Stress affects seizure susceptibility in animals and humans, but the underlying mechanisms are obscure. Here, we provide evidence that GABA(A) receptor-modulating neurosteroids derived from deoxycorticosterone (DOC) play a role in stress-related changes in seizure control. DOC, an adrenal steroid whose synthesis is enhanced during stress, undergoes sequential metabolic reduction by 5alpha-reductase and 3alpha-hydroxysteroid oxidoreductase to form 5alpha-dihydrodeoxycorticosterone (DHDOC) and allotetrahydrodeoxycorticosterone (THDOC), a GABA(A) receptor-modulating neurosteroid with anticonvulsant properties. Acute swim stress in rats significantly elevated plasma THDOC concentrations and raised the pentylenetetrazol (PTZ) seizure threshold. Small systemic doses of DOC produced comparable increases in THDOC and PTZ seizure threshold. Pretreatment with finasteride, a 5alpha-reductase inhibitor that blocks the conversion of DOC to DHDOC, reversed the antiseizure effects of stress. DOC also elevated plasma THDOC levels and protected mice against PTZ, methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate, picrotoxin, and amygdala-kindled seizures in mice (ED50 values, 84-97 mg/kg). Finasteride reversed the antiseizure activity of DOC (ED50, 7.2 mg/kg); partial antagonism was also obtained with indomethacin (100 mg/kg), an inhibitor of 3alpha-hydroxysteroid oxidoreductase. Finasteride had no effect on seizure protection by DHDOC and THDOC, whereas indomethacin partially reversed DHDOC but not THDOC. DHDOC, like THDOC, potentiated GABA-activated Cl- currents in cultured hippocampal neurons (< or =1 microm) and directly activated GABA(A) receptor currents (> or =1 microm), compatible with a role for DHDOC in the antiseizure activity of DOC. DOC is a mediator of the physiological effects of acute stress that could contribute to stress-induced changes in seizure susceptibility through its conversion to neurosteroids with modulatory actions on GABA(A) receptors including THDOC and possibly also DHDOC.

Christian et al.

SUMMARY Objective This review summarizes the therapeutic potential of midazolam as an anticonvulsant antidote for organophosphate (OP) intoxication. Methods Benzodiazepines are widely used for acute seizures and status epilepticus (SE), a neurological emergency of persistent seizures that can lead to severe neuronal damage or death. Midazolam is a benzodiazepine hypnotic with a rapid onset and short duration of action. Results Midazolam is considered the new drug of choice for persistent acute seizures and SE, including those caused by neurotoxic OPs and nerve agents. Midazolam is a positive allosteric modulator of synaptic GABA-A receptors in the brain. It potentiates GABAergic inhibition and thereby controls hyperexcitability and seizures. Midazolam is administered intravenously or intramuscularly to control acute seizures and SE. Due to its favorable pharmacokinetic features, midazolam is being considered as a replacement anticonvulsant for diazepam in the antidote kit for nerve agents. Clinical studies such as the recent RAMPART trial have confirmed the anticonvulsant efficacy of midazolam in SE in prehospital settings. Significance In experimental models, midazolam is effective when given at the onset of seizures caused by nerve agents. However, benzodiazepines are less effective at terminating seizures when given 30 min or later after OP exposure or seizure onset likely because of internalization or down-regulation of synaptic, but not extrasynaptic, GABA-A receptors, which can lead to diminished potency and seizure recurrence.

This article provides an overview of neuroimaging biomarkers in experimental epileptogenesis and refractory epilepsy. Neuroimaging represents a gold standard and clinically translatable technique to identify neuropathological changes in epileptogenesis and longitudinally monitor its progression after a precipitating injury. Neuroimaging studies, along with molecular studies from animal models, have greatly improved our understanding of the neuropathology of epilepsy, such as the hallmark hippocampus sclerosis. Animal models are effective for differentiating the different stages of epileptogenesis. Neuroimaging in experimental epilepsy provides unique information about anatomic, functional, and metabolic alterations linked to epileptogenesis. Recently, several in vivo biomarkers for epileptogenesis have been investigated for characterizing neuronal loss, inflammation, blood-brain barrier alterations, changes in neurotransmitter density, neurovascular coupling, cerebral blood flow and volume, network connectivity, and metabolic activity in the brain. Magnetic resonance imaging (MRI) is a sensitive method for detecting structural and functional changes in the brain, especially to identify region-specific neuronal damage patterns in epilepsy. Positron emission tomography (PET) and single-photon emission computerized tomography are helpful to elucidate key functional alterations, especially in areas of brain metabolism and molecular patterns, and can help monitor pathology of epileptic disorders. Multimodal procedures such as PET-MRI integrated systems are desired for refractory epilepsy. Validated biomarkers are warranted for early identification of people at risk for epilepsy and monitoring of the progression of medical interventions.

No abstract

Midazolam is a benzodiazepine anticonvulsant with rapid onset and short duration of action. Midazolam is the current drug of choice for acute seizures and status epilepticus, including those caused by organophosphate nerve agents. The antiseizure activity of midazolam is thought to result from its allosteric potentiation of synaptic GABA A receptors in the brain. However, there are indications that benzodiazepines promote neurosteroid synthesis via the 18-kDa cholesterol transporter protein (TSPO). Therefore, we investigated the role of neurosteroids and their extrasynaptic GABA A receptor targets in the antiseizure activity of midazolam. Here, we used d-subunit knockout (DKO) mice bearing a targeted deletion of the extrasynaptic receptors to investigate the contribution of the extrasynaptic receptors to the antiseizure activity of midazolam using the 6-Hz and hippocampus kindling seizure models. In both models, midazolam produced rapid and dose-dependent protection against seizures (ED 50 , 0.4 mg/kg). Moreover, the antiseizure potency of midazolam was undiminished in DKO mice compared with control mice. Pretreatment with PK11195 [1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxamide], a TSPO blocker, or finasteride, a 5a-reductase neurosteroid inhibitor, did not affect the antiseizure effect of midazolam. The antiseizure activity of midazolam was significantly reversed by pretreatment with flumazenil, a benzodiazepine antagonist. Plasma and brain levels of the neurosteroid allopregnanolone were not significantly greater in midazolam-treated animals. These studies therefore provide strong evidence that neurosteroids and extrasynaptic GABA A receptors are not involved in the antiseizure activity of midazolam, which mainly occurs through synaptic GABA A receptors via direct binding to benzodiazepine sites. This study reaffirms midazolam's use for controlling acute seizures and status epilepticus.

No abstract

Epilepsy is a chronic brain disease characterized by repeated unprovoked seizures. Currently, no drug therapy exists for curing epilepsy or disease modification in people at risk. Despite several emerging mechanisms, there have been few studies of epigenetic signaling in epileptogenesis, the process whereby a normal brain becomes progressively epileptic because of precipitating factors. Here, we report a novel role of histone deacetylation as a critical epigenetic mechanism in epileptogenesis. Experiments were conducted using the histone deacetylase (HDAC) inhibitor sodium butyrate in the hippocampus kindling model of temporal lobe epilepsy (TLE), a classic model heavily used to approve drugs for treatment of epilepsy. Daily treatment with butyrate significantly inhibited HDAC activity and retarded the development of limbic epileptogenesis without affecting after-discharge signal. HDAC inhibition markedly impaired the persistence of seizure expression many weeks after epilepsy development. Moreover, subchronic HDAC inhibition for 2 weeks resulted in a striking retardation of epileptogenesis. HDAC inhibition, unexpectedly, also showed erasure of the epileptogenic state in epileptic animals. Finally, butyrate-treated animals exhibited a powerful reduction in mossy fiber sprouting, a morphologic index of epileptogenesis. Together these results underscore that HDAC inhibition prevents the development of TLE, indicating HDAC's critical signaling role in epileptogenesis. These findings, therefore, envisage a unique novel therapy for preventing or curing epilepsy by targeting the epigenetic HDAC pathway.