This review highlights the role of major endogenous neurosteroids in seizure disorders and the promise of neurosteroid replacement therapy in epilepsy. Neurosteroids are endogenous modulators of seizure susceptibility. Neurosteroids such as allopregnanolone (3α-hydroxy-5α-pregnane-20-one) and allotetrahydrodeoxycorticosterone (3α,21-dihydroxy-5α-pregnan-20-one) are positive modulators of GABA-A receptors. Aside from peripheral tissues, neurosteroids are synthesized within the brain, mostly in principal neurons. Neurosteroids potentiate synaptic GABA-A receptor function and also activate δ-subunit-containing extrasynaptic GABA-A receptors that mediate tonic currents and thus may play an important role in neuronal network excitability and seizure susceptibility. Our studies over the past decade have shown that neurosteroids are broad-spectrum anticonvulsants and confer seizure protection in various animal models. They protect against seizures induced by GABA-A receptor antagonists, 6-Hz model, pilocarpine-induced limbic seizures, and seizures in kindled animals. Unlike benzodiazepines, tolerance does not occur to their actions during chronic administration. Our recent studies provide compelling evidence that neurosteroids may have antiepileptogenic properties. There is emerging evidence that endogenous neurosteroids may play a key role in the pathophysiology of catamenial epilepsy, stress–sensitive seizure conditions, temporal lobe epilepsy, and alcohol-withdrawal seizures. It is suggested that neurosteroid replacement with natural or synthetic neurosteroids may be useful in the treatment of epilepsy. Synthetic analogs of neurosteroids that are devoid of hormonal side effects show promise in the treatment of diverse seizure disorders. Agents that stimulate endogenous production of neurosteroids may also be useful for treatment of epilepsy.
allopregnanolone; THDOC; neurosteroids; seizure; epilepsy; catamenial epilepsy; epileptogenesis; GABA-A receptor
Perimenstural catamenial epilepsy, the cyclical occurrence of seizure exacerbations near the time of menstruation, affects a high proportion of women of reproductive age with drug refractory epilepsy. Enhanced seizure susceptibility in perimenstrual catamenial epilepsy is believed to be due to the withdrawal of the progesterone-derived GABAA receptor modulating neurosteroid allopregnanolone as a result of the fall in progesterone at the time of menstruation. Studies in a rat pseudopregnancy model of catamenial epilepsy indicate that following neurosteroid withdrawal there is enhanced susceptibility to chemoconvulsant seizures. There is also a transitory increase in the frequency of spontaneous seizures in epleptic rats that had experienced pilocarpine-induced status epilepticus. In the catamenial epilepsy model, there is a marked reduction in the antiseizure potency of anticonvulsant drugs, including benzodiazepines and valproate, but an increase in the anticonvulsant potency and protective index of neurosteroids such as allopregnanolone and the neurosteroid analog ganaxolone. The enhanced seizure susceptibility and benzodiazepine-resistance following neurosteroid withdrawal may be related to reduced expression and altered kinetics of synaptic GABAA receptors and increased expression of GABAA receptor subunits (such as α4) that confer benzodiazepine insensitivity. The enhanced potency of neurosteroids may be due to a relative increase following neurosteroid withdrawal in the expression of neurosteroid-sensitive δ-subunit-containing perisynaptic/extrasynaptic GABAA receptors. Positive allosteric modulatory neurosteroids and synthetic analogs such as ganaxolone may be administered to prevent catamenial seizure exacerbations, which we refer to as “neurosteroid replacement therapy.”
catamenial epilepsy; progesterone; neurosteroid; allopregnanolone; ganaxolone; GABAA receptor
Neurosteroids, such as the progesterone metabolite 3α-OH-5α[β]-pregnan-20-one (THP or [allo]pregnanolone), function as potent positive modulators of the GABAA receptor (GABAR) when acutely administered. However, fluctuations in the circulating levels of this steroid at puberty, across endogenous ovarian cycles, during pregnancy or following chronic stress produce periods of prolonged exposure and withdrawal, where changes in GABAR subunit composition may occur as compensatory responses to sustained levels of inhibition. A number of laboratories have demonstrated that both chronic administration of THP as well as its withdrawal transiently increase expression of the α4 subunit of the GABAR in several areas of the central nervous system (CNS) as well as in in vitro neuronal systems. Receptors containing this subunit are insensitive to benzodiazepine (BDZ) modulation and display faster deactivation kinetics, which studies suggest underlie hyperexcitability states. Similar increases in α4 expression are triggered by withdrawal from other GABA-modulatory compounds, such as ethanol and BDZ, suggesting a common mechanism. Other studies have reported puberty or estrous cycle-associated increases in δ-GABAR, the most sensitive target of these steroids which underlies a tonic inhibitory current. In the studies reported here, the effect of steroids on inhibition, which influence anxiety state and seizure susceptibility, depend not only on the subunit composition of the receptor but also on the direction of Cl- current generated by these target receptors. The effect of neurosteroids on GABAR function thus results in behavioral outcomes relevant for pubertal mood swings, premenstrual dysphoric disorder and catamenial epilepsy, which are due to fluctuations in endogenous steroids.
GABAA receptor; Alpha-4; Delta; Neurosteroid; Allopregnanolone; Pregnanolone; THP; GABA; Hippocampus; Anxiety; Panic; Premenstrual syndrome; Premenstrual dysphoric disorder; Puberty; Mood
γ-Aminobutyric acid type A receptors (GABAA-Rs) have been implicated in mediating some of the behavioral effects of ethanol (EtOH), but the contribution of specific GABAA-R subunits is not fully understood. The GABAA-R α4 subunit often partners with β2/3 and δ subunits to form extrasynaptic GABAA-Rs that mediate tonic inhibition. Several in vitro studies have suggested that these extrasynaptic GABAA-Rs may be particularly relevant to the intoxicating effects of low doses of EtOH. In α4 subunit knockout mice tonic inhibition was greatly reduced, as were the potentiating effects of EtOH. We therefore hypothesized that those behavioral responses to EtOH that are mediated by α4-containing GABAA-Rs would be diminished in α4 knockout mice.
We investigated behavioral responses to acute administration of moderate/high dose EtOH or pentylenetetrazol in α4 subunit knockout mice. We compared behavioral responses to EtOH in α4 knockout and wild type littermates in the elevated plus maze (0.0, 1.0 g/kg EtOH), screen test (1.5, 2.0 g/kg), hypothermia (1.5, 2.0 g/kg), fixed speed rotarod (1.5, 2.0. 2.5 g/kg), open field (0.0, 1.0, 2.0 g/kg), radiant tail flick (2.0 g/kg), loss of righting reflex (3.5 g/kg), and EtOH metabolism and clearance assays. Sensitivity to pentylenetetrazol-induced seizures was also analyzed.
No differences were observed between α4 knockout mice and wild type controls in terms of the baseline behavior in the absence of EtOH treatment or in the behavioral effects of EtOH in the assays tested. In contrast, α4 knockout mice were significantly more sensitive to pentylenetetrazol-induced seizures.
We conclude that GABAA-Rs containing the α4 subunit are not absolutely required for the acute behavioral responses to moderate/high dose EtOH that were assessed with the elevated plus maze, screen test, hypothermia, fixed speed rotarod, open field, radiant tail flick, and loss of right reflex assays. We further suggest that these findings are complicated by the demonstrated compensatory alterations in synaptic GABAA-R EtOH sensitivity and function in α4 knockout mice.
GABA; GABA type A receptor; gene knockout mice; alcohol; extrasynaptic receptors
Epilepsies are disorders of neuronal excitability characterized by spontaneous and recurrent seizures. Ion channels are critical for regulating neuronal excitability and, therefore, can contribute significantly to epilepsy pathophysiology. In particular, large conductance, Ca2+-activated K+ (BKCa) channels play an important role in seizure etiology. These channels are activated by both membrane depolarization and increased intracellular Ca2+. This unique coupling of Ca2+ signaling to membrane depolarization is important in controlling neuronal hyperexcitability, as outward K+ current through BKCa channels hyperpolarizes neurons.
This review focuses on BKCa channel structure-function and discusses the role of these channels in epilepsy pathophysiology.
Loss-of-function BKCa channels contribute neuronal hyperexcitability that can lead to temporal lobe epilepsy, tonic-clonic seizures and alcohol withdrawal seizures. Similarly, BKCa channel blockade can trigger seizures and status epilepticus. Paradoxically, some mutations in BKCa channel subunit can give rise to the channel gain-of-function that leads to development of idiopathic epilepsy (primarily absence epilepsy). Seizures themselves also enhance BKCa channel currents associated with neuronal hyperexcitability, and blocking BKCa channels suppresses generalized tonic-clonic seizures. Thus, both loss-of-function and gain-of-function BKCa channels might serve as molecular targets for drugs to suppress certain seizure phenotypes including temporal lobe seizures and absence seizures, respectively.
Anticonvulsant; Epileptogenesis; Gain-of-function; Gene mutation; Loss-of-function; Seizures
Ethanol withdrawal is a dysphoric condition that arises from termination of ethanol intake by dependent individuals. Common withdrawal symptoms include anxiety, increased reactivity to stimuli and increased seizure susceptibility as well as the risk of increased seizure severity. We use an animal model of dependence and withdrawal to study withdrawal behaviors and potential underlying neurobiological mechanisms. For a number of years, we have quantified pentylenetetrazol seizure thresholds as an assessment of ethanol withdrawal at both one day and three days of withdrawal. Typically, we see a significant decrease in seizure threshold (increased sensitivity to seizure induction) that persists through three days of withdrawal for male rats. Increasing evidence indicates that voluntary exercise affords protection against various challenges to physical and psychological health, including ethanol-related challenges. Therefore, the current study investigated the effect of voluntary wheel running on seizure susceptibility following chronic ethanol administration and withdrawal. We found that voluntary wheel running attenuated the increased sensitivity to pentylenetetrazol-induced seizures observed with ethanol withdrawal, at both the one-day and three-day time points. This result was especially interesting as animals with access to the running wheels consumed more of the ethanol-containing diet. These findings showed that chronic voluntary wheel running reduces the severity of ethanol withdrawal in our animal model and suggest that exercise-based interventions may have some utility in the clinical management of heavy drinking and alcohol withdrawal.
Ethanol withdrawal; Activity wheel; GABAA receptors; Stress; Seizure susceptibility
This is an updated version of the original Cochrane review published in Issue 4, 2001.
Worldwide, phenytoin and phenobarbitone are commonly used antiepileptic drugs. They are more likely to be used in the developing world than the developed world, primarily because they are inexpensive. The aim of this review is to summarize data from existing trials comparing phenytoin and phenobarbitone.
To review the effects of phenobarbitone compared to phenytoin when used as monotherapy in patients with partial onset seizures or generalized tonic-clonic seizures with or without other generalized seizure types.
We searched the Cochrane Epilepsy Group trials register (20 October 2009), the Cochrane Central Register of Controlled Trials (The Cochrane Library Issue 4, 2009) and MEDLINE (1950 to October week 2, 2009). In addition, we handsearched relevant journals, and contacted pharmaceutical companies and researchers in the field to seek any ongoing or unpublished studies.
Randomized controlled trials in children or adults with partial onset seizures or generalized onset tonic-clonic seizures. Trials must have included a comparison of phenobarbitone monotherapy with phenytoin monotherapy.
Data collection and analysis
This was an individual patient data review. Outcomes were time to (a) withdrawal of allocated treatment, (b) 12-month remission and (c) first seizure post randomization. Data were analyzed using a stratified logrank analysis with results expressed as hazard ratios (HR) and 95% confidence intervals (95% CI), where a HR > 1 indicates an event is more likely to occur earlier on phenobarbitone than phenytoin.
To date, data have been obtained for four of ten studies meeting the inclusion criteria, amounting to 599 individuals, or approximately 65% of the potential data. The main overall results (HR) were (a) time to treatment withdrawal 1.62 (95% confidence interval 1.22 to 2.14); (b) time to 12-month remission 0.93 (95% confidence interval 0.70 to 1.23) and (c) time to first seizure 0.84 (95% confidence interval 0.68 to 1.05). These results indicate a statistically significant clinical advantage for phenytoin in terms of treatment withdrawal and a non-significant advantage in terms of 12-month remission. Results for time to first seizure suggest a non-significant clinical advantage for phenobarbitone.
The results of this review favour phenytoin over phenobarbitone, as phenobarbitone was significantly more likely to be withdrawn than phenytoin. Given that no significant differences for seizure outcomes were found, the higher withdrawal rate with phenobarbitone may be due to adverse effects.
Anticonvulsants [* therapeutic use]; Epilepsies, Partial [* drug therapy]; Epilepsy, Generalized [* drug therapy]; Phenobarbital [* therapeutic use]; Phenytoin [* therapeutic use]; Randomized Controlled Trials as Topic; Seizures [* drug therapy]; Humans
Alcohol use disorders (AUD) constitute the most common form of substance abuse. The development of AUD involves repeated alcohol use leading to tolerance, alcohol withdrawal syndrome (AWS), physical and psychological dependence, with loss of ability to control excessive drinking. Currently there is no effective therapeutic agent for AUD without major side-effects. Dihydromyricetin (DHM, 1 mg/kg, i.p. injection), a flavonoid component of herbal medicines, counteracted acute alcohol (EtOH) intoxication, and also withdrawal signs in rats including tolerance, increased anxiety and seizure susceptibility; DHM greatly reduced EtOH consumption in an intermittent voluntary EtOH intake paradigm in rats. GABAA receptors (GABAARs) are major targets of acute and chronic EtOH actions on the brain. At the cellular levels, DHM (1 μM) antagonized both acute EtOH-induced potentiation of GABAARs and EtOH exposure/withdrawal-induced GABAAR plasticity, including alterations in responsiveness of extra- and post-synaptic GABAARs to acute EtOH, and most importantly, increases in GABAAR α4 subunit expression in hippocampus and cultured neurons. DHM anti-alcohol effects on both behavior and CNS neurons were antagonized by flumazenil (10 mg/kg in vivo, 10 μM in vitro), the benzodiazepine (BZ) antagonist. DHM competitively inhibited BZ-site [3H]flunitrazepam binding (IC50, 4.36 μM), suggesting DHM interaction with EtOH involves the BZ-sites on GABAARs. In summary, we determined DHM anti-alcoholic effects on animal models, and determined a major molecular target and cellular mechanism of DHM for counteracting alcohol intoxication and dependence. We demonstrated pharmacological properties of DHM consistent with those expected to underlie successful medical treatment of AUD; therefore DHM is a therapeutic candidate.
The abrupt discontinuation of prolonged benzodiazepine treatment elicits a withdrawal syndrome with increased anxiety as a major symptom. The neural mechanisms underlying benzodiazepine physical dependence are still insufficiently understood. Flumazenil, the non-selective antagonist of the benzodiazepine binding site of GABAA receptors was capable of preventing and reversing the increased anxiety during benzodiazepine withdrawal in animals and humans in some, but not all studies. On the other hand, a number of data suggest that GABAA receptors containing α1 subunits are critically involved in processes developing during prolonged use of benzodiazepines, such are tolerance to sedative effects, liability to physical dependence and addiction. Hence, we investigated in the elevated plus maze the level of anxiety 24 h following 21 days of diazepam treatment and the influence of flumazenil or a preferential α1-subunit selective antagonist βCCt on diazepam withdrawal syndrome in rats. Abrupt cessation of protracted once-daily intraperitoneal administration of 2 mg/kg diazepam induced a withdrawal syndrome, measured by increased anxiety-like behavior in the elevated plus maze 24 h after treatment cessation. Acute challenge with either flumazenil (10 mg/kg) or βCCt (1.25, 5 and 20 mg/kg) alleviated the diazepam withdrawal-induced anxiety. Moreover, both antagonists induced an anxiolytic-like response close, though not identical, to that seen with acute administration of diazepam. These findings imply that the mechanism by which antagonism at GABAA receptors may reverse the withdrawal-induced anxiety involves the α1 subunit and prompt further studies aimed at linking the changes in behavior with possible adaptive changes in subunit expression and function of GABAA receptors.
elevated plus maze; βCCt; antagonism; benzodiazepines; physical dependence
Alcohol withdrawal, refers to a cluster of symptoms that may occur from suddenly ceasing the use of alcohol after chronic or prolonged ingestion. These symptoms make alcohol abstinence difficult and increase the risk of relapse in recovering alcoholics. In previous studies, we demonstrated that treatment with N/OFQ significantly reduces alcohol consumption and attenuates alcohol-seeking behaviour induced by environmental conditioning factors or by stress in rats. In the present study we evaluated whether activation of brain NOP receptors may also attenuate alcohol withdrawal signs in rats.
For this purpose animals were subjected to a 6 day chronic alcohol intoxication (by intragastric administration) and at 8, 10 and 12 hours following cessation of alcohol exposure they were treated intracerebroventricularly (ICV) with N/OFQ (0.0, 1.0 and 3.0 μg/rat). Somatic withdrawal signs were scored after ICV treatment. In a subsequent experiment, to evaluate N/OFQ effects on alcohol withdrawal-induced anxiety another group of rats was subjected to ethanol intoxication and after one week was tested for anxiety behavior in the elevated plus maze (EPM). In the last experiment an additional group of rats was tested for anxiety elicited by acute ethanol intoxication (hangover anxiety). For this purpose, animals received an acute dose (3.0 g/kg) of 20% alcohol and 12-h later were tested in the EPM following ICV N/OFQ (0.0, 1.0 and 2.0μg/rat).
Results showed that N/OFQ significantly reduced the expression of somatic withdrawal signs and reversed anxiety-like behaviors associated with both chronic and acute alcohol intoxication. N/OFQ did not affect anxiety scores in nondependent animals.
The present findings suggest that the N/OFQ-NOP receptor system may represent a promising target for the development of new treatments to ameliorate alcohol withdrawal symptoms.
Nociceptin; Orphanin FQ; Alcoholism; Withdrawal; Anxiety
Many of the neurobehavioral effects of ethanol are mediated by inhibition of excitatory N-methyl-d-aspartate (NMDA) and enhancement of inhibitory γ-amino-butyric-acid (GABA) receptor systems. There is growing interest in drugs that alter these systems as potential medications for problems associated with alcoholism. The drug riluzole, approved for treatment of amyotrophic lateral sclerosis (ALS), inhibits NMDA and enhances GABAA receptor system activity. This study was designed to determine the preclinical efficacy of riluzole to modulate ethanol self-administration and withdrawal.
Male C57BL/6J mice were trained to lever press on a concurrent fixed-ratio 1 schedule of ethanol (10% v/v) versus water reinforcement during daily 16-hour sessions. Riluzole (1 to 40 mg/kg, IP) was evaluated on ethanol self-administration after acute and chronic (2 week) treatment. To determine if riluzole influences ethanol withdrawal-associated seizures, mice were fed an ethanol-containing or control liquid diet for 18 days. The effects of a single injection of riluzole (30 mg/kg) were examined on handling-induced convulsions after ethanol withdrawal.
Acute riluzole (30 and 40 mg/kg) reduced ethanol self-administration during the first 4 hours of the session, which corresponds to the known pharmacokinetics of this drug. Ethanol self-administration was also reduced by riluzole after chronic treatment. Riluzole (30 mg/kg) significantly decreased the severity of ethanol-induced convulsions 2 hours after ethanol withdrawal.
These results demonstrate that riluzole decreases ethanol self-administration and may reduce ethanol withdrawal severity in mice. Thus, riluzole may have utility in the treatment of problems associated with alcoholism.
Alcohol Drinking; Alcoholism; Self-Administration; GABA; NMDA; PKC; Riluzole
The parahippocampal areas including the subiculum, pre- and parasubiculum, and notably the entorhinal cortex (EC) are intimately involved in the generation of limbic seizures in temporal lobe epilepsy. We investigated changes in the expression of 10 major GABAA receptor subunit mRNAs in subfields of the ventral hippocampus, ventral subiculum, EC, and perirhinal cortex (PRC) at different intervals (1, 8, 30, and 90 days) after kainic acid (KA)-induced status epilepticus priming epileptogenesis in the rat. The most pronounced and ubiquitous changes were a transient (24 h after KA only) down-regulation of γ2 mRNA and lasting decreases in subunit α5, β3, and δ mRNAs that were prominent in all hippocampal and parahippocampal areas. In the subiculum similarly as in sectors CA1 and CA3, levels of subunit α1, α2, α4, and γ2 mRNAs decreased transiently (1 day after KA-induced status epilepticus). They were followed by increased expression of subunit α1 and α3 mRNAs in the dentate gyrus (DG) and sectors CA1 and CA3, and subunit α1 also in the EC layer II (30 and 90 days after KA). We also observed sustained overexpression of subunits α4 and γ2 in the subiculum and in the Ammon’s horn. Subunit γ2 mRNA was also increased in sector CA1 at the late intervals after KA. Taken together, our results suggest distinct regulation of mRNA expression for individual GABAA receptor subunits. Especially striking was the wide-spread down-regulation of the often peri- or extrasynaptically located subunits α5 and δ. These subunits are often associated with tonic inhibition. Their decrease could be related to decreased tonic inhibition or may merely reflect compensatory changes. In contrast, expression of subunit α4 that may also mediate tonic inhibition when associated with the δ-subunit was significantly upregulated in the DG and in the proximal subiculum at late intervals. Thus, concomitant up-regulation of subunit γ2, α1 and α4 mRNAs (and loss in δ-subunits) ultimately indicates significant rearrangement of GABAA receptor composition after KA-induced seizures.
epilepsy; tonic inhibition; GABAA-receptor; temporal lobe epilepsy; subiculum; entorhinal cortex; epileptogenesis
Generalized tonic-clonic seizures (GTCS) are the commonest seizure type associated with Sudden Unexplained Death in Epilepsy (SUDEP). This study examines semiological and electroencephalographic differences (EEG) in the GTCS of adults as compared to children. The rationale lies in epidemiological observations that have noted a ten-fold higher incidence of SUDEP in adults. We analyzed video-EEG data of 105 GTCS in 61 consecutive patients (12 children, 23 seizures and 49 adults, 82 seizures) recruited from the Epilepsy Monitoring Unit. Semiological, EEG and 3-channel EKG features were studied. Peri-ictal seizure phase durations were analyzed including tonic, clonic, total seizure, post-ictal EEG suppression (PGES) and recovery phases. Heart rate variability (HRV) measures including RMSSD (root mean square successive difference of R-R intervals), SDNN (standard deviation of NN intervals) and SDSD (standard deviation of differences) were analyzed (including low frequency/high frequency power ratios) during pre-ictal baseline, ictal and post-ictal phases. Generalized estimating equations (GEE) were used to find associations between electro-clinical features. Separate subgroup analyses were carried out on adult and pediatric age groups as well as medication groups (no anti-epileptic medication cessation versus unchanged or reduced medication) during admission. Major differences were seen in adult and pediatric seizures with total seizure duration, tonic phase, PGES and recovery phases being significantly shorter in children (p<0.01). GEE analysis using tonic phase duration as the dependent variable, found age to correlate significantly (p<0.001) and this remained significant during subgroup analysis (adults and children) such that each 0.12 second increase in tonic phase duration correlated with a 1 second increase in PGES duration. PGES durations were on average 28 seconds shorter in children. With cessation of medication, total seizure duration was significantly increased by a mean value of 8 seconds in children and 11 seconds in adults (p<0.05). Tonic phase duration also significantly increased with medication cessation and although PGES durations increased, this was not significant. RMSSD was negatively correlated with PGES duration (longer PGES durations were associated with decreased vagally mediated heart rate variability; p<0.05) but not with tonic phase duration. This study clearly points out identifiable electro-clinical differences between adult and pediatric GTCS that may be relevant in explaining lower SUDEP risk in children. The findings suggest that some prolonged seizure phases and prolonged PGES duration may be electro-clinical markers of SUDEP risk and merit further study.
Generalized tonic-clonic seizures; Age-specific; SUDEP; PGES
The aim of this study is to characterize the clinical profile of patients with alcohol related seizures (ARS) and to identify the prevalence of idiopathic generalized epilepsy (IGE) in the same.
Materials and Methods:
100 consecutive male patients presenting to a tertiary care center in South India with new onset ARS were analyzed with alcohol use disorders identification test (AUDIT) score. All underwent 19 channel digital scalp electroencephalography (EEG) and at least computed tomography (CT) scan.
A total of 27 patients (27%) who had cortical atrophy on CT had a mean duration of alcohol intake of 23.62 years compared with 14.55 years in patients with no cortical atrophy (P < 0.001). Twenty-two patients (22%) had clustering in the current episode of whom 18 had cortical atrophy. Nearly, 88% patients had generalized tonic clonic seizures while 12% who had partial seizures underwent magnetic resonance imaging (MRI), which identified frontal focal cortical dysplasia in one. Mean lifetime duration of alcohol intake in patients presenting with seizures within 6 hours (6H-gp) of intake of alcohol was significantly lower (P = 0.029). One patient in the 6H-gp with no withdrawal symptoms had EEG evidence for IGE and had a lower AUDIT score compared with the rest.
CT evidence of cortical atrophy is related to the duration of alcohol intake and portends an increased risk for clustering. Partial seizures can be a presenting feature of ARS and those patients may benefit from MRI to identify underlying symptomatic localization related epilepsy (8.3% of partial seizures). IGE is more likely in patients presenting with ARS within first 6 hours especially if they do not have alcohol withdrawal symptoms and scalp EEG is helpful to identify this small subgroup (~1%) who may require long-term anti-epileptic medication.
Alcohol use disorders identification test; anti-epileptic drugs; convulsions; electroencephalography; ethanol; magnetic resonance imaging
This case is the first report of a patient who had phenobarbital (PB) withdrawal seizures after having been seizure-free for three years following temporal lobe surgery. The patient had been taking PB for 14 years when a gradual taper of PB was started. When PB was at 60 mg/d, a titration of lamotrigine (LTG) was started. However, typical complex seizures occurred when the patient was on PB 60 mg/d, along with LTG 25 mg/d. PB was increased back to 90 mg/d and levetiracetam (LEV) was titrated. Seizures appeared when the patient was on PB 30 mg/d and LEV 750 mg BID and continued for three weeks after PB was stopped and the patient was on LEV 1000 mg BID. For the following six months, her aura frequency remained elevated in comparison to her baseline aura of two auras per month for the previous year before the start of the PB taper. She was followed for 24 months after her last PB withdrawal seizure. During the last eight months, her aura frequency returned to her baseline. As suggested by animal studies, the PB withdrawal seizures and increase in aura frequency in this patient may be explained by changes in her levels of GABAA receptor subunits.
Phenobarbital; withdrawal seizures; Auras; temporal lobe epilepsy; simple partial seizures; GABAA receptor
Generalized tonic-clonic seizures cause widespread physiological changes throughout the cerebral cortex and subcortical structures in the brain. Using combined blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) at 9.4 T and electroencephalography (EEG) these changes can be characterized with high spatiotemporal resolution. We studied BOLD changes in anesthetized Wistar rats during bicuculline-induced tonic-clonic seizures. Bicuculline, a GABAA receptor antagonist, was injected systemically and seizure activity was observed on EEG as high amplitude, high-frequency polyspike discharges followed by clonic paroxysmal activity of lower frequency, with mean electrographic seizure duration of 349 s. Our aim was to characterize the spatial localization, direction, and timing of BOLD signal changes during the pre-ictal, ictal and post-ictal periods. Group analysis was performed across seizures using paired t-maps of BOLD signal superimposed on high resolution anatomical images. Regional analysis was then performed using volumes of interest to quantify BOLD timecourses. In the pre-ictal period we found focal BOLD increases in specific areas of somatosensory cortex (S1, S2) and thalamus several seconds before seizure onset. During seizures we observed BOLD increases in cortex, brainstem and thalamus and BOLD decreases in the hippocampus. The largest ictal BOLD increases remained in the focal regions of somatosensory cortex showing pre-ictal increases. During the post-ictal period we observed widespread BOLD decreases. These findings support a model in which “generalized” tonic-clonic seizures begin with focal changes before electrographic seizure onset, which progress to non-uniform changes during seizures, possibly shedding light on the etiology and pathophysiology of similar seizures in humans.
tonic-clonic seizure; fMRI; cortex; thalamus; bicuculline; cortical focus theory
This report addresses recent advances in our understanding of the role of the dorsolateral (DLS), dorsomedial (DMS), and ventral striatum in behavioral responses to alcohol, including alcohol craving in abstinent alcoholics, and alcohol consumption and withdrawal in rat, mouse and nonhuman primate models. Recent data are discussed showing that reduced neuronal activity as well as dysfunctional connectivity between the ventral striatum and the dorsolateral prefrontal cortex is associated with alcohol craving and impairment of new learning processes in abstinent alcoholics. Emerging results show that, within the DLS of mice and nonhuman primates withdrawn from alcohol after chronic exposure, glutamatergic transmission in striatal projection neurons (medium spiny neurons, MSNs) is increased, while GABAergic transmission is decreased. Glutamatergic transmission in DMS MSNs is also increased in ethanol withdrawn rats. Ex vivo or in vivo ethanol exposure and withdrawal causes a long-lasting increase in NR2B subunit-containing NMDA receptor activity in the DMS, contributing to ethanol-drinking. Analyses of neuronal activation associated with alcohol withdrawal and site-directed lesions implicate the rostroventral caudate putamen (rvCP), a ventrolateral segment of the DMS, in genetically determined differences in risk for alcohol withdrawal in mice. The influence of the identified risk factor on alcohol withdrawal may be involved in physical association of the multi-PDZ domain protein, MPDZ, with 5-HT2C receptors and/or NR2B within the rvCP. Taken together, these studies increase our understanding of the role of dopaminergic, glutamatergic and GABAergic signaling within different regions of the striatum in alcohol craving, consumption, dependence and withdrawal in humans and animal models.
PET; fMRI; electrophysiology; self-administration; Fyn kinase; c-Fos
An increasingly compelling literature points to a major role for the glutamate system in mediating the effects of alcohol on behavior and the pathophysiology of alcoholism. Preclinical studies indicate that glutamate signaling mediates certain aspects of ethanol’s intoxicating and rewarding effects, and undergoes adaptations following chronic alcohol exposure that may contribute to the withdrawal, craving and compulsive drug-seeking that drive alcohol abuse and alcoholism.
We discuss the potential for targeting the glutamate system as a novel pharmacotherapeutic approach to treating alcohol use disorders, focusing on five major components of the glutamate system: the N-methyl-D-aspartate (NMDA) receptor and specific NMDA subunits, the glycineB site on the NMDA receptors (NMDAR), L-alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid ionotropic (AMPA) and kainate (KAR) receptors, metabotropic receptors (mGluR), and glutamate transporters.
Chronic alcohol abuse produces a hyperglutamatergic state, characterized by elevated extracellular glutamate and altered glutamate receptors and transporters. Pharmacologically manipulating glutamatergic neurotransmission alters alcohol-related behaviors including intoxication, withdrawal, and alcohol-seeking, in rodents and human subjects. Blocking NMDA and AMPA receptors reduces alcohol consumption in rodents, but side-effects may limit this as a therapeutic approach. Selectively targeting NMDA and AMPA receptor subunits (e.g., GluN2B, GluA3), or the NMDAR glycineB site offers an alternative approach. Blocking mGluR5 potently affects various alcohol-related behaviors in rodents, and mGluR2/3 agonism also suppresses alcohol consumption. Finally, glutamate transporter upregulation may mitigate behavioral and neurotoxic sequelae of excess glutamate caused by alcohol.
Despite the many challenges that remain, targeting the glutamate system offers genuine promise for developing new treatments for alcoholism.
Ethanol; Craving; NMDA; GluN2A; GluN2B; mGluR2/3; mGluR5; Memantine; Addiction; Glycine
Long-term alcohol exposure gives rise to development of physical dependence on alcohol in consequence of changes in certain neurotransmitter functions. Accumulating evidence suggests that the glutamatergic neurotransmitter system, especially the N-methyl-D-aspartate (NMDA) type of glutamate receptors is a particularly important site of ethanol’s action, since ethanol is a potent inhibitor of the NMDA receptors (NMDARs) and prolonged ethanol exposition leads to a compensatory “upregulation” of NMDAR mediated functions supposedly contributing to the occurrence of ethanol tolerance, dependence as well as the acute and delayed signs of ethanol withdrawal.
Recently, expression of different types of NMDAR subunits was found altered after long-term ethanol exposure. Especially, the expression of the NR2B and certain splice variant forms of the NR1 subunits were increased in primary neuronal cultures treated intermittently with ethanol. Since NMDA ion channels with such an altered subunit composition have increased permeability for calcium ions, increased agonist sensitivity, and relatively slow closing kinetics, the abovementioned alterations may underlie the enhanced NMDAR activation observed after long-term ethanol exposure. In accordance with these changes, the inhibitory potential of NR2B subunit-selective NMDAR antagonists is also increased, demonstrating excellent potency against alcohol withdrawal-induced in vitro cytotoxicity. Although in vivo data are few with these compounds, according to the effectiveness of the classic NMDAR antagonists in attenuation, not only the physical symptoms, but also some affective and motivational components of alcohol withdrawal, novel NR2B subunit selective NMDAR antagonists may offer a preferable alternative in the pharmacotherapy of alcohol dependence.
Alcohol; dependence; withdrawal; NMDA receptor; NR2B subunit selective antagonist; pharmacotherapy
SK2 potassium channels control excitability and contribute to plasticity by reducing excitatory postsynaptic potentials. Recent evidence suggests that SK2 channels form a calcium-dependent negative-feedback loop with synaptic NMDA receptors. Addiction to alcohol and other drugs of abuse induces plastic changes in glutamatergic synapses that include the targeting of NMDA receptors to synaptic sites; however, the role of SK2 channels in alcohol-associated homeostatic plasticity is unknown.
Electrophysiology, Western blot, and behavioral analyses were used to quantify changes in hippocampal SK channel function and expression using well-characterized in-vitro and in-vivo models of chronic alcohol exposure.
Chronic ethanol reduced apamin-sensitive SK currents in CA1 pyramidal neurons that were associated with a down-regulation of surface SK2 channels. Blocking SK channels with apamin potentiated excitatory post-synaptic potentials in control but not ethanol treated CA1 pyramidal neurons, suggesting that chronic ethanol disrupts the SK channel-NMDA receptor feedback loop. Alcohol reduced expression of SK2 channels and increased expression of NMDA receptors at synaptic sites in a mouse model. Positive modulation of SK function by 1-EBIO decreased alcohol withdrawal hyperexcitability and attenuated ethanol withdrawal neurotoxicity in hippocampus. 1-EBIO also reduced seizure activity in mice undergoing withdrawal.
These results provide evidence that SK2 channels contribute to alcohol-associated adaptive plasticity of glutamatergic synapses and that positive modulation of SK channels reduces the severity of withdrawal-related hyperexcitability. Therefore, SK2 channels appear to be critical regulators of alcohol-associated plasticity and may be novel therapeutic targets for the treatment of addiction.
SK2; adaptive plasticity; alcoholism; glutamatergic synapses; withdrawal hyperexcitability; 1-EBIO
The relative anticonvulsant potential of the γ-aminobutyric acid (GABA) agonist, muscimol, was compared after microinjection into either the inferior colliculus, substantia nigra or medial septum of ethanol-dependent rats. Bilateral microinjection of muscimol (10–30 ng) into the inferior colliculus 15 to 60 min before testing suppressed all sound-induced seizure components (wild running, clonus and tonus) in rats withdrawn from ethanol for 6.5 to 8.5 hr. However, forelimb tremors were not altered. Audiogenic seizures were suppressed for at least 3 hr after muscimol (30 ng). In the medial septum and substantia nigra, microinjection of muscimol (30–100 ng) only partially reduced the tonic component of audiogenic seizures and exerted no effect on the frequency of wild running or clonus. GABA (10 μg) and two other GABA agonists [4,5,6,7-tetrahydroisoxa-zolo[5,40c]pyridin-3-ol (THIP), 300 ng and chlordiazepoxide, 10–30 μg], microinjected into the inferior colliculus, also reduced audiogenic seizure susceptibility. However, 1,3-butanediol, which suppresses ethanol withdrawal seizures after peripheral administration in rats, was inactive. The relative proconvulsant potential of the GABA antagonist, bicuculline methiodide, also was compared after microinjection into either the inferior colliculus, substantia nigra or medial septum of ethanol naive rats. In each animal, audiogenic seizure-like wild running, clonus and tonus were evoked by microinjecting bicuculline methiodide into the inferior colliculus at the rate of 6.0 ng/6 min. However, these reactions did not occur when bicuculline methiodide was applied at a slower rate (1.8 ng/6 min). Similar injections of bicuculline methiodide (600 ng/6 min) into the substantia nigra caused only clonus and tonus without wild running. A smaller dose (180 ng/6 min) had no effect. In the medial septum, microinjection of this GABA antagonist (1800 ng/6 min) did not exert any obvious seizure-like activity. These results suggest that the inferior colliculus is important in GABAmimetic suppression of audiogenic seizures and that reduced GABAergic activity in this nucleus may be responsible for the increased susceptibility to audiogenic seizures in rats during ethanol withdrawal.
Neurosteroids regulate GABA-A receptor plasticity. Neurosteroid withdrawal occurs during menstruation and is associated with a marked increase in expression of GABA-A receptor α4-subunit, a key subunit linked to enhanced neuronal excitability, seizure susceptibility and benzodiazepine resistance. However, the molecular mechanisms underlying the upregulation of α4-subunit expression remain unclear. Here we utilized the progesterone receptor (PR) knockout mouse to investigate molecular pathways of PR and the transcription factor early growth response factor-3 (Egr3) in regulation of the GABA-A receptor α4-subunit expression in the hippocampus in a mouse neurosteroid withdrawal paradigm. Neurosteroid withdrawal induced a threefold increase in α4-subunit expression in wild-type mice, but this upregulation was unchanged in PR knockout mice. The expression of Egr3, which controls α4-subunit transcription, was increased significantly following neurosteroid withdrawal in wild-type and PR knockout mice. Neurosteroid withdrawal-induced α4-subunit upregulation was completely suppressed by antisense Egr3 inhibition. In the hippocampus kindling model of epilepsy, there was heightened seizure activity, significant reduction in the antiseizure sensitivity of diazepam (a benzodiazepine insensitive at α4βγ-receptors) and conferral of increased seizure protection of flumazenil (a low-affinity agonist at α4βγ-receptors) in neurosteroid-withdrawn wild-type and PR knockout mice. These observations are consistent with enhanced α4-containing receptor abundance in vivo. Neurosteroid withdrawal-induced seizure exacerbation, diazepam insensitivity, and flumazenil efficacy in the kindling model were reversed by inhibition of Egr3. These results indicate that neurosteroid withdrawal-induced upregulation of GABA-A receptor α4-subunit expression is mediated by the Egr3 via a PR-independent signaling pathway. These findings help advance our understanding of the molecular basis of catamenial epilepsy, a neuroendocrine condition that occurs around the perimenstrual period and is characterized by neurosteroid withdrawal-linked seizure exacerbations in women with epilepsy.
Allopregnanolone; diazepam; Egr3; GABA-A receptor; kindling; neurosteroid withdrawal; progesterone; progesterone receptor; α4-subunit; seizure
Benzodiazepines are the current first-line standard-of-care treatment for status epilepticus but fail to terminate seizures in about one-third of cases. Synaptic GABAA receptors, which mediate phasic inhibition in central circuits, are the molecular target of benzodiazepines. As status epilepticus progresses, these receptors are internalized and become functionally inactivated, conferring bezodiazepine resistance, which is believed to be a major cause of treatment failure. GABAA receptor positive allosteric modulator neuroactive steroids, such as allopregnanolone, also potentiate synaptic GABAA receptors, but in addition they enhance extrasynaptic GABAA receptors that mediate tonic inhibition. Extrasynaptic GABAA receptors are not internalized and desensitization of these receptors does not occur during continuous seizures in status epilepticus models. Here we review the broad-spectrum antiseizure activity of allopregnanolone in animal seizure models and the evidence for its activity in models of status epilepticus. We also demonstrate that allopregnanolone inhibits ongoing behavioral and electrographic seizures in a model of status epilepticus, even when there is benzodiazepine resistance. Parenteral allopregnanolone may provide an improved treatment for refractory status epilepticus.
Refractory status epilepticus; Seizure; Allopregnanolone; Neurosteroid; Allosteric modulator
Generalized tonic–clonic seizures are among the most dramatic physiological events in the nervous system. The brain regions involved during partial seizures with secondary generalization have not been thoroughly investigated in humans. We used single photon emission computed tomography (SPECT) to image cerebral blood flow (CBF) changes in 59 secondarily generalized seizures from 53 patients. Images were analysed using statistical parametric mapping to detect cortical and subcortical regions most commonly affected in three different time periods: (i) during the partial seizure phase prior to generalization; (ii) during the generalization period; and (iii) post-ictally. We found that in the pre-generalization period, there were focal CBF increases in the temporal lobe on group analysis, reflecting the most common region of partial seizure onset. During generalization, individual patients had focal CBF increases in variable regions of the cerebral cortex. Group analysis during generalization revealed that the most consistent increase occurred in the superior medial cerebellum, thalamus and basal ganglia. Post-ictally, there was a marked progressive CBF increase in the cerebellum which spread to involve the bilateral lateral cerebellar hemispheres, as well as CBF increases in the midbrain and basal ganglia. CBF decreases were seen in the fronto-parietal association cortex, precuneus and cingulate gyrus during and following seizures, similar to the ‘default mode’ regions reported previously to show decreased activity in seizures and in normal behavioural tasks. Analysis of patient behaviour during and following seizures showed impaired consciousness at the time of SPECT tracer injections. Correlation analysis across patients demonstrated that cerebellar CBF increases were related to increases in the upper brainstem and thalamus, and to decreases in the fronto-parietal association cortex. These results reveal a network of cortical and subcortical structures that are most consistently involved in secondarily generalized tonic–clonic seizures. Abnormal increased activity in subcortical structures (cerebellum, basal ganglia, brainstem and thalamus), along with decreased activity in the association cortex may be crucial for motor manifestations and for impaired consciousness in tonic–clonic seizures. Understanding the networks involved in generalized tonic–clonic seizures can provide insights into mechanisms of behavioural changes, and may elucidate targets for improved therapies.
default mode; cerebellum; thalamus; SPECT; epilepsy
Taurine is one of the most abundant free amino acids especially in excitable tissues, with wide physiological actions. Chronic supplementation of taurine in drinking water to mice increases brain excitability mainly through alterations in the inhibitory GABAergic system. These changes include elevated expression level of glutamic acid decarboxylase (GAD) and increased levels of GABA. Additionally we reported that GABAA receptors were down regulated with chronic administration of taurine. Here, we investigated pharmacologically the functional significance of decreased / or change in subunit composition of the GABAA receptors by determining the threshold for picrotoxin-induced seizures. Picrotoxin, an antagonist of GABAA receptors that blocks the channels while in the open state, binds within the pore of the channel between the β2 and β3 subunits. These are the same subunits to which GABA and presumably taurine binds.
Two-month-old male FVB/NJ mice were subcutaneously injected with picrotoxin (5 mg kg-1) and observed for a) latency until seizures began, b) duration of seizures, and c) frequency of seizures. For taurine treatment, mice were either fed taurine in drinking water (0.05%) or injected (43 mg/kg) 15 min prior to picrotoxin injection.
We found that taurine-fed mice are resistant to picrotoxin-induced seizures when compared to age-matched controls, as measured by increased latency to seizure, decreased occurrence of seizures and reduced mortality rate. In the picrotoxin-treated animals, latency and duration were significantly shorter than in taurine-treated animas. Injection of taurine 15 min before picrotoxin significantly delayed seizure onset, as did chronic administration of taurine in the diet. Further, taurine treatment significantly increased survival rates compared to the picrotoxin-treated mice.
We suggest that the elevated threshold for picrotoxin-induced seizures in taurine-fed mice is due to the reduced binding sites available for picrotoxin binding due to the reduced expression of the beta subunits of the GABAA receptor. The delayed effects of picrotoxin after acute taurine injection may indicate that the two molecules are competing for the same binding site on the GABAA receptor. Thus, taurine-fed mice have a functional alteration in the GABAergic system. These include: increased GAD expression, increased GABA levels, and changes in subunit composition of the GABAA receptors. Such a finding is relevant in conditions where agonists of GABAA receptors, such as anesthetics, are administered.