Infraslow oscillations modulate excitability and interictal epileptic activity in the human cortex during sleep

Human cortical activity has been intensively examined at frequencies ranging from 0.5 Hz to several hundred Hz. Recent studies have, however, reported also infraslow fluctuations in neuronal population activity, magnitude of electroencephalographic oscillations, discrete sleep events, as well as in the occurrence of interictal events. Here we use direct current electroencephalography to demonstrate large-scale infraslow oscillations in the human cortex at frequencies ranging from 0.02 to 0.2 Hz. These oscillations, which are not detectable in conventional electroencephalography because of its limited recording bandwidth (typical lower limit 0.5 Hz), were observed in widespread cortical regions. Notably, the infraslow oscillations were strongly synchronized with faster activities, as well as with the interictal epileptic events and K complexes. Our findings suggest that the infraslow oscillations represent a slow, cyclic modulation of cortical gross excitability, providing also a putative mechanism for the as yet enigmatic aggravation of epileptic activity during sleep.     

BDNF modulates GABAA receptors microtransplanted from the human epileptic brain to Xenopus oocytes

Cell membranes isolated from brain tissues, obtained surgically from six patients afflicted with drug-resistant temporal lobe epilepsy and from one nonepileptic patient afflicted with a cerebral oligodendroglioma, were injected into frog oocytes. By using this approach, the oocytes acquire human GABAA receptors, and we have shown previously that the "epileptic receptors" (receptors transplanted from epileptic brains) display a marked run-down during repetitive applications of GABA. It was found that exposure to the neurotrophin BDNF increased the amplitude of the "GABA currents" (currents elicited by GABA) generated by the epileptic receptors and decreased their run-down; both events being blocked by K252A, a neurotrophin tyrosine kinase receptor B inhibitor. These effects of BDNF were not mimicked by nerve growth factor. In contrast, the GABAA receptors transplanted from the nonepileptic human hippocampal uncus (obtained during surgical resection as part of the nontumoral tissue from the oligodendroglioma margins) or receptors expressed by injecting rat recombinant alpha1beta2gamma2 GABAA receptor subunit cDNAs generated GABA currents whose time-course and run-down were not altered by BDNF. Loading the oocytes with the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetate-acetoxymethyl ester (BAPTA-AM), or treating them with Rp-8-Br-cAMP, an inhibitor of the cAMP-dependent PKA, did not alter the GABA currents. However, staurosporine (a broad spectrum PK inhibitor), bisindolylmaleimide I (a PKC inhibitor), and U73122 (a phospholipase C inhibitor) blocked the BDNF-induced effects on the epileptic GABA currents. Our results indicate that BDNF potentiates the epileptic GABAA currents and antagonizes their use-dependent run-down, thus strengthening GABAergic inhibition, probably by means of activation of tyrosine kinase receptor B receptors and of both PLC and PKC.     

Adenosine receptor antagonists alter the stability of human epileptic GABAA receptors

We examined how the endogenous anticonvulsant adenosine might influence γ-aminobutyric acid type A (GABA_A) receptor stability and which adenosine receptors (ARs) were involved. Upon repetitive activation (GABA 500 μM), GABA_A receptors, microtransplanted into Xenopus oocytes from neurosurgically resected epileptic human nervous tissues, exhibited an obvious GABA_A-current (I_GABA) run-down, which was consistently and significantly reduced by treatment with the nonselective adenosine receptor antagonist CGS15943 (100 nM) or with adenosine deaminase (ADA) (1 units/ml), that inactivates adenosine. It was also found that selective antagonists of A2B (MRS1706, 10 nM) or A3 (MRS1334, 30 nM) receptors reduced I_GABA run-down, whereas treatment with the specific A1 receptor antagonist DPCPX (10 nM) was ineffective. The selective A2A receptor antagonist SCH58261 (10 nM) reduced or potentiated I_GABA run-down in ≈40% and ≈20% of tested oocytes, respectively. The ADA-resistant, AR agonist 2-chloroadenosine (2-CA) (10 μM) potentiated I_GABA run-down but only in ≈20% of tested oocytes. CGS15943 administration again decreased I_GABA run-down in patch-clamped neurons from either human or rat neocortex slices. I_GABA run-down in pyramidal neurons was equivalent in A1 receptor-deficient and wt neurons but much larger in neurons from A2A receptor-deficient mice, indicating that, in mouse cortex, GABA_A-receptor stability is tonically influenced by A2A but not by A1 receptors. I_GABA run-down from wt mice was not affected by 2-CA, suggesting maximal ARs activity by endogenous adenosine. Our findings strongly suggest that cortical A2–A3 receptors alter the stability of GABA_A receptors, which could offer therapeutic opportunities.     

Serum prolactin level and lactate dehydrogenase activity in patients with epileptic and nonepileptic seizures: A cross-sectional study

It is important to diagnose epilepsy in a timely and accurate manner, and also to distinguish it from non-epileptic conditions. The present study was aimed at determining postictal serum prolactin levels and lactate dehydrogenase (LDH) activities in patients with new-onset seizure admitted to the emergency department in order to assess whether they could be used in the differentiation of epileptic seizure (ES) from nonepileptic seizure (NES).Eighty-five patients were included prospectively in this study. Patients were divided into 2 groups with respect to epilepsy diagnosis, and the final groups were comprised of 36 patients with ES and 49 patients with NES. Blood samples were obtained within 1 hour of seizure.No significant differences between groups were observed in prolactin levels and in the percentage of patients with abnormal prolactin level (P = .569 and .239, respectively). The median LDH activity was significantly higher in those with ES compared with those with NES (P = .031). The percentage of patients with elevated LDH levels was similar between 2 groups (P = .286).This was the first study to examine LDH activities in terms of its role in differentiation of seizure origin in the postictal period in patients hospitalized with seizure. Our study demonstrated that serum LDH activities within 1 hour after the seizure appear to be increased in patients with ES compared with those with NES, suggesting the potential role of LDH activities as a diagnostic tool in distinction of seizure types. Our study supports the hypothesis that LDH-antagonists may have a role in the management of seizure and epilepsy.     

A molecular mechanism underlying the neural-specific defect in torsinA mutant mice

A striking but poorly understood feature of many diseases is the unique involvement of neural tissue. One example is the CNS-specific disorder DYT1 dystonia, caused by a 3-bp deletion (“ΔE”) in the widely expressed gene TOR1A. Disease mutant knockin mice (Tor1a^ΔE/ΔE) exhibit disrupted nuclear membranes selectively in neurons, mimicking the tissue specificity of the human disease and providing a model system in which to dissect the mechanisms underlying neural selectivity. Our in vivo studies demonstrate that lamina-associated polypeptide 1 (LAP1) and torsinB function with torsinA to maintain normal nuclear membrane morphology. Moreover, we show that nonneuronal cells express dramatically higher levels of torsinB and that RNAi-mediated depletion of torsinB (but not other torsin family members) causes nuclear membrane abnormalities in Tor1a^ΔE/ΔE nonneuronal cells. The Tor1a^ΔE/ΔE neural selective phenotype therefore arises because high levels of torsinB protect nonneuronal cells from the consequences of torsinA dysfunction, demonstrating how tissue specificity may result from differential susceptibility of cell types to insults that disrupt ubiquitous biological pathways.     

依达拉奉对癫痫大鼠海马中MDR1产物P-gp表达的影响

目的研究自由基清除剂依达拉奉对癫痫持续状态(SE)大鼠海马中多药耐药基因(MDR1)产物P-糖蛋白(P-gp)表达的影响,以探讨自由基清除剂对难治性癫痫(IE)的防治作用。方法成年SD大鼠随机分为对照组、模型组、依达拉奉组。采用氯化锂-毛果芸香碱腹腔注射制备癫痫持续状态模型,经腹腔注射给药,依达拉奉组于造模成功后即刻腹腔注射依达拉奉,2次/d,3 d后断头取海马,免疫组化检测P-gp表达,图像分析测其表达的灰度值。结果模型组P-gp表达明显高于对照组及依达拉奉组(P<0.01)。结论癫痫发作本身可能是IE的成因,依达拉奉通过清除自由基减轻神经元损伤,进而抑制P-gp表达,可能成为防治IE的有效方法。     

4E-BP2–dependent translation in parvalbumin neurons controls epileptic seizure threshold

The mechanistic/mammalian target of rapamycin complex 1 (mTORC1) integrates multiple signals to regulate critical cellular processes such as mRNA translation, lipid biogenesis, and autophagy. Germline and somatic mutations in mTOR and genes upstream of mTORC1, such as PTEN, TSC1/2, AKT3, PIK3CA, and components of GATOR1 and KICSTOR complexes, are associated with various epileptic disorders. Increased mTORC1 activity is linked to the pathophysiology of epilepsy in both humans and animal models, and mTORC1 inhibition suppresses epileptogenesis in humans with tuberous sclerosis and animal models with elevated mTORC1 activity. However, the role of mTORC1-dependent translation and the neuronal cell types mediating the effect of enhanced mTORC1 activity in seizures remain unknown. The eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) and 2 (4E-BP2) are translational repressors downstream of mTORC1. Here we show that the ablation of 4E-BP2, but not 4E-BP1, in mice increases the sensitivity to pentylenetetrazole (PTZ)- and kainic acid (KA)–induced seizures. We demonstrate that the deletion of 4E-BP2 in inhibitory, but not excitatory neurons, causes an increase in the susceptibility to PTZ-induced seizures. Moreover, mice lacking 4E-BP2 in parvalbumin, but not somatostatin or VIP inhibitory neurons exhibit a lowered threshold for seizure induction and reduced number of parvalbumin neurons. A mouse model harboring a human PIK3CA mutation that enhances the activity of the PI3K-AKT pathway (Pik3ca^H1047R-Pvalb) selectively in parvalbumin neurons shows susceptibility to PTZ-induced seizures. Our data identify 4E-BP2 as a regulator of epileptogenesis and highlight the central role of increased mTORC1-dependent translation in parvalbumin neurons in the pathophysiology of epilepsy.

Epilepsy is a prevalent (0.5 to 1% of the general population) (1) heterogeneous neurological disorder affecting all age groups and is characterized by seizures and associated psychological and social stigmas (2–4). Hyperactivation of the mechanistic/mammalian target of rapamycin (mTOR) pathway has been reported in brain lesions of epileptic patients with neurodevelopmental disorders (5, 6), and human genetic studies have shown that mutations in mTOR (7, 8) and other components of its pathway are linked to epileptogenesis (6, 9–13). mTOR is a highly conserved serine/threonine protein kinase that forms two distinct complexes: mTORC1 and mTORC2. mTORC1 integrates multiple environmental and intracellular signals to modulate brain functions by controlling key cellular processes such as mRNA translation, nucleotide, lipid and mitochondrial biogenesis, and autophagy (14, 15). Germline or somatic mutations, which result in enhanced mTORC1 activity, including in PIK3CA, PTEN, AKT3, TSC1/2, RHEB, and MTOR, are associated with neurodevelopmental disorders with epilepsy (16–23). Recent studies have also identified mutations in mTORC1 upstream amino acid–sensing GATOR1-KICSTOR-Rag GTPase pathways as a common cause of epilepsy (24), revealing that mutations in GATOR1 (DEPDC5, NPRL2, and NPRL3) (25, 26) and KICSTOR (ITFG2, KPTN, SZT2, and C12ORF66) (6, 7, 27) genes are often found in epileptic pathologies. The link between the mTORC1 and epilepsy has been recapitulated in animal models with enhanced mTORC1 activity (e.g., Pten^+/−, TSC1/2^+/−, and activating mutations in Pik3ca Nestin-Cre knockin (KI), Akt3 KI, MTOR, and Rheb KI) (18, 20, 23, 28–31) while inhibition of mTORC1 reversed epileptogenesis in TSC1^GFAP-Cre and Pten^+/− mice (20, 31). Notably, the mTORC1 rapalog, everolimus, has been approved by the US Food and Drug Administration (FDA) for the treatment of epilepsy in tuberous sclerosis complex (TSC) patients (32, 33).mTORC1 is a master regulator of mRNA translation. Upon activation, mTORC1 phosphorylates S6 protein kinases 1 and 2 (S6K1/2) and 4E-binding proteins (4E-BPs) (34, 35). In the hypophosphorylated form, 4E-BPs bind and prevent the association of the cap-binding protein eIF4E with the large scaffolding protein eIF4G, thereby inhibiting the formation of the eIF4F complex (composed of eIF4E, eIF4G, and an mRNA helicase eIF4A), which is essential for the initiation of cap-dependent translation. Phosphorylation of 4E-BPs by mTORC1 results in the release of eIF4E from 4E-BPs, allowing eIF4F complex formation and initiation of translation (36, 37). Among the three 4E-BP family members (4E-BP1, 4E-BP2, and 4E-BP3), 4E-BP2 is the most abundant paralog in the mammalian brain (38, 39). A recent study (5) has identified aberrant activation of eIF4E as a major mechanism for translational changes in focal malformations of cortical development (FMCD), a condition that is often caused by brain somatic activating mutations in MTOR and presents with intractable epilepsy in children, accompanied by developmental abnormalities and autism spectrum disorder (ASD) (5, 40–42). Increased eIF4E activity has a pathogenic role in inducing epileptic seizures in FMCD as eIF4E knockdown prevented spontaneous seizures in mTOR Cys1483Tyr and Leu2427Pro mutant mice (5), which show mTORC1 hyperactivation.Despite the progress in understanding the causal link between enhanced mTORC1 activity and epilepsy, the mTORC1-downstream molecular mechanisms promoting epileptogenesis and the cell types mediating the effect on seizure threshold and severity remain poorly understood. In this work, we investigated the role of two main mTORC1-downstream effectors, 4E-BP1 and 4E-BP2, in regulating seizure susceptibility and studied the neuronal cell types mediating epileptogenic effects. We report that mice with whole-body or parvalbumin neuron–specific deletion of 4E-BP2 exhibit reduced threshold and increased severity of epileptic seizures. Moreover, we show that Pik3ca^H1047R-Pvalb mutant mice harboring a conditional parvalbumin neuron–specific KI gain-of-function mutation (H1047R) in the PIK3CA kinase domain are prone to seizures. Collectively, these findings demonstrate a central role of 4E-BP2 and parvalbumin neurons in mediating mTORC1-dependent epileptogenesis, thus expanding our understanding of cell type–specific molecular mechanisms of translation dysregulation in epilepsy and other neurodevelopmental disorders.     

老年人癫痫发作的临床特征分析

目的探讨老年人癫痫发作的临床表现、病因及其诊断与鉴别诊断。方法回顾性分析139例患者的临床资料,其中癫痫发作125例,非癫痫发作误诊为癫痫发作14例。结果主要病因为脑血管病(46.4%),其次为病因不详(29.6%)。125例癫痫发作患者中,部分性发作86例(68.8%),全面性发作39例(31.2%);53例行常规脑电图检查,12例(22.6%)出现非特异性异常,1例(1.9%)出现癫痫样电发放;43例行长程视频脑电图检查,38例(88.4%)出现癫痫样电发放。14例非癫痫发作均误诊为癫痫发作。结论脑血管病是老年患者癫痫发作最常见的病因,部分性发作为老年患者癫痫发作最常见的发作形式。Todd麻痹和非抽搐性癫痫持续状态为癫痫发作的特殊形式,极易误诊。代谢障碍性疾病、晕厥、短暂性全面性遗忘、短暂性脑缺血发作所致的非癫痫发作与癫痫发作的鉴别诊断较为困难。     

Spontaneous seizure and memory loss in mice expressing an epileptic encephalopathy variant in the calmodulin-binding domain of Kv7.2

Epileptic encephalopathy (EE) is characterized by seizures that respond poorly to antiseizure drugs, psychomotor delay, and cognitive and behavioral impairments. One of the frequently mutated genes in EE is KCNQ2, which encodes the K_v7.2 subunit of voltage-gated K_v7 potassium channels. K_v7 channels composed of K_v7.2 and K_v7.3 are enriched at the axonal surface, where they potently suppress neuronal excitability. Previously, we reported that the de novo dominant EE mutation M546V in human K_v7.2 blocks calmodulin binding to K_v7.2 and axonal surface expression of K_v7 channels via their intracellular retention. However, whether these pathogenic mechanisms underlie epileptic seizures and behavioral comorbidities remains unknown. Here, we report conditional transgenic cKcnq2^+/M547V mice, in which expression of mouse K_v7.2-M547V (equivalent to human K_v7.2-M546V) is induced in forebrain excitatory pyramidal neurons and astrocytes. These mice display early mortality, spontaneous seizures, enhanced seizure susceptibility, memory impairment, and repetitive behaviors. Furthermore, hippocampal pathology shows widespread neurodegeneration and reactive astrocytes. This study demonstrates that the impairment in axonal surface expression of K_v7 channels is associated with epileptic seizures, cognitive and behavioral deficits, and neuronal loss in KCNQ2-related EE.

Epileptic encephalopathies (EEs) are a collection of heterogeneous disorders in which early-onset severe seizures contribute to developmental delay and progressive cognitive and behavioral impairments (1). Current treatments for EEs have limited efficacy in alleviating seizures and comorbidities (2), posing an urgent need to understand the etiology of EEs and find new therapeutic targets. Recent discoveries of epilepsy-related genes in multiple laboratories and through the large Epi4K, EpiPM, and EuroEPINOMICS-RES consortia have identified a diverse array of proteins that may contribute to epileptogenesis (3–5). Among them, dominant variants associated with benign familial neonatal epilepsy (BFNE) and EE have been found in KCNQ2 and KCNQ3 genes, which encode the K_v7.2 and K_v7.3 subunits of voltage-gated potassium (K⁺) channel subfamily Q (K_v7) (https://www.rikee.org; ClinVar Database, National Center for Biotechnology Information [NCBI]).Neuronal K_v7 channels are mostly heterotetrameric channels of K_v7.2 and K_v7.3 subunits (6), which have overlapping distribution in the central nervous system including the cerebral cortex and hippocampus (7). In neurons, they are preferentially localized to the axonal plasma membrane with the highest concentration at the axonal initial segment (AIS) (7, 8), where the action potential (AP) initiates (9). They give rise to the slowly activating and noninactivating outward K⁺ current termed M current (I_M) (6). Because they open at subthreshold potentials (6), I_M potently suppresses AP firing (6, 10, 11), underscoring their critical roles in reducing neuronal excitability. By contrast, activation of G_q-coupled receptors, including muscarinic acetylcholine receptors, inhibits I_M by depleting the lipid cofactor PIP₂, resulting in enhanced AP firing (12).To date, 193 dominant variants in KCNQ2 and 2 variants in KCNQ3 have been identified in patients with EE (https://www.rikee.org; ClinVar Database, NCBI). EE variants are clustered at the functional domains of K_v7.2 important for voltage-dependent opening of K_v7 channels (13) and typically decrease the function of heterotetrameric channels by 20 to 75% (13–17). EE variants are also enriched at helices A and B in the intracellular C-terminal tail of K_v7.2 (13, 14, 16), which mediate calmodulin (CaM) binding critical for axonal enrichment of K_v7 channels (18). Among these variants, a mutation of methionine at amino acid position 546 to valine (M546V) was found in a male patient who displayed drug-resistant neonatal tonic-clonic seizures and later developed profound intellectual and language disability, spasticity, and autistic behavior (15). While this mutation in helix B abolishes current expression of homomeric but not heteromeric channels in heterologous cells (14, 17), it severely reduces CaM binding and axonal surface expression of heteromeric channels in cultured hippocampal neurons (14). This mutation also induces ubiquitination and proteasomal degradation of K_v7.2, whereas the presence of K_v7.3 blocks this degradation and accumulates ubiquitinated K_v7.2 (14). However, whether these pathogenic mechanisms underlie epileptic seizures and behavioral deficits in EE remains unknown.In this study, we investigated the contribution of the EE variant M546V by generating conditional transgenic mice in which heterozygous expression of mouse K_v7.2-M547V was induced in forebrain excitatory pyramidal neurons. M546 in the human K_v7.2 is conserved in the mouse K_v7.2 at amino acid position 547. These mice showed widespread neurodegeneration and reactive astrogliosis in the hippocampus and cortex, and displayed spontaneous seizures and cognitive deficit, providing a causal link between M546V-mediated disruption of axonal surface expression of K_v7 channels and KCNQ2-associated EE.     

Hierarchical timescales in the neocortex: Mathematical mechanism and biological insights

A cardinal feature of the neocortex is the progressive increase of the spatial receptive fields along the cortical hierarchy. Recently, theoretical and experimental findings have shown that the temporal response windows also gradually enlarge, so that early sensory neural circuits operate on short timescales whereas higher-association areas are capable of integrating information over a long period of time. While an increased receptive field is accounted for by spatial summation of inputs from neurons in an upstream area, the emergence of timescale hierarchy cannot be readily explained, especially given the dense interareal cortical connectivity known in the modern connectome. To uncover the required neurobiological properties, we carried out a rigorous analysis of an anatomically based large-scale cortex model of macaque monkeys. Using a perturbation method, we show that the segregation of disparate timescales is defined in terms of the localization of eigenvectors of the connectivity matrix, which depends on three circuit properties: 1) a macroscopic gradient of synaptic excitation, 2) distinct electrophysiological properties between excitatory and inhibitory neuronal populations, and 3) a detailed balance between long-range excitatory inputs and local inhibitory inputs for each area-to-area pathway. Our work thus provides a quantitative understanding of the mechanism underlying the emergence of timescale hierarchy in large-scale primate cortical networks.

The brain is organized with a delicate structure to integrate and process both spatial and temporal information received from the external world. For spatial information processing, neurons along cortical visual pathways possess increasingly large spatial receptive fields, and its underlying mechanism has been understood as neurons in higher-level visual areas receive input from many neurons with smaller receptive fields in lower-level visual areas, thereby aggregating information across space (1). More recently, a computational model (2) revealed that the timescale over which neural integration occurs also gradually increases from area to area along the cortical hierarchy. The model was based on the anatomically measured directed- and weighted-interareal connectivity of the macaque cortex (3) and incorporated heterogeneity of synaptic excitation calibrated by spine count per pyramidal neuron (4). It has been observed that the decay times increased progressively along the cortical hierarchy when signals propagate in the network, and the temporal hierarchy could change dynamically in response to different types of sensory inputs (e.g., different hierarchy of timescales for somatosensory input versus visual input) (2). By manipulating parameters of the model, simulation results further demonstrated that both within and between regions of anatomical properties could affect the hierarchy of timescales in neuronal population activity (2). A hierarchy of temporal receptive windows is functionally desirable, so that the circuit dynamics operate on short timescales in early sensory areas to encode and process rapidly changing external stimuli, whereas parietal and frontal areas can accumulate information over a relatively long period of time in decision-making and other cognitive processes (5, 6).Despite the accumulating evidence in support of timescale hierarchy across cortical areas in mice (7, 8), monkeys (9–15), and humans (16–23), its underlying mechanism remains unclear. In particular, since interareal connections are dense, with roughly 65% of all possible connections present in the macaque cortex (3) and even higher connection density in the mouse cortex (24), what circuit properties are required to ensure that dynamical modes with disparate time constants are spatially localized? How do intraareal anatomical properties determine the intrinsic timescale of each area, and how do these intrinsic timescales remain to be segregated rather than mixed up in the presence of dense interareal connections? In this work, we addressed these questions by a mathematical analysis of the model (2). Using a perturbation method, we identified key required conditions, in particular a detailed excitation–inhibition balance for long-distance interareal connections that is experimentally testable.     

A key mechanism underlying sensory experience-dependent maturation of neocortical GABAergic circuits in vivo

Mechanisms underlying experience-dependent refinement of cortical connections, especially GABAergic inhibitory circuits, are unknown. By using a line of mutant mice that lack activity-dependent BDNF expression (bdnf-KIV), we show that experience regulation of cortical GABAergic network is mediated by activity-driven BDNF expression. Levels of endogenous BDNF protein in the barrel cortex are strongly regulated by sensory inputs from whiskers. There is a severe alteration of excitation and inhibition balance in the barrel cortex of bdnf-KIV mice as a result of reduced inhibitory but not excitatory conductance. Within the inhibitory circuits, the mutant barrel cortex exhibits significantly reduced levels of GABA release only from the parvalbumin-expressing fast-spiking (FS) interneurons, but not other interneuron subtypes. Postnatal deprivation of sensory inputs markedly decreased perisomatic inhibition selectively from FS cells in wild-type but not bdnf-KIV mice. These results suggest that postnatal experience, through activity-driven BDNF expression, controls cortical development by regulating FS cell-mediated perisomatic inhibition in vivo.     

Blockage of A2A and A3 adenosine receptors decreases the desensitization of human GABAA receptors microtransplanted to Xenopus oocytes

We previously found that the endogenous anticonvulsant adenosine, acting through A_2A and A₃ adenosine receptors (ARs), alters the stability of currents (I_GABA) generated by GABA_A receptors expressed in the epileptic human mesial temporal lobe (MTLE). Here we examined whether ARs alter the stability (desensitization) of I_GABA expressed in focal cortical dysplasia (FCD) and in periglioma epileptic tissues. The experiments were performed with tissues from 23 patients, using voltage-clamp recordings in Xenopus oocytes microinjected with membranes isolated from human MTLE and FCD tissues or using patch-clamp recordings of pyramidal neurons in epileptic tissue slices. On repetitive activation, the epileptic GABA_A receptors revealed instability, manifested by a large I_GABA rundown, which in most of the oocytes (≈70%) was obviously impaired by the new A_2A antagonists ANR82, ANR94, and ANR152. In most MTLE tissue-microtransplanted oocytes, a new A₃ receptor antagonist (ANR235) significantly improved I_GABA stability. Moreover, patch-clamped pyramidal neurons from human neocortical slices of periglioma epileptic tissues exhibited altered I_GABA rundown on ANR94 treatment. Our findings indicate that antagonizing A_2A and A₃ receptors increases the I_GABA stability in different epileptic tissues and suggest that adenosine derivatives may offer therapeutic opportunities in various forms of human epilepsy.     

A simple mechanism underlying the behavior of reentrant atrial tachycardia during ablation

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Pattern of trauma determines the threshold for epileptic activity in a model of cortical deafferentation

Epileptic activity often occurs in the cortex after a latent period after head trauma; this delay has been attributed to the destabilizing influence of homeostatic synaptic scaling and changes in intrinsic properties. However, the impact of the spatial organization of cortical trauma on epileptogenesis is poorly understood. We addressed this question by analyzing the dynamics of a large-scale biophysically realistic cortical network model subjected to different patterns of trauma. Our results suggest that the spatial pattern of trauma can greatly affect the propensity for developing posttraumatic epileptic activity. For the same fraction of lesioned neurons, spatially compact trauma resulted in stronger posttraumatic elevation of paroxysmal activity than spatially diffuse trauma. In the case of very severe trauma, diffuse distribution of a small number of surviving intact neurons alleviated posttraumatic epileptogenesis. We suggest that clinical evaluation of the severity of brain trauma should take into account the spatial pattern of the injured cortex.     

Nonrandom connectivity of the epileptic dentate gyrus predicts a major role for neuronal hubs in seizures

Many complex neuronal circuits have been shown to display nonrandom features in their connectivity. However, the functional impact of nonrandom network topologies in neurological diseases is not well understood. The dentate gyrus is an excellent circuit in which to study such functional implications because proepileptic insults cause its structure to undergo a number of specific changes in both humans and animals, including the formation of previously nonexistent granule cell-to-granule cell recurrent excitatory connections. Here, we use a large-scale, biophysically realistic model of the epileptic rat dentate gyrus to reconnect the aberrant recurrent granule cell network in four biologically plausible ways to determine how nonrandom connectivity promotes hyperexcitability after injury. We find that network activity of the dentate gyrus is quite robust in the face of many major alterations in granule cell-to-granule cell connectivity. However, the incorporation of a small number of highly interconnected granule cell hubs greatly increases network activity, resulting in a hyperexcitable, potentially seizure-prone circuit. Our findings demonstrate the functional relevance of nonrandom microcircuits in epileptic brain networks, and they provide a mechanism that could explain the role of granule cells with hilar basal dendrites in contributing to hyperexcitability in the pathological dentate gyrus.     

Allelic dropout in long QT syndrome genetic testing: A possible mechanism underlying false-negative results

BACKGROUND: Genetic testing for congenital long QT syndrome (LQTS) has been performed in research laboratories for the past decade. Approximately 75% of patients with high clinical probability for LQTS have a mutation in one of five LQTS-causing cardiac channel genes. Possible explanations for the remaining genotype-negative cases include LQTS mimickers, novel LQTS-causing genes, unexplored regions of the known genes, and genetic testing detection failures. OBJECTIVES: The purpose of this study was to explore the possibility of allelic dropout as a possible mechanism underlying false-negative test results. METHODS: The published primers currently used by many research laboratories to conduct a comprehensive analysis of the 60 translated exons in the KCNQ1 (LQT1), KCNH2 (LQT2), SCN5A (LQT3), KCNE1 (LQT5), and KCNE2 (LQT6) genes were analyzed for the presence of common intronic single nucleotide polymorphisms (SNPs). Repeat mutational analysis, following primer/amplicon redesign using polymerase chain reaction, denaturing high-performance liquid chromatography, and DNA sequencing, was performed on a cohort of 541 consecutive, unrelated patients referred for LQTS genetic testing. RESULTS: Common (>1% minor allele frequency) intronic SNPs were discovered within the primer sequences of five of 60 translated exons. Following primer redesign to eliminate the possibility of allelic dropout, four previously genotype-negative index cases were found to possess LQTS-causing mutations: R591H-KCNQ1 and R594Q-KCNQ1 for exon 15 and E229X-KCNH2 in two unrelated cases. Repeat examination of these two amplicons in 400 reference alleles did not identify these or any additional amino acid variants. CONCLUSION: Allelic dropout secondary to intronic SNP-primer mismatch prevented the discovery of LQTS-causing mutations in four cases. Considering that many LQTS genetic testing research laboratories have used these primers, patients who reportedly are genotype negative may benefit from re-examination of those regions susceptible to allelic dropout due to primer-disrupting SNPs, particularly exon 15 in KCNQ1 and exon 4 in KCNH2.     

Cumulative inactivation of the outward potassium current: a likely mechanism underlying electrical memory in human atrial myocytes

The influence of the mode of cell stimulation on the outward K+ current (I(o)) was studied in whole-cell patch-clamped human atrial myocytes. Acceleration of the rate of membrane depolarization at 1 Hz or during prolonged 5-s test pulses at 0.1 Hz increased the rate and extent of I(o) inactivation, resulting in enhanced inactivating (4.9+/-0.6 v 6.3+/-0.7 pA/pF) and suppressed maintained (5.9+/-1.2 v 3.2+/-0.3 pA/pF) current components. These alterations were associated with a leftward shift of the voltage-dependency of I(o), and persisted on returning to a control depolarization protocol (750-ms test pulses delivered at 0.1 Hz). The effects of increasing external K+ concentrations (40 m m) on the kinetics of I(o) were more pronounced following both rapid and prolonged depolarization (changes in I(t)/I(o)caused by 40 m m K+: 8.9+/-3.5% v 15.5+/-3.1% before and after prolonged depolarization; and 9.2+/-1.2% v 15.4+/-1.7% before and after rapid depolarization). The phosphatase inhibitor, okadaic acid, enhanced the effect of rapid and prolonged depolarization on I(o)whereas the inhibition of Ca2+/calmodulin-dependent protein kinase II (CaMK-II) with KN-62 or KN-93, or by intracellular application of the autocamtide-2-related inhibitory peptide, suppressed it. In conclusion, rapid and prolonged membrane depolarization both cause a cumulative increase in the rate and extent of I(o)inactivation. This process involves slow potassium channel inactivation mechanisms, is regulated by CaMK-II, and may contribute to the electrical memory of the atrial myocardium.     

Circadian variation in ischemic threshold. A mechanism underlying the circadian variation in ischemic events.

BACKGROUND. There is a circadian pattern in the occurrence of cardiac events in patients with coronary artery disease. Whether changes in coronary vascular tone contribute to these phenomena is unknown. We measured the ischemic threshold, defined as either the heart rate or rate-pressure product at 1-mm ST segment depression during treadmill exercise and used it as an index of the lowest coronary vascular resistance; the premise was that when ischemic threshold became lower, coronary vascular resistance was higher, and vice versa. METHODS AND RESULTS. Fifteen patients (group A) with stable coronary artery disease underwent four identical treadmill exercise tests in 24 hours, and ischemic threshold was measured as the heart rate at the onset of 1-mm ST depression. Before each treadmill test, postischemic forearm vascular resistance was measured after 5 minutes of forearm occlusion, using strain-gauge plethysmography. Sixteen additional patients (group B) underwent two treadmill tests at 8 AM and 1 PM, and ischemic threshold was measured as the heart rate-blood pressure product at 1-mm ST depression. A circadian variation was noted: In group A, the heart rate-derived ischemic threshold was lower at 8 AM and 9 PM compared with noon and 5 PM (p less than 0.03). Also, in group B, the rate-pressure product-derived ischemic threshold was 8 +/- 2% lower at 8 AM compared with 1 PM (p = 0.008). A circadian variation parallel to the observed variation in ischemic threshold was also noted in the postischemic forearm blood flow, which was lower in the morning and at night (p less than 0.004). There was a strong correlation between postischemic forearm blood flow and ischemic threshold (p less than 0.0001), such that ischemic threshold was lower at the time of day when postischemic forearm blood flow was lower, and vice versa. CONCLUSIONS. A lower ischemic threshold in the morning suggests that the ischemia-induced coronary vascular resistance is increased at this time, a finding supported by a similar variation in postischemic forearm vascular resistance. Parallel changes in forearm and coronary resistance suggest that generalized (neural or humoral factors) rather than local factors are responsible for the observed circadian changes. Increased coronary tone in the mornings may not only contribute to the higher incidence of transient ischemia but may help trigger acute cardiac events at this time.     

褪黑素对匹罗卡品致癫癎大鼠海马神经发生和突触重建的影响

目的探讨褪黑素(Mel)在匹罗卡品(PILO)致癫癎犬鼠模型中的抗癫癎作用机制。方法将45只Wistar大鼠按癫癎持续状态(SE)后6 h,14、28天分为PILO组(1 5只),PILO+Mel组(15只)和对照组(15只),采用PILO诱导大鼠慢性颞叶癫癎模型,用5溴-2-脱氧尿嘧啶核苷标记增殖细胞,Timms染色评价苔藓纤维发芽(MFS)等技术,动态观察MeI对癫癎大鼠海马神经发生和MFS的影响及其与反复自发性癫癎发作(SRS)发生的关系。结果与对照组比较,PILO组大鼠SE后6 h,14、28天细胞数明显增加,差异有统计学意义(P<0.01);与PILO组比较,PILO+Mel组大鼠在SE后6 h,14、28天,细胞数量明显减少(P<0.05),28天SRS数量明显减少,差异有统计学意义(P<0.05)。与PILO+Mel组比较,PILO组大鼠SE后14天,Timms染色密度开始增强,28天密度明显增强,差异有统计学意义(P<0.05)。结论Mel对SRS的预防作用可能与其对癫癎诱导的神经发生和MFS的抑制作用有关。