strategies to repair damaged brains.

Nestin reporter transgene labels multiple central nervous system precursor cells

Embryonic neuroepithelia and adult subventricular zone (SVZ) stem and progenitor cells express nestin. We characterized a transgenic line that expresses enhanced green fluorescent protein (eGFP) specified to neural tissue by the second intronic enhancer of the nestin promoter that had several novel features. During embryogenesis, the dorsal telencephalon contained many and the ventral telencephalon few eGFP+ cells. eGFP+ cells were found in postnatal and adult neurogenic regions. eGFP+ cells in the SVZ expressed multiple phenotype markers, glial fibrillary acidic protein, Dlx, and neuroblast-specific molecules suggesting the transgene is expressed through the lineage. eGFP+ cell numbers increased in the SVZ after cortical injury, suggesting this line will be useful in probing postinjury neurogenesis. In non-neurogenic regions, eGFP was strongly expressed in oligodendrocyte progenitors, but not in astrocytes, even when they were reactive. This eGFP+ mouse will facilitate studies of proliferative neuroepithelia and adult neurogenesis, as well as of parenchymal oligodendrocytes.

Voluntary exercise enhances survival and migration of neural progenitor cells after intracerebral haemorrhage in mice

PRIMARY OBJECTIVE

This study explored the long-term effects of exercise on the proliferation, survival and migration of endogenous neural progenitor cells (NPCs) in the subventricular zone (SVZ) of the brain after intracerebral haemorrhage (ICH).

RESEARCH DESIGN

ICH was induced by an injection of collagenase into the striatum. Animals in the voluntary running exercise group ran freely on a running wheel for 1, 3 and 6 weeks following the induction of ICH.

METHODS AND PROCEDURE

Immunohistochemical labelling was performed to incorporate specific cell markers, such as Ki67 (proliferating cells), 5-bromodeoxyuridien (BrdU; surviving newborn cells) and doublecortin (DCX; neuroblasts or migrating cells).

MAIN OUTCOMES AND RESULTS

Voluntary exercise for 3 and 6 weeks sustained more Ki67- or BrdU-immunostained cells in the SVZ after ICH than in the brains of sedentary mice. DCX-immunostained cells were more prominent in the striatum of the group that had exercised for 6 weeks compared to the time-matched sedentary group. Moreover, it was observed that proliferating green fluorescent protein (GFP)-positive cells that were infected with retrovirus were located more distally from the injection site in the exercise group than in the sedentary group.

CONCLUSIONS

These data indicate that long-term exercise may enhance the proliferation and survival of NPCs and their migration toward injured areas, suggesting that exercise may contribute to neuronal injury recovery in cell-based therapies after ICH.

Dopamine stimulation of postnatal murine subventricular zone neurogenesis via the D3 receptor

We investigated the expression and role of the dopamine receptor 3 (D3R) in postnatal mouse subventricular zone (SVZ). In situ hybridization detected selective D3R mRNA expression in the SVZ. Fluorescence activated cell sorting (FACS) of adult SVZ subtypes using hGFAP-GFP and Dcx-GFP mice showed that transit amplifying progenitor cells and niche astrocytes expressed D3R whereas stem cell-like astrocytes and neuroblasts did not. To determine D3R's role in SVZ neurogenesis, we administered U-99194A, a D3R preferential antagonist, and bromodeoxyuridine in postnatal mice. In vivo D3R antagonism decreased the numbers of newborn neurons reaching the core and the periglomerular layer of the olfactory bulb. Moreover, it decreased progenitor cell proliferation but did not change the number of label-retaining (stem) cells, commensurate with its expression on transit amplifying progenitor cells but not SVZ stem cell-like astrocytes. Collectively, this study suggests that dopaminergic stimulation of D3R drives proliferation via rapidly amplifying progenitor cells to promote murine SVZ neurogenesis.

Dynamic features of postnatal subventricular zone cell motility: a two-photon time-lapse study

Neuroblasts migrate long distances in the postnatal subventricular zone (SVZ) and rostral migratory stream (RMS) to the olfactory bulbs. Many fundamental features of SVZ migration are still poorly understood, and we addressed several important questions using two-photon time-lapse microscopy of brain slices from postnatal and adult eGFP(+) transgenic mice. 1) Longitudinal arrays of neuroblasts, so-called chain migration, have never been dynamically visualized in situ. We found that neuroblasts expressing doublecortin-eGFP (Dcx-eGFP) and glutamic acid decarboxylase-eGFP (Gad-eGFP) remained within arrays, which maintained their shape for many hours, despite the fact that there was a wide variety of movement within arrays. 2) In the dorsal SVZ, neuroblasts migrated rostrocaudally as expected, but migration shifted to dorsoventral orientations throughout ventral regions of the lateral ventricle. 3) Whereas polarized bipolar morphology has been a gold standard for inferring migration in histologic sections, our data indicated that migratory morphology was not predictive of motility. 4) Is there local motility in addition to long distance migration? 5) How fast is SVZ migration? Unexpectedly, one-third of motile neuroblasts moved locally in complex exploratory patterns and at average speeds slower than long distance movement. 6) Finally, we tested, and disproved, the hypothesis that all motile cells in the SVZ express doublecortin, indicating that Dcx is not required for migration of all SVZ cell types. These data show that cell motility in the SVZ and RMS is far more complex then previously thought and involves multiple cell types, behaviors, speeds, and directions.

Characterization of the subventricular zone neurogenic response to rat malignant brain tumors

The subventricular zone (SVZ) is one of the neurogenic regions of the adult brain. We characterized the neurogenic response of the SVZ to the growth of brain tumors in the rat striatum. Abundant nestin positive cells, most likely representing reactive astrocytes, were found surrounding the tumor. However, we observed no substantial migration of nestin positive cells from the SVZ toward the tumor. Tumor growth resulted in decreased numbers of bromodeoxyuridine positive and Ki-67 positive proliferating cells and a concomitant increase in doublecortin and polysialylated neural cell adhesion molecule immunoreactivity within the SVZ. Neuroblasts were observed in high numbers in the area between the SVZ and the tumor, most likely pointing to the SVZ as the principal source of these cells. Neuroblasts located between the SVZ and the tumor expressed the transcription factor Pbx, a marker for immature striatal neurons. However, no evidence of neuroblast differentiation into fully mature neurons was found. This study thus demonstrates increased neuroblast immunoreactivity within the SVZ ipsilateral to a brain tumor in the striatum. SVZ-derived neuroblasts attracted by the tumor adopt an immature striatal phenotype indicating a region specific reparative mechanism in response to a malignant tumor.

Enriched environment promotes adult neural progenitor cell mobilization in mouse demyelination models

Since the discovery of adult neural stem cells, mobilization of endogenous stem cells from the subventricular zone (SVZ) emerges as a promising strategy to promote brain repair. Here, we examined the effect of environment enrichment on SVZ cell mobilization in demyelinating pathologies. We showed that enriched housing conditions reduced functional impairment in experimental autoimmune encephalomyelitis (EAE), a rodent model of multiple sclerosis. Furthermore, both in a focal demyelination model (lysolecithin injection) and in the inflammatory EAE model, SVZ mitotic activity and the number of SVZ-derived cells in demyelinated areas were significantly increased by environment enrichment. Enriched housing conditions also promoted the oligodendrocyte fate of SVZ-recruited cells in the EAE lesions. Altogether our results show that environment enrichment provides beneficial conditions to promote the mobilization of neural progenitors into demyelinating lesions and to favour functional recovery.

Differential activation of microglia in neurogenic versus non-neurogenic regions of the forebrain

Proliferation decreases in the neurogenic subventricular zone (SVZ) of mice after aspiration lesions of the cerebral cortex. We hypothesized that microglial activation may contribute to this given microglial activation attenuates neurogenesis in the hippocampus. Using CD45, CD11b, IB4, and IL-6 immunohistochemistry (IHC), BrdU IHC, and fluorescent bead tracking of peripheral monocytes into the brain, we compared microglial activation in the SVZ to non-neurogenic forebrain regions. SVZ microglia exhibited greater constitutive activation and proliferation than did microglia in non-neurogenic regions. In contrast to the SVZ, the dentate gyrus (DG) contained relatively few CD45(+) cells. After aspiration cerebral cortex lesions, microglia became activated in the cerebral cortex, corpus callosum, and striatum. SVZ microglial activation did not increase, and similarly, microglia in the DG were less activated after injury than in adjacent non-neurogenic regions. We next showed that SVZ microglia are not categorically refractory to activation, since deep cortical contusion injuries increased SVZ microglial activation. Macrophages migrate into the brain during development, but it is unclear if this is recapitulated after injury. Infiltration of microbead-labeled macrophages into the brain did not change after injury, but resident SVZ microglia were induced to migrate toward the injury. Our data show that both constitutive and postlesion levels of microglial activation differ between neurogenic and non-neurogenic regions.

PSA-NCAM in mammalian structural plasticity and neurogenesis

Polysialic acid (PSA) is a linear homopolymer of alpha2-8-N acetylneuraminic acid whose major carrier in vertebrates is the neural cell adhesion molecule (NCAM). PSA serves as a potent negative regulator of cell interactions via its unusual biophysical properties. PSA on NCAM is developmentally regulated thus playing a prominent role in different forms of neural plasticity spanning from embryonic to adult nervous system, including axonal growth, outgrowth and fasciculation, cell migration, synaptic plasticity, activity-induced plasticity, neuronal-glial plasticity, embryonic and adult neurogenesis. The cellular distribution, developmental changes and possible function(s) of PSA-NCAM in the central nervous system of mammals here are reviewed, along with recent findings and theories about the relationships between NCAM protein and PSA as well as the role of different polysialyltransferases. Particular attention is focused on postnatal/adult neurogenesis, an issue which has been deeply investigated in the last decade as an example of persisting structural plasticity with potential implications for brain repair strategies. Adult neurogenic sites, although harbouring all subsequent steps of cell differentiation, from stem cell division to cell replacement, do not faithfully recapitulate development. After birth, they undergo morphological and molecular modifications allowing structural plasticity to adapt to the non-permissive environment of the mature nervous tissue, that are paralled by changes in the expression of PSA-NCAM. The use of PSA-NCAM as a marker for exploring differences in structural plasticity and neurogenesis among mammalian species is also discussed.

Subventricular zone cells remain stable in vitro after brain injury

Subventricular zone (SVZ) cells emigrate toward brain injury but relatively few survive. Thus, if they are to be used for repair, ex vivo expansion and autologous transplantation of SVZ cells may be necessary. Since it is unclear how brain injury alters SVZ cell culture, we studied neurosphere formation, differentiation, and migration, after cortical lesions. The number of neurosphere forming cells from lesioned mice was comparable to controls. Also, the proportion of astrocytes and neurons generated in vitro remained unchanged after cortical lesions. Cell emigration from neurospheres was characterized by increased cell-cell contact after injury in adults and neonates. However, neither molecules implicated in SVZ migration nor the extent of migration changed after injury. Thus, neurospheres can be successfully cultured after extensive brain damage, and they are remarkably stable in vitro, suggesting suitability for ex vivo expansion and autologous transplantation.

Mechanisms of neuroprotection by estrogen

Over the past decade our recognition that estrogens function as important neurotrophic and neuroprotective factors has grown rapidly. Accumulating evidence from basic science studies demonstrates that estrogens exert profound protective actions against various forms of neurodegenerative diseases and injury. Although a thorough understanding of the mechanisms underlying the protective effect of estrogens is far from complete, significant progress has been achieved through the use of in vivo as well as in vitro models. Here we review the results from our laboratory demonstrating that low physiological levels of estradiol therapy exert powerful protection against ischemic stroke-like injury. Using an animal model of cerebrovascular stroke and in vitro explant cultures, we have begun to decipher under what circumstances 17beta-estradiol protects against neuronal death and to uncover its mechanisms of action. In addition, we will review recent work demonstrating that estradiol may additionally enhance the ability of the adult brain to undergo repair by influencing the production of new neurons under neuropathological conditions, as well as by promoting an anti-inflammatory response. As we uncover the important protective roles of ovarian steroid hormones in brain disease and injury, we increasingly appreciate that the mechanisms by which estrogens achieve these effects are diverse and complex.

Subventricular zone neuroblasts emigrate toward cortical lesions

Adult subventricular zone (SVZ) neuroblasts migrate in the rostral migratory stream to the olfactory bulbs. Brain lesions generally increase SVZ neurogenesis or gliogenesis and cause SVZ cell emigration to ectopic locations. We showed previously that glia emigrate from the SVZ toward mechanical injuries of the somatosensory cerebral cortex in mice. Here we tested the hypotheses that SVZ neurogenesis increases, that neuroblasts emigrate, and that epidermal growth factor expression increases after cortical injuries. Using immunohistochemistry for phenotypic markers and BrdU, we show that newborn doublecortin-positive SVZ neuroblasts emigrated toward cerebral cortex lesions. However, the number of doublecortin-positive cells in the olfactory bulbs remained constant, suggesting that dorsal emigration was not at the expense of rostral migration. Although newborn neuroblasts emigrated, rates of SVZ neurogenesis did not increase after cortical lesions. Finally, we examined molecules that may regulate emigration and neurogenesis after cortical lesions and found that epidermal growth factor was increased in the SVZ, corpus callosum, and cerebral cortex. These results suggest that after injuries to the cerebral cortex, neuroblasts emigrate from the SVZ, that emigration does not depend either on redirection of SVZ cells or on increased neurogenesis, and that epidermal growth factor may induce SVZ emigration.

Estradiol enhances neurogenesis following ischemic stroke through estrogen receptors α and β

Neurogenesis persists throughout life under normal and degenerative conditions. The adult subventricular zone (SVZ) generates neural stem cells capable of differentiating to neuroblasts and migrating to the site of injury in response to brain insults. In the present study, we investigated whether estradiol increases neurogenesis in the SVZ in an animal model of stroke to potentially promote the ability of the brain to undergo repair. Ovariectomized C57BL/6J mice were implanted with capsules containing either vehicle or 17beta-estradiol, and 1 week later they underwent experimental ischemia. We utilized double-label immunocytochemistry to identify the phenotype of newborn cells (5-bromo-2'-deoxyuridine-labeled) with various cellular markers; doublecortin and PSA-NCAM as the early neuronal marker, NeuN to identify mature neurons, and glial fibrillary acidic protein to identify astrocytes. We report that low physiological levels of estradiol treatment, which exert no effect in the uninjured state, significantly increase the number of newborn neurons in the SVZ following stroke injury. This effect of estradiol is limited to the dorsal region of the SVZ and is absent from the ventral SVZ. The proliferative actions of estradiol are confined to neuronal precursors and do not influence gliosis. Furthermore, we show that both estrogen receptors alpha and beta play pivotal functional roles, insofar as knocking out either of these receptors blocks the ability of estradiol to increase neurogenesis. These findings clearly demonstrate that estradiol stimulates neurogenesis in the adult SVZ, thus potentially facilitating the brain to remodel and repair after injury.

Cellular proliferation and migration following a controlled cortical impact in the mouse

Neurogenesis following neural degeneration has been demonstrated in many models of disease and injury. The present study further examines the early proliferative and migratory response of the brain to a controlled cortical impact (CCI) model of traumatic brain injury. The CCI was centered over the forelimb sensorimotor cortex, unilaterally, in the adult mouse. To examine proliferation, bromo-deoxyuridine (BrdU) was injected i.p. immediately post-injury and on post-injury days 1, 2, and 3. To assess migration, we labeled SVZ cells with inert latex microspheres immediately post-injury. By combining microsphere labeling with BrdU, we determined if migrating cells had gone through the S-phase of the cell cycle after the lesion. In addition, we used a marker of neurogenesis and migration, doublecortin, to further characterize the response of the SVZ to the injury. Lastly, we determined whether subregions of the SVZ respond differentially to injury. The current study demonstrates that 3 days following CCI cellular proliferation is seen around the cortex, in the SVZ, corpus callosum, and subcortical areas anatomically connected to, but not directly damaged by the impact. It delineates that an increase in proliferation occurs in the dorsal-most aspect of the ipsilateral SVZ following impact. Lastly, it demonstrates that proliferating cells migrate from the SVZ to cortical and subcortical structures affected by the injury and that some of these cells are migrating neuroblasts.

Hypoxic-ischemic injury stimulates subventricular zone proliferation and neurogenesis in the neonatal rat

Neurogenesis persists throughout life in the rodent subventricular zone (SVZ) and increases in the adult after brain injury. In this study, postnatal day 7 (P7) rats underwent right carotid artery ligation followed by 8% O2 exposure for 90 min, a lesioning protocol that resulted in ipsilateral forebrain hypoxic-ischemic (HI) injury. The effects of HI injury on SVZ cell proliferation and neurogenesis were examined 1-3 wk later by morphometric measurement of dorsolateral SVZ size; by immunoassays to detect incorporation of bromodeoxyuridine (BrdU) in proliferating cells; and by immunoassays of doublecortin, a microtubule-associated protein expressed only by immature neurons. For determining the cell phenotypes of newly generated cells, tissue sections were double labeled with antibodies to BrdU and markers of mature neurons (neuronal nuclear protein), astrocytes (glial fibrillary acidic protein), or oligodendroglia (RIP). HI injury resulted in enlargement of the ipsilateral SVZ at P14-28 and a corresponding increase in BrdU cell numbers both in the ipsilateral SVZ and striatum at P21. HI injury also stimulated SVZ neurogenesis, based on increased doublecortin immunostaining in the SVZ ipsilateral to lesioning at P14-28. However, 4 wk after HI injury, in the lesioned striatum, although BrdU/glial fibrillary acidic protein and BrdU/RIP-labeled cells were identified, no BrdU/neuronal nuclear protein double-labeled cells were found. These results suggest that although acute neonatal HI injury stimulates SVZ proliferation and neurogenesis, there is inadequate trophic support for survival of newly generated neurons. Identification of the trophic factors that enhance maturation and survival of immature neurons could provide important clues for improving recovery after neonatal brain injury.

Mechanisms of subventricular zone expansion after focal cortical ischemic injury

The rodent subventricular zone (SVZ) contains neural precursor cells that divide and then die in place or migrate to the olfactory bulb through the rostral migratory stream (RMS) to become new neurons. Despite the normally tight control in cell numbers in this region in adults, previous work from our laboratory and others has shown that SVZ cell number increases after a variety of brain injuries. The relative contribution of changes in rostral migration, cell proliferation, and cell death to increased cell number is poorly understood. We examined these parameters after focal cortical ischemic lesions distal from the SVZ in adult rats. Stereological analysis revealed that cell numbers remain constant in the SVZ and RMS until 5 days postinjury but then rapidly expanded by 150,000 cells by day 7 in each region. Rostral migration of SVZ cells was unaffected by the injury. Both cell death and proliferation increased in the SVZ as early as day 5. However, these two mechanisms became uncoupled when cell number increased, indicating that a distant brain injury expands the SVZ by disrupting the balance between cell death and proliferation in this adult neurogenic zone.

Migration patterns of subventricular zone cells in adult mice change after cerebral cortex injury

The subventricular zone (SVZ) generates the largest number of migratory cells in the adult brain. SVZ neuroblasts migrate to the olfactory bulbs (OB) in the adult, whereas during development, SVZ cells migrate into many adjacent nuclei. Previously, we showed that cerebral cortex injury in the adult causes molecular and cellular changes which may recapitulate the developmental migratory directions. Consistent with this, growth factors, as well as models of illness or injury can cause adult SVZ cells to migrate into non-olfactory bulb nuclei. Here, we tested the hypothesis that cerebral cortex injury in the adult mouse induces changes in migration, by labeling adult SVZ cells with a retroviral vector and examining the distribution of cells 4 days and 3 weeks later. Four days after cortical lesions, disproportionately fewer retrovirally-labeled cells had migrated to the olfactory bulb in lesioned mice than in controls. Conversely, the number of cells found in non-olfactory bulb regions (primarily the area of the lesion and the corpus callosum) was increased in lesioned mice. The morphology of these emigrated cells suggested that they were differentiating into glial cells. Three weeks after cortical injury, the majority of retrovirally-labeled cells in both groups of mice had migrated into the granule and periglomerular layers of the olfactory bulb. At 3 weeks, we still observed retrovirally-labeled glial cells in the corpus callosum and in the area of the injury in lesioned mice. These results suggest that cortical lesions cause a transient change in migration patterns of SVZ progeny, which is characterized by decreases in migration to the olfactory bulb but increased migration towards the injury. Our studies also suggest that cortical lesions induce the production of new glial cells which survive for at least 3 weeks after injury. The data support the concept that in the adult, SVZ cells can generate progeny that migrate towards injured areas and thus potentially be harnessed for neural repair.