okadaic-acid and Seizures

Tau hyperphosphorylation has been implicated in the pathogenesis of a variety of forms of human epilepsy. Here we investigated whether treatment with sodium selenate, a drug which reduces pathological hyperphosphorylated tau by enhancement of PP2A activity, would inhibit seizures in rodent models. In vitro, sodium selenate reduced tau phosphorylation in human neuroblastoma cells and reversed the increase in tau phosphorylation induced by the PP2A inhibitor, okadaic acid. Sodium selenate treatment was then tested against three different rodent seizure models. Firstly the propensity of 6-Hz electrical corneal stimulation to induce seizures in adult mice was assessed following acute treatment with different doses of sodium selenate. Secondly, the number of seizures induced by pentylenetetrazole (PTZ) was quantified in rats following chronic sodium selenate treatment via drinking water. Finally, amygdala kindled rats were chronically treated with sodium selenate in drinking water and the length and the severity of the seizures evoked by stimulation of the amygdala recorded. The results demonstrated a dose-dependent protection of sodium selenate against 6-Hz stimulation induced seizures, and significant reduction in the total number of seizures following PTZ injection. Amygdala kindled rats chronically treated with sodium selenate had significantly shorter seizure duration compared controls, with more pronounced effects observed as the duration of treatment increased. The results of this study indicate that targeting hyperphosphorylated tau by treatment with sodium selenate has anti-seizure effects in a broad range of rodent models, and may represent a novel approach to treatment of patients with epilepsy.

Topics: Amygdala; Analysis of Variance; Animals; Antioxidants; Cell Line, Tumor; Convulsants; Disease Models, Animal; Dose-Response Relationship, Drug; Electric Stimulation; Enzyme Inhibitors; Gene Expression Regulation; Humans; Leucine; Male; Mutation; Neuroblastoma; Okadaic Acid; Pentylenetetrazole; Phosphorylation; Proline; Rats; Rats, Sprague-Dawley; Rats, Wistar; Seizures; Selenic Acid; Selenium Compounds; tau Proteins; Time Factors; Transfection

Voltage-dependent Kv2.1 K(+) channels, which mediate delayed rectifier Kv currents (I(K)), are expressed in large clusters on the somata and dendrites of principal pyramidal neurons, where they regulate neuronal excitability. Here we report activity-dependent changes in the localization and biophysical properties of Kv2.1. In the kainate model of continuous seizures in rat, we find a loss of Kv2.1 clustering in pyramidal neurons in vivo. Biochemical analysis of Kv2.1 in the brains of these rats shows a marked dephosphorylation of Kv2.1. In cultured rat hippocampal pyramidal neurons, glutamate stimulation rapidly causes dephosphorylation of Kv2.1, translocation of Kv2.1 from clusters to a more uniform localization, and a shift in the voltage-dependent activation of I(K). An influx of Ca(2+) leading to calcineurin activation is both necessary and sufficient for these effects. Our finding that neuronal activity modifies the phosphorylation state, localization and function of Kv2.1 suggests an important link between excitatory neurotransmission and the intrinsic excitability of pyramidal neurons.

Topics: Animals; Animals, Newborn; Blotting, Western; Cadmium Chloride; Calcimycin; Calcium Channel Blockers; Cell Count; Cells, Cultured; Cyclosporine; Delayed Rectifier Potassium Channels; Dendrites; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Glutamic Acid; Hippocampus; Ion Channel Gating; Ionophores; Kainic Acid; Membrane Potentials; Neuronal Plasticity; Nitrendipine; Nitriles; Okadaic Acid; Patch-Clamp Techniques; Phosphoprotein Phosphatases; Phosphorylation; Potassium; Potassium Channel Blockers; Potassium Channels; Potassium Channels, Voltage-Gated; Potassium Chloride; Pyramidal Cells; Pyrethrins; Rats; Seizures; Shab Potassium Channels; Time Factors; Translocation, Genetic

The development of symptomatic epilepsy is a model of long-term plasticity changes in the central nervous system. The rat pilocarpine model of epilepsy was utilized to study persistent alterations in calcium/calmodulin-dependent kinase II (CaM kinase II) activity associated with epileptogenesis. CaM kinase II-dependent substrate phosphorylation and autophosphorylation were significantly inhibited for up to 6 weeks following epileptogenesis in both the cortex and hippocampus, but not in the cerebellum. The net decrease in CaM kinase II autophosphorylation and substrate phosphorylation was shown to be due to decreased kinase activity and not due to increased phosphatase activity. The inhibition in CaM kinase II activity and the development of epilepsy were blocked by pretreating seizure rats with MK-801 indicating that the long-lasting decrease in CaM kinase II activity was dependent on N-methyl-D-aspartate receptor activation. In addition, the inhibition of CaM kinase II activity was associated in time and regional localization with the development of spontaneous recurrent seizure activity. The decrease in enzyme activity was not attributed to a decrease in the alpha or beta kinase subunit protein expression level. Thus, the significant inhibition of the enzyme occurred without changes in kinase protein expression, suggesting a long-lasting, post-translational modification of the enzyme. This is the first published report of a persistent, post-translational alteration of CaM kinase II activity in a model of epilepsy characterized by spontaneous recurrent seizure activity.

Topics: Animals; Brain; Calcium-Calmodulin-Dependent Protein Kinases; Dizocilpine Maleate; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Intercellular Signaling Peptides and Proteins; Isoenzymes; Male; Okadaic Acid; Peptides; Phosphoric Monoester Hydrolases; Phosphorylation; Pilocarpine; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Secondary Prevention; Seizures; Status Epilepticus; Time Factors

The aim of this study was to identify changes in gene expression during neuronal apoptosis using the differential display (DD) technique. Potassium deprivation was used to induce neuronal apoptosis in cultured rat cerebellar granule cells. DD analysis of about 1600 transcripts resulted in 8 cDNA clones that confirmed differential expression in a slot blot analysis. One of these clones was homologous to the 3' end of seizure-related PTZ-17 RNA. Northern blot analysis showed a marked upregulation of a 2.2 kb RNA 24 hours after potassium withdrawal. This upregulation was prevented by the RNA synthesis inhibitor actinomycin D. The increase in PTZ-17 expression was specific for potassium deprivation induced apoptosis, since the other apoptosis inducers, okadaic acid and staurosporine, did not affect PTZ-17 expression. The level of PTZ-17 RNA was not significantly affected by aging in rat cerebellum. Our data suggest that the upregulation of the PTZ-17 RNA is a part of the steps leading to apoptosis during potassium deprivation in cerebellar granule cells.

Topics: Aging; Animals; Apoptosis; Cells, Cultured; Cerebellum; Dactinomycin; Nerve Tissue Proteins; Neurons; Okadaic Acid; Oncogene Proteins; Potassium Deficiency; Rats; Rats, Wistar; RNA, Messenger; Seizures; Staurosporine; Transcription, Genetic