Impaired maturation of cortical GABA(A) receptor expression in pediatric epilepsy

Knockdown of SIK3 in the CA1 Region can Reduce Seizure Susceptibility in Mice by Inhibiting Decreases in GABAAR α1 Expression

Imbalance between excitation and inhibition is an important cause of epilepsy. Salt-inducible kinase 1 (SIK1) gene mutation can cause epilepsy. In this study, we first found that the expression of SIK3 is increased after epilepsy. Furthermore, the role of SIK3 in epilepsy was explored. In cultured hippocampal neurons, we used Pterosin B, a selective SIK3 inhibitor that can inhibit epileptiform discharges induced by the convulsant drug cyclothiazide (a positive allosteric modulator of AMPA receptors, CTZ). Knockdown of SIK3 inhibited epileptiform discharges and increased the amplitude of miniature inhibitory postsynaptic currents (mIPSCs). In mice, knockdown of SIK3 reduced epilepsy susceptibility in a pentylenetetrazole (a GABAA receptor antagonist, PTZ) acute kindling experiment and increased the expression of GABAA receptor α1. In conclusion, our results suggest that blockade or knockdown of SIK3 can inhibit epileptiform discharges and that SIK3 has the potential to be a novel target for epilepsy treatment.

Neurodevelopment and early pharmacological interventions in Fragile X Syndrome

Fragile X Syndrome (FXS) is a neurodevelopmental disorder and the leading monogenic cause of autism and intellectual disability. For years, several efforts have been made to develop an effective therapeutic approach to phenotypically rescue patients from the disorder, with some even advancing to late phases of clinical trials. Unfortunately, none of these attempts have completely succeeded, bringing urgency to further expand and refocus research on FXS therapeutics. FXS arises at early stages of postnatal development due to the mutation and transcriptional silencing of the Fragile X Messenger Ribonucleoprotein 1 gene (FMR1) and consequent loss of the Fragile X Messenger Ribonucleoprotein (FMRP) expression. Importantly, FMRP expression is critical for the normal adult nervous system function, particularly during specific windows of embryogenic and early postnatal development. Cellular proliferation, migration, morphology, axonal guidance, synapse formation, and in general, neuronal network establishment and maturation are abnormally regulated in FXS, underlying the cognitive and behavioral phenotypes of the disorder. In this review, we highlight the relevance of therapeutically intervening during critical time points of development, such as early postnatal periods in infants and young children and discuss past and current clinical trials in FXS and their potential to specifically target those periods. We also discuss potential benefits, limitations, and disadvantages of these pharmacological tools based on preclinical and clinical research.

Excitatory/inhibitory balance in epilepsies and neurodevelopmental disorders: Depolarizing γ-aminobutyric acid as a common mechanism

Epilepsy is one of the most common neurological disorders. Although many factors contribute to epileptogenesis, seizure generation is mostly linked to hyperexcitability due to alterations in excitatory/inhibitory (E/I) balance. The common hypothesis is that reduced inhibition, increased excitation, or both contribute to the etiology of epilepsy. Increasing evidence shows that this view is oversimplistic, and that increased inhibition through depolarizing γ-aminobutyric acid (GABA) similarly contributes to epileptogenisis. In early development, GABA signaling is depolarizing, inducing outward Cl- currents due to high intracellular Cl- concentrations. During maturation, the mechanisms of GABA action shift from depolarizing to hyperpolarizing, a critical event during brain development. Altered timing of this shift is associated with both neurodevelopmental disorders and epilepsy. Here, we consider the different ways that depolarizing GABA contributes to altered E/I balance and epileptogenesis, and discuss that alterations in depolarizing GABA could be a common denominator underlying seizure generation in neurodevelopmental disorders and epilepsies.

Correlation of age at seizure onset with GABAA receptor subunit and chloride Co-transporter configuration in Focal cortical dysplasia (FCD)

Focal cortical dysplasia (FCD) represents a group of malformations of cortical development, which are speculated to be related to early developmental defects in the cerebral cortex. According to dysmature cerebral development hypothesis of FCD altered GABAA receptor function is known to contribute to abnormal neuronal network. Here, we studied the possible association between age at seizure onset in FCD with the subunit configuration of GABAA receptors in resected brain specimens obtained from patients with FCD. We observed a significantly higher ratio of α4/α1 subunit-containing GABAA receptors in patients with early onset (EO) FCD as compared to those with late onset (LO) FCD as is seen during the course of development where α4-containing GABAA receptors expression is high as compared to α1-containing GABAA receptors expression. Likewise, the influx to efflux chloride co-transporter expression of NKCC1/KCC2 was also increased in patients with EO FCD as seen during brain development. In addition, we observed that the ratio of GABA/Glutamate neurotransmitters was lower in patients with EO FCD as compared to that in patients with LO FCD. Our findings suggest altered configuration of GABAA receptors in FCD which could be contributing to aberrant depolarizing GABAergic activity. In particular, we observed a correlation of age at seizure onset in FCD with subunit configuration of GABAA receptors, levels of NKCC1/KCC2 and the ratio of GABA/Glutamate neurotransmitters such that the patients with EO FCD exhibited a more critically modulated GABAergic network.

Physiologically based pharmacokinetic/pharmacodynamic modeling to evaluate the absorption of midazolam rectal gel

OBJECTIVE

We aimed to 1) develop physiologically based pharmacokinetic/pharmacodynamic (PBPK/PD) models of a novel midazolam rectal gel in healthy adults, 2) assess the contribution of different physiologically relevant factors in rectal absorption, and 3) to provide supports for future clinical studies of midazolam rectal gel.

METHODS

We developed the rectal PBPK model after built the intravenous and the oral PBPK model. Then, the physiological progress of rectal route was described in terms of the drug release, the rectal absorption and the particle first-pass elimination. Next, the validated PBPK model was combined with the sigmoid E_max PD model. This PBPK/PD model was used to identify the dose range and the critical parameters to ensure safety sedation.

RESULTS

Based on the simulations, the recommended maximum dose for adults' sedation was 15 mg. And the retention time of midazolam rectal gel should be longer than 3 h to reach over 80% pharmacokinetics and pharmacodynamics effects.

CONCLUSION

We successfully developed a PBPK/PD model for the midazolam rectal gel, which accurately described the PK/PD behavior in healthy adults and indicated the transit time of rectum was the most sensitive parameter for absorption. This PBPK/PD model would be expected to support the future clinical studies and pediatric application.

Redefining the age-specific therapeutic ranges of lamotrigine for patients with epilepsy: A step towards optimizing treatment and increasing cost-effectiveness

OBJECTIVE

The pharmacokinetics of lamotrigine exhibits age-related characteristics. Nevertheless, current evidence regarding the therapeutic range of lamotrigine has been derived almost exclusively from studies in adult patients, and the applicability of this therapeutic range to the pediatric population remains unclear. The purpose of this study was to establish the appropriate age-specific therapeutic ranges of lamotrigine corresponding to adequate clinical responses for patients with epilepsy.

METHODS

This prospective cohort study of therapeutic drug monitoring included 582 Chinese epilepsy patients receiving lamotrigine monotherapy. Patients were divided into three age-related subgroups: (1) toddler and school-age group (2-12 years old, n = 168), (2) adolescent group (12-18 years old, n = 171), and (3) adult group (>18 years old, n = 243). Patients with a reduction in seizure frequency of 50 % or greater than baseline were defined as responders, and the remaining patients were non-responders. The relationship between lamotrigine serum concentrations and clinical response was assessed using multivariate logistic regression analysis. A receiver operating characteristic curve was generated to determine the representative cut-off values of lamotrigine trough levels, to distinguish responders from non-responders. The upper margin of the therapeutic range of lamotrigine was determined by developing concentration-effect curves for the three age-related subgroups.

RESULTS

The median trough levels of lamotrigine were significantly higher in responders than in non-responders from all three age-related groups (P < 0.0001). Results of logistic regression analysis revealed that higher serum concentrations of lamotrigine predicted a higher probability that seizure frequency would be reduced by more than 50 % compared to baseline (adjusted odds ratio: 1.228, 95 % CI: 1.137-1.327; P < 0.0001), and younger children were less likely to be responders (adjusted odds ratio: 1.027, 95 % CI: 1.012-1.043; P = 0.001). Based on a trade-off between sensitivity and specificity, the optimal cut-off values for lamotrigine trough concentrations corresponding to clinical response were 3.29 mg/L, 2.06 mg/L, and 1.61 mg/L in the toddler and school-age group, adolescent group, and adult group, respectively. By reducing interpatient variability, the results of the concentration-effect curves suggested no additional clinical benefit from a continued increase of doses for lamotrigine concentrations exceeding 9.08 mg/L, 8.43 mg/L, and 10.38 mg/L in the toddler and school-age group, adolescent group, and adult group, respectively. In conclusion, the therapeutic ranges of lamotrigine trough concentrations corresponding to adequate clinical response were 3.29-9.08 mg/L in the toddler and school-age group, 2.06-8.43 mg/L in the adolescent group, and 1.61-10.38 mg/L in the adult group.

CONCLUSIONS

The study determined age-specific therapeutic ranges corresponding to optimal clinical efficacy for lamotrigine. Our findings lay the foundation for catalyzing novel opportunities to optimize treatment and reduce therapeutic costs. Based on the age-specific therapeutic ranges identified in this study, individualized and cost-effective algorithms for lamotrigine treatment of epilepsy patients may be developed and validated in larger cohort studies of therapeutic drug monitoring.

Pathology-selective antiepileptic effects in the focal freeze-lesion rat model of malformation of cortical development

Malformations of cortical development (MCD) represent a group of rare diseases with severe clinical presentation as epileptic and pharmacoresistant encephalopathies. Morphological studies in tissue from MCD patients have revealed reduced GABAergic efficacy and increased intracellular chloride concentration in neuronal cells as important pathophysiological mechanisms in MCD. Also, in various animal models, alterations of GABAergic inhibition have been postulated as a predominant factor contributing to perilesional hyperexcitability. Along with this line, the NKCC1 inhibitor bumetanide has been postulated as a potential drug for treatment of epilepsy, mediating its antiepileptic effect by reduction of the intracellular chloride and increased inhibitory efficacy of GABAergic transmission. In the present study, we focused on the focal freeze-lesion model of MCD to compare antiepileptic drugs with distinct mechanisms of action, including NKCC1 inhibition by bumetanide. For this purpose, we combined electrophysiological and optical methods in slice preparations and assessed the properties of seizure like events (SLE) induced by 4-aminopyridine. In freeze-lesioned but not control slices, SLE onset was confined to the perilesional area, confirming that this region is hyperexcitable and likely triggers pathological activity. Bumetanide selectively reduced epileptic activity in lesion-containing slices but not in slices from sham-treated control rats. Moreover, bumetanide caused a shift in the SLE onset site away from the perilesional area. In contrast, effects of other antiepileptic drugs including carbamazepine, lacosamide, acezatolamide and zonisamide occurred mostly independently of the lesion and did not result in a shift of the onset region. Our work adds evidence for the functional relevance of chloride homeostasis in the pathophysiology of microgyrus formation as represented in the focal freeze-lesion model. Further studies in different MCD models and human tissue will be required to validate the effects across different MCD subtypes and species and to assess the translational value of our findings.

Increased levels of α4-containing GABAA receptors in focal cortical dysplasia: A possible cause of benzodiazepine resistance

Benzodiazepines are the first choice of anti-epileptic drugs used to treat seizures. However, it has been seen that their efficacy decreases with time leading to drug insensitivity, plausibly caused by an alteration in the expression of the benzodiazepine biding site on GABA_A receptors. This study was designed to investigate if the differential expression of GABA_A receptor subunits α1/α4/γ2/δ across the postsynaptic sites could contribute to benzodiazepine resistance in patients with focal cortical dysplasia (FCD), the most common cause of drug resistant epilepsy in pediatric population. Differential gene and cellular expression of GABA_A receptor subunits α1, α4, γ2 and δ were evaluated and validated using qPCR and immunohistochemistry. Whole cell patch clamp studies were performed on pyramidal neurons of resected cortical FCD samples to measure the spontaneous GABA_A receptor activity. Upregulation of α4-and γ2-subunits containing GABA_A receptors were observed at both mRNA and protein level. α1-and δ-subunits containing GABA_A receptors did not show any significant changes. Flumazenil treatment did not affect the kinetics of GABAergic events in FCD; however, it significantly reduced the frequency and amplitude of spontaneous GABAergic activity in non-seizure control samples. Our results demonstrate the enhanced expression of α4-containing GABA_A receptors and GABAergic activity in pyramidal neurons which in turn may contribute to benzodiazepine resistance in FCD patients.

Warped rhythms: Epileptic activity during critical periods disrupts the development of neural networks for human communication

It is well established that temporal lobe epilepsy-the most common and well-studied form of epilepsy-can impair communication by disrupting social-emotional and language functions. In pediatric epilepsy, where seizures co-occur with the development of critical brain networks, age of onset matters: The earlier in life seizures begin, the worse the disruption in network establishment, resulting in academic hardship and social isolation. Yet, little is known about the processes by which epileptic activity disrupts developing human brain networks. Here we take a synthetic perspective-reviewing a range of research spanning studies on molecular and oscillatory processes to those on the development of large-scale functional networks-in support of a novel model of how such networks can be disrupted by epilepsy. We seek to bridge the gap between research on molecular processes, on the development of human brain circuitry, and on clinical outcomes to propose a model of how epileptic activity disrupts brain development.

Challenges in Physiological Phenotyping of hiPSC-Derived Neurons: From 2D Cultures to 3D Brain Organoids

Neurons derived from human induced pluripotent stem cells (hiPSC-derived neurons) offer novel opportunities for the development of preclinical models of human neurodegenerative diseases (NDDs). Recent advances in the past few years have increased substantially the potential of these techniques and have uncovered new challenges that the field is facing. Here, we outline and discuss challenges related to the functional characterization of hiPSC-derived neurons and propose ways to overcome current difficulties. In particular, the enormous variability among studies in the electrical properties of hiPSC-derived neurons and broad differences in cell maturation are factors that impair reproducibility. Furthermore, we discuss how the use of 3D brain organoids are of help in resolving some difficulties posed by 2D cultures. Finally, we elaborate on recent and future advances that may help to overcome the discussed challenges and speed-up progress in the field.

Reduced neurosteroid potentiation of GABAA receptors in epilepsy and depolarized hippocampal neurons

OBJECTIVE

Neurosteroids regulate neuronal excitability by potentiating γ-aminobutyric acid type-A receptors (GABARs). In animal models of temporal lobe epilepsy, the neurosteroid sensitivity of GABARs is diminished and GABAR subunit composition is altered. We tested whether similar changes occur in patients with epilepsy and if depolarization-induced increases in neuronal activity can replicate this effect.

METHODS

We determined GABAR α4 subunit expression in cortical tissue resected from pediatric epilepsy patients. Modulation of human GABARs by allopregnanolone and Ro15-4513 was measured in Xenopus oocytes using whole-cell patch clamp. To extend the findings obtained using tissue from epilepsy patients, we evaluated GABAR expression and modulation by allopregnanolone and Ro15-4513 in cultured rat hippocampal neurons exposed to high extracellular potassium (HK) to increase neuronal activity.

RESULTS

Expression of α4 subunits was increased in pediatric cortical epilepsy specimens encompassing multiple pathologies. The potentiation of GABA-evoked currents by the neurosteroid allopregnanolone was decreased in Xenopus oocytes expressing GABARs isolated from epilepsy patients. Furthermore, receptors isolated from epilepsy but not control tissue were sensitive to potentiation by Ro15-4513, indicating higher expression of α4 βx γ2 subunit-containing receptors. Correspondingly, increasing the activity of cultured rat hippocampal neurons reduced allopregnanolone potentiation of miniature inhibitory postsynaptic currents (mIPSCs), increased modulation of tonic GABAR current by Ro15-4513, upregulated the surface expression of α4 and γ2 subunits, and increased the colocalization of α4 and γ2 subunit immunoreactivity.

INTERPRETATION

These findings suggest that seizure activity-induced upregulation of α4 βx γ2 subunit-containing GABARs could affect the anticonvulsant actions of neurosteroids.

Role of NKCC1 and KCC2 in Epilepsy: From Expression to Function

As a main inhibitory neurotransmitter in the central nervous system, γ-aminobutyric acid (GABA) activates chloride-permeable GABAa receptors (GABAa Rs) and induces chloride ion (Cl⁻) flow, which relies on the intracellular chloride concentration ([Cl⁻]_i) of the postsynaptic neuron. The Na-K-2Cl cotransporter isoform 1 (NKCC1) and the K-Cl cotransporter isoform 2 (KCC2) are two main cation-chloride cotransporters (CCCs) that have been implicated in human epilepsy. NKCC1 and KCC2 reset [Cl⁻]_i by accumulating and extruding Cl⁻, respectively. Previous studies have shown that the profile of NKCC1 and KCC2 in neonatal neurons may reappear in mature neurons under some pathophysiological conditions, such as epilepsy. Although increasing studies focusing on the expression of NKCC1 and KCC2 have suggested that impaired chloride plasticity may be closely related to epilepsy, additional neuroelectrophysiological research aimed at studying the functions of NKCC1 and KCC2 are needed to understand the exact mechanism by which they induce epileptogenesis. In this review, we aim to briefly summarize the current researches surrounding the expression and function of NKCC1 and KCC2 in epileptogenesis and its implications on the treatment of epilepsy. We will also explore the potential for NKCC1 and KCC2 to be therapeutic targets for the development of novel antiepileptic drugs.

Mechanisms underlying a critical period of respiratory development in the rat

Twenty-five years ago, Filiano and Kinney (1994) proposed that a critical period of postnatal development constitutes one of the three risk factors for sudden infant death syndrome (SIDS). The underlying mechanism was poorly understood. In the last 17 years, much has been uncovered on this period in the rat. Against several expected trends of development, abrupt neurochemical, metabolic, ventilatory, and electrophysiological changes occur in the respiratory system at P12-13. This results in a transient synaptic imbalance with suppressed excitation and enhanced inhibition, and the response to acute hypoxia is the weakest at this time, both at the cellular and system's levels. The basis for the synaptic imbalance is likely to be contributed by a reduced expression of brain-derived neurotrophic factor (BDNF) and its TrkB receptors in multiple brain stem respiratory-related nuclei during the critical period. Exogenous BDNF or a TrkB agonist partially reverses the synaptic imbalance, whereas a TrkB antagonist accentuates the imbalance. A transient down-regulation of pituitary adenylate cyclase-activating polypeptide (PACAP) at P12 in respiratory-related nuclei also contributes to the vulnerability of this period. Carotid body denervation during this time or perinatal hyperoxia merely delays and sometimes prolongs, but not eliminate the critical period. The rationale for the necessity of the critical period in postnatal development is discussed.

Gamma-aminobutyric acidergic transmission underlies interictal epileptogenicity in pediatric focal cortical dysplasia

OBJECTIVE

Dysregulation of γ-aminobutyric acidergic (GABAergic) transmission has been reported in lesional acquired epilepsies (gliomas, hippocampal sclerosis). We investigated its involvement in a developmental disorder, human focal cortical dysplasia (FCD), focusing on chloride regulation driving GABAergic signals.

METHODS

In vitro recordings of 47 human cortical acute slices from 11 pediatric patients who received operations for FCD were performed on multielectrode arrays. GABAergic receptors and chloride regulators were pharmacologically modulated. Immunostaining for chloride cotransporter KCC2 and interneurons were performed on recorded slices to correlate electrophysiology and expression patterns.

RESULTS

FCD slices retain intrinsic epileptogenicity. Thirty-six of 47 slices displayed spontaneous interictal discharges, along with a pattern specific to the histological subtypes. Ictal discharges were induced in proepileptic conditions in 6 of 8 slices in the areas generating spontaneous interictal discharges, with a transition to seizure involving the emergence of preictal discharges. Interictal discharges were sustained by GABAergic signaling, as a GABA_A receptor blocker stopped them in 2 of 3 slices. Blockade of NKCC1 Cl^- cotransporters further controlled interictal discharges in 9 of 12 cases, revealing a Cl^- dysregulation affecting actions of GABA. Immunohistochemistry highlighted decreased expression and changes in KCC2 subcellular localization and a decrease in the number of GAD67-positive interneurons in regions generating interictal discharges.

INTERPRETATION

Altered chloride cotransporter expression and changes in interneuron density in FCD may lead to paradoxical depolarization of pyramidal cells. Spontaneous interictal discharges are consequently mediated by GABAergic signals, and targeting chloride regulation in neurons may be considered for the development of new antiepileptic drugs. Ann Neurol 2019; 1-14 ANN NEUROL 2019;85:204-217.

Histone deacetylases mediate GABA(A) receptor expression, physiology, and behavioral maladaptations in rat models of alcohol dependence

Alcohol use disorders are chronic debilitating diseases characterized by severe withdrawal symptoms that contribute to morbidity and relapse. GABA_A receptor (GABA_AR) adaptations have long been implicated in the chronic effects of alcohol and contribute to many withdrawal symptoms associated with alcohol dependence. In rodents, GABA_AR hypofunction results from decreases in Gabra1 expression, although the underlying mechanism controlling Gabra1 expression after chronic ethanol exposure is still unknown. We found that chronic ethanol exposure using either ethanol gavage or two-bottle choice voluntary access paradigms decreased Gabra1 expression and increased Hdac2 and Hdac3 expression. Administration of the HDAC inhibitor trichostatin A (TSA) after chronic ethanol exposure prevents the decrease in Gabra1 expression and function as well as the increase in Hdac2 and Hdac3 expression in both the cortex and the medial prefrontal cortex (mPFC). Chronic ethanol exposure and withdrawal, but not acute ethanol exposure or acute withdrawal, cause a selective upregulation of HDAC2 and HDAC3 associated with the Gabra1 promoter that accompanies a decrease in H3 acetylation of the Gabra1 promoter and the reduction in GABA_AR α1 subunit expression. TSA administration prevented each of these molecular events as well as behavioral manifestations of ethanol dependence, including tolerance to zolpidem-induced loss of righting reflex, reduced open-arm time in the elevated plus maze, reduced center-time and locomotor activity in the open-field assay, and TSA reduced voluntary ethanol consumption. The results show how chronic ethanol exposure regulates the highly prominent GABA_AR α1 subunit by an epigenetic mechanism that represents a potential treatment modality for alcohol dependence.

Review: Roles for astrocytes in epilepsy: insights from malformations of cortical development

Malformations of cortical development (MCDs), such as cortical dysplasia and tuberous sclerosis complex, are common causes of intractable epilepsy, especially in paediatric patients. Recently, mounting evidence points to a common pathology of these disorders. Hyperactivation of mammalian target of rapamycin (mTOR) has been proposed as a central mechanism in most, if not all, MCDs. The transition from mTOR hyperactivation and cellular abnormalities to large-scale functional changes and seizure is, however, not fully understood. In this article we set out to review currently available information regarding MCD pathology, focusing on glial cells - especially astrocytes - and their interactions with the brain vascular system. A large body of evidence points to these elements as potential targets in MCD. Here, we attempt to provide a review of this evidence and propose some hypotheses regarding the possible chain of events linking primary glial dysfunction and epilepsy. We focus on extracellular matrix remodelling, blood-brain barrier leakage and failure of astrocyte-dependent removal of extracellular debris. We posit that the failure of these systems results in a chronically pro-inflammatory environment, maintaining local astrocytes in a state of gliosis, with increased susceptibility to seizures as a consequence.

Alterations of Hippocampal Myelin Sheath and Axon Sprouting by Status Convulsion and Regulating Lingo-1 Expression with RNA Interference in Immature and Adult Rats

Seizure-induced brain damage is age-dependent, as evidenced by the different alterations of neural physiopathology in developing and mature brains. However, little is known about the age-dependent characteristics of myelinated fiber injury induced by seizures. Considering the critical functions of oligodendrocyte progenitor cells (OPCs) in myelination and Lingo-1 signaling in regulating OPCs' differentiation, the present study aimed to explore the effects of Lingo-1 on myelin and axon in immature and adult rats after status convulsion (SC) induced by lithium-pilocarpine, and the differences between immature and adult brains. Dynamic variations in electrophysiological activity and spontaneous recurrent seizures were recorded by electroencephalogram monitoring after SC. The impaired microstructures of myelin sheaths and decrease in myelin basic protein caused by SC were observed through transmission electron microscopy and western blot analysis respectively, which became more severe in adult rats, but improved gradually in immature rats. Aberrant axon sprouting occurred in adult rats, which was more prominent than in immature rats, as shown by a Timm stain. This damage was improved or negatively affected after down or upregulating Lingo-1 expression. These results demonstrated that in both immature and adult brains, Lingo-1 signaling plays important roles in seizure-induced damage to myelin sheaths and axon growth. The plasticity of the developing brain may provide a potential window of opportunity to prevent the brain from damage.

Bumetanide treatment during early development rescues maternal separation-induced susceptibility to stress

Stress is a major risk factor for psychiatric disorders, such as depression, posttraumatic stress disorder, and schizophrenia. Early life stress, such as maternal separation, can have long-term effects on the development of the central nervous system and pathogenesis of psychiatric disorders. In the present study, we found that maternal separation increased the susceptibility to stress in adolescent rats, increased the expression of Na+/K+/2Cl- cotransporter 1 (NKCC1) on postnatal day 14, and increased the expression of K+/2Cl- cotransporter 2 (KCC2) and γ-aminobutyric acid A (GABAA) receptor subunits on postnatal day 40 in the hippocampus. NKCC1 inhibition by the U.S. Food and Drug Administration-approved drug bumetanide during the first two postnatal weeks rescued the depressive- and anxiety-like behavior that was induced by maternal separation and decreased the expression of NKCC1, KCC2 and GABAA receptor α1 and β2,3 subunits in the hippocampus. Bumetanide treatment during early development did not adversely affect body weight or normal behaviors in naive rats, or affect serum osmolality in adult rats. These results suggest that bumetanide treatment during early development may prevent the maternal separation-induced susceptibility to stress and impairments in GABAergic transmission in the hippocampus.

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.

Developmental Expression Patterns of KCC2 and Functionally Associated Molecules in the Human Brain

Work on rodents demonstrated that steep upregulation of KCC2, a neuron-specific Cl- extruder of cation-chloride cotransporter (CCC) family, commences in supraspinal structures at around birth, leading to establishment of hyperpolarizing GABAergic responses. We describe spatiotemporal expression profiles of the entire CCC family in human brain. KCC2 mRNA was observed already at 10th postconceptional week (PCW) in amygdala, cerebellum, and thalamus. KCC2-immunoreactive (KCC2-ir) neurons were abundant in subplate at 18 PCW. By 25 PCW, numerous subplate and cortical plate neurons became KCC2-ir. The mRNA expression profiles of α- and β-isoforms of Na-K ATPase, which fuels cation-chloride cotransport, as well of tropomyosin receptor kinase B (TrkB), which promotes developmental upregulation of KCC2, were consistent with data from studies on rodents about their interactions with KCC2. Thus, in human brain, expression of KCC2 and its functionally associated proteins begins in early fetal period. Our work facilitates translation of results on CCC functions from animal studies to human and refutes the view that poor efficacy of anticonvulsants in the term human neonate is attributable to the lack of KCC2. We propose that perinatally low threshold for activation of Ca2+-dependent protease calpain renders neonates susceptible to downregulation of KCC2 by traumatic events, such as perinatal hypoxia ischemia.

Neonatal seizures are associated with redistribution and loss of GABAA α-subunits in the hypoxic-ischaemic pig

Seizures are a common manifestation of hypoxic-ischaemic brain injury in the neonate. In status epilepticus models alterations to GABA_A R subunit expression have been suggested to contribute to (i) abnormal development of the GABAergic system, (ii) why seizures become self-sustaining and (iii) the development of pharmacoresistance. Detailed investigation of GABA_A R subunit protein expression after neonatal hypoxia-ischaemia (HI) is currently insufficient. Using our pig model of HI and subsequent spontaneous neonatal seizures, we investigated changes in protein expression of the three predominant α-subunits of the GABA_A R; α₁ , α₂ and α₃ . Anaesthetized, ventilated newborn pigs (< 24 h old) were subjected to 30 min HI and subsequently recovered to 24 or 72 h. Amplitude-integrated electroencephalography was used to monitor brain activity and identify seizure activity. Brain tissue was collected post-mortem and GABA_A R α-subunit protein expression was analysed using western blot and immunohistochemistry. GABA_A R α₁ and α₃ protein expression was significantly reduced in animals that developed seizures after HI; HI animals that did not develop seizures did not exhibit the same reductions. Immunohistochemistry revealed decreased α₁ and α₃ expression, and α₁ redistribution from the cell membrane to the cytosol, in the hippocampus of seizure animals. Multivariate analyses, controlling for HI severity and neuronal injury, revealed that seizures were independently associated with significant GABA_A R α₃ reduction. This is the first study to show loss and redistribution of GABA_A R α-subunits in a neonatal brain experiencing seizures. Our findings are similar to those reported in models of SE and in chronic epilepsy.

Developmental pharmacology of benzodiazepines under normal and pathological conditions

Benzodiazepines are allosteric agonists of GABAA receptors (GABAAR), pentameric ligand-gated Cl(-) channels, which serve both an important neurodevelopmental role but are also the principal inhibitory system in the brain. However, their subunit composition, channel properties, and function, as well as their region-specific expression patterns, change through development. These processes have been extensively studied in rodents and to some extent confirmed in higher species. Specifically, GABAARs acquire faster kinetics with age and their pharmacology changes rendering them more sensitive to drugs that have higher affinity for α1 subunit-containing GABAARs, such as benzodiazepines, but also, their inhibitory function becomes more potent as they shift from having depolarising to hyperpolarising responses due to a shift in Cl(-) gradient and cation chloride cotransporter expression. Concerns have been raised about possible pro-apoptotic and paradoxical effects of benzodiazepines in the neonatal normal rat brain, although it is unclear, as yet, whether this extends to brains exposed to seizures. Growing evidence indicates that the pharmacology and physiology of GABAARs may be altered in the brain of rats or humans with seizures or epilepsy, or different aetiologies that predispose to epilepsy. These changes follow different paths, depending on sex, age, region, cell type, aetiology, or time-point specific factors. Identification of dynamic biomarkers that could enable these changes in vivo to be monitored would greatly facilitate the selection of more effective agonists with fewer side effects.

Postnatal Erythropoietin Mitigates Impaired Cerebral Cortical Development Following Subplate Loss from Prenatal Hypoxia-Ischemia

Preterm birth impacts brain development and leads to chronic deficits including cognitive delay, behavioral problems, and epilepsy. Premature loss of the subplate, a transient subcortical layer that guides development of the cerebral cortex and axonal refinement, has been implicated in these neurological disorders. Subplate neurons influence postnatal upregulation of the potassium chloride co-transporter KCC2 and maturation of γ-amino-butyric acid A receptor (GABAAR) subunits. We hypothesized that prenatal transient systemic hypoxia-ischemia (TSHI) in Sprague-Dawley rats that mimic brain injury from extreme prematurity in humans would cause premature subplate loss and affect cortical layer IV development. Further, we predicted that the neuroprotective agent erythropoietin (EPO) could attenuate the injury. Prenatal TSHI induced subplate neuronal loss via apoptosis. TSHI impaired cortical layer IV postnatal upregulation of KCC2 and GABAAR subunits, and postnatal EPO treatment mitigated the loss (n ≥ 8). To specifically address how subplate loss affects cortical development, we used in vitro mechanical subplate ablation in slice cultures (n ≥ 3) and found EPO treatment attenuates KCC2 loss. Together, these results show that subplate loss contributes to impaired cerebral development, and EPO treatment diminishes the damage. Limitation of premature subplate loss and the resultant impaired cortical development may minimize cerebral deficits suffered by extremely preterm infants.

Models of cortical malformation--Chemical and physical

Pharmaco-resistant epilepsies, and also some neuropsychiatric disorders, are often associated with malformations in hippocampal and neocortical structures. The mechanisms leading to these cortical malformations causing an imbalance between the excitatory and inhibitory system are largely unknown. Animal models using chemical or physical manipulations reproduce different human pathologies by interfering with cell generation and neuronal migration. The model of in utero injection of methylazoxymethanol (MAM) acetate mimics periventricular nodular heterotopia. The freeze lesion model reproduces (poly)microgyria, focal heterotopia and schizencephaly. The in utero irradiation model causes microgyria and heterotopia. Intraperitoneal injections of carmustine 1-3-bis-chloroethyl-nitrosurea (BCNU) to pregnant rats produces laminar disorganization, heterotopias and cytomegalic neurons. The ibotenic acid model induces focal cortical malformations, which resemble human microgyria and ulegyria. Cortical dysplasia can be also observed following prenatal exposure to ethanol, cocaine or antiepileptic drugs. All these models of cortical malformations are characterized by a pronounced hyperexcitability, few of them also produce spontaneous epileptic seizures. This dysfunction results from an impairment in GABAergic inhibition and/or an increase in glutamatergic synaptic transmission. The cortical region initiating or contributing to this hyperexcitability may not necessarily correspond to the site of the focal malformation. In some models wide-spread molecular and functional changes can be observed in remote regions of the brain, where they cause pathophysiological activities. This paper gives an overview on different animal models of cortical malformations, which are mostly used in rodents and which mimic the pathology and to some extent the pathophysiology of neuronal migration disorders associated with epilepsy in humans.

Efficacy and safety of felbamate in children with refractory epilepsy

BACKGROUND

Despite the introduction of multiple new antiepileptic drugs in the past two decades, many patients with epilepsy continue to experience uncontrolled seizures or significant side effects.

AIM

To present our experience with felbamate therapy in children with drug-resistant epilepsy.

METHODS

We retrospectively reviewed the medical charts and video-EEG recordings of all patients receiving felbamate until May 2012. Efficacy was determined according to seizure frequency during the week prior to treatment initiation and the week after the maximal dosage of felbamate was reached.

RESULTS

Fifty patients (34 boys) aged 4 months to 17 years (mean--5.5 years) were identified. Nearly third of the patients had Lennox-Gastaut syndrome. Mean epilepsy duration was 3.4 years (range--1 month to 13 years). The mean number of previous antiepileptic drugs was 7.5. The mean duration of follow-up was 1.1 years. Seizure frequency decreased by at least 50% in 29 (58%) patients. Side effects were reported in 22 (44%) patients, none of them included aplastic anemia or liver failure. In the responder group, the maximal dose of felbamate was lower and the patients were older compared to non-responders.

CONCLUSIONS

Despite current recommendations, felbamate is initiated following multiple AEDs. Based on its efficacy and safety data, earlier initiation of felbamate is recommended in children with refractory epilepsy.

Sex-specific consequences of early life seizures

Seizures are very common in the early periods of life and are often associated with poor neurologic outcome in humans. Animal studies have provided evidence that early life seizures may disrupt neuronal differentiation and connectivity, signaling pathways, and the function of various neuronal networks. There is growing experimental evidence that many signaling pathways, like GABAA receptor signaling, the cellular physiology and differentiation, or the functional maturation of certain brain regions, including those involved in seizure control, mature differently in males and females. However, most experimental studies of early life seizures have not directly investigated the importance of sex on the consequences of early life seizures. The sexual dimorphism of the developing brain raises the question that early seizures could have distinct effects in immature females and males that are subjected to seizures. We will first discuss the evidence for sex-specific features of the developing brain that could be involved in modifying the susceptibility and consequences of early life seizures. We will then review how sex-related biological factors could modify the age-specific consequences of induced seizures in the immature animals. These include signaling pathways (e.g., GABAA receptors), steroid hormones, growth factors. Overall, there are very few studies that have specifically addressed seizure outcomes in developing animals as a function of sex. The available literature indicates that a variety of outcomes (histopathological, behavioral, molecular, epileptogenesis) may be affected in a sex-, age-, region-specific manner after seizures during development. Obtaining a better understanding for the gender-related mechanisms underlying epileptogenesis and seizure comorbidities will be necessary to develop better gender and age appropriate therapies.

Does epilepsy cause a reversion to immature function?

Seizures have variable effects on brain. Numerous studies have examined the consequences of seizures, in light of the way that these may alter the susceptibility of the brain to seizures, promote epileptogenesis, or functionally alter brain leading to seizure-related comorbidities. In many -but not all- situations, seizures shift brain function towards a more immature state, promoting the birth of newborn neurons, altering the dendritic structure and neuronal connectivity, or changing neurotransmitter signaling towards more immature patterns. These effects depend upon many factors, including the seizure type, age of seizure occurrence, sex, and brain region studied. Here we discuss some of these findings proposing that these seizure-induced immature features do not simply represent rejuvenation of the brain but rather a de-synchronization of the homeostatic mechanisms that were in place to maintain normal physiology, which may contribute to epileptogenesis or the cognitive comorbidities.

Malformations of cortical development and neocortical focus

Developmental neocortical malformations resulting from abnormal neurogenesis, disturbances in programmed cell death, or neuronal migration disorders may cause a long-term hyperexcitability. Early generated Cajal-Retzius and subplate neurons play important roles in transient cortical circuits, and structural/functional disorders in early cortical development may induce persistent network disturbances and epileptic disorders. In particular, depolarizing GABAergic responses are important for the regulation of neurodevelopmental events, like neurogenesis or migration, while pathophysiological alterations in chloride homeostasis may cause epileptic activity. Although modern imaging techniques may provide an estimate of the structural lesion, the site and extent of the cortical malformation may not correlate with the epileptogenic zone. The neocortical focus may be surrounded by widespread molecular, structural, and functional disturbances, which are difficult to recognize with imaging technologies. However, modern imaging and electrophysiological techniques enable focused hypotheses of the neocortical epileptogenic zone, thus allowing more specific epilepsy surgery. Focal cortical malformation can be successfully removed with minimal rim, close to or even within eloquent cortex with a promising risk-benefit ratio.

NKCC1 and KCC2 protein expression is sexually dimorphic in the hippocampus and entorhinal cortex of neonatal rats

Seizure susceptibility appears to be greater in males than females during the early developmental stages of the brain when the gamma-aminobutyric acid (GABA), acting through its GABA-A receptor, predominantly produces neuronal depolarization. GABA-mediated excitation has been observed when the NKCC1 (chloride importer) expression level is higher than KCC2 (chloride exporter). In this study, the relative protein expression of NKCC1 and KCC2 over β-actin was evaluated in the hippocampus and entorhinal cortex of male and female rats during postnatal days (PND) 1, 3, 5, 7, 9, 11, 13 and 15 using Western blotting assays. For both cerebral regions in the females, the NKCC1/β-actin expression ratio was constant during all evaluated ages, whereas the KCC2/β-actin expression ratio increased gradually until reaching a maximal level at PND9 that was nearly three- and ten-fold higher in the hippocampus and entorhinal cortex, respectively, compared with the initial level. In males, the NKCC1/β-actin expression ratio was constant during the first week, peaking almost three-fold higher than the initial level at PND9 in the hippocampus and at PND11 in the entorhinal cortex and then returning to the initial values at PND13, whereas the KCC2/β-actin expression ratio increased gradually to reach a maximal and steady level at PND5, which were nearly two- and four-fold higher in the hippocampus and entorhinal cortex, respectively, compared with the intial level. In conclusion, the NKCC1/β-actin and KCC2/β-actin expression ratios displayed a specific expression profile for each gender and cerebral region, which could be related with the differences in seizure susceptibility observed between genders.

Correlations in timing of sodium channel expression, epilepsy, and sudden death in Dravet syndrome

Dravet Syndrome (DS) is an intractable genetic epilepsy caused by loss-of-function mutations in SCN1A, the gene encoding brain sodium channel Nav 1.1. DS is associated with increased frequency of sudden unexpected death in humans and in a mouse genetic model of this disease. Here we correlate the time course of declining expression of the murine embryonic sodium channel Nav 1.3 and the rise in expression of the adult sodium channel Nav 1.1 with susceptibility to epileptic seizures and increased incidence of sudden death in DS mice. Parallel studies with unaffected human brain tissue demonstrate similar decline in Nav 1.3 and increase in Nav 1.1 with age. In light of these results, we introduce the hypothesis that the natural loss Nav 1.3 channel expression in brain development, coupled with the failure of increase in functional Nav 1.1 channels in DS, defines a tipping point that leads to disinhibition of neural circuits, intractable seizures, co-morbidities, and premature death in this disease.

What is special about the adolescent (JME) brain?

Juvenile myoclonic epilepsy (JME) involves cortico-thalamo-cortical networks. Thalamic, frontal gray matter, connectivity, and neurotransmitter disturbances have been demonstrated by structural/functional imaging studies. Few patients with JME show mutations in genes coding ion channels or GABAA (gamma-aminobutyric acid) receptor subunits. Recent research points to EFHC1 gene mutations leading to microdysgenesis and possible aberrant circuitry. Imaging studies have shown massive structural/functional changes of normally developing adolescent brain structures maturing at strikingly different rates and times. Gray matter (GM) volume diminishes in cortical areas (frontal and parietal) and deep structures (anterior thalamus, putamen, and caudate). Diffusion tensor imaging (DTI) findings support continued microstructural change in WM (white matter) during late adolescence with robust developmental changes in thalamocortical connectivity. The GABAA receptor distribution and specific receptor subunits' expression patterns change with age from neonate to adolescent/adult, contributing to age-related changes in brain excitability. Hormonal influence on brain structure development during adolescence is presented. Possible implications of brain changes during adolescence on the course of JME are discussed.

A common susceptibility factor of both autism and epilepsy: functional deficiency of GABA A receptors

Autism and epilepsy are common childhood neurological disorders with a great heterogeneity of clinical phenotypes as well as risk factors. There is a high co-morbidity of autism and epilepsy. The neuropathology of autism and epilepsy has similar histology implicating the processes of neurogenesis, neural migration, programmed cell death, and neurite outgrowth. Genetic advances have identified multiple molecules that participate in neural development, brain network connectivity, and synaptic function which are involved in the pathogenesis of autism and epilepsy. Mutations in GABA(A) receptor subunit have been frequently associated with epilepsy, autism, and other neuropsychiatric disorders. In this paper, we address the hypothesis that functional deficiency of GABAergic signaling is a potential common molecular mechanism underpinning the co-morbidity of autism and epilepsy.

Tissue localization during resective epilepsy surgery

Object

Imaging-guided surgery (IGS) systems are widely used in neurosurgical practice. During epilepsy surgery, the authors routinely use IGS landmarks to localize intracranial electrodes and/or specific brain regions. The authors have developed a technique to coregister these landmarks with pre- and postoperative scans and the Montreal Neurological Institute (MNI) standard space brain MRI to allow 1) localization and identification of tissue anatomy; and 2) identification of Brodmann areas (BAs) of the tissue resected during epilepsy surgery. Tracking tissue in this fashion allows for better correlation of patient outcome to clinical factors, functional neuroimaging findings, and pathological characteristics and molecular studies of resected tissue.

Methods

Tissue samples were collected in 21 patients. Coordinates from intraoperative tissue localization were downloaded from the IGS system and transformed into patient space, as defined by preoperative high-resolution T1-weighted MRI volume. Tissue landmarks in patient space were then transformed into MNI standard space for identification of the BAs of the tissue samples.

Results

Anatomical locations of resected tissue were identified from the intraoperative resection landmarks. The BAs were identified for 17 of the 21 patients. The remaining patients had abnormal brain anatomy that could not be meaningfully coregistered with the MNI standard brain without causing extensive distortion.

Conclusions

This coregistration and landmark tracking technique allows localization of tissue that is resected from patients with epilepsy and identification of the BAs for each resected region. The ability to perform tissue localization allows investigators to relate preoperative, intraoperative, and postoperative functional and anatomical brain imaging to better understand patient outcomes, improve patient safety, and aid in research.

Stable respiratory activity requires both P/Q-type and N-type voltage-gated calcium channels

P/Q-type voltage-gated calcium channels (Ca(v)2.1) play critical presynaptic and postsynaptic roles throughout the nervous system and have been implicated in a variety of neurological disorders. Here we report that mice with a genetic ablation of the Ca(v)2.1 pore-forming α(1A) subunit (α(1A)⁻/⁻) encoded by CACNA1a (Jun et al., 1999) suffer during postnatal development from increasing breathing disturbances that lead ultimately to death. Breathing abnormalities include decreased minute ventilation and a specific loss of sighs, which was associated with lung atelectasis. Similar respiratory alterations were preserved in the isolated in vitro brainstem slice preparation containing the pre-Bötzinger complex. The loss of Ca(v)2.1 was associated with an alteration in the functional dependency on N-type calcium channels (Ca(v)2.2). Blocking N-type calcium channels with conotoxin GVIA had only minor effects on respiratory activity in slices from control (CT) littermates, but abolished respiratory activity in all slices from α(1A)⁻/⁻ mice. The amplitude of evoked EPSPs was smaller in inspiratory neurons from α(1A)⁻/⁻ mice compared with CTs. Conotoxin GVIA abolished all EPSPs in inspiratory neurons from α(1A)⁻/⁻ mice, while the EPSP amplitude was reduced by only 30% in CT mice. Moreover, neuromodulation was significantly altered as muscarine abolished respiratory network activity in α(1A)⁻/⁻ mice but not in CT mice. We conclude that excitatory synaptic transmission dependent on N-type and P/Q-type calcium channels is required for stable breathing and sighing. In the absence of P/Q-type calcium channels, breathing, sighing, and neuromodulation are severely compromised, leading to early mortality.

Lamotrigine serum concentration in children with epilepsy

The correlation between lamotrigine serum concentration, efficacy, and toxicity in children is controversial. The database of the Clinical Pharmacology Laboratory at Assaf Harofeh Medical Center was retrospectively searched to identify lamotrigine serum concentrations in children aged 2-19 years with refractory epilepsy who received lamotrigine as monotherapy or polytherapy from 2007-2010. Data collected included age at epilepsy onset, additional antiepileptic drugs, lamotrigine dose, monthly seizure frequency before and after lamotrigine treatment, and side effects. Sixty blood samples were collected from 42 children aged 10.1 ± 4.9 years (range, 2-20 years). Seizure types included complex partial (n = 28), simple partial (n = 7), absence (n = 2), and generalized tonic-clonic (n = 23). Decreased seizure frequency was observed in 38 (63.3%) patients. No correlation with lamotrigine serum concentration was evident, but seizure frequency was significantly influenced by age and lamotrigine dose. Side effects were reported in 21 (35%) patients. Only diplopia was significantly correlated with lamotrigine serum concentration. Lamotrigine was more effective at lower doses and in older children. Lamotrigine serum concentration correlated significantly with diplopia, but not with other side effects or with clinical efficacy. Overall, lamotrigine is effective and safe in children with refractory epilepsy.

Genetics and function of neocortical GABAergic interneurons in neurodevelopmental disorders

A dysfunction of cortical and limbic GABAergic circuits has been postulated to contribute to multiple neurodevelopmental disorders in humans, including schizophrenia, autism, and epilepsy. In the current paper, I summarize the characteristics that underlie the great diversity of cortical GABAergic interneurons and explore how the multiple roles of these cells in developing and mature circuits might contribute to the aforementioned disorders. Furthermore, I review the tightly controlled genetic cascades that determine the fate of cortical interneurons and summarize how the dysfunction of genes important for the generation, specification, maturation, and function of cortical interneurons might contribute to these disorders.

Altered GABA signaling in early life epilepsies

The incidence of seizures is particularly high in the early ages of life. The immaturity of inhibitory systems, such as GABA, during normal brain development and its further dysregulation under pathological conditions that predispose to seizures have been speculated to play a major role in facilitating seizures. Seizures can further impair or disrupt GABA_A signaling by reshuffling the subunit composition of its receptors or causing aberrant reappearance of depolarizing or hyperpolarizing GABA_A receptor currents. Such effects may not result in epileptogenesis as frequently as they do in adults. Given the central role of GABA_A signaling in brain function and development, perturbation of its physiological role may interfere with neuronal morphology, differentiation, and connectivity, manifesting as cognitive or neurodevelopmental deficits. The current GABAergic antiepileptic drugs, while often effective for adults, are not always capable of stopping seizures and preventing their sequelae in neonates. Recent studies have explored the therapeutic potential of chloride cotransporter inhibitors, such as bumetanide, as adjunctive therapies of neonatal seizures. However, more needs to be known so as to develop therapies capable of stopping seizures while preserving the age- and sex-appropriate development of the brain.

Functional and structural correlates of the aging brain: relating visual cortex (V1) gamma band responses to age-related structural change

The gamma band response is thought to be a key neural signature of information processing in the mammalian brain, yet little is known about how age-related maturation influences the γ-band response. Recent MRI-based studies have shown that brain maturation is accompanied by clear structural changes in both gray and white matter, yet the correspondence of these changes to brain function is unclear. The objective of this study was to relate visual cortex (V1) γ-band responses to age-related structural change. We evaluated MEG measured γ-band responses to contrast gratings stimuli and structural MRIs from participants observed from two separate research centers (MEG lab at CUBRIC, Cardiff University, UK, and the Lurie Family Foundations MEG Imaging Center, (CHOP) at the Children's Hospital of Philadelphia). Pooled participant data (N = 59) ranged in age from 8.7 to 45.3 years. We assessed linear associations between age and MEG γ-band frequency and amplitude, as well as between age and MRI volumetric parameters of the occipital lobe. Our MEG findings revealed a significant negative correlation for gamma band frequency versus age. Volumetric brain analysis from the occipital lobe also revealed significant negative correlations between age and the cortical thickness of pericalcarine and cuneus areas. Our functional MEG and structural MRI findings shows regionally specific changes due to maturation and may thus be informative for understanding physiological processes of neural development, maturation, and age-related decline. In addition, this study represents (to our knowledge), the first published demonstration of multicenter data sharing across MEG centers.

Iomazenil hyperfixation in single photon emission computed tomography study of malformations of cortical development during infancy

We present 2 cases of malformations of cortical development and early onset epilepsy. The first case is of a patient with left hemimegalencephaly who developed focal epilepsy at the age of 2 days and cluster spasms at 1.5 months. After left functional hemispherectomy, seizures originated from the contralateral hemisphere, which had shown normal signals in the preoperative magnetic resonance imaging study. The second case is of a patient with lissencephaly, caused by a missense mutation in the doublecortin gene, who developed West syndrome at the age of 5 months. In both the cases, (123)I-iomazenil single photon emission computed tomography performed during infancy showed significant hyperfixation in the dysplastic lesions. This finding indicates the immaturity of the affected neurons and a gamma-aminobutyric acidergic involvement in epileptogenesis associated with malformations of cortical development during infancy.

Mutation screening of three Chinese families with genetic epilepsy with febrile seizures plus

Genetic epilepsy with febrile seizures plus (GEFS+) is a familial autosomal dominant condition characterized by genetic heterogeneity. Five genes for GEFS+ identified in large families account for only a small proportion of families. Mutation in the majority of families with GEFS+ has not identified yet. The aim of our study is to search for the gene responsible for GEFS+ in three Chinese families by linkage analyses and a sequencing approach and to investigate the importance of coding and noncoding regions variations of four known GEFS+ genes (SCN1A, SCN1B, GABRG2 and SCN2A) in Chinese families. Results showed that a 6-cM candidate interval at 5q33-34 with a maximum LOD scores of 2.043 was identified in families B. Sequencing candidate gene GABRG2 and GABRA1 in this region did not identify a causative mutation. Moreover, no mutation was found in coding and noncoding regions of the four genes in three Chinese families. Besides excluding coding regions of four known GEFS+ genes, we also excluded the possibility of a mutation in the promoter, exon-intron boundaries, 5' untranslated regions (5' UTRs), and 3' UTRs of four known GEFS+ genes in three Chinese families. In conclusion, the present study demonstrates the heterogeneity of the etiologies of GEFS+. There are as yet undiscovered mechanisms underlying GEFS+.

Altered GABA(A) receptor subunit expression and pharmacology in human Angelman syndrome cortex

The neurodevelopmental disorder Angelman syndrome is most frequently caused by deletion of the maternally derived chromosome 15q11-q13 region, which includes not only the causative UBE3A gene, but also the beta(3)-alpha(5)-gamma(3) GABA(A) receptor subunit gene cluster. GABAergic dysfunction has been hypothesized to contribute to the occurrence of epilepsy and cognitive and behavioral impairments in this condition. In the present study, analysis of GABA(A) receptor subunit expression and pharmacology was performed in cerebral cortex from four subjects with Angelman syndrome and compared to that from control tissue. The membrane fraction of frozen postmortem neocortical tissue was isolated and subjected to quantitative Western blot analysis. The ratios of beta(3)/beta(2) and alpha(5)/alpha(1) subunit protein expression in Angelman syndrome cortex were significantly decreased when compared with controls. An additional membrane fraction was injected into Xenopus oocytes, resulting in incorporation of the brain membrane vesicles with their associated receptors into the oocyte cellular membrane. Two-electrode voltage-clamp analysis of GABA(A) receptor currents was then performed. Studies of GABA(A) receptor pharmacology in Angelman syndrome cortex revealed increased current enhancement by the alpha(1)-selective benzodiazepine-site agonist zolpidem and by the barbiturate phenobarbital, while sensitivity to current inhibition by zinc was decreased. GABA(A) receptor affinity and modulation by neurosteroids were unchanged. This shift in GABA(A) receptor subunit expression and pharmacology in Angelman syndrome is consistent with impaired extrasynaptic but intact to augmented synaptic cortical GABAergic inhibition, which could contribute to the epileptic, behavioral, and cognitive phenotypes of the disorder.