Kainic acid induced seizures: neurochemical and histopathological changes

Variation in Galr1 expression determines susceptibility to exocitotoxin-induced cell death in mice

Inbred strains of mice differ in their susceptibility to excitotoxin-induced cell death, but the genetic basis of individual variation in differential susceptibility is unknown. Previously, we identified a highly significant quantitative trait locus (QTL) on chromosome 18 that influenced susceptibility to kainic acid-induced cell death (Sicd1). Comparison of susceptibility to seizure-induced cell death between reciprocal congenic lines for Sicd1 and parental background mice indicates that genes influencing this trait were captured in both strains. Two positional gene candidates, Galr1 and Mbp, map to 55 cM, where the Sicd1 QTL had been previously mapped. Thus, this study was undertaken to determine if Galr1 and/or Mbp could be considered as candidate genes. Genomic sequence comparison of these two functional candidate genes from the C57BL/6J (resistant at Sicd1) and the FVB/NJ (susceptible at Sicd1) strains showed no single-nucleotide polymorphisms. However, expression studies confirmed that Galr1 shows significant differential expression in the congenic and parental inbred strains. Galr1 expression was downregulated in the hippocampus of C57BL/6J mice and FVB.B6-Sicd1 congenic mice when compared with FVB/NJ or B6.FVB-Sicd1 congenic mice. A survey of Galr1 expression among other inbred strains showed a significant effect such that 'susceptible' strains showed a reduction in Galr1 expression as compared with 'resistant' strains. In contrast, no differences in Mbp expression were observed. In summary, these results suggest that differential expression of Galr1 may contribute to the differences in susceptibility to seizure-induced cell death between cell death-resistant and cell death-susceptible strains.

Imidazenil, a non-sedating anticonvulsant benzodiazepine, is more potent than diazepam in protecting against DFP-induced seizures and neuronal damage

Organophosphate (OP)-nerve agent poisoning may lead to prolonged epileptiform seizure activity, which can result in irreversible neuronal brain damage. A timely and effective control of seizures with pharmacological agents can minimize the secondary and long-term neuropathology that may result from this damage. Diazepam, the current anticonvulsant of choice in the management of OP poisoning, is associated with unwanted effects such as sedation, amnesia, cardio-respiratory depression, anticonvulsant tolerance, and dependence liabilities. In search for an efficacious and safer anticonvulsant benzodiazepine, we studied imidazenil, a potent anticonvulsant that is devoid of sedative action and has a low intrinsic efficacy at alpha1- but is a high efficacy positive allosteric modulator at alpha5-containing GABA(A) receptors. We compared the potency of a combination of 2 mg/kg, i.p. atropine with: (a) imidazenil 0.05-0.5 mg/kg i.p. or (b) equipotent anti-bicuculline doses of diazepam (0.5-5 mg/kg, i.p.), against diisopropyl fluorophosphate (DFP; 1.5 mg/kg, s.c.)-induced status epilepticus and its associated neuronal damage. The severity and frequency of seizure activities were determined by continuous radio telemetry recordings while the extent of neuronal damage and neuronal degeneration were assessed using the TUNEL-based cleaved DNA end-labeling technique or neuron-specific nuclear protein (NeuN)-immunolabeling and Fluoro-Jade B (FJB) staining, respectively. We report here that the combination of atropine and imidazenil is at least 10-fold more potent and longer lasting than the combination with diazepam at protecting rats from DFP-induced seizures and the associated neuronal damage or ongoing degeneration in the anterior cingulate cortex, CA1 hippocampus, and dentate gyrus. While 0.5 mg/kg imidazenil effectively attenuated DFP-induced neuronal damage and the ongoing neuronal degeneration in the anterior cingulate cortex, dentate gyrus, and CA1 hippocampus, 5 mg/kg or a higher dose of diazepam is required to produce similar protective effects. These finding suggests that imidazenil, a non-sedating anticonvulsant BZ ligand, is a more potent, effective, and safer drug than diazepam in protecting rats from DFP-induced seizures and the associated neuronal damage and/or ongoing neuronal degeneration.

Status epilepticus induces a particular microglial activation state characterized by enhanced purinergic signaling

Microglia cells are the resident macrophages of the CNS, and their activation plays a critical role in inflammatory reactions associated with many brain disorders, including ischemia, Alzheimer's and Parkinson's diseases, and epilepsy. However, the changes of microglia functional properties in epilepsy have rarely been studied. Here, we used a model of status epilepticus (SE) induced by intraperitoneal kainate injections to characterize the properties of microglial cells in hippocampal slices from CX3CR1(eGFP/+) mice. SE induced within 3 h an increased expression of inflammatory mediators in the hippocampus, followed by a modification of microglia morphology, a microglia proliferation, and a significant neurodegeneration in CA1. Changes in electrophysiological intrinsic membrane properties of hippocampal microglia were detected at 24-48 h after SE with, in particular, the appearance of new voltage-activated potassium currents. Consistent with the observation of an upregulation of purinergic receptor mRNAs in the hippocampus, we also provide pharmacological evidence that microglia membrane currents mediated by the activation of P2 receptors, including P2X(7), P2Y(6), and P2Y(12), were increased 48 h after SE. As a functional consequence of this modification of purinergic signaling, motility of microglia processes toward a source of P2Y(12) receptor agonist was twice as fast in the epileptic hippocampus. This study is the first functional description of microglia activation in an in vivo model of inflammation and provides evidence for the existence of a particular microglial activation state after a status epilepticus.

Effect of oxcarbazepine pretreatment on convulsive activity and brain damage induced by kainic acid administration in rats

Temporal lobe epilepsy is one of the most common types of epilepsy. Progress in the understanding and treatment of this type of epilepsy would be greatly facilitated by the availability of an animal model, which reproduced the behavioral and electrographic features of this condition. In this context, kainic acid (KA, 2-carboxy-3-carboxymethyl-4-isopropenylpyrrolidine) administration causes a syndrome characterized by an acute status epilepticus and subsequent brain damage similar to that in temporal lobe epilepsy of humans. The aim of the present study was to investigate whether oxcarbazepine (10,11-dihydro-10-oxo-5 H -dibenz(b,f)azepine-5-carboxamide), an antiepileptic drug, protects against both epileptic activity and brain damage induced by KA administration. Chronically implanted adult male Wistar rats were polygraphically recorded during 10 continuous hours under 4 different conditions: a) control, b) after KA administration alone, c) after KA administration in oxcarbazepine pretreated animals and d) after the administration of oxcarbazepine alone. Animals treated with KA alone presented behavioral and electrophysiological convulsive activity as well as brain damage. Latency of seizure installation was lengthened significantly and convulsive activity was slightly reduced, however, brain damage was still present in oxcarbazepine pretreated animals. Administration of oxcarbazepine alone induced a hypnotic behavior and brain damage was also present.

Directed differentiation of hippocampal stem/progenitor cells in the adult brain

Adult neurogenesis is a lifelong feature of brain plasticity; however, the potency of adult neural stem/progenitor cells in vivo remains unclear. We found that retrovirus-mediated overexpression of a single gene, the bHLH transcription factor Ascl1, redirected the fate of the proliferating adult hippocampal stem/progenitor (AHP) progeny and lead to the exclusive generation of cells of the oligodendrocytic lineage at the expense of newborn neurons, demonstrating that AHPs in the adult mouse brain are not irrevocably specified in vivo. These data indicate that AHPs have substantial plasticity, which might have important implications for the potential use of endogenous AHPs in neurological disease.

Effect of age on kainate-induced seizure severity and cell death

While the onset and extent of epilepsy increases in the aged population, the reasons for this increased incidence remain unexplored. The present study used two inbred strains of mice (C57BL/6J and FVB/NJ) to address the genetic control of age-dependent neurodegeneration by building upon previous experiments that have identified phenotypic differences in susceptibility to hippocampal seizure-induced cell death. We determined if seizure induction and seizure-induced cell death are affected differentially in young adult, mature, and aged male C57BL/6J and FVB/NJ mice administered the excitotoxin, kainic acid. Dose response testing was performed in three to four groups of male mice from each strain. Following kainate injections, mice were scored for seizure activity and brains from mice in each age group were processed for light microscopic histopathologic evaluation 7 days following kainate administration to evaluate the severity of seizure-induced brain damage. Irrespective of the dose of kainate administered or the age group examined, resistant strains of mice (C57BL/6J) continued to be resistant to seizure-induced cell death. In contrast, aged animals of the FVB/NJ strain were more vulnerable to the induction of behavioral seizures and associated neuropathology after systemic injection of kainic acid than young or middle-aged mice. Results from these studies suggest that the age-related increased susceptibility to the neurotoxic effects of seizure induction and seizure-induced injury is regulated in a strain-dependent manner, similar to previous observations in young adult mice.

DeltaRR vaccination protects from KA-induced seizures and neuronal loss through ICP10PK-mediated modulation of the neuronal-microglial axis

Ischemic brain injury and epilepsy are common neurodegenerative diseases caused by excitotoxicity. Their pathogenesis includes microglial production of inflammatory cytokines. Our studies were designed to examine whether a growth compromised HSV-2 mutant (Delta RR) prevents excitotoxic injury through modulation of microglial responses by the anti-apoptotic HSV-2 protein ICP10PK. EOC2 and EOC20 microglial cells, which are differentially activated, were infected with Delta RR or the ICP10PK deleted virus (Delta PK) and examined for virus-induced neuroprotective activity. Both cell lines were non-permissive for virus growth, but expressed ICP10PK (Delta RR) or the PK deleted ICP10 protein p95 (Delta PK). Conditioned medium (CM) from Delta RR-, but not Delta PK-infected cells prevented N-methyl-D-aspartate (NMDA)-induced apoptosis of primary hippocampal cultures, as determined by TUNEL and caspase-3 activation (76.9 +/- 5.3% neuroprotection). Neuroprotection was associated with inhibition of TNF-alpha and RANTES and production of IL-10. The CM from Delta PK-infected EOC2 and EOC20 cells did not contain IL-10, but it contained TNF-alpha and RANTES. IL-10 neutralization significantly (p < 0.01) decreased, but did not abrogate, the neuroprotective activity of the CM from Delta RR-infected microglial cultures indicating that ICP10PK modulates the neuronal-microglial axis, also through induction of various microglial neuroprotective factors. Rats given Delta RR (but not Delta PK) by intranasal inoculation were protected from kainic acid (KA)-induced seizures and neuronal loss in the CA1 hippocampal fields. Protection was associated with a significant (p < 0.001) increase in the numbers of IL-10+ microglia (CD11b+) as compared to Delta PK-treated animals. Delta RR is a promising vaccination/therapy platform for neurodegeneration through its pro-survival functions in neurons as well as microglia modulation.

Photostability of kainic acid in seawater

The environmental degradation of a mixture of domoic acid (DA) and kainic acid (KA) in seawater with and without added transition metals is reported. The association constants for kainic acid with Fe (III) and Cu (II) were determined using (1)H nuclear magnetic resonance (NMR; K1,Fe(III) = 2.27 x 10(12), K2,Fe(III) = 8.99 x 10(8), K1,Cu(II) = 1.38 x 10(10), and K2,Cu(II) = 4.35 x 10(7)). The photochemical half-life of kainic acid has been determined to be significantly longer (40-100 h) than that of domoic acid in corresponding marine systems (12-34 h). The significance of this finding was highlighted by a comparison of the quantification of a mixture of kainic and domoic acids during photodegradation by liquid chromatography-tandem mass spectrometry (LC-MS/MS) techniques and the widely used competitive enzyme-linked immunosorbent assay (cELISA; Biosense Laboratories) method. The MS-based analysis showed that approximately 50% of the DA was photodegraded within 15 h. In contrast, the domoic acid cELISA assay reported that the concentration essentially remained unchanged over this period. The possibility of interference from naturally occurring kainic acid during cELISA measurements could lead to the overestimation of total domoic acid, especially if they occur in mixtures in sunlit waters.

The effect of electroacupuncture on spontaneous recurrent seizure and expression of GAD(67) mRNA in dentate gyrus in a rat model of epilepsy

Concerns regarding the side effects of pharmacological approaches have recently increased interest in the use of acupuncture for treatment of epilepsy. Although clinical evidence for the acupunctural anti-epileptic effect has been demonstrated, the precise mechanism still remains unknown. The purpose of this study was to investigate the effect of electroacupuncture (EA) on spontaneous recurrent seizure (SRS) and expression of GAD(67) mRNA in dentate gyrus (DG) in epileptic rats. EA at bilateral acupoints of Zusanli (St36) was administered. Two sham EA controls were set: sham EA at bilateral nearby nonacupoints in the hamstring muscles, and sham EA at bilateral St36 without electrical stimulation. Lithium-pilocarpine injection was performed to establish the rat model of epilepsy at the 1st day. Three time points were set according to the day when the rats were killed (30th, 45th, 60th day). The results showed that EA at St36 significantly reduced the times of spontaneous recurrent seizure, neither of the two sham EA controls displayed significant effect on spontaneous recurrent seizure. Moreover, EA at St36 significantly elevated the expression of GAD(67) mRNA in DG granule cell layer (GCL), but not in the hilus; neither of the two sham controls showed significant effect on the expression of GAD(67) mRNA in granule cell layer or hilus. The findings suggest that EA at St36 possess some curative effect on epileptic rats, related with change of GAD(67) mRNA level in DG region.

Gambogic amide, a selective agonist for TrkA receptor that possesses robust neurotrophic activity, prevents neuronal cell death

Nerve growth factor (NGF) binds to TrkA receptor and triggers activation of numerous signaling cascades, which play critical roles in neuronal plasticity, survival, and neurite outgrowth. To mimic NGF functions pharmacologically, we developed a high-throughput screening assay to identify small-molecule agonists for TrkA receptor. The most potent compound, gambogic amide, selectively binds to TrkA, but not TrkB or TrkC, and robustly induces its tyrosine phosphorylation and downstream signaling activation, including Akt and MAPKs. Further, it strongly prevents glutamate-induced neuronal cell death and provokes prominent neurite outgrowth in PC12 cells. Gambogic amide specifically interacts with the cytoplasmic juxtamembrane domain of TrkA receptor and triggers its dimerization. Administration of this molecule in mice substantially diminishes kainic acid-triggered neuronal cell death and decreases infarct volume in the transient middle cerebral artery occlusion model of stroke. Thus, gambogic amide might not only establish a powerful platform for dissection of the physiological roles of NGF and TrkA receptor but also provide effective treatments for neurodegenerative diseases and stroke.

Pyruvate protects against kainate-induced epileptic brain damage in rats

Although the majority of epileptic seizures can be effectively controlled with antiepileptic drugs and/or surgery, a significant number progress to status epilepticus of sufficient duration to cause permanent brain damage. Combined treatment with antiepileptic drugs and neuroprotective agents, however, may help protect these individuals from permanent brain damage. Since toxicity induced by endogenous zinc contributes to epileptic brain injury, and since pyruvate is effective in reducing zinc-triggered neuronal death in cortical culture as well as ischemic neuronal death in vivo, we examined whether systemic pyruvate administration reduces seizure-induced brain damage. Na pyruvate (500 mg/kg) or osmolarity-matched saline (265 mg/kg NaCl, i.p.) were given to adult SD rats 30 or 150 min after 10 mg/kg kainite injection (i.p.), and there was no significant difference in the time course or severity of seizures between these groups. Zinc accumulation in neuronal cell bodies in the hippocampus, however, was much lower in the pyruvate than in the saline group. There was a close correlation between zinc accumulation and cell death, as assessed by acid-fuchsin and TUNEL staining. Pyruvate treatment markedly reduced neuronal death in the hippocampus, neocortex and thalamus. Pyruvate increased HSP-70 expression in hippocampal neurons. These results suggest that pyruvate, a natural glucose metabolite, may be useful as adjunct treatment in status epilepticus to reduce permanent brain damage.

Domoic acid preconditioning and seizure induction in young and aged rats

Clinical reports suggest that the elderly are hypersensitive to the neurological effects of domoic acid (DOM). In the present study we assessed DOM-induced seizures in young and aged rats, and seizure attenuation following low-dose DOM pretreatment (i.e. preconditioning). Seizure behaviours following saline or DOM administration (0.5-2mg/kg i.p.) were continuously monitored for 2.5h in naïve and DOM preconditioned rats. Competitive ELISA was used to determine serum and brain DOM concentrations. Dose- and age-dependent increases in seizure activity were evident in response to DOM. Lower doses of DOM in young and aged rats promoted low level seizure behaviours. Animals administered high doses (2mg/kg in young; 1mg/kg in aged) progressed through various stages of stereotypical behaviour (e.g., head tics, scratching, wet dog shakes) before ultimately exhibiting tonic-clonic convulsions. Serum and brain DOM analysis indicated impaired renal clearance as contributory to increased DOM sensitivity in aged animals, and this was supported by seizure analysis following direct intrahippocampal administration of DOM. Preconditioning young and aged animals with low-dose DOM 45-90 min before high-dose DOM significantly reduced seizure intensity. We conclude that age-related supersensitivity to DOM is related to reduced clearance rather than increased neuronal sensitivity, and that preconditioning mechanisms underlying an inducible tolerance to excitotoxins are robustly expressed in both young and aged CNS.

Limbic Structures Show Altered Glial–Neuronal Metabolism in the Chronic Phase of Kainate Induced Epilepsy

A better understanding is needed of how glutamate metabolism is affected in mesial temporal lobe epilepsy (MTLE). Here we investigated glial-neuronal metabolism in the chronic phase of the kainate (KA) model of MTLE. Thirteen weeks following systemic KA, rats were injected i.p. with [1-(13)C]glucose. Brain extracts from hippocampal formation, entorhinal cortex, and neocortex, were analyzed by (13)C and (1)H magnetic resonance spectroscopy to quantify (13)C labeling and concentrations of metabolites, respectively. The amount and (13)C labeling of glutamate were reduced in the hippocampal formation and entorhinal cortex of epileptic rats. Together with the decreased concentration of NAA, these results indicate neuronal loss. Additionally, mitochondrial dysfunction was detected in surviving glutamatergic neurons in the hippocampal formation. In entorhinal cortex glutamine labeling and concentration were unchanged despite the reduced glutamate content and label, possibly due to decreased oxidative metabolism and conserved flux of glutamate through glutamine synthetase in astrocytes. This mechanism was not operative in the hippocampal formation, where glutamine labeling was decreased. In neocortex labeling and concentration of GABA were increased in epileptic rats, possibly representing a compensatory mechanism. The changes in the hippocampus might be of pathophysiological importance and merit further studies aiming at resolving metabolic causes and consequences of MTLE.

In vivo mapping of temporospatial changes in manganese enhancement in rat brain during epileptogenesis

Mesial temporal lobe epilepsy is associated with structural and functional abnormalities, such as hippocampal sclerosis and axonal reorganization. The temporal evolution of these changes remains to be determined, and there is a need for in vivo imaging techniques that can uncover the epileptogenic processes at an early stage. Manganese-enhanced magnetic resonance imaging may be useful in this regard. The aim of this study was to analyze the temporospatial changes in manganese enhancement in rat brain during the development of epilepsy subsequent to systemic kainate application (10 mg/kg i.p.). MnCl(2) was given systemically on day 2 (early), day 15 (latent), and 11 weeks (chronic phase) after the initial status epilepticus. Twenty-four hours after MnCl(2) injection T1-weighted 3D MRI was performed followed by analysis of manganese enhancement. In the medial temporal lobes, there was a pronounced decrease in manganese enhancement in CA1, CA3, dentate gyrus, entorhinal cortex and lateral amygdala in the early phase. In the latent and chronic phases, recovery of the manganese enhancement was observed in all these structures except CA1. A significant increase in manganese enhancement was detected in the entorhinal cortex and the amygdala in the chronic phase. In the latter phase, the structurally intact cerebellum showed significantly decreased manganese enhancement. The highly differentiated changes in manganese enhancement are likely to represent the net outcome of a number of pathological and pathophysiological events, including cell loss and changes in neuronal activity. Our findings are not consistent with the idea that manganese enhancement primarily reflects changes in glial cells.

A quantitative trait locus on chromosome 18 is a critical determinant of excitotoxic cell death susceptibility

C57BL/6J (B6) and FVB/NJ (FVB) mice are phenotypically distinct in their susceptibility to seizure-induced cell death after kainate administration. Previous studies using quantitative trait loci (QTLs) mapping established that the distal region of mouse chromosome 18 contains a gene(s) that is probably responsible for the difference in seizure-induced cell death susceptibility between two inbred strains, B6 and FVB, that are relatively resistant and susceptible, respectively, to seizure-induced cell death. The genetic locus has been mapped to a approximately 12-centimorgan region of chromosome 18, designated as seizure-induced cell death 1 (Sicd1). In order to confirm the Sicd1 QTL, we have developed congenic mouse strains containing the relevant donor segment from the resistant B6 strain on the susceptible FVB background, also referred to as the FVB.B6-Sicd1 congenic strain. Congenic and FVB littermate controls were tested in a seizure-induced cell death paradigm. The presence of B6 chromosome 18 alleles on an FVB genetic background conferred protection against seizure-induced cell death, as compared with FVB littermate controls. To further localize the Sicd1 QTL, new congenic lines carrying overlapping intervals of the B6 segment were created [interval-specific congenic lines (ISCLs)-1-4] and assessed for seizure-induced cell death phenotype. All of the ISCLs exhibited reduced cell death associated with the B6 phenotype, as compared with the parental FVB strain. The most dramatic of these, ISCL-4, showed a nearly four-fold reduction in the extent of seizure-induced cell death. This suggests that ISCL-4 contains the putative gene(s) of the Sicd1 QTL.

Upregulation of synaptotagmin IV protein in kainate-induced seizures

Synaptotagmin IV is a product of immediate early-response gene. It is involved in the regulated neurosecretion in the brain. Its putative role, however, in vesicular transport and localization in secretor y vesicles is still a matter of debate. Here we followed the spatiotemporal pattern of synaptotagmin IV protein upregulation in the hippocampus, caudate putamen, nucleus accumbens, nucleus amygdalae, piriform and entorhinal cortices of rats with kainate-induced seizures. We found that upregulation pattern paralleled the direction of depolarization through the hippocampus and also reflecting seizure activity spreading to other brain regions. We speculate that synaptotagmin IV may have a role in the vesicular transport of the upregulated peptides and proteins involved in the plasticity and/or neurodegeneration provoked by the kainate.

UDP acting at P2Y6 receptors is a mediator of microglial phagocytosis

Microglia, brain immune cells, engage in the clearance of dead cells or dangerous debris, which is crucial to the maintenance of brain functions. When a neighbouring cell is injured, microglia move rapidly towards it or extend a process to engulf the injured cell. Because cells release or leak ATP when they are stimulated or injured, extracellular nucleotides are thought to be involved in these events. In fact, ATP triggers a dynamic change in the motility of microglia in vitro and in vivo, a previously unrecognized mechanism underlying microglial chemotaxis; in contrast, microglial phagocytosis has received only limited attention. Here we show that microglia express the metabotropic P2Y6 receptor whose activation by endogenous agonist UDP triggers microglial phagocytosis. UDP facilitated the uptake of microspheres in a P2Y6-receptor-dependent manner, which was mimicked by the leakage of endogenous UDP when hippocampal neurons were damaged by kainic acid in vivo and in vitro. In addition, systemic administration of kainic acid in rats resulted in neuronal cell death in the hippocampal CA1 and CA3 regions, where increases in messenger RNA encoding P2Y6 receptors that colocalized with activated microglia were observed. Thus, the P2Y6 receptor is upregulated when neurons are damaged, and could function as a sensor for phagocytosis by sensing diffusible UDP signals, which is a previously unknown pathophysiological function of P2 receptors in microglia.

Effect of novel AMPA antagonist, NS1209, on status epilepticus

The current first line treatment of status epilepticus (SE) is based on the use of compounds that enhance GABAergic transmission or block sodium channels. These treatments discontinue SE in only two-thirds of patients, and therefore new therapeutic approaches are needed. We investigated whether a novel water-soluble AMPA antagonist, NS1209, discontinues SE in adult rats. SE was induced by electrical stimulation of the amygdala or subcutaneous administration of kainic acid. Animals were monitored continuously with video-electroencephalography during SE and drug treatment. We found that NS1209 could be safely administered to rats undergoing electrically induced SE at doses up to 50mg/kg followed by intravenous infusion of 5mg/kg for up to 24h. NS1209 administered as a bolus dose of 10-50mg/kg (i.p. or i.v.) followed by infusion of 4 or 5mg/kg h (i.v.) for 2-24h effectively discontinued electrically induced SE in all animals within 30-60 min, and there was no recurrence of SE after a 24-h infusion. Kainate-induced SE was similarly blocked by 10 or 30 mg/kg NS1209 (i.v.). To compare the efficacy and neuroprotective effects of NS1209 with those of diazepam (DZP), one group of rats received DZP (20mg/kg, i.p. and another dose of 10 mg/kg 6h later). By using the administration protocols described, the anticonvulsant effect of NS1209 was faster and more complete than that of DZP. NS1209 treatment (20 mg/kg bolus followed by 5mg/kg h infusion for 24 h) was neuroprotective against SE-induced hippocampal neurodegeneration, but to a lesser extent than DZP. These findings suggest that AMPA receptor blockade by NS1209 provides a novel and mechanistically complimentary addition to the armamentarium of drugs used to treat SE in humans.

Effects of Manganese Complexes of Curcumin and Diacetylcurcumin on Kainic Acid-Induced Neurotoxic Responses in the Rat Hippocampus

This study aimed to investigate the mechanism underlying the protective effects of manganese complexes of curcumin (Cp-Mn) and diacetylcurcumin (DiAc-Cp-Mn) on kainic acid (KA)-induced excitotoxicity in the rat hippocampus. Systemic injection of KA (10 mg/kg, i.p.) caused seizures and increased the expression of neurotoxic markers, immediate early genes [c-jun, cyclooxygenase 2 (COX-2), brain-derived neurotrophic factor (BDNF), and heat shock protein 70 (hsp70)] and a delayed response gene [inducible nitric oxide synthase (iNOS)], which were measured at 6 and 72 h after KA injection, respectively, in the hippocampus. Pretreatment with Cp-Mn (50 mg/kg, i.p.) and DiAc-Cp-Mn (50 mg/kg, i.p.) but not with curcumin (50 mg/kg, i.p.) delayed the onset of KA-induced seizure without affecting the seizure score. KA injection induced c-Fos immunoreactivity in DG, CA1, and CA3 hippocampal regions, the expression of which peaked at 6 h after injection. Cp-Mn and DiAc-Cp-Mn treatment significantly decreased c-Fos expression elicited by KA. Moreover, Cp-Mn and DiAc-Cp-Mn administration suppressed the KA-induced expression of c-jun, COX-2, BDNF, and iNOS mRNA, whereas curcumin attenuated only iNOS mRNA expression. No compounds tested had an effect on KA-induced hsp70 expression. It is therefore likely that in addition to radical scavenging and SOD-like activities, the suppression of potential neuronal injury marker expression by Cp-Mn and DiAc-Cp-Mn, contributes to the neuroprotective activities of these compounds, which are superior to those of curcumin, on KA-induced excitotoxicity in the hippocampus. These results suggest the beneficial effects of Cp-Mn, and DiAc-Cp-Mn on the treatment of excitotoxicity-induced neurodegenerative diseases.

Kainic acid dose affects delayed cell death mechanism after status epilepticus

Kainic acid (KA)-induced status epilepticus (SE) produces hippocampal neuronal death, which varies from necrosis to apoptosis or programmed cell death (PCD). We examined whether the type of neuronal death was dependent on KA dose. Adult rats were induced SE by intraperitoneal injection of KA at 9 mg/kg (K9) or 12 mg/kg (K12). Hippocampal neuronal death was assessed by TUNEL staining, electron microscopy, and Western blotting of caspase-3 on days 1, 3 and 7 after SE induction. K12 rats showed higher a mortality rate and shorter latency to the onset of SE when compared with K9 rats. In both groups, acidophilic and pyknotic neurons were evident in CA1 at 24h after SE and neuronal loss developed from day 3. The degenerated neurons became TUNEL-positive on days 3 and 7 in K9 rats but not in K12 rats. Caspase-3 activation was detected on days 3 and 7 in K9 rats but was undetectable in K12 rats. Ultrastructural study revealed shrunken neurons exhibiting pyknotic nuclei containing small and dispersed chromatin clumps 24h after SE in CA1. No cells exhibited apoptosis. On days 3 and 7, the degenerated neurons were necrotic with high electron density and small chromatin clumps. There were no ultrastructural differences between the K9 and K12 groups. These results revealed that differences in KA dose affected the delayed cell death (3 and 7 days after SE); however, no effect was seen on the early cell death (24h after SE). Moderate-dose KA induced necrosis, while low-dose KA induced PCD.

Preferential neuron loss in the rat piriform cortex following pilocarpine-induced status epilepticus

Structures within the piriform cortex (PC) including the endopiriform nucleus (DEN) and pre-endopiriform nucleus (pEn) have been implicated to be involved in seizure genesis in models of temporal lobe epilepsy. We used stereological methods to examine the specificity and extent of neuron loss in the PC of pilocarpine-treated rats. Both 7 days and 2 months post-status epilepticus rats showed significant neuron loss in the pEn and DEN, layer III of the intermediate PC, and layers II and III of the caudal PC. Total losses in the PC were 40 and 46% in 7 days and 2 months post-status epilepticus rats, respectively (p<0.01). The numbers of parvalbumin (PV)- and cholecystokinin (CCK)-immunopositive neuron profiles significantly decreased, and somatostatin (SS)-immunopositive neuron profiles tended to decrease. A large decrease in the number of PV-immunopositive neuron profiles occurred in the pEn, adjoining parts of the DEN and deep layer III of the PC, portions of the DEN bordering the claustrum and agranular insular cortex, and layer III of the caudal PC. The regions with decreased numbers of PV-, CCK-, and SS-immunopositive neuron profiles overlapped with those where many Nissl-stained neurons were lost and many degenerating cell bodies were detected. These results suggest that the decreases in the numbers of PV/SS/CCK-immunopositive neurons are related to neuron loss rather than to a low rate of synthesis of their peptides or proteins.

Comparison of seizure phenotype and neurodegeneration induced by systemic kainic acid in inbred, outbred, and hybrid mouse strains

We assessed inbred, outbred and hybrid mouse strains for susceptibility to seizures and neurodegeneration induced by systemic administration of kainic acid (KA). Each strain showed a unique pattern of susceptibility to seizures as assessed by the dose necessary to induce continuous tonic clonic seizures, progression through six seizure levels, the number of mice that failed to satisfy seizure criteria, and seizure-induced mortality. In general, the C57BL/6, ICR, FVB/N, and BALB/c strains were resistant to seizures while the C57BL/10, DBA/2 J, and F1 C57BL/6*CBA/J strains were vulnerable. Neuronal cell death was quantified in four subfields of the hippocampus: CA3, the hilus of the dentate gyrus, CA1, and the dentate granule cell layer. Neurodegeneration was also semiquantitatively assessed in other brain regions including the neocortex, striatum, thalamus, hypothalamus and amygdala. Although there was variability in the extent of cell death within strains, there were significant differences in the amount of hippocampal cell death between strains and also different patterns of neurodegeneration in affected brain areas. In general, the C57BL/6, C57BL/10, and F1 C57BL/6*CBA/J strains were resistant to neurodegeneration while the FVB/N, ICR and DBA/2 J strains were vulnerable. The BALB/c strain was unique in that neurodegeneration was confined to the hippocampus. Consistent with previous findings, the resistant neurodegeneration phenotype was dominant in an F1 cross of resistant and vulnerable inbred strains. Our results, using a large number of mouse strains, definitively demonstrate that a mouse strain's seizure phenotype is not related to its neurodegeneration phenotype.

Neuroprotection of Tat-GluR6-9c against neuronal death induced by kainate in rat hippocampus via nuclear and non-nuclear pathways

Previous studies have suggested that glutamate receptor 6 (GluR6) subunit- and JNK-deficient mice can resist kainate-induced epileptic seizure and neuronal toxicity (Yang, D. D., Kuan, C.-Y., Whitmarsh, A. J., Rinoćn, M., Zheng, T. S., Davis, R. J., Rakic, P., and Flavell, R. A. (1997) Nature 389, 865-870; Mulle, C., Seiler, A., Perez-Otano, I., Dickinson-Anson, H., Castillo, P. E., Bureau, I., Maron, C., Gage, F. H., Mann, J. R., Bettler, B., and Heinemmann, S. F. (1998) Nature 392, 601-605). In this study, we show that kainate can enhance the assembly of the GluR6-PSD95-MLK3 module and facilitate the phosphorylation of JNK in rat hippocampal CA1 and CA3/dentate gyrus (DG) subfields. More important, a peptide containing the Tat protein transduction sequence (Tat-GluR6-9c) perturbed the assembly of the GluR6-PSD95-MLK3 signaling module and suppressed the activation of MLK3, MKK7, and JNK. As a result, the inhibition of JNK activation by Tat-GluR6-9c diminished the phosphorylation of the transcription factor c-Jun and down-regulated Fas ligand expression in hippocampal CA1 and CA3/DG regions. The inhibition of JNK activation by Tat-Glur6-9c attenuated Bax translocation, the release of cytochrome c, and the activation of caspase-3 in CA1 and CA3/DG subfields. Furthermore, kainate-induced neuronal loss in hippocampal CA1 and CA3 subregions was prevented by intracerebroventricular injection of Tat-Glur6 - 9c. Taken together, our findings strongly suggest that the GluR6-PSD95-MLK3 signaling module mediates activation of the nuclear and non-nuclear pathways of JNK, which is involved in brain injury induced by kainate. Tat-GluR6-9c, the peptide we constructed, gives new insight into seizure therapy.

Increased estrogen receptor beta expression correlates with decreased spine formation in the rat hippocampus

Estrogens play an important role in the brain function acting through two receptor types, ERalpha and ERbeta, both well-recognized as transcription factors. In this study, we investigated the ERbeta mRNA and protein levels in the rat hippocampus by using two in vivo models that are known to affect synapse formation. Natural estrous-proestrous cycle was used as a model in which a marked decrease in the density of hippocampal synapses was previously observed between proestrus and estrus. We have found that ERbeta mRNA and protein were displayed in high levels in the estrus and in low levels in the proestrous phase. By applying kainic acid (KA) to adult rats, we demonstrated that up-regulation of ERbeta mRNA and protein in hippocampal CA regions was vulnerable to KA-induced excitotoxicity. Furthermore, we note a concomitant decrease of ERbeta in the excitotoxicity-resistant denate gyrus that undergoes intense plastic changes, including synaptogenesis. These data suggested that decreases in ERbeta expression correlated with increase in synapse formation. This notion has been tested in vitro in hippocampal cultures, in which overexpression of ERbeta by means of gene transfection resulted in the lowering of the dendritic spine density that was elevated by estrogen. In summary, our results suggest that ERbeta inhibits synapse formation in hippocampal neurons.

Profile and regulation of apolipoprotein E (ApoE) expression in the CNS in mice with targeting of green fluorescent protein gene to the ApoE locus

To study the profile and regulation of apolipoprotein E (apoE) expression in the CNS, we generated mice in which apoE expression can be detected in vivo with unprecedented sensitivity and resolution. cDNA encoding enhanced green fluorescent protein (EGFP) with a stop codon was inserted by gene targeting into the apoE gene locus (EGFPapoE) immediately after the translation initiation site. Insertion of EGFP into one apoE allele provides a real-time location marker of apoE expression in vivo; the remaining allele is sufficient to maintain normal cellular physiology. In heterozygous EGFPapoE mice, EGFP was highly expressed in hepatocytes and peritoneal macrophages. EGFP was also expressed in brain astrocytes; however some astrocytes (approximately 25%) expressed no EGFP, suggesting that a subset of these cells does not express apoE. EGFP was expressed in <10% of microglia after kainic acid treatment, suggesting that microglia are not a major source of brain apoE. Although hippocampal neurons did not express EGFP under normal conditions, kainic acid treatment induced intense expression of EGFP in injured neurons, demonstrating apoE expression in neurons in response to excitotoxic injury. The neuronal expression was confirmed by in situ hybridization of mouse apoE mRNA and by anti-apoE immunostaining. Smooth muscle cells of large blood vessels and cells surrounding small vessels in the CNS also strongly expressed EGFP, as did cells in the choroid plexus. EGFPapoE reporter mice will be useful for studying the regulation of apoE expression in the CNS and might provide insights into the diverse mechanisms of apoE4-related neurodegeneration.

Mutations in amyloid precursor protein and presenilin-1 genes increase the basal oxidative stress in murine neuronal cells and lead to increased sensitivity to oxidative stress mediated by amyloid beta-peptide (1-42), HO and kainic acid: implications for Alzheimer's disease

Oxidative stress is observed in Alzheimer's disease (AD) brain, including protein oxidation and lipid peroxidation. One of the major pathological hallmarks of AD is the brain deposition of amyloid beta-peptide (Abeta). This 42-mer peptide is derived from the beta-amyloid precursor protein (APP) and is associated with oxidative stress in vitro and in vivo. Mutations in the PS-1 and APP genes, which increase production of the highly amyloidogenic amyloid beta-peptide (Abeta42), are the major causes of early onset familial AD. Several lines of evidence suggest that enhanced oxidative stress, inflammation, and apoptosis play important roles in the pathogenesis of AD. In the present study, primary neuronal cultures from knock-in mice expressing mutant human PS-1 and APP were compared with those from wild-type mice, in the presence or absence of various oxidizing agents, viz, Abeta(1-42), H2O2 and kainic acid (KA). APP/PS-1 double mutant neurons displayed a significant basal increase in oxidative stress as measured by protein oxidation, lipid peroxidation, and 3-nitrotyrosine when compared with the wild-type neurons (p < 0.0005). Elevated levels of human APP, PS-1 and Abeta(1-42) were found in APP/PS-1 cultures compared with wild-type neurons. APP/PS-1 double mutant neuron cultures exhibited increased vulnerability to oxidative stress, mitochondrial dysfunction and apoptosis induced by Abeta(1-42), H2O2 and KA compared with wild-type neuronal cultures. The results are consonant with the hypothesis that Abeta(1-42)-associated oxidative stress and increased vulnerability to oxidative stress may contribute significantly to neuronal apoptosis and death in familial early onset AD.

Neuroprotection of adenoviral-vector-mediated GDNF expression against kainic-acid-induced excitotoxicity in the rat hippocampus

Glial-cell-line-derived neurotrophic factor (GDNF) is a potent survival factor for several types of neurons. In the present study, we examined the protective roles of adenoviral-vector-delivered GDNF (Ad-GDNF) in the hippocampus damaged by kainic-acid (KA)-induced excitotoxicity using GAD-67 immunoreactivity, immunoblot analysis, behavioral test, 5-bromo-2-deoxyuridine (BrdU) and TUNEL assay. Ad-GDNF was pre-inoculated into the KA-treated rat hippocampus 7 days before KA injection. Ad-GDNF resulted in the suppression of KA-induced tonic-clonic convulsions. In situ apoptosis assay demonstrated a significant reduction in apoptotic cells in the CA3 and dentate hilus regions of the Ad-GDNF-pre-inoculated rats (Ad-GDNF-KA), compared to the KA rats. Striking reductions in the density of GAD-67 neurons were also observed in the CA3 and dentate hilus regions of the KA rats. On the other hand, the number of GAD-67-positive cells was recovered to the control levels in the Ad-GDNF-KA rats. Immunoblot analysis further confirmed that GAD-67 and Bcl-2 expression increased in the Ad-GDNF-KA rats compared to KA rats. Taken together, these results suggest that Ad-GDNF may serve to control KA-induced hippocampal cell loss and behavioral seizure.

Alterations of taurine in the brain of chronic kainic acid epilepsy model

The aim of the study was to investigate the changes of taurine in the kainic acid (KA, 10 mg/kg, s.c.) chronic model of epilepsy, six months after KA application. The KA-rats used were divided into a group of animals showing weak behavioural response to KA (WDS, rare focal convulsion; rating scale <2 up to 3 h after KA injection) and a group of strong response to KA (WDS, seizures; rating >3 up to 3 h after KA injection). The brain regions investigated were caudate nucleus, substantia nigra, septum, hippocampus, amygdala/piriform cortex, and frontal, parietal, temporal and occipital cortices. KA-rats with rating <2 developed spontaneous WDS which occurred chronically and six months after KA injection increased taurine levels were found in the hippocampus (125.4% of control). KA-rats with rating >3 developed spontaneous recurrent seizures and six months after injection increased taurine levels were found in the caudate nucleus (162.5% of control) and hippocampus (126.6% of control), while reduced taurine levels were seen in the septum (78.2% of control). In summary, increased taurine levels in the hippocampus may involve processes for membrane stabilisation, thus favouring recovery after neuronal hyperactivity. The increased taurine levels in the caudate nucleus could be involved in the modulation of spontaneous recurrent seizure activity.

Neuroprotection by ovarian hormones in animal models of neurological disease

Ovarian hormones can protect against brain injury, neurodegeneration, and cognitive decline. Most attention has focused on estrogens and accumulating data demonstrate that estrogen seems to specifically protect cortical and hippocampal neurons from ischemic injury and from damage due to severe seizures. Although multiple studies demonstrate protection by estrogen, in only a few instances is the issue of how the steroid confers protection known. Here, we first review data evaluating the neuroprotective effects of estrogens, a selective estrogen receptor modulator (SERM), and estrogen receptor alpha- and beta-selective ligands in animal models of focal and global ischemia. Using focal ischemia in ovariectomized ERalphaKO, ERbetaKO, and wild-type mice, we clearly established that the ERalpha subtype is the critical ER mediating neuroprotection in mouse focal ischemia. In rats and mice, the middle cerebral artery occlusion (MCAO) model was used to represent cerebrovascular stroke, while in gerbils the two-vessel occlusion model, representing global ischemia, was used. The gerbil global ischemia model was used to evaluate the neuroprotective effects of estrogen, SERMs, and ERalpha- and ERbeta-selective compounds in the hippocampus. Analysis of neurogranin mRNA, a marker of viability of hippocampal neurons, with in situ hybridization, revealed that estrogen treatment protected the dorsal CA1 regions not only when administered before, but also when given 1 h after occlusion. Estrogen rarely is secreted alone and studies of neuroprotection have been less extensive for a second key ovarian hormone progesterone. In the second half of this review, we present data on neuroprotection by estrogen and progesterone in animal model of epilepsy followed by exploration into ovarian steroid effects on neuronal damage in models of multiple sclerosis and traumatic brain injury.

Increased uptake of divalent metals lead and cadmium into the brain after kainite-induced neuronal injury

An increase in iron level, number of iron positive cells and ferritin expression has been observed in the rat hippocampus after neuronal injury induced by the excitotoxin, kainate. This is accompanied by an increased expression of divalent metal transporter-1 (DMT1) in the lesioned hippocampus, suggesting that the transporter may be partially responsible for the iron accumulation. DMT1 has a broad substrate range that includes other divalent metals such as lead (Pb) and cadmium (Cd), and the present study was carried out to elucidate the uptake of these metals in the kainate-injected brain. The technique of atomic absorption spectroscopy was used for analyses. Significantly higher lead and cadmium levels were detected in the hippocampus and other brain areas of intracerebroventricular kainate-injected rats treated with lead and cadmium in the drinking water, compared to intracerebroventricular saline-injected rats treated with lead and cadmium in the drinking water. Since very low levels of lead and cadmium are present in the normal animal, these results indicate increased uptake of lead and cadmium into brain areas as a result of the kainate injections. Increased iron levels were also detected in the hippocampus of the kainate-injected rats. The above results show increased uptake of divalent metals into brain areas undergoing neurodegeneration.

Intranasal administration of the growth-compromised HSV-2 vector DeltaRR prevents kainate-induced seizures and neuronal loss in rats and mice

Identification of targets and delivery platforms for gene therapy of neurodegenerative disorders is a clinical challenge. We describe a novel paradigm in which the neuroprotective gene is the herpes simplex virus type 2 (HSV-2) antiapoptotic gene ICP10PK and the vector is the growth-compromised HSV-2 mutant DeltaRR. DeltaRR is delivered intranasally. It is not toxic in rats and mice. ICP10PK is expressed in the hippocampus of the DeltaRR-treated animals for at least 42 days in the absence of virus replication and late virus gene expression. Its expression is regulated by an AP-1 amplification loop. Intranasally delivered DeltaRR prevents kainic acid-induced seizures, neuronal loss, and inflammation, in both rats and mice. The data suggest that DeltaRR is a promising therapeutic platform for neurodegenerative diseases.

Sustained activation of Akt by melatonin contributes to the protection against kainic acid-induced neuronal death in hippocampus

In the present study, the underlying protective mechanism of melatonin on kainic acid (KA)-induced excitotoxicity was examined in the hippocampus of mice. KA, administered intracerebroventricularly (i.c.v.), induced marked neuronal cell death with concurrent microglial activation and subsequent induction of inducible nitric oxide synthase (iNOS) in the hippocampus. Histopathological analysis demonstrated that melatonin (10 mg/kg), administered 1 hr prior to KA, attenuated KA-induced death of pyramidal neurons in the CA3 region. Melatonin obviously suppressed KA-induced microglial activation and consequent iNOS expression that were determined by increased immunoreactivities of microglial marker OX-6 and iNOS, respectively. Increased phosphorylation of Akt in pyramidal neurons was observed as early as 2 hr after administration of melatonin. Further, melatonin resulted in increased expression of astroglial glial cell line-derived neurotrophic factor (GDNF), which started to appear approximately 6 hr after administration of melatonin. The results of the present study demonstrate that melatonin exerts its neuroprotective action against KA-induced excitotoxicity both through the activation of neuronal Akt and via the direct action on hippocampal neurons and through the increased expression of astroglial GDNF, which subsequently activates neuronal PI3K/Akt pathway. Therefore, the present study suggests that melatonin, pineal secretory product, is potentially useful in the treatment of acute brain pathologies associated with excitotoxic neuronal damage such as epilepsy, stroke, and traumatic brain injury.

Regional neuropathology following kainic acid intoxication in adult and aged C57BL/6J mice

We evaluated regional neuropathological changes in adult and aged male mice treated systemically with kainic acid (KA) in a strain reported to be resistant to excitotoxic neuronal damage, C57BL/6. KA was administered in a single intraperitoneal injection. Adult animals were dosed with 35 mg/kg KA, while aged animals received a dose of 20 mg/kg in order to prevent excessive mortality. At time-points ranging from 12 h to 7 days post-treatment, animals were sacrificed and prepared for histological evaluation utilizing the cupric-silver neurodegeneration stain, immunohistochemistry for GFAP and IgG, and lectin staining. In animals of both ages, KA produced argyrophilia in neurons throughout cortex, hippocampus, thalamus, and amygdala. Semi-quantitative analysis of neuropathology revealed a similar magnitude of damage in animals of both ages, even though aged animals received less toxicant. Additional animals were evaluated for KA-induced reactive gliosis, assayed by an ELISA for GFAP, which revealed a 2-fold elevation in protein levels in adult mice, and a 2.5-fold elevation in aged animals. Histochemical evaluation of GFAP and lectin staining revealed activation of astrocytes and microglia in regions with corresponding argyrophilia. IgG immunostaining revealed a KA-induced breach of the blood-brain barrier in animals of both ages. Our data indicate widespread neurotoxicity following kainic acid treatment in C57BL/6J mice, and reveal increased sensitivity to this excitotoxicant in aged animals.

Stereological analysis of forebrain regions in kainate-treated epileptic rats

Patients and models of temporal lobe epilepsy display neuron loss in the hippocampal formation, but neuropathological changes also occur in other forebrain regions. We sought to evaluate the specificity and extent of volume loss of the major forebrain regions in epileptic rats months after kainate-induced status epilepticus. In systematic series of Nissl-stained sections, the areas of major forebrain regions were measured, and volumes were estimated using the Cavalieri principle. In some regions, the optical fractionator method was used to estimate neuron numbers. Most kainate-treated rats showed significant volume loss in the amygdala, olfactory cortex, and septal region, but others displayed different patterns, with significant loss only in the hippocampus or thalamus, for example. Average volume loss was most severe in the amygdala and olfactory cortex (82-83% of controls), especially the caudal parts of both regions. In the piriform cortex (including the endopiriform nucleus) of epileptic rats, an average of approximately one-third of Nissl-stained neurons and one-third of the GABAergic interneurons labeled by in situ hybridization for GAD67 mRNA were lost, and the extent of neuron loss was correlated with the extent of volume loss. Volumetric analysis of major forebrain regions was insensitive to specific neuron loss in subregions such as layer III of the entorhinal cortex and the hilus of the dentate gyrus. These findings provide quantitative evidence that kainate-treated rats tend to display extensive neuron and volume loss in the amygdala and olfactory cortex, although the patterns and extent of loss in forebrain regions vary considerably among individuals. In this status epilepticus-based model, extrahippocampal damage appears to be more extensive and hippocampal damage appears to be less extensive than that reported for patients with temporal lobe epilepsy.

Glycogen synthase kinase 3beta links neuroprotection by 17beta-estradiol to key Alzheimer processes

Estrogen exerts many of its receptor-mediated neuroprotective functions through the activation of various intracellular signal transduction pathways including the mitogen activating protein kinase (MAPK), phospho inositol-3 kinase and protein kinase C pathways. Here we have used a hippocampal slice culture model of kainic acid-induced neurotoxic cell death to show that estrogen can protect against oxidative cell death. We have previously shown that MAPK and glycogen synthase kinase-3beta (GSK-3beta) are involved in the cell death/cell survival induced by kainic acid. In this model and other cellular and in vivo models we have shown that estrogen can also cause the phosphorylation and hence inactivation of GSK-3beta, a known mediator of neuronal cell death. The effect of estrogen on GSK-3beta activity is estrogen receptor mediated. Further, this estrogen/GSK-3beta interaction may have functional consequences in cellular models of some key pathogenic pathways associated with Alzheimer's disease. More specifically, estrogen affects the basal levels of tau phosphorylation at a site known to be phosphorylated by GSK-3beta. Taken together, these data indicate a novel molecular and functional link between estrogen and GSK-3beta and may have implications for estrogen receptor modulation as a target for the prevention of neurodegenerative disorders.

Proechimys guyannensis: an animal model of resistance to epilepsy

PURPOSE

The potential interest of Proechimys guyannensis (PG), a spiny rat species living in the Amazonian region, as an animal model of anticonvulsant mechanisms, prompted the investigation of the susceptibility of this animal species to different epileptogenic treatments.

METHODS

Adult male Wistar and PG animals were submitted to amygdala kindling, the pilocarpine model and the intrahippocampal kainic acid (KA) model. Electrographic, behavioral, and neuropathological changes were compared between Wistar and PG animals.

RESULTS

PG animals demonstrated a striking resistance to reaching stage 5 of kindling. Of the 43 PG rats submitted to the kindling process, only three animals reached stage 5. In the pilocarpine and KA models, doses lower than those used in Wistar rats were able to induce status epilepticus (SE) in PG animals. Pilocarpine-induced SE in PG had a shorter duration, rarely exceeding 2 h, in contrast to the 8- to 12- h long SE in the Wistar rat. Of the 61 PG animals injected with pilocarpine, 48 presented with SE and only two presented with some spontaneous seizures after silent periods of 60 and 66 days. KA elicited self-sustained electrographic SE in PG animals, which lasted for 72 h. None of the surviving animals presented with spontaneous seizures in the long-term observation period (up to 120 days).

CONCLUSIONS

These findings indicate that the PG animal may have natural endogenous anticonvulsant mechanisms and also may be an animal model that is resistant to epileptogenic treatments.

Long-term cosequences of intrahippocampal kainate injection in the Proechimys guyannensis rodent

The Proechimys guyannensis (PG), a spiny rodent specie living in the Amazonian region has been recently studied as an animal model of anti-convulsant mechanisms. The PG was found to be resistant to the administration of the muscarinic cholinergic agonist pilocarpine or the amygdala kindling development. This study examined the susceptibility of this animal species to the intrahippocampal kainic acid (KA) injection. Electrographic, behavioral and neuropathological changes induced by intrahippocampal KA injections were analyzed. PG showed to be extremely sensitive to the acute effects of the KA injection. Although the EEG findings in PG rodents were similar to those typically obtained in Wistar rats the pattern of electrographic activity in PG animals was longer than in Wistar rats. Neuropathological examinations of PG brains that survived KA-induced SE revealed severe cell loss in CA1/CA3 areas of the hippocampus, an extensive cell dispersion in the hilus of DG at the injected site with mossy fiber sprouting in the dentate gyrus supragranular layer. None of PG animals presented spontaneous seizures during the 120 days of observation. These findings confirm our previous observation on the resistance of this animal specie to experimental models of limbic epilepsy.

In vivo treatment with the K+ channel blocker 4-aminopyridine protects against kainate-induced neuronal cell death through activation of NMDA receptors in murine hippocampus

Activation of NMDA receptors has been shown to induce either neuronal cell death or neuroprotection against excitotoxicity in cultured neurons in vitro. To elucidate in vivo neuroprotective role of NMDA receptors, we investigated the effects of activation of NMDA receptors by endogenous glutamate on kainate-induced neuronal damage to the mouse hippocampus in vivo. The systemic administration of the K+ channel blocker 4-aminopyridine (4-AP, 5 mg/kg, i.p.) induced expression of c-Fos in the hippocampal neuronal cell layer, which expression was completely abolished by the noncompetitive NMDA receptor antagonist MK-801, thus indicating that the administration of 4-AP would activate NMDA receptors in the hippocampal neurons. The prior administration of 4-AP at 1 h to 1 day before significantly prevented kainate-induced pyramidal cell death in the hippocampus and expression of pyramidal cells immunoreactive with an antibody against single-stranded DNA. Further immunohistochemical study on deoxyribonuclease II revealed that the pretreatment with 4-AP led to complete abolition of deoxyribonuclease II expression induced by kainate in the CA1 and CA3 pyramidal cells. The neuroprotection mediated by 4-AP was blocked by MK-801 and by the adenosine A1 antagonist 8-cyclopenthyltheophylline. Taken together, in vivo activation of NMDA receptors is capable of protecting against kainate-induced neuronal damage through blockade of DNA fragmentation induced by deoxyribonuclease II in the murine hippocampus.

ADAM9, ADAM10, and ADAM15 mRNA levels in the rat brain after kainic acid-induced status epilepticus

ADAM metalloprotease-disintegrins mediate cell adhesion, proteolytic processing, and signal transduction. In the present study, the mRNA levels of ADAM9, ADAM10, and ADAM15 were examined in rat brain after kainic acid (KA)-induced status epilepticus. ADAM9 and ADAM10 expression was induced in dentate gyrus of hippocampus. ADAM15 expression remained unchanged. The spatiotemporal expression of ADAM9 and ADAM10 suggests that their regulation after the KA-induced status epilepticus could be related to neuroprotection.

Up-regulation of neuropeptide Y levels and modulation of glutamate release through neuropeptide Y receptors in the hippocampus of kainate-induced epileptic rats

Kainate-induced epilepsy has been shown to be associated with increased levels of neuropeptide Y (NPY) in the rat hippocampus. However, there is no information on how increased levels of this peptide might modulate excitation in kainate-induced epilepsy. In this work, we investigated the modulation of glutamate release by NPY receptors in hippocampal synaptosomes isolated from epileptic rats. In the acute phase of epilepsy, a transient decrease in the efficiency of NPY and selective NPY receptor agonists in inhibiting glutamate release was observed. Moreover, in the chronic epileptic hippocampus, a decrease in the efficiency of NPY and the Y(2) receptor agonist, NPY13-36, was also found. Simultaneously, we observed that the epileptic hippocampus expresses higher levels of NPY, which may account for an increased basal inhibition of glutamate release. Consistently, the blockade of Y(2) receptors increased KCl-evoked glutamate release, and there was an increase in Y(2) receptor mRNA levels 30 days after kainic acid injection, suggesting a basal effect of NPY through Y(2) receptors. Taken together, these results indicate that an increased function of the NPY modulatory system in the epileptic hippocampus may contribute to basal inhibition of glutamate release and control hyperexcitability.

Locomotor activity detects subunit-selective effects of agonists and decahydroisoquinoline antagonists at AMPA/kainic acid ionotropic glutamate receptors in adult rats

RATIONALE

In vitro studies have identified a series of decahydroisoquinoline compounds with differential selectivity for the subunits that comprise AMPA/kainic acid receptors. Compounds have been identified that have preferential activity at AMPA receptors (LY302679), whereas others (LY377770) have affinity for GluR5-kainic acid preferring subunit, which is activated by ATPA and kainic acid.

OBJECTIVES

These studies set out to determine if locomotor activity could differentiate these profiles in vivo.

METHODS

Locomotor activity was assessed in photocell drums in male Lister Hooded rats.

RESULTS

AMPA, kainic acid and the GluR5 selective agonist ATPA, all suppressed spontaneous locomotor activity (SLA) in rats at doses of 1.0, 5.0 and 20 mg/kg resp. All three agonists achieve micromolar concentrations measured in whole brain after dosing with 10 mg/kg SC. The decahydroisoquinoline antagonist compounds, LY302679 (GluR2), LY293558 (GluR2, 5) and LY377770 (GluR5) all decreased SLA in rats (ED(min) 2.5, 5.0 and 20 mg/kg respectively). The rank order of potency at GluR2 subunits (LY302679>LY293558>LY377770) was reflected in the same rank order of activity for suppression of SLA. LY293558 reversed the suppression of SLA induced by all three agonists (0.62--2.5 mg/kg). LY377770 reversed the effects of ATPA only (ED(min) 1.0 mg/kg), LY302679 (ED(min) 2.5 mg/kg) attenuated the effect of kainic acid but was ineffective against AMPA and ATPA.

CONCLUSIONS

Both agonist and antagonist suppression of SLA is associated with greater affinity for the GluR2 subunit, while compounds with affinity for the GluR5 subunit were less potent in suppressing SLA.

Role of nicotinic acetylcholine receptors in the regulation of kainic acid-induced hippocampal cell death in mice

Kainic acid (KA) is a well-known excitatory, neurotoxic substance. In mice, morphological damage of hippocampus induced by KA administered intracerebroventricularly (i.c.v.) was markedly concentrated on the CA3 pyramidal neurons. In the present study, the possible role of nicotinic acetylcholine receptors (nAchRs) in hippocampal cell death induced by KA (0.1 microg) administered i.c.v. was examined. Methyllycaconitine (MC; nAchRs antagonist, 20 microg) attenuated KA-induced CA3 pyramidal cell death. KA increased immunoreactivities (IRs) of phorylated extracellular signal-regulated kinase (p-ERK; at 30 min), p-CaMK II (at 30 min), c-Fos (at 2 h), c-Jun (at 2 h), glial fibrillary acidic protein (GFAP at 1 day), and the complement receptor type 3 (OX-42; at 1 day) in hippocampal area. MC attenuated selectively KA-induced p-CaMK II, GFAP and OX-42 IR in the hippocampal CA3 region. Our results suggest that p-CaMK II may play as an important regulator responsible for the hippocampal cell death induced by KA administered i.c.v. in mice. Reactive astrocytes, which was meant by GFAP IR, and activated microglia, which was meant by OX-42 IR, may be a good indicator for measuring the cell death in hippocampal regions by KA-induced excitotoxicity. Furthermore, it is implicated that niconitic receptors appear to be involved in hippocampal CA3 pyramidal cell death induced by KA administered i.c.v. in mice.

Choline acetyltransferase, glutamic acid decarboxylase and somatostatin in the kainic acid model for chronic temporal lobe epilepsy

The aim of the study was to investigate neurochemical changes in a kainic acid (KA; 10 mg/kg, s.c.)-induced spontaneous recurrent seizure model of epilepsy, 6 months after the initial KA-induced seizures. The neuronal markers of cholinergic and gamma-aminobutyric acid (GABA)ergic systems, i.e. choline acetyltransferase (ChAT) and glutamic acid decarboxylase (GAD) activities, and a marker for neuropeptide, i.e. level of somatostatin, have been investigated. The brain regions investigated were the hippocampus, amygdala/piriform cortex, caudate nucleus, substantia nigra and the frontal, parietal, temporal and occipital cortices. Six months after KA injection, reduced ChAT activity was observed in the amygdala/piriform cortex (47% of control; p<0.001), increased ChAT activity in the hippocampus (119% of control; p<0.01) and normal ChAT activity in the other brain regions. The activity of GAD was significantly increased in all analysed cortical regions (between 146 and 171% of control), in the caudate nucleus (144% of control; p<0.01) and in the substantia nigra (126% of control; p<0.01), whereas in the amygdala/piriform cortex, the GAD activity was moderately lowered. The somatostatin level was significantly increased in all cortical regions (between 162 and 221% of control) as well as in the hippocampus (119% of control), but reduced in the amygdala/piriform cortex (45% of control; p<0.01). Six months after KA injection, the somatostatin:GAD ratio was lowered in the amygdala/piriform cortex (49% of control) and in the caudate nucleus (41% of control), whereas it was normal in the hippocampus and moderately increased in the cortical brain regions. A positive correlation was found between seizure severity and the reduction of both ChAT activities and somatostatin levels in the amygdala/piriform cortex. The results show a specific pattern of changes for cholinergic, GABAergic and somatostatinergic activities in the chronic KA model for epilepsy. The revealed data suggest a functional role for them in the new network that follows spontaneous repetitive seizures.

Sensitive indicators of injury reveal hippocampal damage in C57BL/6J mice treated with kainic acid in the absence of tonic-clonic seizures

Sensitive indices of neural injury were used to evaluate the time course of kainic acid (KA)-induced hippocampal damage in adult C57BL/6J mice (4 months), a strain previously reported to be resistant to kainate-induced neurotoxicity. Mice were injected systemically with saline or kainate, scored for seizure severity (Racine scale), and allowed to survive 12 h, one, three, or seven days following which they were evaluated for neuropathological changes using histological or biochemical endpoints. Most kainate-treated mice exhibited limited seizure activity (stage 1); however, cupric-silver and Fluoro-Jade B stains revealed significant damage by 12 h post-treatment. Immunohistochemistry and immunoassay of glial fibrillary acidic protein and lectin staining revealed a strong treatment-induced reactive gliosis and microglial activation. Immunostaining for immunoglobulin G revealed a kainate-induced breach in the blood-brain barrier. Nissl and hematoxylin stains provided little information regarding neuronal damage, but revealed the identity of non-resident cells which infiltrated the pyramidal layer. Our data suggest sensitive indicators of neural injury evaluated over a time course, both proximal and distal to treatment, are necessary to reveal the full extent of neuropathological changes which may be underestimated by traditional histological stains. The battery of neuropathological indices reported here reveals the C57BL/6J mouse is sensitive to excitotoxic neural damage caused by kainic acid, in the absence of tonic-clonic seizures.