Phenobarbital but Not Diazepam Reduces AMPA/kainate Receptor Mediated Currents and Exerts Opposite Actions on Initial Seizures in the Neonatal Rat Hippocampus

A Comparison of Epileptogenic Effect of Status Epilepticus Treated With Diazepam, Midazolam, and Pentobarbital in the Mouse Pilocarpine Model of Epilepsy

Status epilepticus (SE) is a medical emergency associated with acute severe systemic damage and high mortality. Moreover, symptomatic SE is one of the highest risk factors for epileptogenesis. While the antiepileptic drugs (AEDs) are chosen in favor of acute control of SE, the potential short-term and long-term effects of such AEDs have been ignored in clinics. In this study, we hypothesized that AEDs that are used to control acute SE might affect the feasibility for the chronic development of epileptogenesis after SE. Therefore, we sought to compare the epileptogenic effects of SE that are terminated by three AEDs, i.e., diazepam, midazolam, and pentobarbital, which are widely used as first-line anti-SE AEDs. For this purpose, we used a mouse model of SE induced by intraperitoneal (i.p.) injection of lithium chloride (LiCl)-pilocarpine. The pilocarpine-induced SE was terminated with diazepam, midazolam, or pentobarbital. Then we compared short-term and long-term effects of SE with different AED treatments by examining SE-associated mortality and behavioral spontaneous recurrent seizures (SRSs) and by using magnetic resonance imaging (MRI) and immunohistochemistry to evaluate pathological and cellular alterations of mice in the different treatment groups. We found that i.p. injections of diazepam (5 mg/kg), midazolam (10 mg/kg), and pentobarbital (37.5 mg/kg) were able to terminate acute pilocarpine-SE effectively, while pentobarbital treatment showed less neuroprotective action against lethality in the short phase following SE. Long-term evaluation following SE revealed that SE treated with midazolam had resulted in relatively less behavioral SRS, less hippocampal atrophy, and milder neuronal loss and gliosis. Our data revealed an obvious advantage of midazolam vs. diazepam or pentobarbital in protecting the brain from epileptogenesis. Therefore, if midazolam provides as strong action to quench SE as other AEDs in clinics, midazolam should be the first choice of anti-SE AEDs as it provides additional benefits against epileptogenesis.

Why won't it stop? The dynamics of benzodiazepine resistance in status epilepticus

Status epilepticus is a life-threatening neurological emergency that affects both adults and children. Approximately 36% of episodes of status epilepticus do not respond to the current preferred first-line treatment, benzodiazepines. The proportion of episodes that are refractory to benzodiazepines is higher in low-income and middle-income countries (LMICs) than in high-income countries (HICs). Evidence suggests that longer episodes of status epilepticus alter brain physiology, thereby contributing to the emergence of benzodiazepine resistance. Such changes include alterations in GABA_A receptor function and in the transmembrane gradient for chloride, both of which erode the ability of benzodiazepines to enhance inhibitory synaptic signalling. Often, current management guidelines for status epilepticus do not account for these duration-related changes in pathophysiology, which might differentially impact individuals in LMICs, where the average time taken to reach medical attention is longer than in HICs. In this Perspective article, we aim to combine clinical insights and the latest evidence from basic science to inspire a new, context-specific approach to efficiently managing status epilepticus.

Secondary Epileptogenesis: Common to See, but Possible to Treat?

Secondary epileptogenesis is a common phenomenon in epilepsy, characterized by epileptiform discharges from the regions outside the primary focus. It is one of the major reasons for pharmacoresistance and surgical failure. Compared with primary epileptogenesis, the mechanism of secondary epileptogenesis is usually more complex and diverse. In this review, we aim to summarize the characteristics of secondary epileptogenesis from both clinical and laboratory studies in a historical view. Mechanisms of secondary epileptogenesis in molecular, cellular, and circuity levels are further presented. Potential treatments targeting the process are discussed as well. At last, we highlight the importance of circuitry studies, which would further illustrate precise treatments of secondary epileptogenesis in the future.

Combination of antiseizure medications phenobarbital, ketamine, and midazolam reduces soman-induced epileptogenesis and brain pathology in rats

Objective

Cholinergic‐induced status epilepticus (SE) is associated with a loss of synaptic gamma‐aminobutyric acid A receptors (GABA_AR) and an increase in N‐methyl‐D‐aspartate receptors (NMDAR) and amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid receptors (AMPAR) that may contribute to pharmacoresistance when treatment with benzodiazepine antiseizure medication is delayed. The barbiturate phenobarbital enhances inhibitory neurotransmission by binding to a specific site in the GABA_AR to increase the open state of the channel, decrease neuronal excitability, and reduce glutamate‐induced currents through AMPA/kainate receptors. We hypothesized that phenobarbital as an adjunct to midazolam would augment the amelioration of soman‐induced SE and associated neuropathological changes and that further protection would be provided by the addition of an NMDAR antagonist.

Methods

We investigated the efficacy of combining antiseizure medications to include a benzodiazepine and a barbiturate allosteric GABA_AR modulator (midazolam and phenobarbital, respectively) to correct loss of inhibition, and ketamine to reduce excitation caused by increased synaptic localization of NMDAR and AMPAR, which are NMDA‐dependent. Rats implanted with transmitters to record electroencephalographic (EEG) activity were exposed to soman and treated with atropine sulfate and HI‐6 one min after exposure and with antiseizure medication(s) 40 minutes after seizure onset.

Results

The triple therapy combination of phenobarbital, midazolam, and ketamine administered at 40 minutes after seizure onset effectively prevented soman‐induced epileptogenesis and reduced neurodegeneration. In addition, dual therapy with phenobarbital and midazolam or ketamine was more effective than monotherapy (midazolam or phenobarbital) in reducing cholinergic‐induced toxicity.

Significance

Benzodiazepine efficacy is drastically reduced with time after seizure onset and inversely related to seizure duration. To overcome pharmacoresistance in severe benzodiazepine‐refractory cholinergic‐induced SE, simultaneous drug combination to include drugs that target both the loss of inhibition (eg, midazolam, phenobarbital) and the increased excitatory response (eg, ketamine) is more effective than benzodiazepine or barbiturate monotherapy.

Sedative-Hypnotic Agents That Impact Gamma-Aminobutyric Acid Receptors: Focus on Flunitrazepam, Gamma-Hydroxybutyric Acid, Phenibut, and Selank

There are many nonopioid central nervous system depressant substances that share a gamma-aminobutyric acid (GABA) receptor-related mechanism of action. These sedatives-hypnotics can be indicated to treat anxiety, seizures, depression, and insomnia but are also used as substances of abuse and used to facilitate sexual assault. Barbiturates, methaqualone, and glutethimide were among the first type A GABA receptor-mediated sedative-hypnotics. Their clinical use was limited for most indications by serious adverse events and strong abuse potential but continue to be used illicitly around the world. The benzodiazepines supplanted barbiturates for most indications because they were less likely to cause severe adverse events in monotherapy. Flunitrazepam is a newer benzodiazepine that is preferentially used recreationally and to facilitate sexual assault. Flunitrazepam has greater potency and higher affinity for the type A GABA receptor than most benzodiazepines. Gamma-hydroxybutyric acid is sought illicitly for its hypnotic, euphoric and anabolic effects as well as to facilitate sexual assault. When any of these GABAergic drugs are used in high doses or with other sedative hypnotic agents, respiratory depression, coma, and death have occurred. Chronic use of these GABAergic drugs can lead to significant withdrawal syndromes. Phenibut and selank are poorly studied Russian drugs with GABAergic mechanisms that are inexplicably sold to US consumers as dietary supplements. Poison control center calls regarding phenibut have increased substantially over the past 5 years. Desired euphoriant effects account for the recreational and illicit use of many GABA-modulating agents. However, illicit use can lead to significant toxicities related to abuse, dependence, and subsequent withdrawal syndromes. Significant evaluation of developing agents with GABA properties should be conducted to determine abuse potential before public access ensues.

The Effect of Anti-seizure Medications on the Propagation of Epileptic Activity: A Review

The propagation of epileptiform events is a highly interesting phenomenon from the pathophysiological point of view, as it involves several mechanisms of recruitment of neural networks. Extensive in vivo and in vitro research has been performed, suggesting that multiple networks as well as cellular candidate mechanisms govern this process, including the co-existence of wave propagation, coupled oscillator dynamics, and more. The clinical importance of seizure propagation stems mainly from the fact that the epileptic manifestations cannot be attributed solely to the activity in the seizure focus itself, but rather to the propagation of epileptic activity to other brain structures. Propagation, especially when causing secondary generalizations, poses a risk to patients due to recurrent falls, traumatic injuries, and poor neurological outcome. Anti-seizure medications (ASMs) affect propagation in diverse ways and with different potencies. Importantly, for drug-resistant patients, targeting seizure propagation may improve the quality of life even without a major reduction in simple focal events. Motivated by the extensive impact of this phenomenon, we sought to review the literature regarding the propagation of epileptic activity and specifically the effect of commonly used ASMs on it. Based on this body of knowledge, we propose a novel classification of ASMs into three main categories: major, minor, and intermediate efficacy in reducing the propagation of epileptiform activity.

Phenobarbital, midazolam, bumetanide, and neonatal seizures: The devil is in the details

Kaila, Löscher, and colleagues report that phenobarbital (PHB) and midazolam (MDZ) attenuate neonatal seizures following birth asphyxia, but the former only when applied before asphyxia and the latter before or after the triggering insult. In contrast, the NKCC1 chloride importer antagonist bumetanide (BUM) had no effect whether applied alone or with PHB. The observations are compelling and in accord with earlier studies. However, there are several general issues that deserve discussion. What is the clinical relevance of these data and the validity of animal models of encephalopathic seizures? Why is it that although they act on similar targets, these agents have different efficacy? Are both PHB and MDZ actions restricted to γ-aminobutyric acidergic (GABAergic) mechanisms? Why is BUM inefficient in attenuating seizures but capable of reducing the severity of other brain disorders? We suggest that the relative failure of antiepileptic drugs (AEDs) to treat this severe life-threatening condition is in part explicable by the recurrent seizures that shift the polarity of GABA, thereby counteracting their effects on their target. AEDs might be efficient after a few seizures but not recurrent ones. In addition, PHB and MDZ actions are not limited to GABA signals. BUM efficiently attenuates autism symptomatology notably in patients with tuberous sclerosis but does not reduce the recurrent seizures, illustrating the uniqueness of epilepsies. Therefore, the efficacy of AEDs to treat babies with encephalopathic seizures will depend on the history and severity of the seizures prior to their administration, challenging a universal common underlying mechanism.

Regulation of GABAARs by Transmembrane Accessory Proteins

The vast majority of fast inhibitory transmission in the brain is mediated by GABA acting on GABAA receptors (GABAARs), which provides inhibitory balance to excitatory drive and controls neuronal output. GABAARs are also effectively targeted by clinically important drugs for treatment in a number of neurological disorders. It has long been hypothesized that function and pharmacology of GABAARs are determined by the channel pore-forming subunits. However, recent studies have provided new dimensions in studying GABAARs due to several transmembrane proteins that interact with GABAARs and modulate their trafficking and function. In this review, we summarize recent findings on these novel GABAAR transmembrane regulators and highlight a potential avenue to develop new GABAAR psychopharmacology by targeting these receptor-associated membrane proteins.

Successful treatment of severe, treatment resistant GHB withdrawal through thiopental-coma

BACKGROUND

In patients with gamma-hydroxybutyrate (GHB) use disorder (GUD), withdrawal can have a fulminant course with rapid progression of severe, potentially life-threatening complications. Case: We present a 45-year old man with severe GHB withdrawal, resistant to conventional treatment with pharmaceutical GHB, high doses of benzodiazepines and baclofen. GHB withdrawal finally responded to thiopental-induced coma therapy, with burst suppression pattern on electroencephalography (EEG). The patient fully recovered, without withdrawal or residual neuropsychiatric symptoms. Discussion: To our knowledge, this is the first case report in which barbiturates were used to induce a coma to treat severe, treatment resistant GHB withdrawal. This case suggests barbiturate coma therapy might be considered in severe GHB withdrawal which does not respond to conventional treatment.

The evolution of the pilocarpine animal model of status epilepticus

The pilocarpine animal model of status epilepticus is a well-established, clinically translatable model that satisfies all of the criteria essential for an animal model of status epilepticus: a latency period followed by spontaneous recurrent seizures, replication of behavioural, electrographic, metabolic, and neuropathological changes, as well as, pharmacoresistance to anti-epileptic drugs similar to that observed in human status epilepticus. However, this model is also characterized by high mortality rates and studies in recent years have also seen difficulties in seizure induction due to pilocarpine resistant animals. This can be attributed to differences in rodent strains, species, gender, and the presence of the multi-transporter, P-glycoprotein at the blood brain barrier. The current paper highlights the various alterations made to the original pilocarpine model over the years to combat both the high mortality and low induction rates. These range from the initial lithium-pilocarpine model to the more recent Reduced Intensity Status Epilepticus (RISE) model, which finally brought the mortality rates down to 1%. These modifications are essential to improve animal welfare and future experimental outcomes.

2-Deoxyglucose terminates pilocarpine-induced status epilepticus in neonatal rats

OBJECTIVE

Neonatal status epilepticus (SE) is a life-threatening medical emergency. Unfortunately, up to 50% of neonates with SE are resistant to current antiseizure drugs, highlighting the need for better treatments. This study aims to explore a novel metabolic approach as a potential alternative treatment to control neonatal SE, using the glycolytic inhibitor 2-deoxyglucose (2-DG).

METHODS

SE was induced by pilocarpine (300 mg/kg, intraperitoneally [ip]) in neonatal Sprague Dawley rats (postnatal day 10 [P10]-P17) and was monitored by video-electroencephalography (V-EEG). After 30 minutes of SE, 2-DG or one of two conventional antiseizure drugs with different mechanisms of action, phenobarbital or levetiracetam, was administrated ip, and V-EEG recording was continued for ~60 additional minutes. The time to seizure cessation after drug injection, EEG scores, and power spectra before and after drug or saline treatment were used to assess drug effects.

RESULTS

Once SE became sustained, administration of 2-DG (50, 100, or 500 mg/kg, ip) consistently stopped behavioral and electrographic seizures within 10-15 minutes; lower doses took longer (25-30 minutes) to stop SE, demonstrating a dose-dependent effect. Administration of phenobarbital (30 mg/kg, ip) or levetiracetam (100 mg/kg, ip) also stopped SE within 10-15 minutes in neonatal rats.

SIGNIFICANCE

Our results suggest that the glycolysis inhibitor 2-DG acts quickly to reduce neuronal hyperexcitability and effectively suppress ongoing seizure activity, which may provide translational value in the treatment of neonatal SE.

Prevalence and clinical characteristics of phenobarbitone-associated adverse effects in epileptic cats

OBJECTIVES

The study objective was to investigate the prevalence and clinical characteristics of phenobarbitone-associated adverse effects in epileptic cats.

METHODS

The medical records of two veterinary referral clinics from 2007 to 2017 were searched for cats fulfilling the inclusion criteria of a diagnosis of epilepsy, treatment with phenobarbitone and available follow-up information on the occurrence of adverse effects. Follow-up information was obtained from the medical records of the primary veterinarian and referral institutions and a questionnaire completed by the cats' owners.

RESULTS

Seventy-seven cats met the inclusion criteria. Fifty-eight were affected by idiopathic epilepsy and 19 by structural epilepsy. One or more of the following adverse effects were reported in 47% of the cats: sedation (89%); ataxia (53%); polyphagia (22%); polydipsia (6%); polyuria (6%); and anorexia (6%). Logistic regression analyses revealed significant associations between adverse effect occurrence and both phenobarbitone starting dosage and administration of a second antiepileptic drug (AED). For each 1 mg/kg q12h increment of phenobarbitone, the likelihood of adverse effects increased 3.1 times. When a second AED was used, the likelihood of adverse effects increased 3.2 times. No association was identified between epilepsy aetiology and adverse effect occurrence. An idiosyncratic adverse effect, characterised by severe neutropenia and granulocytic hypoplasia, was diagnosed in one cat. This resolved following phenobarbitone discontinuation.

CONCLUSIONS AND RELEVANCE

The prevalence of phenobarbitone-associated adverse effects was 47%. Sedation and ataxia were most common. These are type A adverse effects and are predictable from phenobarbitone's known pharmacological properties. In the majority of cases, adverse effects occurred within the first month of treatment and were transient. Idiosyncratic (type B) adverse effects, which were not anticipated given the known properties of the drug, occurred in one cat. Increased phenobarbitone starting dosage and the addition of a second AED were significantly associated with the occurrence of adverse effects.

Excitatory GABAergic signalling is associated with benzodiazepine resistance in status epilepticus

Status epilepticus is defined as a state of unrelenting seizure activity. Generalized convulsive status epilepticus is associated with a rapidly rising mortality rate, and thus constitutes a medical emergency. Benzodiazepines, which act as positive modulators of chloride (Cl-) permeable GABAA receptors, are indicated as first-line treatment, but this is ineffective in many cases. We found that 48% of children presenting with status epilepticus were unresponsive to benzodiazepine treatment, and critically, that the duration of status epilepticus at the time of treatment is an important predictor of non-responsiveness. We therefore investigated the cellular mechanisms that underlie acquired benzodiazepine resistance, using rodent organotypic and acute brain slices. Removing Mg2+ ions leads to an evolving pattern of epileptiform activity, and eventually to a persistent state of repetitive discharges that strongly resembles clinical EEG recordings of status epilepticus. We found that diazepam loses its antiseizure efficacy and conversely exacerbates epileptiform activity during this stage of status epilepticus-like activity. Interestingly, a low concentration of the barbiturate phenobarbital had a similar exacerbating effect on status epilepticus-like activity, while a high concentration of phenobarbital was effective at reducing or preventing epileptiform discharges. We then show that the persistent status epilepticus-like activity is associated with a reduction in GABAA receptor conductance and Cl- extrusion capability. We explored the effect on intraneuronal Cl- using both gramicidin, perforated-patch clamp recordings and Cl- imaging. This showed that during status epilepticus-like activity, reduced Cl- extrusion capacity was further exacerbated by activity-dependent Cl- loading, resulting in a persistently high intraneuronal Cl-. Consistent with these results, we found that optogenetic stimulation of GABAergic interneurons in the status epilepticus-like state, actually enhanced epileptiform activity in a GABAAR dependent manner. Together our findings describe a novel potential mechanism underlying benzodiazepine-resistant status epilepticus, with relevance to how this life-threatening condition should be managed in the clinic.

Action of antiepileptic drugs on neurons

The recent development of various new antiepileptic drugs (AEDs) has provided a wide range of therapeutic strategies for epilepsy. Information regarding the mechanisms of the action of AEDs is valuable when selecting drugs for individual epilepsy patients. AEDs can be categorized as those acting at the excitatory synapse, at the inhibitory synapse, on the extrasynaptic neuronal membrane, or with multiple or miscellaneous mechanisms of action. We herein briefly summarize and illustrate the action of AEDs on neurons and related findings that are pertinent to the clinical aspect of epileptology.

Mannitol decreases neocortical epileptiform activity during early brain development via cotransport of chloride and water

Seizures and brain injury lead to water and Cl^- accumulation in neurons. The increase in intraneuronal Cl^- concentration ([Cl^-]_i) depolarizes the GABA_A reversal potential (E_GABA) and worsens seizure activity. Neocortical neuronal membranes have a low water permeability due to the lack of aquaporins necessary to move free water. Instead, neurons use cotransport of ions including Cl^- to move water. Thus, increasing the extracellular osmolarity during seizures should result in an outward movement of water and salt, reducing [Cl^-]_i and improving GABA_A receptor-mediated inhibition. We tested the effects of hyperosmotic therapy with a clinically relevant dose of mannitol (20 mM) on epileptiform activity, spontaneous multiunit activity, spontaneous inhibitory post-synaptic currents (sIPSCs), [Cl^-]_i, and neuronal volume in layer IV/V of the developing neocortex of C57BL/6 and Clomeleon mice. Using electrophysiological techniques and multiphoton imaging in acute brain slices (post-natal day 7-12) and organotypic neocortical slice cultures (post-natal day 14), we observed that mannitol: 1) decreased epileptiform activity, 2) decreased neuronal volume and [Cl^-]_i through CCCs, 3) decreased spontaneous multi-unit activity frequency but not amplitude, and 4) restored the anticonvulsant efficacy of the GABA_A receptor modulator diazepam. Increasing extracellular osmolarity by 20 mOsm with hypertonic saline did not decrease epileptiform activity. We conclude that an increase in extracellular osmolarity by mannitol mediates the efflux of [Cl^-]_i and water through CCCs, which results in a decrease in epileptiform activity and enhances benzodiazepine actions in the developing neocortex in vitro. Novel treatments aimed to decrease neuronal volume may concomitantly decrease [Cl^-]_i and improve seizure control.

Barbiturates enhance itch-associated scratching in atopic dermatitis mice: A possible clue to understanding nocturnal pruritus in atopic dermatitis

In chronic pruritic diseases such as atopic dermatitis, pruritus is exacerbated during nocturnal sleep; however, the underlying mechanism remains unclear. We previously demonstrated that acute administration of the sedative-hypnotics ethanol markedly enhanced itch-associated spontaneous scratching in a diet-induced mouse model of atopic dermatitis. In the present study, to expand our previous finding and provide a general mechanism for the central modulation of chronic itch, we examined whether other hypnotic drugs, such as barbiturates and benzodiazepines, also enhance scratching, and further investigated the underlying mechanism. Barbiturates markedly enhanced spontaneous scratching in the atopic dermatitis model but not controls. However, unexpectedly, benzodiazepines only slightly increased scratching, and the selective γ-aminobutyric acid type A (GABA_A) receptor agonist, muscimol, had no effect. Local injection studies have demonstrated that barbiturates act at the supraspinal level to enhance scratching. Barbiturate-induced scratching was inhibited not only by GABA_A receptor antagonists but also by an L-type voltage-dependent calcium channel (L-VDCC) agonist and an α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptor agonist. An intracisternally injected AMPA receptor antagonist alone or in combination with an L-VDCC antagonist sufficiently enhanced scratching. Barbiturate-induced scratching enhancement was observed in another atopic dermatitis model, NC/Nga, but not in histamine-induced acute itch model in normal healthy mice. Overall, our results suggest that a synergistic effect among AMPA receptor inhibition, GABA_A receptor activation, and L-VDCC inhibition in the brain mediates barbiturate-induced scratching in atopic dermatitis mice. This observation may provide a novel clue to understanding a supraspinal itch mechanism in chronic diseases such as atopic dermatitis.

Behavioral disinhibition and antiepileptic treatment in childhood epilepsy: A retrospective cohort study

OBJECTIVE

To test whether specific classes of antiepileptic drugs increase the risk for behavioral disinhibition, a frequent complication of treatment of childhood epilepsy.

METHODS

In a sample of children with active epilepsy and antiepileptic drug (AED) treatment (n = 146, age 4-17 years), we performed a retrospective chart analysis of the occurrence of symptoms indicating reduced behavioral disinhibition following AED treatment. We used a risk-set approach to analyze whether the presence or recent addition of AED categories defined by their mechanism of action were associated with enhanced risk for behavioral disinhibition symptoms.

RESULTS

Mean duration of follow-up was 2,343 days (range 218-6,292, standard deviation [SD] 1,437). Episodes of behavioral disinhibition were reported in 51 (34.9%) children, with variable latencies between latest change and occurrence of behavioral disinhibition symptoms (mean 67 days, range 2-367). Current use of AEDs targeting gamma-aminobutyric acid (GABA) (odds ratio [OR] 1.8, 95% confidence interval [CI] 1.02-3.29, p = 0.04) and SV2A-mediated neurotransmitter release (SV2A)-mediated (2.0, 1.13-3.60, p = 0.02) neurotransmitter release was associated with increased risk for behavioral disinhibition. Restricting the analysis to the 90 days before behavioral disinhibition episode occurrence revealed that only addition of GABAergic AEDs (OR = 26.88, 95% CI = 6.71-107.76, p < 0.001) was associated with behavioral disinhibition. In contrast to our expectations, seizure control was reported to have improved parallel to most behavioral disinhibition episodes.

SIGNIFICANCE

This exploration of behavioral disinhibition in relation to antiepileptic drug treatment indicates that GABA potentiating drugs are specifically associated with behavioral problems during treatment of childhood epilepsy. Behavioral disinhibition episodes often occurred while seizure control improved, which may have reduced alertness for the consequences of AEDs on interictal symptoms. Our findings may be related to the increasing evidence for a role for excitatory actions of GABA in childhood epilepsy.

Pharmacological Treatment in γ-Hydroxybutyrate (GHB) and γ-Butyrolactone (GBL) Dependence: Detoxification and Relapse Prevention

The misuse of γ-hydroxybutyrate (GHB) for recreational purposes has resulted in an increase in GHB-related problems such as intoxications, dependence and withdrawal in several countries in Europe, Australia and the US over the last decade. However, prevalence rates of misuse of GHB and its precursor, γ-butyrolactone (GBL), are still relatively low. In this qualitative review paper, after a short introduction on the pharmacology of GHB/GBL, followed by a summary of the epidemiology of GHB abuse, an overview of GHB dependence syndrome and GHB/GBL withdrawal syndrome is provided. Finally, the existing literature on management of GHB detoxification, both planned and unplanned, as well as the available management of GHB withdrawal syndrome, is summarized. Although no systematic studies on detoxification and management of withdrawal have been performed to date, general recommendations are given on pharmacological treatment and preferred treatment setting.

The Neurobiological Mechanisms of Gamma-Hydroxybutyrate Dependence and Withdrawal and Their Clinical Relevance: A Review

OBJECTIVE

x03B3;-Hydroxybutyrate (GHB) has gained popularity as a drug of abuse. In the Netherlands the number of patients in treatment for GHB dependence has increased sharply. Clinical presentation of GHB withdrawal can be life threatening. We aim, through this overview, to explore the neurobiological pathways causing GHB dependency and withdrawal, and their implications for treatment choices.

METHODS

In this work we review the literature discussing the findings from animal models to clinical studies focused on the neurobiological pathways of endogenous but mainly exogenous GHB.

RESULTS

Chronic abuse of GHB exerts multifarious neurotransmitter and neuromodulator effects on x03B3;-aminobutyric acid (GABA), glutamate, dopamine, serotonin, norepinephrine and cholinergic systems. Moreover, important effects on neurosteroidogenesis and oxytocin release are wielded. GHB acts mainly via a bidirectional effect on GABAB receptors (GABABR; subunits GABAB1 and GABAB2), depending on the subunit of the GIRK (G-protein-dependent ion inwardly rectifying potassium) channel involved, and an indirect effect of the cortical and limbic inputs outside the nucleus accumbens. GHB also activates a specific GHB receptor and β1-subunits of α4-GABAAR. Reversing this complex interaction of neurobiological mechanisms by the abrupt cessation of GHB use results in a withdrawal syndrome with a diversity of symptoms of different intensity, depending on the pattern of GHB abuse.

CONCLUSION

The GHB withdrawal symptoms cannot be related to a single mechanism or neurological pathway, which implies that different medication combinations are needed for treatment. A single drug class, such as benzodiazepines, gabapentin or antipsychotics, is unlikely to be sufficient to avoid life-threatening complications. Detoxification by means of titration and tapering of pharmaceutical GHB can be considered as a promising treatment that could make polypharmacy redundant.

Barbiturates Bind in the GLIC Ion Channel Pore and Cause Inhibition by Stabilizing a Closed State

Barbiturates induce anesthesia by modulating the activity of anionic and cationic pentameric ligand-gated ion channels (pLGICs). Despite more than a century of use in clinical practice, the prototypic binding site for this class of drugs within pLGICs is yet to be described. In this study, we present the first X-ray structures of barbiturates bound to GLIC, a cationic prokaryotic pLGIC with excellent structural homology to other relevant channels sensitive to general anesthetics and, as shown here, to barbiturates, at clinically relevant concentrations. Several derivatives of barbiturates containing anomalous scatterers were synthesized, and these derivatives helped us unambiguously identify a unique barbiturate binding site within the central ion channel pore in a closed conformation. In addition, docking calculations around the observed binding site for all three states of the receptor, including a model of the desensitized state, showed that barbiturates preferentially stabilize the closed state. The identification of this pore binding site sheds light on the mechanism of barbiturate inhibition of cationic pLGICs and allows the rationalization of several structural and functional features previously observed for barbiturates.

Phenobarbital reduces EEG amplitude and propagation of neonatal seizures but does not alter performance of automated seizure detection

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Phenobarbital reduces both amplitude and propagation of neonatal seizures.

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These changes may help to explain electroclinical uncoupling.

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The performance of our seizure detection algorithm was unaffected.

Objective

Phenobarbital increases electroclinical uncoupling and our preliminary observations suggest it may also affect electrographic seizure morphology. This may alter the performance of a novel seizure detection algorithm (SDA) developed by our group.

The objectives of this study were to compare the morphology of seizures before and after phenobarbital administration in neonates and to determine the effect of any changes on automated seizure detection rates.

Methods

The EEGs of 18 term neonates with seizures both pre- and post-phenobarbital (524 seizures) administration were studied. Ten features of seizures were manually quantified and summary measures for each neonate were statistically compared between pre- and post-phenobarbital seizures. SDA seizure detection rates were also compared.

Results

Post-phenobarbital seizures showed significantly lower amplitude (p < 0.001) and involved fewer EEG channels at the peak of seizure (p < 0.05). No other features or SDA detection rates showed a statistical difference.

Conclusion

These findings show that phenobarbital reduces both the amplitude and propagation of seizures which may help to explain electroclinical uncoupling of seizures. The seizure detection rate of the algorithm was unaffected by these changes.

Significance

The results suggest that users should not need to adjust the SDA sensitivity threshold after phenobarbital administration.

Retigabine, a Kv7.2/Kv7.3-Channel Opener, Attenuates Drug-Induced Seizures in Knock-In Mice Harboring Kcnq2 Mutations

The hetero-tetrameric voltage-gated potassium channel K_v7.2/K_v7.3, which is encoded by KCNQ2 and KCNQ3, plays an important role in limiting network excitability in the neonatal brain. K_v7.2/K_v7.3 dysfunction resulting from KCNQ2 mutations predominantly causes self-limited or benign epilepsy in neonates, but also causes early onset epileptic encephalopathy. Retigabine (RTG), a K_v7.2/ K_v7.3-channel opener, seems to be a rational antiepileptic drug for epilepsies caused by KCNQ2 mutations. We therefore evaluated the effects of RTG on seizures in two strains of knock-in mice harboring different Kcnq2 mutations, in comparison to the effects of phenobarbital (PB), which is the first-line antiepileptic drug for seizures in neonates. The subjects were heterozygous knock-in mice (Kcnq2^Y284C/+ and Kcnq2^A306T/+) bearing the Y284C or A306T Kcnq2 mutation, respectively, and their wild-type (WT) littermates, at 63–100 days of age. Seizures induced by intraperitoneal injection of kainic acid (KA, 12mg/kg) were recorded using a video-electroencephalography (EEG) monitoring system. Effects of RTG on KA-induced seizures of both strains of knock-in mice were assessed using seizure scores from a modified Racine’s scale and compared with those of PB. The number and total duration of spike bursts on EEG and behaviors monitored by video recording were also used to evaluate the effects of RTG and PB. Both Kcnq2^Y284C/+ and Kcnq2^A306T/+ mice showed significantly more KA-induced seizures than WT mice. RTG significantly attenuated KA-induced seizure activities in both Kcnq2^Y284C/+ and Kcnq2^A306T/+ mice, and more markedly than PB. This is the first reported evidence of RTG ameliorating KA-induced seizures in knock-in mice bearing mutations of Kcnq2, with more marked effects than those observed with PB. RTG or other K_v7.2-channel openers may be considered as first-line antiepileptic treatments for epilepsies resulting from KCNQ2 mutations.

Proinflammatory mesenchymal effects of the non-genotoxic hepatocarcinogen phenobarbital: a novel mechanism of antiapoptosis and tumor promotion

Many environmental pollutants and drugs, including steroid hormones, hypolipidemics and antiepileptics, are non-genotoxic carcinogens (NGC) in rodent liver. The mechanism of action and the risk for human health are still insufficiently known. Here, we study the effects of phenobarbital (PB), a widely used model NGC, on hepatic epithelial-mesenchymal crosstalk and the impact on hepatic apoptosis. Mesenchymal cells (MC) and hepatocytes (HC) were isolated from control and PB-treated rat livers. PB induced extensive changes in gene expression in MC and much less in HC as shown by transcriptomics with oligoarrays. In MC only, transcript levels of numerous proinflammatory cytokines were elevated. Correspondingly, ELISA on the supernatant of MC from PB-treated rats revealed enhanced release of various cytokines. In cultured HC, this supernatant caused (i) nuclear translocation and activation of nuclear factor-κB (shown by immunoblots of nuclear extracts and reporter gene assays), (ii) elevated expression of proinflammatory genes and (iii) protection from the proapoptotic action of transforming growth factor beta 1 (TGFß1). PB treatment in vivo or in vitro elevated the production and release of tumor necrosis factor alpha from MC, which was identified as mainly responsible for the inhibition of apoptosis in HC. In conclusion, our findings reveal profound proinflammatory effects of PB on hepatic mesenchyme and mesenchymal-epithelial interactions. The resulting release of cytokines acts antiapoptotic in HC, an effect crucial for tumor promotion and carcinogenesis by NGC.

Paradoxical Benzodiazepine Response: A Rationale for Bumetanide in Neurodevelopmental Disorders?

The diuretic agent bumetanide has recently been put forward as a novel, promising treatment of behavioral symptoms in autism spectrum disorder (ASD) and related conditions. Bumetanide can decrease neuronal chloride concentrations and may thereby reinstate γ-aminobutyric acid (GABA)-ergic inhibition in patients with neurodevelopmental disorders. However, strategies to select appropriate candidates for bumetanide treatment are lacking. We hypothesized that a paradoxical response to GABA-enforcing agents such as benzodiazepines may predict the efficacy of bumetanide treatment in neurodevelopmental disorders. We describe a case of a 10-year-old girl with ASD, epilepsy, cortical dysplasia, and a 15q11.2 duplication who had exhibited marked behavioral arousal after previous treatment with clobazam, a benzodiazepine. We hypothesized that this response indicated the presence of depolarizing excitatory GABA and started bumetanide treatment with monitoring of behavior, cognition, and EEG. The treatment resulted in a marked clinical improvement in sensory behaviors, rigidity, and memory performance, which was substantiated by questionnaires and cognitive assessments. At baseline, the girl's EEG showed a depression in absolute α power, an electrographic sign previously related to ASD, which was normalized with bumetanide treatment. The effects of bumetanide on cognition and EEG seemed to mirror the "nonparadoxical" responses to benzodiazepines in healthy subjects. In addition, temporal lobe epilepsy and cortical dysplasia have both been linked to disturbed chloride homeostasis and seem to support our assumption that the observed paradoxical response was due to GABA-mediated excitation. This case highlights that a paradoxical behavioral response to GABA-enforcing drugs may constitute a framework for targeted treatment with bumetanide.

The GABA excitatory/inhibitory developmental sequence: a personal journey. Neuroscience. 2014;279:187-219. [PMID: 25168736 DOI: 10.1016/j.neuroscience.2014.08.001]

The developing brain is talkative but its language is not that of the adult. Most if not all voltage and transmitter-gated ionic currents follow a developmental sequence and network-driven patterns differ in immature and adult brains. This is best illustrated in studies engaged almost three decades ago in which we observed elevated intracellular chloride (Cl(-))i levels and excitatory GABA early during development and a perinatal excitatory/inhibitory shift. This sequence is observed in a wide range of brain structures and animal species suggesting that it has been conserved throughout evolution. It is mediated primarily by a developmentally regulated expression of the NKCC1 and KCC2 chloride importer and exporter respectively. The GABAergic depolarization acts in synergy with N-methyl-d-aspartate (NMDA) receptor-mediated and voltage-gated calcium currents to enhance intracellular calcium exerting trophic effects on neuritic growth, migration and synapse formation. These sequences can be deviated in utero by genetic or environmental insults leading to a persistence of immature features in the adult brain. This "neuroarcheology" concept paves the way to novel therapeutic perspectives based on the use of drugs that block immature but not adult currents. This is illustrated notably with the return to immature high levels of chloride and excitatory actions of GABA observed in many pathological conditions. This is due to the fact that in the immature brain a down regulation of KCC2 and an up regulation of NKCC1 are seen. Here, I present a personal history of how an unexpected observation led to novel concepts in developmental neurobiology and putative treatments of autism and other developmental disorders. Being a personal account, this review is neither exhaustive nor provides an update of this topic with all the studies that have contributed to this evolution. We all rely on previous inventors to allow science to advance. Here, I present a personal summary of this topic primarily to illustrate why we often fail to comprehend the implications of our own observations. They remind us - and policy deciders - why Science cannot be programed, requiring time, and risky investigations that raise interesting questions before being translated from bench to bed. Discoveries are always on sideways, never on highways.

Improving emotional face perception in autism with diuretic bumetanide: A proof-of-concept behavioral and functional brain imaging pilot study

Clinical observations have shown that GABA-acting benzodiazepines exert paradoxical excitatory effects in autism, suggesting elevated intracellular chloride (Cl–)i and excitatory action of GABA. In a previous double-blind randomized study, we have shown that the diuretic NKCC1 chloride importer antagonist bumetanide, that decreases (Cl–)i and reinforces GABAergic inhibition, reduces the severity of autism symptoms. Here, we report results from an open-label trial pilot study in which we used functional magnetic resonance imaging and neuropsychological testing to determine the effects of 10 months bumetanide treatment in adolescents and young adults with autism. We show that bumetanide treatment improves emotion recognition and enhances the activation of brain regions involved in social and emotional perception during the perception of emotional faces. The improvement of emotion processing by bumetanide reinforces the usefulness of bumetanide as a promising treatment to improve social interactions in autism.

Mechanisms and effects of seizures in the immature brain

The developing immature brain is not simply a small adult brain but rather possesses unique physiological properties. These include neuronal ionic currents that differ markedly from those in the adult brain, typically being longer-lasting and less selective. This enables immature heterogeneous neurons to connect and fire together but at the same time, along with other features may contribute to the enhanced propensity of the developing brain to become epileptic. Indeed, immature neurons tend to readily synchronize and thus generate seizures. Here, we review the differences between the immature and adult brain, with particular focus on the developmental sequence of γ-aminobutyric acid that excites immature neurons while being inhibitory in the normal adult brain. We review the mechanisms underlying the developmental changes to intracellular chloride levels, as well as how epileptiform activity can drive pathologic changes to chloride balance in the brain. We show that regulation of intracellular chloride is one important factor that underlies both the ease with which seizures can be generated and the facilitation of further seizures. We stress in particular the importance of understanding normal developmental sequences and how they are interrupted by seizures and other insults, and how this knowledge has led to the identification of potential novel treatments for conditions such as neonatal seizures.

Cation-chloride cotransporters NKCC1 and KCC2 as potential targets for novel antiepileptic and antiepileptogenic treatments

In cortical and hippocampal neurons, cation-chloride cotransporters (CCCs) control the reversal potential (EGABA) of GABAA receptor-mediated current and voltage responses and, consequently, they modulate the efficacy of GABAergic inhibition. Two members of the CCC family, KCC2 (the major neuron-specific K-Cl cotransporter; KCC isoform 2) and NKCC1 (the Na-K-2Cl cotransporter isoform 1 which is expressed in both neurons and glial cells) have attracted much interest in studies on GABAergic signaling under both normal and pathophysiological conditions, such as epilepsy. There is tentative evidence that loop diuretic compounds such as furosemide and bumetanide may have clinically relevant antiepileptic actions, especially when administered in combination with conventional GABA-mimetic drugs such as phenobarbital. Furosemide is a non-selective inhibitor of CCCs while at low concentrations bumetanide is selective for NKCCs. Search for novel antiepileptic drugs (AEDs) is highly motivated especially for the treatment of neonatal seizures which are often resistant to, or even aggravated by conventional AEDs. This review shows that the antiepileptic effects of loop diuretics described in the pertinent literature are based on widely heterogeneous mechanisms ranging from actions on both neuronal NKCC1 and KCC2 to modulation of the brain extracellular volume fraction. A promising strategy for the development of novel CCC-blocking AEDs is based on prodrugs that are activated following their passage across the blood-brain barrier. This article is part of the Special Issue entitled 'New Targets and Approaches to the Treatment of Epilepsy'.

Antioxidant, anticonvulsive and neuroprotective effects of dapsone and phenobarbital against kainic acid-induced damage in rats

Excitotoxicity due to glutamate receptors (GluRs) overactivation is a leading mechanism of oxidative damage and neuronal death in various diseases. We have shown that dapsone (DDS) was able to reduce both neurotoxicity and seizures associated to the administration of kainic acid (KA), an agonist acting on AMPA/KA receptors (GluK1-GluK5). Recently, it has been shown that phenobarbital (PB) is also able to reduce epileptic activity evoked by that receptor. In the present study, we tested the antioxidative, anticonvulsive and neuroprotective effects of DDS and PB administered alone or in combination upon KA toxicity to rats. Results showed that KA increased lipid peroxidation and diminished reduced glutathione (GSH), 24 h after KA administration and both drugs in combination or individually inhibited these events. Likewise, KA promotes mortality and this event was antagonized by effect of both treatments. Additionally, the behavioral evaluation showed that DDS and PB administered alone or in combination decreased the number of limbic seizures and reduced the percentage of animals showing tonic-clonic seizures versus the control group, which was administered only with KA. Finally, our study demonstrated that all of the treatments prevented the neuronal death of the pyramidal cell layer of hippocampal CA-3. In conclusion, the treatment with DDS and PB administrated alone or in combination exerted antioxidant, anticonvulsive and neuroprotective effects against the neurotoxicity induced by KA in rats, but their effects were not additive. Thus, it may be good options of treatment in diseases such as epilepsy and status epilepicus, administered separately.

How theories evolved concerning the mechanism of action of barbiturates

The barbiturate phenobarbital has been in use in the treatment of epilepsy for 100 years. It has long been recognized that barbiturates act by prolonging and potentiating the action of γ-aminobutyric acid (GABA) on GABA(A) receptors and at higher concentrations directly activating the receptors. A large body of data supports the concept that GABA(A) receptors are the primary central nervous system target for barbiturates, including the finding that transgenic mice with a point mutation in the β3 GABA(A) -receptor subunit exhibit diminished sensitivity to the sedative and immobilizing actions of the anesthetic barbiturate pentobarbital. Although phenobarbital is only modestly less potent as a GABA(A) -receptor modulator than pentobarbital, phenobarbital is minimally sedating at effective anticonvulsant doses. Possible explanations for the reduced sedative effect of phenobarbital include more regionally restricted action; partial agonist activity; reduced propensity to directly activate GABA(A) receptors (possibly including extrasynaptic receptors containing δ subunits); and reduced activity at other ion channel targets, including voltage-gated calcium channels. In recent years, substantial progress has been made in defining the structural features of GABA(A) receptors responsible for gating and allosteric modulation by drugs. Although the precise sites of action of barbiturates have not yet been defined, the second and third transmembrane domains of the β subunit appear to be critical; binding may involve a pocket formed by β-subunit methionine 286 as well as α-subunit methionine 236. In addition to effects on GABA(A) receptors, barbiturates block AMPA/kainate receptors, and they inhibit glutamate release through an effect on P/Q-type high-voltage activated calcium channels. The combination of these various actions likely accounts for their diverse clinical activities. Despite the remarkable progress of the last century, there is still much to learn about the actions of barbiturates that can be applied to the discovery of new, more therapeutically useful agents.

Hippocampal body changes in pure partial onset sleep and pure partial onset waking epileptic patients

The aim of the current study was to evaluate for the first time the hippocampal changes in patients with pure sleep and pure waking epilepsy. A total of 35 patients with pure partial onset sleep epilepsy and 35 patients with pure partial onset waking epilepsy matched for age and sex ratio were enrolled. MR images were analyzed to determine hippocampal body changes. Rounding ratio of hippocampal body was defined as short axis divided by long axis and hippocampal bodies with ratios ≥ 0.70 were considered rounded. Hippocampal sclerosis and atrophy were found in nine (25.7 %) and seven (20.0 %) patients with pure sleep epilepsy, and in 12 (34.3 %) and 11 (31.4 %) patients with pure waking epilepsy, respectively (P > 0.05 for the comparison between sleep and waking epilepsy). However, proportion of subjects with rounded hippocampal bodies (15, 42.9 % vs. 3, 8.6 % for patients with sleep and waking epilepsy, respectively) and rounding ratios of both left and right hippocampal bodies (0.66 ± 0.13 and 0.61 ± 0.12, respectively for left and right hippocampal bodies in sleep epileptic patients vs. 0.57 ± 0.11 and 0.55 ± 0.11, respectively for left and right hippocampal bodies in waking epileptic patients) were increased in patients with sleep epilepsy (P < 0.05). Further, in sleep epileptic patients with left sided hippocampal body rounding, epileptiform discharges were more readily lateralized to the left temporal lobe (P < 0.05). In conclusion, hippocampal sclerosis and atrophy are not different between pure partial onset sleep and waking epileptic patients. However, rounding ratio and frequency of hippocampal body rounding are increased in sleep epileptic patients.