Genetic Model Of Absence Epilepsy Research Articles

Barrel cortex development lacks a key stage of hyperconnectivity from deep to superficial layers in a rat model of Absence Epilepsy

During development of the sensory cortex, the ascending innervation from deep to upper layers provides a temporary scaffold for the construction of other circuits that remain at adulthood. Whether an alteration in this sequence leads to brain dysfunction in neuro-developmental diseases remains unknown. Using functional approaches in a genetic model of Absence Epilepsy (GAERS), we investigated in barrel cortex, the site of seizure initiation, the maturation of excitatory and inhibitory innervations onto layer 2/3 pyramidal neurons and cell organization into neuronal assemblies. We found that cortical development in GAERS lacks the early surge of connections originating from deep layers observed at the end of the second postnatal week in normal rats and the concomitant structuring into multiple assemblies. Later on, at seizure onset (1 month old), excitatory neurons are hyper-excitable in GAERS when compared to Wistar rats. These findings suggest that early defects in the development of connectivity could promote this typical epileptic feature and/or its comorbidities.

Behavioral and Cognitive Comorbidities in Genetic Rat Models of Absence Epilepsy (Focusing on GAERS and WAG/Rij Rats).

Absence epilepsy is a non-convulsive type of epilepsy characterized by the sudden loss of awareness. It is associated with thalamo-cortical impairment, which may cause neuropsychiatric and neurocognitive problems. Rats with spontaneous absence-like seizures are widely used as in vivo genetic models for absence epilepsy; they display behavioral and cognitive problems similar to epilepsy in humans, such as genetic absence epilepsy rats from Strasbourg (GAERS) and Wistar Albino rats from Rijswijk (WAG/Rij). Depression- and anxiety-like behaviors were apparent in GAERS, but no anxiety and depression-like symptoms were found in WAG/Rij rats. Deficits in executive functions and memory impairment in WAG/Rij rats, i.e., cognitive comorbidities, were linked to the severity of epilepsy. Wistar rats can develop spontaneous seizures in adulthood, so caution is advised when using them as a control epileptic strain. This review discusses challenges in the field, such as putative high emotionality in genetically prone rats, sex differences in the expression of cognitive comorbidities, and predictors of cognitive problems or biomarkers of cognitive comorbidities in absence epilepsy, as well as the concept of "the cognitive thalamus". The current knowledge of behavioral and cognitive comorbidities in drug-naive rats with spontaneous absence epilepsy is beneficial for understanding the pathophysiology of absence epilepsy, and for finding new treatment strategies.

An In Vivo Electroencephalographic Analysis of the Effect of Riluzole against Limbic and Absence Seizure and Comparison with Glutamate Antagonists.

Riluzole (RLZ) has demonstrated neuroprotective effects in several neurological disorders. These neuroprotective effects seem to be mainly due to its ability to inhibit the excitatory glutamatergic neurotransmission, acting on different targets located both at the presynaptic and postsynaptic levels. In the present study, we evaluated the effects of Riluzole (RLZ) against limbic seizures, induced by AMPA, kainate, and NMDA receptor agonists in Sprague-Dawley rats, and in a well-validated genetic model of absence epilepsy, the WAG/Rij rat. Furthermore, in this latter model, we also studied the effect of RLZ in co-administration with the competitive NMDA receptor antagonist, CPP, or the non-competitive AMPA receptor antagonist, THIQ-10c, on spike-wave discharges (SWDs) in WAG/Rij rats, to understand the potential involvement of AMPA and NMDA receptors in the anti-absence effect of RLZ. In Sprague-Dawley rats, RLZ pretreatment significantly reduced the limbic seizure severity induced by glutamatergic agonists, suggesting an antagonism of RLZ mainly on NMDA rather than non-NMDA receptors. RLZ also reduced SWD parameters in WAG/Rij rats. Interestingly, the co-administration of RLZ with CPP did not increase the anti-absence activity of RLZ in this model, advocating a competitive effect on the NMDA receptor. In contrast, the co-administration of RLZ with THIQ-10c induced an additive effect against absence seizure in WAG/Rij rats. these results suggest that the antiepileptic effects of RLZ, in both seizure models, can be mainly due to the antagonism of the NMDA glutamatergic receptors.

The Effect of Maternal Methyl-Enriched Diet on the Number of Dopaminergic Neurons in the Ventral Tegmental Area in Adult Offspring of WAG/Rij Rats

WAG/Rij rats are genetic model of absence epilepsy with comorbid depression. Pathologic phenotype in WAG/Rij rats was shown to be associated with reduced dopamine (DA) tone within the mesolimbic DAergic brain system. Previously, it was found that maternal methyl-enriched diet (MED) in the perinatal period increases DA content in the mesolimbic DAergic brain system and reduces absence seizures and comorbid depression in adult offspring of WAG/Rij rats. Ventral tegmental area (VTA), containing DA cells bodies, is a main source of the mesolimbic DA synthesis. The aim of this study was to test the hypothesis that increases in the mesolimbic DAergic tone induced by maternal MED in offspring may be due to an increase in the number of DA-synthesizing neurons in the VTA. Immunohistochemistry for thyrosine hydroxylase (TH) was used to assess the number of TH-immunopositive cells in adult offspring of WAG/Rij rats born to mothers fed control diet or MED and subjected or not subjected to behavioral testing for 2 consecutive days in the light-dark choice, open field, elevated plus maze and forced swimming tests. One hour after the forced swimming test animals were anesthetized. Brains were fixed using transcardial perfusion. The number of DAergic neurons was determined by the number of TH-immunopositive cells on brain slices at the level of VTA. The number of TH-immunopositive cells was counted in left and right hemispheres separately. A significant effect of maternal MED on the number of cells in the VTA expressing TH has been established. Adult WAG/Rij offspring born to mothers fed MED had an increased number of TH-immunopositive cells as compared with the offspring born to mothers fed control diet. Moreover, in WAG/Rij offspring born to mothers fed MED, the number of TH-immunopositive cells was greater in animals subjected to behavioral testing compared with animals not subjected to behavioral testing. The effects of maternal MED and behavioral testing on the number of TH-immunopositive cells in the VTA were equally expressed in the left and right hemispheres of the brain. Results suggest that maternal MED in the perinatal period can affect the developing mesolimbic DAergic brain system, promoting the generation and/or maintenance of DA neurons in the VTA, and thereby prevent the occurrence of genetic absence epilepsy and comorbid depression in the offspring of WAG/Rij rats.

The analysis of histological features and morphometric parameters of the ovaries in absenсe epilepsy

BACKGROUND: Absence epilepsy is one of the most common epileptic syndromes and is more common in girls. Often in adolescence, generalized tonic-clonic seizures (up to 50%) join. In women suffering from epilepsy, reproductive dysfunction is often noted. In this regard, it seems relevant to study the morphofunctional state of the ovaries in absence epilepsy.
 AIM: Assessment of morphological and morphometric parameters of the ovaries in absence epilepsy.
 MATERIALS AND METODS: Using histological and morphometric methods, the ovaries of Wistar and WAG/Rij rats (a genetic model of human absence epilepsy) were studied.
 RESULTS: In WAG/Rij rats, destruction of the cortical and medulla of the ovary was found: the layer of granulosa cells surrounding the oocyte had a looser structure compared to the norm, destructive changes in the follicular epithelium and apoptotic death of granulosa cells were observed. Morphometric analysis showed that in WAG/Rij rats the weight of the ovaries was 2 times less than in Wistar rats: 37.300.93 mg versus 55.842.36 mg. The thickness of the epithelial layer was 7.810.25 m, which is 26.2% less than in Wistar rats (p 0.05). The ovarian follicles of WAG/Rij rats were irregular in shape, smaller in diameter and area, and the numerical density of all types of follicles was lower compared to Wistar rats, which indicates a violation of ovulation processes.
 CONCLUSION: Structural and quantitative changes in the ovaries of WAG/Rij rats were observed in absence epilepsy, which indicates violations of the endocrine function of the ovaries and process of folliculogenesis.

Optogenetic stimulation of the superior colliculus suppresses genetic absence seizures.

While anti-seizure medications are effective for many patients, nearly one-third of individuals have seizures that are refractory to pharmacotherapy. Prior studies using evoked preclinical seizure models have shown that pharmacological activation or excitatory optogenetic stimulation of the deep and intermediate layers of the superior colliculus (DLSC) display multi-potent anti-seizure effects. Here we monitored and modulated DLSC activity to suppress spontaneous seizures in the WAG/Rij genetic model of absence epilepsy. Female and male WAG/Rij adult rats were employed as study subjects. For electrophysiology studies, we recorded single unit activity from microwire arrays placed within the DLSC. For optogenetic experiments, animals were injected with virus coding for channelrhodopsin-2 or a control vector, and we compared the efficacy of continuous neuromodulation to that of closed-loop neuromodulation paradigms. For each, we compared three stimulation frequencies on a within-subject basis (5, 20, 100 Hz). For closed-loop stimulation, we detected seizures in real time based on the EEG power within the characteristic frequency band of spike-and-wave discharges (SWDs). We quantified the number and duration of each SWD during each 2 h-observation period. Following completion of the experiment, virus expression and fibre-optic placement was confirmed. We found that single-unit activity within the DLSC decreased seconds prior to SWD onset and increased during and after seizures. Nearly 40% of neurons displayed suppression of firing in response to the start of SWDs. Continuous optogenetic stimulation of the DLSC (at each of the three frequencies) resulted in a significant reduction of SWDs in males and was without effect in females. In contrast, closed-loop neuromodulation was effective in both females and males at all three frequencies. These data demonstrate that activity within the DLSC is suppressed prior to SWD onset, increases at SWD onset, and that excitatory optogenetic stimulation of the DLSC exerts anti-seizure effects against absence seizures. The striking difference between open- and closed-loop neuromodulation approaches underscores the importance of the stimulation paradigm in determining therapeutic effects.

Metyrapone abolishes Spike-Wave Discharge seizures in GAERS by reducing stress hormones.

Stress is one of the most commonly reported triggers for seizures in patients with epilepsy, although the mechanisms which mediate this effect are not established. The clinical evidence supporting this is derived from patient's subjective experience of stress, and how this influences their own seizures. Animal models can be used to explore this phenomenon in controlled environments, free from subjective bias. Here we used GAERS, a genetic rat model of absence epilepsy, to explore the influence of stress and stress hormones on spontaneous seizures. Adult male GAERS (n=38) and Non-Epileptic Controls (NEC: n=4) were used. First, rats were subjected to 30 minutes restraint stress to assess Hypothalamic-Pituitary-Adrenal (HPA) axis function. Next, we assessed the effects of 30-minute noise stress, and cage tilt stress, on Spike-Wave Discharge seizures in GAERS. We then performed pharmacological experiments to assess the direct effects of stress hormones on seizures, including corticosterone, metyrapone and deoxycorticosterone. GAERS exhibited elevated baseline corticosterone levels, compared to NEC rats. Noise stress and cage tilt stress significantly enhanced seizure incidence (p<0.05), but only during stress periods. Exogenous corticosterone administration also significantly increased seizure occurrence (p<0.05). Metyrapone, an inhibitor of corticosterone synthesis, completely abolished seizures in GAERS, and seizures remained suppressed for over 2 hours. However, deoxycorticosterone, the precursor of corticosterone, increased seizures. These results suggest that GAERS exhibit elevations in stress hormones, and this may contribute to seizures. Inhibiting corticosterone synthesis with metyrapone prevents seizures in GAERS, and shows potential for repurposing this drug as a future anti-seizure medication.

Investigating the mechanism of action of ginkgolides and bilobalide on absence seizures in male WAG/Rij rats.

The effects of a single and multiple doses of ginkgolide A, B, C, and bilobalide, active components of Ginkgo biloba extract (EGb 761), on absence seizures were investigated in male WAG/Rij rats, a genetic animal model of absence epilepsy. Furthermore, the interactions of ginkgolide A together with NMDA receptor antagonist MK-801, AMPA/kainate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), or L-type calcium channel blocker nicardipine were studied to figure out how ginkgolide A affects spike-wave discharges (SWDs) in the brain. The experiments were done using 6-8-month-old male WAG/Rij rats with infusion cannula and EEG electrode implanted. Ginkgolide A, B, C, and bilobalide were administered intraperitoneally for 7 days at a dose of 6mg/kg. In interaction groups, 6μg ginkgolide A was injected intracerebroventricularly in combination with MK-801 (10μg), CNQX (1μg), and nicardipine (50 μg) for 7 days. EEG was recorded from animals at the baseline, first dose, and seventh dose periods for 4 h. Ginkgolide A (p=.028), C (p=.046), and bilobalide (p=.043) significantly increased the frequency of SWDs in WAG/Rij rats. Ginkgolide A injected into the lateral ventricle with MK-801 (p=.046), CNQX (p=.043), and nicardipine (p=.046) significantly increased the number of SWDs after seventh dose. Finally, the EGb 761-related increase in absence epilepsy was determined to be caused by ginkgolide A, C, and bilobalide. All three receptor antagonists/channel blockers do not inhibit the pro-absence effect of ginkgolide A. The findings revealed that ginkgolide A's pro-absence effect is mediated by brain circuits other than ionotropic glutamate receptors or L-type calcium channels.

The impact of early-life environment on absence epilepsy and neuropsychiatric comorbidities.

This review discusses the long-term effects of early-life environment on epileptogenesis, epilepsy, and neuropsychiatric comorbidities with an emphasis on the absence epilepsy. The WAG/Rij rat strain is a well-validated genetic model of absence epilepsy with mild depression-like (dysthymia) comorbidity. Although pathologic phenotype in WAG/Rij rats is genetically determined, convincing evidence presented in this review suggests that the absence epilepsy and depression-like comorbidity in WAG/Rij rats may be governed by early-life events, such as prenatal drug exposure, early-life stress, neonatal maternal separation, neonatal handling, maternal care, environmental enrichment, neonatal sensory impairments, neonatal tactile stimulation, and maternal diet. The data, as presented here, indicate that some early environmental events can promote and accelerate the development of absence seizures and their neuropsychiatric comorbidities, while others may exert anti-epileptogenic and disease-modifying effects. The early environment can lead to phenotypic alterations in offspring due to epigenetic modifications of gene expression, which may have maladaptive consequences or represent a therapeutic value. Targeting DNA methylation with a maternal methyl-enriched diet during the perinatal period appears to be a new preventive epigenetic anti-absence therapy. A number of caveats related to the maternal methyl-enriched diet and prospects for future research are discussed.

Reduction of Hippocampal High-Frequency Activity in Wag/Rij Rats with a Genetic Predisposition to Absence Epilepsy.

In temporal lobe epilepsy, high frequency oscillations serve as electroencephalographic (EEG) markers of epileptic hippocampal tissue. In contrast, absence epilepsy and other idiopathic epilepsies are known to result from thalamo-cortical abnormalities, with the hippocampus involvement considered to be only indirect. We aimed to uncover the role of the hippocampus in absence epilepsy using a genetic rat model of absence epilepsy (WAG/Rij rats), in which spike-wave discharges (SWDs) appear spontaneously in cortical EEG. We performed simultaneous recordings of local field potential from the hippocampal dentate gyrus using pairs of depth electrodes and epidural cortical EEG in freely moving rats. Hippocampal ripples (100-200 Hz) and high frequency oscillations (HFO, 50-70 Hz) were detected using GUI RIPPLELAB in MatLab (Navarrete et al., 2016). Based on the dynamics of hippocampal ripples, SWDs were divided into three clusters, which might represent different seizure types in reference to the involvement of hippocampal processes. This might underlie impairment of hippocampus-related cognitive processes in some patients with absence epilepsy. A significant reduction to nearly zero-ripple-density was found 4-8 s prior to SWD onset and during 4 s immediately after SWD onset. It follows that hippocampal ripples were not just passively blocked by the onset of SWDs, but they were affected by spike-wave seizure initiation mechanisms. Hippocampal HFO were reduced during the preictal, ictal and postictal periods in comparison to the baseline. Therefore, hippocampal HFO seemed to be blocked with spike-wave seizures. All together, this might underlie impairment of hippocampus-related cognitive processes in some patients with absence epilepsy. Further investigation of processes underlying SWD-related reduction of hippocampal ripples and HFO oscillations may help to predict epileptic attacks and explain cognitive comorbidities in patients with absence epilepsy.

Alteration in Neuregulin 1/ERbB4 in Absence Epilepsy: Regulatory Effect on TRPV1 Expression.

The footprint of Neuregulin 1 (NRG1) / ERbB4 in the pathophysiology of some neurological disorders and TRPV1 regulation has been indicated. The alterations in NRG1 and ErbB4 as well as the TRPV1 signaling pathway were investigated during the development of absence epilepsy in the genetic animal model of absence epilepsy. Male WAG/Rij and Wistar rats were divided into four experimental groups of two and six months of age. The protein levels of NRG1, ERbB4, and TRPV1 were measured in the somatosensory cortex and hippocampus. The cortical protein levels of NRG1 and ErbB4 in the 6-month-old WAG/Rij rats were lower than in Wistar rats. Protein levels of TRPV1 were lower in two- and six-month-old WAG/Rij rats compared to age-matched Wistar rats.Hippocampal protein levels of NRG1 in 6-month-old WAG/Rij rats were lower than two-month-old WAG/Rij rats. Low levels of ErbB4 protein in two-month-old and high levels in six-month-old WAG/Rij rats were found compared to Wistar rats. Protein levels of TRPV1 were lower in the two-month-old and higher in the six-month-old WAG/Rij rats compared to age-matched Wistar rats.Furthermore, a high correlation between NRG1/ERbB4 and TRPV1 expressions in the cortex and hippocampus was indicated. The expression of NRG1/ERbB4 and TRPV1 followed a similar pattern during the life span of Wistar and WAG/Rij rats. Our findings indicated the potential role of the NRG1/ErbB4 pathway as well as TRPV1 in the pathogenesis of absence epilepsy. The regulatory effect of the ERbB4 receptor on the TRPV1 expression has been suggested following the similar pattern of expression.

Oh, What a Tangled Web Epilepsy Genes May Weave.

Aberrant Neuronal Connectivity in the Cortex Drives Generation of Seizures in Rat Absence Epilepsy Studer F, Jarre G, Pouyatos B, et al. Brain 2022;145(6):1978-1991. doi:10.1093/brain/awab438.Absence epilepsy belongs to genetic epilepsies and is characterized by recurrent generalized seizures that are concomitant with alterations of consciousness and associated with cognitive comorbidities. Little is known about the mechanisms leading to occurrence of epileptic seizures (i.e., epileptogenesis) and, in particular, it remains an open question whether neuronal hypersynchronization, a key feature in seizure initiation, could result from aberrant structural connectivity within neuronal networks endowing them with epileptic properties. In the present study, we addressed this question using a genetic model of absence epilepsy in the rat where seizures initiate in the whisker primary somatosensory cortex. We hypothesized that alterations in structural connectivity of neuronal networks within wS1 contribute to pathological neuronal synchronization responsible for seizures. First, we used rabies virus-mediated retrograde synaptic tracing and evidenced that cortical neurons located in both upper- and deep-layers of whisker primary somatosensory cortex displayed aberrant and significantly increased connectivity the genetic model of absence epilepsy, as highlighted by a higher number of presynaptic partners. Next, we showed at the functional level that disrupting these aberrant whisker primary somatosensory cortex neuronal networks with synchrotron X-ray-mediated cortical microtransections drastically decreased both whisker primary somatosensory cortex neuron synchronization and seizure power, as revealed by in vivo local field potential recordings with multichannel probes. Taken together, our data provide for the first time strong evidence that increased structural connectivity patterns of cortical neurons represent critical pathological substrates for increased neuronal synchronization and generation of absence seizures.

Putrescine Intensifies Glu/GABA Exchange Mechanism and Promotes Early Termination of Seizures.

Endogenous anticonvulsant mechanisms represent a reliable and currently underdeveloped strategy against recurrent seizures and may recall novel original therapeutics. Here, we investigated whether the intensification of the astroglial Glu-GABA exchange mechanism by application of the GABA precursor putrescine (PUT) may be effective against convulsive and non-convulsive seizures. We explored the potential of PUT to inhibit spontaneous spike-and-wave discharges (SWDs) in WAG/Rij rats, a genetic model of absence epilepsy. Significant shortening of SWDs in response to intraperitoneally applied PUT has been observed, which could be antagonized by blocking GAT-2/3-mediated astrocytic GABA release with the specific inhibitor SNAP-5114. Direct application of exogenous GABA also reduced SWD duration, suggesting that PUT-triggered astroglial GABA release through GAT-2/3 may be a critical step in limiting seizure duration. PUT application also dose-dependently shortened seizure-like events (SLEs) in the low-[Mg2+] in vitro model of temporal lobe epilepsy. SNAP-5114 reversed the antiepileptic effect of PUT in the in vitro model as well, further confirming that PUT reduces seizure duration by triggering glial GABA release. In accordance, we observed that PUT specifically reduces the frequency of excitatory synaptic potentials, suggesting that it specifically acts at excitatory synapses. We also identified that PUT specifically eliminated the tonic depolarization-induced desynchronization of SLEs. Since PUT is an important source of glial GABA and we previously showed significant GABA release, it is suggested that the astroglial Glu-GABA exchange mechanism plays a key role in limiting ictal discharges, potentially opening up novel pathways to control seizure propagation and generalization.

Intrathecal application of ethosuximide is highly efficient in suppressing seizures in a genetic model of absence epilepsy

Systemic drug application is the main approach in epilepsy treatment. However, the central nervous system (CNS) is a challenging target for drug delivery as the blood-brain barrier (BBB) restricts the transfer of drugs into the brain. Accordingly, there is a general interest in developing new therapeutic strategies to improve CNS drug accessibility. Intrathecal administration of antiseizure drugs (ASDs) e.g. via pumps or advanced materials could be a possible approach to bypass the BBB and increase the availability of neuroactive compounds in the CNS. The aim of this study was the evaluation of intracerebroventricular (i.c.v.) compared to systemic drug application in generalized epilepsy. The i.c.v. administration of the established ASD ethosuximide (ETX) in Genetic Absence Epilepsy Rats from Strasbourg (GAERS) caused a robust and dose-dependent reduction of spike-wave discharges (SWDs) without causing obvious behavioral abnormalities. Additionally, we could show that i.c.v. treatment with ETX is significantly more effective in seizure suppression than systemic treatment with the same dose. The localized application resulted in reduced systemic drug exposure compared to standard systemic ETX therapy. The tracing of dye distribution throughout the CNS supported the view that i.c.v. applied drugs cross into brain tissue surrounding the ventricles but largely remain restricted to the site of injection. Our data suggest that intrathecal application represents a possible route for the treatment in generalized epilepsy through direct drug penetration from CSF into brain tissue.

Automatic detection of the spike-and-wave discharges in absence epilepsy for humans and rats using deep learning

Automatic detection of spike-and-wave discharges (SWDs) of absence seizures, is a highly time-consuming process requiring trained technicians or neurologists to categorize thousands of non-overlapping epochs of electroencephalography (EEG) data by visually inspecting several interconnections among different channels. This paper aims to develop an algorithm for a non-invasive real-time detection of SWDs in the EEG recordings of humans with absence epilepsy and a genetic model of absence epilepsy. We develop a SWD detection framework using Convolutional Neural Networks. Our approach utilizes the nature of EEG signals; as the brain signals are dynamics in discrete time, we found that it is more efficient and useful to represent the signal’s power as a function of frequency and time using Thomson’s multitaper power spectral density estimation analysis. Our experiments show that the developed method classified SWDs in humans and rats with high diagnostic performance similar to that of the trained neurologists while using fewer channels, proving that the proposed algorithm can be applied to different domains where the main focus is the detection of SWDs. Although there are different methods to detect SWDs in humans and animals, we showed the need for efficient and more accurate SWD detection. The proposed method, characterized by low computational and memory requirements using non-invasive EEG techniques with fewer channels, offers an efficient multi-purposed deep learning framework to be implemented in wearable or portable devices for accurate real-time detection of SWD patterns in EEG signals. Eventually, the proposed method is a step towards detecting seizures and closed-loop seizure interventions.

Spike-Wave Seizures, NREM Sleep and Micro-Arousals in WAG/Rij Rats with Genetic Predisposition to Absence Epilepsy: Developmental Aspects.

The current study was done in Wistar Albino Glaxo Rijswijk (WAG/Rij) rats, which are genetically prone to develop spontaneous spike-wave discharges (SWDs) and are widely used as a genetic model of absence epilepsy. Here, we examined functional links between sleep and spike-wave epilepsy in aging WAG/Rij rats using advanced techniques of EEG analysis. SWDs, periods of NREM sleep and micro-arousals were automatically detected in three-channel epidural EEG recorded in freely moving WAG/Rij rats consequently at the age 5, 7 and 9 months. We characterized the developmental profile of spike-wave epilepsy in drug-naïve WAG/Rij rats and defined three epi-phenotypes—severe, mild and minor epilepsy. Age-related changes of SWDs were associated with changes in NREM sleep. Several signs of NREM sleep fragmentation were defined in epileptic WAG/Rij rats. It seems that spike-wave epilepsy per se promotes micro-arousals during NREM sleep. However, subjects with a higher number of micro-arousals (and NREM sleep episodes) at the age of 5 months were characterized by a reduction of SWDs between 5 and 7 months of age.

440 Modulating decreases in Superior Colliculus activity through optogenetic activation attenuates seizures in the WAG/Rij genetic model of Absence Epilepsy

OBJECTIVES/GOALS: While anti-seizure medications are effective, nearly one third of patients have seizures that go untreated. Prior studies using evoked seizure models have shown that activation of the Superior Colliculus (SC) display anti-seizure effects. Here we monitored and modulated the DLSC to suppress spontaneous seizures in a genetic model of epilepsy. METHODS/STUDY POPULATION: WAG/Rij rats (4 months old) were employed as study subjects. Animals were surgically prepared for virus injection (ChR2 excitatory opsin, or control vector), fiber optic implantation and cortical EEG for optogenetic studies. For In vivo electrophysiology, animals were implanted with a 16 wire multi-electrode array into the DLSC. In optogenetic experiments, we compared the efficacy of continuous neuromodulation to that of on-demand neuromodulation (real time detection of seizures) paradigms on a within-subject basis. We compared three stimulation frequencies on a within-subject basis (5, 20, 100 Hz). We quantified the number and duration of each spike wave discharge (SWD) during each two-hour-long trial. Electrode array single units were sorted and analyzed for activity before, during and after seizures. RESULTS/ANTICIPATED RESULTS: In vivo electrophysiology found there to be a significant decrease in single unit activity leading up to the start of SWDs. Interestingly, on-demand neuromodulation was effective in both females and males – where the greatest reduction in seizure duration was under 100 Hz light delivery. As expected, male and female animals injected with a control vector did not show a reduction in seizures in response to light delivery. In the open-loop (continuous) stimulation paradigm, optogenetic activation of the DLSC was without effect on the number or duration of SWDs at any of the frequencies examined. DISCUSSION/SIGNIFICANCE: SC activity is significantly decreased prior to the start of seizures. Furthermore, activation of the SC displays anti-seizure effects in a model of spontaneous seizures. A striking difference between open and closed-loop neuromodulation approaches underscores the importance of stimulation paradigm in determining therapeutic effect.

Aberrant neuronal connectivity in the cortex drives generation of seizures in rat absence epilepsy.

Absence epilepsy belongs to genetic epilepsies and is characterized by recurrent generalized seizures that are concomitant with alterations of consciousness and associated with cognitive comorbidities. Little is known about the mechanisms leading to occurrence of epileptic seizures (i.e. epileptogenesis) and, in particular, it remains an open question as to whether neuronal hypersynchronization, a key feature in seizure initiation, could result from aberrant structural connectivity within neuronal networks endowing them with epileptic properties. In the present study, we addressed this question using a genetic model of absence epilepsy in the rat where seizures initiate in the whisker primary somatosensory cortex (wS1). We hypothesized that alterations in structural connectivity of neuronal networks within wS1 contribute to pathological neuronal synchronization responsible for seizures. First, we used rabies virus-mediated retrograde synaptic tracing and showed that cortical neurons located in both upper- and deep-layers of wS1 displayed aberrant and significantly increased connectivity in the genetic model of absence epilepsy, as highlighted by a higher number of presynaptic partners. Next, we showed at the functional level that disrupting these aberrant wS1 neuronal networks with synchrotron X-ray-mediated cortical microtransections drastically decreased both the synchronization and seizure power of wS1 neurons, as revealed by in vivo local field potential recordings with multichannel probes. Taken together, our data provide for the first time strong evidence that increased structural connectivity patterns of cortical neurons represent critical pathological substrates for increased neuronal synchronization and generation of absence seizures.

Modulation of pacemaker channel function in a model of thalamocortical hyperexcitability by demyelination and cytokines.

A consensus is yet to be reached regarding the exact prevalence of epileptic seizures or epilepsy in multiple sclerosis (MS). In addition, the underlying pathophysiological basis of the reciprocal interaction among neuroinflammation, demyelination, and epilepsy remains unclear. Therefore, a better understanding of cellular and network mechanisms linking these pathologies is needed. Cuprizone-induced general demyelination in rodents is a valuable model for studying MS pathologies. Here, we studied the relationship among epileptic activity, loss of myelin, and pro-inflammatory cytokines by inducing acute, generalized demyelination in a genetic mouse model of human absence epilepsy, C3H/HeJ mice. Both cellular and network mechanisms were studied using in vivo and in vitro electrophysiological techniques. We found that acute, generalized demyelination in C3H/HeJ mice resulted in a lower number of spike–wave discharges, increased cortical theta oscillations, and reduction of slow rhythmic intrathalamic burst activity. In addition, generalized demyelination resulted in a significant reduction in the amplitude of the hyperpolarization-activated inward current (Ih) in thalamic relay cells, which was accompanied by lower surface expression of hyperpolarization-activated, cyclic nucleotide-gated channels, and the phosphorylated form of TRIP8b (pS237-TRIP8b). We suggest that demyelination-related changes in thalamic Ih may be one of the factors defining the prevalence of seizures in MS.

Seizure Prediction in Genetic Rat Models of Absence Epilepsy: Improved Performance through Multiple-Site Cortico-Thalamic Recordings Combined with Machine Learning.

Seizure prediction is the grand challenge of epileptology. However, effort was devoted to prediction of focal seizures, while generalized seizures were regarded as stochastic events. Long-lasting local field potential (LFP) recordings containing several hundred generalized spike and wave discharges (SWDs), acquired at eight locations in the cortico-thalamic system of absence epileptic rats, were iteratively analyzed in all possible combinations of either two or three recording sites, by a wavelet-based algorithm, calculating the product of the wavelet-energy signaling increases in synchronicity. Sensitivity and false alarm rate of prediction were compared between various combinations, and wavelet spectra of true and false positive predictions were fed to a random forest machine learning algorithm to further differentiate between them. Wavelet analysis of intracortical and cortico-thalamic LFP traces showed a significantly smaller number of false alarms compared with intrathalamic combinations, while predictions based on recordings in Layers IV, V, and VI of the somatosensory-cortex significantly outreached all other combinations in terms of prediction sensitivity. In 24-h out-of-sample recordings of nine Genetic Absence Epilepsy Rats from Strasbourg (GAERS), containing diurnal fluctuations of SWD occurrence, classification of true and false positives by the trained random forest further reduced the false alarm rate by 71%, although at some trade-off between false alarms and sensitivity of prediction, as reflected in relatively low F1 score values. Results provide support for the cortical-focus theory of absence epilepsy and allow the conclusion that SWDs are predictable to some degree. The latter paves the way for the development of closed-loop SWD prediction-prevention systems. Suggestions for a possible translation to human data are outlined.