Extremely low frequency electromagnetic fields promote cognitive function and hippocampal neurogenesis of rats with cerebral ischemia

Extremely low frequency electromagnetic fields(ELF-EMF) can improve the learning and memory impairment of rats with Alzheimer's disease, however, its effect on cerebral ischemia remains poorly understood.In this study, we established rat models of middle cerebral artery occlusion/reperfusion.One day after modeling, a group of rats were treated with ELF-EMF(50 Hz, 1 mT) for 2 hours daily on 28 successive days.Our results showed that rats treated with ELF-EMF required shorter swimming distances and latencies in the Morris water maze test than those of untreated rats.The number of times the platform was crossed and the time spent in the target quadrant were greater than those of untreated rats.The number of BrdU~+/NeuN~+ cells, representing newly born neurons, in the hippocampal subgranular zone increased more in the treated than in untreated rats.Up-regulation in the expressions of Notch1, Hes1, and Hes5 proteins, which are the key factors of the Notch signaling pathway, was greatest in the treated rats.These findings suggest that ELF-EMF can enhance hippocampal neurogenesis of rats with cerebral ischemia, possibly by affecting the Notch signaling pathway.The study was approved by the Institutional Ethics Committee of Sichuan University, China(approval No.2019255A) on March 5, 2019.     

Delayed treatment with sildenafil enhances neurogenesis and improves functional recovery in aged rats after focal cerebral ischemia

Increasing age decreases the number of new neurons in the dentate gyrus and the subventricular zone (SVZ). Sildenafil, a phosphodiesterase type 5 (PDE5) inhibitor, enhances neurogenesis in young rats. The present study tested the hypothesis that sildenafil augments neurogenesis in aged rats after focal cerebral ischemia. Nonischemic aged (18 months, n = 6) Wistar rats exhibited a significant reduction of actively proliferating and relatively quiescent cells in the SVZ measured by the number of minichromosome maintenance protein-2-positive (MCM-2+) cells, a marker of the proliferating cells, compared with nonischemic young (3-4 months, n = 8) rats. Occlusion of the middle cerebral artery did not increase the number of MCM-2+ cells in the SVZ of aged rats at 3 months after focal ischemia. However, treatment with sildenafil at a dose of 3 mg/kg (n = 8) daily for 7 consecutive days starting 7 days after focal ischemia significantly increased the number of MCM-2+ cells in the SVZ of aged rats compared with aged rats treated with saline (n = 8). Double immunostaining revealed that substantially more Ki67+ cells (a marker of proliferating cells) were doublecortin+ (a marker of migrating neuroblasts) in sildenafil-treated than in saline-treated aged animals. In addition, treatment with sildenafil significantly improved functional recovery compared with saline-treated rats. These data suggest that inhibition of PDE5 activity by sildenafil augments neurogenesis in the SVZ of aged ischemic rats, although these rats have reduced numbers of neural progenitor and stem cells in the SVZ.     

Progranulin promotes hippocampal neurogenesis and alleviates anxiety‐like behavior and cognitive impairment in adult mice subjected to cerebral ischemia

AimsCerebral ischemia can lead to anxiety and cognitive impairment due to the loss of hippocampal neurons. Facilitation of endogenous neurogenesis in the hippocampus is a potential therapeutic strategy for alleviating ischemia‐induced anxiety and cognitive impairment. Progranulin (PGRN), a secretory glycoprotein, has been reported to have a mitogentic effect on many cell types. However, it is not clear whether PGRN enhances hippocampal neurogenesis and promotes functional recovery.MethodsAdult male C57BL/6 mice were subjected to permanent middle cerebral artery occlusion (pMCAO) and injected intracerebroventricularly with recombinant mouse PGRN 30 min after pMCAO. Anxiety‐like behavior was detected by the open field and the elevated plus maze tests, and spatial learning and memory abilities were evaluated by Morris water maze. Neurogenesis was examined by double labeling of BrdU and neural stem cells or neurons markers. For mechanism studies, the level of ERK1/2 and AKT phosphorylation were assessed by western blotting.ResultsProgranulin significantly alleviated anxiety‐like behavior and spatial learning and memory impairment induced by cerebral ischemia in mice. Consistent with the functional recovery, PGRN promoted neural stem cells (NSCs) proliferation and neuronal differentiation in the dentate gyrus (DG) after cerebral ischemia. PGRN upregulated the expression of phosphorylated ERK1/2 and Akt in the DG after cerebral ischemia.ConclusionsProgranulin alleviates ischemia‐induced anxiety‐like behavior and spatial learning and memory impairment in mice, probably via stimulation of hippocampal neurogenesis mediated by activation of MAPK/ERK and PI3K/Akt pathways. PGRN might be a promising candidate for coping with ischemic stroke‐induced mood and cognitive impairment in clinic.     

Electroconvulsive seizures increase hippocampal neurogenesis after chronic corticosterone treatment

Major depression is often associated with elevated glucocorticoid levels. High levels of glucocorticoids reduce neurogenesis in the adult rat hippocampus. Electroconvulsive seizures (ECS) can enhance neurogenesis, and we investigated the effects of ECS in rats where glucocorticoid levels were elevated in order to mimic conditions seen in depression. Rats given injections of corticosterone or vehicle for 21 days were at the end of this period treated with either a single or five daily ECSs. Proliferating cells were labelled with bromodeoxyuridine (BrdU). After 3 weeks, BrdU-positive cells in the dentate gyrus were quantified and analyzed for co-labelling with the neuronal marker neuron-specific nuclear protein (NeuN). In corticosterone-treated rats, neurogenesis was decreased by 75%. This was counteracted by a single ECS. Multiple ECS further increased neurogenesis and no significant differences in BrdU/NeuN positive cells were detected between corticosterone- and vehicle-treated rats given five ECS. Approximately 80% of the cells within the granule cell layer and 10% of the hilar cells were double-labelled with BrdU and NeuN. We therefore conclude that electroconvulsive seizures can increase hippocampal neurogenesis even in the presence of elevated levels of glucocorticoids. This further supports the hypothesis that induction of neurogenesis is an important event in the action of antidepressant treatment.     

Voluntary exercise-induced neurogenesis in the postischemic dentate gyrus is associated with spatial memory recovery from stroke

Spatial cognitive impairment is common after stroke insults. Voluntary exercise could improve the impaired spatial memory. Newly generated neurons in the dentate gyrus are necessary for the acquisition of new hippocampus-dependent memories. However, it is not well known whether voluntary exercise after stroke promotes neurogenesis in the adult dentate gyrus, thereby promoting spatial memory recovery. Here, we examined in mice subjected to focal cerebral ischemia the effect of voluntary or forced exercise on neurogenesis in the ischemic dentate gyrus and spatial memory. Exposure to voluntary wheel running after stroke enhanced newborn cell survival and up-regulated the phosphorylation of cAMP response element binding protein (CREB) in the dentate gyrus and reversed ischemia-induced spatial memory impairment. However, the enhanced newborn cell survival and CREB phosphorylation in the dentate gyrus and improved spatial memory were not observed in the mice exposed to forced swimming. Moreover, there was a significant correlation between the total number of surviving newborn cells in the dentate gyrus and the ability of mice to locate the platform in the Morris water maze. These results suggest that, in the adult mice, exposure to voluntary exercise after ischemic stroke may promote newborn cells survival in the dentate gyrus by up-regulating CREB phosphorylation and consequently restore impaired hippocampus-dependent memory.     

Increase in neurogenesis and behavioural benefit after chronic fluoxetine treatment in Wistar rats

Objective –  Disturbances in hippocampal neurogenesis may be involved in the pathophysiology of depression and it has been argued that an increase in the generation of new nerve cells in the hippocampus is involved in the mechanism of action of antidepressants.
Materials and Methods –  Adult Wistar rats were treated with fluoxetine (10 mg/kg) 1 h, daily for 5 (subchronic) or 28 days (chronic) before the Novelty Suppressed Feeding test was performed. Cell proliferation and neurogenesis were analysed using the markers 5-bromo-deoxy-2'-uridine, Ki-67, and doublecortin.
Results –  A significant behavioural effect was found after 28 days of fluoxetine administration. However, no behavioural improvement was demonstrated after acute and subchronic treatment with fluoxetine. We further demonstrate that chronic antidepressant treatment increases cell proliferation as well as neurogenesis in the dentate gyrus, here using Wistar rats.
Conclusions –  In further development of antidepressants, neurogenesis may serve as an important parameter to examine the efficacy and mechanism of action of novel drugs.     

Microglial activation and adult neurogenesis after brain stroke

The discovery that new neurons are produced in some regions of the adult mammalian brain is a paradigm-shift in neuroscience research.These new-born cells are produced from neuroprogenitors mainly in the subventricular zone at the margin of the lateral ventricle,subgranular zone in the hippocampal dentate gyrus and in the striatum,a component of the basal ganglia,even in humans.In the human hippocampus,neuroblasts are produced even in elderlies.The regulation of adult neurogenesis is a complex phenomenon involving a multitude of molecules,neurotransmitters and soluble factors released by different sources including glial cells.Microglia,the resident macrophages of the central nervous system,are considered to play an important role on the regulation of adult neurogenesis both in physiological and pathological conditions.Following stroke and other acute neural disorders,there is an increase in the numbers of neuroblast production in the neurogenic niches.Microglial activation is believed to display both beneficial and detrimental role on adult neurogenesis after stroke,depending on the activation level and brain location.In this article,we review the scientific evidence addressing the role of microglial activation on adult neurogenesis after ischemia.A comprehensive understanding of the microglial role after stroke and other neural disorders it is an important step for development of future therapies based on manipulation of adult neurogenesis.     

Chronic metformin treatment improves post‐stroke angiogenesis and recovery after experimental stroke

Metformin is currently the first‐line treatment drug for type 2 diabetes. Metformin is a well‐known activator of AMP‐activated protein kinase (AMPK). In experimental studies, metformin has been shown to exert direct vascular effects by increasing vascular endothelial growth factor expression and improving microvascular density. As stroke is the leading cause of long‐term disability and angiogenesis is implicated as an important mechanism in functional recovery, we hypothesized that chronic metformin treatment would improve post‐stroke functional recovery by enhancing functional microvascular density. For this study, C57BL/6N male mice were subjected to a 60‐min middle cerebral artery occlusion, and were given 50 mg/kg/day metformin beginning 24 h post‐stroke for 3 weeks. Behavioral recovery was assessed using adhesive‐tape removal and the apomorphine‐induced turning test. The role of angiogenesis was assessed by counting vessel branch points from fluorescein‐conjugated lectin‐perfused brain sections. Importantly even if metformin treatment was initiated 24 h after injury it enhanced recovery and significantly improved stroke‐induced behavioral deficits. This recovery occurred in parallel with enhanced angiogenesis and with restoration of endogenous cerebral dopaminergic tone and revascularization of ischemic tissue. We assessed if the effects on recovery and angiogenesis were mediated by AMPK. When tested in AMPK α‐2 knockout mice, we found that metformin treatment did not have the same beneficial effects on recovery and angiogenesis, suggesting that metformin‐induced angiogenic effects are mediated by AMPK. The results from this study suggest that metformin mediates post‐stroke recovery by enhancing angiogenesis, and these effects are mediated by AMPK signaling.     

Effects of CXCR7-neutralizing antibody on neurogenesis in the hippocampal dentate gyrus and cognitive function in the chronic phase of cerebral ischemia

Stromal cell-derived factor-1 and its receptor CXCR4 are essential regulators of the neurogenesis that occurs in the adult hippocampal dentate gyrus.However,the effects of CXCR7,a new atypical receptor of stromal cell-derived factor-1,on hippocampal neurogenesis after a stroke remain largely unknown.Our study is the first to investigate the effect of a CXCR7-neutralizing antibody on neurogenesis in the dentate gyrus and the associated recovery of cognitive function of rats in the chronic stage of cerebral ischemia.The rats were randomly divided into sham,sham+anti-CXCR7,ischemia and ischemia+anti-CXCR7 groups.Endothelin-1 was injected in the ipsilateral motor cortex and striatum to induce focal cerebral ischemia.Sham group rats were injected with saline instead of endothelin-1 via intracranial injection.Both sham and ischemic rats were treated with intraventricular infusions of CXCR7-neutralizing antibodies for 6 days 1 week after surgery.Immunofluorescence staining with doublecortin,a marker for neuronal precursors,was performed to assess the neurogenesis in the dentate gyrus.We found that anti-CXCR7 antibody infusion enhanced the proliferation and dendritic development of doublecortin-labeled cells in the dentate gyrus in both ischemic and sham-operated rats.Spatial learning and memory functions were assessed by Morris water maze tests 30-32 days after ischemia.CXCR7-neutralizing antibody treatment significantly reduced the escape latency of the spatial navigation trial and increased the time spent in the target quadrant of spatial probe trial in animals that received ischemic insult,but not in sham operated rats.These results suggest that CXCR7-neutralizing antibody enhances the neurogenesis in the dentate gyrus and improves the cognitive function after cerebral ischemia in rats.All animal experimental protocols and procedures were approved by the Institutional Animal Care and Use Committee of China Medical University(CMU16089 R)on December 8,2016.     

蛛网膜下腔出血诱导小鼠长期认知功能损害

目的了解蛛网膜下腔出血（SAH）小鼠模型是否存在认知功能损害及探讨造成认知功能损害的可能机制。方法经枕大池注射自身动脉血建立SAH小鼠模型;14d时测量大脑主要动脉直径;通过8一臂迷宫实验评估SAH30d后动物空间学习和记忆功能;加高效液相色谱分析海码组织谷氨酸和天门冬氨酸水平。结果SAH后2周,大脑主要动脉无明显痉挛;SAH30d后,小鼠工作记忆能力和参考记忆能力明显低于对照组和假手术组（P〈0．05）;SAH后24h、48h和72h,海马区谷氨酸和天门冬氨酸含量明显增高（P〈0．01）,30d后,这两种氨基酸的浓度明显下降（P〈0．05）。结论SAH不引起迟发性脑血管痉挛,但可引起小鼠长时间认知功能损害。SAH引起急性脑血流量降低,海马区兴奋性氨基酸大量释放,可能引起海马区神经细胞损害,迟发性海马区兴奋性氨基酸（EAA）降低和认知功能损害是海马损害后的结果。     

Endogenous adult neurogenesis and cognitive function recovery following traumatic brain injury in the rat hippocampus

BACKGROUND:Endogenous neural progenitor cells play a beneficial role for cognitive recovery following traumatic brain injury.However,there are few classification-control studies aimed at varying graded brain trauma.OBJECTIVE:To observe the effects of adult endogenous neurogenesis on cognitive function repair and regeneration of neural progenitor cells following varying graded traumatic hippocampal injury to determine the significance of endogenous neurogenesis in the repair of brain injury.DESIGN,TIME AND SETTING:A randomized,controlled,animal experiment was performed at the Key Laboratory of Injuries,Variations and Regeneration of Nervous System,Tianjin Medical University General Hospital,from February to October 2009.MATERIALS:Mouse anti-rat 5-bromodeoxyuridine (BrdU) and neuronal nuclei (NeuN) monoclonal antibodies were purchased from Millipore Corporation,USA.METHODS:A total of 45 Wistar rats were randomly assigned to three groups.Mild and severe injury groups were respectively subjected to (182 ± 2) kPa and (284 ± 4) kPa lateral fluid percussion to establish models of brain injury,and the control group was subjected to surgery with no lateral fluid percussion.MAIN OUTCOME MEASURES:Cognitive function was estimated using the Morris water maze.Proliferation,survival,and differentiation of newly generated cells in the injured hippocampus were observed through the use of immunofluorescent staining.RESULTS:At 7 days post-injury,the number of BrdU+ cells in the hippocampal dentate gyrus significantly increased in the mild and severe injury groups compared with the control group (P<0.01).At 61 days post-injury,the number of BrdU7NeuN+ cells in the hippocampal dentate gyrus was significantly greater in the mild injury group compared with the severe injury and control groups (P< 0.01).In addition,the control group exhibited the greatest proportion of surviving cells that differentiated into mature neurons compared with the injury groups (P< 0.01).Moreover,at 61 days post-injury,cognitive function in rats with mild injury recovered to normal levels,whereas the severe injury group exhibited cognitive deficits (P< 0.01).CONCLUSION:Traumatic brain injury may be a stimulation factor for proliferation of neural progenitor cells in the adult hippocampus but severe brain trauma does not lead to an increased number of newly generated cells.Endogenous adult neurogenesis repairs neurological functions to an extent.However,recovery of neurological function remains limited following severe traumatic brain injury.     

Acute treatment with MgSO4 attenuates long-term hippocampal tissue loss after brain trauma in the rat

Previous studies have shown that magnesium salts and the noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, NPS 1506, attenuated short-term cognitive deficits and histopathological changes associated with traumatic brain injury (TBI). We evaluated the long-term effects of both therapies after brain trauma. Young adult rats were subjected to parasagittal fluid-percussion brain injury and received either MgSO(4) (125 micromol/400 g rat; n = 12) 15 min post-injury, NPS 1506 (1.15 mg/kg; n = 12) 15 min and 4 hr post-injury, or vehicle (n = 9) 15 min post-injury. Uninjured animals (sham) received vehicle (n = 10). Learning function in these animals was evaluated using a water maze paradigm 8 months after injury or sham treatment, and the brains were examined for cortical and hippocampal tissue loss. Compared to sham animals, injured vehicle-treated animals displayed a substantial learning dysfunction, indicated by an increased latency to find a hidden platform in the water maze (P < 0.001). No improvements in learning, however, were found for injured animals treated with NPS 1506 or MgSO(4). Injury induced >30% loss of tissue in the ipsilateral cortex in vehicle-treated animals that was not reduced in animals treated with either NPS 1506 or MgSO(4). Treatment with MgSO(4) significantly reduced progressive tissue loss in the hippocampus (P < 0.001). These findings are the first to demonstrate long-term neuroprotection of hippocampal tissue by an acute treatment in a TBI model. These data also show that the previously reported broad efficacy of MgSO(4) or NPS 1506 observed shortly after brain trauma could not be detected 8 months post-injury.     

Intercellular adhesion molecule-1 expression in the hippocampal CA1 region of hyperlipidemic rats with chronic cerebral ischemia

Chronic cerebral ischemia is a pathological process in many cerebrovascular diseases and it is induced by long-term hyperlipidemia,hypertension and diabetes mellitus.After being fed a high-fat diet for 4 weeks,rats were subjected to permanent occlusion of bilateral common carotid arteries to establish rat models of chronic cerebral ischemia with hyperlipidemia.Intercellular adhesion molecule-1 expression in rat hippocampal CA1 region was determined to better understand the mechanism underlying the effects of hyperlipidemia on chronic cerebral ischemia.Water maze test results showed that the cognitive function of rats with hyperlipidemia or chronic cerebral ischemia,particularly in rats with hyperlipidemia combined with chronic cerebral ischemia,gradually decreased between 1 and 4 months after occlusion of the bilateral common carotid arteries.This correlated with pathological changes in the hippocampal CA1 region as detected by hematoxylin-eosin staining.Immunohistochemical staining showed that intercellular adhesion molecule-1 expression in the hippocampal CA1 region was noticeably increased in rats with hyperlipidemia or chronic cerebral ischemia,in particular in rats with hyperlipidemia combined with chronic cerebral ischemia.These findings suggest that hyperlipidemia aggravates chronic cerebral ischemia-induced neurological damage and cognitive impairment in the rat hippocampal CA1 region,which may be mediated,at least in part,by up-regulated expression of intercellular adhesion molecule-1.     

Bumetanide promotes neural precursor cell regeneration and dendritic development in the hippocampal dentate gyrus in the chronic stage of cerebral ischemia

Bumetanide has been shown to lessen cerebral edema and reduce the infarct area in the acute stage of cerebral ischemia. Few studies focus on the effects of bumetanide on neuroprotection and neurogenesis in the chronic stage of cerebral ischemia. We established a rat model of cerebral ischemia by injecting endothelin-1 in the left cortical motor area and left corpus striatum. Seven days later, bumetanide 200 μg/kg/day was injected into the lateral ventricle for 21 consecutive days with a mini-osmotic pump. Results demonstrated that the number of neuroblasts cells and the total length of dendrites increased, escape latency reduced, and the number of platform crossings increased in the rat hippocampal dentate gyrus in the chronic stage of cerebral ischemia. These findings suggest that bumetanide promoted neural precursor cell regeneration, dendritic development and the recovery of cognitive function, and protected brain tissue in the chronic stage of ischemia.