Heinz Eric Krestel

Reduced cortical inhibition in a mouse model of familial childhood absence epilepsy

Mutations in the GABAA receptor γ2 subunit are associated with childhood absence epilepsy and febrile seizures. To understand better the molecular basis of absence epilepsy in man, we developed a mouse model harboring a γ2 subunit point mutation (R43Q) found in a large Australian family. Mice heterozygous for the mutation demonstrated behavioral arrest associated with 6-to 7-Hz spike-and-wave discharges, which are blocked by ethosuximide, a first-line treatment for absence epilepsy in man. Seizures in the mouse showed an abrupt onset at around age 20 days corresponding to the childhood nature of this disease. Reduced cell surface expression of γ2(R43Q) was seen in heterozygous mice in the absence of any change in α1 subunit surface expression, ruling out a dominant-negative effect. GABAA-mediated synaptic currents recorded from cortical pyramidal neurons revealed a small but significant reduction that was not seen in the reticular or ventrobasal thalamic nuclei. We hypothesize that a subtle reduction in cortical inhibition underlies childhood absence epilepsy seen in humans harboring the R43Q mutation.

A Genetic Switch for Epilepsy in Adult Mice

Premature death from seizures afflicts gene-targeted mice expressing the Q/R site-unedited glutamate receptor subunit GluR-B(Q) of AMPA receptors in central neurons. Early seizure-related death has now been circumvented by a genetic switch that restricts GluR-B(Q) expression to forebrain principal neurons from postnatal stages onward, prominently in hippocampus and striatum and less so in cortex and amygdala. When switched on, functional receptor incorporation of GluR-B(Q) could be demonstrated by imaging evoked AMPA channel-mediated spinous Ca2+ transients in CA1 pyramidal cells. Sustained GluR-B(Q) expression in adult mice led to smaller excitatory postsynaptic responses in the CA1 region with unchanged presynaptic fiber excitability. Notably, despite the smaller excitatory response, the CA1 cells exhibited a reduced population spike threshold, which might underlie the spontaneous manifestations of epilepsy, including myocloni and generalized seizures with limbic components, observed by synchronous video monitoring and electroencephalographic recordings. No neuropathological symptoms developed when GluR-B(Q) expression was restricted to only hippocampal neurons. Our results show that seizure susceptibility is triggered by GluR-B(Q) expression also in the adult brain and that circuit hyperexcitability is not an immediate consequence of GluR-B(Q) but requires yet unknown downstream events, likely to be induced by non-Hebbian plasticity from Ca2+-permeable AMPA channels in principal neurons.

Neuronal co-expression of EGFP and β-galactosidase in mice causes neuropathology and premature death ☆

Dose-dependent co-expression of enhanced green fluorescent protein (EGFP) and beta-galactosidase (beta-gal) in the cytoplasm of forebrain neurons of two independent mouse lines resulted in growth retardation, weakness, and premature lethality. In primary motor cortex and striatum, apoptosis, glial fibrillary acidic protein proliferation, and cell loss were found. In addition, we observed aggregations of EGFP and beta-gal that colocalized with ubiquitin. GFP is unlikely to be toxic per se, as a third mouse line that expressed twice as much GFP in the cytoplasm of forebrain neurons as the two affected lines was normal. Cytoplasmic aggregations of EGFP and beta-gal occurred in affected and phenotypically normal mice suggesting a storage function rather than being detrimental. We successfully prolonged survival of affected mice with granulocyte colony-stimulating factor (GCSF) and the antibiotic minocycline. These compounds could protect neurons from EGFP and beta-gal-induced dysfunction, as demise of mice started after treatment was discontinued.

Studies on Conditional Gene Expression in the Brain

ABSTRACT: This manuscript summarizes our recent attempts to regulate in vitro and in vivo the expression of genes encoding components and regulators of the postsynaptic machinery along with marker genes such as lacZ and GFP. In particular, we studied tTA‐dependent regulation and utilized Cre in combination with reversible silencing by intron engineering of dominant negative alleles. We further present a “knockin” approach for on‐site artificial regulation of chromosomal genes.

RNA Editing—Systemic Relevance and Clue to Disease Mechanisms?

Recent advances in sequencing technologies led to the identification of a plethora of different genes and several hundreds of amino acid recoding edited positions. Changes in editing rates of some of these positions were associated with diseases such as atherosclerosis, myopathy, epilepsy, major depression disorder, schizophrenia and other mental disorders as well as cancer and brain tumors. This review article summarizes our current knowledge on that front and presents glycine receptor C-to-U RNA editing as a first example of disease-associated increased RNA editing that includes assessment of disease mechanisms of the corresponding gene product in an animal model.

Spike-triggered reaction-time EEG as a possible assessment tool for driving ability

The impact of interictal epileptic activity (IEA) on driving is a rarely investigated issue. We analyzed the impact of IEA on reaction time in a pilot study. Reactions to simple visual stimuli (light flash) in the Flash test or complex visual stimuli (obstacle on a road) in a modified car driving computer game, the Steer Clear, were measured during IEA bursts and unremarkable electroencephalography (EEG) periods. Individual epilepsy patients showed slower reaction times (RTs) during generalized IEA compared to RTs during unremarkable EEG periods. RT differences were approximately 300 ms (p < 0.001) in the Flash test and approximately 200 ms (p < 0.001) in the Steer Clear. Prior work suggested that RT differences >100 ms may become clinically relevant. This occurred in 40% of patients in the Flash test and in up to 50% in the Steer Clear. When RT were pooled, mean RT differences were 157 ms in the Flash test (p < 0.0001) and 116 ms in the Steer Clear (p < 0.0001). Generalized IEA of short duration seems to impair brain function, that is, the ability to react. The reaction‐time EEG could be used routinely to assess driving ability.

Identification of a New Genomic Hot Spot of Evolutionary Diversification of Protein Function

Establishment of phylogenetic relationships remains a challenging task because it is based on computational analysis of genomic hot spots that display species-specific sequence variations. Here, we identify a species-specific thymine-to-guanine sequence variation in the Glrb gene which gives rise to species-specific splice donor sites in the Glrb genes of mouse and bushbaby. The resulting splice insert in the receptor for the inhibitory neurotransmitter glycine (GlyR) conveys synaptic receptor clustering and specific association with a particular synaptic plasticity-related splice variant of the postsynaptic scaffold protein gephyrin. This study identifies a new genomic hot spot which contributes to phylogenetic diversification of protein function and advances our understanding of phylogenetic relationships.

Focal and Generalized Patterns of Cerebral Cortical Veins Due to Non-Convulsive Status Epilepticus or Prolonged Seizure Episode after Convulsive Status Epilepticus - A MRI Study Using Susceptibility Weighted Imaging.

Objective The aim of this study was to investigate variant patterns of cortical venous oxygenation during status epilepticus (SE) using susceptibility-weighted imaging (SWI). Methods We analyzed magnetic resonance imaging (MRI) scans of 26 patients with clinically witnessed prolonged seizures and/or EEG-confirmed SE. All MRI exams encompassed SWI, dynamic susceptibility contrast perfusion MRI (MRI-DSC) and diffusion-weighted imaging (DWI). We aimed to identify distinct patterns of SWI signal alterations that revealed regional or global increases of cerebral blood flow (CBF) and DWI restrictions. We hypothesized that SWI-related oxygenation patterns reflect ictal or postictal patterns that resemble SE or sequelae of seizures. Results Sixteen patients were examined during nonconvulsive status epilepticus (NCSE) as confirmed by EEG, a further ten patients suffered from witnessed and prolonged seizure episode ahead of imaging without initial EEG. MRI patterns of 15 of the 26 patients revealed generalized hyperoxygenation by SWI in keeping with either global or multifocal cortical hyperperfusion. Eight patients revealed a focal hyperoxygenation pattern related to focal CBF increase and three patients showed a focal deoxygenation pattern related to focal CBF decrease. Conclusions SWI-related hyper- and deoxygenation patterns resemble ictal and postictal CBF changes within a range from globally increased to focally decreased perfusion. In all 26 patients the SWI patterns were in keeping with ictal hyperperfusion (hyperoxygenation patterns) or postictal hypoperfusion (deoxygenation patterns) respectively. A new finding of this study is that cortical venous patterns in SWI can be not only focally, but globally attenuated. SWI may thus be considered as an alternative contrast-free MR sequence to identify perfusion changes related to ictal or postictal conditions.

Yawning—Its anatomy, chemistry, role, and pathological considerations

&NA; Yawning is a clinical sign of the activity of various supra‐ and infratentorial brain regions including the putative brainstem motor pattern, hypothalamic paraventricular nucleus, probably the insula and limbic structures that are interconnected via a fiber network. This interaction can be seen in analogy to other cerebral functions arising from a network or zone such as language. Within this network, yawning fulfills its function in a stereotype, reflex‐like manner; a phylogenetically old function, preserved across species barriers, with the purpose of arousal, communication, and maybe other functions including respiration. Abnormal yawning with ≥3 yawns/15 min without obvious cause arises from lesions of brain areas involved in the yawning zone, its trajectories causing a disconnection syndrome, or from alteration of network activity by physical or metabolic etiologies including medication. HighlightsPhysiological yawning occurs activity‐dependent within intact circuits of a yawning network or zone.The putative yawning center resides in the ponto‐medullary brainstem near central pattern generators for respiration and circulation, and cranial nerve motor nuclei.The insula may be a brain region for serotonin‐mediated yawning.Probably 3 supratentorial pathways fine‐tune the innate activity of the brainstem yawning center.Abnormal yawning may arise from brain lesions, pathway disconnection, or activity alteration of the yawning zone.

Virtual car accidents of epilepsy patients, interictal epileptic activity, and medication

To investigate effects of interictal epileptic activity (IEA) and antiepileptic drugs (AEDs) on reactivity and aspects of the fitness to drive for epilepsy patients.