Extracellular amino acid levels in hippocampus during pilocarpine-induced seizures

Brain network properties of clinical versus subclinical seizures among critically ill children

OBJECTIVE

Electrographic seizures are common among critically ill children, and have been associated with worse outcomes. Despite their often-widespread cortical representation, most of these seizures remain subclinical, a phenomenon which remains poorly understood. We compared the brain network properties of clinical versus subclinical seizures to gain insight into their relative potential deleterious effects.

METHODS

Functional connectivity (phase lag index) and graph measures (global efficiency and clustering coefficients) were computed for 2178 electrographic seizures recorded during 48-hours of 19-channel continuous EEG monitoring obtained in 20 comatose children. Frequency-specific group differences in clinical versus subclinical seizures were analyzed using a non-parametric ANCOVA, adjusting for age, sex, medication exposure, treatment intensity and seizures per subject.

RESULTS

Clinical seizures demonstrated greater functional connectivity than subclinical seizures at alpha frequencies, but less connectivity than subclinical seizures at delta frequencies. Clinical seizures also demonstrated significantly higher median global efficiency than subclinical seizures (p < 0.01), and significantly higher median clustering coefficients across all electrodes at alpha frequencies.

CONCLUSIONS

Clinical expression of seizures correlates with greater alpha synchronization of distributed brain networks.

SIGNIFICANCE

The stronger global and local alpha-mediated functional connectivity observed during clinical seizures may indicate greater pathological network recruitment. These observations motivate further studies to investigate whether the clinical expression of seizures may influence their potential to cause secondary brain injury.

Pretreatment with a glutamine synthetase inhibitor MSO delays the onset of initial seizures induced by pilocarpine in juvenile rats

The contribution of glutamatergic transmission to generation of initial convulsive seizures (CS) is debated. We tested whether pretreatment with a glutamine synthetase (GS) inhibitor, methionine sulfoximine (MSO), affects the onset and progression of initial CS by cholinergic stimulus in juvenile rats. Male rats (24 days old, Sprague Dawley) sequentially received i.p. injections of lithium-carbonate, MSO, methyl-scopolamine, and pilocarpine (Pilo). Pilo was given 150 min after MSO. Animals were continuously monitored using the Racine scale, EEG/EMG and intrahippocampal glutamate (Glu) biosensors. GS activity as measured in hippocampal homogenates, was not altered by MSO at 150 min, showed initial, varied inhibition at 165 (15 min post-Pilo), and dropped down to 11% of control at 60 min post-Pilo, whereas GS protein expression remained unaltered throughout. Pilo did neither modulate the effect of MSO on GS activity nor affect GS activity itself, at any time point. MSO reduced from 32% to 4% the number of animals showing CS during the first 12 min post-Pilo, delayed by ~6 min the appearance of electrographic seizures, and tended to decrease EMG power during ~15 min post-Pilo. The results indicate that MSO impairs an aspect of glutamatergic transmission involved in the transition from the first cholinergic stimulus to the onset of seizures. A continuous rise of extracellular Glu lasting 60 min was insignificantly affected by MSO, leaving the nature of the Glu pool(s) involved in altered glutamatergic transmission undefined.

Neurobiology, Functions, and Relevance of Excitatory Amino Acid Transporters (EAATs) to Treatment of Refractory Epilepsy

Epilepsy is one of the most prevalent and devastating neurological disorders characterized by episodes of unusual sensations, loss of awareness, and reoccurring seizures. The frequency and intensity of epileptic fits can vary to a great degree, with almost a third of all cases resistant to available therapies. At present, there is a major unmet need for effective and specific therapeutic intervention. Impairments of the exquisite balance between excitatory and inhibitory synaptic processes in the brain are considered key in the onset and pathophysiology of the disease. As the primary excitatory neurotransmitter in the central nervous system, glutamate has been implicated in the process, with the glutamatergic system holding center stage in the pathobiology as well as in developing disease-modifying therapies. Emerging data pinpoint impairments of glutamate clearance as one of the key causative factors in drug-resistant disease forms. Reinstatement of glutamate homeostasis using pharmacological and genetic modulation of glutamate clearance is therefore considered to be of major translational relevance. In this article, we review the neurobiological and clinical evidence suggesting complex aberrations in the activity and functions of excitatory amino acid transporters (EAATs) in epilepsy, with knock-on effects on glutamate homeostasis as a leading cause for the development of refractory forms. We consider the emerging data on pharmacological and genetic manipulations of EAATs, with reference to seizures and glutamate dyshomeostasis, and review their fundamental and translational relevance. We discuss the most recent advances in the EAATs research in human and animal models, along with numerous questions that remain open for debate and critical appraisal. Contrary to the widely held view on EAATs as a promising therapeutic target for management of refractory epilepsy as well as other neurological and psychiatric conditions related to glutamatergic hyperactivity and glutamate-induced cytotoxicity, we stress that the true relevance of EAAT2 as a target for medical intervention remains to be fully appreciated and verified. Despite decades of research, the emerging properties and functional characteristics of glutamate transporters and their relationship with neurophysiological and behavioral correlates of epilepsy challenge the current perception of this disease and fit unambiguously in neither EAATs functional deficit nor in reversal models. We stress the pressing need for new approaches and models for research and restoration of the physiological activity of glutamate transporters and synaptic transmission to achieve much needed therapeutic effects. The complex mechanism of EAATs regulation by multiple factors, including changes in the electrochemical environment and ionic gradients related to epileptic hyperactivity, impose major therapeutic challenges. As a final note, we consider the evolving views and present a cautious perspective on the key areas of future progress in the field towards better management and treatment of refractory disease forms.

The Transient Receptor Potential Melastatin 7 (TRPM7) Inhibitors Suppress Seizure-Induced Neuron Death by Inhibiting Zinc Neurotoxicity

Transient receptor potential melastatin 7 (TRPM7) is an ion channel that mediates monovalent cations out of cells, as well as the entry of divalent cations, such as zinc, magnesium, and calcium, into the cell. It has been reported that inhibitors of TRPM7 are neuroprotective in various neurological diseases. Previous studies in our lab suggested that seizure-induced neuronal death may be caused by the excessive release of vesicular zinc and the subsequent accumulation of zinc in the neurons. However, no studies have evaluated the effects of carvacrol and 2-aminoethoxydiphenyl borate (2-APB), both inhibitors of TRPM7, on the accumulation of intracellular zinc in dying neurons following seizure. Here, we investigated the therapeutic efficacy of carvacrol and 2-APB against pilocarpine-induced seizure. Carvacrol (50 mg/kg) was injected once per day for 3 or 7 days after seizure. 2-APB (2 mg/kg) was also injected once per day for 3 days after seizure. We found that inhibitors of TRPM7 reduced seizure-induced TRPM7 overexpression, intracellular zinc accumulation, and reactive oxygen species production. Moreover, there was a suppression of oxidative stress, glial activation, and the blood–brain barrier breakdown. In addition, inhibitors of TRPM7 remarkably decreased apoptotic neuron death following seizure. Taken together, the present study demonstrates that TRPM7-mediated zinc translocation is involved in neuron death after seizure. The present study suggests that inhibitors of TRPM7 may have high therapeutic potential to reduce seizure-induced neuron death.

Anti-Epileptic Effects of FABP3 Ligand MF1 through the Benzodiazepine Recognition Site of the GABAA Receptor

Recently, we developed the fatty acid-binding protein 3 (FABP3) ligand MF1 (4-(2-(1-(2-chlorophenyl)-5-phenyl-1H-pyrazol-3-yl)phenoxy) butanoic acid) as a therapeutic candidate for α-synucleinopathies. MF1 shows affinity towards γ-aminobutyric acid type-A (GABA_A) receptor, but its effect on the receptor remains unclear. Here, we investigate the pharmacological properties of MF1 on the GABA_A receptor overexpressed in Neuro2A cells. While MF1 (1–100 μm) alone failed to evoke GABA currents, MF1 (1 μm) promoted GABA currents during GABA exposure (1 and 10 μm). MF1-promoted GABA currents were blocked by flumazenil (10 μm) treatment, suggesting that MF1 enhances receptor function via the benzodiazepine recognition site. Acute and chronic administration of MF1 (0.1, 0.3 and 1.0 mg/kg, p.o.) significantly attenuated status epilepticus (SE) and the mortality rate in pilocarpine (PILO: 300 mg/kg, i.p.)-treated mice, similar to diazepam (DZP: 5.0 mg/kg, i.p.). The anti-epileptic effects of DZP (5.0 mg/kg, i.p.) and MF1 (0.3 mg/kg, p.o.) were completely abolished by flumazenil (25 mg/kg, i.p.) treatment. Pentylenetetrazol (PTZ: 90 mg/kg, i.p.)-induced seizures in mice were suppressed by DZP (5.0 mg/kg, i.p.), but not MF1. Collectively, this suggests that MF1 is a mild enhancer of the GABA_A receptor and exercises anti-epileptic effects through the receptor’s benzodiazepine recognition site in PILO-induced SE models.

Unexpected Effects of Acetylcholine Precursors on Pilocarpine Seizure- Induced Neuronal Death

BACKGROUND

Choline alfoscerate (α-GPC) and Cytidine 5'-diphosphocholine (CDPCholine) are both acetylcholine precursors and are considered to act as pro-cholinergic nootropic agents. Acetylcholine precursors have also recently found frequent use in the neurology clinic. Stroke and many types of dementia have been shown to respond favorably after treatment with these agents, not only in terms of cognitive dysfunction but also behavioral and psychological symptoms. The primary mechanisms of Acetylcholine precursors are the following: 1) Acetylcholine precursors themselves are used in the biosynthesis of acetylcholine and 2) byproducts like glycerophosphate have protective functions for neuronal phospholipids. However, whether acetylcholine precursors have a similar effect in treating cognitive impairment in patients with epilepsy remains controversial.

METHODS

Our previous studies investigating acetylcholine precursors in seizure-experienced animals have produced variable results that were dependent on the timing of administration.

RESULTS

Early administration of CDP-choline immediately after seizure increased neuronal death, blood-brain barrier (BBB) disruption and microglial activation in the hippocampus. However, administration of α-GPC starting 3 weeks after seizure (late administration) improved cognitive function through reduced neuronal death and BBB disruption, and increased neurogenesis in the hippocampus.

CONCLUSION

These seemingly contradictory results may be attributed to both epileptogenic features and neuroprotective functions of several acetylcholine precursors.

Anticonvulsant activity, organotypic hippocampal neuroprotection assay and in-silico sodium channel blocking potential of 2-amino-6-nitrobenzothiazole derived semicarbazones

Epilepsy is one of the dreadful neurodegenerative disorder characterized by recurrent, unprovoked seizures. Currently available antiepileptic drugs are still associated with enormous side effects resulting in search of newer, more effective and safer agents. In view of this, we have investigated anticonvulsant activity of 2-amino-6-nitrobenzothiazole derived semicarbazones (7-32) in various in-vivo animal seizure models viz. maximal electroshock (MES), subcutaneous pentylenetetrazole (scPTZ) and 6Hz psychomotor seizure model. Neurotoxicity was estimated by rotarod test. The compounds were also assessed for their neuroprotective potential from excitotoxic insult using organotypic hippocampal slice culture neuroprotection assay. Several compounds exhibited excellent anticonvulsant activity in MES and scPTZ models compared to reference drugs, phenytoin and levetiracetam. The results of kainic acid (KA) - induced neuroprotection assay indicated that compounds 26 and 24 were found to be most potent with IC₅₀ of 99.54±1.27 and 101.00±1.20μM respectively. Both the compounds attenuated KA-mediated cell death in organotypic hippocampal slice cultures. Some of the compounds were found to be good antidepressants, better than the reference drug citalopram, when analyzed in forced swim test. Since semicarbazones exhibited profile resembling phenytoin, an attempt was made to screen them against human neuronal sodium channel isoform (hNa_v1.2) by performing computational molecular docking using AutoDock 4.2. Compound 30, 1-(5-Chloro-2-oxoindolin-3-ylidene)-4-(6-nitrobenzothiazol-2-yl)semicarbazide emerged as lead candidate possessing excellent in-vivo MES activity and high binding affinity computationally, better than the reference drug phenytoin and also exhibited neuroprotection from excitotoxic insult in KA-induced neuroprotection assay (IC₅₀=126.80±1.24μM). However, some of the active compounds were neurotoxic at their anticonvulsant doses. Further optimization studies are needed to reduce toxicity and develop them as novel therapeutic agents for epilepsy.

Amiodarone reduces depolarization-evoked glutamate release from hippocampual synaptosomes

Decreased brain glutamate level has emerged as a new therapeutic approach for epilepsy. This study investigated the effect and mechanism of amiodarone, an anti-arrhythmic drug with antiepileptic activity, on glutamate release in the rat hippocampus. In a synaptosomal preparation, amiodarone reduced 4-aminopyridine-evoked Ca²⁺-dependent glutamate release and cytosolic Ca²⁺ concentration elevation. Amiodarone did not affect the 4-aminopyridine-evoked depolarization of the synaptosomal membrane potential or the Na⁺ channel activator veratridine-evoked glutamate release, indicating that the amiodarone-mediated inhibition of glutamate release is not caused by a decrease in synaptosomal excitability. The inhibitory effect of amiodarone on 4-aminopyridine-evoked glutamate release was markedly decreased in synaptosomes pretreated with the Ca_v2.2 (N-type) and Ca_v2.1 (P/Q-type) channel blocker ω-conotoxin MVIIC, the calmodulin antagonists W7 and calmidazolium, or the protein kinase A inhibitors H89 and KT5720. However, the intracellular Ca²⁺-release inhibitors dantrolene and CGP37157 had no effect on the amiodarone-mediated inhibition of glutamate release. Furthermore, amiodarone reduced the frequency of miniature excitatory postsynaptic currents without affecting their amplitude in hippocampal slices. Our data suggest that amiodarone reduces Ca²⁺ influx through N- and P/Q-type Ca²⁺ channels, subsequently reducing the Ca²⁺-calmodulin/protein kinase A cascade to inhibit the evoked glutamate release from rat hippocampal nerve terminals.

Glutamate imaging (GluCEST) lateralizes epileptic foci in nonlesional temporal lobe epilepsy

When neuroimaging reveals a brain lesion, drug-resistant epilepsy patients show better outcomes after resective surgery than do the one-third of drug-resistant epilepsy patients who have normal brain magnetic resonance imaging (MRI). We applied a glutamate imaging method, GluCEST (glutamate chemical exchange saturation transfer), to patients with nonlesional temporal lobe epilepsy based on conventional MRI. GluCEST correctly lateralized the temporal lobe seizure focus on visual and quantitative analyses in all patients. MR spectra, available for a subset of patients and controls, corroborated the GluCEST findings. Hippocampal volumes were not significantly different between hemispheres. GluCEST allowed high-resolution functional imaging of brain glutamate and has potential to identify the epileptic focus in patients previously deemed nonlesional. This method may lead to improved clinical outcomes for temporal lobe epilepsy as well as other localization-related epilepsies.

Transcranial focal electrical stimulation reduces the convulsive expression and amino acid release in the hippocampus during pilocarpine-induced status epilepticus in rats

The aim of the present study was to evaluate the effects of transcranial focal electrical stimulation (TFS) on γ-aminobutyric acid (GABA) and glutamate release in the hippocampus under basal conditions and during pilocarpine-induced status epilepticus (SE). Animals were previously implanted with a guide cannula attached to a bipolar electrode into the right ventral hippocampus and a concentric ring electrode placed on the skull surface. The first microdialysis experiment was designed to determine, under basal conditions, the effects of TFS (300 Hz, 200 μs biphasic square pulses, for 30 min) on afterdischarge threshold (ADT) and the release of GABA and glutamate in the hippocampus. The results obtained indicate that at low current intensities (<2800 μA), TFS enhances and decreases the basal extracellular levels of GABA and glutamate, respectively. However, TFS did not modify the ADT. During the second microdialysis experiment, a group of animals was subjected to SE induced by pilocarpine administration (300 mg/kg, i.p.; SE group). The SE was associated with a significant rise of GABA and glutamate release (up to 120 and 182% respectively, 5h after pilocarpine injection) and the prevalence of high-voltage rhythmic spikes and increased spectral potency of delta, gamma, and theta bands. A group of animals (SE-TFS group) received TFS continuously during 2h at 100 μA, 5 min after the establishment of SE. This group showed a significant decrease in the expression of the convulsive activity and spectral potency in gamma and theta bands. The extracellular levels of GABA and glutamate in the hippocampus remained at basal conditions. These results suggest that TFS induces anticonvulsant effects when applied during the SE, an effect associated with lower amino acid release. This article is part of a Special Issue entitled "Status Epilepticus".

Protective effect of hispidulin on kainic acid-induced seizures and neurotoxicity in rats

Hispidulin is a flavonoid compound which is an active ingredient in a number of traditional Chinese medicinal herbs, and it has been reported to inhibit glutamate release. The purpose of this study was to investigate whether hispidulin protects against seizures induced by kainic acid, a glutamate analog with excitotoxic properties. The results indicated that intraperitoneally administering hispidulin (10 or 50mg/kg) to rats 30 min before intraperitoneally injecting kainic acid (15 mg/kg) increased seizure latency and decreased seizure score. In addition, hispidulin substantially attenuated kainic acid-induced hippocampal neuronal cell death, and this protective effect was accompanied by the suppression of microglial activation and the production of proinflammatory cytokines such as interleukin-1β, interleukin-6, and tumor necrosis factor-α in the hippocampus. Moreover, hispidulin reduced kainic acid-induced c-Fos expression and the activation of mitogen-activated protein kinases in the hippocampus. These data suggest that hispidulin has considerable antiepileptic, neuroprotective, and antiinflammatory effects on kainic acid-induced seizures in rats.

Comparison of concentrations of γ-aminobutyric acid and glutamate in cerebrospinal fluid of dogs with idiopathic epilepsy with and without seizure-related magnetic resonance imaging hyperintense areas in the limbic system

OBJECTIVE

To investigate differences in CSF concentrations of excitatory and inhibitory neurotransmitters in dogs with and without T2-weighted (T2W) MRI hyperintense areas in the limbic system.

SAMPLE

Archived CSF samples and stored brain MRI images of 5 healthy research dogs (group 1), 8 dogs with idiopathic epilepsy (IE) with no abnormal MRI findings (group 2), and 4 dogs with IE with hyperintense areas in the limbic system detected by means of T2W MRI (group 3).

PROCEDURES

Archived CSF samples and stored MRI images obtained from all dogs were evaluated. Dogs in groups 2 and 3 were matched on the basis of age and breed. High-performance liquid chromatography was used to evaluate glutamate and γ-aminobutyric acid (GABA) concentrations in CSF samples.

RESULTS

Glutamate concentrations were higher in CSF of both groups of dogs with IE than in healthy dogs. However, glutamate concentrations in CSF were not significantly higher in dogs with IE and with hyperintense areas than in dogs with IE but no abnormal MRI findings. Concentrations of GABA in CSF were higher in group 3 than in group 2 and in group 2 than in group 1.

CONCLUSIONS AND CLINICAL RELEVANCE

No significant difference was evident between glutamate concentrations in CSF of dogs with IE and with and without hyperintense areas detected by means of T2W MRI. However, glutamate concentrations typically were higher in CSF of dogs with IE and MRI hyperintense areas. Future studies with larger sample sizes should be conducted to confirm this finding and to determine the clinical importance of high glutamate concentrations in CSF of dogs with IE.

Are vesicular neurotransmitter transporters potential treatment targets for temporal lobe epilepsy?

The vesicular neurotransmitter transporters (VNTs) are small proteins responsible for packing synaptic vesicles with neurotransmitters thereby determining the amount of neurotransmitter released per vesicle through fusion in both neurons and glial cells. Each transporter subtype was classically seen as a specific neuronal marker of the respective nerve cells containing that particular neurotransmitter or structurally related neurotransmitters. More recently, however, it has become apparent that common neurotransmitters can also act as co-transmitters, adding complexity to neurotransmitter release and suggesting intriguing roles for VNTs therein. We will first describe the current knowledge on vesicular glutamate transporters (VGLUT1/2/3), the vesicular excitatory amino acid transporter (VEAT), the vesicular nucleotide transporter (VNUT), vesicular monoamine transporters (VMAT1/2), the vesicular acetylcholine transporter (VAChT) and the vesicular γ-aminobutyric acid (GABA) transporter (VGAT) in the brain. We will focus on evidence regarding transgenic mice with disruptions in VNTs in different models of seizures and epilepsy. We will also describe the known alterations and reorganizations in the expression levels of these VNTs in rodent models for temporal lobe epilepsy (TLE) and in human tissue resected for epilepsy surgery. Finally, we will discuss perspectives on opportunities and challenges for VNTs as targets for possible future epilepsy therapies.

Bupropion attenuates kainic acid-induced seizures and neuronal cell death in rat hippocampus

Excessive release of glutamate is believed to be a major component of cell damage following excitotoxicity associated with epilepsy. Bupropion, an atypical antidepressant, has been shown to inhibit glutamate release from rat cerebrocortical nerve terminals. The present study was undertaken to investigate whether bupropion has anti-seizure and anti-excitotoxic effects by using a kainic acid (KA) rat seizure model, an animal model for temporal lobe epilepsy and excitotoxic neurodegeneration. Our results show that bupropion (10 or 50mg/kg), administrated intraperitoneally to the rats 30 min before the KA (15 mg/kg) intraperitoneal injection, increased the seizure latency and decreased the seizure score. Bupropion pretreatment attenuated KA-induced neuronal cell death and microglia activation in the CA3 region of the hippocampus. Furthermore, KA-induced c-Fos expression and extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation in the hippocampus were also reduced by bupropion pretreatment. These results suggest that bupropion has therapeutic potential in the treatment of seizure and other neurological diseases associated with excitotoxicity.

AMPA receptor properties are modulated in the early stages following pilocarpine-induced status epilepticus

Glutamate over-activation and the consequent neuronal excitotoxicity have been identified as crucial players in brain dysfunctions such as status epilepticus (SE). Owing to the central function of 2-amino-3-(hydroxyl-5-methylisoxazole-4-yl) propionic acid receptors (AMPARs) in fast excitatory neurotransmission, these receptors have been recognized to play a prominent role in the development and generation of epileptic seizure. This study was undertaken to investigate both the early changes that affect glutamatergic neurons in the rat cerebral cortex and hippocampus and the level and channel properties of AMPARs in response to SE. The results obtained after 3 h of pilocarpine (PILO)-induced SE showed a disorganization of glutamatergic neurons in the CA3 and a thinner neuronal cell layer in the dentate gyrus (DG) region as compared with controls. A significant increase in AMPAR GluA2 protein expression, a decrease in GluA1, GluA3, and GluA4 expression, and a reduction in the phosphorylation of Ser831-GluA1 and Ser880-GluA2 were also observed. In addition, we report a downregulation of R/G editing levels and of Flip splicing isoforms, with a prominent effect on the hippocampus of PILO-treated rats. Our results suggest the presence of an attenuation of AMPARs' post-synaptic excitatory response to glutamate after PILO treatment, thus conferring neuronal protection from the excitotoxic conditions observed in the SE. This study suggests a role for AMPARs in alterations of the glutamatergic pathway during the onset and early progression of epilepsy, thus indicating additional targets for potential therapeutic interventions.

Hispidulin inhibits the release of glutamate in rat cerebrocortical nerve terminals

Hispidulin, a naturally occurring flavone, has been reported to have an antiepileptic profile. An excessive release of glutamate is considered to be related to neuropathology of epilepsy. We investigated whether hispidulin affected endogenous glutamate release in rat cerebral cortex nerve terminals (synaptosomes) and explored the possible mechanism. Hispidulin inhibited the release of glutamate evoked by the K⁺ channel blocker 4-aminopyridine (4-AP). The effects of hispidulin on the evoked glutamate release were prevented by the chelation of extracellular Ca²⁺ ions and the vesicular transporter inhibitor bafilomycin A1. However, the glutamate transporter inhibitor dl-threo-beta-benzyl-oxyaspartate did not have any effect on hispidulin action. Hispidulin reduced the depolarization-induced increase in cytosolic free Ca²⁺ concentration ([Ca²⁺](C)), but did not alter 4-AP-mediated depolarization. Furthermore, the effect of hispidulin on evoked glutamate release was abolished by blocking the Ca(v)2.2 (N-type) and Ca(v)2.1 (P/Q-type) channels, but not by blocking ryanodine receptors or mitochondrial Na⁺/Ca²⁺ exchange. Mitogen-activated protein kinase kinase (MEK) inhibition also prevented the inhibitory effect of hispidulin on evoked glutamate release. Western blot analyses showed that hispidulin decreased the 4-AP-induced phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1/2) and synaptic vesicle-associated protein synapsin I, a major presynaptic substrate for ERK; this decrease was also blocked by the MEK inhibitor. Moreover, the inhibition of glutamate release by hispidulin was strongly attenuated in mice without synapsin I. These results show that hispidulin inhibits glutamate release from cortical synaptosomes in rats through the suppression of presynaptic voltage-dependent Ca²⁺ entry and ERK/synapsin I signaling pathway.

Clinical and Neuropathological Findings of Acute Carbon Monoxide Toxicity in Chihuahuas Following Smoke Inhalation

Three adult Chihuahuas were presented for evaluation after smoke inhalation during a house fire. All three dogs received supportive care and supplemental oxygen. After initial improvement, the dogs developed seizures. Despite anticonvulsant therapy and supportive care, the dogs died. The brains of two dogs were examined. Lesions were identified that were compatible with acute carbon monoxide (CO) toxicity. Lesions were confined to the caudate nucleus, the globus pallidus, and the substantia nigra bilaterally, as well as the cerebellum, cerebral cortex, and dorsal thalamus. This case report describes the clinicopathological sequelae in acute CO toxicity.

Akt pathway activation and increased neuropeptide Y mRNA expression in the rat hippocampus: implications for seizure blockade

The aim of this study was to analyze the expression of survival-related molecules such Akt and integrin-linked kinase (ILK) to evaluate Akt pathway activation in epileptogenesis process. Furthermore, was also investigated the mRNA expression of neuropeptide Y, a considered antiepileptic neuropeptide, in the pilocarpine-induced epilepsy. Male Wistar rats were submitted to the pilocarpine model of epilepsy. Hippocampi were removed 6h (acute phase), 12h (late acute), 5d (silent) and 60d (chronic) after status epilepticus (SE) onset, and from animals that received pilocarpine but did not develop SE (partial group). Hippocampi collected were used to specify mRNA expression using Real-Time PCR. Immunohistochemistry assay was employed to place ILK distribution in the hippocampus and Western blot technique was used to determine Akt activation level. A decrease in ILK mRNA content was found during acute (0.39+/-0.03) and chronic (0.48+/-0.06) periods when compared to control group (0.87+/-0.10). Protein levels of ILK were also diminished during both periods. Partial group showed increased ILK mRNA expression (0.80+/-0.06) when compared with animals in the acute stage. Silent group had ILK mRNA and immunoreactivity similar to control group. Western blot assay showed an augmentation in Akt activation in silent period (0.52+/-0.03) in comparison with control group (0.44+/-0.01). Neuropeptide Y mRNA expression increased in the partial group (1.67+/-0.22) and in the silent phase (1.45+/-0.29) when compared to control group (0.36+/-0.12). Results suggest that neuropeptide Y (as anticonvulsant) might act in protective mechanisms occurred during epileptic phenomena. Together with ILK expression and Akt activation, these molecules could be involved in hippocampal neuroprotection in epilepsy.

Elevated cardiac troponin I in a dog with an intracranial meningioma and evidence of myocardial necrosis

A 10-year-old, spayed female Weimaraner was referred for an acute onset of generalized tremors, seizures, and obtundation. Neurological examination revealed severe obtundation and a right-sided menace response deficit. Neuroanatomical diagnosis was consistent with a left prosencephalic lesion. The serum cardiac troponin I level was high, indicative of acute myocardial necrosis. With magnetic resonance imaging, a mass was observed in the left olfactory bulb and tract, with extensive edema in the white matter of the left cerebrum. The hippocampus was hyperintense on T2-weighted and T2-weighted fluid-attenuated inversion recovery images. At necropsy, a meningioma of the left olfactory bulb and ischemic cell change in the neurons of the hippocampus were identified. In the heart, microscopic lesions consistent with myocardial necrosis were observed. This is the first case to document an elevated cardiac troponin I level in a dog with intracranial disease and myocardial necrosis.

Glutamate is critically involved in seizure-induced overexpression of P-glycoprotein in the brain

About 30% of patients with epilepsy do not respond adequately to drug therapy, making pharmacoresistance a major problem in the treatment of this common brain disorder. Mechanisms of intractability are not well understood, but may include limitation of antiepileptic drug access to the seizure focus by overexpression of the drug efflux transporter P-glycoprotein (Pgp) at the blood-brain barrier. Increased expression of Pgp has been determined both in epileptogenic brain tissue of patients with intractable epilepsy and in rodent models of temporal lobe epilepsy, including the pilocarpine model. The mechanisms underlying the increase of Pgp after seizures are unclear. We have recently suggested that the excitatory neurotransmitter glutamate, which is excessively released by seizures, is involved in the seizure-induced overexpression of Pgp in the brain. This hypothesis was evaluated in the present study in the pilocarpine model in rats. After 90 min of status epilepticus (SE), diazepam was administered, followed by either vehicle or the glutamate receptor antagonist MK-801 (dizocilpine). Following SE in vehicle treated rats, Pgp expression in brain capillary endothelial cells increased about twofold in the hippocampus, which was completely prevented by MK-801. Furthermore, neurodegeneration developing in the hippocampus and parahippocampal regions was reduced by the glutamate antagonist. In contrast, the Pgp inhibitor tariquidar did not affect the SE-induced overexpression of Pgp or neurodegeneration in most regions examined. The data indicate that seizure-induced glutamate release is involved in the regulation of Pgp expression, which can be blocked by MK-801. The finding that MK-801 counteracts both Pgp overexpression and neuronal damage when administered after SE may offer a clinically useful therapeutic option in patients with refractory SE.

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

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

Acute induction of epileptiform discharges by pilocarpine in the in vitro isolated guinea-pig brain requires enhancement of blood-brain barrier permeability

Systemic application of the muscarinic agonist, pilocarpine, is commonly utilized to induce an acute status epilepticus that evolves into a chronic epileptic condition characterized by spontaneous seizures. Recent findings suggest that the status epilepticus induced by pilocarpine may be triggered by changes in the blood-brain barrier (BBB) permeability. We tested the role of the BBB in an acute pilocarpine model by using the in vitro model brain preparation and compared our finding with in vivo data. Arterial perfusion of the in vitro isolated guinea-pig brain with <1 mM pilocarpine did not cause epileptiform activity, but rather reduced synaptic transmission and induced steady fast (20-25 Hz) oscillatory activity in limbic cortices. These effects were reversibly blocked by co-perfusion of the muscarinic antagonist atropine sulfate (5 microM). Brain pilocarpine measurements in vivo and in vitro suggested modest BBB penetration. Pilocarpine induced epileptiform discharges only when perfused with compounds that enhance BBB permeability, such as bradykinin (n=2) or histamine (n=10). This pro-epileptic effect was abolished when the BBB-impermeable muscarinic antagonist atropine methyl bromide (5 microM) was co-perfused with histamine and pilocarpine. In the absence of BBB permeability enhancing drugs, pilocarpine induced epileptiform activity only after arterial perfusion at concentrations >10 mM. Ictal discharges correlated with a high intracerebral pilocarpine concentration measured by high pressure liquid chromatography. We propose that acute epileptiform discharges induced by pilocarpine treatment in the in vitro isolated brain preparation are mediated by a dose-dependent, atropine-sensitive muscarinic effect promoted by an increase in BBB permeability. Pilocarpine accumulation secondary to BBB permeability changes may contribute to in vivo ictogenesis in the pilocarpine epilepsy model.

Seizure activity and changes in hippocampal extracellular glutamate, GABA, dopamine and serotonin

Increases in hippocampal extracellular neurotransmitter levels have consistently been observed during temporal lobe seizures in humans, but animal studies on this subject have yielded conflicting results. Our aim was to better characterise the relationship between seizure activity and changes in hippocampal glutamate, GABA, dopamine and serotonin by comparing three limbic seizure models which differ only in the pharmacological mechanism used to induce seizures. Seizures were evoked in freely moving rats by intrahippocampal microperfusion, via a microdialysis probe, of the muscarinic receptor agonist pilocarpine (10mM), GABA(A) receptor antagonist picrotoxin (100microM) or group I metabotropic glutamate receptor agonist (R,S)-3,5-dihydroxyphenylglycine (DHPG) (1mM). Seizure-related behavioural changes were scored and hippocampal extracellular glutamate, GABA, dopamine and serotonin concentrations were monitored. Seizures were of comparable severity in all groups. During seizures, hippocampal glutamate, GABA and dopamine concentrations increased in all groups. Glutamate increases were significantly higher in the picrotoxin group. Hippocampal serotonin concentration increased following pilocarpine and picrotoxin, but not DHPG. Our results suggest a direct relationship between seizure activity and increased hippocampal extracellular concentrations of glutamate, GABA and dopamine, but not serotonin. The fact that picrotoxin induces seizures by disinhibition, rather than direct excitation, may account for the larger glutamate increases in this group.

In vitro status epilepticus but not spontaneous recurrent seizures cause cell death in cultured hippocampal neurons

It is established that the majority but not all of the seizure-induced cell death is associated with status epilepticus while spontaneous recurrent seizures associated with epilepsy do not cause neuronal death. Extracellular effects and compensatory changes in brain physiology complicate assessment of neuronal death in vivo as the result of seizures. In this study we utilized a well-characterized in vitro hippocampal neuronal culture model of both continuous high-frequency epileptiform discharges (status epilepticus) and spontaneous recurrent epileptiform discharges (acquired epilepsy) to investigate the direct effects of continuous and episodic electrographic epileptiform discharges on cell death in a carefully controlled extracellular environment. The results from this study indicate that continuous high-frequency epileptiform discharges can cause neuronal death in a time-dependent manner. Episodic epileptiform seizure activity occurring for the life of the neurons in culture was not associated with increased neuronal cell death. Our data confirm observations from clinical and some animal studies that spontaneous recurrent seizures do not initiate cell death. The hippocampal neuronal culture model provides a powerful in vitro tool for carefully evaluating the effects of seizure activity alone on neuronal viability in the absence of various confounding factors and may provide new insights into the development of novel therapeutic agents to prevent neuronal injury during status epilepticus.

Childhood status epilepticus and excitotoxic neuronal injury

This report describes the case of an 11-year-old girl with a prior history of epilepsy and multiple episodes of status epilepticus who presented with generalized convulsive status epilepticus and left hemiclonic seizures. Magnetic resonance imaging, including diffusion-weighted sequences and spectroscopy, and neuropathology at autopsy were consistent with excitotoxic neuronal injury to the hippocampus, cortex, thalamus, mammillary bodies, and cerebellum. Review of the literature revealed 11 similar cases that support the hypothesis of excitotoxic neuronal cell death after status epilepticus.

Abnormal mGluR2/3 expression in the perforant path termination zones and mossy fibers of chronically epileptic rats

Epilepsy is characterized by hyperexcitability of hippocampal networks, excessive release of glutamate, and progressive neurodegeneration. Presynaptic group II metabotropic receptors (mGluR2 and mGluR3) are among different mechanisms that modulate presynaptic release of glutamate, especially at the mossy fibers in the hippocampus. Here, we explore whether mGluR2/3 expression is affected in a rat model of temporal lobe epilepsy obtained via pilocarpine-induced status epilepticus (SE). Immunohistochemical assays were performed in age-matched controls and two groups of epileptic rats sacrificed at 25-35 days (1 month post-SE) and at 55-65 days (2 months post-SE) following SE onset. A dramatic lessening of mGluR2/3 immunofluorescence was observed at CA1 and CA3 stratum lacunosum/molecular (SLM) declining to 60% and 68% of control values in 1-month and 2-month post-SE, respectively. Additionally, thickness of mGluR2/3-stained SLM layer narrowed up to 70% of controls indicating atrophy at this branch of the perforant path. Epileptic rats exhibited a marked and progressive down-regulation of mGluR2/3 expression in mossy fiber at hilus and CA3 stratum lucidum in contrast with an enhanced expression of vesicular glutamate transporter type 1 (VGluT1) at the mossy fibers. Intense VGluT1 punctated staining was detected at the inner third molecular layer indicating glutamatergic sprouting. In the molecular layer, mGluR2/3 labeling slightly declined in the 1-month post-SE group but then increased in the 2-month post-SE group although it was diffusely distributed. Down-regulation of mGluR2/3 at the mossy fibers and the SLM may render epileptic hippocampal networks hyperexcitable and susceptible to glutamate-mediated excitotoxicity and neurodegeneration.

Convulsant bicuculline modifies CNS muscarinic receptor affinity

Background

Previous work from this laboratory has shown that the administration of the convulsant drug 3-mercaptopropionic acid (MP), a GAD inhibitor, modifies not only GABA synthesis but also binding of the antagonist [³H]-quinuclidinyl benzilate ([³H]-QNB) to central muscarinic receptors, an effect due to an increase in affinity without modifications in binding site number. The cholinergic system has been implicated in several experimental epilepsy models and the ability of acetylcholine to regulate neuronal excitability in the neocortex is well known. To study the potential relationship between GABAergic and cholinergic systems with seizure activity, we analyzed the muscarinic receptor after inducing seizure by bicuculline (BIC), known to antagonize the GABA-A postsynaptic receptor subtype.

Results

We analyzed binding of muscarinic antagonist [³H]-QNB to rat CNS membranes after i.p. administration of BIC at subconvulsant (1.0 mg/kg) and convulsant (7.5 mg/kg) doses. Subconvulsant BIC dose failed to develop seizures but produced binding alteration in the cerebellum and hippocampus with roughly 40% increase and 10% decrease, respectively. After convulsant BIC dose, which invariably led to generalized tonic-clonic seizures, binding increased 36% and 15% to cerebellar and striatal membranes respectively, but decreased 12% to hippocampal membranes. Kd value was accordingly modified: with the subconvulsant dose it decreased 27% in cerebellum whereas it increased 61% in hippocampus; with the convulsant dose, Kd value decreased 33% in cerebellum but increased 85% in hippocampus. No change in receptor number site was found, and Hill number was invariably close to unity.

Conclusion

Results indicate dissimilar central nervous system area susceptibility of muscarinic receptor to BIC. Ligand binding was modified not only by a convulsant BIC dose but also by a subconvulsant dose, indicating that changes are not attributable to the seizure process itself. Findings support the notion that the muscarinic receptors play a major role in experimental epilepsy and provide a new example of differential neuronal plasticity.

In vivo modulatory action of extracellular glutamate on the anticonvulsant effects of hippocampal dopamine and serotonin

PURPOSE

Our recent work (Clinckers et al., J Neurochem 2004;89:834-43) demonstrated that intrahippocampal perfusion of 2 nM dopamine or serotonin via a microdialysis probe offered complete protection against focal pilocarpine-induced limbic seizures and did not influence basal extracellular hippocampal glutamate levels. Ten nanomolar dopamine or serotonin perfusion, however, worsened seizures and was accompanied by significant extracellular glutamate increases to approximately 200%. The significance of these glutamate elevations in seizure generation remains unclear. The present microdialysis study investigated the modulatory role of extracellular hippocampal glutamate levels in these monoaminergic protective and proconvulsant effects.

METHODS

A first group of male Wistar albino rats was perfused intrahippocampally for 240 min with 6.25 microM glutamate alone to increase extracellular levels by 200%. Other animals were perfused with anticonvulsant concentrations of monoamines throughout the experiments while receiving continuous coperfusions of 6.25 microM glutamate either before, during, and after (240 min) or only after (100 min) pilocarpine perfusion (40 min). Rats were scored for epileptic behavior, and the mean scores were compared with those of the control group. Microdialysates were analyzed for monoamine and glutamate content with microbore liquid chromatography.

RESULTS

No convulsions occurred during glutamate perfusion alone. When monoamines and glutamate were coperfused before pilocarpine administration, the anticonvulsant effect of the monoamines was lost. Glutamate addition after pilocarpine administration did not affect monoaminergic seizure protection.

CONCLUSIONS

These results indicate that extracellular glutamate increases per se do not necessarily induce seizures but that they can modulate the anticonvulsant effects exerted by hippocampal monoamines.

Hippocampal melatonin receptors modulate seizure threshold

PURPOSE

The pineal hormone melatonin has been shown to enhance hippocampal excitability. We therefore investigated whether inactivation of hippocampal melatonin receptors affects behavioral seizures.

METHODS

Intrahippocampal infusions were performed in rats to study the effect of different melatonin receptor antagonists on behavioral activity, EEG, and seizure susceptibility. Experiments were conducted at 2 times of the day that coincided with the peak and trough of the daily melatonin rhythm.

RESULTS

Local infusion of the Mel(1b) receptor antagonist 4-phenyl-2-propionamidotetralin (4-P-PDOT) into the hippocampus, but not the overlying neocortex, significantly increased seizure latency and in some cases provided complete protection against seizure development. In addition, 4-P-PDOT suppressed open field activity and hippocampal EEG amplitude. The mixed Mel(1a)/Mel(1b) receptor antagonist luzindole also increased seizure latency but to a lesser degree than 4-P-PDOT. The behavioral effects of Mel(1b) receptor inhibition were comparable to those of the gamma-aminobutyric acid (GABA)(A) receptor agonist muscimol and were observed during the dark phase (2400-0200 h) but not the light phase (1200-1400 h) of the daily photocycle. The anticonvulsant effect of intrahippocampal infusion of 4P-P-DOT was blocked by coadministration of the GABA(A) antagonist bicuculline.

CONCLUSIONS

Our results suggest that nocturnal activation of hippocampal Mel(1b) receptors depresses GABA(A) receptor function in the hippocampus and enhances seizure susceptibility.

Plasma and cerebrospinal fluid amino acids in epileptic patients

Altered plasma and cerebrospinal fluid amino acid levels may be associated with human epilepsy. We studied three groups of patients, those with a generalized epileptic syndrome, juvenile myoclonic epilepsy, patients with refractory localization-related epilepsies, and patients with acute seizures (within 24 h). Plasma levels of amino acids were studied in all patient groups, as were those in the cerebrospinal fluid (CSF) of patients with acute seizures. After acute seizures, the amino acid changes in the CSF were limited to a reduction in the level of taurine, whereas the levels of most amino acids in plasma were decreased. On the other hand, levels of the excitatory amino acids glutamate and aspartate were increased. The most notable finding in the juvenile myoclonic epilepsy patients was an increase in glutamate level in the plasma. Our study supports the conception of an altered metabolism of glutamate in generalized epilepsies.

Pilocarpine-induced status epilepticus increases glutamate release in rat hippocampal synaptosomes

A pronounced glutamate release has been related to neuronal death in several structures due to status epilepticus (SE). We investigated the glutamate uptake and release by both cortical and hippocampal synaptosome in pilocarpine model of epilepsy. Animals were submitted to long-lasting SE (12 h) induced by pilocarpine and compared with non-treated animals. Animals presenting SE did not modify the glutamate uptake by synaptosomes. An increase in the glutamate efflux in the absence (1.43-fold) and in the presence of KCl (1.25-fold) was found in hippocampal synaptosomes. Pilocarpine added to the medium did not modify the glutamate release profile, showing that SE is necessary to modify the glutamate release. As the glutamate uptake is not modified, the hippocampal excitotoxicity may be related to impairment only in the mechanism of the glutamate release.

Ketogenic diet, brain glutamate metabolism and seizure control

We do not know the mode of action of the ketogenic diet in controlling epilepsy. One possibility is that the diet alters brain handling of glutamate, the major excitatory neurotransmitter and a probable factor in evoking and perpetuating a convulsion. We have found that brain metabolism of ketone bodies can furnish as much as 30% of glutamate and glutamine carbon. Ketone body metabolism also provides acetyl-CoA to the citrate synthetase reaction, in the process consuming oxaloacetate and thereby diminishing the transamination of glutamate to aspartate, a pathway in which oxaloacetate is a reactant. Relatively more glutamate then is available to the glutamate decarboxylase reaction, which increases brain [GABA]. Ketosis also increases brain [GABA] by increasing brain metabolism of acetate, which glia convert to glutamine. GABA-ergic neurons readily take up the latter amino acid and use it as a precursor to GABA. Ketosis also may be associated with altered amino acid transport at the blood-brain barrier. Specifically, ketosis may favor the release from brain of glutamine, which transporters at the blood-brain barrier exchange for blood leucine. Since brain glutamine is formed in astrocytes from glutamate, the overall effect will be to favor the release of glutamate from the nervous system.

Amino acid composition of brain cysts: levels of excitatory amino acids in cyst fluid fail to predict seizures

A recent study describing two epileptic patients with brain cysts has suggested that elevated concentrations of excitatory amino acids in cysts may play a role in induction and maintenance of epileptogenesis [Epilepsy Res. 28 (1997) 245]. Here, we report that only in 3 out of 22 patients with brain cysts undergoing brain surgery cyst fluids displayed highly increased amounts of the excitatory amino acids aspartate and/or glutamate. Two of these patients experienced epileptic seizures prior to neurosurgical intervention. Thus, highly increased excitatory amino acid levels are present only in a subset of patients with brain cysts. Our observation that one patient with highly increased glutamate and aspartate concentrations in the cyst did not display seizures or typical epileptiform potentials in the EEG questions that these excitatory amino acids in the cyst fluid are directly involved in epileptogenicity. This patient displayed an increased level of adenosine in the cyst fluid, which is known to have anticonvulsant properties and might provide protection from seizures. In summary, there is no evidence for a close correlation between excitatory amino acids in brain cysts and the occurrence of seizures.

Effectiveness of muscimol-containing microparticles against pilocarpine-induced focal seizures

PURPOSE

To investigate the efficacy of in situ lipid-protein-sugar particles (LPSPs) in mitigating the epileptogenic and histologic effects of intrahippocampal pilocarpine in rats.

METHODS

LPSPs with and without muscimol were produced by spray-drying, sized by Coulter counter, and muscimol content determined by high-pressure liquid chromatography (HLPC). Particles, free muscimol or saline, were injected into the hippocampi of Sprague-Dawley rats before 40 mM pilocarpine, and seizure activity was scored. The trajectories of behavioral scores between groups were compared with two-way repeated measures analysis of variance. Animals were killed after 2 weeks. Brain sections were stained (Timm and thionin) and scored.

RESULTS

LPSPs were 4 to 5 microm in diameter, and contained 0 or 2% (wt/wt) muscimol. In vitro, muscimol was released over a 5-day period. Intrahippocampal injections of normal saline and blank LPSPs did not deter seizure activity from pilocarpine. The rise of the trajectory in behavior scores in animals given LPSPs containing 5 microg muscimol was significantly slower than in those receiving saline, blank particles, or 5 microg of unencapsulated muscimol. There was less apparent neuronal injury and CA3 and supragranular mossy fiber sprouting in hippocampi of animals receiving muscimol-containing particles than in animals that did not receive muscimol. Hippocampi of animals that received 5 microg of encapsulated muscimol showed less supragranular sprouting than did those receiving 5 microg of unencapsulated muscimol, but showed no difference in cell loss or CA3 sprouting.

CONCLUSIONS

Focally delivered biodegradable microparticles loaded with muscimol are effective in reducing seizure activity from pilocarpine in animals and mitigate the histologic effects.

Behavioral, morphologic, and electroencephalographic evaluation of seizures induced by intrahippocampal microinjection of pilocarpine

PURPOSE

We studied, by means of video-EEG and neo-Timm histochemistry, the behavioral, electrophysiologic, and structural characteristics of seizures induced by intrahippocampal microinjection of pilocarpine (HIP-PILO), a selective model of temporal lobe epilepsy (TLE).

METHODS

We investigated the behavioral and electrophysiologic (hippocampus and amygdala EEG) evaluation of status epilepticus (SE) induced by HIP-PILO and the consequent spontaneous recurrent seizures (SRSs). We evaluated hippocampal structural rearrangements after SE by means of neo-Timm staining.

RESULTS

HIP-PILO induced SE in 17 (71%) of 24 animals. Although three animals displayed spontaneous remission of SE (not used in analysis) before the established SE duration (90 min), none of those undergoing SE died. Of SE animals, 10 (71%) of 14 had SRSs. All animals with SE had clear-cut mossy fiber sprouting (MFS) in the inner molecular layer of the dentate gyrus and epileptiform activity in hippocampus and amygdala.

CONCLUSIONS

HIP-PILO rats displayed SE, SRS, MFS, and limbic epileptiform activity, without animal loss after SE. Thus, our data support this as a selective and efficient model of TLE.

Short-term effects of pilocarpine on rat hippocampal neurons in culture

PURPOSE

Status epilepticus (SE) has been considered an epileptogenic factor in humans. In the pilocarpine (PILO) model, after a brief period marked by SE, the rats exhibit recurrent spontaneous seizures, mimicking the clinical features of temporal lobe epilepsy. The aim of our study was to identify the molecular actions of PILO that could account for its ability to induce SE.

METHODS

Whole-cell mode of the patch-clamp technique was applied to cultured hippocampal neurons (2-3 weeks old) in the absence and in the presence of PILO (1-10 microM), to study the spontaneous activity, the evoked, and the miniature postsynaptic currents. The postsynaptic currents were isolated pharmacologically.

RESULTS

PILO (1 and 10 microM) caused an initial increase followed by a decrease in the frequency of spontaneous activity. The increase in the frequency of excitatory postsynaptic currents (EPSCs) and inhibitory PSCs (IPSCs) was blocked by atropine (1 microM), indicating that this effect is mediated through muscarinic receptors. PILO also promoted a brief increase of the amplitude of IPSCs indirectly evoked by stimulation of a neuron synaptically connected to the neuron under study. Conversely, PILO promoted a sustained increase on the amplitude of electrically evoked EPSCs. In presence of tetrodotoxin (TTX; 300 nM), PILO (1 microM) increased the frequency of miniature EPSCs and IPSCs without changing their amplitude during the first 3 min of application.

CONCLUSIONS

These results indicate that PILO acting through muscarinic receptor causes an imbalance between excitatory and inhibitory transmission that can result in the generation of SE observed in animals acutely treated with PILO.

New insights from the use of pilocarpine and kainate models

Local or systemic administration of pilocarpine and kainate in rodents leads to a pattern of repetitive limbic seizures and status epilepticus, which can last for several hours. A latent period follows status epilepticus and precedes a chronic phase, which is characterized by the occurrence of spontaneous limbic seizures. These distinct features, in a single animal preparation, of an acute damage induced by status epilepticus, a silent interval between injury and the onset of spontaneous seizures, and a chronic epileptic state have allowed antiepileptic drug (AED) studies with different purposes, (a) in the acute phase, identification of compounds with efficacy against refractory status epilepticus and/or neuroprotection against damage induced by sustained seizures; (b) in the latent period, identification of agents with a potential for preventing epileptogenesis and/or against seizure-induced long-term behavioral deficits and (c) in the chronic phase, testing drugs effective against partial and secondarily generalized seizures. Studies on pilocarpine and kainate models have pointed out that some AEDs or other compounds exert an antiepileptogenic effect. The analogy of the latent phase of pilocarpine and kainate models with the acquisition of amygdala kindling should encourage testing of drugs that have proved to suppress the evolution of amygdala kindling. Drug testing in the chronic phase should not address only the suppression of secondarily generalized motor seizures. Most of current tools used to quantify spontaneous seizure events need to be coupled to electrophysiology and more sophisticated systems for recording and analyzing behavior.

Ketogenic diet, amino acid metabolism, and seizure control

The ketogenic diet has been utilized for many years as an adjunctive therapy in the management of epilepsy, especially in those children for whom antiepileptic drugs have not permitted complete relief. The biochemical basis of the dietary effect is unclear. One possibility is that the diet leads to alterations in the metabolism of brain amino acids, most importantly glutamic acid, the major excitatory neurotransmitter. In this review, we explore the theme. We present evidence that ketosis can lead to the following: 1) a diminution in the rate of glutamate transamination to aspartate that occurs because of reduced availability of oxaloacetate, the ketoacid precursor to aspartate; 2) enhanced conversion of glutamate to GABA; and 3) increased uptake of neutral amino acids into the brain. Transport of these compounds involves an uptake system that exchanges the neutral amino acid for glutamine. The result is increased release from the brain of glutamate, particularly glutamate that had been resident in the synaptic space, in the form of glutamine. These putative adaptations of amino acid metabolism occur as the system evolves from a glucose-based fuel economy to one that utilizes ketone bodies as metabolic substrates. We consider mechanisms by which such changes might lead to the antiepileptic effect.