Lithium-pilocarpine-induced status epilepticus produces necrotic neurons with internucleosomal DNA fragmentation in adult rats

Evaluation of the anticonvulsant and neuroprotective effect of intracerebral administration of growth hormone in rats

INTRODUCTION

The growth hormone (GH) has been reported as a crucial neuronal survival factor in the hippocampus against insults of diverse nature. Status epilepticus (SE) is a prolonged seizure that produces extensive neuronal cell death. The goal of this study was to evaluate the effect of intracerebroventricular administration of GH on seizure severity and SE-induced hippocampal neurodegeneration.

METHODOLOGY

Adult male rats were implanted with a guide cannula in the left ventricle and different amounts of GH (70, 120 or 220ng/3μl) were microinjected for 5 days; artificial cerebrospinal fluid was used as the vehicle. Seizures were induced by the lithium-pilocarpine model (3mEq/kg LiCl and 30mg/kg pilocarpine hydrochloride) one day after the last GH administration. Neuronal injury was assessed by Fluoro-Jade B (F-JB) staining.

RESULTS

Rats injected with 120ng of GH did not had SE after 30mg/kg pilocarpine, they required a higher number of pilocarpine injections to develop SE than the rats pretreated with the vehicle, 70ng or 220ng GH. Prefrontal and parietal cortex EEG recordings confirmed that latency to generalized seizures and SE was also significantly higher in the 120ng group when compared with all the experimental groups. FJ-B positive cells were detected in the hippocampus after SE in all rats, and no significant differences in the number of F-JB cells in the CA1 area and the hilus was observed between experimental groups.

CONCLUSION

Our results indicate that, although GH has an anticonvulsive effect in the lithium-pilocarpine model of SE, it does not exert hippocampal neuroprotection after SE.

The standardized extract of Centella asiatica L. Urb attenuates the convulsant effect induced by lithium/pilocarpine without affecting biochemical and haematological parameters in rats

BACKGROUND

Status epilepticus (SE) is a type of epileptic activity characterized by a failure of the inhibitory mechanisms that limit seizures, which are mainly regulated by the GABAergic system. This imbalance increases glutamatergic neurotransmission and consequently produces epileptic activity. It is also associated with oxidative stress due to an imbalance between reactive oxygen species (ROS) and antioxidant defences. Unfortunately, long-term treatment with anti-epileptic drugs (AEDs) may produce hepatotoxicity, nephrotoxicity, and haematological alterations. In this way, some secondary metabolites of plants have been used to ameliorate the deterioration of nervous system disorders through their antioxidant properties, in addition to their anticonvulsant effects. An example is Centella asiatica, a plant noted to have a reputed neuroprotective effect related to its antioxidant activity. However, similar to conventional drugs, natural molecules may produce side effects when consumed in high doses, which could occur with Centella asiatica. Therefore, we aimed to evaluate the effect of a standardized extract of Centella asiatica L. Urb with tested anticonvulsant activity on biochemical and haematological parameters in rats subjected to lithium/pilocarpine-induced seizures.

METHODS

Twenty-eight adult male Wistar rats were randomly divided into four groups (n = 7 each): vehicle (purified water), Centella asiatica (200 and 400 mg/kg), and carbamazepine (CBZ) (300 mg/kg) as a pharmacological control of anticonvulsant activity. Treatments were administered orally every 24 h for 35 consecutive days. On Day 36, SE was induced using the lithium/pilocarpine model (3 mEq/kg, i.p. and 30 mg/kg s.c., respectively), and the behavioural and biochemical effects were evaluated.

RESULTS

Centella asiatica 400 mg/kg increased the latency to the first generalized seizure and SE onset and significantly reduced the time to the first generalized seizure compared to values in the vehicle group. Biochemical parameters, i.e., haematic cytometry, blood chemistry, and liver function tests, showed no significant differences among the different treatments.

CONCLUSION

The dose of Centella asiatica that produces anticonvulsant activity in the lithium/pilocarpine model devoid of hepatotoxicity, nephrotoxicity, and alterations in haematological parameters suggests that the standardized extract of this plant could be of utility in the development of new safe therapies for the treatment of convulsions associated with epilepsy.

A modification to the Kuramoto model to simulate epileptic seizures as synchronization

The Kuramoto model was developed to describe the coupling of oscillators, motivated by the natural synchronization phenomena. We are interested in modeling an epileptic seizure considering it as the synchronization of action potentials using and modifying this model. In this article, we propose to modify this model, changing the constant coupling force for a function with logistic growth to simulate the onset and epileptic seizure level in an adult male rat caused by the administration of lithium-pilocarpine. Later, we select some frequencies and their respective amplitude values using an algorithm based on the fast Fourier transform (FFT) from an electroencephalography signal when the rat is in basal conditions. Then, we take these values as the natural frequencies of the oscillators in the modified Kuramoto model, considering every oscillator as a single neuron to simulate the emergence of an epileptic seizure numerically by increasing the synchronization value in the coupling function. Finally, using Dynamic Time Warping algorithm, we compare the simulated signal by the Kuramoto model with an FFT approximation of the epileptic seizure.

Programmed Mechanisms of Status Epilepticus-induced Neuronal Necrosis

Excitotoxicity is the underlying mechanism for all acute neuronal injury, from cerebral ischemia, status epilepticus, traumatic CNS injury and hypoglycemia. It causes morphological neuronal necrosis, and it triggers a programmed cell death program. Excessive calcium entry through the NMDA-receptor-operated cation channel activates two key enzymes-calpain I and neuronal nitric oxide synthase (nNOS). Calpain I, a cytosolic enzyme, translocates to mitochondrial and lysosomal membranes, causing release of cytochrome c, endonuclease G and apoptosis-inducing factor (AIF) from mitochondria and DNase II and cathepsins B and D from lysosomes. These all translocate to neuronal nuclei, creating DNA damage, which activates poly(ADP) ribose polymerase-1 (PARP-1) to form excessive amounts of poly(ADP) ribose (PAR) polymers, which translocate to mitochondrial membranes, causing release of truncated AIF (tAIF). The free radicals that are released from mitochondria and peroxynitrite, formed from nitric oxide (NO) from nNOS catalysis of L-arginine to L-citrulline, damage mitochondrial and lysosomal membranes and DNA. The end result is the necrotic death of neurons. Another programmed necrotic pathway, necroptosis, occurs through a parallel pathway. As investigators of necroptosis do not recognize the excitotoxic pathway, it is unclear to what extent each contributes to programmed neuronal necrosis. We are studying the extent to which each contributes to acute neuronal necrosis and the extent of cross-talk between these pathways.

Evaluation of the anticonvulsant and neuroprotective effect of intracerebral administration of growth hormone in rats

INTRODUCTION

The growth hormone (GH) has been reported as a crucial neuronal survival factor in the hippocampus against insults of diverse nature. Status epilepticus (SE) is a prolonged seizure that produces extensive neuronal cell death. The goal of this study was to evaluate the effect of intracerebroventricular administration of GH on seizure severity and SE-induced hippocampal neurodegeneration.

METHODOLOGY

Adult male rats were implanted with a guide cannula in the left ventricle and different amounts of GH (70, 120 or 220ng/3μl) were microinjected for 5 days; artificial cerebrospinal fluid was used as the vehicle. Seizures were induced by the lithium-pilocarpine model (3mEq/kg LiCl and 30mg/kg pilocarpine hydrochloride) one day after the last GH administration. Neuronal injury was assessed by Fluoro-Jade B (F-JB) staining.

RESULTS

Rats injected with 120ng of GH did not had SE after 30mg/kg pilocarpine, they required a higher number of pilocarpine injections to develop SE than the rats pretreated with the vehicle, 70ng or 220ng GH. Prefrontal and parietal cortex EEG recordings confirmed that latency to generalized seizures and SE was also significantly higher in the 120ng group when compared with all the experimental groups. FJ-B positive cells were detected in the hippocampus after SE in all rats, and no significant differences in the number of F-JB cells in the CA1 area and the hilus was observed between experimental groups.

CONCLUSION

Our results indicate that, although GH has an anticonvulsive effect in the lithium-pilocarpine model of SE, it does not exert hippocampal neuroprotection after SE.

Depression and Anxiety in the Epilepsies: from Bench to Bedside

PURPOSE OF REVIEW

Depression and anxiety substantially contribute to interictal disability in patients with epilepsy (PWE). This review summarizes current studies that shed light on mechanisms of comorbidity.

RECENT FINDINGS

Mounting epidemiological data implicate shared risk factors for anxiety/depression and seizure propensity, but these remain largely elusive and probably vary by epilepsy type. Within PWE, these symptoms appear to be associated with unique genetic, neuropathological, and connectivity profiles. Temporal lobe epilepsy has received enormous emphasis particularly in preclinical studies of comorbidity, where candidate neurobiological mechanisms underlying bidirectionality have been tested without psychopharmacological confounds. Depression and anxiety in epilepsy reflect dysfunction within broadly distributed limbic networks that may be the cause or consequence of epileptogenesis. In refractory epilepsy, seizures and/or certain anticonvulsants may distort central emotional homeostatic mechanisms that perpetually raise seizure risk. Developing future safe and effective combined anticonvulsant-antidepressant treatments will require a detailed understanding of anatomical and molecular nodes that pleiotropically enhance seizure risk and negatively alter emotionality.

Phosphoproteomic analysis reveals Akt isoform-specific regulation of cytoskeleton proteins in human temporal lobe epilepsy with hippocampal sclerosis

Akt is one of the most important downstream effectors of phosphatidylinositol 3-kinase/mTOR pathway. Hyperactivation and expression of this pathway are seen in a variety of neurological disorders including human temporal lobe epilepsy with hippocampal sclerosis (TLE-HS). Nevertheless, the expression and activation profiles of the Akt isoforms, Akt1, Akt2, and Akt3 and their functional roles in human TLE-HS have not been studied. We examined the protein expression and activation (phosphorylation) patterns of Akt and its isoforms in human hippocampal tissue from TLE and non-TLE patients. A phosphoproteomic approach followed by interactome analysis of each Akt isoform was used to understand protein-protein interactions and their role in TLE-HS pathology. Our results demonstrated activation of the Akt/mTOR pathway as well as activation of Akt downstream substrates like GSK3β, mTOR, and S6 in TLE-HS samples. Akt1 isoform levels were significantly increased in the TLE-HS samples as compared to the non-TLE samples. Most importantly, different isoforms were activated in different TLE-HS samples, Akt2 was activated in three samples, Akt2 and Akt1 were simultaneously activated in one sample and Akt3 was activated in two samples. Our phosphoproteomic screen across six TLE-HS samples identified 183 proteins phosphorylated by Akt isoforms, 29 of these proteins belong to cytoskeletal modification. Also, we were able to identify proteins of several other classes involved in glycolysis, neuronal development, protein folding and excitatory amino acid transport functions as Akt substrates. Taken together, our data offer clues to understand the role of Akt and its isoforms in underlying the pathology of TLE-HS and further, modulation of Akt/mTOR pathway using Akt isoforms specific inhibitors may offer a new therapeutic window for treatment of human TLE-HS.

Hydrogen Alleviates Necroptosis and Cognitive Deficits in Lithium-Pilocarpine Model of Status Epilepticus

Status epilepticus without prompt seizure control always leads to neuronal death and long-term cognitive deficits, but effective intervention is still absent. Here, we found that hydrogen could alleviate the hippocampus-dependent spatial learning and memory deficit in lithium-pilocarpine model of status epilepticus in rats, as evidenced by the results in Morris water maze test. Hydrogen treatment downregulated the expression of necroptosis-related proteins, such as MLKL, phosphorylated-MLKL, and RIPK3 in hippocampus, and further protected neurons and astrocytes from necroptosis which was here first verified to occur in status epilepticus. Hydrogen also protected cells from apoptosis, which was indicated by the decreased cleaved-Caspase 3 expression. Meanwhile, Iba1+ microglial activation by status epilepticus was reduced by hydrogen treatment. These findings confirm the utility of hydrogen treatment in averting cell death including necroptosis and alleviating cognitive deficits caused by status epilepticus. Therefore, hydrogen may provide a potential and powerful clinical treatment for status epilepticus-related cognitive deficits.

Starting ketamine for neuroprotection earlier than its current use as an anesthetic/antiepileptic drug late in refractory status epilepticus

Ketamine is currently being used as an anesthetic/antiepileptic drug in refractory status epilepticus. To validate its use, 2 clinical trials are recruiting patients. However, preclinical studies of its use in chemically induced status epilepticus in rodents have shown that it is remarkably neuroprotective, through N-methyl-d-aspartate-receptor blockade, even when given after the onset of status epilepticus. Human studies have shown that status epilepticus-induced brain damage can be caused by a glutamate analogue and that it occurs in the same brain regions as in the animal studies. We therefore propose that ketamine be started early in the course of human status epilepticus as a neuroprotectant and that it be continued until epileptic discharges are eliminated. Using it as an anesthetic/antiepileptic drug late in the course of refractory status epilepticus only ensures that it is given after widespread brain damage has occurred.

The cannabinoid receptor agonist WIN55.212 reduces consequences of status epilepticus in rats

An acute brain insult can cause a spectrum of primary and secondary pathologies including increased risk for epilepsy, mortality and neurodegeneration. The endocannabinoid system, involved in protecting the brain against network hyperexcitability and excitotoxicity, is profoundly dysregulated by acute brain insults. We hypothesize that post-insult dysregulation of the endocannabinoid signaling may contribute to deleterious effects of an acute brain injury and potentiation of endocannabinoid transmission soon after an insult may reduce its pathological outcomes. Effects of an acute post-insult administration of the endocannabinoid receptor agonist WIN55,212-2 on early seizure occurrence, animal mortality and hippocampal cell loss were studied in the lithium-pilocarpine status model. A single dose of WIN55,212-2 (5mg/kg) administered four hours after the end of status epilepticus (SE) reduced the incidence of early seizures during the first two post-SE days though did not change their duration and latency. Brief 4-6-Hz spike-wave discharges appeared de novo in the latent post-SE period and the acute administration of WIN55,212-2 also reduced the incidence of the epileptiform events. A single dose of WIN55,212-2 administered soon after SE improved survival of animals and reduced cell loss in the dentate hilus but did not prevent appearance of spontaneous recurrent seizures in the chronic period. Thus, a brief pharmacological stimulation of the endocannabinoid system soon after a brain insult exerts beneficial effects on its pathological outcome though does not prevent epileptogenesis.

Necrotic pyknosis is a morphologically and biochemically distinct event from apoptotic pyknosis

Classification of apoptosis and necrosis by morphological differences has been widely used for decades. However, this usefulness of this method has been seriously questioned in recent years, mainly due to a lack of functional and biochemical evidence to interpret the morphology changes. To address this matter, we devised genetic manipulations in Drosophila to study pyknosis, a process of nuclear shrinkage and chromatin condensation that occurs in apoptosis and necrosis. By following the progression of necrotic pyknosis, we surprisingly observed a transient state of chromatin detachment from the nuclear envelope, followed by the nuclear envelope completely collapsing onto chromatin. This phenomenon led us to discover that phosphorylation of barrier-to-autointegration factor (BAF) mediates this initial separation of nuclear envelope from chromatin. Functionally, inhibition of BAF phosphorylation suppressed necrosis in both Drosophila and human cells, suggesting that necrotic pyknosis is conserved in the propagation of necrosis. In contrast, during apoptotic pyknosis the chromatin did not detach from the nuclear envelope and inhibition of BAF phosphorylation had no effect on apoptotic pyknosis and apoptosis. Our research provides the first genetic evidence supporting a morphological classification of apoptosis and necrosis through different forms of pyknosis.

Methamphetamine-induced neuronal necrosis: the role of electrographic seizure discharges

We have evidence that methamphetamine (METH)-induced neuronal death is morphologically necrotic, not apoptotic, as is currently believed, and that electrographic seizures may be responsible. We administered 40mg/kg i.p. to 12 male C57BL/6 mice and monitored EEGs continuously and rectal temperatures every 15min, keeping rectal temperatures <41.0°C. Seven of the 12 mice had repetitive electrographic seizure discharges (RESDs) and 5 did not. The RESDs were often not accompanied by behavioral signs of seizures-i.e., they were often not accompanied by clonic forelimb movements. The 7 mice with RESDs had acidophilic neurons (the H&E light-microscopic equivalent of necrotic neurons by ultrastructural examination) in all of 7 brain regions (hippocampal CA1, CA2, CA3 and hilus, amygdala, piriform cortex and entorhinal cortex), the same brain regions damaged following generalized seizures, 24h after METH administration. The 5 mice without RESDs had a few acidophilic neurons in 4 of the 7 brain regions, but those with RESDs had significantly more in 6 of the 7 brain regions. Maximum rectal temperatures were comparable in mice with and without RESDs, so that cannot explain the difference between the two groups with respect to METH-induced neuronal death. Our data show that METH-induced neuronal death is morphologically necrotic, that EEGs must be recorded to detect electrographic seizure activity in rodents without behavioral evidence of seizures, and that RESDs may be responsible for METH-induced neuronal death.

The progressive changes of filamentous actin cytoskeleton in the hippocampal neurons after pilocarpine-induced status epilepticus

In a previous study, we reported a persistent reduction of F-actin puncta but a compensating increase in puncta size in the mouse hippocampus at 2 months after pilocarpine-induced status epilepticus (Epilepsy Res. 108 (2014), 379-389). However, the F-actin changes during the period of epileptogenesis remain unknown. This study was designed to examine the temporal and spatial changes of F-actin during the period of epileptogenesis in a pilocarpine-induced epilepsy model, primarily by the histological and TUNEL evaluation of cell loss, phalloidin detection of F-actin, and immunohistochemical analysis of glial reactions. The results demonstrated that F-actin continued to decrease after pilocarpine treatment, which was consistent in its time course with hippocampal neuronal death. Within different hippocampal subfields, the spatial changes of F-actin exhibited similar features. First, the F-actin puncta decreased in number. Thereafter, F-actin was transiently aggregated in dendritic shafts and neuronal cell bodies and eventually was completely lost in the degenerated neurons. The progressive changes of F-actin in the degenerating neurons reported in this study may help to elucidate a cytoskeletal mechanism that may link to the delayed cell loss that occurs during epileptogenesis.

The role of excitotoxic programmed necrosis in acute brain injury

Excitotoxicity involves the excessive release of glutamate from presynaptic nerve terminals and from reversal of astrocytic glutamate uptake, when there is excessive neuronal depolarization. N-methyl-d-aspartate (NMDA) receptors, a subtype of glutamate receptor, are activated in postsynaptic neurons, opening their receptor-operated cation channels to allow Ca^2 + influx. The Ca^2 + influx activates two enzymes, calpain I and neuronal nitric oxide synthase (nNOS). Calpain I activation produces mitochondrial release of cytochrome c (cyt c), truncated apoptosis-inducing factor (tAIF) and endonuclease G (endoG), the lysosomal release of cathepsins B and D and DNase II, and inactivation of the plasma membrane Na⁺–Ca^2 + exchanger, which add to the buildup of intracellular Ca^2 +. tAIF is involved in large-scale DNA cleavage and cyt c may be involved in chromatin condensation; endoG produces internucleosomal DNA cleavage. The nuclear actions of the other proteins have not been determined. nNOS forms nitric oxide (NO), which reacts with superoxide (O₂⁻) to form peroxynitrite (ONOO⁻). These free radicals damage cellular membranes, intracellular proteins and DNA. DNA damage activates poly(ADP-ribose) polymerase-1 (PARP-1), which produces poly(ADP-ribose) (PAR) polymers that exit nuclei and translocate to mitochondrial membranes, also releasing AIF. Poly(ADP-ribose) glycohydrolase hydrolyzes PAR polymers into ADP-ribose molecules, which translocate to plasma membranes, activating melastatin-like transient receptor potential 2 (TRPM-2) channels, which open, allowing Ca^2 + influx into neurons. NADPH oxidase (NOX1) transfers electrons across cellular membranes, producing O₂⁻. The result of these processes is neuronal necrosis, which is a programmed cell death that is the basis of all acute neuronal injury in the adult brain.

Oxidative stress associated with neuronal apoptosis in experimental models of epilepsy

Epilepsy is considered one of the most common neurological disorders worldwide. Oxidative stress produced by free radicals may play a role in the initiation and progression of epilepsy; the changes in the mitochondrial and the oxidative stress state can lead mechanism associated with neuronal death pathway. Bioenergetics state failure and impaired mitochondrial function include excessive free radical production with impaired synthesis of antioxidants. This review summarizes evidence that suggest what is the role of oxidative stress on induction of apoptosis in experimental models of epilepsy.

Automated immunohistochemical method to quantify neuronal density in brain sections: application to neuronal loss after status epilepticus

BACKGROUND

To study neurotoxic processes, it is necessary to quantify the number of neurons in a given brain structure and estimate neuronal loss. Neuronal densities can be estimated by immunohistochemical quantitation of a neuronal marker such as the protein NeuN. However, NeuN expression may vary, depending on certain pathophysiological conditions and bias such quantifications.

NEW METHOD

We have developed a simple automatic quantification of neuronal densities in brain sections stained with DAPI and antibody to NeuN. This method determines the number of DAPI-positive nuclei also positive for NeuN in at least two adjacent sections within a Z-stack of optical sections.

RESULTS

We tested this method in animals with induced status epilepticus (SE) a state of intractable persistent seizure that produces extensive neuronal injury. We found that SE significantly reduced neuronal density in the piriform cortex, the amygdala, the dorsal thalamus, the CA3 area of the hippocampus, the dentate gyrus and the hilus, but not in the somatosensory cortex or the CA1 area. SE resulted in increases in the total density of cellular nuclei within these brain structures, suggesting gliosis.

COMPARISON WITH EXISTING METHODS

This automated method was more accurate than simply estimating the overall NeuN fluorescence intensity in the brain section, and as accurate, but less time-consuming, than manual cell counts.

CONCLUSION

This method simplifies and accelerates the unbiased quantification of neuronal density. It can be easily applied to other models of brain injury and neurodegeneration, or used to screen the efficacy of neuroprotective treatments.

Hippocampal MRI and other structural biomarkers: experimental approach to epileptogenesis

The present review is devoted to application of MRI techniques to the epileptic brain and the search for potential biomarkers of epileptogenicity and/or epileptogenesis in rodents that could be translated to the clinic. Diffusion-weighted imaging reveals very early changes in water movements. T(2)-weighted hypersignal indicates edema or gliosis within brain regions and is most often used along with histological assessment of neuronal loss. (31)P magnetic resonance spectroscopy measures the energy reserve of the tissue while (1)H spectroscopy assesses neuronal loss and mitochondrial dysfunction. (13)C spectroscopy analyzes, separately, neuronal and astrocytic metabolism and interactions between the two cell types. Finally, diffusion tensor imaging and tractography have been applied to the study of plasticity and show a good coherence with circuit changes assessed by Timm staining. The potential of these techniques as reliable biomarkers of epileptogenesis is still disputed. At the moment, one study has provided a reliable temporal evolution of the T(2) signal, predicting epileptogenesis in 100% of the cases, and further imaging approaches based on the techniques described here are still needed to identify potential early imaging biomarkers of epileptogenicity and/or epileptogenesis.

Mild as well as severe insults produce necrotic, not apoptotic, cells: evidence from 60-min seizures

We tested the hypothesis that mild insults produce apoptotic, and severe insults necrotic, cells by subjecting adult Wistar rats to 60-min instead of 3-h generalized seizures. Rats' brains were evaluated 6 and 24h later for evidence of neuronal necrosis by light and electron microscopy, the presence of TUNEL staining and active caspase-3 immunoreactivity, and for evidence of DNA laddering 24h after seizures. Apoptotic neurons from the retrosplenial cortex of postnatal day 8 rat pups served as positive controls. Six and 24h after seizures, 16 and 15 brain regions respectively out of 24 showed significant numbers of acidophilic neurons by hematoxylin and eosin stain. Three brain regions had significant numbers of TUNEL-positive neurons 24h after seizures. No neurons showed active caspase-3 immunoreactivity. Acidophilic neurons were necrotic by electron-microscopic examination. Ultrastructurally, they were shrunken and electron-dense, with shrunken, pyknotic nuclei and swollen mitochondria with disrupted cristae. Nuclei did not contain the irregular chromatin clumps found after 3-h seizures. None of the six brain regions studied ultrastructurally that show DNA laddering 24h after 3-h seizures showed DNA laddering 24h after 60-min seizures, probably because there were too few damaged neurons, although the lack of chromatin clumping might have been a contributing factor. Following seizures, a mild as well as a severe insult produces caspase-3-negative necrotic neurons. These results do not support the hypothesis that mild insults produce apoptotic, and severe insults, necrotic, cells.

Preservation of mitochondrial integrity and energy metabolism during experimental status epilepticus leads to neuronal apoptotic cell death in the hippocampus of the rat

Status epilepticus results in mitochondrial damage or dysfunction and preferential neuronal cell loss in the hippocampus. Since a critical determinant of the eventual cell death fate resides in intracellular ATP concentration, we investigated whether mitochondrial integrity and level of energy metabolism are related with apoptotic cell death in specific hippocampal neuronal populations. A kainic acid (KA)-induced experimental temporal lobe status epilepticus model was used. Qualitative and quantitative analysis of DNA fragmentation, TUNEL immunohistochemistry, double immunofluorescence staining for activated caspase-3, electron microscopy or measurement of ATP level in the bilateral hippocampus was carried out 1, 3 or 7 days after microinjection unilaterally of a low dose of KA (0.5 nmol) into the CA3 hippocampal subfield. Characteristic biochemical (DNA fragmentation), histochemical (TUNEL or activated caspase-3 staining) or ultrastructural (electron microscopy) features of apoptotic cell death were presented bilaterally in the hippocampus 7 days after the elicitation of sustained hippocampal seizure activity by microinjection of KA into the unilateral CA3 subfield. At the same time, CA3 or CA1 subfield on either side manifested a maintained ATP level; alongside relatively intact mitochondria, rough endoplasmic reticulum, Golgi apparatus or cytoplasmic membrane in hippocampal neurons that exhibited ultrastructural features of apoptotic cell death. Our results demonstrated that preserved mitochondrial ultrastructural integrity and maintained energy metabolism during experimental temporal lobe status epilepticus is associated specifically with apoptotic, not necrotic, cell death in hippocampal CA3 or CA1 neurons.

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.

Region-specific plasticity in the epileptic rat brain: a hippocampal and extrahippocampal analysis

PURPOSE

Recent evidence suggests that aberrant neuro/gliogenesis and/or inflammation play critical roles in epileptogenesis. Although the plastic and inflammatory changes have been described in the postseizure hippocampus, little data is available concerning extrahippocampal regions, notably in the piriform and entorhinal cortices, amygdala, and parts of the thalamus. In this study, we examined histological changes in whole epileptic rat brain, with respect to cell death, cell genesis, and inflammation.

METHODS AND RESULTS

Experimental status epilepticus (SE) was induced using a lithium-pilocarpine injection. Neuronal death was evident in the amygdala, piriform, and entorhinal cortices, as well as the subfields of hippocampus. Microglial activation was observed in more extended limbic areas, such as, the hippocampus, entorhinal, perirhinal and piriform cortices, amygdala, thalamus, and hypothalamus, and a robust increase of cell genesis was noted in these damaged areas. The majority of newly generated cells in extrahippocampal areas proliferated in situ, and differentiated mainly into astrocytes or oligodendrocytes. In addition, stromal cell-derived factor-1alpha was found to be induced in close temporal and anatomical association with seizure-induced plasticity.

DISCUSSION

These findings indicate that neuronal death, inflammation, and cell genesis are substantially associated throughout the entire brain and that they may influence the epileptogenic process and clinical manifestations.

The pilocarpine model of temporal lobe epilepsy

Understanding the pathophysiogenesis of temporal lobe epilepsy (TLE) largely rests on the use of models of status epilepticus (SE), as in the case of the pilocarpine model. The main features of TLE are: (i) epileptic foci in the limbic system; (ii) an “initial precipitating injury”; (iii) the so-called “latent period”; and (iv) the presence of hippocampal sclerosis leading to reorganization of neuronal networks. Many of these characteristics can be reproduced in rodents by systemic injection of pilocarpine; in this animal model, SE is followed by a latent period and later by the appearance of spontaneous recurrent seizures (SRSs). These processes are, however, influenced by experimental conditions such as rodent species, strain, gender, age, doses and routes of pilocarpine administration, as well as combinations with other drugs administered before and/or after SE. In the attempt to limit these sources of variability, we evaluated the methodological procedures used by several investigators in the pilocarpine model; in particular, we have focused on the behavioural, electrophysiological and histopathological findings obtained with different protocols. We addressed the various experimental approaches published to date, by comparing mortality rates, onset of SRSs, neuronal damage, and network reorganization. Based on the evidence reviewed here, we propose that the pilocarpine model can be a valuable tool to investigate the mechanisms involved in TLE, and even more so when standardized to reduce mortality at the time of pilocarpine injection, differences in latent period duration, variability in the lesion extent, and SRS frequency.

Neuronal apoptosis in the resected sclerotic hippocampus in patients with mesial temporal lobe epilepsy

To further confirm at the molecular level that neuronal apoptosis occurs in mesial temporal sclerosis (MTS), the main substrate of mesial temporal lobe epilepsy (MTLE), 24 resected sclerotic hippocampi from 24 patients with drug-resistant MTLE associated with MTS were studied microscopically, electronmicroscopically and immunohistochemically, with detection of expression of apoptosis-associated genes including bcl-2, p53, bax, fas and caspase-3. Early apoptosis changes were found morphologically in hippocampi from three patients with MTLE using transmission electron microscopy. Positive immunostained neurons for bcl-2, p53, fas and caspase-3 were found in the sclerotic hippocampi of 19/24, 14/24, 22/24 and 20/24 patients respectively, which was statistically different from controls. Correlative analysis showed the expression of p53, fas and caspase-3 were positively correlated with seizure frequency. Apoptosis may contribute to MTS, and seizures may induce apoptosis, and thus contribute to neuronal loss in MTS.

Status Epilepticus Triggers Caspase-3 Activation and Necrosis in the Immature Rat Brain

The mode and mechanism of neuronal death induced by status epilepticus (SE) in the immature brain have not been fully characterized. In this study, we analyzed the contribution of neuronal necrosis and caspase-3 activation to CA1 damage following lithium-pilocarpine SE in P14 rat pups. By electron microscopy, many CA1 neurons displayed evidence of early necrosis 6 hours following SE, and the full ultrastructural features of necrosis at 24-72 hours. Caspase-3 was activated in injured (acidophilic) neurons 24 hours following SE, raising the possibility that they died by caspase-dependent "programmed" necrosis.

Caspase-dependent programmed cell death pathways are not activated in generalized seizure-induced neuronal death

Activation of the caspase-dependent cell death pathways has been shown in focal seizures, but whether this occurs in prolonged generalized seizures is not known. We investigated whether the initiator caspase in the extrinsic pathway, caspase-8, or the intrinsic pathway, caspase-9, is activated during the first 24 h following lithium-pilocarpine-induced status epilepticus, when neuronal death is maximal and widespread. The thymuses of rats given methamphetamine were used as positive controls for caspase-3-activated cellular apoptosis. Following methamphetamine treatment, caspase-9 but not caspase-8 was activated in thymocytes. However, 6 or 24 h following status epilepticus, none of 26 brain regions studied showed either caspase-8 or -9 activation by immunohistochemistry, western blotting and enzyme activity assays. Our results provide evidence against the activation of the extrinsic and intrinsic caspase pathways in generalized seizures, which produce morphologically necrotic neurons with internucleosomal DNA cleavage (DNA laddering), a programmed process. In contrast, there is increasing evidence that caspase-independent programmed mechanisms play a prominent role in seizure-induced neuronal death.

The combination of topiramate and diazepam is partially neuroprotective in the hippocampus but not antiepileptogenic in the lithium-pilocarpine model of temporal lobe epilepsy

Lithium-pilocarpine induces status epilepticus (SE), leading to extensive damage and spontaneous recurrent seizures (SRS). Neuroprotective and antiepileptogenic effects of topiramate (TPM) associated with diazepam (DZP) were investigated in this model. SE was induced by LiCl and pilocarpine. TPM (10, 30 or 60 mg/kg) was injected at the onset of SE and 10h later and DZP (2.5 and 1.25mg/kg) at 2 and 10h after SE. TPM treatment was continued twice daily for 6 days. Other rats received two injections of DZP on the day of SE. Cell counting was performed on thionine-stained sections 14 days after SE and after 2 months of epilepsy. Occurrence and frequency of SRS were video-recorded. The MRI T2-weighted signal was quantified in hippocampus and ventral cortices. DZP-TPM treatment induced partial neuroprotection in CA1 and hilus, and tended to increase the percentage of rats with protected neurons in layer III/IV of the ventral entorhinal cortex. The latency to and frequency of SRS were not modified by DZP-TPM. T2-weighted signal was decreased in hippocampus 3 days after SE at all TPM doses and in ventral hippocampus after epilepsy onset. In conclusion, although DZP-TPM treatment was able to partially protect two areas critical for epileptogenesis, the hippocampus and ventral entorhinal cortex, it was not sufficient to prevent epileptogenesis.

EAAC1 glutamate transporter expression in the rat lithium-pilocarpine model of temporal lobe epilepsy

Glutamate excitotoxicity has been involved in the pathophysiology of epilepsy. Normal functioning of glutamate transporters clears the synaptically released glutamate to prevent excitotoxic neuronal death. Using densitometric immunohistochemical analysis, we examined the temporal expression of the neuronal glutamate transporter (EAAC1) in the lithium-pilocarpine rat model of temporal lobe epilepsy. During the acute period of lithium-pilocarpine-induced status epilepticus, EAAC1 transporter expression increased in the pyramidal neurons of cornus ammonis (CA)1, CA2 and CA3 (fields of the hippocampus), in dentate gyrus (DG) granule cells and in olfactory tubercle (Tu). During the latent period, EAAC1 expression was strongly expressed in the DG granular and molecular layers, Tu, cerebral cortex and septum, and went back to control levels in CA1, CA2 and CA3 layers. The overexpression of EAAC1 occurred mainly in structures prone to develop Fluoro-Jade-B-positive degenerating neurons. It is, however, not clear to what extent the overexpression of EAAC1 contributes to epileptogenesis and in which area it may represent a preventive or compensatory or response to injury.

Prolonged seizures recruit caudal subventricular zone glial progenitors into the injured hippocampus

Neurogenesis persists in the adult rat rostral forebrain subventricular zone (SVZ) and is stimulated by status epilepticus (SE). More caudal SVZ (cSVZ) neural progenitors migrate to the hippocampus after ischemic injury and contribute to CA1 pyramidal cell regeneration. Because SE also damages the hippocampus, we examined the effects of SE on cSVZ precursors. SE was induced in adult rats with pilocarpine, and cell proliferation in cSVZ and hippocampus was examined by bromodeoxyuridine (BrdU) and retroviral reporter labeling. Neural precursors were assayed by immunostaining for specfic markers between 1 and 35 days after SE. BrdU-positive cells labeled prior to SE markedly increased in numbers within 1-2 weeks in the cSVZ and infracallosal region, but not in the corpus callosum. Doublecortin-, polysialic acid neural cell adhesion molecule-, and TUC-4 (TOAD/Ulip/CRMP family-4)-immunostained cells with migrating morphology increased with a similar time course after SE and extended from the cSVZ to CA1 and CA3 regions. Retroviral reporters injected into the cSVZ of controls showed labeled cells with oligodendroglial morphology located in the cSVZ and corpus callosum; when injected 2 days prior to SE, many more reporter-labeled cells appeared several weeks later and were located in the cSVZ, corpus callosum, and hippocampus. Labeled cells showed glial morphologies and expressed astrocyte or oligodendrocyte markers. Neither BrdU- nor retroviral reporter-labeled cells coexpressed neuronal markers in controls or pilocarpine-treated rats. These results indicate that SE increases cSVZ gliogenesis and attracts newly generated glia to regions of hippocampal damage. Further study of seizure-induced gliogenesis may provide insight into mechanisms of adult neural progenitor regulation and epileptogenesis.

Prolonged seizures and cellular injury: understanding the connection

Status epilepticus (SE)-induced neuronal death is morphologically necrotic and is initiated by excessive glutamate release, which activates postsynaptic N-methyl-D-aspartate (NMDA) receptors and triggers receptor-mediated calcium influx (excitotoxicity). This results in activation of intracellular proteases and neuronal nitric oxide synthase, with generation of free radicals, and damage to cellular membranes, structural proteins, and essential enzymes. Programmed cell death mechanisms, such as p53 activation, activation of cell death-promoting Bcl-2 family members, and endonuclease-induced DNA laddering, occur in SE-induced neuronal death. Caspase-independent excitotoxic mechanisms, such as NMDA-induced calpain I activation, with activation and translocation of the cell death-promoting Bcl-2 family member Bid from cytoplasm to mitochondria, and subsequent translocation of apoptosis-inducing factor and endonuclease G to nuclei (which cause large-scale and internucleosomal DNA cleavage, respectively), may be triggered by SE. Poly(ADP-ribose) polymerase-1 (PARP-1) activation and cysteinyl cathepsin and DNase II release from lysosomes may occur following SE as well, but these events await future investigation. In the future, rational combinations of central nervous system-penetrable neuroprotective agents, based on our knowledge of excitotoxic mechanisms, may be useful in refractory human SE.

Comparison of Neuroprotective Effects Induced by α-Phenyl-N-tert-butyl nitrone (PBN) and N-tert-Butyl-α-(2 sulfophenyl) nitrone (S-PBN) in Lithium-Pilocarpine Status Epilepticus

The status epilepticus (SE) induced in rats by lithium-pilocarpine (Li-pilo) shares many common features with soman-induced SE including extensive limbic neuropathology. Reactive oxygen species are hypothesized to play a role in the SE induced neuropathology and we propose that the free radical scavengers alpha-phenyl-N-tert-butyl nitrone (PBN) and N-tert-butyl-alpha-(2 sulfophenyl) nitrone (S-PBN) may be neuroprotective. PBN or S-PBN were administered either immediately following pilocarpine (exposure treatment) or 5 min after the onset of SE as determined by ECoG activity. SE was allowed to continue for 3 h before termination with propofol. The rats were sacrified 24 h following pilocarpine administration. S-PBN induced minor effects to reduce SE duration and improve neurological deficit 24 h following pilocarpine administration. One hundred and fifty milligrams per kilograms PBN administered 5 min after SE onset produced significant neuroprotection in the parietal, occipital, perirhinal and piriform cortices as well as the lateral amygdala. One hundred and fifty milligrams per kilograms S-PBN was neuroprotective only in the occipital and perirhinal cortex while 300 mg/kg S-PBN exacerbated cortical neuropathology. S-PBN administered 5 min after SE onset exacerbated neuropathology in thalamic regions. In contrast, PBN and S-PBN administered as exposure treatment exacerbated neuropathology in thalamic and CA3 regions. The differential neuroprotective effects of PBN and S-PBN may be the result of the poor brain penetration by S-PBN. The results suggest that free radical scavenger activity is neuroprotective in cortical regions during cholinergic convulsions. Regional variations in drug-induced neuroprotectant activity in Li-pilo SE are common and suggest multiple mechanisms of neuropathology.

Programmed neuronal necrosis and status epilepticus

We examined the mechanism of neuronal necrosis induced by hypoxia in dentate gyrus cultures or by status epilepticus (SE) in adult mice. Our observations showed that hypoxic necrosis can be an active process starting with early mitochondrial swelling and loss of the mitochondrial membrane potential, followed by cytochrome c release and caspase-9-dependent activation of caspase-3. This sequence of events (or program) was independent of protein synthesis and may be induced by energy failure and/or calcium overloading of mitochondria. We called this form of necrosis "programmed necrosis." After SE in adult mice, CA1 and CA3 pyramidal neurons displayed a necrotic morphology, associated with caspase-3 immunoreactivity and with double-stranded DNA breaks, suggesting that "programmed necrosis" may be involved in SE-induced neuronal loss.

Expression time course and spatial distribution of activated caspase-3 after experimental status epilepticus: contribution of delayed neuronal cell death to seizure-induced neuronal injury

Pilocarpine-induced status epilepticus (PCSE) is a widely used model to study neurodegeneration in limbic structures after prolonged epileptic seizures. However, mechanisms mediating neuronal cell death in this model require further characterization. Examining the expression time course and spatial distribution of activated caspase-3, we sought to determine the role of apoptosis in PCSE-mediated neuronal cell death. Expression of activated caspase-3, predominantly located in neurons, was detected 24 h (amygdala; piriform and temporal cortex) and 7 days (hippocampus; amygdala; piriform, temporal and parietal cortex; thalamus) after PCSE with strongest induction being observed in the amygdala, the piriform cortex, and the hippocampus. Further analysis revealed TUNEL positivity (24 h and 7 days after SE) and a significant, progressive neuronal cell loss in all brain regions displaying caspase-3 activation. Corresponding to high levels of activated caspase-3 expression, neuronal cell loss was most pronounced in the amygdala, piriform cortex, and dorsal CA-1 hippocampus. These results demonstrate that apoptosis contributes significantly to PCSE-induced neuronal cell death.

Kainic acid induces rapid cell death followed by transiently reduced cell proliferation in the immature granule cell layer of rat organotypic hippocampal slice cultures

Brain injury due to seizures results in transiently increased cell proliferation and neurogenesis in the subgranular zone of the adult dentate gyrus. In contrast, the immature postnatal brain appears to be more resistant to cell death after seizure-induced brain injury and paradoxically reacts to seizures by reducing SGZ proliferation. Organotypic hippocampal slice cultures are a useful paradigm for modelling the early postnatal hippocampus. We have investigated the temporal relationship between cell death and cell proliferation after kainate in the granule cell layer of rat organotypic hippocampal slice cultures equivalent to post natal day 11 animals. We found stable numbers and densities of mature thionine stained cells in the granule cell layer over 72 h in control cultures grown in defined medium. We also found a slowly declining cell proliferation rate over the same time period under control conditions. We report evidence of early cell death in the granule cell layer after just 2 h exposure to 5 microM kainate, followed by a significant decrease in cell proliferation in the granule cell layer at 24 h. In contrast to control conditions, cell proliferation rose significantly in the kainate exposed cultures by 72 h back to levels seen at 2 h. There were no significant changes in cell labelling with antibody to activated caspase-3 between kainate treated and control cultures at any time point examined. Our results suggest that kainate-induced injury in the early postnatal hippocampus damages precursor cells contributing to a reduction in granule layer cell proliferation.

Degenerative neuronal changes in the rat thalamus induced by status epilepticus at different developmental stages

SE was induced in Wistar rats at post-natal (P) days 12, 15, 18, 21, and 25 to determine distribution and severity of thalamic damage in relation to time after SE. Six different intervals from 4 h up to 1 week were studied using Fluoro-Jade B (FJB) staining. Severity of damage was semi-quantified for every age-and-interval group. Distribution of neuronal damage within various thalamic nuclei was mapped by a computer-aided digitizing system. A consistent neuronal damage occurred in functionally heterogenous thalamic nuclei. Damage was found in all age groups although its extension and time course as well as the number of involved thalamic nuclei varied. Number of injured thalamic nuclei rapidly increased with age on SE-onset. In P12 group, degenerating neurons were consistently seen in the mediodorsal and lateral dorsal thalamic nuclei. Since P15, neurodegeneration was observed additionally in midline, ventral and caudal thalamic nuclei (visual and auditory thalamic nuclei), in the lateral posterior and in the reticular nucleus. In P21 and P25 animals, the majority of thalamic nuclei exhibited marked neuronal damage. Nuclei with a small number (anterior and intralaminar) or no FJB-positive neurons (the ventral nucleus of the lateral geniculate body) were exceptional. The pattern of thalamic damage is age-specific; its extent and severity increases with age.

Patterns of seizures, hippocampal injury and neurogenesis in three models of status epilepticus in galanin receptor type 1 (GalR1) knockout mice

The neuropeptide galanin exhibits anticonvulsant effects in experimental epilepsy. Two galanin receptor subtypes, GalR1 and GalR2, are present in the brain. We examined the role of GalR1 in seizures by studying the susceptibility of GalR1 knockout (KO) mice to status epilepticus (SE) and accompanying neuronal injury. SE was induced in GalR1 KO and wild type (WT) mice by Li-pilocarpine, 60 min electrical perforant path stimulation (PPS), or systemic kainic acid (KA). Seizures were analyzed using Harmonie software. Cell injury was examined by FluoroJade B- and terminal deoxynucleotidyl transferase-mediated uridine triphosphate nick end labeling; neurogenesis was studied using bromodeoxyuridine labeling. Compared with WT littermates, GalR1 KO showed more severe seizures, more profound injury to the CA1 pyramidal cell layer, as well as injury to hilar interneurons and dentate granule cells upon Li-pilocarpine administration. PPS led to more severe seizures in KO, as compared with WT mice. No difference in the extent of neuronal degeneration was observed between the mice of two genotypes in CA1 pyramidal cell layer; however, in contrast to WT, GalR1 KO developed mild injury to hilar interneurons on the side of PPS. KA-induced seizures did not differ between GalR1 KO and WT animals, and led to no injury to the hippocampus in either of experimental group. No differences were found between KO and WT mice in both basal and seizure-induced neuronal progenitor proliferation in all seizure types. Li-pilocarpine led to more extensive glia proliferation in GalR1 KO than in WT, and in both mouse types in two other SE models. In conclusion, GalR1 mediate galanin protection from seizures and seizure-induced hippocampal injury in Li-pilocarpine and PPS models of limbic SE, but not under conditions of KA-induced seizures. The results justify the development and use of GalR1 agonists in the treatment of certain forms of epilepsy.

Domoic acid-induced neurotoxicity in the hippocampus of adult rats

Domoic acid (DA), an agonist of non-N-methyl-D-aspartate (non-NMDA) receptor subtype including kainate receptor, was identified as a potent neurotoxin showing involvement in neuropathological processes like neuronal degeneration and atrophy. In the past decade evidence indicating a role for excitatory amino acids in association with neurological disorders has been accumulating. Although the mechanisms underlying the neuronal damage induced by DA are not yet fully understood, many intracellular processes are thought to contribute towards DA-induced excitotoxic injury, acting in combination leading to cell death. In this review article, we report the leading hypotheses in the understanding of DA-induced neurotoxicity, which focus on the role of DA in neuropathological manifestations, the formation of the retrograde messenger molecule nitric oxide (NO) for the production of free radicals in the development of neuronal damage, the activation of glial cells (microglia and astrocytes) in response to DA-induced neuronal damage and the neuroprotective role of melatonin as a free radical scavenger or antioxidant in DA-induced neurotoxicity. The possible implications of molecular mechanism underlying the neurotoxicity in association with necrosis, apoptosis, nitric oxide synthases (nNos and iNOS) and glutamate receptors (NMDAR1 and GluR2) related genes and their expression in DA-induced neuronal damage in the hippocampus have been discussed.

Differential Neuroprotective Effects of the NMDA Receptor-Associated Glycine Site Partial Agonists 1-Aminocyclopropanecarboxylic Acid (ACPC) and d-Cycloserine in Lithium-Pilocarpine Status Epilepticus

The status epilepticus (SE) induced in rats by lithium-pilocarpine (Li-pilo) shares many common features with soman-induced SE including a glutamatergic phase that is inhibited by NMDA antagonists. The present study determined whether 1-aminocyclopropanecarboxylic acid (ACPC) or D-cycloserine (DCS), both partial agonists of the strychnine-insensitive glycine site on the NMDA receptor ionophore complex, exerted anticonvulsant or neuroprotectant activity in Li-pilo SE. ACPC or DCS were administered either immediately following pilocarpine (exposure treatment) or 5 min after the onset of SE as determined by ECoG activity. SE was allowed to proceed for 3 h before termination with propofol. The rats were sacrificed 24 h following pilocarpine administration. Neither drug had an effect on the latency to seizure onset or the duration of seizure activity. ACPC administered 5 min after SE onset produced significant neuroprotection in cortical regions, amygdala and CA1 of the hippocampus. In contrast, when administered as exposure treatment ACPC enhanced the neural damage in the thalamus and CA3 of the hippocampus suggesting the neuropathology in those regions is mediated by a different subset of NMDA receptors. DCS had no neuroprotectant activity in Li-pilo SE but exacerbated neuronal damage in the thalamus. Neither drug affected the cholinergic convulsions but both had differential effects on neural damage. This suggests that the SE-induced seizure activity and subsequent neuronal damage involve independent mechanisms.

Normal spatial and contextual learning for ketamine-treated rats in the pilocarpine epilepsy model

Cognitive impairments frequently accompany epileptic disorders. Here, we examine two neuroprotective agents, the noncompetitive NMDA antagonist ketamine and the dopaminergic antagonist acepromazine, for their efficacy in attenuating cognitive impairments in the lithium-pilocarpine (LI-PILO) model of rat limbic epilepsy. Declarative-like cognitive behaviors were assessed in a Morris water maze task that consisted successively of spatial and nonspatial (cued platform) training. Whereas the ketamine-treated (Ket) LI-PILO rats performed equally in all respects to nonseized control rats for the spatial and nonspatial components of the water maze task, the acepromazine-treated (Ace) LI-PILO rats failed to demonstrate learning in either the hidden or cued platform variants of the task and did not demonstrate any place learning in the platform-removed probe trials. We further assessed nondeclarative (associative) cognitive behaviors with a standard contextual fear-conditioning protocol. LI-PILO rats treated with acepromazine failed to learn the Pavlovian relationship; Ket LI-PILO rats performed equivalently to nonseized controls. Cumulatively, these data suggest robust cognitive sparing for LI-PILO rats with pharmacological NMDA receptor antagonism following induction of status epilepticus (SE). This cognitive sparing occurs despite earlier findings that the mean amount of total brain damage with LI-PILO is equivalent for Ket and Ace rats.

Latency to onset of status epilepticus determines molecular mechanisms of seizure-induced cell death

The molecular mechanisms mediating degeneration in response to neuronal insults, including damage evoked by prolonged seizure activity, show substantial variability across laboratories and injury models. Here we investigate the extent to which the proportion of cell death occurring by apoptotic vs. necrotic mechanisms may be shifted by changing the temporal parameters of the insult. In initial studies with continuous seizures (status epilepticus, SE), signs of apoptotic degeneration were most clearly observed when SE occurred following a long latency (>86 min) after injection of kainic acid as compared with a short-latency SE (<76 min). Therefore, in this study we directly compared short- with long-latency SE for the expression of molecular markers for apoptosis and necrosis in an especially vulnerable brain region (rhinal cortex). Molecular markers of apoptosis (DNA fragmentation, cleavage of ICAD, an inhibitor of "caspase-activated DNase" (CAD), and prevalence of a caspase-generated fragment of alpha-spectrin) were detected following long-latency SE. Short-latency SE resulted in expression of predominantly necrotic features of cell death, such as "non-ladder" pattern of genomic DNA degradation, prevalence of a calpain-generated alpha-spectrin fragment, and absence of ICAD cleavage. Silver staining revealed no significant difference in the extent and spatial distribution of degeneration between long- or short-latency SE. These data indicate that the latency to onset of SE determines the extent to which apoptotic or necrotic mechanisms contribute to the degeneration following SE. The presence of a long latency period, during which multiple brief seizure episodes may occur, favors the occurrence of apoptotic cell death. It is possible that the absence of such "preconditioning" period in short-latency SE favors predominantly necrotic profile.

Expression and activation of caspase 3 following status epilepticus in the rat

It is in dispute whether caspase 3 contributes to status epilepticus (SE)-induced cell loss. We hypothesized that caspase 3-mediated cell death continues beyond the acute phase of SE. We induced SE with either kainic acid or electrical stimulation of the amygdala in Wistar and Sprague-Dawley rats. Caspase 3 immunohistochemistry, Western blot analysis and enzyme activity measurements were used to determine cellular localization and the time course of caspase 3 expression and activation. Immunohistochemistry indicated that caspase 3 protein expression increased following SE, peaking at 16-24 h. Cleavage of procaspase 3 to active fragments (p20-17) was detected 2-7 days after SE. Caspase 3 enzyme activity was elevated at 8 h and further increased up to 19.4-fold at 7 days following SE. Activation of caspase 3 after SE occurred in the hippocampus and the extrahippocampal temporal lobe but not in the thalamus. Caspase 3-immunoreactive cells represented only a minority of degenerating cells as assessed by Fluoro-Jade B and TUNEL staining. Analysis of double-labelled sections indicated that active caspase 3 was located in astrocytes rather than neurons or microglia. There was increased caspase 3 expression in both rat strains, and it was independent of the method used to induce SE. These data demonstrate that caspase 3 contributes to the cell death occurring within the first week after SE, but in only a small proportion of degenerating cells. These results suggest that, contrary to expectations, caspase 3 inhibitors would have only limited benefits in the treatment of SE.

Prevalence of necrosis in C2-ceramide-induced cytotoxicity in NB16 neuroblastoma cells

The mechanism of cell death triggered by C2-ceramide was investigated using the NB16 neuroblastoma cell line. Treatment of NB16 cells with 20 microM C2-ceramide for 20 h resulted in approximately 75% loss of cell viability, but only 25% of cells were scored as apoptotic based on terminal deoxynucleotidyl transferase nick-end labeling. Ultrastructural analysis revealed early development of necrotic cytoplasmic vacuolization. After 20 h of treatment with C2-ceramide, the majority of cells possessed necrotic morphology with pronounced cytoplasmic vacuolization and without any nuclear changes, although a quarter of the cell population also exhibited clear perinuclear chromatin condensation characteristic of apoptosis. Flow cytometric analysis of cells labeled with both annexin V and propidium iodide showed the rapid accumulation of C2-ceramide-treated cells in the necrotic/late apoptotic fraction. In contrast, cells treated with tumor necrosis factor alpha plus cycloheximide (TNFalpha + CHX) first appeared in the early apoptotic fraction and then accumulated in the necrotic/late apoptotic fraction. Both C2-ceramide and TNFalpha + CHX increased caspase 8- and 3-like activities in cytosolic extracts; however, treatment of cells with the broad-spectrum caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone protected NB16 cells from TNFalpha + CHX-induced cell death but did not prevent C2-ceramide cytotoxicity. Although C2-ceramide triggered apoptosis in a fraction of the cells, cell death in the population was primarily caused by necrosis. Thus, C2-ceramide does not faithfully mimic the effects of apoptotic ligands such as TNFalpha, which are thought to be mediated by an accumulation of endogenous ceramide. The inhibition of phosphatidylcholine synthesis is a target for C2-ceramide-mediated cytotoxicity, and this work suggests that other agents that kill cells by inhibiting this pathway may also use a mixture of mechanisms, including necrosis as well as apoptosis.

In the lithium-pilocarpine model of epilepsy, brain lesions are not linked to changes in blood-brain barrier permeability: an autoradiographic study in adult and developing rats

Lithium-pilocarpine-induced status epilepticus (SE) leads to the genesis of massive neuronal loss in adult rats and to a lesser extent in P21 rats. Neuronal damage occurs mainly via a process of necrosis in limbic forebrain, cerebral cortex, thalamus, and substantia nigra. It is not known, however, whether damage is the result of local excitotoxic hyperactivity or if leakage at the blood-brain barrier (BBB) could participate in the damaging process. Therefore, we investigated the permeability of the BBB in adult and P21 rats using [alpha-(14)C]aminoisobutyric acid, which does not cross an intact BBB, at 90 min after the onset of SE. At both ages, BBB opening occurred both in structures that will undergo damage (thalamus, septum, amygdala) and structures that will not be injured (globus pallidus, hypothalamus). In addition, neuronal damage occurs in the absence of increased BBB permeability in hippocampus, entorhinal cortex, and substantia nigra. Moreover, the increase in the intensity and distribution of BBB permeability changes is age-related, suggesting a differential activation of seizure circuits in adult and P21 rats. In summary, there is no clear correlation between the anatomical distribution of BBB opening and the occurrence of neuronal damage which, in this model, appears to rather depend on excitotoxic mechanisms due to major neuronal hyperexcitability.

Dentate gyrus: alterations that occur with hippocampal injury

Injury to the brain usually manifests not in a diffuse uniform manner but rather with selective sites of damage indicative of differential vulnerability. This question of neuronal susceptibility has been one of major interest both in disease processes as well as damage induced by environmental factors. For experimental examination, brain structures with obvious neuronal subpopulations and organization such as the cerebellum and the hippocampus have offered the most promise. In the hippocampus distinct neuronal populations exist that demonstrate differential vulnerability to various forms of insult including ischemia, excitotoxicity, and environmental factors. The more recent data regarding the presence of neuronal progenitor cells in the subgranular zone of the dentate offers the opportunity to expand such experimental examination to the process of injury-induced neurogenesis. Thus, more recent studies have expanded the examination of the hippocampus to include models of damage to the dentate neurons in addition to the highly vulnerable pyramidal neurons. A number of these models are presented for both human disease and experimental animal conditions. Examination of the responses between these distinct cell populations offers the potential for understanding factors that are critical in neuronal death and survival.

Molecular mechanisms of cerebral ischemia-induced neuronal death

The mode of neuronal death caused by cerebral ischemia and reperfusion appears on the continuum between the poles of catastrophic necrosis and apoptosis: ischemic neurons exhibit many biochemical hallmarks of apoptosis but remain cytologically necrotic. The position on this continuum may be modulated by the severity of the ischemic insult. The ischemia-induced neuronal death is an active process (energy dependent) and is the result of activation of cascades of detrimental biochemical events that include perturbion of calcium homeostasis leading to increased excitotoxicity, malfunction of endoplasmic reticulum and mitochondria, elevation of oxidative stress causing DNA damage, alteration in proapoptotic gene expression, and activation of the effector cysteine proteases (caspases) and endonucleases leading to the final degradation of the genome. In spite of strong evidence showing that brain infarction can be reduced by inhibiting any one of the above biochemical events, such as targeting excitotoxicity, up-regulation of an antiapoptotic gene, or inhibition of a down-stream effector caspase, it is becoming clear that targeting a single gene or factor is not sufficient for stroke therapeutics. An effective neuroprotective therapy is likely to be a cocktail aimed at all of the above detrimental events evoked by cerebral ischemia and the success of such therapeutic intervention relies upon the complete elucidation of pathways and mechanisms of the cerebral ischemia-induced active neuronal death.