Alpha-2a adrenergic receptor activation in genetic absence epilepsy: An absence status model?

OBJECTIVE

The objective of the study was to propose a candidate animal model of absence status epilepticus induced by specific alpha-2a adrenergic receptor (α2AR) activation. We also aim to investigate the responsiveness of this model to classical anti-status or anti-absence medications.

METHODS

An α2AR agonist, dexmedetomidine (DEX), was injected intracerebroventricularly into adult rats with genetic absence epilepsy, and their electroencephalography (EEG) was recorded. The total duration, number, and mean duration of each spike-and-wave discharges (SWDs) were evaluated. The blocks of absence status events were classified as the initial and second sets of absence statuses. Ethosuximide (ETX) was administered as a pretreatment to another group of rats and later injected with 2.5 μg DEX. In addition, ETX, valproic acid (VPA), diazepam (DIAZ), and atipamezole (ATI) were administered after induced status-like events following DEX administration. Power spectral characteristics and coherence analysis were performed on the EEG to assess the absence status events and sleep.

RESULTS

The 2.5 μg dose of DEX increased the total SWD duration and induced continuous SWDs up to 26 min. Following the initial absence status event, sleep was induced; then, the second period of absence status-like activities were initiated. ETX pretreatment blocked the occurrence of absence status-like activities. Power spectral density analyses revealed that DEX-induced post-sleep activities had higher power in delta frequency band (1-4 Hz) and attenuated power of 7 Hz harmonics (14 and 21 Hz) than the pre-injection seizure. The mean duration of SWDs were decreased in all the groups, but occasional prolonged activities were seen in ETX or VPA-injected rats but not with DIAZ or ATI.

SIGNIFICANCE

This study presents an absence status epilepticus animal model that is activated by α2AR activation to investigate the pathophysiological role of absence status. Unlike other agents ATI switched off the second set of absence statuses to normal SWDs, without sedation or lethargy, can show it may preferentially block absence status-like activity.

THE PLAIN LANGUAGE SUMMARY

This study proposes a rat model for prolonged seizures, resembling absence status epilepticus. Activating the brain's alpha-2a adrenergic receptor with dexmedetomidine induced seizures lasting up to 26 minutes. Ethosuximide pretreatment and post-treatment with valproic acid, diazepam, and atipamezole decreased induced seizures. The findings suggest this model is valuable for studying absence status epilepticus. In addition, atipamezole normalized abnormal seizures without sedation, hinting at its potential for targeted treatment and further research.

BAER-101, a selective potentiator of α2- and α3-containing GABAA receptors, fully suppresses spontaneous cortical spike-wave discharges in Genetic Absence Epilepsy Rats from Strasbourg (GAERS)

BAER-101 (formerly AZD7325) is a selective partial potentiator of α2/3-containing γ-amino-butyric acid A receptors (GABAARs) and produces minimal sedation and dizziness. Antiseizure effects in models of Dravet and Fragile X Syndromes have been published. BAER-101 has been administered to over 700 healthy human volunteers and patients where it was found to be safe and well tolerated. To test the extent of the antiseizure activity of BAER-1010, we tested BAER-101 in the Genetic Absence Epilepsy Rats from Strasbourg (GAERS) model, a widely used and translationally relevant model. GAERS rats with recording electrodes bilaterally located over the frontal and parietal cortices were used. Electroencepholographic (EEG) signals in freely moving awake rats were analyzed for spike-wave discharges (SWDs). BAER-101 was administered orally at doses of 0.3-100 mg/kg and diazepam was used as a positive control using a cross-over protocol with a wash-out period between treatments. The number of SWDs was dose-dependently reduced by BAER-101 with 0.3 mg/kg being the minimally effective dose (MED). The duration of and total time in SWDs were also reduced by BAER-101. Concentrations of drug in plasma achieved an MED of 10.1 nM, exceeding the Ki for α2 or α3, but 23 times lower than the Ki for α5-GABAARs. No adverse events were observed up to a dose 300× MED. The data support the possibility of antiseizure efficacy without the side effects associated with other GABAAR subtypes. This is the first report of an α2/3-selective GABA PAM suppressing seizures in the GAERS model. The data encourage proceeding to test BAER-101 in patients with epilepsy.

Epilepsy-related functional brain network alterations are already present at an early age in the GAERS rat model of genetic absence epilepsy

Introduction

Genetic Absence Epilepsy Rats from Strasbourg (GAERS) represent a model of genetic generalized epilepsy. The present longitudinal study in GAERS and age-matched non-epileptic controls (NEC) aimed to characterize the epileptic brain network using two functional measures, resting state-functional magnetic resonance imaging (rs-fMRI) and manganese-enhanced MRI (MEMRI) combined with morphometry, and to investigate potential brain network alterations, following long-term seizure activity.

Methods

Repeated rs-fMRI measurements at 9.4 T between 3 and 8 months of age were combined with MEMRI at the final time point of the study. We used graph theory analysis to infer community structure and global and local network parameters from rs-fMRI data and compared them to brain region-wise manganese accumulation patterns and deformation-based morphometry (DBM).

Results

Functional connectivity (FC) was generally higher in GAERS when compared to NEC. Global network parameters and community structure were similar in NEC and GAERS, suggesting efficiently functioning networks in both strains. No progressive FC changes were observed in epileptic animals. Network-based statistics (NBS) revealed stronger FC within the cortical community, including regions of association and sensorimotor cortex, and with basal ganglia and limbic regions in GAERS, irrespective of age. Higher manganese accumulation in GAERS than in NEC was observed at 8 months of age, consistent with higher overall rs-FC, particularly in sensorimotor cortex and association cortex regions. Functional measures showed less similarity in subcortical regions. Whole brain volumes of 8 months-old GAERS were higher when compared to age-matched NEC, and DBM revealed increased volumes of several association and sensorimotor cortex regions and of the thalamus.

Discussion

rs-fMRI, MEMRI, and volumetric data collectively suggest the significance of cortical networks in GAERS, which correlates with an increased fronto-central connectivity in childhood absence epilepsy (CAE). Our findings also verify involvement of basal ganglia and limbic regions. Epilepsy-related network alterations are already present in juvenile animals. Consequently, this early condition seems to play a greater role in dynamic brain function than chronic absence seizures.

Transmembrane α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor regulatory protein expression during the development of absence seizures in genetic absence epilepsy rats from Strasbourg

The transmembrane α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) regulatory proteins (TARPs), γ2 (stargazin), γ3, γ4, γ5, γ7, and γ8, are a family of proteins that regulate AMPAR trafficking, expression, and biophysical properties that could have a role in the development of absence seizures. Here, we evaluated the expression of TARPs and AMPARs across the development of epilepsy in the genetic absence epilepsy rats from Strasbourg (GAERS) model of idiopathic generalized epilepsy (IGE) with absence seizures. Pre-epileptic (7-day-old), early epileptic (6-week-old), and chronically epileptic (16-week-old) GAERS, and age-matched male nonepileptic control rats (NEC) were used. Electroencephalographic (EEG) recordings were acquired from the 6- and 16-week-old animals to quantify seizure expression. Somatosensory cortex (SCx) and whole thalamus were collected from all the animals to evaluate TARP and AMPAR mRNA expression. Analysis of the EEG demonstrated a gradual increase in the number and duration of seizures across GAERS development. mRNA expression of the TARPs γ2, γ3, γ4, γ5, and γ8 in the SCx, and γ4 and γ5 in the thalamus, increased as the seizures started and progressed in the GAERS compared to NEC. There was a temporal association between increased TARP expression and seizures in GAERS, highlighting TARPs as potential targets for developing novel treatments for IGE with absence seizures.

Dexmedetomidine, an alpha 2A receptor agonist, triggers seizures unilaterally in GAERS during the pre-epileptic phase: does the onset of spike-and-wave discharges occur in a focal manner?

Introduction

The genetic absence epilepsy rat from Strasbourg (GAERS) is a rat model for infantile absence epilepsy with spike-and-wave discharges (SWDs). This study aimed to investigate the potential of alpha 2A agonism to induce seizures during the pre-epileptic period in GAERS rats.

Methods

Stereotaxic surgery was performed on male pups and adult GAERS rats to implant recording electrodes in the frontoparietal cortices (right/left) under anesthesia (PN23-26). Following the recovery period, pup GAERS rats were subjected to electroencephalography (EEG) recordings for 2 h. Before the injections, pup epileptiform activity was examined using baseline EEG data. Dexmedetomidine was acutely administered at 0.6 mg/kg to pup GAERS rats 2-3 days after the surgery and once during the post-natal (PN) days 25-29. Epileptiform activities before injections triggered unilateral SWDs and induced sleep durations, and power spectral density was evaluated based on EEG traces.

Results

The most prominent finding of this study is that unilateral SWD-like activities were induced in 47% of the animals with the intraperitoneal dexmedetomidine injection. The baseline EEGs of pup GAERS rats had no SWDs as expected since they are in the pre-epileptic period but showed low-amplitude non-rhythmic epileptiform activity. There was no difference in the duration of epileptiform activities between the basal EEG groups and DEX-injected unilateral SWD-like-exhibiting and non-SWD-like activities groups; however, the sleep duration of the unilateral SWD-like-exhibiting group was shorter. Power spectrum density (PSD) results revealed that the 1.75-Hz power in the left hemisphere peaks significantly higher than in the right.

Discussion

As anticipated, pup GAERS rats in the pre-epileptic stage showed no SWDs. Nevertheless, they exhibited sporadic epileptiform activities. Specifically, dexmedetomidine induced SWD-like activities solely within the left hemisphere. These observations imply that absence seizures might originate unilaterally in the left cortex due to α2AAR agonism. Additional research is necessary to explore the precise cortical focal point of this activity.

Diurnal circadian clock gene expression is altered in models of genetic and acquired epilepsy

OBJECTIVES

Growing evidence demonstrates a relationship between epilepsy and the circadian system. However, relatively little is known about circadian function in disease states, such as epilepsy. This study aimed to characterize brain and peripheral core circadian clock gene expression in rat models of genetic and acquired epilepsy.

METHODS

For the Genetic Absence Epilepsy Rats from Strasbourg (GAERS) study, we used 40 GAERS and 40 non-epileptic control (NEC) rats. For the kainic acid status epilepticus (KASE) study, we used 40 KASE and 40 sham rats. Rats were housed in a 7 am:7 pm light-dark cycle. Hypothalamus, hippocampus, liver, and small intestine samples were collected every 3 h throughout the light period. We then assessed core diurnal clock gene expression of per1, cry1, clock, and bmal1.

RESULTS

In the GAERS rats, all tissues exhibited significant changes in clock gene expression (P < 0.05) when compared to NEC. In the KASE rats, there were fewer effects of the epileptic condition in the hypothalamus, hippocampus, or small intestine (P > 0.05) compared with shams.

SIGNIFICANCE

These results indicate marked diurnal disruption to core circadian clock gene expression in rats with both generalized and focal chronic epilepsy. This could contribute to epileptic symptomology and implicate the circadian system as a viable target for future treatments.

Cognitive comorbidities of experimental absence seizures are independent of anxiety

Typical absence seizures (ASs) are brief periods of lack of consciousness, associated with 2.5-4 Hz spike-wave discharges (SWDs) in the EEG, which are highly prevalent in children and teenagers. The majority of probands in these young epileptic cohorts show neuropsychological comorbidities, including cognitive, memory and mood impairments, even after the seizures are pharmacologically controlled. Similar cognition and memory deficits have been reported in different, but not all, genetic animal models of ASs. However, since these impairments are subtle and highly task-specific their presence may be confounded by an anxiety-like phenotype and no study has tested anxiety and memory in the same animals. Moreover, the majority of studies used non-epileptic inbred animals as the only control strain and this may have contributed to a misinterpretation of these behavioural results. To overcome these issues, here we used a battery of behavioural tests to compare anxiety and memory in the same animals from the well-established inbred model of Genetic Absence Epilepsy Rats from Strasbourg (GAERS), their inbred strain of Non-Epileptic Control (NEC) strain (that lack ASs) and normal outbred Wistar rats. We found that GAERS do not exhibit increased anxiety-like behavior and neophobia compared to both NEC and Wistar rats. In contrast, GAERS show decreased spontaneous alternation, spatial working memory and cross-modal object recognition compared to both NEC and Wistar rats. Furthermore, GAERS preferentially used egocentric strategies to perform spatial memory tasks. In summary, these results provide solid evidence of memory deficits in GAERS rats that do not depend on an anxiety or neophobic phenotype. Moreover, the presence of differences between NEC and Wistar rats stresses the need of using both outbred and inbred control rats in behavioural studies involving genetic models of ASs.

Effects of the T-type calcium channel CaV3.2 R1584P mutation on absence seizure susceptibility in GAERS and NEC congenic rats models

RATIONALE

Low-voltage-activated or T-type Ca²⁺ channels play a key role in the generation of seizures in absence epilepsy. We have described a homozygous, gain of function substitution mutation (R1584P) in the Ca_V3.2 T-type Ca²⁺ channel gene (Cacna1h) in the Genetic Absence Epilepsy Rats from Strasbourg (GAERS). The non-epileptic control (NEC) rats, derived from the same original Wistar strains as GAERS but selectively in-breed not to express seizures, are null for the R1584P mutation. To study the effects of this mutation in rats who otherwise have a GAERS or NEC genetic background, we bred congenic GAERS-Cacna1hNEC (GAERS null for R1584P mutation) and congenic NEC-Cacna1hGAERS (NEC homozygous for R1584P mutation) and evaluated the seizure and behavioral phenotype of these strains in comparison to the original GAERS and NEC strains.

METHODS

To evaluate seizure expression in the congenic strains, EEG electrodes were implanted in NEC, GAERS, GAERS^-Cacna1hNEC without the R1584P mutation, and NEC^{-Cacna1hGAERS} with the R1584P mutation rats. In the first study, continuous EEG recordings were acquired from week 4 (when seizures begin to develop in GAERS) to week 14 of age (when GAERS display hundreds of seizures per day). In the second study, the seizure and behavioral phenotype of GAERS and NEC^{-Cacna1hGAERS} strains were evaluated during young age (6 weeks of age) and adulthood (16 weeks of age) of GAERS, NEC, GAERS^-Cacna1hNEC and NEC^{-Cacna1hGAERS}. The Open field test (OFT) and sucrose preference test (SPT) were performed to evaluate anxiety-like and depressive-like behavior, respectively. This was followed by EEG recordings at 18 weeks of age to quantify the seizures, and spike-wave discharge (SWD) cycle frequency. At the end of the study, the whole thalamus was collected for T-type calcium channel mRNA expression analysis.

RESULTS

GAERS had a significantly shorter latency to first seizures and an increased number of seizures per day compared to GAERS^-Cacna1hNEC. On the other hand, the presence of the R1584P mutation in the NEC^{-Cacna1hGAERS} was not enough to generate spontaneous seizures in their seizure-resistant background. 6 and 16-week-old GAERS and GAERS^-Cacna1hNEC rats showed anxiety-like behavior in the OFT, in contrast to NEC and NEC^{-Cacna1hGAERS}. Results from the SPT showed that the GAERS developed depressive-like in the SPT compared to GAERS^-Cacna1hNEC, NEC, and NEC^{-Cacna1hGAERS}. Analysis of the EEG at 18 weeks of age showed that the GAERS had an increased number of seizures per day, increased total seizure duration and a higher cycle frequency of SWD relative to GAERS^-Cacna1hNEC. However, the average seizure duration was not significantly different between strains. Quantitative real-time PCR showed that the T-type Ca²⁺ channel isoform Ca_V3.2 channel expression was significantly increased in GAERS compared to NEC, GAERS^-Cacna1hNEC and NEC^{-Cacna1hGAERS}. The presence of the R1584P mutation increased the total ratio of Ca_V3.2 + 25/-25 splice variants in GAERS and NEC^{-Cacna1hGAERS} compared to NEC and GAERS^-Cacna1hNEC.

DISCUSSION

The data from this study demonstrate that the R1584P mutation in isolation on a seizure-resistant NEC genetic background was insufficient to generate absence seizures, and that a GAERS genetic background can cause seizures even without the mutation. However, the study provides evidence that the R1584P mutation acts as a modulator of seizures development and expression, and depressive-like behavior in the SPT, but not the anxiety phenotype of the GAERS model of absence epilepsy.

Metyrapone abolishes spike-wave discharge seizures in genetic absence epilepsy rats from Strasbourg by reducing stress hormones

OBJECTIVE

Stress is one of the most commonly reported triggers for seizures in patients with epilepsy, although the mechanisms that mediate this effect are not established. The clinical evidence supporting this is derived from patients' 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 genetic absence epilepsy rats from Strasbourg (GAERS), a genetic rat model of absence epilepsy, to explore the influence of stress and stress hormones on spontaneous seizures.

METHODS

Adult male GAERS (n = 38) and nonepileptic control (NEC) rats (n = 4) were used. First, rats were subjected to 30-min restraint stress to assess hypothalamic-pituitary-adrenal axis function. Next, we assessed the effects of 30-min 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.

RESULTS

GAERS exhibited elevated baseline corticosterone levels, compared to NEC rats. Noise stress and cage tilt stress significantly enhanced seizure incidence (p < .05), but only during stress periods. Exogenous corticosterone administration also significantly increased seizure occurrence (p < .05). Metyrapone, an inhibitor of corticosterone synthesis, completely abolished seizures in GAERS, and seizures remained suppressed for >2 h. However, deoxycorticosterone, the precursor of corticosterone, increased seizures.

SIGNIFICANCE

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 antiseizure medication.

MEPIRAPIM-derived synthetic cannabinoids inhibit T-type calcium channels with divergent effects on seizures in rodent models of epilepsy

Background: T-type Ca²⁺ channels (Ca_v3) represent emerging therapeutic targets for a range of neurological disorders, including epilepsy and pain. To aid the development and optimisation of new therapeutics, there is a need to identify novel chemical entities which act at these ion channels. A number of synthetic cannabinoid receptor agonists (SCRAs) have been found to exhibit activity at T-type channels, suggesting that cannabinoids may provide convenient chemical scaffolds on which to design novel Ca_v3 inhibitors. However, activity at cannabinoid type 1 (CB₁) receptors can be problematic because of central and peripheral toxicities associated with potent SCRAs. The putative SCRA MEPIRAPIM and its analogues were recently identified as Ca_v3 inhibitors with only minimal activity at CB₁ receptors, opening the possibility that this scaffold may be exploited to develop novel, selective Ca_v3 inhibitors. Here we present the pharmacological characterisation of SB2193 and SB2193F, two novel Ca_v3 inhibitors derived from MEPIRAPIM. Methods: The potency of SB2193 and SB2193F was evaluated in vitro using a fluorometric Ca²⁺ flux assay and confirmed using whole-cell patch-clamp electrophysiology. In silico docking to the cryo-EM structure of Ca_v3.1 was also performed to elucidate structural insights into T-type channel inhibition. Next, in vivo pharmacokinetic parameters in mouse brain and plasma were determined using liquid chromatography-mass spectroscopy. Finally, anticonvulsant activity was assayed in established genetic and electrically-induced rodent seizure models. Results: Both MEPIRAPIM derivatives produced potent inhibition of Ca_v3 channels and were brain penetrant, with SB2193 exhibiting a brain/plasma ratio of 2.7. SB2193 was further examined in mouse seizure models where it acutely protected against 6 Hz-induced seizures. However, SB2193 did not reduce spontaneous seizures in the Scn1a ^+/- mouse model of Dravet syndrome, nor absence seizures in the Genetic Absence Epilepsy Rat from Strasbourg (GAERS). Surprisingly, SB2193 appeared to increase the incidence and duration of spike-and-wave discharges in GAERS animals over a 4 h recording period. Conclusion: These results show that MEPIRAPIM analogues provide novel chemical scaffolds to advance Ca_v3 inhibitors against certain seizure types.

Effects of in utero exposure to valproate or levetiracetam on the seizures and newborn histopathology of genetic absence epilepsy rats

Valproate (VPA) and levetiracetam (LEV), the two broad spectrum antiseizure drugs with antiabsence effects were previously tested for their antiepileptogenic effects when administered in the early postnatal period and revealed possible modification of the epileptogenic process though the effect being not persistent. The aim of this study was to investigate the effects of in utero exposure to these drugs on the absence epilepsy seizures of Genetic Absence Epilepsy Rats from Strasbourg (GAERS) rats on electroencephalogram (EEG) which are characterised by bilateral, symmetrical, and synchronized spike-and-wave discharges (SWDs). Considering LEV was proposed as a safer drug of choice in pregnancy, its effects on the newborn histopathology of GAERS was also investigated. Adult female GAERS were randomly grouped as VPA-(400 mg/kg/day), LEV- (100 mg/kg/day), and saline-treated. The drugs were injected into the animals intraperitoneally starting before pregnancy until parturition. The lungs, kidneys, and brains of the LEV-exposed newborns were evaluated histologically to be compared with unexposed naïve Wistar and GAERS newborns. Rest of the VPA-, LEV-, and saline-exposed offsprings were taken for EEG recordings on postnatal day 90. VPA or LEV did not show significant effect on mean cumulative duration and mean number of SWDs on EEG. The lungs of the LEV-exposed offsprings showed thickened alveolar epithelium in most regions, suggesting incomplete development of the alveoli. The renal examination revealed dilated Bowman's spaces in some renal corpuscles, which may be interpreted as a deleterious effect of LEV on the kidney. In addition, brain examination of LEV- and saline-exposed groups revealed irregularities in cortical thickness compared to Wistar control group. Lack of significant difference on SWD parameters may indicate that the mechanism responsible for the antiepileptogenic effects of VPA and LEV may not be operating in the prenatal period. The detrimental effect of LEV exposure observed in our study on the lungs and the kidneys of the newborns should be investigated by further studies with advanced molecular and biochemical techniques.

Prolongation of absence seizures and changes in serotonergic and dopaminergic neurotransmission by nigrostriatal pathway degeneration in genetic absence epilepsy rats

OBJECTIVE

Basal ganglia structures play an important role in the pathophysiology of absence epilepsy, known as remote control of absence seizures. We examined the role of the nigrostriatal dopaminergic pathway in absence epilepsy through behavioral and electroencephalography (EEG) parameters, immunohistochemical, and biochemical characteristics of dopamine and serotonin in the genetic absence epilepsy rat model.

METHODS

The nigrostriatal pathway was degenerated by the injection of chemical 6-hydroxydopamine hydrobromide (6-OHDA) into the medial forebrain bundle (MFB) in Wistar and genetic absence epilepsy rats from Strasbourg (GAERS). On the 21st day after stereotaxic surgery, spike-and-wave discharges (SWDs) on EEG were recorded in GAERS groups. Thereafter, Wistar-Control, GAERS-Control, Wistar-6OHDA, GAERS-6OHDA rats were subjected to the cylinder and apomorphine-induced rotation tests. Dopaminergic or serotonergic immunoreactivity was examined in the cortex, striatum, and substantia nigra pars compacta. High-performance liquid chromatography method was used for biochemical analysis of dopamine and serotonin in the cortex and thalamus.

RESULTS

In behavioral analysis, the number of rotations in the GAERS-6OHDA group was significantly higher than in Wistar-6OHDA rats. The degeneration of the nigrostriatal dopaminergic pathway produced a significant increase in the cumulative duration of SWDs and the duration of each SWD in GAERS-6OHDA rats. GAERS-Control rats displayed significantly higher cortical and striatal serotonin immunoreactivity and cortical serotonin level compared to Wistar-Control animals. Moreover, cortical and striatal serotonin immunoreactivity and cortical serotonin levels increased in Wistar-6OHDA and GAERS-6OHDA groups compared to their control groups.

SIGNIFICANCE

The effect of 6-OHDA-induced MFB lesion on absence epilepsy was examined for the first time by comparing Wistar and GAERS rats. The nigrostriatal dopaminergic pathway as a part of the remote-control system is likely to participate in the seizure network.

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.

Retrosplenial Cortex Contributes to Network Changes during Seizures in the GAERS Absence Epilepsy Rat Model

Resting state-fMRI was performed to explore brain networks in Genetic Absence Epilepsy Rats from Strasbourg and in nonepileptic controls (NEC) during monitoring of the brain state by simultaneous optical Ca2+-recordings. Graph theoretical analysis allowed for the identification of acute and chronic network changes and revealed preserved small world topology before and after seizure onset. The most prominent acute change in network organization during seizures was the segregation of cortical regions from the remaining brain. Stronger connections between thalamic with limbic regions compared with preseizure state indicated network regularization during seizures. When comparing between strains, intrathalamic connections were prominent in NEC, on local level represented by higher thalamic strengths and hub scores. Subtle differences were observed for retrosplenial cortex (RS), forming more connections beyond cortex in epileptic rats, and showing a tendency to lateralization during seizures. A potential role of RS as hub between subcortical and cortical regions in epilepsy was supported by increased numbers of parvalbumin-positive (PV+) interneurons together with enhanced inhibitory synaptic activity and neuronal excitability in pyramidal neurons. By combining multimodal fMRI data, graph theoretical methods, and electrophysiological recordings, we identified the RS as promising target for modulation of seizure activity and/or comorbidities.

Absence seizures and their relationship to depression and anxiety: Evidence for bidirectionality

Absence seizures (AS), presenting as short losses of consciousness with staring spells, are a common manifestation of childhood epilepsy that is associated with behavioral, emotional, and social impairments. It has also been suggested that patients with AS are more likely to suffer from mood disorders such as depression and anxiety. This systematic review and meta-analysis synthesizes human and animal models that investigated mood disorders and AS. Of the 1019 scientific publications identified, 35 articles met the inclusion criteria for this review. We found that patients with AS had greater odds of developing depression and anxiety when compared to controls (odds ratio = 4.93, 95% confidence interval = 2.91-8.35, p < .01). The included studies further suggest a strong correlation between AS and depression and anxiety in the form of a bidirectional relationship. The current literature emphasizes that these conditions likely share underlying mechanisms, such as genetic predisposition, neurophysiology, and anatomical pathways. Further research will clarify this relationship and ensure more effective treatment for AS and mood disorders.

Ultrastructural GABA immunogold labeling in the substantia nigra pars reticulata of kindled genetic absence epilepsy rats

Genetic Absence Epilepsy Rats from Strasbourg (GAERS) is a well-known animal model of absence epilepsy and they are resistant to electrical kindling stimulations. The present study aimed to examine possible differences in gamma-aminobutyric acid (GABA) levels and synapse counts in the substantia nigra pars reticulata anterior (SNRa) and posterior (SNRp) regions between GAERS and Wistar rats receiving kindling stimulations. Animals in the kindling group either received six stimulations in the amygdala and had grade 2 seizures or they were kindled, having grade five seizures. Rats were decapitated one hour after the last stimulation. SNR regions were obtained after vibratome sectioning of the brain tissue. GABA immunoreactivity was detected by immunogold method and synapses were counted. Sections were observed by transmission electron microscope and analyzed by Image J program. GABA density in the SNRa region of fully kindled GAERS and Wistar groups increased significantly compared to that of their corresponding grade 2 groups. The number of synapses increased significantly in kindled and grade 2 GAERS groups, compared to kindled and grade 2 Wistar groups, respectively, in the SNRa region. GABA density in the SNRp region of kindled GAERS group increased significantly compared to that of GAERS grade 2 group. In the SNRp region, both kindled and grade 2 GAERS groups were found to have increased number of synapses compared to that of GAERS control group. We concluded that both SNRa and SNRp regions may be important in modulating resistance of GAERS to kindling stimulations.

Atipamezole, a specific α2A antagonist, suppresses spike-and-wave discharges and alters Ca2⁺ /calmodulin-dependent protein kinase II in the thalamus of genetic absence epilepsy rats

OBJECTIVE

The role of α_2A adrenergic receptors (α_2A ARs) in absence epilepsy is not well characterized. Therefore, we investigated the outcomes of the specific antagonism of α_2A ARs on the spike-and-wave discharges (SWDs) in genetic absence epilepsy rats from Strasbourg (GAERSs), together with its influence on the behavior and second messenger systems, which may point to the mechanisms to which a possible SWD modulation can be related.

METHODS

Atipamezole, an α_2A AR antagonist, was administered intracerebroventricularly to the adult GAERSs, and electroencephalography (EEG) was conducted. The cumulative duration and number of SWDs, and the mean duration of each SWD complex were counted. The relative power of the EEG frequency bands and behavioral activity after the acute application of two doses (12 and 31 μg/5 μL) of atipamezole were evaluated. The levels of cyclic adenosine monophosphate and calcium/calmodulin-dependent kinase II (CaMKII) were measured in the cortex, thalamus, and hippocampus of naive Wistar rats and GAERSs, administered with artificial cerebrospinal fluid (aCSF) as a vehicle, or either acute or chronic atipamezole (12 μg), the latter being administered for 5 consecutive days.

RESULTS

Atipamezole significantly suppressed SWDs dose-dependently, without affecting the relative power values of EEG frequency spectrum. The stereotypic activity was significantly lower in both naive Wistar rats and GAERSs receiving the highest dose (31 μg) of atipamezole compared to GAERSs receiving aCSF. In GAERSs, CaMKII levels were found to be higher in the thalamus after the acute and chronic application of SWD-suppressing doses of atipamezole (12 and 31 μg) compared to aCSF.

SIGNIFICANCE

This study emphasizes the α₂ AR-related modulation of absence epilepsy and particularly the significance of α₂ AR antagonism in suppressing SWDs. Atipamezole's SWD-suppressive actions may be through CaMKII-mediated second messenger systems in the thalamus.

A rat model of valproate teratogenicity from chronic oral treatment during pregnancy

OBJECTIVE

Sodium valproate (VPA), the most effective antiepileptic drug for patients with genetic generalized epilepsy (GGE), is a potent human teratogen that increases the risk of a range of congenital malformations, including spina bifida. The mechanisms underlying this teratogenicity are not known, but may involve genetic risk factors. This study aimed to develop an animal model of VPA-induced birth defects.

METHODS

We used three different rat strains: inbred Genetic Absence Epilepsy Rats From Strasbourg (GAERS), a model of GGE with absence seizures; inbred Non-Epileptic Controls (NEC); and outbred nonepileptic Wistars. Female rats were fed standard chow or VPA (20 g/kg food) mixed in standard chow for 2 weeks prior to conception, and then mated with same-strain males. Treatment continued throughout pregnancy. Fetuses were extracted via C-section on gestational day 21 and examined for birth defects, including external assessment and spinal measurements.

RESULTS

VPA-exposed pups showed significant reductions in weight, length, and whole-body development compared with controls of all three strains (P < .0001). Gestational VPA treatment altered intravertebral distances, and resulted in underdeveloped vertebral arches between thoracic region T11 and caudal region C2 in most pups (GAERS, 100%; NEC, 95%; Wistar, 80%), more frequently than in controls (9%, 13%, 19%).

SIGNIFICANCE

Gestational VPA treatment results in similar developmental and morphological abnormalities in three rat strains, including one with GGE, indicating that the genetic underpinnings of epilepsy do not contribute markedly to VPA-induced birth defects. This model may be used in future studies to investigate mechanisms involved in the pathogenesis of antiepileptic drug-induced birth defects.

Evidence for altered insulin signalling in the brains of genetic absence epilepsy rats from Strasbourg

Insulin-mediated signalling in the brain is critical for neuronal functioning. Insulin resistance is implicated in the development of some neurological diseases, although changes associated with absence epilepsy have not been established yet. Therefore, we examined the major components of PI3K/Akt-mediated insulin signalling in cortical, thalamic, and hippocampal tissues collected from Genetic Absence Epilepsy Rats from Strasbourg (GAERS) and Non-Epileptic Control (NEC) rats. Insulin levels were also measured in plasma and cerebrospinal fluid (CSF). For the brain samples, the nuclear fraction (NF) and total homogenate (TH) were isolated and investigated for insulin signalling markers including insulin receptor beta (IRβ), IR substrate-1 and 2 (IRS1 & 2), phosphatase and tensin homologue (PTEN), phosphoinositide 3-kinase phospho-85 alpha (PI3K p85α), phosphatidylinositol 4,5-bisphosphate, phosphatidylinositol (3,4,5)-trisphosphate, protein kinase B (PKB/Akt1/2/3), glucose transporter-1 and 4 (GLUT1 & 4) and glycogen synthase kinase-3β (GSK3β) using western blotting. A significant increase in PTEN and GSK3β levels and decreased PI3K p85α and pAkt1/2/3 levels were observed in NF of GAERS cortical and hippocampal tissues. IRβ, IRS1, GLUT1, and GLUT4 levels were significantly decreased in hippocampal TH of GAERS compared to NEC. A non-significant increase in insulin levels was observed in plasma and CSF of GAERS rats. An insulin sensitivity assay showed decreased p-Akt level in cortical and hippocampal tissues. Together, altered hippocampal insulin signalling was more prominent in NF and TH compared to cortical and thalamic regions in GAERS. Restoring insulin signalling may improve the pathophysiology displayed by GAERS, including the spike-and-wave discharges that relate to absence seizures in patients.

The effect of prenatal and postnatal caffeine exposure on pentylentetrazole induced seizures in the non-epileptic and epileptic offsprings

Caffeine, a central nervous system stimulant, has been reported to modulate seizure activity in various studies. In this study the effects of caffeine exposure on the pentylenetetrazole (PTZ) induced seizure thresholds and seizure stages in the Wistar and genetic absence epilepsy model offsprings were examined. Adult female and male Wistar rats and genetic absence epilepsy rats from Strasbourg (GAERS) consumed caffeine dissolved in water (0.3 g/L) before conception, during the gestational periods and lactation period whereas control groups of each strain received tap water. All offsprings at postnatal day 30 (PN30) subjected to 70 mg/kg of PTZ were evaluated in terms of overall seizure stages, the latency to the first generalized seizure and the c-Fos protein activity in the brain regions of somatosensorial cortex (SSCx), reticular thalamic nucleus (Rt), ventrobasal thalamus (VB), centromedial nucleus (CM) and lateral geniculate nucleus (LGN). The Wistar caffeine group had significantly shorter latency to the first generalized seizure (1.53 ± 0.49 min) comparing to the Wistar control offsprings (3.40 ± 0.68 min). GAERS caffeine group (6.52 ± 2.48 min) showed significantly longer latency comparing to Wistar caffeine group (1.53 ± 0.49 min). Although statistically not significant, GAERS caffeine group showed a longer latency comparing to the GAERS control group (4.71 ± 1.82 min). In all regions of SSCx, Rt, VB, CM and LGN, GAERS caffeine group had lower c-Fos protein expression comparing to the GAERS control group (p < 0.05). Wistar caffeine rats had lower expression of c-Fos protein comparing to the Wistar control group only in SSCx. In CM, GAERS rats expressed lower c-Fos protein comparing to the Wistar control (p < 0.05). In conclusion differential effects of caffeine in the seizure modulation may involve c-Fos protein activity-dependent protection mechanisms.

Do the Dento-Thalamic Connections of Genetic Absence Epilepsy Rats from Strasbourg Differ from Those of Control Wistar Rats?

The thalamo-cortical circuit is important in the genesis of absence epilepsy. This circuit can be influenced by connecting pathways from various parts of central nervous system. The aim of the present study is to define the dento-thalamic connections in Wistar animals and compare the results with genetic absence epilepsy rats from Strasbourg (GAERS) using the biotinylated dextran amine (BDA) tracer. We injected BDA into the dentate nucleus of 13 (n = 6 Wistar and n = 7 GAERS) animals. The dento-thalamic connections in the Wistar animals were denser and were connected to a wider range of thalamic nuclei compared with GAERS. The dentate nucleus was bilaterally connected to the central (central medial [CM], paracentral [PC]), ventral (ventral medial [VM], ventral lateral [VL], and ventral posterior lateral [VPL]), and posterior (Po) thalamic nuclei in Wistar animals. The majority of these connections were dense contralaterally and scarce ipsilaterally. Contralateral connections were present with the parafascicular (PF), ventral posterior medial, ventral anterior (VA), and central lateral (CL) thalamic nuclei in Wistar animals. Whereas in GAERS, bilateral connections were observed with the VL and CM. Contralateral connections were present with the PC, VM, VA, and PF thalamic nuclei in GAERS. The CL, VPL, and Po thalamic nucleus connections were not observed in GAERS. The present study showed weak/deficit dento-thalamic connections in GAERS compared with control Wistar animals. The scarce information flow from the dentate nucleus to thalamus in GAERS may have a deficient modulatory role on the thalamus and thus may affect modulation of the thalamo-cortical circuit.

Pronounced antiepileptic activity of the subtype-selective GABAA -positive allosteric modulator PF-06372865 in the GAERS absence epilepsy model

AIM

Antiepileptic drugs that modulate GABA have the potential to aggravate or improve the symptoms of absence epilepsy. PF-06372865 is a positive allosteric modulator (PAM) of α2/3/5 subunit-containing GABA_A receptors with minimal activity at α1-containing receptors, which are believed to mediate many of the adverse events associated with benzodiazepines. The aim of this study was to assess the antiepileptic effect of PF-06372865 in a preclinical model of absence seizures.

METHODS

Genetic absence epilepsy rats from Strasbourg (GAERS) was implanted with four cortical electrodes over the frontoparietal cortex, and the number and cumulated duration of spike-and-wave discharges (SWDs) were recorded for 10-90 minutes following administration of vehicle, PF-06372865, and positive controls diazepam and valproate.

RESULTS

PF-06372865 (0.3, 1, 2, 10 mg kg^-1 ) dose-dependently reduced the expression of SWDs, including full suppression at the highest doses by 30 minutes after administration.

CONCLUSIONS

PF-06372865 demonstrated robust efficacy in suppressing SWDs in the GAERS model of absence epilepsy. To our knowledge, this is the first demonstration of antiepileptic activity of an α2/3/5-subtype-selective GABA_A PAM in a model of absence epilepsy. Further study of the antiepileptic properties of PF-06372865 is warranted in patients with absence seizures.

Suppressive effect of Rho-kinase inhibitors Y-27632 and fasudil on spike-and-wave discharges in genetic absence epilepsy rats from Strasbourg (GAERS)

Rho/Rho-kinase (ROCK) signaling contributes to neuroinflammation, epileptogenesis, and seizures in convulsive-type epilepsies. However, this pathway has not been investigated in absence epilepsy. We investigated RhoA activity in genetic absence epilepsy rats from Strasburg (GAERS) and the effects of ROCK inhibitors Y-27632 and fasudil on spike-and-wave discharges (SWDs) of GAERS. ROCK level and activity were measured by Western blot analysis in the brain areas involved in absence seizures (i.e., cortex and thalamus) and hippocampus. Male GAERS were stereotaxically implanted with bilateral cortical electrodes for electroencephalogram (EEG) recordings and/or guide cannula into the right ventricle. ROCK inhibitors were administered by intraperitoneal injection (1-10 mg/kg for Y-27632 or fasudil) or intracerebroventricular injection (7-20 nmol/5 μl for Y-27632 or 10-100 nmol/5 μl for fasudil). EEG was recorded under freely moving conditions. Compared with Wistar rats, GAERS exhibited increased RhoA activity in the somatosensory cortex but not in the thalamus or hippocampus. The single systemic administration of Y-27632 and fasudil partially suppressed the duration and frequency of absence seizure, respectively. However, local brain administration caused a widespread suppressive effect on the total seizure duration, number of seizures, and the average individual seizure length. In summary, Rho/ROCK signaling may be involved in the pathophysiology of absence epilepsy. Furthermore, ROCK inhibitors can control the expression of absence seizure in GAERS, thus indicating that Y-27632 and fasudil have the potential to be used as novel anti-absence drugs.

Elevated sterol regulatory elementary binding protein 1 and GluA2 levels in the hippocampal nuclear fraction of Genetic Absence Epilepsy Rats from Strasbourg

Studies in animal models and human tissues show that nuclear translocation of sterol regulatory element binding protein 1 (SREBP1) and glutamate A2 subunit (GluA2) of cell-surface AMPA receptor (AMPAR) trigger neuronal excitotoxicity-induced apoptosis in stroke. However, it is not known whether a similar type of underlying pathophysiology occurs in absence epilepsy. To explore this issue, we examined the levels of mature SREBP1, GluA2, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), p53, and activated to total caspase 3 ratio in nuclear fractions (NF) of hippocampal homogenate from 8 to 10 week old male Genetic Absence Epilepsy Rats from Strasbourg (GAERS) and non-epileptic control (NEC) strains. Mature SREBP1 and GluA2 levels were elevated approximately two-fold in NFs of GAERS hippocampal homogenates compared to NEC animals. Significant increases in GAPDH (∼15-fold) and total caspase 3 (∼10-fold) levels were also found in NFs of GAERS hippocampal homogenates in comparison to the non-epileptic strain. Data from the current study suggest that absence epilepsy in GAERS is associated with nuclear translocation of mature SREBP1, GluA2 subunit of AMPARs, and recruitment of pro-cell death signaling proteins such as GAPDH and caspase 3. These changes may contribute to hippocampal neuronal/glial cell death in GAERS. Therefore, inhibiting the nuclear accumulation of mature SREBP1 and GluA2 translocation may reduce the pathophysiology of absence epilepsy.

Evaluation of GAD67 immunoreactivity in the region of substantia nigra pars reticulata in resistance to development of convulsive seizure in genetic absence epilepsy rats

OBJECTIVE:

Nonconvulsive absence epilepsy and convulsive epilepsy seizures are rarely seen in the same patient. It has been demonstrated that there is a resistance to development of convulsive seizures in genetic absence epilepsy models. The present study investigated glutamic acid decarboxylase (GAD) immunoreactivity in the brain region related to the interaction of these two seizure types, namely substantia nigra pars reticulata (SNR) subregions, SNR_anterior and SNR_posterior.

METHODS:

Nonepileptic adult male Wistar rats and Genetic Absence Epilepsy Rats from Strasbourg (GAERS) were used. Experimental groups of Wistar and GAERS were electrically stimulated for kindling model to induce convulsive epileptic seizures. An electrical stimulation cannula was stereotaxically implanted to the basolateral amygdala and recording electrodes were placed on the cortex. Sagittal sections of SNR were used to evaluate immunohistochemical reaction. Sections were incubated with anti-GAD67 antibody. Densitometric analysis of GAD67 immunoreactive neurons was performed using photographs of stained sections. One-way analysis of variance and post hoc Bonferroni test were used for statistical analysis of the data.

RESULTS:

There was no difference in GAD67 immunoreactivity of SNR subregions of control Wistar and control GAERS. An increase in GAD67 immunoreactivity was detected in SNR_posterior subregion of stimulated Wistar rats, whereas there was a decrease in GAD67 immunoreactivity in SNR_posterior of stimulated GAERS. The difference in GAD67 immunoreactivity between these two groups was statistically significant.

CONCLUSION:

Level of synthetized gamma-aminobutyric acid in SNR_posterior subregion plays an important role in the interaction of nonconvulsive absence epilepsy seizures and convulsive epilepsy seizures.

Can Patel's τ accurately estimate directionality of connections in brain networks from fMRI?

PURPOSE

Investigating directional interactions between brain regions plays a critical role in fully understanding brain function. Consequently, multiple methods have been developed for noninvasively inferring directional connectivity in human brain networks using functional MRI (fMRI). Recent simulations by Smith et al. showed that Patel's τ, a method based on higher-order statistics, was the best approach for inferring directional interactions from fMRI. Because simulations make restrictive assumptions about reality, we set out to verify this finding using experimental fMRI data obtained from a three-region network in a rat model with electrophysiological validation.

METHODS

Previous studies have shown that dynamic causal modeling can correctly estimate the directionality of this three-region network; Granger causality can also work after the deconvolution of the hemodynamic response. Therefore, we set out to test the hypothesis that Patel's τ obtained from either raw or deconvolved fMRI data should correctly estimate the directionality of neuronal influences obtained from intracerebral electroencephalogram in this network.

RESULTS

Our results indicate that the accuracy of network directionality estimated using Patel's τ was not better than chance.

CONCLUSION

First, our results highlight the necessity of experimental validation of simulation results. Second, it is unclear which brain mechanism is modeled by a directionality inferred from Patel's τ. Third, this study shows that a directional connection ascertained by different methods may mean different things and more experimental studies are needed for investigating the neuronal mechanisms underlying the direction of a connection in the brain ascertained by fMRI using different methods. M Magn Reson Med 78:2003-2010, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

Increased inhibitory synaptic activity in the hippocampus (CA1) of genetic absence epilepsy rats: Relevance of kindling resistance

PURPOSE

Genetic absence epilepsy rats from Strasbourg (GAERS), a well-validated genetic rat model for typical absence epilepsy, are known to manifest a resistance to secondary generalization of abnormal focal electrical activity evoked by kindling. The mechanism of this resistance is still unclear. In order to understand the possible mechanism of kindling resistance, we investigated for the first time, the differences of short-term synaptic plasticity by using a paired-pulse paradigm as an indicator of GABAergic activity in CA1 region of hippocampus in GAERS and non-epileptic Wistar rats in-vivo.

METHODS

Rats were subjected to kindling process, basolateral amygdala was stimulated twice a day, with a supra-threshold current, until they displayed limbic or convulsive seizures. One hour after the last kindling stimulation, evoked field potentials from CA1 pyramidal layer of hippocampus were recorded in-vivo under urethane anesthesia.

RESULTS

In response to supra-threshold kindling stimulations GAERS showed a significantly delayed kindling progression and displayed a significant increase in hippocampal excitability at early stages of kindling that is the critical for the development of convulsive seizures. In control rats that were not received kindling stimulation, paired-pulse depression (PPD) was significantly pronounced in GAERS with respect to the Wistar group. During the kindling course, PPD was gradually reduced in the Wistar rats as kindling progression was advanced. However in GAERS, PPD ratios were not significantly changed at early stages of kindling. When GAERS reached convulsive stage, their PPD ratios became similar to that of Wistar rats.

DISCUSSION

The increased inhibition in paired-pulse responses at early stages of kindling in GAERS suggests the role of augmented GABAergic activity as one of the underlying mechanisms of kindling resistance observed in genetic rat models of absence epilepsy.

The T-type calcium channel antagonist Z944 rescues impairments in crossmodal and visual recognition memory in Genetic Absence Epilepsy Rats from Strasbourg

Childhood absence epilepsy (CAE) is often comorbid with behavioral and cognitive symptoms, including impaired visual memory. Genetic Absence Epilepsy Rats from Strasbourg (GAERS) is an animal model closely resembling CAE; however, cognition in GAERS is poorly understood. Crossmodal object recognition (CMOR) is a recently developed memory task that examines not only purely visual and tactile memory, but also requires rodents to integrate sensory information about objects gained from tactile exploration to enable visual recognition. Both the visual and crossmodal variations of the CMOR task rely on the perirhinal cortex, an area with dense expression of T-type calcium channels. GAERS express a gain-in-function missense mutation in the Cav3.2 T-type calcium channel gene. Therefore, we tested whether the T-type calcium channel blocker Z944 dose dependently (1, 3, 10mg/kg; i.p.) altered CMOR memory in GAERS compared to the non-epileptic control (NEC) strain. GAERS demonstrated recognition memory deficits in the visual and crossmodal variations of the CMOR task that were reversed by the highest dose of Z944. Electroencephalogram recordings determined that deficits in CMOR memory in GAERS were not the result of seizures during task performance. In contrast, NEC showed a decrease in CMOR memory following Z944 treatment. These findings suggest that T-type calcium channels mediate CMOR in both the GAERS and NEC strains. Future research into the therapeutic potential of T-type calcium channel regulation may be particularly fruitful for the treatment of CAE and other disorders characterized by visual memory deficits.

Environmental enrichment imparts disease-modifying and transgenerational effects on genetically-determined epilepsy and anxiety

INTRODUCTION

The absence epilepsies are presumed to be caused by genetic factors, but the influence of environmental exposures on epilepsy development and severity, and whether this influence is transmitted to subsequent generations, is not well known. We assessed the effects of environmental enrichment on epilepsy and anxiety outcomes in multiple generations of GAERS - a genetic rat model of absence epilepsy that manifests comorbid elevated anxiety-like behaviour.

METHODS

GAERS were exposed to environmental enrichment or standard housing beginning either prior to, or after epilepsy onset, and underwent EEG recordings and anxiety testing. Then, we exposed male GAERS to early enrichment or standard housing and generated F1 progeny, which also underwent EEG recordings. Hippocampal CRH mRNA expression and DNA methylation were assessed using RT-PCR and pyrosequencing, respectively.

RESULTS

Early environmental enrichment delayed the onset of epilepsy in GAERS, and resulted in fewer seizures in adulthood, compared with standard housed GAERS. Enrichment also reduced the frequency of seizures when initiated in adulthood. Anxiety levels were reduced by enrichment, and these anti-epileptogenic and anxiolytic effects were heritable into the next generation. We also found reduced expression of CRH mRNA in GAERS exposed to enrichment, but this was not due to changes in DNA methylation.

CONCLUSIONS

Environmental enrichment produces disease-modifying effects on genetically determined absence epilepsy and anxiety, and these beneficial effects are transferable to the subsequent generation. Reduced CRH expression was associated with these phenotypic improvements. Environmental stimulation holds promise as a naturalistic therapy for genetically determined epilepsy which may benefit subsequent generations.

The role of the substantia nigra pars reticulata in kindling resistance in rats with genetic absence epilepsy

OBJECTIVE

Genetic Absence Epilepsy Rats from Strasbourg (GAERS) show a resistance to secondary generalization of focal limbic seizures evoked by kindling. The substantia nigra pars reticulata (SNR) is involved in the propagation and modulation of seizures in kindling. We first examined the role of the SNRanterior and SNRposterior subregions in the resistance to the development of kindling in GAERS. Subsequently, to determine whether kindling resistance relates to differential sensitivity of γ-aminobutyric acid γ-aminobutyric acid (GABA)ergic or dopaminergic SNR neurons to kindling, we studied the effects of kindling-inducing stimulations on parvalbumin (PRV; GABAergic neuron marker) or tyrosine hydroxylase (TH; dopaminergic neuron marker) immunoreactivity (ir), respectively, in GAERS and in nonepileptic control (NEC) Wistar rats that lack kindling resistance.

METHODS

Adult male GAERS were implanted with a stimulation electrode in the amygdala, and bilateral injection cannulas for lidocaine or saline injection (30 min before each kindling stimulation until the animals reached three stage 5 seizures or the 22 stimulations) into the SNRanterior or SNRposterior . In another experiment, PRV-ir in SNRanterior and SNRposterior and TH-ir in SNRposterior only were densitometrically compared in GAERS-SHAM, NEC-SHAM GAERS-STIM, and NEC-STIM animals (6 kindling stimulations).

RESULTS

Bilateral SNRposterior infusions of lidocaine eliminated the kindling resistance and resulted in stage 5 generalized motor seizures in all kindled rats. Bilateral lidocaine infusions in the SNRanterior failed to alter the kindling resistance in GAERS. PRV-ir in the SNRposterior was unaltered in GAERS-STIM but increased in NEC-STIM group. Cellular TH-ir in the SNRposterior significantly increased by kindling stimulations in both NEC-STIM and GAERS-STIM groups.

SIGNIFICANCE

The kindling resistance in GAERS is mediated by the SNRposterior in a lidocaine-sensitive manner. The insensitivity to kindling stimulation of PRV-ir in SNRposterior of GAERS but not NEC rats, implicate GABAergic SNRposterior neurons in kindling resistance. In contrast, the observed stimulation-specific increase in TH-ir in the SNRposterior is unrelated to kindling resistance.

Evaluation of an automated spike-and-wave complex detection algorithm in the EEG from a rat model of absence epilepsy

The aim of this prospective blinded study was to evaluate an automated algorithm for spike-and-wave discharge (SWD) detection applied to EEGs from genetic absence epilepsy rats from Strasbourg (GAERS). Five GAERS underwent four sessions of 20-min EEG recording. Each EEG was manually analyzed for SWDs longer than one second by two investigators and automatically using an algorithm developed in MATLAB®. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated for the manual (reference) versus the automatic (test) methods. The results showed that the algorithm had specificity, sensitivity, PPV and NPV >94%, comparable to published methods that are based on analyzing EEG changes in the frequency domain. This provides a good alternative as a method designed to mimic human manual marking in the time domain.

Methods of automated absence seizure detection, interference by stimulation, and possibilities for prediction in genetic absence models

BACKGROUND

Genetic rat models for childhood absence epilepsy have become instrumental in developing theories on the origin of absence epilepsy, the evaluation of new and experimental treatments, as well as in developing new methods for automatic seizure detection, prediction, and/or interference of seizures.

METHOD

Various methods for automated off and on-line analyses of ECoG in rodent models are reviewed, as well as data on how to interfere with the spike-wave discharges by different types of invasive and non-invasive electrical, magnetic, and optical brain stimulation. Also a new method for seizure prediction is proposed.

RESULTS

Many selective and specific methods for off- and on-line spike-wave discharge detection seem excellent, with possibilities to overcome the issue of individual differences. Moreover, electrical deep brain stimulation is rather effective in interrupting ongoing spike-wave discharges with low stimulation intensity. A network based method is proposed for absence seizures prediction with a high sensitivity but a low selectivity. Solutions that prevent false alarms, integrated in a closed loop brain stimulation system open the ways for experimental seizure control.

CONCLUSIONS

The presence of preictal cursor activity detected with state of the art time frequency and network analyses shows that spike-wave discharges are not caused by sudden and abrupt transitions but that there are detectable dynamic events. Their changes in time-space-frequency characteristics might yield new options for seizure prediction and seizure control.

Thalamocortical relationships and network synchronization in a new genetic model "in mirror" for absence epilepsy

Electroencephalographic generalized spike and wave discharges (SWD), the hallmark of human absence seizures, are generated in thalamocortical networks. However, the potential alterations in these networks in terms of the efficacy of the reciprocal synaptic activities between the cortex and the thalamus are not known in this pathology. Here, the efficacy of these reciprocal connections is assessed in vitro in thalamocortical slices obtained from BS/Orl mice, which is a new genetic model of absence epilepsy. These mice show spontaneous SWD, and their features can be compared to that of BR/Orl mice, which are free of SWD. In addition, since gap junctions may modulate the efficacy of these connections, their implications in pharmacologically-induced epileptiform discharges were studied in the same slices. The thalamus and neocortex were independently stimulated and the electrically-evoked responses in both structures were recorded from the same slice. The synaptic efficacy of thalamocortical and corticothalamic connections were assessed by measuring the dynamic range of synaptic field potential changes in response to increasing stimulation strengths. The connection efficacy was weaker in epileptic mice however, this decrease in efficacy was more pronounced in thalamocortical afferents, thus introducing an imbalance in the reciprocal connections between the cortex and thalamus. However, short-term facilitation of the thalamocortical responses were increased in epileptic mice compared to non-epileptic animals. These features may favor occurrence of rhythmical activities in thalamocortical networks. In addition, carbenoxolone (a gap junction blocker) decreased the cumulative duration of 4-aminopyridine-induced ictal-like activities, with a slower time course in epileptic mice. However, the 4-aminopyridine-induced GABA-dependent negative potentials, which appeared to trigger the ictal-like activities, remained. Our results show that the balance of the reciprocal connections between the thalamus and cortex is altered in favor of the corticothalamic connections in epileptic mice, and suggest that gap junctions mediate a stronger cortical synchronization in this strain.