GABAergic Neuron Deficit As An Idiopathic Generalized Epilepsy Mechanism: The Role Of BRD2 Haploinsufficiency In Juvenile Myoclonic Epilepsy

Idiopathic generalized epilepsy (IGE) syndromes represent about 30% of all epilepsies. They have strong, but elusive, genetic components and sex-specific seizure expression. Multiple linkage and population association studies have connected the bromodomain-containing gene BRD2 to forms of IGE. In mice, a null mutation at the homologous Brd2 locus results in embryonic lethality while heterozygous Brd2+/− mice are viable and overtly normal. However, using the flurothyl model, we now show, that compared to the Brd2+/+ littermates, Brd2+/− males have a decreased clonic, and females a decreased tonic-clonic, seizure threshold. Additionally, long-term EEG/video recordings captured spontaneous seizures in three out of five recorded Brd2+/− female mice. Anatomical analysis of specific regions of the brain further revealed significant differences in Brd2+/− vs +/+ mice. Specifically, there were decreases in the numbers of GABAergic (parvalbumin- or GAD67-immunopositive) neurons along the basal ganglia pathway, i.e., in the neocortex and striatum of Brd2+/− mice, compared to Brd2+/+ mice. There were also fewer GABAergic neurons in the substantia nigra reticulata (SNR), yet there was a minor, possibly compensatory increase in the GABA producing enzyme GAD67 in these SNR cells. Further, GAD67 expression in the superior colliculus and ventral medial thalamic nucleus, the main SNR outputs, was significantly decreased in Brd2+/− mice, further supporting GABA downregulation. Our data show that the non-channel-encoding, developmentally critical Brd2 gene is associated with i) sex-specific increases in seizure susceptibility, ii) the development of spontaneous seizures, and iii) seizure-related anatomical changes in the GABA system, supporting BRD2's involvement in human IGE

Update on the Role of Substantia Nigra Pars Reticulata in the Regulation of Seizures

The substantia nigra pars reticulata (SNR) represents an endogenous seizure suppressing system, which may be targeted to develop treatments for generalized or multifocal epilepsies. This review summarizes the region-, age-, and sex-specific features of the SNR-based seizure-controlling network

The role of substantia nigra pars reticulata in modulating clonic seizures is determined by testosterone levels during the immediate postnatal period

GABAergic activation of substantia nigra pars reticulata (SNR) at postnatal day (PN) 15 has sex-specific features on seizure control in vivo and electrophysiological responses in vitro. In males, the GABAA-receptor agonist muscimol has proconvulsant effects and induces depolarizing responses. In females, muscimol has no effect on seizures and evokes hyperpolarizing responses. We determined the time period during which sex hormones must be present to produce the sex-specific muscimol effects on seizures and their influence on SNR GABAA receptor-mediated postsynaptic currents. Exposure to testosterone or its metabolites (estrogen or dihydrotestosterone) during PN0-2 in females or males castrated at PN0 was sufficient to produce proconvulsant muscimol effects but did not affect the in vitro GABA responses, which remained hyperpolarizing. The data suggest that the PN0-2 period is critical for the development of the seizure-controlling SNR system; the hormonal effect on seizure control is independent from their effect on GABA conductance. © 2006 Elsevier Inc. All rights reserved

Prenatal betamethasone exposure increases corticotropin-releasing hormone expression along with increased hippocampal slice excitability in the developing hippocampus

Background: The objective of this study was to determine whether prenatal exposure to betamethasone alters hippocampal expression of corticotropin-releasing hormone (CRH) and resultant hippocampal circuit excitability. Methods: Real time (RT)-PCR and western blots were used to determine CRH mRNA and protein expression levels, respectively, in hippocampal extracts of two-week old rat pups prenatally primed with betamethasone or saline on gestational day 15. The data were compared to changes in epileptiform activity induced by kainic acid (KA) or depletion of [Mg] in combined hippocampus-entorhinal cortex slices. Results: RT-PCR analysis showed 3-fold increased levels of CRH mRNA in hippocampal extracts from prenatally betamethasone-primed pups compared to saline controls (p 0.05). Also in the low-Mg-induced epileptiform activity, there was increased excitability, in the form of enhanced inter-ictal discharges, in slices from betamethasone primed compared to saline exposed rat pups (p < 0.05). Conclusions: Our study suggests a possible mechanistic link to prenatal betamethasone priming-induced increase in postnatal hippocampal excitability that involves enhanced expression of CRH acting at CRH R2. This is important in regards to the links between prenatal stress/corticosteroid-exposure and syndromes, such as epilepsy, autism spectrum disorders and other psychiatric disorders associated with neuronal hyperexcitability

ACTH and PMX53 recover synaptic transcriptome alterations in a rat model of infantile spasms

We profiled the gene expression in the hypothalamic arcuate nuclei (ARC) of 20 male and 20 female rats to determine the infantile spasms (IS) related transcriptomic alteration of neurotransmission and recovery following two treatments. Rats were prenatally exposed to betamethasone or saline followed by repeated postnatal subjection to NMDA-triggered IS. Rats with spasms were treated with ACTH, PMX53 or saline. Since ACTH, the first line treatment for IS, has inconsistent efficacy and potential harsh side effects, PMX53, a potent complement C5ar1 antagonist, was suggested as a therapeutic alternative given its effects in other epilepsy models. Novel measures that consider all genes and are not affected by arbitrary cut-offs were used, in addition to standard statistical tests, to quantify regulation and recovery of glutamatergic, GABAergic, cholinergic, dopaminergic and serotonergic pathways. Although IS alters expression of ~30% of the ARC genes in both sexes the transcriptomic effects are 3× more severe in males than their female counterparts, as indicated by the Weighted Pathway Regulation measure. Both treatments significantly restored the ARC neurotransmission transcriptome to the non-IS condition with PMX53 performing slightly better, as measured by the Pathway Restoration Efficiency, suggesting these treatments may reduce autistic traits often associated with IS

Combined EEG/videorecordings of spontaneous seizures in <i>Brd2+/−</i> mice.

<p>(A) Scheme of head mounted electrodes with one reference (REF) in the nasal bone, one common ground in the occipital area, and active electrodes in the left and right frontal area (LF, RF, respectively) and in both occipital areas (BiO). (B) EEG recordings of interictal discharges (one indicated by an arrow) in a <i>Brd2+/−</i> mouse associated with myoclonic jerks (twitches of body musculature). (C) EEG recordings from the same mouse showing a long EEG seizure consisting of spike-and-wave pattern. Onset of seizure is marked by an arrowhead. (D) EEG recordings of spindle-shaped sharp wave episodes associated with behavioral freezing in another <i>Brd2+/−</i> mouse. Onset of two spindles (about 3 s and 1 s long) is marked by arrowheads. (E) Frozen video frames (under infrared lighting) showing onset of a violent clonic seizure (E1) in a <i>Brd2+/−</i> mouse and the end of status epilepticus (after more than an hour of clonic seizures) in the same mouse (E2).</p

Susceptibility of <i>Brd2</i> heterozygous KO mice (<i>+/-</i>) and control littermates (+/+) to flurothyl-induced seizures.

<p>Seizure threshold is depicted in µl of flurothyl necessary to induce specific seizure type (Mean±S.E.M.). (A) In females, tonic-clonic seizures in <i>Brd2+/-</i> mice had significantly lower threshold than in <i>Brd2+/+</i> littermate controls. (B) In males, clonic seizures in <i>Brd2+/−</i> mice had significantly lower threshold than in <i>Brd2+/+</i> littermate controls.</p