Death mechanisms in status epilepticus-generated neurons and effects of additional seizures on their survival

IL-1β and HMGB1 are anti-neurogenic to endogenous neural stem cells in the sclerotic epileptic human hippocampus

BACKGROUND

The dentate gyrus exhibits life-long neurogenesis of granule-cell neurons, supporting hippocampal dependent learning and memory. Both temporal lobe epilepsy patients and animal models frequently have hippocampal-dependent learning and memory difficulties and show evidence of reduced neurogenesis. Animal and human temporal lobe epilepsy studies have also shown strong innate immune system activation, which in animal models reduces hippocampal neurogenesis. We sought to determine if and how neuroinflammation signals reduced neurogenesis in the epileptic human hippocampus and its potential reversibility.

METHODS

We isolated endogenous neural stem cells from surgically resected hippocampal tissue in 15 patients with unilateral hippocampal sclerosis. We examined resultant neurogenesis after growing them either as neurospheres in an ideal environment, in 3D cultures which preserved the inflammatory microenvironment and/or in 2D cultures which mimicked it.

RESULTS

3D human hippocampal cultures largely replicated the cellular composition and inflammatory environment of the epileptic hippocampus. The microenvironment of sclerotic human epileptic hippocampal tissue is strongly anti-neurogenic, with sustained release of the proinflammatory proteins HMGB1 and IL-1β. IL-1β and HMGB1 significantly reduce human hippocampal neurogenesis and blockade of their IL-1R and TLR 2/4 receptors by IL1Ra and Box-A respectively, significantly restores neurogenesis in 2D and 3D culture.

CONCLUSION

Our results demonstrate a HMGB1 and IL-1β-mediated environmental anti-neurogenic effect in human TLE, identifying both the IL-1R and TLR 2/4 receptors as potential drug targets for restoring human hippocampal neurogenesis in temporal lobe epilepsy.

Brain pathology in focal status epilepticus: evidence from experimental models

Status Epilepticus (SE) is often a neurological emergency characterized by abnormally sustained, longer than habitual seizures. The new ILAE classification reports that SE "…can have long-term consequences including neuronal death, neuronal injury…depending on the type and duration of seizures". While it is accepted that generalized convulsive SE exerts detrimental effects on the brain, it is not clear if other forms of SE, such as focal non-convulsive SE, leads to brain pathology and contributes to long-term deficits in patients. With the available clinical and experimental data, it is hard to discriminate the specific action of the underlying SE etiologies from that exerted by epileptiform activity. This information is highly relevant in the clinic for better treatment stratification, which may include both medical and surgical intervention for seizure control. Here we review experimental studies of focal SE, with an emphasis on focal non-convulsive SE. We present a repertoire of brain pathologies observed in the most commonly used animal models and attempt to establish a link between experimental findings and human condition(s). The extensive literature on focal SE animal models suggest that the current approaches have significant limitations in terms of translatability of the findings to the clinic. We highlight the need for a more stringent description of SE features and brain pathology in experimental studies in animal models, to improve the accuracy in predicting clinical translation.

Adult Neurogenesis in Epileptogenesis: An Update for Preclinical Finding and Potential Clinical Translation

Epileptogenesis refers to the process in which a normal brain becomes epileptic, and is characterized by hypersynchronous spontaneous recurrent seizures involving a complex epileptogenic network. Current available pharmacological treatment of epilepsy is generally symptomatic in controlling seizures but is not disease-modifying in epileptogenesis. Cumulative evidence suggests that adult neurogenesis, specifically in the subgranular zone of the hippocampal dentate gyrus, is crucial in epileptogenesis. In this review, we describe the pathological changes that occur in adult neurogenesis in the epileptic brain and how adult neurogenesis is involved in epileptogenesis through different interventions. This is followed by a discussion of some of the molecular signaling pathways involved in regulating adult neurogenesis, which could be potential druggable targets for epileptogenesis. Finally, we provide perspectives on some possible research directions for future studies.

Application of stem cell biology in treating neurodegenerative diseases

BACKGROUND

The appropriate strategies are needed for stimulating the endogenous neurogenesis or introducing extrinsic neural progenitors, which could be harnessed as the regenerative resources for cueing the neurodegenerations. Adult neurogenesis is the endogenous continuing physiology in limited brain regions such as hippocampus, olfactory system, and hypothalamus. Besides adult neurogenesis, induced pluripotent stem cells (iPSCs) induced functional neurons could be another option for regenerative therapies.

OBJECTIVE

Current studies are trying to improve the adult neurogenesis and enable the iPSCs induced neurons into neural regeneration. Methods: Here in this review, we mainly introduced the recent progress in neural stem cell biology and its application in the treatment of the neurodegenerations. We main separated the strategy in summarizing the mediators and potential targets to promoting endogenous neural regeneration and transplantation of neural progenitors.

CONCLUSION

By collecting and comparing the advantages disadvantages between above-mentioned two strategies, we will offer the insight on future development of stem cell therapy in treating neurodegenerative patients.

The evolving role of neuro-immune interaction in brain repair after cerebral ischemic stroke

Stroke is the world's leading cause of disability with limited brain repair treatments which effectively improve long-term neurological deficits. The neuroinflammatory responses persist into the late repair phase of stroke and participate in all brain repair elements, including neurogenesis, angiogenesis, synaptogenesis, remyelination and axonal sprouting, shedding new light on post-stroke brain recovery. Resident brain glial cells, such as astrocytes not only contribute to neuroinflammation after stroke, but also secrete a wide range of trophic factors that can promote post-stroke brain repair. Alternatively, activated microglia, monocytes, and neutrophils in the innate immune system, traditionally considered as major damaging factors after stroke, have been suggested to be extensively involved in brain repair after stroke. The adaptive immune system may also have its bright side during the late regenerative phase, affecting the immune suppressive regulatory T cells and B cells. This review summarizes the recent findings in the evolving role of neuroinflammation in multiple post-stroke brain repair mechanisms and poses unanswered questions that may generate new directions for future research and give rise to novel therapeutic targets to improve stroke recovery.

Neural stem cells and epilepsy: functional roles and disease-in-a-dish models

Epilepsy is a disorder of the central nervous system characterized by spontaneous recurrent seizures. Although current therapies exist to control the number and severity of clinical seizures, there are no pharmacological cures or disease-modifying treatments available. Use of transgenic mouse models has allowed an understanding of neural stem cells in their relation to epileptogenesis in mesial temporal lobe epilepsy. Further, with the significant discovery of factors necessary to reprogram adult somatic cell types into pluripotent stem cells, it has become possible to study monogenic epilepsy-in-a-dish using patient-derived neurons. This discovery along with some of the newest technological advances in recapitulating brain development in a dish has brought us closer than ever to a platform in which to study and understand the mechanisms of this disease. These technologies will be critical in understanding the mechanism of epileptogenesis and ultimately lead to improved therapies and precision medicine for patients with epilepsy.

Multi-omics profile of the mouse dentate gyrus after kainic acid-induced status epilepticus

Temporal lobe epilepsy (TLE) can develop from alterations in hippocampal structure and circuit characteristics, and can be modeled in mice by administration of kainic acid (KA). Adult neurogenesis in the dentate gyrus (DG) contributes to hippocampal functions and has been reported to contribute to the development of TLE. Some of the phenotypical changes include neural stem and precursor cells (NPSC) apoptosis, shortly after their birth, before they produce hippocampal neurons. Here we explored these early phenotypical changes in the DG 3 days after a systemic injection of KA inducing status epilepticus (KA-SE), in mice. We performed a multi-omics experimental setup and analyzed DG tissue samples using proteomics, transcriptomics and microRNA profiling techniques, detecting the expression of 2327 proteins, 13401 mRNAs and 311 microRNAs. We here present a description of how these data were obtained and make them available for further analysis and validation. Our data may help to further identify and characterize molecular mechanisms involved in the alterations induced shortly after KA-SE in the mouse DG.

Immune response in the eye following epileptic seizures

BACKGROUND

Epileptic seizures are associated with an immune response in the brain. However, it is not known whether it can extend to remote areas of the brain, such as the eyes. Hence, we investigated whether epileptic seizures induce inflammation in the retina.

METHODS

Adult rats underwent electrically induced temporal status epilepticus, and the eyes were studied 6 h, 1, and 7 weeks later with biochemical and immunohistochemical analyses. An additional group of animals received CX3CR1 antibody intracerebroventricularly for 6 weeks after status epilepticus.

RESULTS

Biochemical analyses and immunohistochemistry revealed no increased cell death and unaltered expression of several immune-related cytokines and chemokines as well as no microglial activation, 6 h post-status epilepticus compared to non-stimulated controls. At 1 week, again, retinal cytoarchitecture appeared normal and there was no cell death or micro- or macroglial reaction, apart from a small decrease in interleukin-10. However, at 7 weeks, even if the cytoarchitecture remained normal and no ongoing cell death was detected, the numbers of microglia were increased ipsi- and contralateral to the epileptic focus. The microglia remained within the synaptic layers but often in clusters and with more processes extending into the outer nuclear layer. Morphological analyses revealed a decrease in surveying and an increase in activated microglia. In addition, increased levels of the chemokine KC/GRO and cytokine interleukin-1β were found. Furthermore, macroglial activation was noted in the inner retina. No alterations in numbers of phagocytic cells, infiltrating macrophages, or vascular pericytes were observed. Post-synaptic density-95 cluster intensity was reduced in the outer nuclear layer, reflecting seizure-induced synaptic changes without disrupted cytoarchitecture in areas with increased microglial activation. The retinal gliosis was decreased by a CX3CR1 immune modulation known to reduce gliosis within epileptic foci, suggesting a common immunological reaction.

CONCLUSIONS

Our results are the first evidence that epileptic seizures induce an immune response in the retina. It has a potential to become a novel non-invasive tool for detecting brain inflammation through the eyes.

Neuronal Hyperactivity Disturbs ATP Microgradients, Impairs Microglial Motility, and Reduces Phagocytic Receptor Expression Triggering Apoptosis/Microglial Phagocytosis Uncoupling

Phagocytosis is essential to maintain tissue homeostasis in a large number of inflammatory and autoimmune diseases, but its role in the diseased brain is poorly explored. Recent findings suggest that in the adult hippocampal neurogenic niche, where the excess of newborn cells undergo apoptosis in physiological conditions, phagocytosis is efficiently executed by surveillant, ramified microglia. To test whether microglia are efficient phagocytes in the diseased brain as well, we confronted them with a series of apoptotic challenges and discovered a generalized response. When challenged with excitotoxicity in vitro (via the glutamate agonist NMDA) or inflammation in vivo (via systemic administration of bacterial lipopolysaccharides or by omega 3 fatty acid deficient diets), microglia resorted to different strategies to boost their phagocytic efficiency and compensate for the increased number of apoptotic cells, thus maintaining phagocytosis and apoptosis tightly coupled. Unexpectedly, this coupling was chronically lost in a mouse model of mesial temporal lobe epilepsy (MTLE) as well as in hippocampal tissue resected from individuals with MTLE, a major neurological disorder characterized by seizures, excitotoxicity, and inflammation. Importantly, the loss of phagocytosis/apoptosis coupling correlated with the expression of microglial proinflammatory, epileptogenic cytokines, suggesting its contribution to the pathophysiology of epilepsy. The phagocytic blockade resulted from reduced microglial surveillance and apoptotic cell recognition receptor expression and was not directly mediated by signaling through microglial glutamate receptors. Instead, it was related to the disruption of local ATP microgradients caused by the hyperactivity of the hippocampal network, at least in the acute phase of epilepsy. Finally, the uncoupling led to an accumulation of apoptotic newborn cells in the neurogenic niche that was due not to decreased survival but to delayed cell clearance after seizures. These results demonstrate that the efficiency of microglial phagocytosis critically affects the dynamics of apoptosis and urge to routinely assess the microglial phagocytic efficiency in neurodegenerative disorders.

Phagocytosis by microglia is tightly coupled to apoptosis, swiftly removing apoptotic cells and actively maintaining tissue homeostasis, but the neuronal hyperactivity associated with epilepsy disrupts the ATP gradients that drive phagocytosis, leading to the accumulation of apoptotic cells and inflammation.

Phagocytosis, the engulfment and digestion of cellular debris, is at the core of the regenerative response of the damaged tissue, because it prevents the spillover of toxic intracellular contents and is actively anti-inflammatory. In the brain, the professional phagocytes are microglia, whose dynamic processes rapidly engulf and degrade cells undergoing apoptosis—programmed cell death—in physiological conditions. Thus, microglia hold the key to brain regeneration, but their efficiency as phagocytes in the diseased brain is only presumed. Here, we have discovered a generalized response of microglia to apoptotic challenge induced by excitotoxicity and inflammation, in which they boost their phagocytic efficiency to account for the increase in apoptosis. To our surprise, this apoptosis/microglial phagocytosis coupling was lost in the hippocampus from human and experimental mesial temporal lobe epilepsy (MTLE), a major neurodegenerative disorder characterized by excitotoxicity, inflammation, and seizures. This uncoupling was due to widespread ATP release during neuronal hyperactivity, which “blinded” microglia to the ATP microgradients released by apoptotic cells as “find-me” signals. The impairment of phagocytosis led to the accumulation of apoptotic cells and the build-up of a detrimental inflammatory reaction. Our data advocates for systematic assessment of the efficiency of microglial phagocytosis in brain disorders.

Control of Cell Survival in Adult Mammalian Neurogenesis

The fact that continuous proliferation of stem cells and progenitors, as well as the production of new neurons, occurs in the adult mammalian central nervous system (CNS) raises several basic questions concerning the number of neurons required in a particular system. Can we observe continued growth of brain regions that sustain neurogenesis? Or does an elimination mechanism exist to maintain a constant number of cells? If so, are old neurons replaced, or are the new neurons competing for limited network access among each other? What signals support their survival and integration and what factors are responsible for their elimination? This review will address these and other questions regarding regulatory mechanisms that control cell-death and cell-survival mechanisms during neurogenesis in the intact adult mammalian brain.

Dendritic morphology, synaptic transmission, and activity of mature granule cells born following pilocarpine-induced status epilepticus in the rat

To understand the potential role of enhanced hippocampal neurogenesis after pilocarpine-induced status epilepticus (SE) in the development of epilepsy, we quantitatively analyzed the geometry of apical dendrites, synaptic transmission, and activation levels of normotopically distributed mature newborn granule cells in the rat. SE in male Sprague-Dawley rats (between 6 and 7 weeks old) lasting for more than 2 h was induced by an intraperitoneal injection of pilocarpine. The complexity, spine density, miniature post-synaptic currents, and activity-regulated cytoskeleton-associated protein (Arc) expression of granule cells born 5 days after SE were studied between 10 and 17 weeks after CAG-GFP retroviral vector-mediated labeling. Mature granule cells born after SE had dendritic complexity similar to that of granule cells born naturally, but with denser mushroom-like spines in dendritic segments located in the outer molecular layer. Miniature inhibitory post-synaptic currents (mIPSCs) were similar between the controls and rats subjected to SE; however, smaller miniature excitatory post-synaptic current (mEPSC) amplitude with a trend toward less frequent was found in mature granule cells born after SE. After maturation, granule cells born after SE did not show denser Arc expression in the resting condition or 2 h after being activated by pentylenetetrazol-induced transient seizure activity than vicinal GFP-unlabeled granule cells. Thus our results suggest that normotopic granule cells born after pilocarpine-induced SE are no more active when mature than age-matched, naturally born granule cells.

MicroRNA-124 and -137 cooperativity controls caspase-3 activity through BCL2L13 in hippocampal neural stem cells

Adult neurogenesis continuously contributes new neurons to hippocampal circuits and the programmed death of a subset of immature cells provides a primary mechanism controlling this contribution. Epileptic seizures induce strong structural changes in the hippocampus, including the induction of adult neurogenesis, changes in gene expression and mitochondrial dysfunction, which may all contribute to epileptogenesis. However, a possible interplay between this factors remains largely unexplored. Here, we investigated gene expression changes in the hippocampal dentate gyrus shortly after prolonged seizures induced by kainic acid, focusing on mitochondrial functions. Using comparative proteomics, we identified networks of proteins differentially expressed shortly after seizure induction, including members of the BCL2 family and other mitochondrial proteins. Within these networks, we report for the first time that the atypical BCL2 protein BCL2L13 controls caspase-3 activity and cytochrome C release in neural stem/progenitor cells. Furthermore, we identify BCL2L13 as a novel target of the cooperative action of microRNA-124 and microRNA-137, both upregulated shortly after seizure induction. This cooperative microRNA-mediated fine-tuning of BCL2L13 expression controls casp3 activity, favoring non-apoptotic caspase-3 functions in NSPC exposed to KA and thereby may contribute to the early neurogenic response to epileptic seizures in the dentate gyrus.

Status epilepticus increases mature granule cells in the molecular layer of the dentate gyrus in rats

Enhanced neurogenesis in the dentate gyrus of the hippocampus following seizure activity, especially status epilepticus, is associated with ectopic residence and aberrant integration of newborn granule cells. Hilar ectopic granule cells may be detrimental to the stability of dentate circuitry by means of their electrophysiological properties and synaptic connectivity. We hypothesized that status epilepticus also increases ectopic granule cells in the molecular layer. Status epilepticus was induced in male Sprague-Dawley rats by intraperitoneal injection of pilocarpine. Immunostaining showed that many doublecortin-positive cells were present in the molecular layer and the hilus 7 days after the induction of status epilepticus. At least 10 weeks after status epilepticus, the estimated number of cells positive for both prospero homeobox protein 1 and neuron-specific nuclear protein in the hilus was significantly increased. A similar trend was also found in the molecular layer. These findings indicate that status epilepticus can increase the numbers of mature and ectopic newborn granule cells in the molecular layer.

Mood stabilizers commonly restore staurosporine-induced increase of p53 expression and following decrease of Bcl-2 expression in SH-SY5Y cells

Adult neurogenesis in dentate gyrus (DG) is involved in the action mechanism of mood stabilizers. However, it is poorly understood how mood stabilizers affect adult neurogenesis in DG. Neurogenesis consists of proliferation, survival (anti-apoptosis) and differentiation of neural precursor cells in adult DG. Using in vitro culture of adult rat DG-derived neural precursor cells (ADP), we have already shown that four mood stabilizers, such as lithium (Li), valproate (VPA), carbamazepine (CBZ) and lamotrigine (LTG), commonly decrease staurosporine (STS)-induced apoptosis of ADP. These suggest that the common anti-apoptotic effect of mood stabilizers could be involved in mood-stabilizing effects. Past studies have shown that Li and VPA increase the expression of Bcl-2, an anti-apoptotic gene. In addition, it has been shown that Li decreases the expression of p53, which plays a prominent role in apoptosis and regulates the expression of Bcl-2. Therefore, p53 and Bcl-2 can be considered to mediate the common anti-apoptotic effects of Li, VPA, CBZ and LTG. To elucidate the molecular mechanism underlying the common anti-apoptotic effects of mood stabilizers, we investigated the effects of Li, VPA, CBZ and LTG on STS-induced expression changes of p53, Bcl-2 and other p53-related molecules using SH-SY5Y cells as a model of neural precursor-like cells. STS increased the expression of p53 and decreased that of Bcl-2. These effects of STS on p53 and Bcl-2 are restored by all of Li, VPA, CBZ and LTG. In addition, p53 overexpression decreased the expression of Bcl-2. Taken together, these results suggest that p53 and Bcl-2 may be involved in a part of mood-stabilizing effects.

Proton MR spectroscopy of neural stem cells: does the proton-NMR peak at 1.28 ppm function as a biomarker for cell type or state?

Recently, a peak at 1.28 ppm in proton magnetic resonance spectroscopy ((1)H-MRS) of neural stem cells (NSCs) was introduced as a noninterventional biomarker for neurogenesis in vivo. This would be an urgently needed requisite for translational studies in humans regarding the beneficial role of adult neurogenesis for the structural and functional integrity of the brain. However, many concerns have risen about the validity of the proposed signal as a specific marker for NSCs. The peak has also been related to cell-type-independent phenomena such as apoptosis or necrosis. Thus, we compared the 1.28-ppm peak in various immature stem cell populations, including embryonic stem cells, mouse embryonic fibroblasts, embryonic stem cell- and induced pluripotent stem cell-derived NSCs, ex vivo isolated embryonic NSCs, as well as mature and tumor cell types from different germ layers. To correlate the integral peak intensity with cell death, we induced both apoptosis with camptothecin and necrosis with sodium azide. A peak at 1.28 ppm was found in most cell types, and in most, but not all, NSCH cultures, demonstrating no specificity for NSCs. The intensities of the 1.28-ppm resonance significantly correlated with the rate of apoptosis, but not with the rate of necrosis, cell cycle phase distribution, cell size, or type. Multiple regression analysis displayed a significant predictive value of the peak intensity for apoptosis only. In this context, its specificity for apoptosis as a major selection process during neurogenesis may suggest this resonance as an indirect marker for neurogenesis in vivo.

Microglia shape adult hippocampal neurogenesis through apoptosis-coupled phagocytosis

In the adult hippocampus, neuroprogenitor cells in the subgranular zone (SGZ) of the dentate gyrus give rise to newborn neuroblasts. However, only a small subset of these cells integrates into the hippocampal circuitry as mature neurons at the end of a 4 week period. Here, we show that the majority of the newborn cells undergo death by apoptosis in the first 1 to 4 days of their life, during the transition from amplifying neuroprogenitors to neuroblasts. These apoptotic newborn cells are rapidly cleared out through phagocytosis by unchallenged microglia present in the adult SGZ niche. Phagocytosis by the microglia is efficient and undeterred by increased age or inflammatory challenge. Our results suggest that the main critical period of newborn cell survival occurs within a few days of birth and reveal a new role for microglia in maintaining the homeostasis of the baseline neurogenic cascade.

Effects of mood stabilizers on adult dentate gyrus-derived neural precursor cells

Neurogenesis in the adult dentate gyrus (DG) is considered to be partly involved in the action of mood stabilizers. However, it remains unclear how mood stabilizers affect neural precursor cells in adult DG. We have established a culture system of adult rat DG-derived neural precursor cells (ADP) and have shown that lithium, a mood stabilizer, and dexamethasone, an agonist of glucocorticoid receptor, reciprocally regulate ADP proliferation. Neurogenesis constitutes not only proliferation of neural precursor cells but also apoptosis and differentiation. To develop further understanding of mood stabilizer effects on neural precursor cells in adult DG, we investigated and compared the effects of four common mood stabilizers-lithium, valproate, carbamazepine, and lamotrigine-on ADP proliferation, apoptosis, and differentiation. ADP proliferation, decreased by dexamethasone, was examined using Alamar Blue assay. Using TUNEL assay, ADP apoptosis induced by staurosporine was examined. The differentiated ADP induced by retinoic acid was characterized by immunostaining with anti-GFAP or anti-Tuj1 antibody. Lithium and valproate, but not carbamazepine and lamotrigine, recovered ADP proliferation decreased by dexamethasone. All four mood stabilizers decreased ADP apoptosis. Retinoic acid differentiated ADP into both neurons and astrocytes. Lithium and carbamazepine increased the ratio of neurons and decreased that of astrocytes. However, valproate and lamotrigine increased the ratio of astrocytes and decreased that of neurons. Therefore, these four stabilizers exhibited both common and differential effects on ADP proliferation, apoptosis, and differentiation.

Water maze experience and prenatal choline supplementation differentially promote long-term hippocampal recovery from seizures in adulthood

Status epilepticus (SE) in adulthood dramatically alters the hippocampus and produces spatial learning and memory deficits. Some factors, like environmental enrichment and exercise, may promote functional recovery from SE. Prenatal choline supplementation (SUP) also protects against spatial memory deficits observed shortly after SE in adulthood, and we have previously reported that SUP attenuates the neuropathological response to SE in the adult hippocampus just 16 days after SE. It is unknown whether SUP can ameliorate longer-term cognitive and neuropathological consequences of SE, whether repeatedly engaging the injured hippocampus in a cognitive task might facilitate recovery from SE, and whether our prophylactic prenatal dietary treatment would enable the injured hippocampus to more effectively benefit from cognitive rehabilitation. To address these issues, adult offspring from rat dams that received either a control (CON) or SUP diet on embryonic days 12-17 first received training on a place learning water maze task (WM) and were then administered saline or kainic acid (KA) to induce SE. Rats then either remained in their home cage, or received three additional WM sessions at 3, 6.5, and 10 weeks after SE to test spatial learning and memory retention. Eleven weeks after SE, the brains were analyzed for several hippocampal markers known to be altered by SE. SUP attenuated SE-induced spatial learning deficits and completely rescued spatial memory retention by 10 weeks post-SE. Repeated WM experience prevented SE-induced declines in glutamic acid decarboxylase (GAD) and dentate gyrus neurogenesis, and attenuated increased glial fibrilary acidic protein (GFAP) levels. Remarkably, SUP alone was similarly protective to an even greater extent, and SUP rats that were water maze trained after SE showed reduced hilar migration of newborn neurons. These findings suggest that prophylactic SUP is protective against the long-term cognitive and neuropathological effects of KA-induced SE, and that rehabilitative cognitive enrichment may be partially beneficial.

Effects of lamotrigine and topiramate on hippocampal neurogenesis in experimental temporal-lobe epilepsy

Lamotrigine (LTG) and topiramate (TPM), two of the most commonly used new-generation antiepileptic drugs (AEDs), have been shown to produce no adverse and impaired cognitive effects in patients with epilepsy, respectively. As seizure-induced neurogenesis might contribute to cognitive deficits that are associated with status epilepticus (SE), we examined whether these two drugs produce differential effects on seizure-induced neurogenesis in the hippocampus of adult rats. Lithium pilocarpine model was used to mimic human temporal-lobe epilepsy. Five hours after SE, LTG and TPM were administered intragastrically twice daily throughout the entire length of the experiment with total daily dose of 20 and 80 mg/kg, respectively. The hippocampal neurogenesis was examined using 5-bromodeoxyuridine and doublecortin immunohistochemistry. Both LTG and TPM treatments significantly inhibited seizure-induced proliferation of neural progenitors in the hippocampus, but did not affect the neuronal differentiation of newborn cells. Long-term treatment with both AEDs decreased the number of spontaneous recurrent seizures after SE and alleviated chronic seizure-induced neuronal injury in the dentate hilus. Eventually, TPM significantly increased the number of newborn neurons in the dentate granular cell layer after seizures likely by promoting the survival of newborn neurons. In contrast, LTG treatment significantly reduced the number of ectopic hilar newborn neurons after seizures. Neither of them prevented the formation of hilar basal dendrites of newborn neurons in the epileptic hippocampus. These results indicate that TPM but not LTG promotes aberrant neuron regeneration in the hippocampus after SE, which might be partially related to their differential effects on cognitive function.

Long-term accumulation of microglia with proneurogenic phenotype concomitant with persistent neurogenesis in adult subventricular zone after stroke

Neural stem cells (NSCs) in the adult rat subventricular zone (SVZ) generate new striatal neurons during several months after ischemic stroke. Whether the microglial response associated with ischemic injury extends into SVZ and influences neuroblast production is unknown. Here, we demonstrate increased numbers of activated microglia in ipsilateral SVZ concomitant with neuroblast migration into the striatum at 2, 6, and 16 weeks, with maximum at 6 weeks, following 2 h middle cerebral artery occlusion in rats. In the peri-infarct striatum, numbers of activated microglia peaked already at 2 weeks and declined thereafter. Microglia in SVZ were resident or originated from bone marrow, with maximum proliferation during the first 2 weeks postinsult. In SVZ, microglia exhibited ramified or intermediate morphology, signifying a downregulated inflammatory profile, whereas amoeboid or round phagocytic microglia were frequent in the peri-infarct striatum. Numbers of microglia expressing markers of antigen-presenting cells (MHC-II, CD86) increased in SVZ but very few lymphocytes were detected. Using quantitative PCR, strong short- and long-term increase (at 1 and 6 weeks postinfarct) of insulin-like growth factor-1 (IGF-1) gene expression was detected in SVZ tissue. Elevated numbers of IGF-1-expressing microglia were found in SVZ at 2, 6, and 16 weeks after stroke. At 16 weeks, 5% of microglia but no other cells in SVZ expressed the IGF-1 protein, which mitigates apoptosis and promotes proliferation and differentiation of NSCs. The long-term accumulation of microglia with proneurogenic phenotype in the SVZ implies a supportive role of these cells for the continuous neurogenesis after stroke.

Time course and mechanism of hippocampal neuronal death in an in vitro model of status epilepticus: role of NMDA receptor activation and NMDA dependent calcium entry

The hippocampus is especially vulnerable to seizure-induced damage and excitotoxic neuronal injury. This study examined the time course of neuronal death in relationship to seizure duration and the pharmacological mechanisms underlying seizure-induced cell death using low magnesium (Mg2+) induced continuous high frequency epileptiform discharges (in vitro status epilepticus) in hippocampal neuronal cultures. Neuronal death was assessed using cell morphology and fluorescein diacetate-propidium iodide staining. Effects of low Mg2+ and various receptor antagonists on spike frequency were assessed using patch clamp electrophysiology. We observed a linear and time-dependent increase in neuronal death with increasing durations of status epilepticus. This cell death was dependent upon extracellular calcium (Ca2+) that entered primarily through the N-methyl-d-aspartate (NMDA) glutamate receptor channel subtype. Neuronal death was significantly decreased by co-incubation with the NMDA receptor antagonists and was also inhibited by reduction of extracellular (Ca2+) during status epilepticus. In contrast, neuronal death from in vitro status epilepticus was not significantly prevented by inhibition of other glutamate receptor subtypes or voltage-gated Ca2+ channels. Interestingly this NMDA-Ca2+ dependent neuronal death was much more gradual in onset compared to cell death from excitotoxic glutamate exposure. The results provide evidence that in vitro status epilepticus results in increased activation of the NMDA-Ca2+ transduction pathway leading to neuronal death in a time-dependent fashion. The results also indicate that there is a significant window of opportunity during the initial time of continuous seizure activity to be able to intervene, protect neurons and decrease the high morbidity and mortality associated with status epilepticus.

Microglia induce neurotoxicity via intraneuronal Zn(2+) release and a K(+) current surge

Microglial cells are critical components of the injurious cascade in a large number of neurodegenerative diseases. However, the precise molecular mechanisms by which microglia mediate neuronal cell death have not been fully delineated. We report here that reactive species released from activated microglia induce the liberation of Zn(2+) from intracellular stores in cultured cortical neurons, with a subsequent enhancement in neuronal voltage-gated K(+) currents, two events that have been intimately linked to apoptosis. Both the intraneuronal Zn(2+) release and the K(+) current surge could be prevented by the NADPH oxidase inhibitor apocynin, the free radical scavenging mixture of superoxide dismutase and catalase, as well as by 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato iron(III) chloride. The enhancement of K(+) currents was prevented by neuronal overexpression of metallothionein III or by expression of a dominant negative (DN) vector for the upstream mitogen-activated protein kinase apoptosis signal regulating kinase-1 (ASK-1). Importantly, neurons overexpressing metallothionein-III or transfected with DN vectors for ASK-1 or Kv2.1-encoded K(+) channels were resistant to microglial-induced toxicity. These results establish a direct link between microglial-generated oxygen and nitrogen reactive products and neuronal cell death mediated by intracellular Zn(2+) release and a surge in K(+) currents.

Seizures in the developing brain: cellular and molecular mechanisms of neuronal damage, neurogenesis and cellular reorganization

Epilepsy is a common neurological disorder that occurs more frequently in children than in adults. The extent that prolonged seizure activity, i.e. status epilepticus (SE), and repeated, brief seizures affect neuronal structure and function in both the immature and mature brain has been the subject of increasing clinical and experimental research. Earlier studies suggest that seizure-induced effects in the immature brain compared with the adult brain are different. This is manifested as differences in neuronal vulnerability, cellular and synaptic reorganization and regenerative processes. The focus of this review is first to give a short overview of currently used experimental models of epilepsy in immature rats, and then discuss more thoroughly seizure-induced acute and sub-acute cellular and molecular alterations, highlight the contribution of inflammatory-like reactions and intracellular cytoskeleton to the insult, and reveal changes in the structure and function of inhibitory GABA(A) and excitatory glutamate receptors. The role of seizure-activated reparative, plastic processes, synaptic remodelling, neurogenesis as well as the long-term consequences of seizures are briefly outlined. The main emphasis is put on studies carried out in experimental animals, and the focus of interest is the hippocampus, the brain area of great vulnerability in epilepsy. In vitro studies are discussed only to limited extent. Collectively, recent studies suggest that the deleterious effects of seizures may not solely be a consequence of neuronal damage and loss per se, but could be due to the fact that seizures interfere with the highly regulated developmental processes in the immature brain.

Dynamic changes of proteases and protease inhibitors revealed by microarray analysis in CA3 and entorhinal cortex during epileptogenesis in the rat

We investigated expression of genes involved in the proteolytic process during epileptogenesis in a rat model of temporal lobe epilepsy (TLE). In a previous microarray study we found prominent activation of this process, which reached highest expression during the acute and latent phase (1 week after SE) in CA3 and entorhinal cortex (EC). Detailed analysis shows differences in dynamics of the changes of several protease genes such as cathepsins, caspases, matrix metalloproteinases, and plasminogen activators. Most genes were acutely upregulated while others were mainly activated during the latent phase. Interestingly several proteolytic genes were still elevated in the chronic epileptic phase. Various protease inhibitors followed a similar time course. The identification of changes in the activation of genes involved in proteolysis at critical phases during epileptogenesis could point to potential time specific targets for intervention. The fact that several proteolytic genes were still activated in the chronic epileptic phase makes them interesting candidates to modify and slow down seizure progression.

TDAG51 in the anterior temporal neocortex of patients with intractable epilepsy

TDAG51 (T cell death-associated gene 51) is an apoptosis-associated protein. Our aim was to investigate TDAG51 expression in the anterior temporal neocortex of patients with intractable epilepsy (IE), and then to discuss the possible role of TDAG51 in IE. Tissue samples from the anterior temporal neocortex of 33 patients who had surgery for IE were used to detect TDAG51 expression by immunohistochemistry, immunofluorescence, and Western blotting. We compared these tissues with nine histologically normal anterior temporal lobes from intracranial hypertension patients who had decompression procedures. TDAG51 was mainly expressed in the cytoplasm of neurons and glial cells. TDAG51 in IE was significantly higher than that in the controls. These findings were consistently observed using Western blotting, immunofluorescence, and immunohistochemistry techniques. TDAG51 in patients with IE was significantly higher when compared with levels in the controls. This finding suggests TDAG51 is consistent with a possible role of this gene in the evolution of the pathology in IE.

In vivo EPR estimation of bilateral hippocampal antioxidant ability of rats with epileptogenesis induced by amygdalar FeCl3 microinjection

PURPOSE

To measure the neural antioxidant function in the hippocampus of rats with epileptogenesis induced by microinjection of FeCl3 into the amygdala using the decay rate of the nitroxide radical as estimated by L-band electron paramagnetic resonance (EPR) spectroscopy.

MATERIALS AND METHODS

Region-selected intensity determination (RSID) was used for the estimation of the nitroxide decay ratio. It is possible to estimate the in vivo hippocampal antioxidant ability using the half-life of the EPR signal of the blood-brain barrier-permeable nitroxide radical. Rats were microinjected with aqueous FeCl3 into the right amygdaloid body. Recording from chronically implanted depth electrodes showed the development of spike discharges with recurrent seizures arising from amygdalar regions with propagation into both hippocampi. Rats with unilateral aqueous FeCl3 lesions were injected systemically with the nitroxide radical and then had EPR for RSID estimation at 5, 15, and 30 days after the iron salt injection.

RESULTS

The in vivo antioxidant ability of the dorsal hippocampus was significantly decreased bilaterally in animals with FeCl3-induced seizures when compared to the control.

CONCLUSION

Neural antioxidant function in the hippocampi of rats with chronic seizures induced by amygdalar FeCl3 was decreased early and both ipsilaterally and bilaterally.

Selective vulnerability of hippocampal NAAGergic neurons in experimental temporal lobe epilepsy

The dipeptide N-acetylaspartylglutamate (NAAG) has been recently implicated in numerous neurological disorders. NAAG binds and stimulates group II metabotropic glutamate receptors producing a down-modulation of synaptic glutamate release. In the present immunohistochemical study, we compare the distribution of NAAG-containing (NAAGergic) neurons between the hippocampus of control and chronic epileptic rats obtained with the pilocarpine model of temporal lobe epilepsy. In the hippocampal formation, NAAGergic neurons comprise a subpopulation of GABAergic neurons. Examination by light microscopy revealed a significant reduction of NAAG-immunoreactive neurons in CA3 stratum oriens (35.8%) and CA1 stratum oriens (78.87%), stratum pyramidale (40%), and stratum radiatum (56.6%). Similar loss of NAAGergic neurons was observed in the subiculum characterized by 71.82% and 77.53% reduction in the stratum oriens and radiatum, respectively, when compared with controls. NAAGergic neurons in CA2 and dentate gyrus were apparently resistant to seizure-related cell loss but appeared more complex and exhibited numerous NAAG-positive puncta. Our findings indicate a selective vulnerability of NAAGergic neurons in temporal lobe epilepsy.

Relevance of seizure-induced neurogenesis in animal models of epilepsy to the etiology of temporal lobe epilepsy

Seizure induction in laboratory animals is followed by many changes in structure and function, and one of these is an increase in neurogenesis-the birth of new neurons. This phenomenon may be relevant to temporal lobe epilepsy (TLE), because one of the regions of the brain where seizure-induced neurogenesis is most robust is the dentate gyrus-an area of the brain that has been implicated in the pathophysiology of TLE. Although initial studies predicted that neurogenesis in the dentate gyrus would be important to normal functions, such as learning and memory, the new neurons that are born after seizures may not necessarily promote normal function. There appears to be a complex functional and structural relationship between the new dentate gyrus neurons and preexisting cells, both in the animal models of TLE and in tissue resected from patients with intractable TLE. These studies provide new insights into the mechanisms of TLE, and suggest novel strategies for intervention that could be used to prevent or treat TLE.

Up-regulation of cation-independent mannose 6-phosphate receptor and endosomal-lysosomal markers in surviving neurons after 192-IgG-saporin administrations into the adult rat brain

The cation-independent mannose 6-phosphate receptor (CI-MPR) is a single transmembrane domain glycoprotein that plays a major role in the trafficking of lysosomal enzymes from the trans-Golgi network to the endosomal-lysosomal (EL) system. Because dysfunction of EL system is associated with a variety of neurodegenerative disorders, it is possible that the CI-MPR may have a role in regulating neuronal viability after toxicity/injury. In the present study, we report that 192-IgG-saporin-induced loss of basal forebrain cholinergic neurons causes a transient up-regulation of CI-MPR protein levels in surviving neurons of the basal forebrain and frontal cortex but not in the brainstem region, which was relatively spared by the immunotoxin. This was accompanied by a parallel time-dependent increase in other EL markers, ie, cathepsin D, Rab5, and LAMP2 in the basal forebrain region, whereas in the frontal cortex the levels of cathepsin D, and to some extent Rab5, were increased. Given the critical role of the EL system in the clearance of abnormal proteins in response to changing conditions, it is likely that the observed increase in the CI-MPR and components of the EL system in surviving neurons after 192-IgG-saporin treatment represents an adaptive mechanism to restore the metabolic/structural abnormalities induced by the loss of cholin-ergic neurons.

Prostaglandin E2 and BDNF levels in rat hippocampus are negatively correlated with status epilepticus severity: No impact on survival of seizure-generated neurons

Partial and generalized status epilepticus (pSE and gSE) trigger the same level of progenitor cell proliferation in adult dentate gyrus, but survival of new neurons is poor after gSE. Here, we show markedly elevated levels of prostaglandin E2 (PGE2) and brain-derived neurotrophic factor (BDNF) in rat hippocampal formation at 7 days following pSE but not gSE. Administration of the cyclooxygenase (COX) inhibitor flurbiprofen for 1 week, starting at day 8 post-SE, abated PGE2 and decreased BDNF levels, but did not affect survival of new neurons 4 weeks later. Thus, high PGE2 and BDNF levels induced by pSE are probably not of major importance for survival of new neurons during the first days after formation. We propose that they modulate other aspects of synaptic and cellular plasticity, and thereby may influence epileptogenesis.

Long-term neuronal replacement in adult rat hippocampus after status epilepticus despite chronic inflammation

Dentate gyrus (DG) neurogenesis is transiently increased during the first weeks after status epilepticus (SE). Survival of the new neurons is initially compromised by an acute inflammatory response, but the long-term fate of the remaining ones in the post-SE environment is unknown. Here adult rats were subjected to 2 h electrically evoked self-sustained SE and perfused after 5 weeks or 6 months. Rats exhibited partial or generalized SE followed by spontaneous behavioural seizures and abnormal electroencephalographic activity during 6 months. Numbers of activated microglia in the dentate subgranular zone (SGZ)-granule cell layer (GCL) and in the hilus declined after 5 weeks, but were still elevated at 6 months after SE, with no differences between the milder partial and the more severe generalized SE. At 6 months, partial and generalized SE rats showed a seven-fold increase in the number of mature SGZ-GCL neurons formed during the first 2 weeks along with aberrant neurons in the hilus. Total numbers of mature neurons in SGZ-GCL were unaltered, indicating that SE-generated neurons replaced dead granule cells. Neuroblast formation had returned to normal levels in SGZ-GCL but generation of aberrant neurons in the hilus was still ongoing at 6 months. Our data indicate that long-term impairment of neurogenesis, as reported previously after kainic acid-induced SE, is not a general feature of chronic epilepsy. We have found that a substantial proportion of the mature granule cells at 6 months are generated during the first 2 weeks after SE and survive despite chronic inflammation, and that SE triggers continuous production of aberrant hilar neurons.

Serum Fas and Bcl-2 in patients with epilepsy

OBJECTIVES

The present study aimed to investigate the levels of the biochemical markers of apoptosis (soluble Fas and Bcl-2) in the sera of children and adolescents with idiopathic epilepsy.

MATERIALS AND METHODS

The study included 30 children and adolescents (mean age 8.03 +/- 4.49 years) with idiopathic epilepsy, 16 of them were newly diagnosed, and 15 clinically healthy control subjects. Of the included patients, 22 had focal seizures and eight had generalized seizures. In addition to laboratory and radiological investigations needed for diagnosis and follow-up, soluble Fas (s.Fas) and Bcl-2 were assayed in sera of patients and controls by enzyme-linked immunosorbent assay technique.

RESULTS

Serum levels of s.Fas and Bcl-2 were significantly higher in the patients group than in the control group; however, their levels were comparable in patients with different seizure types. Levels of s.Fas correlated positively with seizure severity and negatively with the duration from the last attack. Bcl-2 levels were positively correlated to each of the duration of epilepsy, the severity of seizures and its frequency. There was a significant positive correlation between serum levels of s.Fas and that of Bcl-2 and both were significantly increased in patients with uncontrolled epilepsy.

CONCLUSION

The present data demonstrate that markers of apoptosis, both the proapoptotic Fas and the anti-apoptotic Bcl-2, were proportionately elevated in sera of patients with idiopathic epilepsy, and their levels were related to the seizure severity and frequency.

Impairment of dentate gyrus neuronal progenitor cell differentiation in a mouse model of temporal lobe epilepsy

Unilateral intrahippocampal injection of kainic acid (KA) in adult mice induces an epileptic focus replicating major histopathological features of temporal lobe epilepsy (TLE). In this model, neurogenesis is impaired in the lesioned dentate gyrus, although cell proliferation transiently is increased bilaterally in the subgranular zone (SGZ). To investigate further the relationship between epileptogenesis and neurogenesis, we compared the differentiation of cells born shortly before and after KA injection. Immunohistochemical staining for doublecortin and PSA-NCAM, two markers of young neurons, revealed a rapid downregulation of both markers ipsilaterally, whereas they were increased transiently on the contralateral side. To determine whether KA treatment directly affects neural progenitors in the SGZ, dividing cells were prelabeled with 5'-bromo-2'deoxyuridine (BrdU) treatment before unilateral injection of KA. Double staining with the proliferation marker PCNA showed that prelabeled BrdU cells survived KA exposure and proliferated bilaterally. Unexpectedly, the neuronal differentiation of these cells, as assessed after 2 weeks with doublecortin and NeuN triple-staining, occurred to the same extent as on the contralateral side. Only 5% of pre-labeled BrdU cells were GFAP-positive within the lesion. Therefore, SGZ progenitor cells committed to a neuronal phenotype before KA treatment complete their differentiation despite the rapid down-regulation of doublecortin and PSA-NCAM. These findings suggest impaired fate commitment and/or early differentiation of proliferating cells in the lesioned dentate gyrus. Loss of neurogenesis in this TLE model likely reflects an irreversible alteration of the SGZ germinal niche during development of the epileptic focus and may therefore be relevant for human TLE.

Kindled seizures enhance young neuron survival in the adult rat dentate gyrus

New neurons continue to be generated throughout adulthood in the dentate gyrus of mammals. This process of neurogenesis is believed to play a role in some forms of learning and memory. Hippocampal-dependent learning tasks have been shown to specifically enhance the survival of new granule neurons. The present study examined the effects of kindled seizures in rats on the survival of young neurons born before the kindling began. Kindled seizures within the perforant path input to the dentate gyrus triggered between 1 and 2 weeks following the injection of bromodeoxyuridine (BrdU), were found to increase the number of BrdU and NeuN co-labeled cells in the granule cell layer by 128% 1 month later. The number of co-labeled cells was not correlated with measures of seizure severity. These results demonstrate that kindled seizures enhance the survival of new born neurons in the adult rat dentate gyrus which may reflect the actions of an activity-dependent mechanism normally involved in hippocampal-dependent learning and memory.

Increased expression of ferritin, an iron-storage protein, in specific regions of the parahippocampal cortex of epileptic rats

PURPOSE

Iron accumulation in the brain has been associated with neurodegenerative disorders, including epilepsy. In our previous SAGE study, we showed that ferritin, an iron-storage protein, was one of the genes (Ferritin-H) that showed overexpression before the chronic epileptic phase. In this study we used ferritin as indicator for disturbed iron homeostasis to acquire insight into whether this could play a role in the pathogenesis of temporal lobe epilepsy.

METHODS

With immunocytochemistry, we studied the regional and cellular distribution of ferritin protein in an animal model for temporal lobe epilepsy in which spontaneous seizures develop a few weeks after electrically induced status epilepticus (SE).

RESULTS

Increased ferritin expression was observed in regions known to be vulnerable to cell death, mainly in reactive microglial cells of epileptic rats. Ferritin expression after SE was initially high, especially throughout the hippocampus, but decreased over time. In the chronic epileptic phase, it was still upregulated in regions where extensive cell loss occurs during the early acute and latent period. Within the parahippocampal region, the most persistent ferritin overexpression was present in microglial cells in layer III of the medial entorhinal area. The upregulation was most extensive in rats that had developed a progressive form of epilepsy with frequent seizures (approximately five to 10 seizures per day).

CONCLUSIONS

The fact that ferritin upregulation is still present in specific limbic regions in chronic epileptic rats, when neuronal loss is absent or minimal, suggests a role of iron in the pathogenesis and progression of epilepsy.

Persistent production of neurons from adult brain stem cells during recovery after stroke

Neural stem cells in the subventricular zone of adult rodents produce new striatal neurons that may replace those that have died after stroke; however, the neurogenic response has been considered acute and transient, yielding only small numbers of neurons. In contrast, we show herein that striatal neuroblasts are generated without decline at least for 4 months after stroke in adult rats. Neuroblasts formed early or late after stroke either differentiate into mature neurons, which survive for several months, or die through caspase-mediated apoptosis. The directed migration of the new neurons toward the ischemic damage is regulated by stromal cell-derived factor-1alpha and its receptor CXCR4. These results show that endogenous neural stem cells continuously supply the injured adult brain with new neurons, which suggests novel self-repair strategies to improve recovery after stroke.

Progenitor cell injury after irradiation to the developing brain can be modulated by mild hypothermia or hyperthermia

Ionizing radiation induced acute cell death in the dentate gyrus subgranular zone (SGZ) and the subventricular zone (SVZ). Hypomyelination was also observed. The effects of mild hypothermia and hyperthermia for 4 h after irradiation (IR) were studied in postnatal day 9 rats. One hemisphere was irradiated with a single dose of 8 Gy and animals were randomized to normothermia (rectal temperature 36 degrees C for 4 h), hypothermia (32 degrees C for 4 h) or hyperthermia (39 degrees C for 4 h). Cellular injury, e.g. chromatin condensation and nitrotyrosine formation, appeared to proceed faster when the body temperature was higher. Caspase-3 activation was more pronounced in the hyperthermia group and nuclear translocation of p53 was less pronounced in the hypothermia group 6 h after IR. In the SVZ the loss of nestin-positive progenitors was more pronounced (48%) and the size was smaller (45%) in the hyperthermia group 7 days post-IR. Myelination was not different after hypo- or hyperthermia. This is the first report to demonstrate that hypothermia may be beneficial and that hyperthermia may aggravate the adverse side-effects after radiation therapy to the developing brain.

Characterization of cell proliferation in the adult dentate under normal conditions and after kainate induced seizures using ribonucleotide reductase and BrdU

Ribonucleotide reductase (RNR), an enzyme for DNA synthesis, was recently used as a marker of proliferating cells in the dentate gyrus and subventricular zone in normal adult mammalian brains. However, the duration of RNR expression in normal adult brain and the expression pattern of RNR in the adult dentate gyrus following brain injury have not been explored. In this study, we examined the duration of the RNR expression in newborn cells in the normal adult rat brain by analysis of RNR and BrdU double-labeled specimens at different time intervals after BrdU application. Secondly, we induced, in adult rats, seizures by kainic acid and investigated the changes in expression of RNR following seizures, and characterized the phenotype of RNR-positive cells using a variety of other markers. Our results revealed that RNR was detectable in proliferating cells from 2 h to at least 1 day. At 7 and 28 days after seizures, there was a fivefold increase in number of clusters of RNR-positive cells in the dentate gyrus, and a doubling of the number of BrdU-labeled cells in each cluster. Proliferating astrocytes and neuronal precursors were recognized in each RNR-positive cell cluster, and both types increased in number after seizures. Colocalization of RNR and activated caspase-3 was observed at 7 days, indicating that proliferating cells were susceptible to status epilepticus induced damage. RNR immunohistochemistry provides a useful approach in experiments investigating a change in cell proliferation, revealing the location, number, morphology and fate of newly formed cells after, e.g., brain injury.

The influence of age on apoptotic and other mechanisms of cell death after cerebral hypoxia-ischemia

Unilateral hypoxia-ischemia (HI) was induced in C57/BL6 male mice on postnatal day (P) 5, 9, 21 and 60, corresponding developmentally to premature, term, juvenile and adult human brains, respectively. HI duration was adjusted to obtain a similar extent of brain injury at all ages. Apoptotic mechanisms (nuclear translocation of apoptosis-inducing factor, cytochrome c release and caspase-3 activation) were several-fold more pronounced in immature than in juvenile and adult brains. Necrosis-related calpain activation was similar at all ages. The CA1 subfield shifted from apoptosis-related neuronal death at P5 and P9 to necrosis-related calpain activation at P21 and P60. Oxidative stress (nitrotyrosine formation) was also similar at all ages. Autophagy, as judged by the autophagosome-related marker LC-3 II, was more pronounced in adult brains. To our knowledge, this is the first report demonstrating developmental regulation of AIF-mediated cell death as well as involvement of autophagy in a model of brain injury.