Cortical neurogenesis in adult rats after reversible photothrombotic stroke

Attenuation of microglial activation with minocycline is not associated with changes in neurogenesis after focal traumatic brain injury in adult mice

Neurogenesis is stimulated following injury to the adult brain and could potentially contribute to tissue repair. However, evidence suggests that microglia activated in response to injury are detrimental to the survival of new neurons, thus limiting the neurogenic response. The aim of this study was to determine the effect of the anti-inflammatory drug minocycline on neurogenesis and functional recovery after a closed head injury model of focal traumatic brain injury (TBI). Beginning 30 min after trauma, minocycline was administered for up to 2 weeks and bromodeoxyuridine was given on days 1-4 to label proliferating cells. Neurological outcome and motor function were evaluated over 6 weeks using the Neurological Severity Score (NSS) and ledged beam task. Microglial activation was assessed in the pericontusional cortex and hippocampus at 1 week post-trauma, using immunohistochemistry to detect F4/80. Following immunolabeling of bromodeoxyuridine, double-cortin, and NeuN, cells undergoing distinct stages of neurogenesis, including proliferation, neuronal differentiation, neuroblast migration, and long-term survival, were quantified at 1 and 6 weeks in the hippocampal dentate gyrus, as well as in the subventricular zone of the lateral ventricles and the pericontusional cortex. Our results show that minocycline successfully reduced microglial activation and promoted early neurological recovery that was sustained over 6 weeks. We also show for the first time in the closed head injury model, that early stages of neurogenesis were stimulated in the hippocampus and subventricular zone; however, no increase in new mature neurons occurred. Contrary to our hypothesis, despite the attenuation of activated microglia, minocycline did not support neurogenesis in the hippocampus, lateral ventricles, or pericontusional cortex, with none of the neurogenic stages being affected by treatment. These data provide evidence that a general suppression of microglial activation is insufficient to enhance neuronal production, suggesting that further work is required to elucidate the relationship between microglia and neurogenesis after TBI.

Long-term stimulation of neural progenitor cell migration after cortical ischemia in mice

BACKGROUND AND PURPOSE

Cortical ischemia induces neural progenitor cell migration toward the injury site; however, whether these cells are capable of maintaining the migratory response for a longer period after injury remains uncertain.

METHODS

We analyzed progenitor migration up to 1 year after induction of photothrombotic stroke to the mouse neocortex. Migrating progenitors identified as doublecortin positive cells (DCX+) were assessed using the immunohistochemistry and immunofluorescence. The thymidine analogues chlorodeoxyuridine and iododeoxyuridine were used to birth-date the progenitor cells.

RESULTS

In the striatum, we detected elevated numbers of DCX+ cells up to 6 weeks postlesion. In the corpus callosum and the peri-infarct cortex (Ctx), DCX+ cell numbers were increased up to 1 year. The orientation of the migrating progenitors was mostly aligned with the corpus callosum fiber tract at all time points; however, in the Ctx, they aligned parallel to the infarct border. The injured cortex continuously receives new progenitors up to 1 year after lesion. Cells born after lesion did not become mature neurons, although a portion of the migrating progenitors showed initial signs of differentiation into neurons.

CONCLUSIONS

Neural progenitors might have a role in brain plasticity after cortical stroke, especially considering the prolonged window of migratory responses of up to 1 year after stroke lesion.

Recent Advances on the Possible Neuroprotective Activities of Epstein-Barr Virus Oncogene BARF1 Protein in Chronic Inflammatory Disorders of Central Nervous System

Multiple sclerosis and neurodegenerative diseases in which cells of the central nervous system (CNS) are lost or damaged are rapidly increasing in frequency, and there is neither effective treatment nor cure to impede or arrest their destructive course. The Epstein-Barr virus is a human gamma-herpesvirus that infects more than 90% of the human population worldwide and persisting for the lifetime of the host. It is associated with numerous epithelial cancers, principally undifferentiated nasopharyngeal carcinoma and gastric carcinoma. Individuals with a history of symptomatic primary EBV infection, called infectious mononucleosis, carry a moderately higher risk of developing multiple sclerosis (MS). It is not known how EBV infection potentially promotes autoimmunity and central nervous system (CNS) tissue damage in MS. Recently it has been found that EBV isolates from different geographic regions have highly conserved BARF1 epitopes. BARF1 protein has the neuroprotective and mitogenic activity, thus may be useful to combat and overcome neurodegenerative disease. BARF1 protein therapy can potentially be used to enhance the neuroprotective activities by combinational treatment with anti-inflammatory antagonists and neuroprotectors in neural disorders.

Disturbance of perineuronal nets in the perilesional area after photothrombosis is not associated with neuronal death

Perineuronal nets (PNNs) are a condensed form of extracellular matrix that covers the surface of a subset of neurons. Their presence limits neuronal plasticity and may protect neurons against harmful agents. Here we analyzed the relationship between spatiotemporal changes in PNN expression and cell death markers after focal cortical photothrombotic stroke in rats. We registered a substantial decrease in PNN density using Wisteria floribunda agglutinin staining and CAT-315 and brevican immunoreactivity; the decrease occurred not only in the lesion core but also in the perilesional and remote cortex as well as in homotopic contralateral cortical regions. Fluoro Jade C and TUNEL staining in perilesional and remote areas, however, showed a low density of dying cells. Our results suggest that the PNN reduction was not a result of cellular death and could be considered an attempt to create conditions favorable for synaptic remodeling.

Injury-induced neurogenesis in the mammalian forebrain

It has been accepted that new neurons are added to the olfactory bulb and the hippocampal dentate gyrus throughout life in the healthy adult mammalian brain. Recent studies have clarified that brain insult raises the proliferation of neural stem cells/neural progenitor cells existing in the subventricular zone and the subgranular zone, which become sources of new neurons for the olfactory bulb and the dentate gyrus, respectively. Interestingly, convincing data has shown that brain insult invokes neurogenesis in various brain regions, such as the hippocampal cornu ammonis region, striatum, and cortex. These reports suggest that neural stem cells/neural progenitor cells, which can be activated by brain injury, might be broadly located in the adult brain or that new neurons may migrate widely from the neurogenic regions. This review focuses on brain insult-induced neurogenesis in the mammalian forebrain, especially in the neocortex.

Neurogenesis and glial proliferation are stimulated following diffuse traumatic brain injury in adult rats

Although increased neurogenesis has been described in rodent models of focal traumatic brain injury (TBI), the neurogenic response occurring after diffuse TBI uncomplicated by focal injury has not been examined to date, despite the pervasiveness of this distinct type of brain injury in the TBI patient population. Here we characterize multiple stages of neurogenesis following a traumatic axonal injury (TAI) model of diffuse TBI as well as the proliferative response of glial cells. TAI was induced in adult rats using an impact-acceleration model, and 5-bromo-2'-deoxyuridine (BrdU) was administered on days 1-4 posttrauma or sham operation to label mitotic cells. Using immunohistochemistry for BrdU combined with phenotype-specific markers, we found that proliferation was increased following TAI in the subventricular zone of the lateral ventricles and in the hippocampal subgranular zone, although the ultimate production of new dentate granule neurons at 8 weeks was not significantly enhanced. Also, abundant proliferating and reactive astrocytes, microglia, and polydendrocytes were detected throughout the brain following TAI, indicating that a robust glial response occurs in this model, although very few new cells in the nonneurogenic brain regions became mature neurons. We conclude that diffuse brain injury stimulates early stages of a neurogenic response similar to that described for models of focal TBI.

Oxygen, a Key Factor Regulating Cell Behavior during Neurogenesis and Cerebral Diseases

Oxygen is vital to maintain the normal functions of almost all the organs, especially for brain which is one of the heaviest oxygen consumers in the body. The important roles of oxygen on the brain are not only reflected in the development, but also showed in the pathological processes of many cerebral diseases. In the current review, we summarized the oxygen levels in brain tissues tested by real-time measurements during the embryonic and adult neurogenesis, the cerebral diseases, or in the hyperbaric/hypobaric oxygen environment. Oxygen concentration is low in fetal brain (0.076-7.6 mmHg) and in adult brain (11.4-53.2 mmHg), decreased during stroke, and increased in hyperbaric oxygen environment. In addition, we reviewed the effects of oxygen tensions on the behaviors of neural stem cells (NSCs) in vitro cultures at different oxygen concentration (15.2-152 mmHg) and in vivo niche during different pathological states and in hyperbaric/hypobaric oxygen environment. Moderate hypoxia (22.8-76 mmHg) can promote the proliferation of NSCs and enhance the differentiation of NSCs into the TH-positive neurons. Next, we briefly presented the oxygen-sensitive molecular mechanisms regulating NSCs proliferation and differentiation recently found including the Notch, Bone morphogenetic protein and Wnt pathways. Finally, the future perspectives about the roles of oxygen on brain and NSCs were given.

Adult human neurogenesis: from microscopy to magnetic resonance imaging

Neural stem cells reside in well-defined areas of the adult human brain and are capable of generating new neurons throughout the life span. In rodents, it is well established that the new born neurons are involved in olfaction as well as in certain forms of memory and learning. In humans, the functional relevance of adult human neurogenesis is being investigated, in particular its implication in the etiopathology of a variety of brain disorders. Adult neurogenesis in the human brain was discovered by utilizing methodologies directly imported from the rodent research, such as immunohistological detection of proliferation and cell-type specific biomarkers in postmortem or biopsy tissue. However, in the vast majority of cases, these methods do not support longitudinal studies; thus, the capacity of the putative stem cells to form new neurons under different disease conditions cannot be tested. More recently, new technologies have been specifically developed for the detection and quantification of neural stem cells in the living human brain. These technologies rely on the use of magnetic resonance imaging, available in hospitals worldwide. Although they require further validation in rodents and primates, these new methods hold the potential to test the contribution of adult human neurogenesis to brain function in both health and disease. This review reports on the current knowledge on adult human neurogenesis. We first review the different methods available to assess human neurogenesis, both ex vivo and in vivo and then appraise the changes of adult neurogenesis in human diseases.

Effect of focal cerebral ischaemia on modulatory neurotransmitter receptors in the rat brain: an autoradiographic study

Neurotransmission is strongly affected after ischaemic insult. It is postulated that modulatory neurotransmitter systems and their receptors play a role in experience-dependent and restoration plasticity. In this study, muscarinic cholinergic, serotonergic 5-HT(2A/2C), dopaminergic D(1) and noradrenergic beta(1) receptors were examined after focal cerebral ischaemia in different brain regions, using quantitative in vitro autoradiography. There were six evaluated time points: 4h, 1, 4, 7, 28 and 60 days after the insult. Rats received unilateral ischaemic lesions through photo-thrombosis in the primary somatosensory cortex. In the lesion core, 5-HT(2A/2C), D(1) and beta(1) receptor binding values return to control levels 28 days after displaying initial decreases, while muscarinic binding remains very low, at 30% of controls. From 4h to 60 days post-stroke no changes are observed in the perilesional tissue. In contrast, in remote brain regions, a bilateral increase of serotonergic 5-HT(2A/2C) receptor binding in the somatosensory cortex at the striatum level is observed after 4h and after 7 days post-stroke. In addition, a bilateral decrease of muscarinic cholinergic receptor binding in the hippocampus is observed at each time point examined. This study points to a complex and remote reaction of modulatory systems in response to ischaemic lesions.

[Donepezil-induced neuroprotection of acetylcholinergic neurons in olfactory bulbectomized mice]

In the brain of Alzheimer's patients, the cholinergic neurons innervated the hippocampus and cerebral cortex degenerates before accumulation of beta-amyloid protein. Donepezil, a potent acetylcholinesterase (AChE) inhibitor is reported to rescue neurons from excitotoxic injury in culture. However, there is no evidence to confirm its neuroprotective effect on ACh neurons in vivo. Using olfactory bulbectomy (OBX) mice, we defined the neuroprotective mechanisms of donepezil on the medial septum cholinergic neurons with concomitant improvement of the impaired cognitive function. Bilateral olfactory bulbs of DDY mouse were removed by surgery. After olfactory bulbectomized (OBX), donepezil (1 or 3 mg/kg/day) was administered for 15 days and mouse brain was fixed with paraformaldehyde perfusion at day 18. Then, the neuroprotective effect of donepezil was evaluated by counting the number of Chdine acetyltrans-ferase (ChAT) immunoreactive neurons in the medial septum. The number of ChAT immunoreactive neurons in the medial septum reduced by 40% of that in sham-operated animals. The reduced ChAT positive neurons were restored by donepezil treatments. Consistent with these observations, the cognitive deficits observed in OBX mice were significantly improved by the donepezil treatment. Taken together, donepezil treatment rescues the cholinergic neurons in the medial septum from the neurodegeneration by OBX. We will also discuss the mechanism underlying the donepezil-induced neuroprotection in the medial septum cholinergic neurons.

Characterization of neural stem/progenitor cells expressing VEGF and its receptors in the subventricular zone of newborn piglet brain

Neural stem/progenitor cell (NSP) biology and neurogenesis in adult central nervous system (CNS) are important both towards potential future therapeutic applications for CNS repair, and for the fundamental function of the CNS. In the present study, we report the characterization of NSP population from subventricular zone (SVZ) of neonatal piglet brain using in vivo and in vitro systems. We show that the nestin and vimentin-positive neural progenitor cells are present in the SVZ of the lateral ventricles of neonatal piglet brain. In vitro, piglet NSPs proliferated as neurospheres, expressed the typical protein of neural progenitors, nestin and a range of well-established neurodevelopmental markers. Upon dissociation and subculture, piglet NSPs differentiated into neurons and glial cells. Clonal analysis demonstrates that piglet NSPs are multipotent and retain the capacity to generate both glia and neurons. These cells expressed VEGF, VEGFR1, VEGFR2 and Neuropilin-1 and -2 mRNAs. Real time PCR revealed that SVZ NSPs from newborn piglet expressed total VEGF and all VEGF splice variants. These findings show that piglet NSPs may be helpful to more effectively design growth factor based strategies to enhance endogenous precursor cells for cell transplantation studies potentially leading to the application of this strategy in the nervous system disease and injury.

Transplantation of human neural precursor cells in Matrigel scaffolding improves outcome from focal cerebral ischemia after delayed postischemic treatment in rats

Transplantation of neural cells is a potential approach for stroke treatment, but disruption of tissue architecture may limit transplant efficacy. One strategy for enhancing the ability of transplants to restore brain structure and function is to administer cells together with biomaterial scaffolding. We electrocoagulated the distal middle cerebral artery in adult rats and, 3 weeks later, injected one of the following into the infarct cavity: artificial cerebrospinal fluid, Matrigel scaffolding, human embryonic stem cell-derived neuronal precursor cells, scaffolding plus cells, or cells cultured in and administered together with scaffolding. Five weeks after transplantation, the latter two groups showed approximately 50% and approximately 60% reductions, respectively, in infarct cavity volume. Rats given cells cultured in and administered together with scaffolding also showed (1) survival and neuronal differentiation of transplanted cells shown by immunostaining for neuronal marker proteins and cleaved caspase-3, and by patch-clamp recording, 8 weeks after transplantation and (2) improved outcome on tests of sensorimotor and cognitive functions, 4 to 9 weeks after transplantation. These results indicate that transplantation of human neural cells together with biomaterial scaffolding has the potential to improve the outcome from stroke, even when treatment is delayed for several weeks after the ischemic event.

Ischemia-induced neurogenesis of neocortical layer 1 progenitor cells

Adult mammalian neurogenesis occurs in the hippocampus and the olfactory bulb, whereas neocortical adult neurogenesis remains controversial. Several occurrences of neocortical adult neurogenesis in injured neocortex were recently reported, suggesting that neural stem cells (NSCs) or neuronal progenitor cells (NPCs) that can be activated by injury are maintained in the adult brain. However, it is not clear whether or where neocortical NSCs/NPCs exist in the brain. We found NPCs in the neocortical layer 1 of adult rats and observed that their proliferation was highly activated by global forebrain ischemia. Using retrovirus-mediated labeling of layer 1 proliferating cells with membrane-targeted green fluorescent protein, we found that the newly generated neurons were GABAergic and that the neurons were functionally integrated into the neuronal circuitry. Our results suggest that layer 1 NPCs are a source of adult neurogenesis under ischemic conditions.

Neurotransmitter synthesis in poststroke cortical neurogenesis in adult rats

Neurogenesis occurs in the cerebral cortex of adult rats after focal cerebral ischemia. Whether or not the newborn neurons could synthesize neurotransmitters is unknown. To elucidate such a possibility, a photothrombotic ring stroke model with spontaneous reperfusion was induced in adult male Wistar rats. The DNA duplication marker BrdU was repeatedly injected, and the rats were sacrificed at various times after stroke. To detect BrdU nuclear incorporation and various neurotransmitters, brain sections were processed for single/double immunocytochemistry and single/double/triple immunofluorescence. Stereological cell counting was performed to assess the final cell populations. At 48 h, 5 days, 7 days, 30 days, 60 days and 90 days after stroke, numerous cells were BrdU-immunolabeled in the penumbral cortex. Some of these were doubly immunopositive to the cholinergic neuron-specific marker ChAT or GABAergic neuron-specific marker GAD. As analyzed by 3-D confocal microscopy, the neurotransmitters acetylcholine and GABA were colocalized with BrdU in the same cortical cells. In addition, GABA was colocalized with the neuron-specific marker Neu N in the BrdU triple-immunolabeled cortical cells. This study suggests that the newborn neurons are capable of synthesizing the neurotransmitters acetylcholine and GABA in the penumbral cortex, which is one of the fundamental requisites for these neurons to function in the poststroke recovery.

Fate and manipulations of endogenous neural stem cells following brain ischemia

Stem cells have been proposed as a new form of cell-based therapy in a variety of disorders, including acute and degenerative brain diseases. Endogenous neural stem cells (eNSCs) have been identified in the central nervous system where they reside largely in the subventricular zone and in the subgranular zone of the hippocampus. eNSCs are capable of self-renewal and differentiation into functional glia and neurons throughout life. However, spontaneous brain regeneration does not suffice to induce significant behavioral improvement in acute or chronic brain injury. Nevertheless, eNSCs responses can be considerably increased by tweaking the pathways governing cell proliferation, migration and differentiation. Contemporary evidence now suggests that such perturbations may lead to better functional outcome after brain injury.

Stem cells for ischemic brain injury: a critical review

No effective therapy is currently available to promote recovery following ischemic stroke. Stem cells have been proposed as a potential source of new cells to replace those lost due to central nervous system injury, as well as a source of trophic molecules to minimize damage and promote recovery. We undertook a detailed review of data from recent basic science and preclinical studies to investigate the potential application of endogenous and exogenous stem cell therapies for treatment of cerebral ischemia. To date, spontaneous endogenous neurogenesis has been observed in response to ischemic injury, and can be enhanced via infusion of appropriate cytokines. Exogenous stem cells from multiple sources can generate neural cells that survive and form synaptic connections after transplantation in the stroke-injured brain. Stem cells from multiple sources cells also exhibit neuroprotective properties that may ameliorate stroke deficits. In many cases, functional benefits observed are likely independent of neural differentiation, although the exact mechanisms remain poorly understood. Future studies of neuroregeneration will require the demonstration of function in endogenously born neurons following focal ischemia. Further, methods are currently lacking to demonstrate definitively the therapeutic effect of newly introduced neural cells. Increased plasticity following stroke may facilitate the functional integration of new neurons, but the loss of appropriate guidance cues and supporting architecture in the infarct cavity will likely impede the restoration of lost circuitry. Thus careful investigation of the mechanisms underlying trophic benefits will be essential. Evidence to date suggests that continued development of stem cell therapies may ultimately lead to viable treatment options for ischemic brain injury.

VEGF enhance cortical newborn neurons and their neurite development in adult rat brain after cerebral ischemia

To study the effect of VEGF overexpression on development of cortical newborn neurons in the brains after stroke, we injected human VEGF(165)-expressive plasmids (phVEGF) into the lateral ventricle of rat brains with a transient middle cerebral artery occlusion (MCAO). An injection of phVEGF significantly promoted angiogenesis (BrdU(+)-von Willebrand's factor(+)) and reduced infarct volume in the rat brain after MCAO. Single labeling of 5'-bromodeoxyuridine (BrdU) and double staining of BrdU with lineage-specific neuronal markers were used to indicate the proliferated cells and maturation of newborn neurons in the brain section of rats at 2, 4, and 8 weeks after MCAO. The results showed that BrdU positive (BrdU(+)) cells existed in ipsilateral frontal cortex within 8 weeks after MCAO and reached the maximum at 2 weeks of reperfusion. The phVEGF treatment significantly increased BrdU(+) cells compared with the control plasmid (pEGFP) injection. Cortical neurogenesis was indicated by the presence of newborn immature (BrdU(+)-Tuj1(+)), newborn mature (BrdU(+)-MAP-2(+)), and newborn GABAergic (BrdU(+)-GAD67(+)) neurons. All these neurons declined within 8 weeks after MCAO in the controls. Injection of phVEGF significantly increased BrdU(+)-Tuj1(+) neurons at 2 weeks, and BrdU(+)-MAP-2(+) neurons and BrdU(+)-GAD67(+) neurons at 4 and 8 weeks, respectively after MCAO. Moreover, phVEGF treatment significantly increased neurite length and branch numbers of BrdU(+)-MAP-2(+) newborn neurons compared with pEGFP treatment. These results demonstrate that VEGF enhances maturation of stroke-induced cortical neurogenesis and dendritic formation of newborn neurons in adult mammalian brains.

Midkine gene transfer protects against focal brain ischemia and augments neurogenesis

BACKGROUND AND PURPOSE

Midkine is a heparin-binding growth factor having various biological activities including chemotaxis of inflammatory cells, angiogenesis and migration of neuronal cells. These biological activities are expected to have a great impact on the pathology of brain infarction in subacute phase. Therefore, we investigated the effect of post-ischemic gene transfer of midkine in the phase.

METHODS

Brain ischemia was produced by the photothrombotic distal middle cerebral artery occlusion in spontaneously hypertensive rats. We measured cerebral blood flow by laser Doppler flowmetry. At 90 min after induction of brain ischemia, adenovirus vectors encoding mouse midkine (AdMK) or enhanced green fluorescence protein (AdGFP) were injected into the lateral ventricle. At 7 days after brain ischemia, the infarct volume, angiogenesis, inflammation and neuronal regeneration were evaluated.

RESULTS

There were no differences in cerebral blood flow changes between AdMK and AdGFP groups. However, infarct volume of AdMK group was significantly smaller than AdGFP group by 33%. The vascular density, the numbers of leukocytes in blood vessels, infiltrated macrophages and proliferated neuronal precursor cells were not significantly different between both groups. Contrastingly the numbers of migrating neuronal precursor cells toward the brain infarction were significantly increased in AdMK group than AdGFP group.

CONCLUSIONS

Neuroprotective effect of midkine gene transfer persisted until the subacute phase of brain infarction. Midkine may contribute to neuronal regeneration. These results suggest the usefulness of midkine gene transfer for treatment of brain infarction.

The HDAC inhibitor, sodium butyrate, stimulates neurogenesis in the ischemic brain

In the healthy adult brain, neurogenesis normally occurs in the subventricular zone (SVZ) and hippocampal dentate gyrus (DG). Cerebral ischemia enhances neurogenesis in neurogenic and non-neurogenic regions of the ischemic brain of adult rodents. This study demonstrated that post-insult treatment with a histone deacetylase inhibitor, sodium butyrate (SB), stimulated the incorporation of bromo-2'-deoxyuridine (BrdU) in the SVZ, DG, striatum, and frontal cortex in the ischemic brain of rats subjected to permanent cerebral ischemia. SB treatment also increased the number of cells expressing polysialic acid-neural cell adhesion molecule, nestin, glial fibrillary acidic protein, phospho-cAMP response element-binding protein (CREB), and brain-derived neurotrophic factor (BDNF) in various brain regions after cerebral ischemia. Furthermore, extensive co-localization of BrdU and polysialic acid-neural cell adhesion molecule was observed in multiple regions after ischemia, and SB treatment up-regulated protein levels of BDNF, phospho-CREB, and glial fibrillary acidic protein. Intraventricular injection of K252a, a tyrosine kinase B receptor antagonist, markedly reduced SB-induced cell proliferation detected by BrdU and Ki67 in the ipsilateral SVZ, DG, and other brain regions, blocked SB-induced nestin expression and CREB activation, and attenuated the long-lasting behavioral benefits of SB. Together, these results suggest that histone deacetylase inhibitor-induced cell proliferation, migration and differentiation require BDNF-tyrosine kinase B signaling and may contribute to long-term beneficial effects of SB after ischemic injury.

Age-dependent regenerative responses in the striatum and cortex after hypoxia-ischemia

Regenerative responses after hypoxia-ischemia (HI) were investigated in the immature (P9) and juvenile (P21) mouse striatum and cortex by postischemic 5-bromo-2-deoxyuridine labeling and phenotyping of labeled cells 4 weeks later. HI stimulated the formation of new cells in striatum and cortex in immature, growing brains (P9), but when brain growth was finished (P21) proliferation could be stimulated only in striatum, not in cortex. However, the relative increase was higher in P21 (460%) than P9 striatum (50%), though starting from a lower level at P21. Starting from this lower level, HI-induced proliferation in P21 striatum reached the same level as in P9 striatum, but not higher. Phenotyping revealed that low levels of neurogenesis were still present in nonischemic P9 cortex and striatum, but only in striatum at P21. Ischemia-induced neurogenesis was found only in P9 striatum. Ischemia-induced gliogenesis occurred in P9 and P21 striatum as well as P9 cortex, but not in P21 cortex. Hence, the regenerative response was stronger in striatum than cortex, and stronger in P9 than P21 cortex. The biggest ischemia-induced change was the 49-fold increase in P21 striatal microglia, and this was accompanied by increased inflammation, as judged by the size and numbers of CCL2- and interleukin-18-positive cells.

Temporal profile of neurogenesis in the subventricular zone, dentate gyrus and cerebral cortex following transient focal cerebral ischemia

BACKGROUND

In the adult mammalian brain, it is considered that neurogenesis persists in limited regions such as the hippocampal dentate gyrus (DG) and the subventricular zone (SVZ) of the lateral ventricle. On the other hand, neurogenesis in the cortex after cerebral ischemia and its role in post-stroke recovery have not been clarified yet. In this study, we investigated neurogenesis in the cortex and the spatiotemporal profile of neural progenitors in SVZ and DG of rats subjected to transient focal cerebral ischemia.

MATERIALS AND METHODS

Male Sprague-Dawley rats (270-300 g) were subjected to 60 minute middle cerebral artery occlusion. Proliferating cells were labeled by the cumulative administration of BrdU 1, 2, 3, 4, 6 and 8 weeks after ischemia induction (at weeks 1-4, 6 and 8). Double labeling was also performed with antibodies against BrdU and NeuN.

RESULTS

BrdU-positive cells proliferated in DG and SVZ of the bilateral hemispheres, and their proliferation peaked at week 3 in SVZ and at week 4 in DG. In the peri-infarct zone of cerebral cortex, BrdU-positive cells co-expressed NeuN from weeks 3 to 8.

CONCLUSION

Neurogenesis was observed in the cerebral cortex and proliferation of neural progenitors occurred in SVZ and DG of rats subjected to transient focal cerebral ischemia. Our data might indicate that endogenous dormant neural stem cells residing in the cortex were activated by ischemic insult to induce the proliferation of neural progenitors and differentiation into mature neurons.

Temporal variation of induction neurogenesis in a rat model of transient middle cerebral artery occlusion

OBJECTIVE

The adult brain is capable of neurogenesis after cerebral ischemia. We investigated the presence of new neural precursors after transient middle cerebral artery ischemia adult rats.

METHODS

Transient middle cerebral artery ischemia was induced in adult Wistar rats (n=13) using the monofilament method. In the experimental group (n=8), animals were harvested at days 3, 7, 10, 17 and 21 after ischemia. Five animals served as controls. Sagittal sections through the ischemic cortex were double-stained for neural (nestin and beta-tubulin, nestin and PCNA), glial (nestin and GFAP) and oligodendroglial (nestin and O4, CNP and PCNA) precursors. Double-stained cells were also counted under high-power view and tabulated over time.

RESULTS

In the subventricular zone (SVZ), there was positive double-staining starting at day 3 showing proliferating astrocytic precursors (nestin + GFAP, 5-20% of cells), neuronal stem cells (nestin + PCNA, 95% of cells) and neuronal precursors (nestin + beta-tubulin, 50% of cells). Within the penumbra, a more robust response showed more astrocytic precursors (50-80% of cells), premature and differentiated oligodendrocytes, neuronal stem cells (85% of cells) and neuronal precursors (15% of cells). In the area of the stroke, there was an intermediate response consisting of more astrocytic precursors (10-20% of cells), premature oligodendrocytes (45-100% of cells), neuronal stem cells (95% of cells) and neuronal precursors (25% of cells). Results were confirmed with cell counting analysis.

DISCUSSION

Our results show that not only do neural precursors proliferate in the SVZ, there is definite and real response in the penumbra and ischemic cortex, suggesting the ability of repair in the central nervous system.

Electrophysiological neurodifferentiation of subventricular zone-derived precursor cells following stroke

Stroke in rodents is associated with increased neurogenesis and the migration of newborn neurons to sites of brain ischemia, where they may participate in repair and recovery. To determine if neurogenesis following stroke yields functional new neurons, we labeled neuronal precursors in the mouse subventricular zone (SVZ) with a lentivirus-green fluorescent protein vector, produced stroke by occluding the middle cerebral artery, and detected newborn neurons 8 weeks later by fluorescence microscopy. Patch-clamp studies on fluorescent neurons in the cortical region surrounding infarction showed tetrodotoxin-sensitive Na(+) action potentials and spontaneous excitatory post-synaptic currents, suggesting that ischemia led to functional neurogenesis with synaptic integration. These findings support the hypothesis that enhancing endogenous neurogenesis after stroke might have therapeutic benefit.

Doublecortin-expressing cells in the ischemic penumbra of a small-vessel stroke

A cortical lesion was induced by disrupting the medium-size pial vessels, which led to a cone-shaped cortical lesion and turned into a fluid-filled cavity surrounded by a glial acidic fibrillary protein-positive (GFAP(+)) glia limitans 21 days after injury. Therefore, it mimics conditions of lacunar infarctions, one of the most frequent human stroke pathologies. Doublecortin (DCX)-positive cells were present in the neocortex and corpus callosum at the base of the lesion. The number of DCX-positive cells in the corpus callosum was significantly increased from day 5 to day 14 compared with the control group. In contrast, there were no DCX-positive cells in neocortex of control animals; the DCX-positive cells appeared in the neocortex after lesioning and were maintained until 14 days postlesioning. Some of the DCX-positive cells were also immunoreactive for beta III-tubulin, another marker of immature neurons. They did not stain positively for markers of glia cells. The presence of these DCX-positive cells near the lesion might indicate a migratory pathway for developing neuroblasts from the subventricular zone (SVZ) through the corpus callosum to the lesion. SVZ cells were labeled with a lipophilic molecule, 5- (and 6-) carboxyfluorescein diacetate succinimidyl ester (CFSE) stereotaxical injections. Although rostral migratory stream and olfactory bulb were intensely labeled, no CFSE-containing cells were found in the cortex beneath the lesion. These results do not support the idea that the DCX-positive cells were originating from neural precursors of the SVZ, but they might be generated from local progenitor cells.

Bis(1-oxy-2-pyridinethiolato)oxovanadium(IV) enhances neurogenesis via phosphatidylinositol 3-kinase/Akt and extracellular signal regulated kinase activation in the hippocampal subgranular zone after mouse focal cerebral ischemia

Although neurogenesis in the hippocampus is critical for improvement of depressive behaviors and cognitive functions in neurodegeneration disorders, there is no therapeutic agent available to promote neurogenesis in adult brain following brain ischemic injury. Here we found that i.p. administration of bis(1-oxy-2-pyridinethiolato)oxovanadium(IV) [VO(OPT)], which stimulates phosphatidylinositol 3-kinase (PI3K)/Akt and extracellular signal regulated kinase (ERK) pathways, markedly enhanced brain ischemia-induced neurogenesis in the subgranular zone (SGZ) of the mouse hippocampus. VO(OPT) treatment enhanced not only the number of proliferating cells but also migration of neuroblasts. VO(OPT)-induced neurogenesis was associated with Akt and ERK activation in neural precursors in the SGZ. Likewise, VO(OPT)-induced neurogenesis was blocked by both PI3K/Akt and mitogen-activated protein kinase/extracellular signal regulated kinase kinase (MEK)/ERK inhibitors. VO(OPT) treatment rescued decreased phosphorylation of glycogen synthesis kinase 3beta (GSK-3beta) at Ser-9. Finally, amelioration of cognitive dysfunction seen following brain ischemia was positively correlated with VO(OPT)-induced neurogenesis. Taken together, VO(OPT) is a potential therapeutic agent that enhances ischemia-induced neurogenesis through PI3K/Akt and ERK activation, thereby improving memory and cognitive deficits following brain ischemia.

The injured nervous system: a Darwinian perspective

Much of the permanent damage that occurs in response to nervous system damage (trauma, infection, ischemia, etc.) is mediated by endogenous secondary processes that can contribute to cell death and tissue damage (excitotoxicity, oxidative damage and inflammation). For humans to evolve mechanisms to minimize secondary pathophysiological events following CNS injuries, selection must occur for individuals who survive such insults. Two major factors limit the selection for beneficial responses to CNS insults: for many CNS disease states the principal risk factor is advanced, post-reproductive age and virtually all severe CNS traumas are fatal in the absence of modern medical intervention. An alternative hypothesis for the persistence of apparently maladaptive responses to CNS damage is that the secondary exacerbation of damage is the result of unavoidable evolutionary constraints. That is, the nervous system could not function under normal conditions if the mechanisms that caused secondary damage (e.g., excitotoxicity) in response to injury were decreased or eliminated. However, some vertebrate species normally inhabit environments (e.g., hypoxia in underground burrows) that could potentially damage their nervous systems. Yet, neuroprotective mechanisms have evolved in these animals indicating that natural selection can occur for traits that protect animals from nervous system damage. Many of the secondary processes and regeneration-inhibitory factors that exacerbate injuries likely persist because they have been adaptive over evolutionary time in the healthy nervous system. Therefore, it remains important that researchers consider the role of the processes in the healthy or developing nervous system to understand how they become dysregulated following injury.

Inducing photochemical cortical lesions in rat brain

In the rat photochemical cortical lesion model described in this unit, an intravascular photochemical reaction induces endothelial damage resulting in platelet aggregation, thrombosis, thrombotic response (secretion of factors by the platelets) and permanent cerebral vascular occlusion. Because thrombosis is produced in pial vessels, the resulting cortical infarct is generally smaller and more reproducible than in the models involving occlusion of the middle cerebral artery. The surgical procedures involved are limited, making this model generally easier to perform and less invasive than most other models of permanent focal ischemia that involve mechanical occlusion of major cerebral arteries.

New interneurons in the adult neocortex: small, sparse, but significant?

During the last decade, the intense study of adult hippocampal neurogenesis has led to several new lines of inquiry in the field of psychiatry. Although it is generally believed that adult mammalian neurogenesis is restricted to the hippocampus and olfactory bulb, a growing number of studies have described new neurons in the adult neocortex in both rodents and nonhuman primates. Interestingly, all of the new neurons observed in these studies have features of interneurons rather than pyramidal cells, the largest neuronal population of the neocortex. In this review, we discuss features of these interneurons that may explain why cortical neurogenesis has been so difficult to detect. In addition, these features suggest ways that production of even a small numbers of new neurons in the adult cortex could make a significant impact on neocortical function.

Neurogenesis associated with endothelin-induced cortical infarction in the mouse

We investigated the effect of small cortical ischemic lesions, produced by intracerebral injection of the vasoconstrictor endothelin-1, on neurogenesis in the adult mouse subventricular zone. Endothelin-1 (0.5-1 microg) produced infarcts restricted to the cortex, and associated neurobehavioral deficits that largely resolved by 3 days. Bromodeoxyuridine labeling of proliferating cells in the subventricular zone was elevated by about 50% in endothelin-1-treated mice, and cells reactive for doublecortin, a marker for immature neurons, were similarly increased in number. These findings indicate that small ischemic lesions restricted to adult cerebral cortex can stimulate neuroproliferation at a distance.

Sustained neocortical neurogenesis after neonatal hypoxic/ischemic injury

OBJECTIVE

Neocortical neurons are sensitive to hypoxic-ischemic (H-I) injuries at term and their demise contributes to neurological disorders. Here we tested the hypothesis that the subventricular zone of the immature brain regenerates neocortical neurons, and that this response is sustained.

METHODS

Systemic injections of 5-bromo-2'-deoxyuridine (BrdU) and intraventricular injections of replication-deficient retroviruses were used to label newly born cells, and confocal microscopy after immunofluorescence was used to phenotype the new cells from several days to several months after perinatal H-I in the postnatal day 6 rat. Quantitative polymerase chain reaction was used to evaluate chemoattractants, growth factors, and receptors.

RESULTS

Robust production of new neocortical neurons after perinatal H-I occurs. These new neurons are descendants of the subventricular zone, and they colonize the cell-sparse columns produced by the injury to the neocortex. These columns are populated by reactive astrocytes and microglia. Surprisingly, this neuronogenesis is sustained for months. Molecular analyses demonstrated increased neocortical production of insulin-like growth factor-1 and monocyte chemoattractant factor-1 (but statistically insignificant production of erythropoietin, brain-derived neurotrophic factor, glial-derived neurotrophic factor, and transforming growth factor-alpha).

INTERPRETATION

The young nervous system has long been known to possess a greater capacity to recover from injury than the adult system. Our data indicate that H-I injury in the neonatal brain initiates an enduring regenerative response from the subventricular zone. These data suggest that additional mechanisms than those previously surmised contribute to the remarkable ability of the immature brain to recover from injury.

VEGF-overexpressing transgenic mice show enhanced post-ischemic neurogenesis and neuromigration

New neurons are generated continuously in the subventricular zone and dentate gyrus of the adult brain. Neuropathologic processes, including cerebral ischemia, can enhance neurogenesis, as can growth factors and other physiologic stimuli. Vascular endothelial growth factor (VEGF) is an angiogenic and neuroprotective growth factor that can promote neurogenesis, but it is unknown whether VEGF can enhance migration of newborn neurons toward sites of ischemic injury, where they might be able to replace neurons that undergo ischemic death. In the present study we produced permanent focal cerebral ischemia in transgenic (Tg) mice that overexpress VEGF. Cell proliferation and neurogenesis were assessed with bromodeoxyuridine (Brdu) labeling and immunostaining for cell type-specific markers. In VEGF-Tg mice, brains examined 7-28 days after cerebral ischemia showed markedly increased subventricular zone (SVZ) neurogenesis, chains of neuroblasts extending from the SVZ to the peri-infarct cortex, and an increase in the number of newly generated cortical neurons at 14-28 days after ischemia. In concert with these effects, VEGF overexpression reduced infarct volume and improved postischemic motor function. These findings provide evidence that VEGF increases SVZ neurogenesis and neuromigration, consistent with a possible role in repair. Our data suggest that in addition to its neuroprotective effects, which are associated with improved outcome in the acute phase after cerebral ischemia, VEGF enhances postischemic neurogenesis, which could provide a therapeutic target for more chronic brain repair.

Getting the right stuff: controlling neural stem cell state and fate in vivo and in vitro with biomaterials

Stem cell therapy holds great promises in medical treatment by, e.g., replacing lost cells, re-constitute healthy cell populations and also in the use of stem cells as vehicles for factor and gene delivery. Embryonic stem cells have rightfully attracted a large interest due to their proven capacity of differentiating into any cell type in the embryo in vivo. Tissue-specific stem cells are however already in use in medical practice, and recently the first systematic medical trials involving human neural stem cell (NSC) therapy have been launched. There are yet many obstacles to overcome and procedures to improve. To ensure progress in the medical use of stem cells increased basic knowledge of the molecular mechanisms that govern stem cell characteristics is necessary. Here we provide a review of the literature on NSCs in various aspects of cell therapy, with the main focus on the potential of using biomaterials to control NSC characteristics, differentiation, and delivery. We summarize results from studies on the characteristics of endogenous and transplanted NSCs in rodent models of neurological and cancer diseases, and highlight recent advancements in polymer compatibility and applicability in regulating NSC state and fate. We suggest that the development of specially designed polymers, such as hydrogels, is a crucial issue to improve the outcome of stem cell therapy in the central nervous system.

Adult neurogenesis and cellular brain repair with neural progenitors, precursors and stem cells

Recent work in neuroscience has shown that the adult central nervous system (CNS) contains neural progenitors, precursors and stem cells that are capable of generating new neurons, astrocytes and oligodendrocytes. While challenging the previous dogma that no new neurons are born in the adult mammalian CNS, these findings bring with them the future possibilities for development of novel neural repair strategies. The purpose of this review is to present the current knowledge about constitutively occurring adult mammalian neurogenesis, highlight the critical differences between 'neurogenic' and 'non-neurogenic' regions in the adult brain, and describe the cardinal features of two well-described neurogenic regions-the subventricular zone/olfactory bulb system and the dentate gyrus of the hippocampus. We also provide an overview of presently used models for studying neural precursors in vitro, mention some precursor transplantation models and emphasize that, in this rapidly growing field of neuroscience, one must be cautious with respect to a variety of methodological considerations for studying neural precursor cells both in vitro and in vivo. The possibility of repairing neural circuitry by manipulating neurogenesis is an intriguing one, and, therefore, we also review recent efforts to understand the conditions under which neurogenesis can be induced in non-neurogenic regions of the adult CNS. This work aims towards molecular and cellular manipulation of endogenous neural precursors in situ, without transplantation. We conclude this review with a discussion of what might be the function of newly generated neurons in the adult brain, and provide a summary of present thinking about the consequences of disturbed adult neurogenesis and the reaction of neurogenic regions to disease.

Role of Endogenous Neural Stem Cells in Neurological Disease and Brain Repair

These examples show that stem-cell-based therapy of neuro-psychiatric disorders will not follow a single scheme, but rather include widely different approaches. This is in accordance with the notion that the impact of stem cell biology on neurology will be fundamental, providing a shift in perspective, rather than introducing just one novel therapeutic tool. Stem cell biology, much like genomics and proteomics, offers a "view from within" with an emphasis on a theoretical or real potential and thereby the inherent openness, which is central to the concept of stem cells. Thus, stem cell biology influences many other, more traditional therapeutic approaches, rather than introducing one distinct novel form of therapy. Substantial advances have been made i n neural stemcell research during the years. With the identification of stem and progenitor cells in the adult brain and the complex interaction of different stem cell compartments in the CNS--both, under physiological and pathological conditions--new questions arise: What is the lineage relationship between t he different progenitor cells in the CNS and how much lineage plasticity exists? What are the signals controlling proliferation and differentiation of neural stem cells and can these be utilized to allow repair of the CNS? Insights in these questions will help to better understand the role of stem cells during development and aging and the possible relation of impaired or disrupted stem cell function and their impact on both the development and treatment of neurological disease. A number o f studies have indicated a limited neuronal and glial regeneration certain pathological conditions. These fundamental observations have already changed our view on understanding neurological disease and the brain's capacity for endogenous repair. The following years will have to show how we can influence andmodulate endogenous repair nisms by increasing the cellular plasticity in the young and aged CNS.

Hormones and adult neurogenesis in mammals

Initial studies on neural stem cell biology were performed mainly with embryonic stem cells, but exciting discoveries and advances in knowledge about tissue-specific stem cells have emerged in the last few years. This review focuses on stem and/or progenitor cells in the brain that drive adult neurogenesis in mammals. Neuronal precursor cells are found in two regions of the adult brain: the subventricular zone and the hippocampus. Adult neurogenesis in the subventricular zone has implications for behavior and olfactory function and, in the hippocampus, is involved in mood, learning and memory. Several neurodegenerative diseases (e.g., Alzheimer's disease, Huntington's disease and Parkinson's disease) are increasing in frequency as the population is aging. Understanding the hormonal aspects of how adult neurogenesis is regulated could lead to advances in understanding, managing and eventually, treating neurodegenerative disorders. In this review, we summarize what is currently known about the influence of hormones on adult neurogenesis. Many hormones that act through nuclear receptors are implicated in regulating neural progenitor cell biology. Given that nuclear receptors are well defined, drugable targets, further research on their mechanisms of action in adult neurogenesis are likely to engender new replacement, repair and therapeutic approaches.

Delayed changes in T1-weighted signal intensity in a rat model of 15-minute transient focal ischemia studied by magnetic resonance imaging/spectroscopy and synchrotron radiation X-ray fluorescence

Previous studies have found that rats subjected to 15-min transient middle cerebral artery occlusion (MCAO) show neurodegeneration in the dorsolateral striatum only, and the resulting striatal lesion is associated with increased T1-weighted (T1W) signal intensity (SI) and decreased T2-weighted (T2W) SI at 2-8 weeks after the initial ischemia. It has been shown that the delayed increase in T1W SI in the ischemic region is associated with deposition of paramagnetic manganese ions. However, it has been suggested that other mechanisms, such as tissue calcification and lipid accumulation, also contribute to the relaxation time changes. To clarify this issue, we measured changes in relaxation times, lipid accumulation, and elemental distributions in the brain of rats subjected to 15-min MCAO using MRI, in vivo 1H MR spectroscopy (MRS), and synchrotron radiation X-ray fluorescence (SRXRF). The results show that a delayed (2 weeks after ischemia) increase in T1W SI in the ischemic striatum is associated with significant increases in manganese, calcium, and iron, but without evident accumulation of MRS-visible lipids or hydroxyapatite precipitation. It was also found that 15-min MCAO results in acutely reduced N-acetylaspartate (NAA)/creatine (Cr) ratio in the ipsilateral striatum, which recovers to the control level at 2 weeks after ischemia.

Growth factors and stroke

Current options for the treatment of stroke are extremely limited, partly because of the rapidity with which brain cells die when deprived of their blood supply. Several recent studies suggest that growth factors can produce improvement in animal models of stroke, even when administered at postischemic intervals of many hours to days, when conventional neuroprotective approaches are typically futile. Several growth factors can access the brain after systemic administration, making them more attractive as therapeutic agents. Finally, growth factors are key mediators of neurogenesis in the adult brain, which could have a role in brain repair and functional recovery following stroke.