Focal administration of neuropeptide Y into the S2 somatosensory cortex maximally suppresses absence seizures in a genetic rat model

Structural changes in the neocortex as correlates of variations in EEG spectra and seizure susceptibility in rat brains with different degrees of dysplasia

Disturbances of the early stages of neurogenesis lead to irreversible changes in the structure of the mature brain and its functional impairment, including increased excitability, which may be the basis for drug‐resistant epilepsy. The range of possible clinical symptoms is as wide as the different stages of disturbed neurogenesis may be. In this study, we used a quadruple model of brain dysplasia by comparing structural and functional disorders in animals whose neurogenesis was disturbed with a single dose of 1 Gy of gamma rays at one of the four stages of neurogenesis, that is, on days 13, 15, 17, or 19 of prenatal development.

When reached adulthood, the prenatally irradiated rats received EEG teletransmitter implantation. Thereafter, pilocarpine was administered and significant differences in susceptibility to seizure behavioral symptoms were detected depending on the degree of brain dysplasia. Before, during, and after the seizures significant correlations were found between the density of parvalbumin‐immunopositive neurons located in the cerebral cortex and the intensity of behavioral seizure symptoms or increases in the power of particular EEG bands. Neurons expressing calretinin or NPY showed also dysplasia‐related increases without, however, correlations with parameters of seizure intensity. The results point to significant roles of parvalbumin‐expressing interneurons, and also to expression of NPY—an endogenous anticonvulsant and neuroprotectant reducing susceptibility to seizures and supporting neuronal survival.

From Physiology to Pathology of Cortico-Thalamo-Cortical Oscillations: Astroglia as a Target for Further Research

The electrographic hallmark of childhood absence epilepsy (CAE) and other idiopathic forms of epilepsy are 2.5-4 Hz spike and wave discharges (SWDs) originating from abnormal electrical oscillations of the cortico-thalamo-cortical network. SWDs are generally associated with sudden and brief non-convulsive epileptic events mostly generating impairment of consciousness and correlating with attention and learning as well as cognitive deficits. To date, SWDs are known to arise from locally restricted imbalances of excitation and inhibition in the deep layers of the primary somatosensory cortex. SWDs propagate to the mostly GABAergic nucleus reticularis thalami (NRT) and the somatosensory thalamic nuclei that project back to the cortex, leading to the typical generalized spike and wave oscillations. Given their shared anatomical basis, SWDs have been originally considered the pathological transition of 11-16 Hz bursts of neural oscillatory activity (the so-called sleep spindles) occurring during Non-Rapid Eye Movement (NREM) sleep, but more recent research revealed fundamental functional differences between sleep spindles and SWDs, suggesting the latter could be more closely related to the slow (<1 Hz) oscillations alternating active (Up) and silent (Down) cortical activity and concomitantly occurring during NREM. Indeed, several lines of evidence support the fact that SWDs impair sleep architecture as well as sleep/wake cycles and sleep pressure, which, in turn, affect seizure circadian frequency and distribution. Given the accumulating evidence on the role of astroglia in the field of epilepsy in the modulation of excitation and inhibition in the brain as well as on the development of aberrant synchronous network activity, we aim at pointing at putative contributions of astrocytes to the physiology of slow-wave sleep and to the pathology of SWDs. Particularly, we will address the astroglial functions known to be involved in the control of network excitability and synchronicity and so far mainly addressed in the context of convulsive seizures, namely (i) interstitial fluid homeostasis, (ii) K⁺ clearance and neurotransmitter uptake from the extracellular space and the synaptic cleft, (iii) gap junction mechanical and functional coupling as well as hemichannel function, (iv) gliotransmission, (v) astroglial Ca²⁺ signaling and downstream effectors, (vi) reactive astrogliosis and cytokine release.

Effects of leptin, ghrelin and neuropeptide y on spike-wave discharge activity and certain biochemical parameters in WAG/Rij rats with genetic absence epilepsy

This study aimed to evaluate the effects of leptin, ghrelin and neuropeptide-Y on the development of nonconvulsive seizure activity and their role on combating oxidative stress and cytokines produced by the systemic immune response in the WAG/Rij rat model for genetic absence epilepsy. Current study showed that all three peptides aggravated spike wave discharges activity and affected the oxidative stress in WAG/Rij rats without any significant changes in the levels of IL-1β, IL-6 and TNF-α except leptin that only induced an increment in the concentration of IL-1β. Our results support the modulatory role of these endogenous peptides on absence epilepsy.

Neuropeptide Y affects thalamic reticular nucleus neuronal firing and network synchronization associated with suppression of spike-wave discharges

OBJECTIVES

Neuropeptide Y (NPY) potently suppresses spike-wave discharges (SWDs) in a genetic rat model of absence epilepsy (GAERS), but the underlying neurophysiologic mechanisms are not clear. We therefore sought to determine the in vivo effects of NPY on neuronal firing in the cortico-thalamo-cortical network activity, known to play a critical role in the generation of SWDs in these rats.

METHODS

NPY was administered intracerebroventricularly (ICV) or in separate experiments locally on the neurons of caudal thalamic reticular nucleus (NRT) by use of juxtacellular iontophoresis in triple-barrel electrodes in male GAERS aged 12-15 weeks, in vivo under neuroleptic anesthesia. Drug infusions and electroencephalography (EEG) monitoring were performed simultaneously with juxtacellular single neuronal recordings. Effect of NPY on electrically induced SWD induction threshold were also measured.

RESULTS

NPY administration ICV led to a decrease in the total length of SWDs in EEG recordings. Both ICV administration and iontophoresis of NPY on NRT neurons led to an increase in interictal neuronal firing of NRT neurons. During ictal periods, ICV NPY administration reduced the number of thalamic action potentials per SWDs, as well as reduced waveform correlations between field potentials within the NRT and the cortical EEG. NPY administration ICV did not significantly alter the firing patterns of relay thalamic neurons interictally and cortical neurons during ictal and interictal periods. In addition, SWD induction threshold in the S2 region of the cortex was significantly increased after NPY administration.

SIGNIFICANCE

Our results show alterations in cortico-thalamo-cortical local and network properties following ICV administration of NPY, suggesting mechanisms of SWD suppression in GAERS. Cellular and network alteration of NRT activity, resulting from a direct action of NPY, may be a contributor to this effect.

Assessment of both serum S-100B protein and neuropeptide-Y levels in childhood breath-holding spells

OBJECTIVE

Breath-holding spells are common paroxysmal events in children. Although the spells have a benign prognosis in the long term, they may be complicated by loss of consciousness, tonic-clonic movements, and occasionally seizures. Hence, this study aimed to measure the levels of serum S-100B proteins and neuropeptide-Y in the blood of children who experience breath-holding spells.

METHODS

The study groups consisted of 45 patients (13 females, 32 males) with breath-holding spells and a control group of 32 healthy individuals (12 females, 20 males). The serum S-100B levels were measured using commercially available ELISA kits. The neuropeptide-Y levels in the serum were measured with RayBio® Human/Mouse/Rat Neuropeptide Y ELISA kits.

RESULTS

The mean serum S-100B protein level of the breath-holding spells group was 56.38 ± 13.26 pg/mL, and of the control group, 48.53 ± 16.77 pg/mL. The mean neuropeptide-Y level was 62.29 ± 13.89 pg/mL in the breath-holding spells group and 58.24 ± 12.30 pg/mL in the control group. There were significant differences between the groups with respect to serum S-100B protein levels (p = 0.025), while there was no statistically significant difference in neuropeptide-Y levels between the breath-holding spells group and the control group (p = 0.192).

CONCLUSIONS

The findings of this study suggest that frequent and lengthy breath-holding may lead to the development of neuronal metabolic dysfunction or neuronal damage which is most likely related to hypoxia. In light of these findings, future studies should be conducted using biochemical and radiological imaging techniques to support these results.

Transplantation of GABAergic Interneurons into the Neonatal Primary Visual Cortex Reduces Absence Seizures in Stargazer Mice

Epilepsies are debilitating neurological disorders characterized by repeated episodes of pathological seizure activity. Absence epilepsy (AE) is a poorly understood type of seizure with an estimated 30% of affected patients failing to respond to antiepileptic drugs. Thus, novel therapies are needed for the treatment of AE. A promising cell-based therapeutic strategy is centered on transplantation of embryonic neural stem cells from the medial ganglionic eminence (MGE), which give rise to gamma-aminobutyric acidergic (GABAergic) interneurons during embyronic development. Here, we used the Stargazer (Stg) mouse model of AE to map affected loci using c-Fos immunohistochemistry, which revealed intense seizure-induce activity in visual and somatosensory cortices. We report that transplantation of MGE cells into the primary visual cortex (V1) of Stg mice significantly reduces AE episodes and lowers mortality. Electrophysiological analysis in acute cortical slices of visual cortex demonstrated that Stg V1 neurons exhibit more pronounced increases in activity in response to a potassium-mediated excitability challenge than wildtypes (WT). The defective network activity in V1 was significantly altered following WT MGE transplantation, associating it with behavioral rescue of seizures in Stgs. Taken together, these findings present MGE grafting in the V1 as a possible clinical approach in the treatment of AE.

Altered expression of neuropeptide Y, Y1 and Y2 receptors, but not Y5 receptor, within hippocampus and temporal lobe cortex of tremor rats

As an endogenous inhibitor of glutamate-mediated synaptic transmission in mammalian central nervous system, neuropeptide Y (NPY) plays a crucial role in regulating homeostasis of neuron excitability. Loss of balance between excitatory and inhibitory neurotransmission is thought to be a chief mechanism of epileptogenesis. The abnormal expression of NPY and its receptors observed following seizures have been demonstrated to be related to the production of epilepsy. The tremor rat (TRM) is a hereditary epileptic animal model. So far, there is no report concerning whether NPY and its receptors may be involved in TRM pathogenesis. In this study, we focused on the expression of NPY and its three receptor subtypes: Y1R, Y2R and Y5R in the TRM brain. We first found the expression of NPY in TRM hippocampus and temporal lobe cortex was increased compared with control (Wistar) rats. The mRNA and protein expression of Y1R was down-regulated in hippocampus but up-regulated in temporal lobe cortex, whereas Y2R expression was significantly increased in both areas. There was no significant change of Y5R expression in either area. The immunohistochemistry data showed that Y1R, Y2R, Y5R were present throughout CA1, CA3, dentate gyrus (DG) and the entorhinal cortex which is included in the temporal lobe cortex of TRM. In conclusion, our results showed the altered expression of NPY, Y1R and Y2R but not Y5R in hippocampus and temporal lobe cortex of TRM brain. This abnormal expression may be associated with the generation of epileptiform activity and provide a candidate target for treatment of genetic epilepsy.

Neuropeptides in epilepsy

Neuropeptides play an important role in modulating seizures and epilepsy. Unlike neurotransmitters which operate on a millisecond time-scale, neuropeptides have longer half lives; this leads to modulation of neuronal and network activity over prolonged periods, so contributing to setting the seizure threshold. Most neuropeptides are stored in large dense vesicles and co-localize with inhibitory interneurons. They are released upon high frequency stimulation making them attractive targets for modulation of seizures, during which high frequency discharges occur. Numerous neuropeptides have been implicated in epilepsy; one, ACTH, is already used in clinical practice to suppress seizures. Here, we concentrate on neuropeptides that have a direct effect on seizures, and for which therapeutic interventions are being developed. We have thus reviewed the abundant reports that support a role for neuropeptide Y (NPY), galanin, ghrelin, somatostatin and dynorphin in suppressing seizures and epileptogenesis, and for tachykinins having pro-epileptic effects. Most in vitro and in vivo studies are performed in hippocampal tissue in which receptor expression is usually high, making translation to other brain areas less clear. We highlight recent therapeutic strategies to treat epilepsy with neuropeptides, which are based on viral vector technology, and outline how such interventions need to be refined in order to address human disease.

Long-term valproate treatment increases brain neuropeptide Y expression and decreases seizure expression in a genetic rat model of absence epilepsy

The mechanisms by which valproate, one of the most widely prescribed anti-epileptic drugs, suppresses seizures have not been fully elucidated but may involve up-regulation of neuropeptide Y (NPY). We investigated the effects of valproate treatment in Genetic Absence Epilepsy Rats from Strasbourg (GAERS) on brain NPY mRNA expression and seizure control. GAERS were administered either valproate (42 mg.kg⁻¹ hr⁻¹) or saline continuously for 5 days. Electroencephalograms were recorded for 24 hrs on treatment days 1, 3 and 5 and the percentage of time spent in seizure activity was analysed. NPY mRNA expression was measured in different brain regions using qPCR. Valproate treatment suppressed seizures by 80% in GAERS (p<0.05) and increased NPY mRNA expression in the thalamus (p<0.05) compared to saline treatment. These results demonstrate that long-term valproate treatment results in an upregulation of thalamic expression of NPY implicating this as a potential contributor to the mechanism by which valproate suppresses absence seizures.

Regulators of synaptic transmission: roles in the pathogenesis and treatment of epilepsy

Synaptic transmission is the communication between a presynaptic and a postsynaptic neuron, and the subsequent processing of the signal. These processes are complex and highly regulated, reflecting their importance in normal brain functioning and homeostasis. Sustaining synaptic transmission depends on the continuing cycle of synaptic vesicle formation, release, and endocytosis, which requires proteins such as dynamin, syndapin, synapsin, and synaptic vesicle protein 2A. Synaptic transmission is regulated by diverse mechanisms, including presynaptic modulators of synaptic vesicle formation and release, postsynaptic receptors and signaling, and modulators of neurotransmission. Neurotransmitters released presynaptically can bind to their postsynaptic receptors, the inhibitory γ-aminobutyric acid (GABA)ergic receptors or the excitatory glutamate receptors. Once released, glutamate activates a variety of postsynaptic receptors including α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), N-methyl-D-aspartate (NMDA), kainate, and metabotropic receptors. The activation of the receptors triggers downstream signaling cascades generating a vast array of effects, which can be modulated by a numerous auxiliary regulatory subunits. Moreover, different neuropeptides such as neuropeptide Y, brain-derived neurotrophic factor (BDNF), somatostatin, ghrelin, and galanin, act as regulators of diverse synaptic functions and along with the classic neurotransmitters. Abnormalities in the regulation of synaptic transmission play a critical role in the pathogenesis of numerous brain diseases, including epilepsy. This review focuses on the different mechanisms involved in the regulation of synaptic transmission, which may play a role in the pathogenesis of epilepsy: the presynaptic modulators of synaptic vesicle formation and release, postsynaptic receptors, and modulators of neurotransmission, including the mechanism by which drugs can modulate the frequency and severity of epileptic seizures.

Rhythmic neuronal activity in S2 somatosensory and insular cortices contribute to the initiation of absence-related spike-and-wave discharges

PURPOSE

  The origin of bilateral synchronous spike-and-wave discharges (SWDs) that underlie absence seizures has been widely debated. Studies in genetic rodent models suggest that SWDs originate from a restricted region in the somatosensory cortex. The properties of this initiation site remain unknown. Our goal was to characterize the interictal, preictal and ictal neuronal activity in the primary and secondary cortical regions (S1, S2) and in the adjacent insular cortex (IC) in Genetic Absence Epilepsy Rats from Strasbourg (GAERS).

METHODS

  We performed electroencephalography (EEG) recordings in combination with multisite local field potential (LFP) and single cell juxtacellular recordings, and cortical electrical stimulations, in freely moving rats and those under neurolept-anesthesia.

KEY FINDINGS

  The onset of the SWDs was preceded by 5-9 Hz field potential oscillations, which were detected earlier in S2 and IC than in S1. Sustained SWDs could be triggered by a 2-s train of 7-Hz electrical stimuli at a lower current intensity in S2 than in S1. In S2 and IC, subsets of neurons displayed rhythmic firing (5-9 Hz) in between seizures. S2 and IC layers V and VI neurons fired during the same time window, whereas in S1 layer VI, neurons fired before layer V neurons. Just before the spike component of each SW complex, short-lasting high-frequency oscillations consistently occurred in IC ∼20 msec before S1.

SIGNIFICANCE

  Our findings demonstrate that the S2/IC cortical areas are a critical component of the macro-network that is responsible for the generation of absence-related SWDs.