Ischemic Hippocampus Research Articles

Pluchea lanceolata protects hippocampal neurons from endothelin-1 induced ischemic injury to ameliorate cognitive deficits

Ischemic brain injury is one of the leading causes of death and disability, where lack of disease modifying treatment strategies make us rely on symptomatic relief. Treatment principles from traditional systems of medicine may fill this gap and its validation in modern medicine perspective is important to bring them to mainstream. Here, we evaluated the neuroprotective efficacy of Ayurvedic medicinal herb Pluchea lanceolata in treating ischemic hippocampal injury. Focal hippocampal ischemia was modeled in Wistar rats through stereotaxic intrahippocampal injection of endothelin-1 (ET-1). Post-surgery, hydroalcoholic extract of the rhizome of Pluchea lanceolata (HAPL) was administered orally, once in a day for 14 consecutive days to ischemic rats. There were two treatment groups based on the HAPL dosage; HAPL200 (200 mg/kg body weight) and HAPL400 (400 mg/kg body weight). Comparisons were made with the ET-1 ischemic rats which received only the vehicle, and the normal surgical control. Ischemic hippocampal injury led to severe cognitive deficits as evaluated by Morris water maze and open field test, along with locomotory dysfunction noted in actophotometer test. HAPL treatment significantly attenuated these behavioural deficits in a dose dependent manner. Loss of pyramidal cells and degenerative phenotype of shrunken hyperdensed soma with pyknotic nuclei in CA1 and CA3 hippocampal neurons in ischemia were reversed after HAPL treatment. We provide first evidence for loss of dendritic architecture in ET-1 induced focal ischemic hippocampal injury using Golgi impregnation, where HAPL could salvage the dendritic branching and intersections. Intriguingly, it enhanced the dentritic arborization beyond what is noted in normal rats. Ability of HAPL to reverse oxidative stress, especially through maintaining glutathione peroxidase levels and lipid peroxidation in ischemic condition evidences that it may exert neuroprotection through its antioxidant properties. Thus, Pluchea lanceolata and its constituents provide potential alternative/adjuvant treatment strategy for ischemic hippocampal stroke.

Phosphatidylethanolamine-binding protein 1 protects CA1 neurons against ischemic damage via ERK-CREB signaling in Mongolian gerbils

In the present study, we made a PEP-1-phosphatidylethanolamine-binding protein 1 (PEP-1-PEBP1) fusion protein to facilitate the transduction of PEBP1 into cells and observed significant ameliorative effects of PEP-1-PEBP1 against H2O2-induced neuronal damage and the formation of reactive oxygen species in the HT22 hippocampal cells. In addition, administration of PEP-1-PEBP1 fusion protein ameliorated H2O2-induced phosphorylation of extracellular signal-regulated kinases (ERK1/2) and facilitated the phosphorylation of cyclic-AMP response element binding protein (CREB) in HT22 cells after exposure to H2O2. We also investigated the temporal and spatial changes of phosphorylated phosphatidylethanolamine-binding protein 1 (pPEBP1) in the hippocampus, after 5 min of transient forebrain ischemia in gerbils. In the sham-operated animals, pPEBP1 immunoreactivity was not detectable in the hippocampal CA1 region. pPEBP1 immunoreactivity was significantly increased in the hippocampal CA1 region, 1–2 days after ischemia, compared to that in the sham-operated group and pPEBP1 immunoreactivity was returned to levels in sham-operated group at 3–4 days after ischemia. pPEBP1 immunoreactivity significantly increased at day 7 after ischemia and decreased to sham-operated group levels by day 10 after ischemia/reperfusion. In addition, administration of PEP-1-PEBP1 fusion protein significantly reduced the ischemia-induced hyperactivity of locomotion, 1 day after ischemia and PEP-1-PEBP1 reduced neuronal damage and reactive gliosis (astrocytosis and microgliosis) in the gerbil hippocampal CA1 region, 4 days after ischemia. Administration of PEP-1-PEBP1 fusion protein ameliorated the ischemia-induced phosphorylation of ERK at 3 h and 6 h after ischemia/reperfusion and accelerated the phosphorylation of CREB in ischemic hippocampus at 6 h after ischemia. These results suggest that the increase in PEBP1 phosphorylation causes neuronal damage in the hippocampus and treatment with PEP-1-PEBP1 fusion protein provides neuroprotection from increasing phosphorylation of ERK-CREB pathways in the hippocampal CA1 region, during ischemic damage.

Photothrombotically induced unilateral selective hippocampal ischemia in rat

IntroductionThe vulnerability of hippocampal formation to ischemic insult has been documented in both humans and animal models. Ischemic injury induction through photothrombosis is an invasive and reproducible model of ischemic stroke which provides the ability to induce ischemia selectively in any desired area. In this study, we describe a method to induce selective unilateral hippocampal ischemia in rat through modified photothrombotic model. MethodsMale wistar rats (n = 66) were subjected to stereotaxic surgery to insert a guide cannula just above the ascending part of hippocampal fissure. After recovery femoral vein was cannulated and rats were mounted in stereotaxic frame to optical fiber insertion in guide cannula and illumination of hippocampal fissure for 25 min. Rose Bengal dye was slowly injected through femoral vein during the first two-minute of illumination. Twenty-four hours later, infarct volume and histological change were evaluated in rat hippocampus. Cognitive function was also evaluated 48 h after ischemia induction. ResultsThis procedure caused significant neuronal necrosis and infarct formation in the right hemisphere hippocampus. The infarct size was consisted in different subjects and was paralleled to cognitive impairment. The mean volume of infarction was 6.5% which affected whole right hippocampus and caused significant cognitive impairment compared to sham group (P < 0.001). DiscussionThe method described in this study provides the ability of selective hippocampal ischemia induction and study of hippocampal injury consequences following ischemia or other neurodegenerative disease that affect hippocampus.

Saturday Night Retinopathy After Intranasal Heroin

Purpose: To describe the clinical features of a case of Saturday night retinopathy (SNR) following intranasal heroin use. Methods: Ophthalmological examination, including optical coherence tomography and fluorescein angiogram, was performed. Serial images were obtained at follow-up visits at 1 week and 1 month. Results: The visual acuity was no light perception vision and there was an afferent pupillary defect in the affected eye. There was also evidence of complete ophthalmoplegia, globe proptosis, conjunctival chemosis, and corneal epitheliopathy and funduscopic evidence of ophthalmic artery occlusion. Follow-up imaging showed choroidal and retinal nonperfusion. Magnetic resonance imaging demonstrated edematous extraocular muscles and a bilateral hippocampal ischemia. Conclusions: This is the first case of SNR following intranasal heroin use and opioid-associated hippocampal ischemia. As physicians witness the impacts of the country’s opioid epidemic, it is important to recognize SNR as a cause of acute visual loss.

A novel cell-penetrating peptide protects against neuron apoptosis after cerebral ischemia by inhibiting the nuclear translocation of annexin A1.

Nuclear translocation of annexin A1 (ANXA1) has recently been reported to participate in neuronal apoptosis after cerebral ischemia. Prevention of the nuclear translocation of ANXA1 should therefore inhibit neuronal apoptosis and protect against cerebral stroke. Here, we found that, in the repeat III domain of ANXA1, the amino-acid residues from R228 to F237 function as a unique nuclear translocation signal (NTS) and are required for nuclear translocation of ANXA1. Intriguingly, we synthesized a cell-penetrating peptide derived by conjugating the trans-activator of transcription (Tat) domain to the NTS sequence. This Tat-NTS peptide specifically blocked the interaction of ANXA1 with importin β and, consequently, the nuclear translocation of ANXA1 without affecting the nucleocytoplasmic shuttling of other proteins. The Tat-NTS peptide inhibited the transcriptional activity of p53, decreased Bid expression, suppressed activation of the caspase-3 apoptosis pathway and improved the survival of hippocampal neurons subjected to oxygen-glucose deprivation and reperfusion in vitro. Moreover, using a focal brain ischemia animal model, we showed that the Tat-NTS peptide could be efficiently infused into the ischemic hippocampus and cortex by unilateral intracerebroventricular injection. Injection of the Tat-NTS peptide alleviated neuronal apoptosis in the ischemic zone. Importantly, further work revealed that administration of the Tat-NTS peptide resulted in a dramatic reduction in infarct volume and that this was correlated with a parallel improvement in neurological function after reperfusion. Interestingly, the effects of Tat-NTS were injury specific, with little impact on neuronal apoptosis or cognitive function in sham-treated nonischemic animals. In conclusion, based on its profound neuroprotective and cognitive-preserving effects, it is suggested that the Tat-NTS peptide represents a novel and potentially promising new therapeutic candidate for the treatment of ischemic stroke.

Changes in the hippocampal and peripheral phospholipid profiles are associated with neurodegeneration hallmarks in a long-term global cerebral ischemia model: Attenuation by Linalool

Phospholipid alterations in the brain are associated with progressive neurodegeneration and cognitive impairment after acute and chronic injuries. Various types of treatments have been evaluated for their abilities to block the progression of the impairment, but effective treatments targeting long-term post-stroke alterations are not available. In this study, we analyzed changes in the central and peripheral phospholipid profiles in ischemic rats and determined whether a protective monoterpene, Linalool, could modify them. We used an in vitro model of glutamate (125 μM) excitotoxicity and an in vivo global ischemia model in Wistar rats. Linalool (0.1 μM) protected neurons and astrocytes by reducing LDH release and restoring ATP levels. Linalool was administered orally at a dose of 25 mg/kg every 24 h for a month, behavioral tests were performed, and a lipidomic analysis was conducted using mass spectrometry. Animals treated with Linalool displayed faster neurological recovery than untreated ischemic animals, accompanied by better motor and cognitive performances. These results were confirmed by the significant reduction in astrogliosis, microgliosis and COX-2 marker, involving a decrease of 24:0 free fatty acid in the hippocampus. The altered profiles of phospholipids composed of mono and polyunsaturated fatty acids (PC 36:1; 42:1 (24:0/18:1)/LPC 22:6)/LPE 22:6) in the ischemic hippocampus and the upregulation of PI 36:2 and other LCFA (long chain fatty acids) in the serum of ischemic rats were prevented by the monoterpene. Based on these data, alterations in the central and peripheral phospholipid profiles after long-term was attenuated by oral Linalool, promoting a phospholipid homeostasis, related to the recovery of brain function.

Ischemic tau protein gene induction as an additional key factor driving development of Alzheimer's phenotype changes in CA1 area of hippocampus in an ischemic model of Alzheimer's disease.

Tauopathies are a class of neurodegenerative illnesses associated with the aberrant accumulation of the tau protein in the brain. The best known out of these diseases is Alzheimer's disease, a disorder where the microtubule associated tau protein becomes hyperphosphorylated (which lowers its binding affinity to microtubules) and accumulates inside neurons in the form of tangles. In this study, we attempt to find out whether brain ischemia may play an important role in tau protein gene alterations. We have investigated the relationship between hippocampal ischemia and Alzheimer's disease by means of a transient 10-min global brain ischemia in rats and determining the effect on Alzheimer's disease tau protein gene expression during 2, 7 and 30 days post injury. We found the significant overexpression of tau protein gene on the 2nd day, but on day's 7 and 30 post-ischemia there a significant opposite tendency was observed. The obtained results offer a novel insight into tau protein gene in regulating delayed neuronal death in the ischemic hippocampus. Finally, these findings further elucidate the long-term impact of brain ischemia on Alzheimer's disease development.

Neuroprotective effect of monophosphoryl lipid A, a detoxified lipid A derivative, in photothrombotic model of unilateral selective hippocampal ischemia in rat

Finding a neuroprotective strategy to rescue patients suffering from acute brain damage is of great interest. Monophosphoryl lipid A (MPL) is a derivative of lipopolysaccharide (LPS) that lacks many of the endotoxic properties of the parent molecule, and yet has similar protective effect. Here, we report the first evidence that MPL preconditioning, similar to LPS preconditioning, can induce neuroprotection against cerebral ischemia. MPL (0.5, 1, 5 μg/rat) was injected unilaterally into the left cerebral ventricle of male rats, and 48 h later, rats were subjected to ipsilateral selective hippocampal ischemia using a modified version of the photothrombotic method. The neuroprotective effects of MPL and LPS were evaluated by measuring infarct size and assessing cognitive function. The expression level of some inflammatory and anti-inflammatory cytokines involving in TLR4 signaling pathway was also measured. Cognitive impairment and infarct size were obvious in control group receiving normal saline intracerebroventricularly and then selective hippocampal ischemia, compared to the sham group. Immunologic preconditioning with MPL or LPS significantly reduced infarct size and improved cognitive function. Additionally, immunologic preconditioning resulted in inflammatory mediators, NF-κB and TNF-α, down-regulation but anti-inflammatory mediators, IRF3, IFN-β, and TGF-β, up-regulation. Our data showed that both MPL and LPS preconditioning may reprogram the TLR4 signaling pathway to produce a cytokine profile which eventually leads to neuroprotection against ischemia injury. MPL, unlike LPS, is safe and well tolerated in clinic, thus it could be considered as a new approach in prevention or even treatment of cerebral ischemic insult consequences.

Temporal Pattern and Crosstalk of Necroptosis Markers with Autophagy and Apoptosis Associated Proteins in Ischemic Hippocampus.

Necroptosis, a novel type of programmed cell death, has been recently implicated as a possible mechanism for cerebral ischemia-reperfusion (I/R) injury. We herein studied time-dependent changes of necroptosis markers along with apoptosis- and autophagy-associated proteins in rat hippocampus at 1, 3, 6, 12, 24, and 48h after global cerebral I/R injury. Furthermore, to determine the cross talk between autophagy and necroptosis, we examined the effects of pretreatment with bafilomycin-A1 (Baf-A1), as a late-stage autophagy inhibitor, on necroptosis. Highest levels of receptor-interacting protein 1 and 3 (RIP1 and RIP3), as key mediators of necroptosis, were observed at 24h after reperfusion. Alongside, activity of glutamate dehydrogenase (GLUD1), downstream enzyme of RIP3, was increased. Peak time of necroptosis was subsequent to caspase-3-dependent cell death that peaked at 12h of reperfusion but concurrent with autophagy. Administration of Baf-A1 could attenuate necroptosis, verified by decrease in RIP1 and RIP3 protein levels, as well as GLUD1 activity. However, there was no significant change in caspase-3-dependent cell death. Taken together, our results highlight that global cerebral I/R activates necroptosis that could be triggered by autophagy and interacts reversely with caspase-3-dependent apoptosis.

An experimental rabbit model of symptomatic cerebral vasospasm with in vivo neuroimaging assessment and ex vivo histological validation.

Cerebral vasospasm (CVS) is a severe complication that occurs following aneurysmal subarachnoid hemorrhage (SAH). Magnetic resonance angiography (MRA) has been used to evaluate brain injury following SAH in humans. The present study was designed to assess a rabbit model of symptomatic CVS (SCVS) and the utility of MRA in evaluating SCVS in rabbits. Japanese white rabbits (n=24) were randomly divided into 2 equal groups: A sham group and a SAH group. Neurological scores were evaluated for 7 days following SAH. Basilar artery (BA) diameters were measured using MRA preoperatively and 7 days postoperatively. Rabbits were sacrificed 7 days following SAH and the BA diameter of each rabbit was determined using histological evaluation. Compared with the Sham group, neurological function was significantly reduced in the SAH group at all time points (P<0.05). Furthermore, the BA diameter was significantly smaller in the SAH group on day 7 compared with the baseline measurement (P<0.05). No significant difference was observed between histological and MRA findings in either group at day 7. Histological changes in the hippocampus consistent with ischemia were observed in the SAH group. Hippocampal ischemia was also identified in the SAH group via MRA and there was no difference in detection rates following the use of MRA and histochemistry. MRA appears to be an effective method for assessing vasospasms of the BA and ischemic changes to the hippocampus in a rabbit model of SCVS. Furthermore, the animal model used in the present study may be beneficial for the future study of SCVS.

Repetitive Transcranial Magnetic Stimulation Ameliorates Cognitive Impairment by Enhancing Neurogenesis and Suppressing Apoptosis in the Hippocampus in Rats with Ischemic Stroke.

Cognitive impairment is a serious mental deficit caused by stroke that can severely affect the quality of a survivor's life. Repetitive transcranial magnetic stimulation (rTMS) is a well-known rehabilitation modality that has been reported to exert neuroprotective effects after cerebral ischemic injury. In the present study, we evaluated the therapeutic efficacy of rTMS against post-stroke cognitive impairment (PSCI) and investigated the mechanisms underlying its effects in a middle cerebral artery occlusion (MCAO) rat model. The results showed that rTMS ameliorated cognitive deficits and tended to reduce the sizes of cerebral lesions. In addition, rTMS significantly improved cognitive function via a mechanism involving increased neurogenesis and decreased apoptosis in the ipsilateral hippocampus. Moreover, brain-derived neurotrophic factor (BDNF) and its receptor, tropomyosin-related kinase B (TrkB), were clearly upregulated in ischemic hippocampi after treatment with rTMS. Additionally, further studies demonstrated that rTMS markedly enhanced the expression of the apoptosis-related B cell lymphoma/leukemia gene 2 (Bcl-2) and decreased the expression of the Bcl-2-associated protein X (Bax) and the number of TUNEL-positive cells in the ischemic hippocampus. Both protein levels and mRNA levels were investigated. Our findings suggest that after ischemic stroke, treatment with rTMS promoted the functional recovery of cognitive impairments by inhibiting apoptosis and enhancing neurogenesis in the hippocampus and that this mechanism might be mediated by the BDNF signaling pathway.

Stress primes microglial polarization after global ischemia: Therapeutic potential of progesterone

Despite the fact that stress is associated with increased risk of stroke and worsened outcome, most preclinical studies have ignored this comorbid factor, especially in the context of testing neuroprotective treatments. Preclinical research suggests that stress primes microglia, resulting in an enhanced reactivity to a subsequent insult and potentially increasing vulnerability to stroke. Ischemia-induced activated microglia can be polarized into a harmful phenotype, M1, which produces pro-inflammatory cytokines, or a protective phenotype, M2, which releases anti-inflammatory cytokines and neurotrophic factors. Selective modulation of microglial polarization by inhibiting M1 or stimulating M2 may be a potential therapeutic strategy for treating cerebral ischemia. Our laboratory and others have shown progesterone to be neuroprotective against ischemic stroke in rodents, but it is not known whether it will be as effective under a comorbid condition of chronic stress. Here we evaluated the neuroprotective effect of progesterone on the inflammatory response in the hippocampus after exposure to stress followed by global ischemia. We focused on the effects of microglial M1/M2 polarization and pro- and anti-inflammatory mediators in stressed ischemic animals. Male Sprague-Dawley rats were exposed to 8 consecutive days of social defeat stress and then subjected to global ischemia or sham surgery. The rats received intraperitoneal injections of progesterone (8mg/kg) or vehicle at 2h post-ischemia followed by subcutaneous injections at 6h and once every 24h post-injury for 7days. The animals were killed at 7 and 14days post-ischemia, and brains were removed and processed to assess outcome measures using histological, immunohistochemical and molecular biology techniques. Pre-ischemic stress (1) exacerbated neuronal loss and neurodegeneration as well as microglial activation in the selectively vulnerable CA1 hippocampal region, (2) dysregulated microglial polarization, leading to upregulation of both M1 and M2 phenotype markers, (3) increased pro-inflammatory cytokine expression, and (4) reduced anti-inflammatory cytokine and neurotrophic factor expression in the ischemic hippocampus. Treatment with progesterone significantly attenuated stress-induced microglia priming by modulating polarized microglia and the inflammatory environment in the hippocampus, the area most vulnerable to ischemic injury. Our findings can be taken to suggest that progesterone holds potential as a candidate for clinical testing in ischemic stroke where high stress may be a contributing factor.

Abstract TP83: Stress Exacerbates Global Ischemia-induced Inflammatory Response: Intervention by Progesterone

Introduction: Stress is associated with increased risk of stroke and poor prognosis, but the mechanisms through which stress may alter stroke outcome remain elusive. Stress compromises neuronal survival and neuroinflammation following an ischemic attack. Post-ischemic inflammatory response involves the activation of microglia, which can be polarized from a harmful M1 phenotype which expresses pro-inflammatory cytokines, to a protective M2 phenotype which releases neurotrophic factors. We hypothesize that progesterone (PROG) will improve global ischemia outcome by modulating microglial polarization in stressed ischemic animals. Methods: Adult male rats were exposed to social defeat stress over 8 consecutive days. Then, rats were subjected to 8 min of global ischemia by the four-vessel occlusion model. PROG (8 mg/Kg/b.w.) was administered by intraperitoneal injection at 2 h post-ischemia followed by subcutaneous injections at 6 h and once every 24 h post-injury for 5 days, and then 2 days with progressively halved dosages. Animals were sacrificed at 7 days post-ischemia. Neuronal loss was assessed by Nissl staining, M1/M2 polarization markers were assessed by immunofluorescence, and pro-inflammatory cytokine and growth factor expression were assessed by western blot. Results: Results revealed extensive neuronal loss and exacerbated microglial activation in hippocampal CA1 region of stressed ischemic rats. Remarkably, both M1 and M2 markers increased. PROG treatment attenuated neuronal loss, robustly reduced M1/M2 markers and significantly increased brain-derived neurotrophic factor expression in the stressed ischemic hippocampus. Conclusion: Our data demonstrate that PROG can modulate neuroinflammation after global ischemic injury by changing microglial phenotype in certain vulnerable brain areas like the hippocampus. These findings support the therapeutic potential of PROG for treating global ischemia with comorbid stress.

The oophorectomy increases the oxidative stress in induced transient ischemic attack rat hippocampus

The oophorectomy increases the oxidative stress in induced transient ischemic attack rat hippocampus

Complete, bilateral hippocampal ischemia: a case series

ABSTRACTAcute and complete ischemia of the hippocampi represents a rare cause of amnesia. This paper describes the features of four such cases presenting to a single tertiary care center over a 3-year period. Interestingly, in three instances, toxicology screening was positive for opioids at the time of presentation, while in the fourth, there was a known, reportedly remote, history of heroin use. Taken together with the known literature on the topic, complete hippocampal ischemia appears at least highly suggestive of a toxic exposure. Further case finding is necessary to better understand the etiology, nature, and prevalence of this unusual clinico-radiologic entity.

Spatiotemporal Progression of Microcalcification in the Hippocampal CA1 Region following Transient Forebrain Ischemia in Rats: An Ultrastructural Study.

Calcification in areas of neuronal degeneration is a common finding in several neuropathological disorders including ischemic insults. Here, we performed a detailed examination of the onset and spatiotemporal profile of calcification in the CA1 region of the hippocampus, where neuronal death has been observed after transient forebrain ischemia. Histopathological examinations showed very little alizarin red staining in the CA1 pyramidal cell layer until day 28 after reperfusion, while prominent alizarin red staining was detected in CA1 dendritic subfields, particularly in the stratum radiatum, by 14 days after reperfusion. Electron microscopy using the osmium/potassium dichromate method and electron probe microanalysis revealed selective calcium deposits within the mitochondria of degenerating dendrites at as early as 7 days after reperfusion, with subsequent complete mineralization occurring throughout the dendrites, which then coalesced to form larger mineral conglomerates with the adjacent calcifying neurites by 14 days after reperfusion. Large calcifying deposits were frequently observed at 28 days after reperfusion, when they were closely associated with or completely engulfed by astrocytes. In contrast, no prominent calcification was observed in the somata of CA1 pyramidal neurons showing the characteristic features of necrotic cell death after ischemia, although what appeared to be calcified mitochondria were noted in some degenerated neurons that became dark and condensed. Thus, our data indicate that intrahippocampal calcification after ischemic insults initially occurs within the mitochondria of degenerating dendrites, which leads to the extensive calcification that is associated with ischemic injuries. These findings suggest that in degenerating neurons, the calcified mitochondria in the dendrites, rather than in the somata, may serve as the nidus for further calcium precipitation in the ischemic hippocampus.

Retraction Note To: Expression of SOCS2 mRNA and protein in the ischemic core and penumbra after transient focal cerebral ischemia in rats.

The suppressor of cytokine signaling 2 (SOCS2) has been reported to be involved in astroglial reactions and adult neurogenesis in the ischemic hippocampus. To elucidate whether SOCS2 is implicated in the pathophysiology of stroke, we investigate spatiotemporal regulation and identification of cell phenotypes expressing SOCS2 after transient focal cerebral ischemia. Weak hybridization signals for SOCS2 mRNA were constitutively observed in striatal neurons and upregulation of SOCS2 mRNA was induced in association with nestin-positive cells in stroke-lesioned rats. Analysis of the characteristics and phenotypes of SOCS2/nestin double-labeled cells revealed spatial differences between infarct and peri-infarct areas. SOCS2/nestin double-labeled cells in the infarct area were associated with the vasculature and were highly proliferative. In contrast, the double-labeled cells in the peri-infarct area were indeed glial fibrillary acidic protein (GFAP)-positive reactive astrocytes forming the glial scar, although nestin-negative reactive astrocytes also exhibited weak SOCS2 expression. In addition, induction of SOCS2 expression was observed in Iba1-positive cells showing a macrophage-like phenotype with amoeboid morphology; these cells were predominantly localized in the infarct area. In the peri-infarct area, only a small proportion of Iba1-positive cells with the morphology of brain macrophages expressed SOCS2 and most activated stellate microglial cells with thick and short processes exhibited weak or negligible SOCS2 expression. Thus, our results revealed the phenotypic and functional heterogeneity of SOCS2-expressing cells within infarct and peri-infarct areas, suggesting the involvement of SOCS2 in astroglial reactions and activation/recruitment of brain macrophages and its potential role in perivascular progenitors/stem cells after ischemic stroke.

The role of erythropoietin in remote renal preconditioning on hippocampus ischemia/reperfusion injury.

Remote ischemic preconditioning (RIPC) is an intriguing approach which exposes a remote organ/tissue to a non-lethal transient ischemia/reperfusion (I/R) in order to potentiate the resistance of the desired organ/tissue against the next unwanted I/R. It has been suggested that RIPC exerts its effect through neuronal and hormonal pathways. The underlying mechanisms of RIPC are obscure and should be elucidated. In this study, we induced RIPC in mice using 3 cycles of 5min ischemia alternating with 5min reperfusion of the left renal artery. Renal failure was induced in mice by intra-peritoneal (i.p.) injection of 200mg/kg body weight of gentamicin twice per day for 4 consecutive days. Global hippocampal ischemia reperfusion (I/R) was performed by bilateral carotid artery occlusion for 20min followed by reperfusion for 72h. Moreover, the retention trial of passive avoidance test was determined 72h after global ischemia. Histopathological changes of hippocampus neurons were observed using Nissl staining to detect neuronal loss. Finally, terminal deoxynucleotidyl transferase mediated dUTP nick end-labeling (TUNEL) was performed to assess the status of apoptotic cells in the hippocampus. The results of this study suggest that renal ischemic preconditioning is a good candidate for prevention of I/R-induced hippocampal injury. However, RRPC (remote renal preconditioning) failed to exert a neuroprotective effect in mice with renal failure (RF), indicating the probable role of a humoral factor which is released from kidneys in response to ischemia. In agreement with this hypothesis, treatment of mice with rhEPO (5000IU/kg intraperitoneal) before induction of RRPC restored the neuroprotective effects of RRPC in RF mice. Accordingly, it is plausible to expect that erythropoietin is released from kidneys to act as a mediator for RRPC-induced neuroprotective effects. Renal ischemic preconditioning prevents I/R-induced hippocampal injury. In contrast, renal failure hampers protective effects of RRPC, while exogenous administration of erythropoietin (EPO) significantly prevents the inhibiting effects of renal failure.

Effects of melatonin on cognitive impairment and hippocampal neuronal damage in a rat model of chronic cerebral hypoperfusion.

Chronic cerebral hypoperfusion (CCH), which induces oxidative stress and inflammation in the brain, has previously been associated with cognitive impairment and neuronal cell damage. Melatonin is a well-known free radical scavenger and antioxidant; therefore, the present study investigated the protective effects of melatonin against CCH-induced cognitive impairment and neuronal cell death in a CCH rat model, which was generated via permanent bilateral common carotid artery occlusion (2VO). The rats in the 2VO group exhibited markedly increased escape latencies in a Morris water maze test, as compared with the rats in the sham group. In addition, increased neuronal cell damage was detected in the hippocampal CA1 region of the 2VO rats, as compared with the rats in the sham group. Treatment of the 2VO rats with melatonin significantly reduced the escape latency and neuronal cell damage, and was associated with reduced levels of malondialdehyde, microglial activation, and tumor necrosis factor-α and interleukin-1β in the ischemic hippocampus. The results of the present study suggest that melatonin may attenuate CCH-induced cognitive impairment and hippocampal neuronal cell damage by decreasing oxidative stress, microglial activation and the production of pro-inflammatory cytokines in the ischemic hippocampus.

Increased expression of Slit2 and its receptors Robo1 and Robo4 in reactive astrocytes of the rat hippocampus after transient forebrain ischemia

Slit2 is a secreted glycoprotein that was originally identified as a chemorepulsive factor in the developing brain; however, it was recently reported that Slit2 is associated with adult neuronal function including a variety of pathophysiological processes. To elucidate whether Slit2 is implicated in the pathophysiology of ischemic injury, we investigated the temporal changes and cellular localization of Slit2 and its predominant receptors, Robo1 and Robo4, for 28 days after transient forebrain ischemia. Slit2 and its receptors had similar overall expression patterns in the control and ischemic hippocampi. The ligand and receptors were constitutively expressed in hippocampal neurons in control animals; however, in animals with ischemic injury, their upregulation was detected in reactive astrocytes, but not in neurons or activated microglia, in the CA1 region. Astroglial induction of Slit2 and its receptors occurred by day 3 after reperfusion, and appeared to increase progressively until the final time point on day 28. Their temporal expression patterns overlapped with the time period in which reactive astrocytes undergo dynamic structural changes and appear hypertrophic in the ischemic hippocampus. The immunohistochemical data were consistent with the results of the immunoblot analyses, indicating that the expression of Slit2 and Robo increased progressively over the relatively long period of 28 days examined here. Collectively, these results suggest that Slit2/Robo signaling may be involved in regulating the astroglial reaction via autocrine or paracrine mechanisms in post-ischemic processes. Moreover, this may contribute to the dynamic morphological changes that occur in astrocytes in response to ischemic injury.