Neurogenesis in dentate subgranular zone and rostral subventricular zone after focal cerebral ischemia in the rat

From angiogenesis to neuropathology

Angiogenesis--the growth of new blood vessels--is a crucial force for shaping the nervous system and protecting it from disease. Recent advances have improved our understanding of how the brain and other tissues grow new blood vessels under normal and pathological conditions. Angiogenesis factors, especially vascular endothelial growth factor, are now known to have roles in the birth of new neurons (neurogenesis), the prevention or mitigation of neuronal injury (neuroprotection), and the pathogenesis of stroke, Alzheimer's disease and motor neuron disease. As our understanding of pathophysiology grows, these developments may point the way towards new molecular and cell-based therapies.

Neurogenesis in the adult rat brain after intermittent hypoxia

Intermittent hypoxia has been found to prevent brain injury and to have a protective role in the CNS. To address the possible causes of this phenomenon, we made investigative effort to find out whether intermittent hypoxia affects neurogenesis in the adult rat brain by examining the newly divided cells in the subventricular zone (SVZ) and dentate gyrus (DG). The adult rats were treated with 3000 and 5000 m high altitude 4 h per day for 2 weeks consecutively. 5-Bromo-2-deoxyuridine-5-monophosphate (BrdU) immunocytochemistry demonstrated that the BrdU-labeled cells in the SVZ and DG increased after 3000 and 5000 m intermittent hypoxia. The number of BrdU-labeled cells in the SVZ returned to normal level 4 weeks following intermittent hypoxia. However, the BrdU-labeled cells in the DG had a twofold increase 4 weeks subsequent to intermittent hypoxia. From these data, we conclude that intermittent hypoxia facilitates the proliferation of neural stem cells in situ, and that the newly divided cells in the SVZ and DG react differently to hypoxia. We are convinced by these findings that the proliferation of neural stem cells in SVZ and DG may contribute to adaptive changes following intermittent hypoxia.

Neuroprotection and neurogenesis: Modulation of cornus ammonis 1 neuronal survival after transient forebrain ischemia by prior fimbria-fornix deafferentation

Severe transient forebrain ischemia causes selective neuronal death in the hippocampal cornus ammonis 1 region. We tested the hypothesis that fimbria-fornix deafferentation can provide long-term protection to cornus ammonis 1 neurons and modulate neurogenesis following ischemia. Fimbria-fornix lesion or sham-fimbria-fornix lesion was performed on Wistar rats 13 days prior to 10 min forebrain ischemia or sham ischemia. Temperature was regulated and rats survived for 7, 14 or 28 days. Immunofluorescent bromodeoxyuridine and neuron specific nuclear protein staining and immunochemistry terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling staining were performed. At 7 days after ischemia, 73%+/-14% of cornus ammonis 1 neurons were damaged, while deafferentation reduced the injury to 36%+/-17% of cornus ammonis 1 neurons. This protection persisted for at least 28 days. Ischemia significantly increased the number of bromodeoxyuridine-positive cells (85-90 cells/section in stroke group vs. 6 to 11 cells/section in normal or sham stroke group), with very few terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling-stained cells adjacent to the hippocampal cornus ammonis 1. Fimbria-fornix lesioning followed by ischemia increased the percentage of new neurons 13-fold over ischemia alone and 6.5-fold over sham lesion plus ischemia. The results indicate that fimbria-fornix deafferentation provides long-term neuroprotection in cornus ammonis 1 following forebrain ischemia and promotes neurogenesis after ischemic insults.

Implication of “Down syndrome cell adhesion molecule” in the hippocampal neurogenesis of ischemic monkeys

Molecular signals regulating adult neurogenesis in primates are largely unknown. Here the authors used differential display to analyze gene expression changes that occur in dentate gyrus of adult monkeys after transient global cerebral ischemia. Among 14 genes upregulated, the authors focused on Down syndrome cell adhesion molecule (DSCAM) known to play crucial role during neuronal development, and characterized its expression pattern at the protein level. In contrast with approximately threefold upregulation of Dscam gene on days 5 and 7, immunoblotting and immunofluorescence analyses using specific antibodies showed a gradual decrease of DSCAM after ischemia until day 9 followed by recovery on day 15. In the control, immunofluorescence reactivity of DSCAM was detected in dentate gyrus granule cells and CA4 neurons but decreased after ischemia, being compatible with the immunoblotting data. However, in the subgranular zone, cerebral ischemia led to a marked increase of DSCAM-positive cells on days 9 and 15. DSCAM upregulation was seen in two cell types: one is immature neurons positive for polysialylated neural cell adhesion molecule or betaIII-tubulin, while another is astrocytes positive for S100beta. Young astrocytes were in intimate contact with newly generated neurons in the subgranular zone. These data suggest implication of DSCAM in the adult neurogenesis of primate hippocampus upregulated after ischemia.

Transcription factor protein expression patterns by neural or neuronal progenitor cells of adult monkey subventricular zone

The anterior subventricular zone of the adult mammalian brain contains progenitor cells which are upregulated after cerebral ischemia. We have previously reported that while a part of the progenitors residing in adult monkey anterior subventricular zone travels to the olfactory bulb, many of these cells sustain location in the anterior subventricular zone for months after injury, exhibiting a phenotype of either neural or neuronal precursors. Here we show that ischemia increased the numbers of anterior subventricular zone progenitor cells expressing developmentally regulated transcription factors including Pax6 (paired-box 6), Emx2 (empty spiracles-homeobox 2), Sox 1-3 (sex determining region Y-box 1-3), Ngn1 (neurogenin 1), Dlx1,5 (distalless-homeobox 1,5), Olig1,3 (oligodendrocyte lineage gene 1,3) and Nkx2.2 (Nk-box 2.2), as compared with control brains. Analysis of transcription factor protein expression by sustained neural or neuronal precursors in anterior subventricular zone revealed that these two cell types were positive for characteristic sets of transcription factors. The proteins Pax6, Emx2, Sox2,3 and Olig1 were predominantly localized to dividing neural precursors while the factors Sox1, Ngn1, Dlx1,5, Olig2 and Nkx2.2 were mainly expressed by neuronal precursors. Further, differences between monkeys and non-primate mammals emerged, related to expression patterns of Pax6, Olig2 and Dlx2. Our results suggest that a complex network of developmental signals might be involved in the specification of primate progenitor cells.

Adult neurogenesis and the ischemic forebrain

The recent identification of endogenous neural stem cells and persistent neuronal production in the adult brain suggests a previously unrecognized capacity for self-repair after brain injury. Neurogenesis not only continues in discrete regions of the adult mammalian brain, but new evidence also suggests that neural progenitors form new neurons that integrate into existing circuitry after certain forms of brain injury in the adult. Experimental stroke in adult rodents and primates increases neurogenesis in the persistent forebrain subventricular and hippocampal dentate gyrus germinative zones. Of greater relevance for regenerative potential, ischemic insults stimulate endogenous neural progenitors to migrate to areas of damage and form neurons in otherwise dormant forebrain regions, such as the neostriatum and hippocampal pyramidal cell layer, of the mature brain. This review summarizes the current understanding of adult neurogenesis and its regulation in vivo, and describes evidence for stroke-induced neurogenesis and neuronal replacement in the adult. Current strategies used to modify endogenous neurogenesis after ischemic brain injury also will be discussed, as well as future research directions with potential for achieving regeneration after stroke and other brain insults.

Both estrogen receptor α and estrogen receptor β agonists enhance cell proliferation in the dentate gyrus of adult female rats

This study investigated the involvement of estrogen receptors alpha and beta in estradiol-induced enhancement of hippocampal neurogenesis in the adult female rat. Subtype selective estrogen receptor agonists, propyl-pyrazole triol (estrogen receptor alpha agonist) and diarylpropionitrile (estrogen receptor beta agonist) were examined for each receptor's contribution, individual and cooperative, for estradiol-enhanced hippocampal cell proliferation. Estradiol increases hippocampal cell proliferation within 4 h [Ormerod BK, Lee TT, Galea LA (2003) Estradiol initially enhances but subsequently suppresses (via adrenal steroids) granule cell proliferation in the dentate gyrus of adult female rats. J Neurobiol 55:247-260]. Therefore, animals received s.c. injections of estradiol (10 microg), propyl-pyrazole triol and diarylpropionitrile alone (1.25, 2.5, 5.0 mg/0.1 ml dimethylsulfoxide) or in combination (2.5 mg propyl-pyrazole triol+2.5 mg diarylpropionitrile/0.1 ml dimethylsulfoxide) and 4 h later received an i.p. injection of the cell synthesis marker, bromodeoxyuridine (200 mg/kg). Diarylpropionitrile enhanced cell proliferation at all three administered doses (1.25 mg, P<0.008; 2.5 mg, P<0.003; 5 mg, P<0.005), whereas propyl-pyrazole triol significantly increased cell proliferation (P<0.0002) only at the dose of 2.5 mg. Our results demonstrate both estrogen receptor alpha and estrogen receptor beta are individually involved in estradiol-enhanced cell proliferation. Furthermore both estrogen receptor alpha and estrogen receptor beta mRNA was found co-localized with Ki-67 expression in the hippocampus albeit at low levels, indicating a potential direct influence of each receptor subtype on progenitor cells and their progeny. Dual receptor activation resulted in reduced levels of cell proliferation, supporting previous studies suggesting that estrogen receptor alpha and estrogen receptor beta may modulate each other's activity. Our results also suggest that a component of estrogen receptor-regulated cell proliferation may take place through alternative ligand and/or cell-signaling mechanisms.

Inhibitor of vascular endothelial growth factor receptor tyrosine kinase attenuates cellular proliferation and differentiation to mature neurons in the hippocampal dentate gyrus after transient forebrain ischemia in the adult rat

Neurogenesis in the adult hippocampal dentate gyrus is promoted by transient forebrain ischemia. The mechanism responsible for this ischemia-induced neurogenesis, however, remains to be determined. It has been suggested that there may be a close relationship between neurogenesis and the expression of vascular endothelial growth factor, an angiogenic factor. The purpose of the present study was to examine the relationship between vascular endothelial growth factor and cell proliferation in the dentate gyrus after transient forebrain ischemia. The mRNA expression of vascular endothelial growth factor was increased in the dentate gyrus on day 1 after ischemia. Immunohistochemical analysis on day 9 after ischemia, when a significant increase in cell proliferation was seen, showed that the cerebral vessel space in the subgranular zone of the dentate gyrus had not been affected by the ischemia. Neither were the vascular densities on days 1 and 3 after ischemia altered compared with those of non-operated naïve control rats. Furthermore, the distance from the center of the proliferative cells to the nearest cerebral vessel of ischemic rats was comparable to that of the sham-operated rats. We demonstrated that transient forebrain ischemia-induced cell proliferation and differentiation to mature neurons in the hippocampal dentate gyrus was attenuated by the i.c.v. administration of a vascular endothelial growth factor receptor tyrosine kinase inhibitor. These results suggest that vascular endothelial growth factor receptor at the early period of reperfusion may contribute to neurogenesis rather than to angiogenesis in the hippocampal dentate gyrus.

Alcohol and adult neurogenesis: Roles in neurodegeneration and recovery in chronic alcoholism

The concept of "structural plasticity" has emerged as a potential mechanism in neurodegenerative and psychiatric diseases such as drug abuse, depression, and dementia. Chronic alcoholism is a progressive neurodegenerative disease while the person continues to abuse alcohol, though clinical and imaging studies show that some recovery may occur with abstinence. The neural plasticity observed in chronic alcoholism coupled with conflicting reports on alcohol-induced hippocampal neuropathology make this disease ripe for reconsideration in terms of the phenomenon of adult neurogenesis. This review describes opposing neurogenic processes that occur with alcohol intoxication and abstinence following alcohol dependence and how these opposing events relate to neurodegeneration and recovery from chronic alcoholism.

Neonatal pinealectomy induces Purkinje cell loss in the cerebellum of the chick: A stereological study

Melatonin plays an important role in certain physiological functions and morphological features of various structures. In the current study, the effects of pinealectomy on Purkinje cell number and morphological features of developing cerebellum in the chick were investigated using stereological methods. Fifteen Hybro Broiler newly hatched chicks were divided into three groups: a pinealectomized group (n = 5), sham-operated group (n = 5) and a non-pinealectomized control group (n = 5). Surgical pinealectomy was performed in 3-day-old chicks. In the 8th week, all animals were sacrificed for histopathological evaluation and subsequent stereological analysis. Each layer volume of molecular (+Purkinje cell), granular and white matter in the cerebellum was estimated in all animals. It was found that there was no significant difference for the volume of whole cerebellum and also molecular (+Purkinje cell) layer in these groups (P > 0.05). Nevertheless, the values of granular layer and white matter of sham-operated group were significantly different from those of control and pinealectomized animals (P < 0.01). It was also observed that pinealectomy significantly reduces the Purkinje cell number in cerebellar cortex (P < 0.01). The present study is the first stereological study to demonstrate the histomorphological effects of pinealectomy on the cerebellum in the chick. Our results suggest that pineal gland/melatonin might play an important role in morphological features of the developing cerebellum in the chick.

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.

Activation of neural stem and progenitor cells after brain injury

Neural stem and progenitor cells in the mammalian brain persist and are functional well into adulthood. Reservoirs for these cells are found in both the subventricular zone and the dentate gyrus of the hippocampus. It is still unclear what role these cells may play in humans during normal brain maturation. In addition, there is currently tremendous speculation regarding the potential role of these cells in providing a substrate for recovery and repair after injury. This review provides an overview of the existing data regarding how neural stem and progenitor cells respond to various types of brain injury. In particular, we focus upon their role in the dentate gyrus since this brain area provides a compelling and tractable model of how the brain may use its ability for endogenous regeneration to recover from a variety of injuries.

Correlation between copper/zinc superoxide dismutase and the proliferation of neural stem cells in aging and following focal cerebral ischemia

Object

Neural stem cells (NSCs) have been demonstrated in the subventricular zone (SVZ) of the lateral ventricle and the subgranular zone of the hippocampal dentate gyrus (DG). Although aging rats manifest a decrease in NSCs, rats exposed to stress (for example, ischemia, epilepsy, radiation, and trauma) show an increase in these cells. In transgenic mice, the overexpression of human copper/zinc superoxide dismutase (SOD1), an endogenous antioxidant, has been reported to be a protective enzyme against transient focal cerebral ischemia. The authors investigated the correlation between SOD1 and the proliferation of NSCs in aging as chronic oxidative stress (Experiment 1) and acute oxidative stress induced by transient focal cerebral ischemia (Experiment 2) in mice.

Methods

Bromodeoxyuridine (BrdU) was used in the evaluation of NSCs. In Experiment 1, NSCs in the SVZ significantly increased in 16-month-old transgenic mice compared with wild-type mice (p = 0.0001). In Experiment 2, mice were subjected to 30-minute occlusions of the middle cerebral artery. The increase in NSCs in the DG in transgenic mice was significantly greater than that in wild-type mice (p < 0.05).

Conclusions

Results in this study suggest that chronic and acute oxidative stress may inhibit the proliferation of NSCs and that SOD1 may play a key role in NSC proliferation.

Enriched environment and spatial learning enhance hippocampal neurogenesis and salvages ischemic penumbra after focal cerebral ischemia

Enriched environment (EE) has been shown to increase neurogenesis in the adult brain. The aim of this study is to determine the effect of EE and spatial learning on neurogenesis following ischemic stroke. Male adult SD rats were subjected to sham surgery or distal middle cerebral artery occlusion (MCAO). MCAO induced a transient increase followed by a sustained depression of progenitor cell proliferation and neuroblast production below baseline level in both ipsilateral and contralateral DG compared to sham. Increased neuronal differentiation and neurogenesis in the DG were observed in both sham and MCAO rats following 8 weeks in the EE combined with spatial learning, compared to rats housed in the standard environment. EE/Learning also restored the total number of neuroblasts in the DG after MCAO compared to sham. Furthermore, EE/learning enhanced the density of NeuN positive cells in the ischemic penumbra, though no new neurons were detected in this region.

Neurogenesis in the adult ischemic brain: generation, migration, survival, and restorative therapy

This article reviews current data on the induction of neurogenesis after stroke in the adult brain. The discussion of neurogenesis is divided into production, migration, and survival of these newly formed cells. For production, the subpopulations and the types of cell division are presented. Discussion of cell migration entails presenting data on both the pathways as well as the molecular targeting of newly formed neural progenitor cells to sites of injury. The role of the vascular and the astrocytic microenvironment in promoting the survival and integration of progenitor cells is also presented. Cell-based and pharmacological therapies designed to restore neurological function that promote neurogenesis are described. These therapies also induce angiogenesis and astrocytic changes that brain tissue, which prime the ischemic brain to foster the survival of the newly formed progenitor cells. Signaling pathways that regulate neurogenesis and angiogenesis are also addressed. This review summarizes recent data on neurogenesis and provides insight into the potential for restorative treatments of stroke.

Sleep deprivation suppresses neurogenesis in the adult hippocampus of rats

We reported previously that 96 h of sleep deprivation (SD) reduced cell proliferation in the dentate gyrus (DG) of the hippocampus in adult rats. We now report that SD reduces the number of new cells expressing a mature neuronal marker, neuronal nuclear antigen (NeuN). Rats were sleep-deprived for 96 h, using an intermittent treadmill system. Total sleep time was reduced to 6.9% by this method in SD animals, but total treadmill movement was equated in SD and treadmill control (CT) groups. Rats were allowed to survive for 3 weeks after 5-bromo-2-deoxyuridine (BrdU) injection. The phenotype of BrdU-positive cells in the DG was assessed by immunofluorescence and confocal microscopy. After 3 weeks the number of BrdU-positive cells was reduced by 39.6% in the SD group compared with the CT. The percentage of cells that co-localized BrdU and NeuN was also lower in the SD group (SD: 46.6 +/- 1.8% vs. CT: 71.9 +/- 2.1, P < 0.001). The percentages of BrdU-labeled cells co-expressing markers of immature neuronal (DCX) or glial (S100-beta) cells were not different in SD and CT groups. Thus, SD reduces neurogenesis in the DG by affecting both total proliferation and the percentage of cells expressing a mature neuronal phenotype. We hypothesize that sleep provides anabolic or signaling support for proliferation and cell fate determination.

Progress in the identification of stroke-related genes: emerging new possibilities to develop concepts in stroke therapy

Stroke is a very complex disease influenced by many risk factors: genetic, environmental and comorbidities, such as hypertension, diabetes mellitus, obesity and having had a previous stroke. Neuroprotective therapies that have been found to be successful in laboratory animals have failed to produce the same benefits in clinical trials. Currently, a re-analysis of the clinical trial failures is underway and new therapeutic approaches using the growing knowledge from neurogenesis and neuroinflammation studies, combined with the information from gene expression studies, are taking place. This review focuses on possible ways to identify therapeutic targets using the new discoveries in neuroinflammation and intrinsic regenerative mechanisms of the brain. Molecular events associated with ischaemia trigger an environment for inflammation. Within the ischaemic region and its penumbra, a battery of chemokines and cytokines are released, which have both detrimental and beneficial effects, depending on the specific timepoint after injury and the current activation status of microglia/macrophages. Preventive therapies and treatments for stroke may be established by identifying the genes that are responsible for the induction of those phenotypic changes of microglia/macrophages that switch them to become players in tissue repair and regeneration processes. To aid in the establishment of new target sources for novel therapeutic agents, animal stroke models should closely mimic stroke in humans. To do so, these models should take into account the various risk factors for stroke. For example, hypertensive animals have a more vulnerable blood-brain barrier that in turn may trigger a greater degree of damage after stroke. Furthermore, in aged animals an accelerated astrocytic and microglial reaction has been observed and the regenerative capacity of aged brains is not as high as young brains. Improvements in animal models may also help to ensure better success rates of potential therapies in clinical studies. Inflammation in the brain is a double-edged sword--characterised by the deleterious effect of nerve cell damage and nerve cell death, as well as the beneficial influence on regeneration. The major challenge to develop successful stroke therapies is to broaden the knowledge regarding the underlying pathologic processes and the intrinsic mechanisms of the brain to drive regenerative and plasticity-related changes. On this basis, new concepts can be created leading to better stroke therapy.

Influence of EGF/bFGF treatment on proliferation, early neurogenesis and infarct volume after transient focal ischemia

The persistence of neurogenesis in the adult mammalian forebrain suggests that endogenous precursors may be a potential source for neuronal replacement after injury or neurodegeneration. On the other hand basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF) can facilitate neural precursor proliferation in the adult rodent subventricular zone (SVZ) and dentate gyrus. As the application of EGF and bFGF was found to boost neurogenesis after global ischemia, in this study we investigated whether a combined intracerebroventricular (i.c.v.) EGF/bFGF treatment over a period of 2 weeks affects the proliferation of newly generated cells in the endothelin-1 model of transient focal ischemia in adult male Sprague-Dawley rats as well. As assessed by toluidine blue staining, EGF/bFGF substantially increased the infarct volume in ischemic animals. Chronic 5'-bromodeoxyuridine (BrdU) i.c.v. application revealed an EGF/bFGF-induced increase in cell proliferation in the lateral ventricle 14 days after surgery. Proliferation in the striatum increased after ischemia, whereas in the dentate gyrus and in the dorsal 3rd ventricle the number of cells decreased. Analysis of the neuronal fate of these cells by co-staining with a doublecortin (DCX) antibody showed that the growth factors concomitantly nearly doubled early neurogenesis in the ipsilateral striatum in ischemic animals but diminished it in the dentate gyrus. Because of the increased infarct volume and unclear long-term outcome further modifications of a chronic treatment schedule are needed before final conclusions concerning the perspectives of such an approach can be made.

Challenges of Neuroprotection and Neurorestoration in Ischemic Stroke Treatment

Currently, the most important therapeutic approaches in the acute phase of ischemic stroke are focused on the restoration of regional cerebral blood flow, early admission to a stroke unit and the attempt to block, using neuroprotective drugs, the biochemical and metabolic changes involved in the 'ischemic cascade'. Treatment with rt-PA in the acute phase, although very effective, is still limited to a small number of patients and positive preclinical results of neuroprotective treatment have not, as yet, been endorsed in clinical trials. The remarkable lack of concordance between the positive results in experimental models and the negative results obtained in clinical trials has led to a change in attitude in the conduct of preclinical studies as well as to a modification of the design of clinical trials, with special attention being paid to patient selection criteria and clinical evaluation. Some neuroprotective drugs, such as citicoline, have shown some efficacy in subgroups of patients with cerebral infarction, even with a therapeutic window of up to 24 h, which would suggest a possible neurorestorative effect. Different degrees of functional recovery, weeks or months after the ischemic event, are currently observed in clinical practice and have been related to endogenous self-repair mechanisms. The growing understanding of the mechanisms involved in the phenomena of brain plasticity and their modulation, together with the possibility of restoring functional deficits by encouraging endogenous neurogenesis or by cell therapy, open up new directions in the treatment of stroke patients.

FGF-2 promotes neurogenesis and neuroprotection and prolongs survival in a transgenic mouse model of Huntington's disease

There is no satisfactory treatment for Huntington's disease (HD), a hereditary neurodegenerative disorder that produces chorea, dementia, and death. One potential treatment strategy involves the replacement of dead neurons by stimulating the proliferation of endogenous neuronal precursors (neurogenesis) and their migration into damaged regions of the brain. Because growth factors are neuroprotective in some settings and can also stimulate neurogenesis, we treated HD transgenic R6/2 mice from 8 weeks of age until death by s.c. administration of FGF-2. FGF-2 increased the number of proliferating cells in the subventricular zone by approximately 30% in wild-type mice, and by approximately 150% in HD transgenic R6/2 mice. FGF-2 also induced the recruitment of new neurons from the subventricular zone into the neostriatum and cerebral cortex of HD transgenic R6/2 mice. In the striatum, these neurons were DARPP-32-expressing medium spiny neurons, consistent with the phenotype of neurons lost in HD. FGF-2 was neuroprotective as well, because it blocked cell death induced by mutant expanded Htt in primary striatal cultures. FGF-2 also reduced polyglutamine aggregates, improved motor performance, and extended lifespan by approximately 20%. We conclude that FGF-2 improves neurological deficits and longevity in a transgenic mouse model of HD, and that its neuroprotective and neuroproliferative effects may contribute to this improvement.

EGF and FGF-2 Infusion Increases Post-Ischemic Neural Progenitor Cell Proliferation in the Adult Rat Brain

OBJECTIVE

Epidermal growth factor (EGF) and fibroblast growth factor-2 (FGF-2) play a critical role in neurogenesis. In the present study, we evaluated the additive effect of administering these two factors on post-ischemic progenitor cell proliferation, survival, and phenotypic maturation in the hippocampal dentate gyrus (DG) and the subventricular zone (SVZ) in the adult rat brain after transient middle cerebral artery occlusion.

METHODS

A combination of EGF+FGF-2 (each 1.44 ng/d) was continuously administered into the lateral ventricles for 3 days, 5-bromodeoxyuridine (BrdUrd) was injected (50 mg/Kg) twice daily for 3 days starting on Day 1 of reperfusion, and cohorts of rats were sacrificed on Day 5 and Day 21 of reperfusion.

RESULTS

Compared with sham controls, ischemic rats showed a significantly higher number of newly proliferated cells in both the DG (by 766 +/- 37%, P < 0.05) and the SVZ (by 650 +/- 43%, P < 0.05). Of the progenitor cells proliferated on Day 5 after ischemia, 41 +/- 6% in the DG and 28 +/- 5% in the SVZ survived to 3 weeks. Compared with vehicle control, the EGF + FGF-2 infusion significantly increased the post-ischemic progenitor cell proliferation (by 319 +/- 40%, P < 0.05 in the DG and by 366 +/- 32%, P < 0.05 in the SVZ) and survival (by 40 +/- 12%, P < 0.05 in the DG and by 522 +/- 47%, P < 0.05 in the SVZ) studied at 5 and 21 days, respectively. Furthermore, of the newly proliferated cells survived to 3 weeks after ischemia, EGF + FGF-2 infusion caused a significantly higher number of neuronal nuclear protein-BrdUrd double-positive mature neurons in the DG (46 +/- 9%, P < 0.05) compared with vehicle control. Neuronal nuclear protein and BrdUrd double-positive mature neurons were also found in the DG. Glial fibrillary acidic protein-positive astrocytes did not show double-positive staining in either region.

CONCLUSION

Specific growth factor infusion enhances post-ischemic progenitor cell proliferation by 5 days of reperfusion and neuronal maturation by 21 days of reperfusion in both the DG and SVZ in the adult rat brain.

Preconditioning-induced ischemic tolerance stimulates growth factor expression and neurogenesis in adult rat hippocampus

Preconditioning (PC) is a phenomenon in which a brief ischemic insult induces tolerance against a subsequent severe ischemic insult. Recent studies showed that cerebral ischemia in adult rat upregulates progenitor cell proliferation in the hippocampal dentate gyrus. We presently evaluated whether PC can also stimulate progenitor cell proliferation in rat brain. Middle cerebral artery was transiently occluded in spontaneously hypertensive rats for 10 min to induce PC and 1h to induce focal ischemia. Progenitor cell proliferation (defined as BrdU(+) cell number) significantly increased after focal ischemia (by 3.9-fold; p<0.05) as well as PC (by 2.7-fold; p<0.05) compared to sham. PC 3 days prior had neither an inhibitory nor an additive effect on focal ischemia-induced progenitor cell proliferation. In both ischemia and PC groups, approximately 45% of the progenitor cells proliferated in week 1 survived to the end of week 3 and approximately 21% of those matured into NeuN(+) neurons. Furthermore, cerebral mRNA expression of the growth factors IGF1, FGF2, TGFbeta1, EGF and PDGF-A was significantly elevated after PC. Thus, we show that the beneficial effects of PC extend beyond providing neuroprotection during the acute phase after ischemia. Induction of growth factor expression and neurogenesis by PC might be a positive adaptation for an efficient repair and plasticity in the event of an ischemic insult.

Enhanced proliferation of progenitor cells in the subventricular zone and limited neuronal production in the striatum and neocortex of adult macaque monkeys after global cerebral ischemia

Cerebral ischemia in adult rodent models increases the proliferation of endogenous neural progenitor cells residing in the subventricular zone along the anterior horn of the lateral ventricle (SVZ a) and induces neurogenesis in the postischemic striatum and cortex. Whether the adult primate brain preserves a similar ability in response to an ischemic insult is uncertain. We used the DNA synthesis indicator bromodeoxyuridine (BrdU) to label newly generated cells in adult macaque monkeys and show here that the proliferation of cells with a progenitor phenotype (double positive for BrdU and the markers Musashi 1, Nestin, and beta III-tubulin) in SVZ a increased during the second week after a 20-min transient global brain ischemia. Subsequent progenitor migration seemed restricted to the rostral migratory stream toward the olfactory bulb and ischemia increased the proportion of adult-generated cells retaining their location in SVZ a with a progenitor phenotype. Despite the lack of evidence for progenitor cell migration toward the postischemic striatum or prefrontal neocortex, a small but sustained proportion of BrdU-labeled cells expressed features of postmitotic neurons (positive for the protein Neu N and the transcription factors Tbr 1 and Islet 1) in these two regions for at least 79 days after ischemia. Taken together, our data suggest an enhanced neurogenic response in the adult primate telencephalon after a cerebral ischemic insult.

Neuronal replacement and integration in the rewiring of cerebellar circuits

Repair of CNS injury or degeneration by cell replacement may lead to significant functional recovery only through faithful reconstruction of the original anatomical architecture. This is particularly relevant for point-to-point systems, where precisely patterned connections have to be re-established to regain adaptive function. Despite the major interest recently drawn on cell therapies, little is known about the mechanisms and the potentialities for specific integration of new neurons in the mature CNS. Major findings and concepts about this issue will be reviewed here, with special focus on work dealing with the Purkinje cell transplantation in the rodent cerebellum. These studies show that the adult CNS may provide some efficient information to direct cell engraftment and process outgrowth. On their side, immature cells may be able to induce adaptive changes in their adult partners to facilitate their incorporation in the recipient network. Despite the rather high degree of specific integration achieved in several different CNS regions, these processes are usually defective and long-distance connections are not rewired. Thus, although some potentialities for cell replacement exist in the mature CNS, full incorporation of new neurons in adult circuits is rarely observed. Indeed, intrinsic mechanisms for growth control as well as injury-induced changes in the properties and architecture of the nervous tissue contribute to hamper repair processes. As a consequence, crucial to obtain successful cell replacement and integration in the mature CNS is a deep understanding of the basic biological mechanisms that regulate the interactions between newly added elements and the recipient environment.

Neurogenesis in rats after focal cerebral ischemia is enhanced by indomethacin

BACKGROUND AND PURPOSE

Newborn cells may participate in repair following ischemic brain injury, but their survival and function may be influenced by inflammation.

METHODS

We investigated the effects of indomethacin, a nonsteroidal antiinflammatory drug, on the fate of newborn cells following transient focal ischemia.

RESULTS

Bromodeoxyuridine (BrdU)-labeled cells, including migrating neuroblasts, were observed in the neighboring striatum and overlying cortex 1 day poststroke. The density of BrdU+ cells labeled with doublecortin, nestin, glial fibrillary acidic protein, or NG2 was increased at 14 and 28 days. Indomethacin increased BrdU+ cells of all lineages and reduced microglial/monocyte activation.

CONCLUSIONS

Indomethacin enhanced the accumulation of newborn cells following stroke.

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.

Nitric oxide and adult neurogenesis in health and disease

Adult neurogenesis may be functionally important as a mechanism of brain plasticity in physiological conditions and brain repair after injury. Nitric oxide (NO), a diffusible intracellular and intercellular messenger in the mammalian nervous system, has been shown to affect adult neurogenesis in different ways. In the normal brain, NO, synthesized by the neuronal isoform of NO synthase in nitrergic neurons, is a negative regulator of precursor cell proliferation. However, after brain damage, NO overproduction in different neural and nonneural cell types promotes neurogenesis. Recently reported results on the effects of NO on new neuron generation in the adult brain are reviewed, with special attention to the proposed mechanisms of action and functional consequences in health and disease.

The human brain and its neural stem cells postmortem: from dead brains to live therapy

Contrary to the traditional dogma of being a relatively invariable and quiescent organ lacking the capability to regenerate, there is now widespread evidence that the human brain harbors multipotent neural stem cells, possibly throughout senescence. These cells can divide and give rise to neuroectodermal progeny in vivo and are now regarded as powerful prospective candidates for repairing or enhancing the functional capability of neural tissue in trauma or diseases associated with degeneration or malperfusion. Hopes primarily rest upon techniques to either recruit endogenous stem cells or to utilize exogenous donor-derived material for transplantation. In the search for suitable human cell sources, embryonic, fetal, and adult stem cells appear highly controversial, as they are accompanied by various still-unresolved moral and legal challenges. Fascinatingly, however, recent reports indicate the successful isolation and expansion of viable neural stem cells from the rodent and human brain within a considerable postmortem interval, suggesting that postmortem neural stem cells could potentially become an acceptable alternative cellular resource. This article will provide a brief overview about neural stem cells, their prominent features, and prospects for a cellular therapy, and will furthermore illuminate the cells in particular with respect to their newly discovered postmortem provenience, their advantage as a potential cell source, and several unfolding forensic considerations. Also, important ethical, social, and legal implications arising from this hitherto unpracticed cellular harvest of brain tissue from the deceased are outlined.

Persistent production of neurons from adult brain stem cells during recovery after stroke

Neural stem cells in the subventricular zone of adult rodents produce new striatal neurons that may replace those that have died after stroke; however, the neurogenic response has been considered acute and transient, yielding only small numbers of neurons. In contrast, we show herein that striatal neuroblasts are generated without decline at least for 4 months after stroke in adult rats. Neuroblasts formed early or late after stroke either differentiate into mature neurons, which survive for several months, or die through caspase-mediated apoptosis. The directed migration of the new neurons toward the ischemic damage is regulated by stromal cell-derived factor-1alpha and its receptor CXCR4. These results show that endogenous neural stem cells continuously supply the injured adult brain with new neurons, which suggests novel self-repair strategies to improve recovery after stroke.

Cell-cycle regulators are involved in transient cerebral ischemia induced neuronal apoptosis in female rats

Recent evidence indicates that cell-cycle regulating proteins are involved in apoptotic process in post-mitotic neurons. In this study, we examined cell-cycle regulators for G1/S cell-cycle progression after a transient focal cerebral ischemia induced by middle cerebral artery (MCA) occlusion. In the cerebral frontoparietal cortex, we observed a marked induction of Cyclin D1 (a coactivator of Cdks), and proliferating cell nuclear antigen (PCNA), together with upregulated Cdk kinase activities. This process is accompanied with multiple phosphorylation of retinoblastoma (Rb) protein at Cdk phosphorylation sites in neurons from the ischemic cortex. We further examined DNA synthesis by the incorporation of BrdU, a nucleotide analog that incorporates into newly synthesized DNA. Within 24-h of reperfusion after 60-min occlusion, substantial BrdU-positive neurons were observed in the ischemic cortex. Inhibition of Cdk4 activity during this ischemia/reperfusion is highly neuroprotective. These results suggest that ischemia/reperfusion cerebral damage induces signalings at the G1/S cell-cycle transition, and may constitute a critical step in the neuronal apoptotic pathway in ischemia/reperfusion induced neuronal damage.

D-galactose injured neurogenesis in the hippocampus of adult mice

OBJECTIVES

We studied the effects of the reactive oxygen species (ROS) on neural progenitor cell proliferation and survival in the dentate gyrus (DG).

METHODS

The adult mice were treated with D-galactose for 7 weeks to mimic natural aging in mice. The level of malondialdehyde (MDA) and the activities of antioxidant enzymes in the serum were detected. Neurodegeneration and neurogenesis in the hippocampus were explored using terminal deoxynucleotidyltransferase-mediated UTP nick-end labeling (TUNEL) to detect the dying cells and bromodeoxyuridine (BrdU) was used to label the newly born cells.

RESULTS

After the treatment of D-galactose, the level of MDA increased and the activities of the antioxidant enzyme decreased in the serum. TUNEL-positive cells significantly increased in the DG, CA1 and CA3 subfields. The BrdU-labeled proliferating cells and surviving cells in the DG decreased significantly in number after D-galactose treatment.

DISCUSSION

D-Galactose induced the impairment of neurogenesis in the DG, which is similar to natural aging in mice. ROS accumulation as a result of D-galactose may be related to the decrease of neurogenesis in the DG.

Environmental enrichment increases progenitor cell survival in the dentate gyrus following lateral fluid percussion injury

Neurons in the hilus of the dentate gyrus are lost following a lateral fluid percussion injury. Environmental enrichment is known to increase neurogenesis in the dentate in intact rats, suggesting that it might also do so following fluid percussion injury, and potentially provide replacements for lost neurons. We report that 1 h of daily environmental enrichment for 3 weeks increased the number of progenitor cells in the dentate following fluid percussion injury, but only on the ipsilesional side. In the dentate granule cell layer, but not the hilus, most progenitors had a neuronal phenotype. The rate of on going cell proliferation was similar across groups. Collectively, these results suggest that the beneficial effects of environmental enrichment on behavioral recovery following FP injury are not attributable to neuronal replacement in the hilus but may be related to increased neurogenesis in the granule cell layer.

Neural precursor cells division and migration in neonatal rat brain after ischemic/hypoxic injury

Ischemia/hypoxia (I/H) causes severe perinatal brain disorders such as cerebral palsy. The neonatal brain possesses much plasticity, and to enhance new cell production would be an innovative means of therapy for such disorders. In order to elucidate the dynamic changes of neural progenitor cells in the neonatal brain after ischemia, we investigated new cells production in the subventricular zone and subsequent migration of these cells to the injured area. Newly produced cells were confirmed by incorporation of bromodeoxyuridine (BrdU), and attempt for differentiation was investigated by immunohistochemistry for molecular markers of each cellular lineage. In the sham-control brain, there were many BrdU-labeled cells which gradually decreased as the animal becomes older. Many of these cells were oligodendroglial progenitor or microglial cells. Although there were only few neuronal cells labeled for BrdU in the sham-control, they dramatically increased after I/H. They were located at just beneath the subventricular zone where the progenitor cells reside and to the injured area, indicating that newly produced cells migrated to the infarct region and differentiated into neuronal precursor cells in order to compensate the lost neural cells. We found that BrdU-labeled astroglial, oligodendroglial progenitor, and microglial cells were also increased after I/H, suggesting that they also play active roles in recovery. Progenitor cells may have potential for treating perinatal brain disorders.

Ischemia-stimulated neurogenesis is regulated by proliferation, migration, differentiation and caspase activation of hippocampal precursor cells

A brief ischemic injury to the gerbil forebrain that caused selective damage in the CA1 region of the hippocampus also enhanced the production of new cells in the hippocampal neurogenic area. When evaluated 1 week after bromodeoxyuridine (BrdU) injection, approximately ten times more labeled cells were detected in the hippocampal dentate gyrus in ischemic animals than controls, indicating a stimulation of mitotic activity. To assess the temporal course of the survival and fate of these newborn cells, we monitored BrdU labeling and cell marker expression up to 60 days after ischemia (DAI). Loss of BrdU-positive cells was observed from both control and ischemic animals, but at 30 DAI and afterward, the ischemic group maintained more than 3 times as many BrdU-positive cells as the control group. In addition, ischemic injury also fostered the neuronal differentiation of these cells beyond the capacity observed in control animals and facilitated the migration of developing neurons to a neuronal cellular layer. The establishment of a temporal correlation between differentiation and migration provides evidence of the functional maturation of these cells. Surprisingly, we found that ischemic injury induced activation of caspase-3, not only in the CA1 region as expected, but also in the dentate subgranular zone (SGZ). Active caspase-3 immunoreactivity in the subgranular layer was co-localized with an early neuronal marker, suggesting that caspase-mediated apoptosis could mediate the loss of neurogenic cells in the SGZ. Inhibiting caspase-3 in the context of ischemia-induced neurogenesis might provide an opportunity for functional repair and a therapeutic outcome in the wake of ischemic injury.

[From bench to bedside: should we believe in the efficacy of stem cells in cerebral ischaemia?]

Stroke is the third cause of mortality and the leading cause of morbidity in industrialized countries. At the present time, ischaemic stroke is treated at the acute phase by thrombolysis with a recombinant of the tissular-plasminogen activator, which must be administered within the first 3 hours. Cell therapy, while using the self-renewal and differentiation potentials of stem cells, brings new hope for the long-term care of ischaemic stroke. Animal studies show that stem cells improve functional deficit without reduction of infarct volume and with very rare differentiation of the stem cell. These experimental studies suggest that stem cells would support cerebral plasticity via growth factor production and stimulation of endogenous mechanisms of local repair. Assessment of effectiveness and safety in the use of stem cells in cerebral ischaemia still require thorough investigation before clinical trials in humans can be developed.

Quantitative analysis of the generation of different striatal neuronal subtypes in the adult brain following excitotoxic injury

Recent findings in adult rodents have provided evidence for the formation of new striatal neurons from subventricular zone (SVZ) precursors following stroke. Little is known about which factors determine the magnitude of striatal neurogenesis in the damaged brain. Here we studied striatal neurogenesis following an excitotoxic lesion to the adult rat striatum induced by intrastriatal quinolinic acid (QA) infusion. New cells were labeled with the thymidine-analogue 5-bromo-2'-deoxyuridine (BrdU) and their identity was determined immunocytochemically with various phenotypic markers. The unilateral lesion gave rise to increased cell proliferation mainly in the ipsilateral SVZ. At 2 weeks following the insult, there was a pronounced increase of the number of new neurons co-expressing BrdU and a marker of migrating neuroblasts, doublecortin, in the ipsilateral striatum, particularly its non-damaged medial parts. About 80% of the new neurons survived up to 6 weeks, when they expressed the mature neuronal marker NeuN and were preferentially located in the outer parts of the damaged area. Lesion-generated neurons expressed phenotypic markers of striatal medium spiny neurons (DARPP-32) and interneurons (parvalbumin or neuropeptide Y). The magnitude of neurogenesis correlated to the size of the striatal damage. Our data show for the first time that an excitotoxic lesion to the striatum can trigger the formation of new striatal neurons with phenotypes of both projection neurons and interneurons.

Immunization with the glutamate receptor-derived peptide GluR3B induces neuronal death and reactive gliosis, but confers partial protection from pentylenetetrazole-induced seizures

Do autoantibodies (Ab's) against glutamate/AMPA receptor subtype 3 affect the severity of seizures? Rats immunized with the GluR3B-peptide (amino acids (aa) 372-395) or with the control GluR3A-peptide (aa 245-274) produced the respective anti-GluR3B and anti-GluR3A Ab's (both types of Ab's found in some epilepsy patients). The GluR3B-immunized rats exhibited neuronal death and reactive gliosis in the brain, but not overt spontaneous seizures. Surprisingly, in response to the chemoconvulsant pentylenetetrazole, the GluR3B-immunized rats displayed fewer jerks, a lower percentage of generalized seizures, and a lower overall seizure-severity score than GluR3A-immunized, scrambled GluR3B-immunized or non-immunized control rats. These findings, combined with the previously demonstrated ability of anti-GluR3B Ab's to bind, activate, and kill neurons and glia, suggest that if these Ab's are present in the brain they may cause neuronal death, which by itself may be pro-epileptic, but they may also decrease the excitability of seizure-related neural circuits, thereby conferring partial protection from seizures induced by other exogenously applied epileptogenic stimuli. The present results could have clinical implications for epilepsy.

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.

Focal cerebral ischemia induces changes in both MMP-13 and aggrecan around individual neurons

INTRODUCTION

To test the hypothesis that matrix metalloprotease-13 (MMP-13) and aggrecan may play roles in post-ischemic neuronal pathophysiology, we examined the impact of middle cerebral artery occlusion/reperfusion (MCAO/R) on the abundance of these proteins in different regions of the infarct by immunohistochemistry (IHC) and Western blotting (WB).

METHODS

The effect of MCAO/R on the abundance of MMP-13 and aggrecan was examined in 23 Wistar rats using antibodies against MMP-13 and aggrecan. BrdU was administered the last 2 days of the experiment. The cellular source of the respective antigens was examined with fluorescent double labeling using the neuronal marker NeuN. Sections were also stained for BrdU. The ischemic zone was defined by MRI on T2-weighted images and also on the tissue sections with the help of H and E counterstain. WB was performed for MMP-13.

RESULTS

MMP-13 protein is highly induced in ischemic brain and is associated with neurons, whereas aggrecan is associated with the perineuronal matrix in non-ischemic brain. After 3 days of cerebral ischemia, the number of MMP-13 positive neurons in the periphery of the ischemic lesion increased compared to the respective area in the non-ischemic brain with a peak on day 7. A stronger staining for aggrecan was observed around MMP-13 positive neurons compared with other neurons. The majority of the MMP-13 positive neurons in normal non-ischemic brain were also NeuN positive. BrdU was incorporated into MMP-13 positive neurons in the periphery of the infarct. WB confirmed this results by detecting MMP-13 bands in ischemic brains and activated MMP-13 up to 14 days after ischemia.

CONCLUSIONS

There is a close spatial association of MMP-13 and aggrecan around individual neurons. Both MMP-13 and aggrecan appear to be involved in perineuronal matrix remodeling suggesting a role in neuronal reorganization after cerebral ischemia.

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.

Motor neuron degeneration promotes neural progenitor cell proliferation, migration, and neurogenesis in the spinal cords of amyotrophic lateral sclerosis mice

The organization, distribution, and function of neural progenitor cells (NPCs) in the adult spinal cord during motor neuron degeneration in amyotrophic lateral sclerosis (ALS) remain largely unknown. Using nestin promoter-controlled LacZ reporter transgenic mice and mutant G93A-SOD1 transgenic mice mimicking ALS, we showed that there was an increase of NPC proliferation, migration, and neurogenesis in the lumbar region of adult spinal cord in response to motor neuron degeneration. The proliferation of NPCs detected by bromodeoxyurindine incorporation and LacZ staining was restricted to the ependymal zone surrounding the central canal (EZ). Once the NPCs moved out from the EZ, they lost the proliferative capability but maintained migratory function vigorously. During ALS-like disease onset and progression, NPCs in the EZ migrated initially toward the dorsal horn direction and then to the ventral horn regions, where motor neurons have degenerated. More significantly, there was an increased de novo neurogenesis from NPCs during ALS-like disease onset and progression. The enhanced proliferation, migration, and neurogenesis of (from) NPCs in the adult spinal cord of ALS-like mice may play an important role in attempting to repair the degenerated motor neurons and restore the dysfunctional circuitry which resulted from the pathogenesis of mutant SOD1 in ALS.

Stroke-Induced Neurogenesis in Aged Brain

Background and Purpose— Stroke induced by middle cerebral artery occlusion (MCAO) triggers increased neurogenesis in the damaged striatum and nondamaged hippocampus of young adult rodents. We explored whether stroke influences neurogenesis similarly in the aged brain.

Methods— Young adult (3 months) and old (15 months) rats were subjected to 1 hour of MCAO, and new cells were labeled by intraperitoneal injection of 5-bromo-2′-deoxyuridine 5′-monophosphate (BrdU), a marker for dividing cells, for 2 weeks thereafter. Animals were euthanized at 7 weeks after the insult, and neurogenesis was assessed immunocytochemically with antibodies against BrdU and neuronal markers with epifluorescence or confocal microscopy.

Results— Young and old rats exhibited the same increased numbers of new striatal neurons after stroke, despite basal cell proliferation in the subventricular zone being reduced in the aged brain. In contrast, both the number of stroke-generated granule cells and basal neurogenesis in the dentate subgranular zone were lower in old compared with young animals. Also, the ability of newly formed cells to differentiate into neurons was impaired in the aged dentate gyrus.

Conclusions— Basal neurogenesis is impaired in the subgranular and subventricular zones of aged animals, but both regions react to stroke with increased formation of new neurons. The magnitude of striatal neurogenesis after stroke is similar in young and old animals, indicating that this potential mechanism for self-repair also operates in the aged brain.

Vascular changes in the subventricular zone after distal cortical lesions

One of the effects of cortical lesions is to produce cell proliferation in the subventricular zone (SVZ), a neurogenic zone of the adult brain distal from the lesion. The mechanisms of these effects are unknown. Recent evidence points to a relationship between the vasculature and neurogenesis both in vitro and in vivo. In the present study, we asked whether cortical lesions induced vascular modifications in the distal SVZ in vivo. Lesions of the frontoparietal cortex were produced by thermocoagulation of pial blood vessels, a method that leads to highly reproducible loss of all cortical layers, sparing the corpus callosum and underlying striatum. These lesions induced increased immunoreactivity for vascular endothelial growth factor (VEGF) around the walls of SVZ vessels, at a considerable distance from the lesion. Vascular permeability was markedly increased in both the SVZ and RMS by 3 days after the injury. A dramatic increase in endothelial proliferation was followed by expansion of the local SVZ vascular tree 7 days after the injury. This time course corresponded to the proliferative changes in the SVZ, and a tight correlation was observed between the number of blood vessels and the increase in SVZ cell number. The data demonstrate that thermocoagulatory cortical lesions induce distal vascular changes that could play a role in lesion-induced SVZ expansion.

The hematopoietic factor G-CSF is a neuronal ligand that counteracts programmed cell death and drives neurogenesis

G-CSF is a potent hematopoietic factor that enhances survival and drives differentiation of myeloid lineage cells, resulting in the generation of neutrophilic granulocytes. Here, we show that G-CSF passes the intact blood-brain barrier and reduces infarct volume in 2 different rat models of acute stroke. G-CSF displays strong anti-apoptotic activity in mature neurons and activates multiple cell survival pathways. Both G-CSF and its receptor are widely expressed by neurons in the CNS, and their expression is induced by ischemia, which suggests an autocrine protective signaling mechanism. Surprisingly, the G-CSF receptor was also expressed by adult neural stem cells, and G-CSF induced neuronal differentiation in vitro. G-CSF markedly improved long-term behavioral outcome after cortical ischemia, while stimulating neural progenitor response in vivo, providing a link to functional recovery. Thus, G-CSF is an endogenous ligand in the CNS that has a dual activity beneficial both in counteracting acute neuronal degeneration and contributing to long-term plasticity after cerebral ischemia. We therefore propose G-CSF as a potential new drug for stroke and neurodegenerative diseases.

Hypoxia-ischemia induces DNA synthesis without cell proliferation in dying neurons in adult rodent brain

Recent studies suggest that postmitotic neurons can reenter the cell cycle as a prelude to apoptosis after brain injury. However, most dying neurons do not pass the G1/S-phase checkpoint to resume DNA synthesis. The specific factors that trigger abortive DNA synthesis are not characterized. Here we show that the combination of hypoxia and ischemia induces adult rodent neurons to resume DNA synthesis as indicated by incorporation of bromodeoxyuridine (BrdU) and expression of G1/S-phase cell cycle transition markers. After hypoxia-ischemia, the majority of BrdU- and neuronal nuclei (NeuN)-immunoreactive cells are also terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling (TUNEL)-stained, suggesting that they undergo apoptosis. BrdU+ neurons, labeled shortly after hypoxia-ischemia, persist for >5 d but eventually disappear by 28 d. Before disappearing, these BrdU+/NeuN+/TUNEL+ neurons express the proliferating cell marker Ki67, lose the G1-phase cyclin-dependent kinase (CDK) inhibitors p16INK4 and p27Kip1 and show induction of the late G1/S-phase CDK2 activity and phosphorylation of the retinoblastoma protein. This contrasts to kainic acid excitotoxicity and traumatic brain injury, which produce TUNEL-positive neurons without evidence of DNA synthesis or G1/S-phase cell cycle transition. These findings suggest that hypoxia-ischemia triggers neurons to reenter the cell cycle and resume apoptosis-associated DNA synthesis in brain. Our data also suggest that the demonstration of neurogenesis after brain injury requires not only BrdU uptake and mature neuronal markers but also evidence showing absence of apoptotic markers. Manipulating the aberrant apoptosis-associated DNA synthesis that occurs with hypoxia-ischemia and perhaps neurodegenerative diseases could promote neuronal survival and neurogenesis.

Blockade of L-type voltage-gated Ca channel inhibits ischemia-induced neurogenesis by down-regulating iNOS expression in adult mouse

Neurogenesis in the adult mammalian hippocampus may contribute to repairing the brain after injury. The signals that regulate neurogenesis in the dentate gyrus following ischemic stroke insult are not well known. We have previously reported that inducible nitric oxide synthase (iNOS) expression is necessary for ischemia-stimulated neurogenesis in the adult dentate gyrus. Here, we show that mice subjected to 90 min of middle cerebral artery occlusion (MCAO) significantly increased the number of new neurons and up-regulated iNOS expression in the dentate gyrus. Blockade of the L-type voltage-gated Ca(2+) channel (L-VGCC) prevented neurogenesis in the dentate gyrus and subventricular zone (SVZ), and down-regulated iNOS expression in the dentate gyrus after cerebral ischemia. This study suggests that Ca(2+) influx through L-VGCC is involved in ischemia-induced neurogenesis by up-regulating iNOS expression.

Cross talk between growth factors and viral and cellular factors alters neuronal signaling pathways: implication for HIV-associated dementia

HIV-associated dementia (HAD) is a serious neurological disorder affecting about 7% of people with AIDS. In the brain, HIV-1 infects a restricted number of cell types, being primarily present in macrophages and microglial cells, less abundant in astrocytes, and rarely seen in oligodendrocytes and neurons. Lack of a productive HIV-1 infection of neuronal cells suggests the presence of an indirect pathway by which the virus may determine the brain pathology and neuronal dysfunction seen in AIDS patients. Among the participants in this event, viral proteins including gp120 and Tat, along with host factors including cytokines, chemokines, and several signaling pathways have received considerable attention. In this article, we discuss the most recent concepts pertaining to the mechanisms of HIV-1-induced neuronal dysfunction by highlighting the interplay between signal transduction pathways activated by viral and host factors and their consequences in neuronal cell function.

Migration and fate of newly born cells after focal cortical ischemia in adult rats

Neural cell migration and differentiation may participate in neural repair after adult brain injury; however, the survival and differentiation of newly born cells after different brain lesions are poorly understood. We have examined the migration and fate of bromodeoxyuridine (BrdU)-labeled cells after a highly reproducible focal ischemic lesion restricted to the frontoparietal cortex in adult rats. Thermocoagulation of pial blood vessels induces a circumscribed degeneration of all cortical layers while sparing the corpus callosum and striatum and increases cell proliferation in the subventricular zone (SVZ) and rostral migratory stream (RMS) within 7 days. We now show that, although the rostral migration of the newly born SVZ cells and their differentiation into neurons in the olfactory bulb were not affected by the lesion, numerous cells expressing the neuroblast marker doublecortin migrated laterally in the striatum and corpus callosum 5 days postinjury. In addition to the SVZ, BrdU-labeled cells were seen in the striatum, in the corpus callosum, and around the lesion. One month later, BrdU-labeled cells in the corpus callosum expressed transferrin and the pi isoform of glutathione-S-transferase (GST-pi), markers of oligodendrocytes. Other BrdU+ cells expressed a marker of astrocytes, but none expressed neuronal markers, suggesting that new neurons do not form or survive under these conditions. Numerous BrdU-labeled cells were still observed in the SVZ and RMS. The data show that focal cortical ischemia does not lead to the long-term survival of new neurons in the striatum or cortex but induces long-term alterations in the SVZ and the production of new oligodendrocytes that may contribute to neural repair.

Effects of Abeta25-35 on neurogenesis in the adult mouse subventricular zone and dentate gyrus

It has been demonstrated that neuorgenesis driven by neural precursor cells persists well into the adult period. This study was to observe the effects of Amyloid-beta (25-35) peptide (Abeta(25-35)) on neurogenesis in the subventricular zone and dentate gyrus of adult mouse brain. Aggregated Abeta(25-35)(1 mg/ml, 3 microl) was injected into the lateral ventricle of adult mouse. Animals were transcardially perfused with 4% paraformaldehyde in PBS, respectively at 5, 10, 20, 30 days after the Abeta(25-35) injection. All the animals were injected with BrdU (50 mg/kg, i. p) to label the neural precursor cells 24 h before the each perfusion. NeuN immunofluorescence and BrdU immunohistology were performed. It was found that Abeta(25-35) could injure the mature neurons and decrease the number of NeuN positive neurons. It also showed that Abeta(25-35) inhibited neurogenesis and significantly decreased the number of BrdU positive cells in the dentate gyrus of hippocampus, but it had no obvious effects on neurogenesis in the subventricular zone. The present results indicated that Abeta(25-35) could impair neurogenesis in the hippocampus of adult mouse brain.

Temporally specific burst in cell proliferation increases hippocampal neurogenesis in protracted abstinence from alcohol

Adult neurogenesis is a newly considered form of plasticity that could contribute to brain dysfunction in psychiatric disease. Chronic alcoholism, a disease affecting over 8% of the adult population, produces cognitive impairments and decreased brain volumes, both of which are partially reversed during abstinence. Clinical data and animal models implicate the hippocampus, a region important in learning and memory. In a model of alcohol dependence (chronic binge exposure for 4 d), we show that adult neurogenesis is inhibited during dependence with a pronounced increase in new hippocampal neuron formation after weeks of abstinence. This increase is attributable to a temporally and regionally specific fourfold increase in cell proliferation at day 7 of abstinence, with a majority of those cells surviving and differentiating at percentages similar to controls, effects that doubled the formation of new neurons. Although increases in cell proliferation correlated with alcohol withdrawal severity, proliferation remained increased when diazepam (10 mg/kg) was used to reduce withdrawal severity. Indeed, those animals with little withdrawal activity still show a twofold burst in cell proliferation at day 7 of abstinence. Thus, alcohol dependence and recovery from dependence continues to alter hippocampal plasticity during abstinence. Because neurogenesis may contribute to hippocampal function and/or learning, memory, and mood, compensatory neurogenesis and the return of normal neurogenesis may also have an impact on hippocampal structure and function. For the first time, these data provide a neurobiological mechanism that may underlie the return of human cognitive function and brain volume associated with recovery from addiction.