DNA fragmentation follows delayed neuronal death in CA1 neurons exposed to transient global ischemia in the rat

Intranasally delivered mesenchymal stromal cells decrease glial inflammation early in prion disease

Mesenchymal stromal cells (MSCs) are an intriguing avenue for the treatment of neurological disorders due to their ability to migrate to sites of neuroinflammation and respond to paracrine signaling in those sites by secreting cytokines, growth factors, and other neuromodulators. We potentiated this ability by stimulating MSCs with inflammatory molecules, improving their migratory and secretory properties. We investigated the use of intranasally delivered adipose-derived MSCs (AdMSCs) in combating prion disease in a mouse model. Prion disease is a rare, lethal neurodegenerative disease that results from the misfolding and aggregation of the prion protein. Early signs of this disease include neuroinflammation, activation of microglia, and development of reactive astrocytes. Later stages of disease include development of vacuoles, neuronal loss, abundant aggregated prions, and astrogliosis. We demonstrate the ability of AdMSCs to upregulate anti-inflammatory genes and growth factors when stimulated with tumor necrosis factor alpha (TNFα) or prion-infected brain homogenates. We stimulated AdMSCs with TNFα and performed biweekly intranasal deliveries of AdMSCs on mice that had been intracranially inoculated with mouse-adapted prions. At early stages in disease, animals treated with AdMSCs showed decreased vacuolization throughout the brain. Expression of genes associated with Nuclear Factor-kappa B (NF-κB) and Nod-Like Receptor family pyrin domain containing 3 (NLRP3) inflammasome signaling were decreased in the hippocampus. AdMSC treatment promoted a quiescent state in hippocampal microglia by inducing changes in both number and morphology. Animals that received AdMSCs showed a decrease in both overall and reactive astrocyte number, and morphological changes indicative of homeostatic astrocytes. Although this treatment did not prolong survival or rescue neurons, it demonstrates the benefits of MSCs in combatting neuroinflammation and astrogliosis.

Protective Effects of PEP-1-GSTA2 Protein in Hippocampal Neuronal Cell Damage Induced by Oxidative Stress

Glutathione S-transferase alpha 2 (GSTA2), a member of the glutathione S-transferase family, plays the role of cellular detoxification against oxidative stress. Although oxidative stress is related to ischemic injury, the role of GSTA2 against ischemia has not been elucidated. Thus, we studied whether GSTA2 prevents ischemic injury by using the PEP-1-GSTA2 protein which has a cell-permeable protein transduction domain. We revealed that cell-permeable PEP-1-GSTA2 transduced into HT-22 cells and markedly protected cell death via the inhibition of reactive oxygen species (ROS) production and DNA damage induced by oxidative stress. Additionally, transduced PEP-1-GSTA2 promoted mitogen-activated protein kinase (MAPK), and nuclear factor-kappaB (NF-κB) activation. Furthermore, PEP-1-GSTA2 regulated Bcl-2, Bax, cleaved Caspase-3 and -9 expression protein levels. An in vivo ischemic animal model, PEP-1-GSTA2, markedly prevented the loss of hippocampal neurons and reduced the activation of microglia and astrocytes. These findings indicate that PEP-1-GSTA2 suppresses hippocampal cell death by regulating the MAPK and apoptotic signaling pathways. Therefore, we suggest that PEP-1-GSTA2 will help to develop the therapies for oxidative-stress-induced ischemic injury.

Cuprizone Affects Hypothermia-Induced Neuroprotection and Enhanced Neuroblast Differentiation in the Gerbil Hippocampus after Ischemia

In the present study, we investigated the effects of cuprizone on cell death, glial activation, and neuronal plasticity induced by hypothermia after ischemia in gerbils. Food was supplemented with cuprizone at 0.2% ad libitum for eight weeks. At six weeks after diet feeing, gerbils received transient forebrain ischemia with or without hypothermic preconditioning. Cuprizone treatment for 8 weeks increased the number of astrocytes, microglia, and pro-inflammatory cytokine levels in the hippocampus. In addition, cuprizone treatment significantly decreased the number of proliferating cells and neuroblasts in the dentate gyrus. Brain ischemia caused cell death, disruption of myelin basic proteins, and reactive gliosis in CA1. In addition, ischemia significantly increased pro-inflammatory cytokines and the number of proliferating cells and differentiating neuroblasts in the dentate gyrus. In contrast, hypothermic conditioning attenuated these changes in CA1 and the dentate gyrus. However, cuprizone treatment decreased cell survival induced by hypothermic preconditioning after ischemia and increased the number of reactive microglia and astrocytes in CA1 as well as that of macrophages in the subcallosal zone. These changes occurred because the protective effect of hypothermia in ischemic damage was disrupted by cuprizone administration. Furthermore, cuprizone decreased ischemia-induced proliferating cells and neuroblasts in the dentate gyrus.

The beneficial roles of metformin on the brain with cerebral ischaemia/reperfusion injury

Cerebral ischaemia/reperfusion (I/R) injury is the transient loss, followed by rapid return, of blood flow to the brain. This condition is often caused by strokes and heart attacks. The underlying mechanisms resulting in brain damage during cerebral I/R injury include mitochondrial dysregulation, increased oxidative stress/reactive oxygen species, blood-brain-barrier breakdown, inflammation of the brain, and increased neuronal apoptosis. Metformin is the first-line antidiabetic drug which has recently been shown to be capable of acting through the aforementioned pathways to improve recovery following cerebral I/R injury. However, some studies have suggested that metformin therapy may have no effect or even worsen recovery following cerebral I/R injury. The present review will compile and examine the available in vivo, in vitro, and clinical data concerning the neuroprotective effects of metformin following cerebral I/R injury. Any contradictory evidence will also be assessed and presented to determine the actual effectiveness of metformin treatment in stroke recovery.

Downregulation of TRB3 protects neurons against apoptosis induced by global cerebral ischemia and reperfusion injury in rats

Global cerebral ischemia and reperfusion injury (GCI/R) can lead to neuronal apoptosis and contributes to permanent neurological sequelae. However, the underlying mechanism is largely unknown. Therefore, the present study aimed to assess the effects of GCI/R on the tribbles homolog 3 (TRB3) and to explore the role of TRB3 in GCI/R. The GCI/R model was developed in Sprague-Dawley male rats by four-vessel occlusion. Subsequently, the expressions of TRB3, endoplasmic reticulum stress markers, and apoptosis-associated proteins were examined by western blot at 1h, 6h, 12h, 24h, and 72h after GCI/R. TRB3 short-hairpin RNA (shRNA) lentivirus was constructed and used to investigate the role of TRB3 in GCI/R-induced neuronal apoptosis. GCI/R increased the level of TRB3, endoplasmic reticulum stress markers, and pro-apoptotic proteins. The level of protein kinase B (Akt) phosphorylation was reduced during GCI/R. Administration of TRB3 shRNA lentivirus attenuated GCI/R-induced up-regulation of TRB3, endoplasmic reticulum stress, and neuronal apoptosis. Furthermore, TRB3 shRNA lentivirus reversed the reduced level of Akt phosphorylation induced by GCI/R. These data implied that TRB3 participated in the GCI/R-induced neuronal apoptosis. Knocking down TRB3 attenuated endoplasmic reticulum stress, enhanced Akt phosphorylation, and protected neurons from apoptosis in response to GCI/R. These results demonstrated that the downregulation of TRB3 may be a promising approach for treating GCI/R.

Effects of long‑term post‑ischemic treadmill exercise on gliosis in the aged gerbil hippocampus induced by transient cerebral ischemia

Therapeutic exercise is an integral component of the rehabilitation of patients who have suffered a stroke. The objective of the present study was to use immunohistochemistry to investigate the effects of post-ischemic exercise on neuronal damage or death and gliosis in the aged gerbil hippocampus following transient cerebral ischemia. Aged gerbils (male; age, 22–24 months) underwent ischemia and were subjected to treadmill exercise for 1 or 4 weeks. Neuronal death was detected in the stratum pyramidale of the hippocampal CA1 region and in the polymorphic layer of the dentate gyrus using cresyl violet and Fluoro-Jade B histofluorescence staining. No significant difference in neuronal death was identified following 1 or 4 weeks of post-ischemic treadmill exercise. However, post-ischemic treadmill exercise affected gliosis (the activation of astrocytes and microglia). Glial fibrillary acidic protein-immunoreactive astrocytes and ionized calcium binding adaptor molecule 1-immunoreactive microglia were activated in the CA1 and polymorphic layer of the dentate gyrus of the group without treadmill exercise. Conversely, 4 weeks of treadmill exercise significantly alleviated ischemia-induced astrocyte and microglial activation; however, 1 week of treadmill exercise did not alleviate gliosis. These findings suggest that long-term post-ischemic treadmill exercise following transient cerebral ischemia does not influence neuronal protection; however, it may effectively alleviate transient cerebral ischemia-induced astrocyte and microglial activation in the aged hippocampus.

Regulation of mRNA following brain ischemia and reperfusion

There is growing appreciation that mRNA regulation plays important roles in disease and injury. mRNA regulation and ribonomics occur in brain ischemia and reperfusion (I/R) following stroke and cardiac arrest and resuscitation. It was recognized over 40 years ago that translation arrest (TA) accompanies brain I/R and is now recognized as part of the intrinsic stress responses triggered in neurons. However, neuron death correlates to a prolonged TA in cells fated to undergo delayed neuronal death (DND). Dysfunction of mRNA regulatory processes in cells fated to DND prevents them from translating stress-induced mRNAs such as heat shock proteins. The morphological and biochemical studies of mRNA regulation in postischemic neurons are discussed in the context of the large variety of molecular damage induced by ischemic injury. Open issues and areas of future investigation are highlighted. A sober look at the molecular complexity of ischemia-induced neuronal injury suggests that a network framework will assist in making sense of this complexity. The ribonomic network sits between the gene network and the various protein and metabolic networks. Thus, targeting the ribonomic network may prove more effective at neuroprotection than targeting specific molecular pathways, for which all efforts have failed to the present time to stop DND in stroke and after cardiac arrest. WIREs RNA 2017, 8:e1415. doi: 10.1002/wrna.1415 For further resources related to this article, please visit the WIREs website.

Metformin protects the brain against ischemia/reperfusion injury through PI3K/Akt1/JNK3 signaling pathways in rats

Although Metformin, a first-line antidiabetic drug, can ameliorate ischemia/reperfusion (I/R) induced brain damage, but how metformin benefits injured hippocampus and the mechanisms are still largely unknown. Therefore, the aim of this study was to investigate the neuroprotective mechanisms of metformin against ischemic brain damage induced by cerebral I/R and to explore whether the Akt-mediated down-regulation of the phosphorylation of JNK3 signaling pathway contributed to the protection provided by metformin. Transient global brain ischemia was induced by 4-vessel occlusion in adult male Sprague-Dawley rats. The open field tasks and Morris water maze were used to assess the effect of metformin on anxiety-like behavioral and cognitive impairment after I/R. Cresyl Violet staining was used to examine the survival of hippocampal CA1 pyramidal neurons. Immunoblotting was performed to measure the phosphorylation of Akt1, JNK3, c-Jun and the expression of cleaved caspase-3. Through ischemia/reperfusion (I/R) rat model, we found that metformin could attenuate the deficits of hippocampal related behaviors and inhibit cell apoptosis. The western blot data showed that metformin could promote the activation of Akt1 and reduce the phosphorylation of JNK3 and c-Jun as well as elevation of cleaved caspase-3 in I/R brains. PI3K inhibitor reversed all the protective effects, further indicating that metformin protect hippocampus from ischemic damage through PI3K/Akt1/JNK3/c-Jun signaling pathway.

Intravenously Infused F3.Olig2 Improves Memory Deficits via Restoring Myelination in the Aged Hippocampus following Experimental Ischemic Stroke

Oligodendrocytes play a crucial role in creating the myelin sheath that is an important component in neural transmission. In an animal model of transient cerebral ischemia, application of oligodendrocyte progenitor cells (OPCs) has not yet been reported. In this study, the effects of F3.Olig2 transplantation on memory and cognitive dysfunction were investigated in the aged gerbil in which ischemic stroke was induced. To investigate the possible mechanisms underlying repair, changes in the expression of myelin basic protein (MBP), oligodendrocyte-specific protein (OSP), and brain-derived neurotrophic factor (BDNF) were examined. Experimental ischemic stroke was induced by occlusion of bilateral common carotid arteries in aged gerbils. Gerbils ( n = 31 per group) were randomly divided into three groups: (1) vehicle sham group, (2) vehicle ischemia group, and (3) F3.Olig2 ischemia group. After 1, 3, and 7 days of ischemia–reperfusion (I-R), saline or F3.Olig2 cells (1 × 10 6 cells in 100 μl) were injected into the gerbils intravenously. The gerbils were sacrificed 10 days after I-R for identification of grafted F3.Olig2 cells, and 15 and 30 days after I-R for tissue analysis after conducting passive avoidance and novel object recognition test. Injected F3.Olig2 cells and MBP, OSP, and BDNF were detected by specific antibodies using immunohistochemistry and/or Western blots. Memory and cognition were significantly increased in the F3.Olig2 ischemia group compared with the vehicle ischemia group. In the F3.Olig2 ischemia group, the neurons were not protected from ischemic damage; however, MBP, OSP, and BDNF expressions were significantly increased. Our results show that injection of F3.Olig2 cells significantly improved impaired memory and cognition, which might be related to increased MBP expression via increasing OSP and BDNF expression in the aged gerbil hippocampus following transient cerebral ischemia.

Tat-PRAS40 prevent hippocampal HT-22 cell death and oxidative stress induced animal brain ischemic insults

Proline rich Akt substrate (PRAS40) is a component of mammalian target of rapamycin complex 1 (mTORC1) and is known to play an important role against reactive oxygen species-induced cell death. However, the precise function of PRAS40 in ischemia remains unclear. Thus, we investigated whether Tat-PRAS40, a cell-permeable fusion protein, has a protective function against oxidative stress-induced hippocampal neuronal (HT-22) cell death in an animal model of ischemia. We showed that Tat-PRAS40 transduced into HT-22 cells, and significantly protected against cell death by reducing the levels of H2O2 and derived reactive species, and DNA fragmentation as well as via the regulation of Bcl-2, Bax, and caspase 3 expression levels in H2O2 treated cells. Also, we showed that transduced Tat-PARS40 protein markedly increased phosphorylated RRAS40 expression levels and 14-3-3σ complex via the Akt signaling pathway. In an animal ischemia model, Tat-PRAS40 effectively transduced into the hippocampus in animal brain and significantly protected against neuronal cell death in the CA1 region. We showed that Tat-PRAS40 protein effectively transduced into hippocampal neuronal cells and markedly protected against neuronal cell damage. Therefore, we suggest that Tat-PRAS40 protein may be used as a therapeutic protein for ischemia and oxidative stress-induced brain disorders.

Long-Term Exercise Improves Memory Deficits via Restoration of Myelin and Microvessel Damage, and Enhancement of Neurogenesis in the Aged Gerbil Hippocampus After Ischemic Stroke

BACKGROUND

The positive correlation between therapeutic exercise and memory recovery in cases of ischemia has been extensively studied; however, long-term exercise begun after ischemic neuronal death as a chronic neurorestorative strategy has not yet been thoroughly examined.

OBJECTIVE

The purpose of this study is to investigate possible mechanisms by which exercise ameliorates ischemia-induced memory impairment in the aged gerbil hippocampus after transient cerebral ischemia.

METHODS

Treadmill exercise was begun 5 days after ischemia-reperfusion (I-R) and lasted for 1 or 4 weeks. The animals were sacrificed 31 days after the induction of ischemia. Changes in short-term memory, as well as the hippocampal expression of markers of cell proliferation, neuroblast differentiation, neurogenesis, myelin and microvessel repair, and growth factors were examined by immunohistochemistry and/or western blots.

RESULTS

Four weeks of exercise facilitated memory recovery despite neuronal damage in the stratum pyramidale (SP) of the hippocampal CA1 region and in the polymorphic layer (PoL) of the dentate gyrus (DG) after I-R. Long-term exercise enhanced cell proliferation and neuroblast differentiation in a time-dependent manner, and newly generated mature cells were found in the granule cell layer of the DG, but not in the SP of the CA1 region or in the PoL of the DG. In addition, long-term exercise ameliorated ischemia-induced damage of myelin and microvessels, which was correlated with increased BDNF expression in the CA1 region and the DG.

CONCLUSIONS

These results suggest that long-term treadmill exercise after I-R can restore memory function through replacement of multiple damaged structures in the ischemic aged hippocampus.

Long-term observation of neuronal degeneration and microgliosis in the gerbil dentate gyrus after transient cerebral ischemia

Ischemic insults in the central nervous system evoke activation of microglia. In this study, we investigated long-term changes of neuronal damage and microglial activation in the gerbil dentate gyrus for 60 days after transient cerebral ischemia using immunohistochemistry and western blot. Neuronal damage or death was hardly found in the dentate gyrus after transient ischemia using cresyl violet staining and NeuN immunohistochemistry; however, neuronal degeneration was detected in the polymorphic layer of the dentate gyrus using Fluoro-Jade (F-J) B staining. F-J B-positive cells were significantly increased after ischemia-reperfusion (I-R) and peaked at 3 days post-ischemia, thereafter, F-J B-positive cells were decreased in a time-dependent manner and shown until 30 days post-ischemia; no F-J B-positive cells were observed 60 days after I-R. On the other hand, Iba-1-immunoreactive microglia were hypertrophied after I-R, and numbers of Iba-1-immunoreactive microglia were significantly increased along with the neuronal degeneration and highest 7 days after I-R, thereafter, numbers of Iba-1-immunoreactive microglia were decreased with time, although microglia activation lasted up to 60 days after I-R. In addition, Iba-1 protein level in the dentate gyrus after I-R was changed like immunohistochemical change. Our results, in brief, indicate that transient ischemia-induced neuronal degeneration in the dentate gyrus is maintained for about 30 days after I-R and that microglial activation lasts up to, at least, 60 days after I-R in the gerbil dentate gyrus after transient cerebral ischemia.

Dexamethasone enhances necrosis-like neuronal death in ischemic rat hippocampus involving μ-calpain activation

Transient forebrain ischemia (TFI) leads to hippocampal CA1 pyramidal cell death which is aggravated by glucocorticoids (GC). It is unknown how GC affect apoptosis and necrosis in cerebral ischemia. We therefore investigated the co-localization of activated caspase-3 (casp-3) with apoptosis- and necrosis-like cell death morphologies in CA1 of rats treated with dexamethasone prior to TFI (DPTI). In addition, apoptosis- (casp-9, casp-3, casp-3-cleaved PARP and cleaved α-spectrin 145/150 and 120kDa) and necrosis-related (calpain-specific casp-9 cleavage, μ-calpain upregulation and cleaved α-spectrin 145/150kDa) cell death mechanisms were investigated by Western blot analysis. DPTI expedited CA1 neuronal death from day 4 to day 1 and increased the magnitude of CA1 neuronal death from 66.2% to 91.3% at day 7. Furthermore, DPTI decreased the overall (days 1-7) percentage of dying neurons displaying apoptosis-like morphology from 4.7% to 0.3% and, conversely, increased the percentage of neurons with necrosis-like morphology from 95.3% to 99.7%. In animals subjected to TFI without dexamethasone (ischemia-only), 7.4% of all dying CA1 neurons were casp-3-immunoreactive (IR), of which 3.1% co-localized with apoptosis-like and 4.3% with necrosis-like changes. By contrast, DPTI decreased the percentage of dying neurons with casp-3 IR to 1.4%, of which 0.3% co-localized with apoptosis-like changes and 1.1% with necrosis-like changes. Western blot analysis from DPTI animals showed a significant elevation of μ-calpain, a calpain-produced necrosis-related casp-9 fragment (25kDa) and cleavage of α-spectrin into 145/150kDa fragments at day 4, whereas in ischemia-only animals a significant increase of casp-3-cleaved PARP, cleavage of α-spectrin into 145/150 and 120kDa fragments was detected at day 7. We conclude that DPTI, in addition to augmenting and expediting CA1 neuronal death, causes a shift from apoptosis-like cell death to necrosis involving μ-calpain activation.

Activation of AMP-activated protein kinase by metformin protects against global cerebral ischemia in male rats: interference of AMPK/PGC-1α pathway

Here, we have investigated the effect of metformin pretreatment in the rat models of global cerebral ischemia. Cerebral ischemia which leads to brain dysfunction is one of the main causes of neurodegeneration and death worldwide. Metformin is used in clinical drug therapy protocols of diabetes. It is suggested that metformin protects cells under hypoxia and ischemia in non-neuronal contexts. Protective effects of metformin may be modulated via activating the AMP activated protein kinase (AMPK). Our results showed that induction of 30 min global cerebral I/R injury using 4-vesseles occlusion model led to significant cell death in the rat brain. Metformin pretreatment (200 mg kg/once/day, p.o., 2 weeks) attenuated apoptotic cell death and induced mitochondrial biogenesis proteins in the ischemic rats, analyzed using histological and Western blot assays. Besides, inhibition of AMPK by compound c showed that metformin resulted in apoptosis attenuation via AMPK activation. Interestingly, AMPK activation was also involved in the induction of mitochondrial biogenesis proteins using metformin, inhibition of AMPK by compound c reversed such effect, further supporting the role of AMPK upstream of mitochondrial biogenesis proteins. In summary, Metformin pretreatment is able to modulate mitochondrial biogenesis and apoptotic cell death pathways through AMPK activation in the context of global cerebral ischemia, conducting the outcome towards neuroprotection.

Neuroprotective effects of the antioxidant action of 2-cyclopropylimino-3-methyl-1,3-thiazoline hydrochloride against ischemic neuronal damage in the brain

Ischemia is characterized by oxidative stress and changes in the antioxidant defense system. Our recent in vitro study showed that 2-cyclopropylimino-3-methyl-1,3-thiazoline hydrochloride protects cortical astrocytes against oxidative stress. In the current study, we examined the effects of 2-cyclopropylimino-3-methyl- 1,3-thiazoline hydrochloride on ischemia-induced neuronal damage in a gerbil ischemia/reperfusion models. Extensive neuronal death in the hippocampal CA1 area was observed 4 days after ischemia/reperfusion. Intraperitoneal injection of 2-cyclopropylimino- 3-methyl-1,3-thiazoline hydrochloride (0.3 mg/kg body weight) significantly prevented neuronal death in the CA1 region of the hippocampus in response to transient forebrain ischemia. 2-Cyclopropylimino-3-methyl-1,3-thiazoline hydrochloride administration reduced ischemia-induced increases in reactive oxygen species levels and malondialdehyde content. It also attenuated the associated reductions in glutathione level and superoxide dismutase, catalase, and glutathione peroxidase activities. Taken together, our results suggest that 2-cyclopropylimino- 3-methyl-1,3-thiazoline hydrochloride protects against ischemia-induced neuronal damage by reducing oxidative stress through its antioxidant actions.

Tat-glyoxalase protein inhibits against ischemic neuronal cell damage and ameliorates ischemic injury

Methylglyoxal (MG), a metabolite of glucose, is the major precursor of protein glycation and induces apoptosis. MG is associated with neurodegeneration, including oxidative stress and impaired glucose metabolism, and is efficiently metabolized to S-D-lactoylglutathione by glyoxalase (GLO). Although GLO has been implicated as being crucial in various diseases including ischemia, its detailed functions remain unclear. Therefore, we investigated the protective effect of GLO (GLO1 and GLO2) in neuronal cells and an animal ischemia model using Tat-GLO proteins. Purified Tat-GLO protein efficiently transduced into HT-22 neuronal cells and protected cells against MG- and H2O2-induced cell death, DNA fragmentation, and activation of caspase-3 and mitogen-activated protein kinase. In addition, transduced Tat-GLO protein increased D-lactate in MG- and H2O2-treated cells whereas glycation end products (AGE) and MG levels were significantly reduced in the same cells. Gerbils treated with Tat-GLO proteins displayed delayed neuronal cell death in the CA1 region of the hippocampus compared with a control. Furthermore, the combined neuroprotective effects of Tat-GLO1 and Tat-GLO2 proteins against ischemic damage were significantly higher than those of each individual protein. Those results demonstrate that transduced Tat-GLO protein protects neuronal cells by inhibiting MG- and H2O2-mediated cytotoxicity in vitro and in vivo. Therefore, we suggest that Tat-GLO proteins could be useful as a therapeutic agent for various human diseases related to oxidative stress including brain diseases.

EGB1212 Post-treatment Ameliorates Hippocampal CA1 Neuronal Death and Memory Impairment Induced by Transient Global Cerebral Ischemia/Reperfusion

Extracts of Ginkgo biloba have been used in traditional medicines for centuries, and have potential for clinical applications in cerebral ischemia/reperfusion injury. However, standardized extracts have proven protective only as pre-treatments, and the major mechanisms of action remain unclear. We explored the potential of the novel extract EGB1212, which meets the United States Pharmacopeia (USP) 31 standardization criteria for pharmaceutical use, as a post-treatment after global cerebral ischemia/reperfusion (GCI/R) injury in a rat model. The pre-treated group was administered EGB1212 for 7 d prior to common carotid artery occlusion (i.e., ischemia, for 20 min). Post-treated rats received the same but starting 2 h after ischemia and continuing for 7 d. Seven days after GCI/R, brains of each group were processed for H&E staining of hippocampal CA1 neurons. Remaining rats underwent the Morris water maze and Y-maze tests of spatial learning and memory, beginning eight days after reperfusion. To assess hippocampal autophagy, light chain (LC)-3-I/LC3-II and Akt/pAkt were determined via a Western blot of rat hippocampi harvested 12, 24, or 72 h after reperfusion. EGB1212 pre- and post-treatments both improved neuronal survival and spatial learning and memory functions. Pre-treatment effectively reduced LC3-II levels and post-treatment resulted in significantly elevated pAkt levels. We conclude that EGB1212 exerted significant neuroprotection in GCI/R in both preventative and post-treatment settings. This extract shows great potential for clinical applications.

Gemfibrozil pretreatment affecting antioxidant defense system and inflammatory, but not Nrf-2 signaling pathways resulted in female neuroprotection and male neurotoxicity in the rat models of global cerebral ischemia-reperfusion

Two important pathophysiological mechanisms involved during cerebral ischemia are oxidative stress and inflammation. In pathological conditions such as brain ischemia the ability of free radicals production is greater than that of elimination by endogenous antioxidative systems, so brain is highly injured due to oxidation and neuroinflammation. Fibrates as peroxisome proliferator-activated receptor (PPAR)-α ligands, are reported to have antioxidant and anti-inflammatory actions. In this study, gemfibrozil, a fibrate is investigated for its therapeutic potential against global cerebral ischemia-reperfusion (I/R) injury of male and female rats. This study particularly has focused on inflammatory and antioxidant signaling pathways, such as nuclear factor erythroid-related factor (Nrf)-2, as well as the activity of some endogenous antioxidant agents. It was found that pretreatment of animals with gemfibrozil prior to I/R resulted in a sexually dimorphic outcome. Within females it proved to be protective, modulating inflammatory factors and inducing antioxidant defense system including superoxide dismutase (SOD), catalase, as well as glutathione level. However, Nrf-2 signaling pathway was not affected. It also decreased malondialdehyde level as an index of lipid peroxidation. In contrast, gemfibrozil pretreatment was toxic to males, enhancing the expression of inflammatory factors such as tumor necrosis factor-α, nuclear factor-κB, and cyclooxygenase-2, and decreasing Nrf-2 expression and SOD activity, leading to hippocampal neurodegeneration. Considering that gemfibrozil is a commonly used anti-hyperlipidemic agent in clinic, undoubtedly more investigations are crucial to exactly unravel its sex-dependent neuroprotective/neurodegenerative potential.

Long-term post-stroke changes include myelin loss, specific deficits in sensory and motor behaviors and complex cognitive impairment detected using active place avoidance

Persistent neurobehavioral deficits and brain changes need validation for brain restoration. Two hours middle cerebral artery occlusion (tMCAO) or sham surgery was performed in male Sprague-Dawley rats. Neurobehavioral and cognitive deficits were measured over 10 weeks included: (1) sensory, motor, beam balance, reflex/abnormal responses, hindlimb placement, forepaw foot fault and cylinder placement tests, and (2) complex active place avoidance learning (APA) and simple passive avoidance retention (PA). Electroretinogram (ERG), hemispheric loss (infarction), hippocampus CA1 neuronal loss and myelin (Luxol Fast Blue) staining in several fiber tracts were also measured. In comparison to Sham surgery, tMCAO surgery produced significant deficits in all behavioral tests except reflex/abnormal responses. Acute, short lived deficits following tMCAO were observed for forelimb foot fault and forelimb cylinder placement. Persistent, sustained deficits for the whole 10 weeks were exhibited for motor (p<0.001), sensory (p<0.001), beam balance performance (p<0.01) and hindlimb placement behavior (p<0.01). tMCAO produced much greater and prolonged cognitive deficits in APA learning (maximum on last trial of 604±83% change, p<0.05) but only a small, comparative effect on PA retention. Hemispheric loss/atrophy was measured 10 weeks after tMCAO and cross-validated by two methods (e.g., almost identical % ischemic hemispheric loss of 33.4±3.5% for H&E and of 34.2±3.5% for TTC staining). No visual dysfunction by ERG and no hippocampus neuronal loss were detected after tMCAO. Fiber tract damage measured by Luxol Fast Blue myelin staining intensity was significant (p<0.01) in the external capsule and striatum but not in corpus callosum and anterior commissure. In summary, persistent neurobehavioral deficits were validated as important endpoints for stroke restorative research in the future. Fiber myelin loss appears to contribute to these long term behavioral dysfunctions and can be important for cognitive behavioral control necessary for complex APA learning.

Effect of celecoxib and L-NAME on global ischemia-reperfusion injury in the rat hippocampus

Transient global ischemia continues to be an important clinical problem with limited treatment options. The present study aimed to investigate the possible protective effects of celecoxib [a selective cyclooxygenase (COX-2) inhibitor] and N-omega-nitro-L-arginine methyl ester (L-NAME) [a nonselective nitric oxide synthase (NOS) inhibitor] against global ischemia-reperfusion (IR) induced biochemical and histological alterations in the rat hippocampus. Global ischemia was induced by bilateral clamping of the common carotid arteries for 60 minutes. Hippocampal cysteinyl aspartate-specific protease-3 (caspase-3) activity, nitrite/nitrate contents (NOX), as well as COX-2 immunoreactivity in the hippocampal Cornu Ammonis 1 (CA1) subregion were dramatically increased 24 hours after global ischemia. After 72-hour of reperfusion, ischemia induced a selective, extensive neuronal loss in the hippocampus CA1 subregion. Celecoxib (3 and 5 mg/kg, intraperitoneally; i.p.), administered 30 minutes before ischemia and at 6, 12, and 22 hours of 24-hour reperfusion, caused significant reductions in hippocampal caspase-3 activity as well as the number of COX-2 immunoreactive (COX-2 ir) neurons in the CA1 subregion. Further, celecoxib (3 or 5 mg/kg, i.p.), administered 30 minutes before ischemia and at 6, 12, 22, and 48 hours of 72-hour reperfusion, provided a notable histological protection of hippocampal CA1 neurons. Meanwhile, L-NAME (3 mg/kg, i.p.), administered twice (immediately after ischemia and 45 minutes after starting the reperfusion period), effectively reduced the elevated NOX level, decreased hippocampal caspase-3 activity and COX-2 immumoreactivity, and ameliorated ischemia-induced damage in the hippocampal CA1 subregion. The present study indicates that celecoxib and L-NAME might be neuroprotective agents of potential benefit in the treatment of cerebral ischemia.

Epileptogenesis in the developing brain

The neonatal brain has poorly developed GABAergic circuits, and in many of them GABA is excitatory, favoring ictogenicity. Frequently repeated experimental seizures impair brain development in an age-dependent manner. At critical ages, they delay developmental milestones, permanently lower seizure thresholds, and can cause very specific cognitive and learning deficits, such as the permanent impairment of neuronal spatial maps. Some types of experimental status epilepticus cause neuronal necrosis and apoptosis, and are followed by chronic epilepsy with spontaneous recurrent seizures, others appear relatively benign, so that seizure-induced neuronal injury and epileptogenesis are highly age-, seizure model-, and species-dependent. Experimental febrile seizures can be epileptogenic, and hyperthermia aggravates both neuronal injury and epileptogenicity. Antiepileptic drugs, the mainstay of treatment, have major risks of their own, and can, at therapeutic or near-therapeutic doses, trigger neuronal apoptosis, which is also age-, drug-, cell type-, and species-dependent. The relevance of these experimental results to human disease is still uncertain, but while their brains are quite different, the basic biology of neurons in rodents and humans is strikingly similar. Further research is needed to elucidate the molecular mechanisms of epileptogenesis and of seizure- or drug-induced neuronal injury, in order to prevent their long-term consequences.

Polyadenylated mRNA staining reveals distinct neuronal phenotypes following endothelin 1, focal brain ischemia, and global brain ischemia/ reperfusion

OBJECTIVES

Most work on ischemia-induced neuronal death has revolved around the relative contributions of necrosis and apoptosis, but this work has not accounted for the role of ischemia-induced stress responses. An expanded view recognizes a competition between ischemia-induced damage mechanisms and stress responses in the genesis of ischemia-induced neuronal death. An important marker of post-ischemic stress responses is inhibition of neuronal protein synthesis, a morphological correlate of which is the compartmentalization of mRNA away from ribosomes in the form of cytoplasmic mRNA granules.

METHODS

Here we assessed the generality of this mRNA granule response following either 10 or 15 minutes global brain ischemia and 1 hour reperfusion, 4 hours focal cerebral ischemia alone, and endothelin 1 intraventricular injection.

RESULTS

Both global and focal ischemia led to prominent neuronal cytoplasmic mRNA granule formation in layer II cortical neurons. In addition, we report here new post-ischemic cellular phenotypes characterized by the loss of nuclear polyadenylated mRNA staining in cortical neurons following endothelin 1 treatment and 15 minutes global ischemia. Both mRNA granulation and loss of nuclear mRNAs occurred in non-shrunken post-ischemic neurons.

DISCUSSION

Where cytoplasmic mRNA granules generally appear to mark a protective response in surviving cells, loss of nuclear mRNAs may mark cellular damage leading to cell atrophy/death. Hence, staining for total mRNA may reveal facets of the competition between stress responses and damage mechanisms at early stages in post-ischemic neurons.

Chlorogenic Acid Improves Neuroprotective Effect of PEP-1-Ribosomal Protein S3 Against Ischemic Insult

Chlorogenic acid (CGA) possesses various biological activities such as anti-oxidant, anti-inflammatory, and anti-diabetic activities. In the present study, we examined the effect of CGA on the transduction efficiency of PEP-1-ribosomal protein S3 (PEP-1-rpS3) into cells and brain tissues, and its neuroprotective potential against ischemia/reperfusion. We found that, in the presence of CGA, the transduction efficiency of PEP-1-rpS3 into astrocytes and the CA1 region of the hippocampus was enhanced, compared to its transduction in the absence of CGA. Also, cell viability data demonstrated that the sample treated with CGA + PEP-1-rpS3 exhibited improved cell viability against hydrogen peroxide (H₂O₂)-induced toxicity more significantly than the sample treated with PEP-1-rpS3 alone. Also, in a gerbil ischemia model, data demonstrated that following the ischemic insult, the group treated with PEP-1-rpS3 + CGA showed markedly enhanced protection of neuron cells in CA1 region of hippocampus, compared to those treated with CGA or PEP-1-rpS3 alone. Taken together, these results suggest that CGA may improve the transduction efficiency of protein transduction domain (PTD) fusion proteins into target cells or tissues, thereby enhancing their therapeutic potential against various diseases.

Bcl-2 homology domain 3-only proteins Puma and Bim mediate the vulnerability of CA1 hippocampal neurons to proteasome inhibition in vivo

Bcl-2 homology domain 3 (BH3)-only proteins are pro-apoptotic Bcl-2 family members that play important roles in upstream cell death signalling during apoptosis. Proteasomal stress has been shown to contribute to the pathology of cerebral ischaemia and many neurodegenerative disorders. Here we explored the contribution of BH3-only proteins in mediating proteasome-inhibition-induced apoptosis in the murine brain in vivo. Stereotactic intrahippocampal microinjection of the selective proteasome inhibitor epoxomicin (2.5 nmol) induced a delayed apoptosis within only the CA1 hippocampal neurons and not neurons within the CA3 or dentate gyrus regions, a selective vulnerability similar to that seen during ischaemia. This injury developed over a time-course of 3 days and was characterized by positive terminal deoxynucleotidyl transferase dUTP nick end labelling staining and nuclear condensation. Previous work from our laboratory has identified the BH3-only protein p53-upregulated mediator of apoptosis (Puma) as mediating proteasome-inhibition-induced apoptosis in cultured neural cells. Genetic deletion of puma reduced the number of terminal deoxynucleotidyl transferase dUTP nick end labelling-positive cells within the CA1 following epoxomicin microinjection but it did not provide a complete protection. Subsequent studies identified the BH3-only protein Bim as also being upregulated during proteasome inhibition in organotypic hippocampal slice cultures and after epoxomicin treatment in vivo. Interestingly, the genetic deletion of bim also afforded significant neuroprotection, although this protection was less pronounced. In summary, we demonstrate that the BH3-only proteins Puma and Bim mediate the delayed apoptosis of CA1 hippocampal neurons induced by proteasome inhibition in vivo, and that either BH3-only protein can only partly compensate for the deficiency of the other.

Protective effects of transduced PEP-1-Frataxin protein on oxidative stress-induced neuronal cell death

Reactive oxygen species (ROS) actively contribute to the development of a number of human diseases including ischemia. In response to oxidative stress, frataxin has a significant ability to improve cell survival though its biological function is unclear in relation to ischemia. To explore frataxin's role in protecting against ischemic cell death, we constructed PEP-1-Frataxin cell-permeable fusion protein. In a dose- and time-dependent manner PEP-1-Frataxin rapidly transduced into astrocyte cells and protected them against oxidative stress-induced cell death. Further, using an animal model, immunohistochemical analysis revealed that PEP-1-Frataxin prevented neuronal cell death in the CA1 region of the hippocampus induced by transient forebrain ischemia. These results demonstrate that transduced PEP-1-Frataxin protects against cell death in vitro and in vivo, suggesting that transduction of PEP-1-Frataxin could be useful as a therapeutic agent for various human diseases related to oxidative stress.

Maintenance of anti-inflammatory cytokines and reduction of glial activation in the ischemic hippocampal CA1 region preconditioned with lipopolysaccharide

Lipopolysaccharide (LPS) induces a strong immune response, and pretreatment with low dose of LPS suppresses the production of proinflammatory mediators. In the present study, we investigated the effect of LPS preconditioning on the delayed neuronal death in the gerbil hippocampal CA1 region after 5 min of transient cerebral ischemia. LPS preconditioning showed neuroprotective effects against ischemic damage in the hippocampal CA1 region after ischemic insult: about 92% of neurons in the CA1 region survived in the LPS-treated ischemia group. LPS preconditioning maintained anti-inflammatory cytokines, such as interleukin (IL)-4 and IL-13, in pyramidal neurons in the CA1 region after ischemia/reperfusion. In addition, IL-4 and IL-13 protein levels in the CA1 region of the LPS-treated ischemia group were similar to the vehicle-treated sham group. We found that reactive gliosis was markedly attenuated in the CA1 region of the LPS-treated ischemia group compared to the vehicle-treated ischemia group using immunohistochemistry of glial fibrillary acidic protein for astrocytes, and ionized calcium-binding adapter molecule 1 and isolectin B4 for microglia. These results indicate that LPS preconditioning may provide neuroprotection in the ischemic hippocampal CA1 region via maintenance of anti-inflammatory cytokines and suppression of glial activation.

Towards a dynamical network view of brain ischemia and reperfusion. Part III: therapeutic implications

The general failure of neuroprotectants in clinical trials of ischemic stroke points to the possibility of a fundamental blind spot in the current conception of ischemic brain injury, the "ischemic cascade". This is the third in a series of four papers whose purpose is to work towards a revision of the concept of brain ischemia by applying network concepts to develop a bistable model of brain ischemia. Here the bistable model of brain ischemia is compared to the ischemic cascade concept. The core weakness of the ischemic cascade concept is revealed to be its assumption of superposition, or that the elements of the ischemic cascade can be summed as linearly independent events. This assumption leads to a concept of neuroprotection as a subtraction of ostensibly independent damage events. The bistable model offers a different concept of neuroprotection where the role of individual molecular pathways decreases in relevance with respect to the efficacy of outcome. Network thinking provides a framework for critical assessment of widely-used preclinical experimental approaches. The importance of allometric scaling is also discussed. We illustrate that the bistable model provides a viable alternative to the ischemic cascade as an explanatory framework and as a guide for therapeutic development.

Transduced human PEP-1-catalase fusion protein attenuates ischemic neuronal damage

Antioxidant enzymes are considered to have beneficial effects against various diseases mediated by reactive oxygen species (ROS). Ischemia is characterized by both oxidative stress and changes in the antioxidant defense system. Catalase (CAT) and superoxide dismutase (SOD) are major antioxidant enzymes by which cells counteract the deleterious effects of ROS. To investigate the protective effects of CAT, we constructed PEP-1-CAT cell-permeative expression vectors. When PEP-1-CAT fusion proteins were added to the culture medium of neuronal cells, they rapidly entered the cells and protected them against oxidative stress-induced neuronal cell death. Immunohistochemical analysis revealed that PEP-1-CAT prevented neuronal cell death in the hippocampus induced by transient forebrain ischemia. Moreover, we showed that the protective effect of PEP-1-CAT was observed in neuronal cells treated with PEP-1-SOD. Therefore, we suggest that transduced PEP-1-CAT and PEP-1-SOD fusion proteins could be useful as therapeutic agents for various human diseases related to oxidative stress, including stroke.

Ischemia-related changes in naive and mutant forms of ubiquitin and neuroprotective effects of ubiquitin in the hippocampus following experimental transient ischemic damage

Ubiquitin binds to short-lived proteins and denatured proteins produced by various forms of injury. The loss of ubiquitin leads to an accumulation of abnormal proteins and may affect cellular structure and function. The aim of the present study is to observe the chronological changes in ubiquitin naive form and its mutant form (ubiquitin(+1)) in the hippocampal CA1 region (CA1) after transient cerebral ischemia in gerbils. Delayed neuronal death in the CA1 was confirmed 4 days after ischemic insult with NeuN immunohistochemistry. Ubiquitin immunoreactivity and protein level in the CA1 were lowest at 12 h after ischemia/reperfusion; thereafter, they were increased with time. Ubiquitin(+1) immunoreactivity and protein levels in the CA1 were slightly decreased at 3 h after ischemia/reperfusion, and they were significantly increased 1 day after ischemia/reperfusion. In addition, ubiquitin and ubiquitin(+1) immunoreaction was expressed in astrocytes after delayed neuronal death in the ischemic CA1. To elucidate the protective effect of ubiquitin on ischemic damage, the animals were treated with ubiquitin (1.5 mg/kg body weight) intravenously via the femoral vein. Ubiquitin treatment significantly reduced ischemia-induced locomotor hyperactivity, neuronal death and reactive gliosis such as astrocytes and microglia. In addition, 5 days after ubiquitin treatment in the ischemic group, ubiquitin immunoreactivity was similar to that in the ubiquitin-treated sham group, however, ubiquitin(+1) immunoreactivity was higher than that in the ubiquitin-treated sham group. These findings indicate that the depletion of ubiquitin and the accumulation of ubiquitin(+1) in CA1 pyramidal neurons after transient cerebral ischemia may inhibit ubiquitin proteolytic pathway and this leads to delayed neuronal death of CA1 pyramidal neurons directly or indirectly after transient cerebral ischemia.

Antioxidant, antiinflammatory and antiapoptotic effects of dapsone in a model of brain ischemia/reperfusion in rats

Although dapsone (4,4'-diaminodiphenylsulfone) has been described as a neuroprotective agent in occlusive focal ischemia in rats, its mechanism of action is still unknown. To explore this mechanism, oxidative, inflammatory and apoptotic processes were evaluated in the striatum of adult rats using a model of ischemia-reperfusion (I/R), either with or without dapsone treatment. Male Wistar rats were submitted to transient middle cerebral artery occlusion for 2 hr, followed by reperfusion. Rats were dosed either with dapsone (12.5 mg/kg i.p.) or vehicle 30 min before or 30 min after the ischemia onset. Lipid peroxidation (LP) and nitrotyrosine contents were measured 22 hr after reperfusion, and myeloperoxidase activity was evaluated 46 hr after I/R. Different markers for apoptosis and necrosis were also evaluated both at 24 and 72 hr after I/R experimental procedure. LP increased by 37% in ischemic animals vs controls, and this effect was reversed by dapsone treatments. A similar effect was observed regarding nitrotyrosine striatal contents. Myeloperoxidase activity, a marker of inflammatory response, increased 3.7-fold in ischemic animals vs. control rats, and dapsone treatment antagonized that effect. Although apoptosis was increased by the effect of ischemia at both evaluation times, dapsone antagonized that effect only at 72 hr after surgery. Dapsone antagonized all of the I/R end points measured, showing a remarkable ability to decrease markers of damage through antioxidant, antiinflammatory, and anti-apoptotic effects.

Hypoxic-ischemic injury in neonatal brain: involvement of a novel neuronal molecule in neuronal cell death and potential target for neuroprotection

Perinatal hypoxia-ischemia (HI) is the most common cause of various neurological disabilities in children with high societal cost. Hypoxic-ischemic brain damage is an evolving process and ample evidence suggests distinct difference between the immature and mature brain in the pathology and consequences of brain injury. Therefore, it is of utmost importance to better understand the mechanisms underlying the hypoxic-ischemic injury in neonatal brain to devise effective therapeutic strategies. Nonetheless, the mechanism(s) involved in this pathology in the developing brain remain inadequately understood. Effective neuroprotective strategies will include either inhibition of the death effector pathways or induction of their regulatory and survival promoting cellular proteins. Neuronal pentraxins (NPs) define a family of novel proteins "long pentraxins" that are exclusively expressed in the central neurons, and are homologous to the C-reactive and acute-phase proteins in the immune system. NPs have been shown to be involved in the excitatory synaptic remodeling. We found that the neuronal protein 'neuronal pentraxin 1' (NP1) is induced in neonatal rat brain following HI, and NP1 induction preceded the time of actual tissue loss in brain. In demonstrating this we also found that NP1 gene silencing is neuroprotective against hypoxia-induced neuronal death. This is the first evidence for a pathophysiological function of NP1 in central neurons. Our results suggest that NP1 is part of a death program triggered by HI. Most importantly, our findings of specific interactions of NP1 with the excitatory glutamate receptors AMPA GluR1 subunit and their co-localization suggest a role for this novel neuronal protein NP1 in the excitotoxic cascade. Blockade of AMPA-induced neuronal death following inhibition of NP1 expression further implicates a regulatory interaction between NP1 and AMPA glutamate receptors. Subsequent experiments using NP1 loss-of-function strategies, we have demonstrated specific requirements of NP1 induction in HI-induced neuronal death. Together our findings clearly identify a novel role for NP1 in the coupling between HI and cerebral cell death. Thus, NP1 could be a new molecular target in the central neurons for preventing hypoxic-ischemic neuronal death in developing brain. These very novel results could lead to more effective neuroprotective strategies against hypoxic-ischemic brain injury in neonates.

Comparative study on Cu,Zn-SOD immunoreactivity and protein levels in the adult and aged hippocampal CA1 region after ischemia-reperfusion

In the present study, we investigated chronological changes in Cu,Zn-superoxide dismutase (SOD1) immunoreactivity and its protein levels in the hippocampal CA1 region of adult and aged gerbils after transient forebrain ischemia to compare ischemia-related changes in SOD1 in adult and aged gerbils. Delayed neuronal death in the CA1 region at 4 days after ischemic insult was prominent in adult gerbils compared to that in aged gerbils. In sham-operated gerbils, SOD1 immunoreactivity and protein level in the aged group were significantly higher than that in the adult group. At 12 h after ischemia-reperfusion, SOD1 immunoreactivity and protein level were increased in both the groups. At 1 day after ischemia, SOD1 immunoreactivity and protein level in the adult group were significantly increased: the SOD1 immunoreactivity was increased in non-pyramidal cells as well as pyramidal cells. At this time after ischemia, SOD1 immunoreactivity and protein level in the aged group were decreased: the immunoreactivity was decreased significantly in pyramidal cells. At 4 days after ischemia, SOD1 immunoreactivity was detected only in non-pyramidal cells of the CA1 region in both the groups. These results suggest that SOD1 in the gerbil hippocampal CA1 region is higher in sham-aged group than that in sham adult one, and that different changes in SOD1 in CA1 pyramidal cells after ischemia in adult and aged gerbils may indicate different processes in delayed neuronal death with time after ischemic insult.

An ultrastructural analysis of cellular death in the CA1 field in the rat hippocampus after transient forebrain ischemia followed by 2, 4 and 10 days of reperfusion

An ultrastructural study was performed to investigate the type of cellular death that occurs in hippocampal CA1 field pyramidal neurons after 10 and 20 min of transient cerebral ischemia in the male adult Wistar rats, followed by 2, 4 and 10 days of reperfusion. The four-vessel occlusion method was used to induce ischemic insult for either 10 or 20 min, following which the animals were submitted to either 2, 4 or 10 days of reperfusion. The animals were then anaesthetised, and their brains removed, dehydrated, embedded, sectioned and examined under a transmission electron microscope. After ischemic insult, neurons from the CA1 field presented alterations, corresponding to the initial, intermediate and final stages of the degenerative process. The only difference observed between the 10 and 20 min ischemic groups was the degree of damage; the reaction was stronger in 20 min groups than in the 10 min groups. While neurons were found in the different stages of oncotic necrosis in all groups, differences were found between the groups in relation to prevalent stages. In both ischemic groups, after 2 days of reperfusion, the initial stage of oncotic necrosis was prevalent and large numbers of neurons appeared normal. In both groups, after 4 days of reperfusion, most of the neurons showed more advanced alterations, typical of an intermediate stage. In both groups, after 10 days of reperfusion, alterations corresponding to the intermediate and final stages of oncotic necrosis were also predominant. However, few intact neurons were identified and the neuropile appeared more organised, with numerous glial cells. In summary, the pyramidal neurons of the CA1 field displayed selective vulnerability and exhibited a morphological death pattern corresponding exclusively to an oncotic necrotic pathway.

Rip immunoreactivity significantly decreases in the stratum oriens of hippocampal CA1 region after transient forebrain ischemia in gerbils

In the present study, we observed ischemia-related changes in Rip recognizing the promyelinating and myelinating oligodendrocytes in the hippocampus proper after 5 min of transient forebrain ischemia in gerbils. Rip immunoreactivity was significantly altered in the hippocampal CA1 region but not in the CA2/3 region after ischemic insult. In the sham-operated group, Rip immunoreactivity was shown in the cell bodies and processes of oligodendrocytes in all layers of the hippocampus proper. From 15 min to 2 days after ischemic insult, Rip immunoreactivity was similar to that of sham-operated group. Three days after ischemic insult, Rip-immunoreactive processes were tangled in the stratum oriens of the CA1 region, and Rip protein level decreased from this time after ischemia. Thereafter, Rip immunoreactivity was decreased time dependently in the CA1 region. Seven days after ischemic insult, Rip-immunoreactive processes were tangled and densely detected in the stratum oriens adjacent to the stratum pyramidale. In brief, these results indicate that the significant decrease of Rip immunoreactivity in processes in the stratum oriens of the hippocampal CA1 region occurs at late time after ischemia, and this decrease in Rip immunoreactivity may be associated with delayed neuronal death of CA1 pyramidal cells.