Acetylsalicylic acid reduces ischemia-induced proliferation of dentate cells in gerbils

Transient global ischemia causes neurogenesis in the dentate gyrus of adult rodents. Ischemic insults to rodents also induce cyclooxygenase-2 (COX-2), an isoform of cyclooxygenases (COXs) and a rate-limiting enzyme for prostanoid synthesis. In the present experiments, adult Mongolian gerbils were chronically treated with acetylsalicylic acid (ASA), a non-selective COX inhibitor, and the proliferation of cells in the dentate gyrus was examined under ischemia. It was proved that BrdU-labeled cells in the dentate gyrus were significantly reduced in number following ASA treatment after 10 min global ischemia. The result strongly suggests that COX, probably COX-2, and prostanoids play an important role in the proliferation of neural cells after ischemia in gerbils.     

Early involvement of synapsin III in neural progenitor cell development in the adult hippocampus

Synapsin III is a synaptic vesicle-associated protein that is expressed in cells of the subgranular layer of the hippocampal dentate gyrus, a brain region known to sustain substantial levels of neurogenesis into adulthood. Here we tested the hypothesis that synapsin III plays a role in adult neurogenesis with synapsin III knockout and wild-type mice. Immunocytochemistry of the adult hippocampal dentate gyrus revealed that synapsin III colocalizes with markers of neural progenitor cell development (nestin, PSA-NCAM, NeuN, and Tuj1) but did not colocalize with markers of mitosis (Ki67 and PCNA). Because neurogenesis consists of a number of stages, the proliferation, survival, and differentiation of neural progenitor cells were systematically quantitated in the hippocampal dentate gyrus of adult synapsin III knockout and wild-type mice. We found a 30% decrease in proliferation and a 55% increase in survival of neural progenitor cells in synapsin III knockout mice. We also observed a 6% increase in the number of neural progenitor cells that differentiated into neurons. No difference in the volume of the dentate gyrus was observed between synapsin III knockout and wild-type mice. Collectively, our results demonstrate a novel role for synapsin III in regulating the proliferation of neural progenitor cells in the adult hippocampal dentate gyrus. These findings suggest a distinct function for this synaptic vesicle protein, in addition to its role in neurotransmission.     

Region-specific proliferative response of neural progenitors to exogenous stimulation by growth factors following ischemia

The most effective way to augment neural progenitor proliferation after ischemia is still unknown. We administered various agents into the rat cerebral ventricle after transient global ischemia and compared the neural progenitor response in the anterior subventricular zone (aSVZ), dentate gyrus subgranular zone, posterior periventricle, and hypothalamus. We demonstrated that cocktail administration of epidermal growth factor (EGF) and fibroblast growth factor-2 (FGF-2) remarkably increased the numbers of neural progenitors in all four regions examined. The addition of Notch ligand DLL4 to the cocktail elicited the largest progenitor response in the aSVZ and hypothalamus. Our results suggest that EGF and FGF-2, combined with DLL4, represent the universally applicable regimen for the expansion of the neural progenitor pool following ischemia.     

大鼠局灶性脑缺血后神经前体细胞增殖迁移的研究

目的研究成年大鼠内源性神经前体细胞在局灶性脑缺血后不同时间窗的增殖分化情况。方法用Longa线栓法制作大鼠脑缺血模型，用免疫组化的方法检测大鼠内源性神经前体细胞最佳增殖时间及最大增殖效果：j结果脑缺血半球室管膜下区、嗅球和头端迁徙渠道(rostral migratory stream，RMS)Brdu阳性细胞数在脑缺血后1d明显增多，3～7d达高峰，14d后开始下降；Brdu阳性细胞数在脑缺血半球室管膜下区和嗅球成止相关；脯缺血侧海马齿状回未见Brdu阳性细胞数明显增多；Brdu阳性细胞在脑缺血缸后第3周数量最大，从第4周开始下降。结论成年大鼠局灶性脑缺血后3～7d内源性神经前体细胞增殖达高峰，住该期进行外源性细胞移植治疗可能更有效。     

Proliferation of neuronal precursor cells in the dentate gyrus is accelerated after transient forebrain ischemia in mice

We investigated the proliferation of neuronal progenitor cells by labeling dividing cells by systemic application of the thymidine analog 5-bromodeoxyuridine (BrdU) during transient forebrain ischemia in mice. At 3 (n=6), 7 (n=6), 10 (n=6), and 17 days (n=6) after reperfusion, BrdU-labeled cells were detected in the dentate gyrus and paraventricle lesion. After ischemia-reperfusion, BrdU-labeled cells in the dentate gyrus significantly increased in number but not in the paraventricle lesion. These observations may help to clarify the mechanism of functional recovery after stroke.     

Insulin-like growth factor-1 is an endogenous mediator of focal ischemia-induced neural progenitor proliferation

The adult mammalian brain contains resident neural progenitors in the subgranular zone of the dentate gyrus (DG) and the subventricular zone (SVZ) of the lateral ventricles. The proliferation of neural progenitors increases after focal cerebral ischemia in both of these regions, but the mechanisms that promote ischemia-induced neural progenitor proliferation are not yet understood. We hypothesize that diffusible factors from the ischemic area play a role in this process as the DG is remote from the area of infarction. In this study, we observed that the peak of neural progenitor proliferation in the ipsilateral DG was between day 2 and day 4 of reperfusion after transient middle cerebral artery occlusion in adult spontaneously hypertensive rats. GeneChip and real-time PCR analysis showed a three- to 102-fold increase in the expression of 15 diffusible, mitogenic factors in the ischemic cortex at 3 days of reperfusion. Of these, insulin-like growth factor-1 (IGF-1) showed increased protein expression in the activated astrocytes in the ischemic penumbra. In addition, the progenitors in both the SVZ and DG showed IGF-1 receptor expression. Inhibiting IGF-1 activity by introcerebroventricular infusion of IGF-1 antibody significantly prevented the ischemia-induced neural progenitor proliferation. These results indicate that IGF-1 formed in the ischemic penumbra might be one of the diffusible factors that mediate post-ischemic neural progenitor proliferation.     

Proliferation of neural and neuronal progenitors after global brain ischemia in young adult macaque monkeys

To investigate the effect of global cerebral ischemia on brain cell proliferation in young adult macaques, we infused 5-bromo-2'-deoxyuridine (BrdU), a DNA replication indicator, into monkeys subjected to ischemia or sham-operated. Subsequent quantification by BrdU immunohistochemistry revealed a significant postischemic increase in the number of BrdU-labeled cells in the hippocampal dentate gyrus, subventricular zone of the temporal horn of the lateral ventricle, and temporal neocortex. In all animals, 20-40% of the newly generated cells in the dentate gyrus and subventricular zone expressed the neural progenitor cell markers Musashi1 or Nestin. A few BrdU-positive cells in postischemic monkeys were double-stained for markers of neuronal progenitors (class III beta-tubulin, TUC4, doublecortin, or Hu), neurons (NeuN), or glia (S100beta or GFAP). Our results suggest that ischemia activates endogenous neuronal and glial precursors residing in diverse locations of the adult primate central nervous system.     

Behavioral control of the stressor modulates stress-induced changes in neurogenesis and fibroblast growth factor-2

The controllability of stressors modulates many of the consequences of stressor exposure. Here, we used immunohistochemistry to examine neural progenitor cell proliferation and survival and basic fibroblast growth factor-2 in the hippocampus of male rats after controllable or uncontrollable tailshock. A series of identical tailshocks were delivered to yoked pairs of rats. One rat could terminate shocks to both rats of the pair. Reductions in neural progenitor cells were observed at 1-2 days and at 28 days in rats exposed to uncontrollable shock. Controllable shock produced an increase in fibroblast growth factor-2 in the dentate gyrus and CA1 2 h after stress and in the dentate gyrus 24 h after stress. Thus, stressor controllability modulates stress-induced decreases in neurogenesis and increases in fibroblast growth factor-2.     

Increased proliferation of neural progenitor cells but reduced survival of newborn cells in the contralateral hippocampus after focal cerebral ischemia in rats.

Recent studies demonstrated that neurogenesis in the adult hippocampus increased after transient global ischemia; however, the molecular mechanism underlying increased neurogenesis after ischemia remains unclear. The finding that proliferation of progenitor cells occurred at least a week after ischemic insult suggests that the stimulus was not an ischemic insult to progenitor cells. To clarify whether focal ischemia increases the rate of neurogenesis in the remote area, the authors examined the contralateral hemisphere in rats subjected to permanent occlusion of the middle cerebral artery. In the subgranular zone of the hippocampal dentate gyrus, the numbers of bromodeoxyuridine (BrdU)-positive cells increased approximately sixfold 7 days after ischemia. In double immunofluorescence staining, more than 80% of newborn cells expressed Musashi1, a marker of neural stem/progenitor cells, but only approximately 10% of BrdU-positive cells expressed glial fibrillary acidic protein (GFAP), a marker of astrocytes. The number of BrdU-positive cells markedly decreased 28 days after BrdU administration after ischemia, but it was still elevated compared with that of sham-operated rats. In double immunofluorescence staining, 80% of newborn cells expressed NeuN, a marker of differentiated neurons, and 10% of BrdU-positive cells expressed GFAP. However, in the other areas of the contralateral hemisphere including the rostral subventricular zone, the number of BrdU-positive cells remained unchanged. These results showed that focal ischemia stimulated the proliferation of neuronal progenitor cells, but did not support survival of newborn cells in the contralateral hippocampus.     

Beneficial effect of cilostazol‐mediated neuronal repair following trimethyltin‐induced neuronal loss in the dentate gyrus

Cilostazol acts as an antiplatelet agent and has other pleiotropic effects based on phosphodiesterase‐3‐dependent mechanisms. We evaluated whether cilostazol would have a beneficial effect on neuronal repair following hippocampal neuronal damage by using a mouse model of trimethyltin (TMT)‐induced neuronal loss/self‐repair in the hippocampal dentate gyrus [Ogita et al. (2005) J Neurosci Res 82:609?621]; these mice will hereafter be referred to as impaired animals. A single treatment with cilostazol (10 mg/kg, i.p.) produced no significant change in the number of 5‐bromo‐2′‐deoxyuridine (BrdU)‐incorporating cells in the dentate granule cell layer (GCL) or subgranular zone on day 3 after TMT treatment. However, chronic treatment with cilostazol on days 3–15 posttreatment resulted in an increase in the number of BrdU‐incorporating cells in the dentate GCL of the impaired animals, and these cells were positive for neuronal nuclear antigen or doublecortin. Cilostazol was effective in elevating the level of phosphorylated cyclic adrenosine monophosphate response element‐binding protein (pCREB) in the dentate gyrus of impaired animals. The results of a forced swimming test revealed that the chronic treatment with cilostazol improved the depression‐like behavior seen in the impaired animals. In the cultures of hippocampal neural stem/progenitor cells, exposure to cilostazol produced not only enhancement of proliferation activity but also elevation of pCREB levels. Taken together, our data suggest that cilostazol has a beneficial effect on neuronal repair following neuronal loss in the dentate gyrus through promotion of proliferation and/or neuronal differentiation of neural progenitor cells in the subgranular zone. © 2014 Wiley Periodicals, Inc.     

A nitric oxide donor induces neurogenesis and reduces functional deficits after stroke in rats.

The adult rodent brain is capable of generating neuronal progenitor cells in the subventricular zone, and in the dentate gyrus of the hippocampus, throughout the life of the animal. Signals that regulate progenitor cell proliferation, differentiation, and migration are not well known. We report that administration of a nitric oxide donor, (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl) aminio]diazen-1-ium-1,2-diolate (DETA/NONOate), to young adult rats significantly increases cell proliferation and migration in the subventricular zone and the dentate gyrus. Treatment with DETA/ NONOate also increases neurogenesis in the dentate gyrus. Furthermore, administration of DETA/NONOate to rats subjected to embolic middle cerebral artery occlusion significantly increases cell proliferation and migration in the subventricular zone and the dentate gyrus, and these rats exhibit significant improvements of neurological outcome during recovery from ischemic stroke. Administration of DETA/NONOate significantly increases cortical levels of guanosine monophosphate both in ischemic and nonischemic rats, supporting the role of nitric oxide in promoting cell proliferation and neurogenesis. Thus, our data indicate that nitric oxide is involved in the regulation of progenitor cells and neurogenesis in the adult brain. This suggests that nitric oxide delivered to the brain well after stroke may have therapeutic benefits.     

Increased neurogenesis after experimental Streptococcus pneumoniae meningitis

Neuronal damage in the hippocampal formation is a common feature in animal models of bacterial meningitis and human disease. In mouse and rabbit models of Streptococcus pneumoniae meningitis, proliferation of neural progenitor cells quantified by bromodeoxyuridine (BrdU) incorporation was enhanced in the subgranular layer of the dentate gyrus. In mice, the density of BrdU-labeled cells was maximal on Day 2 after infection. Approximately 60% of the cells labeled by BrdU between Days 7 and 10 after infection that remained present 28 days later had migrated into deeper layers of the dentate gyrus and differentiated into neurons, as evidenced by immunohistochemical staining for TUC-4, MAP-2 and beta-tubulin. This suggests that endogenous repair mechanisms may limit consequences of neuronal destruction after meningitis.     

Dopamine D2 receptor stimulation promotes the proliferation of neural progenitor cells in adult mouse hippocampus

We initially examined the effects of apomorphine in vitro using mouse embryonic and adult neural progenitor cells. The effects of apomorphine treatment led to dose-dependent increases in the number of embryonic and adult neural progenitor cells, and dopamine D2 receptor antagonist treatment significantly reduced the increases induced by apomorphine. Next, we investigated the effects of apomorphine in vivo in the adult mouse hippocampus. The effects of single-dose apomorphine administration led to an increase of approximately 30% in the number of bromodeoxyuridine-positive cells in the dentate gyrus. Moreover, the chronic apomorphine administration induced an increase in the number of bromodeoxyuridine-positive cells by about 30%. Thus, we suggest that the stimulation of dopamine D2 receptors increases the proliferation of neural progenitor cells both in vivo and in vitro.     

Forebrain neurogenesis after focal Ischemic and traumatic brain injury

Neural stem cells persist in the adult mammalian forebrain and are a potential source of neurons for repair after brain injury. The two main areas of persistent neurogenesis, the subventricular zone (SVZ)-olfactory bulb pathway and hippocampal dentate gyrus, are stimulated by brain insults such as stroke or trauma. Here we focus on the effects of focal cerebral ischemia on SVZ neural progenitor cells in experimental stroke, and the influence of mechanical injury on adult hippocampal neurogenesis in models of traumatic brain injury (TBI). Stroke potently stimulates forebrain SVZ cell proliferation and neurogenesis. SVZ neuroblasts are induced to migrate to the injured striatum, and to a lesser extent to the peri-infarct cortex. Controversy exists as to the types of neurons that are generated in the injured striatum, and whether adult-born neurons contribute to functional restoration remains uncertain. Advances in understanding the regulation of SVZ neurogenesis in general, and stroke-induced neurogenesis in particular, may lead to improved integration and survival of adult-born neurons at sites of injury. Dentate gyrus cell proliferation and neurogenesis similarly increase after experimental TBI. However, pre-existing neuroblasts in the dentate gyrus are vulnerable to traumatic insults, which appear to stimulate neural stem cells in the SGZ to proliferate and replace them, leading to increased numbers of new granule cells. Interventions that stimulate hippocampal neurogenesis appear to improve cognitive recovery after experimental TBI. Transgenic methods to conditionally label or ablate neural stem cells are beginning to further address critical questions regarding underlying mechanisms and functional significance of neurogenesis after stroke or TBI. Future therapies should be aimed at directing appropriate neuronal replacement after ischemic or traumatic injury while suppressing aberrant integration that may contribute to co-morbidities such as epilepsy or cognitive impairment.     

A ginkgo biloba extract promotes proliferation of endogenous neural stem cells in vascular dementia rats

The ginkgo biloba extract EGb761 improves memory loss and cognitive impairments in patients with senile dementia. It also promotes proliferation of neural stem cells in the subventricular zone in Parkinson’s disease model mice and in the hippocampal zone of young epileptic rats. However, it remains unclear whether EGb761 enhances proliferation of endogenous neural stem cells in the brain of rats with vascular dementia. In this study, a vascular dementia model was established by repeatedly clipping and reperfusing the bilateral common carotid arteries of rats in combination with an intraperitoneal injection of a sodium nitroprusside solution. Seven days after establishing the model, rats were intragastrically given EGb761 at 50 mg/kg per day. Learning and memory abilities were assessed using the Morris water maze and proliferation of endogenous neural stem cells in the subventricular zone and dentate gyrus were labeled by 5-bromo-2-deoxyuridine immunofluorescence in all rats at 15 days, and 1, 2, and 4 months after model establishment. The escape latencies in Morris water maze tests of rats with vascular dementia after EGb761 treatment were significantly shorter than the model group. Immunofluorescence staining showed that the number and proliferation of 5-bromo-2-deoxyuridine-positive cells in the subventricular zone and dentate gyrus of the EGb761-treated group were significantly higher than in the model group. These experimental findings suggest that EGb761 enhances proliferation of neural stem cells in the subventricular zone and dentate gyrus, and significantly improves learning and memory in rats with vascular dementia.     

糖皮质激素对大鼠内源性神经前体细胞增殖的影响

目的探讨大剂量糖皮质激素(GCs)对成年大鼠内源性神经前体细胞增殖的影响.方法将25只大鼠随机分为对照组和地塞米松(DEX)作用1、3、7、14 d组,应用免疫组化方法检测神经前体细胞标记物巢蛋白(nestin)的表达,并通过5-溴脱氧尿苷(BrdU)观察神经前体细胞的增殖.结果正常大鼠海马齿状回(DG)和室下区(SVZ)存在神经前体细胞,并且其中一些细胞处于分裂增殖状态.应用大剂量GCs作用3、7、14 d组与对照组相比DG的nestin和BrdU阳性细胞数明显减少,SVZ的nestin和BrdU阳性细胞数在DEX作用7、14 d组与对照组相比明显减少,并且DG与SVZ二者阳性细胞数随着作用时间的延长而减低更为明显.结论大剂量GCs持续作用可抑制大鼠脑内的内源性神经前体细胞的增殖,DG区的神经前体细胞对GCs的反应较SVZ更为敏感.     

Differential expression of Musashi1 and nestin in the adult rat hippocampus after ischemia

Both nestin and the neural RNA-binding protein Musashi1 (Msi1) are expressed in neural stem cells in the subventricular zone. Neurogenesis in the hippocampus has received much attention, so we evaluated the expression of Msi1 and nestin in the adult rat hippocampus after transient forebrain ischemia. Both Msi1 and nestin were induced in the reactive astrocytes after ischemia, especially in the CA1 region, until 35 days after ischemia. Induction of both molecules suggested that reactive astrocytes might have immature characteristics. In the subgranular zone (SGZ) of the hippocampal dentate gyrus, Msi1-positive cells formed clusters after ischemia. These cells were labeled by bromodeoxyuridine (BrdU) but did not express glial fibrillary acidic protein. In contrast, very few nestin-positive cells were labeled by BrdU. Our results suggest that neuronal progenitor cells in the SGZ expressed Msi1 but not nestin.     

Galanin in neuro(glio)genesis: expression of galanin and receptors by progenitor cells in vivo and in vitro and effects of galanin on neurosphere proliferation

Considerable recent evidence suggests that in addition to its neuromodulatory role, galanin, like several other neuropeptides, also plays an important trophic role during development and after adult neural injury. Studies in our laboratory have identified high levels of galanin and galanin receptor expression in the subventricular zone, rostral migratory stream, subgranular zone of dentate gyrus and the medial corpus callosum--which include the main sites for continuing cell proliferation in both adult and developing rat brain. Galanin expression was also strongly and transiently induced in oligodendrocyte progenitor cells (OPCs) throughout the neocortex and corpus callosum by a benign physiological stimulus, cortical spreading depression (CSD). SD-like depolarization also occurs in peri-infarction areas following cerebral ischemia and is associated with proliferation of OPCs and transiently increased galanin expression. Together, these data suggest a putative role for galanin in regulating progenitor or 'stem cell' proliferation, migration and/or differentiation. Cultured adult and embryonic stem cells or 'neurospheres' express galanin and galanin receptor mRNA and preliminary studies suggest that sub-acute galanin treatment of cultured neurospheres decreases cell proliferation/survival, possibly by effects on the rate of apoptosis via GalR2 receptors.