Govert Hoogland

Persistent sodium current in subicular neurons isolated from patients with temporal lobe epilepsy

The persistent sodium current is a common target of anti‐epileptic drugs and contributes to burst firing. Intrinsically burst firing subicular neurons are involved in the generation and spread of epileptic activity. We measured whole‐cell sodium currents in pyramidal neurons isolated from the subiculum resected in drug‐resistant epileptic patients and in rats. In half of the cells from both patients and rats, the sodium current inactivated within 500 ms at −30 mV. Others displayed a tetrodotoxin‐sensitive slowly or non‐inactivating sodium current of up to 53% of the total sodium current amplitude. Compared with the transient sodium current in the same cells, this persistent sodium current activated with normal kinetics but its voltage‐dependent activation occurred 7 mV more hyperpolarized. Depolarizing voltage steps that lasted 10 s completely inactivated the persistent sodium current. Its voltage dependence did not differ from that of the transient sodium current but its slope was less steep. The voltage dependence and kinetics of the persistent sodium current in cells from patients were not different from that in subicular cells from rats. The current density and the relative amplitude contribution were 3–4 times greater in neurons from drug‐resistant epilepsy patients. The abundant presence of persistent sodium current in half of the subicular neurons could lead to a larger number of neurons with intrinsic burst firing. The extraordinarily large amplitude of the persistent sodium current in this subset of subicular neurons might explain why these patients are susceptible to seizures and hard to treat pharmacologically.

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.

The role of interleukin-1 in seizures and epilepsy: a critical review.

Interleukin-1 (IL-1) has a multitude of functions in the central nervous system. Some of them involve mechanisms that are related to epileptogenesis. The role of IL-1 in seizures and epilepsy has been investigated in both patients and animal models. This review aims to synthesize, based on the currently available literature, the consensus role of IL-1 in epilepsy. Three lines of evidence suggest a role for IL-1: brain tissue from epilepsy patients and brain tissue from animal models shows increased IL-1 expression after seizures, and IL-1 has proconvulsive properties when applied exogeneously. However, opposing results have been published as well. More research is needed to fully establish the role of IL-1 in seizure generation and epilepsy, and to explore possible new treatment strategies that are based on interference with intracellular signaling cascades that are initiated when IL-1 binds to its receptor.

Neuropeptides as Targets for the Development of Anticonvulsant Drugs

Epilepsy is a common neurological disorder characterized by recurrent seizures. These seizures are due to abnormal excessive and synchronous neuronal activity in the brain caused by a disruption of the delicate balance between excitation and inhibition. Neuropeptides can contribute to such misbalance by modulating the effect of classical excitatory and inhibitory neurotransmitters. In this review, we discuss 21 different neuropeptides that have been linked to seizure disorders. These neuropeptides show an aberrant expression and/or release in animal seizure models and/or epilepsy patients. Many of these endogenous peptides, like adrenocorticotropic hormone, angiotensin, cholecystokinin, cortistatin, dynorphin, galanin, ghrelin, neuropeptide Y, neurotensin, somatostatin, and thyrotropin-releasing hormone, are able to suppress seizures in the brain. Other neuropeptides, such as arginine-vasopressine peptide, corticotropin-releasing hormone, enkephalin, β-endorphin, pituitary adenylate cyclase-activating polypeptide, and tachykinins have proconvulsive properties. For oxytocin and melanin-concentrating hormone both pro- and anticonvulsive effects have been reported, and this seems to be dose or time dependent. All these neuropeptides and their receptors are interesting targets for the development of new antiepileptic drugs. Other neuropeptides such as nesfatin-1 and vasoactive intestinal peptide have been less studied in this field; however, as nesfatin-1 levels change over the course of epilepsy, this can be considered as an interesting marker to diagnose patients who have suffered a recent epileptic seizure.

Monopolar versus bipolar high frequency stimulation in the rat subthalamic nucleus: differences in histological damage

The aim of the present study was to determine the effects of monopolar and bipolar high frequency stimulation (HFS) on histological damage and current flow using a commonly applied stimulus amplitude (300 microA). Bipolar HFS resulted in a large amount of histological damage whereas with monopolar HFS no damage was observed except for the electrode trajectory. Oscilloscopic readings confirmed that this was due to the application of twice as much current to the target with bipolar HFS. Our results demonstrate that there are differences in tissue damage dependent of polarity. In order to create a better comparison to the clinical condition, we suggest that the present rodent models for studying the effect of chronic HFS require further adjustment. This can be achieved by decreasing the present current densities to a level comparable to the human situation.

Tumor necrosis factor-α levels correlate with postoperative pain severity in lumbar disc hernia patients: Opposite clinical effects between tumor necrosis factor receptor 1 and 2

Summary Tumor necrosis factor‐α and its receptors demonstrated a role in the long‐term outcome of sciatic pain in patients after lumbar disc hernia surgery. ABSTRACT Lumbar disc hernia (LDH) is a leading cause of chronic pain in adults. The underlying pathology of chronic pain after discectomy remains unclear. Chronic local inflammation is considered to underlie painful symptomatology. In this context, we investigated tumor necrosis factor (TNF)‐α, TNF receptor 1 (TNFR1), and TNF receptor 2 (TNFR2) expression at the time of surgery in LDH patients and correlated it with the severity of postoperative pain. We analyzed protein and mRNA levels from muscle, ligamentum flavum (LF), annulus fibrosus (AF), and nucleus pulposus (NP) in LDH patients and scoliosis patients (SP), who served as controls. Pain assessment with the visual analogue scale (VAS) was performed 1 day before surgery and 6 weeks and 12 months postoperatively. TNF‐α protein levels were detected in AF, LF, and NP in all LDH patients, but not in SP. TNF‐α mRNA was significantly greater in LDH patients than in SP; ie, 5‐fold in AF, 3‐fold in NP, and 2‐fold in LF. For NP, TNF‐α protein levels correlated with VAS scores (r = 0.54 at 6‐week and r = 0.65 at 12‐month follow‐up). Also, TNFR1 protein levels in NP positively correlated with VAS scores (r = 0.75 at 6‐week and r = 0.80 at 12‐month follow‐up). However, TNFR2 protein levels in AF negatively correlated with VAS scores (r = −0.60 at 6 weeks and r = −0.60 at 12 months follow‐up). These data indicate that TNF‐α levels could determine the clinical outcome in LDH patients after discectomy. Moreover, the opposite correlation of TNF receptors with pain sensation suggests that an unbalanced expression plays a role in the generation of pain.

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.

Motor and non-motor behaviour in experimental Huntington's disease.

In this study, we investigated motor and non-motor behaviour in the transgenic rat model of Huntingtons disease (tgHD). In particular, we were interested in the development and changes of motor and non-motor features (anxiety, motivation and hedonia) of disease over time and their interactions. We found tgHD animals to be hyperkinetic in the open field test compared to their wild-type littermates at all ages tested, which was accompanied by reduced anxiety-like behaviour in the open field test and the elevated zero maze, but not in the home cage emergence test. No major changes were found in hedonia (sucrose intake test) and motivation for food (food intake test). Our data suggest that hyperkinetic features and reduced-anxiety in the tgHD rats are associated behaviours and are seen in the earlier stages of the disease.

Cerebellar nuclei are involved in impulsive behaviour.

Recent anatomical and clinical evidence has shown that the cerebellum, primarily considered a motor control structure, is also involved in higher cognitive functions and behavioural changes, such as impulsive behaviour. Impulsive behaviour has been shown in several studies to be increased by lesions of the mediodorsal (MD) thalamic nucleus. We performed deep brain stimulation (DBS) of the mediodorsal and ventrolateral (VL) thalamic nuclei in rats, clinically mimicking such a lesion, and tested them for changes in impulsive behaviour in a choice reaction time test. We then analysed the effects of this stimulation on c-Fos expression in both the deep cerebellar nuclei (DCbN) and the prefrontal cortex (PFC), and correlated these outcomes to the measured changes in impulsive behaviour. DBS of the MD thalamic nucleus increased impulsive behaviour without changing motor parameters. This was accompanied by a decrease in the c-Fos expression in all cerebellar nuclei; with a corresponding increase in c-Fos expression in the PFC. DBS of the VL thalamic nucleus caused no significant change in behaviour or c-Fos expression in either region. The present study demonstrates that impulsive behaviour involves the cerebellar nuclei, possibly through a decreased selective attention caused by a disruption of the cerebello-thalamo-cortical pathways through the MD thalamic nucleus.

Short-and long-term limbic abnormalities after experimental febrile seizures

Experimental febrile seizures (FS) are known to promote hyperexcitability of the limbic system and increase the risk for eventual temporal lobe epilepsy (TLE). Early markers of accompanying microstructural and metabolic changes may be provided by in vivo serial MRI. FS were induced in 9-day old rats by hyperthermia. Quantitative multimodal MRI was applied 24 h and 8 weeks later, in rats with FS and age-matched controls, and comprised hippocampal volumetry and proton spectroscopy, and cerebral T2 relaxometry and diffusion tensor imaging (DTI). At 9 weeks histology was performed. Hippocampal T2 relaxation time elevations appeared to be transient. DTI abnormalities detected in the amygdala persisted up to 8 weeks. Hippocampal volumes were not affected. Histology showed increased fiber density and anisotropy in the hippocampus, and reduced neuronal surface area in the amygdala. Quantitative serial MRI is able to detect transient, and most importantly, long-term FS-induced changes that reflect microstructural alterations.