Amygdaloid Kindling and the GABA System

The effect of increased brain GABA levels on fully kindled amygdala seizures was investigated in Long-Evans rats. The newly synthesized GABA-transaminase inhibitor, -Γ-acetylenic GABA (GAG) administered on four consecutive days (100 mg/kg, followed by 50 mg/kg, i.p.) was found to either significantly reduce, or eliminate entirely, the behavioral seizures normally produced by amygdala stimulation. The effect is seen after the first injection of GAG although its magnitude was greater on subsequent days. Behavioral seizures reappeared 2 to 3 days after termination of GAG treatment. The duration of electrographic seizures (self-sustained amygdala after-discharge) was either unchanged or greater on the first day of GAG treatment, but was briefer on subsequent days. The duration of afterdischarges returned to normal levels 1 to 2 days earlier than the behavioral seizures after the termination of GAG. Picrotoxin (1.5-2 mg/kg, i.p.) did not antagonize either electrographic or behavioral effects of inhibition produced with GAG. Electrical stimulation of amygdala delivered during the initial sedation stage induced by picrotoxin resulted in further regression of kindled seizures in the majority of animals. Although in doses employed, GAG alleviates amygdaloid-kindled seizures its use requires caution in view of its ability to reduce arousal level. RÉSUMÉ L'effet de l'ÉlÉvation des taux cÉrÉbraux de GABA sur les crises amygdaliennes par effet d'embrasement complet a ÉtÉÉtudiÉ chez des rats Long-Evans. l'injection pendant 4 jours consÉcutifs de 100 mg/kg suivis de 50 mg/kg i.p. d'un inhibiteur de la GABA. Transaminase nouvellement synthÉtisÉ (Γ-acetylenic GABA ou GAG) a significativement rÉduit ou mÊme supprimÉ les crises normalement provoquÉes par la stimulation amygdalienne. l'effet est observÉ aprÈs la premiere injection de GAG, mais son importance s'accroit les jours suivants. Les crises rÉapparaissent 2 ou 3 jours aprÈs la fin du traitement au GAG. Du point de vue Électrographique, la durÉe de la postdÉcharge amygdalienne autoentretenue est inchingÉe ou accrue le premier jour du traitement, mais elle diminue les jours suivants pour retourner À la normale un ou deux jours avant que les crises ne rÉapparaissent aprÈs la fin de ('administration du GAG. l'injection de picrotoxine (1.5-2 mg/kg i.p.) ne s'oppose pas aux effets inhibiteurs du GAG sur les crises ou leur accompagnement EEG. La stimulation Électrique de l'amygdala pendant l'Étape sÉdative initiate induite par la picrotoxine provoque une rÉgression supplÉmentaire des crises d'embrasement chez la majoritÉ des animaux. Bien que, aux doses utilisÉes, le GAG attÉnue les crises amyg-daliennes d'embrasement, son utilisation nÉcessite des prÉcautions compte tenu de sa tendance À rÉduire le niveau d'Éveil. RESUMEN En ratas Long-Evans se ha investigado el efecto del aumento de los niveles cerebrales de GABA, sobre los ataques originados en la amÍgdala totalmente condicionada, (Kindling). El recientemente sintetizado in-hibidor de la GABA transaminasa, Γ-acetilÉnico GABA (GAG), redujo significativamente o eliminÓ totalmente las crisis de comportamiento que habitualmente se producen con la estimulaciÓn de la amÍgdala. El efecto se observa despuÉs de la primera in-yecciÓn de GAG pero su magnitud aumentÓ en dias subsiguientes. Las crisis de comportamiento reaparecieron a los 2–3 dÍas de la interrupciÓn del tratamiento con GAG. La duraciÓn de los ataques electrogrÁficos (perservaciÓn de la post-descarga de la amigdala) no se modificÓ, o incluso aumentÓ, en el primer dia de la administraciÓn de GAG pero se redujo en los dias siguientes. La duraciÓn de las post-descargas volviÓ a sus niveles normales 1 o 2 dias antes que la reapariciÓn de las crisis de comportamiento una vez terminado el tratamiento con GAG. La picrotoxina (1.5-2 mg/kg, i.p.) no antagonizÓ los efectos inhibitorios producidos por el GAG sobre el electroencefalograma o las crisis de comportamiento. La estimulaciÓn elÉctrica sobre la amÍgdala, aplicada durante la fase de sedaciÓn inicial inducida por la picrotoxina, condujo a una regresiÓn aÚn mÁs intensa de las crisis condicionadas, en la mayorÍa de los animales. A pesar de que, con las dosis utilizadas, el GAG alivia las crisis de la amÍgdala previamente condicionada, se requiere gran precauciÓn en su utilizaciÓn en vista de su propiedad de reducir el nivel del despertar. ZUSAMMENFASSUNG Die Wirkung erhÖhter GABA-Spiegel des Gehirns auf AmygdalonkrÄmpfe nach Kindling wurden bei Long-Evans-Ratten untersucht. Der neuerdings synthetisierte GABA-TYansaminasen-Inhibitor, Gamma-Acetylen-GABA (GAG) wurde an 4 aufeinander-folgenden Tagen in einer Dosis von 100 mg/kg und anschlieliend 50 mg/kg i.p. verabfolgt. Er reduzierte entweder signifikant oder eliminierte vÖllig die anfalls-weisen VerhaltensÄnderungen, die normalerweise durch Stimulation des Amygdalon produziert wurden. Die Wirkung ist nach der Erstinjektion des GAG zu beobachten, obgleich ihr Ausmaß an folgenden Tagen grÖßer war. Die VerhaltensanfÄlle kamen 2 bis 3 Tagen nach Beendigung der GAG-Behandlung wieder. Die Dauer der elektrographischen AnfÄlle (sich selbst un-terhaltende Amydalonnachentladungen) blieben entweder gleich oder sie wurden grÖßer am 1. Tag der GAG-Behandlung, wurden aber kÜrzer an folgenden Tagen. Die Dauer der Nachentladungen nor-malisierte sich 1 bis 2 Tage frÜher als die VerhaltensanfÄlle nach Beendigung des GAG verschwanden. Picrotoxin (1.5 bis 2 mg/kg i.p.) wirken nicht als Antagonist gegenÜber der durch GAG produzierten Hemmung der elektrographischen-oder Verhalten-seffekte. Die elektrische Stimulierung des Amygdalon wÄhrend der initialen Sedierung nach Picrotoxin ver-ursachte bei der Mehrzahl der Tiere einen weiteren RÜckgang der durch Kindling entstandenen AnfÄlle. Obgleich das GAG in den verwandten Dosen, die durch Kindling des Amygdalon erzeugten KrÄmpfe leichter ablaufen lUßt, erfordert seine Anwendung Vorsicht hinsichtlich seiner FÄhigkeit, das Erreg-barkeitsniveau zu senken.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66112/1/j.1528-1157.1980.tb04058.x.pd

Folding Circular Permutants of IL-1β: Route Selection Driven by Functional Frustration

Interleukin-1β (IL-1β) is the cytokine crucial to inflammatory and immune response. Two dominant routes are populated in the folding to native structure. These distinct routes are a result of the competition between early packing of the functional loops versus closure of the β-barrel to achieve efficient folding and have been observed both experimentally and computationally. Kinetic experiments on the WT protein established that the dominant route is characterized by early packing of geometrically frustrated functional loops. However, deletion of one of the functional loops, the β-bulge, switches the dominant route to an alternative, yet, as accessible, route, where the termini necessary for barrel closure form first. Here, we explore the effect of circular permutation of the WT sequence on the observed folding landscape with a combination of kinetic and thermodynamic experiments. Our experiments show that while the rate of formation of permutant protein is always slower than that observed for the WT sequence, the region of initial nucleation for all permutants is similar to that observed for the WT protein and occurs within a similar timescale. That is, even permutants with significant sequence rearrangement in which the functional-nucleus is placed at opposing ends of the polypeptide chain, fold by the dominant WT “functional loop-packing route”, despite the entropic cost of having to fold the N- and C- termini early. Taken together, our results indicate that the early packing of the functional loops dominates the folding landscape in active proteins, and, despite the entropic penalty of coalescing the termini early, these proteins will populate an entropically unfavorable route in order to conserve function. More generally, circular permutation can elucidate the influence of local energetic stabilization of functional regions within a protein, where topological complexity creates a mismatch between energetics and topology in active proteins

A low mortality, high morbidity Reduced Intensity Status Epilepticus (RISE) model of epilepsy and epileptogenesis in the rat

Animal models of acquired epilepsies aim to provide researchers with tools for use in understanding the processes underlying the acquisition, development and establishment of the disorder. Typically, following a systemic or local insult, vulnerable brain regions undergo a process leading to the development, over time, of spontaneous recurrent seizures. Many such models make use of a period of intense seizure activity or status epilepticus, and this may be associated with high mortality and/or global damage to large areas of the brain. These undesirable elements have driven improvements in the design of chronic epilepsy models, for example the lithium-pilocarpine epileptogenesis model. Here, we present an optimised model of chronic epilepsy that reduces mortality to 1% whilst retaining features of high epileptogenicity and development of spontaneous seizures. Using local field potential recordings from hippocampus in vitro as a probe, we show that the model does not result in significant loss of neuronal network function in area CA3 and, instead, subtle alterations in network dynamics appear during a process of epileptogenesis, which eventually leads to a chronic seizure state. The model’s features of very low mortality and high morbidity in the absence of global neuronal damage offer the chance to explore the processes underlying epileptogenesis in detail, in a population of animals not defined by their resistance to seizures, whilst acknowledging and being driven by the 3Rs (Replacement, Refinement and Reduction of animal use in scientific procedures) principles

Effects of Cocaine-Kindling on the Expression of NMDA Receptors and Glutamate Levels in Mouse Brain

In the present study we examined the effects of cocaine seizure kindling on the expression of NMDA receptors and levels of extracellular glutamate in mouse brain. Quantitative autoradiography did not reveal any changes in binding of [3H] MK-801 to NMDA receptors in several brain regions. Likewise, in situ hybridization and Western blotting revealed no alteration in expression of the NMDA receptor subunits, NR1 and NR2B. Basal overflow of glutamate in the ventral hippocampus determined by microdialysis in freely moving animals also did not differ between cocaine-kindled and control groups. Perfusion with the selective excitatory amino acid transporter inhibitor, pyrrolidine-2,4-dicarboxylic acid (tPDC, 0.6 mM), increased glutamate overflow confirming transport inhibition. Importantly, KCl-evoked glutamate overflow under tPDC perfusion was significantly higher in cocaine-kindled mice than in control mice. These data suggest that enhancement of depolarization stimulated glutamate release may be one of the mechanisms underlying the development of increased seizure susceptibility after cocaine kindling

A-Type GABA Receptor as a Central Target of TRPM8 Agonist Menthol

Menthol is a widely-used cooling and flavoring agent derived from mint leaves. In the peripheral nervous system, menthol regulates sensory transduction by activating TRPM8 channels residing specifically in primary sensory neurons. Although behavioral studies have implicated menthol actions in the brain, no direct central target of menthol has been identified. Here we show that menthol reduces the excitation of rat hippocampal neurons in culture and suppresses the epileptic activity induced by pentylenetetrazole injection and electrical kindling in vivo. We found menthol not only enhanced the currents induced by low concentrations of GABA but also directly activated GABAA receptor (GABAAR) in hippocampal neurons in culture. Furthermore, in the CA1 region of rat hippocampal slices, menthol enhanced tonic GABAergic inhibition although phasic GABAergic inhibition was unaffected. Finally, the structure-effect relationship of menthol indicated that hydroxyl plays a critical role in menthol enhancement of tonic GABAAR. Our results thus reveal a novel cellular mechanism that may underlie the ambivalent perception and psychophysical effects of menthol and underscore the importance of tonic inhibition by GABAARs in regulating neuronal activity

Inducible cAMP Early Repressor (ICER) and Brain Functions

The inducible cAMP early repressor (ICER) is an endogenous repressor of cAMP-responsive element (CRE)-mediated gene transcription and belongs to the CRE-binding protein (CREB)/CRE modulator (CREM)/activating transcription factor 1 (ATF-1) gene family. ICER plays an important role in regulating the neuroendocrine system and the circadian rhythm. Other aspects of ICER function have recently attracted heightened attention. Being a natural inducible CREB antagonist, and more broadly, an inducible repressor of CRE-mediated gene transcription, ICER regulates long-lasting plastic changes that occur in the brain in response to incoming stimulation. This review will bring together data on ICER and its functions in the brain, with a special emphasis on recent findings highlighting the involvement of ICER in the regulation of long-term plasticity underlying learning and memory

Search for light top squark pair production in final states with leptons and b -jets with the ATLAS detector in s=7\sqrt{s}=7 TeV proton-proton collisions

The results of a search for pair production of light top squarks are presented, using 4.7 fb^-1 of sqrt(s) = 7 TeV proton-proton collisions collected with the ATLAS detector at the Large Hadron Collider. This search targets top squarks with masses similar to, or lighter than, the top quark mass. Final states containing exclusively one or two leptons (e, mu), large missing transverse momentum, light-jets and b-jets are used to reconstruct the top squark pair system. Global mass scale variables are used to separate the signal from a large ttbar background. No excess over the Standard Model expectations is found. The results are interpreted in the framework of the Minimal Supersymmetric Standard Model, assuming the top squark decays exclusively to a chargino and a b-quark. Light top squarks with masses between 123-167 GeV are excluded for neutralino masses around 55 GeV

A saturated map of common genetic variants associated with human height

Common single-nucleotide polymorphisms (SNPs) are predicted to collectively explain 40-50% of phenotypic variation in human height, but identifying the specific variants and associated regions requires huge sample sizes(1). Here, using data from a genome-wide association study of 5.4 million individuals of diverse ancestries, we show that 12,111 independent SNPs that are significantly associated with height account for nearly all of the common SNP-based heritability. These SNPs are clustered within 7,209 non-overlapping genomic segments with a mean size of around 90 kb, covering about 21% of the genome. The density of independent associations varies across the genome and the regions of increased density are enriched for biologically relevant genes. In out-of-sample estimation and prediction, the 12,111 SNPs (or all SNPs in the HapMap 3 panel(2)) account for 40% (45%) of phenotypic variance in populations of European ancestry but only around 10-20% (14-24%) in populations of other ancestries. Effect sizes, associated regions and gene prioritization are similar across ancestries, indicating that reduced prediction accuracy is likely to be explained by linkage disequilibrium and differences in allele frequency within associated regions. Finally, we show that the relevant biological pathways are detectable with smaller sample sizes than are needed to implicate causal genes and variants. Overall, this study provides a comprehensive map of specific genomic regions that contain the vast majority of common height-associated variants. Although this map is saturated for populations of European ancestry, further research is needed to achieve equivalent saturation in other ancestries.A large genome-wide association study of more than 5 million individuals reveals that 12,111 single-nucleotide polymorphisms account for nearly all the heritability of height attributable to common genetic variants

A saturated map of common genetic variants associated with human height.

Common single-nucleotide polymorphisms (SNPs) are predicted to collectively explain 40-50% of phenotypic variation in human height, but identifying the specific variants and associated regions requires huge sample sizes1. Here, using data from a genome-wide association study of 5.4 million individuals of diverse ancestries, we show that 12,111 independent SNPs that are significantly associated with height account for nearly all of the common SNP-based heritability. These SNPs are clustered within 7,209 non-overlapping genomic segments with a mean size of around 90 kb, covering about 21% of the genome. The density of independent associations varies across the genome and the regions of increased density are enriched for biologically relevant genes. In out-of-sample estimation and prediction, the 12,111 SNPs (or all SNPs in the HapMap 3 panel2) account for 40% (45%) of phenotypic variance in populations of European ancestry but only around 10-20% (14-24%) in populations of other ancestries. Effect sizes, associated regions and gene prioritization are similar across ancestries, indicating that reduced prediction accuracy is likely to be explained by linkage disequilibrium and differences in allele frequency within associated regions. Finally, we show that the relevant biological pathways are detectable with smaller sample sizes than are needed to implicate causal genes and variants. Overall, this study provides a comprehensive map of specific genomic regions that contain the vast majority of common height-associated variants. Although this map is saturated for populations of European ancestry, further research is needed to achieve equivalent saturation in other ancestries