Marlien W. Aalbers

Misplaced NMDA receptors in epileptogenesis contribute to excitotoxicity

Pharmacological blockade of NR2B-containing N-methyl-d-aspartate receptors (NMDARs) during epileptogenesis reduces neurodegeneration provoked in the rodent hippocampus by status epilepticus. The functional consequences of NMDAR activation are crucially influenced by their synaptic vs extrasynaptic localization, and both NMDAR function and localization are dependent on the presence of the NR2B subunit and its phosphorylation state. We investigated whether changes in NR2B subunit phosphorylation, and alterations in its neuronal membrane localization and cellular expression occur during epileptogenesis, and if these changes are involved in neuronal cell loss. We also explored NR2B subunit changes both in the acute phase of status epilepticus and in the chronic phase of spontaneous seizures which encompass the epileptogenesis phase. Levels of Tyr1472 phosphorylated NR2B subunit decreased in the post-synaptic membranes from rat hippocampus during epileptogenesis induced by electrical status epilepticus. This effect was concomitant with a reduced interaction between NR2B and post-synaptic density (PSD)-95 protein, and was associated with decreased CREB phosphorylation. This evidence suggests an extra-synaptic localization of NR2B subunit in epileptogenesis. Accordingly, electron microscopy showed increased NR2B both in extra-synaptic and pre-synaptic neuronal compartments, and a concomitant decrease of this subunit in PSD, thus indicating a shift in NR2B membrane localization. De novo expression of NR2B in activated astrocytes was also found in epileptogenesis indicating ectopic receptor expression in glia. The NR2B phosphorylation changes detected at completion of status epilepticus, and interictally in the chronic phase of spontaneous seizures, are predictive of receptor translocation from synaptic to extrasynaptic sites. Pharmacological blockade of NR2B-containing NMDARs by ifenprodil administration during epileptogenesis significantly reduced pyramidal cell loss in the hippocampus, showing that the observed post-translational and cellular changes of NR2B subunit contribute to excitotoxicity. Therefore, pharmacological targeting of misplaced NR2B-containing NMDARs, or prevention of these NMDAR changes, should be considered to block excitotoxicity which develops after various pro-epileptogenic brain injuries.

Vagus nerve stimulation in children with intractable epilepsy: a randomized controlled trial

Aim  The aim of this study was to evaluate the effects of vagus nerve stimulation (VNS) in children with intractable epilepsy on seizure frequency and severity and in terms of tolerability and safety.

Animal models for vagus nerve stimulation in epilepsy

Vagus nerve stimulation (VNS) is a moderately effective adjunctive treatment for patients suffering from medically refractory epilepsy and is explored as a treatment option for several other disorders. The present review provides a critical appraisal of the studies on VNS in animal models of seizures and epilepsy. So far, these studies mostly applied short-term VNS in seizure models, demonstrating that VNS can suppress and prevent seizures and affect epileptogenesis. However, the mechanism of action is still largely unknown. Moreover, studies with a clinically more relevant setup where VNS is chronically applied in epilepsy models are scarce. Future directions for research and the application of this technology in animal models of epilepsy are discussed.

Behavioural and cognitive effects during vagus nerve stimulation in children with intractable epilepsy – A randomized controlled trial

BACKGROUND/AIMS In addition to effects on seizure frequency in intractable epilepsy, multiple studies report benefits of vagus nerve stimulation (VNS) on behavioural outcomes and quality of life. The present study aims to investigate the effects of VNS on cognition, mood in general, depression, epilepsy-related restrictions and psychosocial adjustment in children with intractable epilepsy, as well as the relation between these effects and seizure reduction. METHODS We conducted a randomized, active-controlled, double-blinded, add-on study in 41 children (age 4-18) with medically refractory epilepsy. We performed cognitive and behavioural testing at baseline (12 weeks), at the end of the blinded phase (20 weeks) in children receiving either high-output or low-output (active control) stimulation, and at the end of the open label phase (19 weeks) with all children receiving high-output stimulation. Seizure frequency was recorded using seizure diaries. RESULTS VNS did not have a negative effect on cognition nor on psychosocial adjustment. At the end of the follow-up phase we noted an improvement of mood in general and the depression subscale for the entire group, unrelated to a reduction of seizure frequency. At the end of the blinded phase a ≥50% reduction of seizure frequency occurred in 16% of the high-stimulation group and 21% of the low-stimulation group. At the end of the open-label follow-up phase, 26% of the children experienced a seizure frequency reduction of 50% or more (responders). CONCLUSIONS VNS has additional beneficial effects in children with intractable epilepsy. As opposed to anti-epileptic drugs, there are no negative effects on cognition. Moreover, we observed an improvement of mood in general and depressed feelings in particular, irrespective of a reduction in seizure frequency. These beneficial effects should be taken into account when deciding whether to initiate or continue VNS treatment in these children.

Acute seizure-suppressing effect of vagus nerve stimulation in the amygdala kindled rat

PURPOSE Vagus nerve stimulation (VNS) is a moderately effective anti-epileptic treatment. Clinically relevant animal models that are suitable to study the mechanism of action of VNS are not available. The aim of the current study was to develop a clinically relevant animal model for VNS-treated epilepsy that can be used to study the mechanism of action of VNS. METHODS The anticonvulsive effect of VNS was studied in fully kindled rats by measuring behavioral and electrophysiological parameters. Afferent vagus nerve activation was confirmed by quantifying nNOS immunoreactive cells in the nucleus of the solitary tract (NTS). RESULTS VNS rats had more nNOS immunoreactive cells/mm(2) in the NTS than shams. VNS induced a >25% decrease in stage 5 duration (S5D) in 32% of rats. Prior to VNS this type of responders suffered from seizures with a longer total seizure duration (TSD) than non-responders. In 21% of rats VNS resulted in a >25% decrease in TSD. This type of responders had a shorter TSD prior to VNS than non-responders. In 29% of rats VNS resulted in >200% increase in stage 5 latency (S5L). This type of responders had higher kindling rates than non-responders. CONCLUSION The VNS-treated kindled rat is a clinically relevant animal model because it is a chronic epilepsy model that responds to VNS with effects that are comparable to the effects of VNS in epilepsy patients. In addition, this study demonstrates that VNS-treated kindled rats can be used to study the mode of action of VNS using immunohistochemical techniques.

A possible role of dystrophin in neuronal excitability: a review of the current literature.

Duchenne muscular dystrophy (DMD) is a recessive hereditary form of muscular dystrophy caused by a mutation in the dystrophin gene on the X chromosome. Clinical observations show that in addition to progressive muscular degeneration, DMD is more often accompanied by neurocognitive symptoms and learning disabilities, especially in automatisation of reading, attention processes, and expressive language skills. Additionally, three studies reported a higher prevalence of epilepsy in DMD, suggesting that the absence of dystrophin might be related to increased CNS excitability. In this article, we aim to review current clinical and experimental evidence for a potential role of brain dystrophin in seizure generation.

Horner's syndrome: a complication of experimental carotid artery surgery in rats.

PURPOSE To report on the occurrence of iatrogenic Horners syndrome (HS) in epileptic rats after implantation of an electrode for vagus nerve stimulation and to describe the possible consequences of this new complication of carotid artery surgery in rats. METHODS A bipolar circular electrode was placed around the left carotid artery and vagus nerve of 31 rats. The incidence of HS was evaluated by visual inspection within 24 h after surgery. RESULTS 68% of rats suffered from HS immediately after surgery. This complication did not affect epileptogenesis. CONCLUSION The occurrence of HS in the rat is a frequent complication of vagus nerve electrode implantation, which does not affect epileptogenesis in this study. However, rats affected by HS may suffer from damage to the sympathetic innervation of the gut, due to rat-specific neuroanatomy. Therefore, caution towards other research questions is warranted.

Tonic GABAA Receptors as Potential Target for the Treatment of Temporal Lobe Epilepsy

Tonic GABAA receptors are a subpopulation of receptors that generate long-lasting inhibition and thereby control network excitability. In recent years, these receptors have been implicated in various neurological and psychiatric disorders, including Parkinson’s disease, schizophrenia, and epilepsy. Their distinct subunit composition and function, compared to phasic GABAA receptors, opens the possibility to specifically modulate network properties. In this review, the role of tonic GABAA receptors in epilepsy and as potential antiepileptic target will be discussed.

Why should I prepare? a mixed method study exploring the motives of medical undergraduate students to prepare for clinical skills training sessions

BackgroundAlthough preparation for educational activities is considered beneficial for student learning, many students do not perform preparatory assignments. This phenomenon has received little attention in the literature although it might provide medical educators with the opportunity to enhance student learning. Therefore, we explored why students prepare or not prepare.MethodsAn explorative mixed methods study was performed. In a qualitative study, 24 short group interviews with medical undergraduate students (n=209) were conducted on why they prepared for skills training sessions. In a subsequent quantitative study the resulting themes were used to construct a questionnaire. The questionnaire was presented to all undergraduate medical students at Maastricht University and 847 students completed it. Scales were constructed by a combination of exploratory factor analysis, reliability analysis, and content analysis. Between-class differences in the scale scores were investigated using ANOVA.ResultsThe qualitative study showed that students’ opinions on preparation are influenced by both personal factors, categorized as ‘personal learning style’, ‘attitudes and beliefs’, and ‘planning and organization’, as well as external factors, including ‘preparatory advice’, ‘pressure, consequence, and checking of preparation’, ‘teacher-related motivations’, and ‘contents and schedule of the training sessions’. The quantitative study showed that ‘the objective structured clinical examination’ and ‘facilitation of both understanding and memorizing the learning material’, were the two most motivating items. The two most demotivating aspects were ‘other students saying that preparation was not useful’ and ‘indistinct preparatory advices’. Factor analyses yielded three scales: ‘urge to learn’, ‘expected difficulties’, and ‘lack of motivation‘. Between group differences were found between the three classes on the first two scales.ConclusionsStudents make an active and complex choice whether to prepare or not, based on multiple factors. Practical implications for educational practice are discussed.

The Effects of Vagus Nerve Stimulation on Pro- and Anti-Inflammatory Cytokines in Children with Refractory Epilepsy: An Exploratory Study

Objectives: The vagus nerve has important immunological and anti-inflammatory actions that might be relevant to the beneficial effects of vagus nerve stimulation (VNS). Therefore, we conducted an exploratory study on VNS effects on cytokine levels in plasma and cerebrospinal fluid of children suffering from refractory epilepsy. Moreover, as predictors of the response are lacking, we also aimed to determine if cytokine changes predict the clinical response. Methods: VNS was performed according to a randomized double-blind design: plasma levels were compared between patients who received 20 weeks of high output (therapeutic) (n = 21) or low output (active control) stimulation (n = 20). Thereupon, all patients received high output stimulation for another 19 weeks; levels during this period were compared to baseline. Interictal interleukin-1β, interleukin-6, and interleukin-10 were determined by ELISA. Results: No significant changes were found between high and low output groups and between the last 19 weeks of stimulation and baseline. Changes in interleukin-1β correlated with improved IQ (τ = 0.42, p < 0.01). Lower baseline plasma levels of interleukin-6 were associated with more seizure frequency reduction [R2 = 0.105 (1, 35), p = 0.050]. Conclusion: Interictal cytokine levels were not altered by VNS but baseline interleukin-6 predicted the clinical response. In the future, patient selection may be aided by determination of the cytokine profile of the patient.