The pilocarpine model of mesial temporal lobe epilepsy: Over one decade later, with more rodent species and new investigative approaches

Glycoprotein Non-metastatic Melanoma Protein B (GPNMB) Protects Against Neuroinflammation and Neuronal Loss in Pilocarpine-induced Epilepsy via the Regulation of Microglial Polarization

Epilepsy is a progressive neurodegenerative disease highlighted by recurrent seizures, neuroinflammation, and the loss of neurons. Microglial dysfunction is commonly found in epileptic foci and contributes to neuroinflammation in the initiation and progression of epilepsy. Glycoprotein non-metastatic melanoma protein B (GPNMB), a transmembrane glycoprotein, has been involved in the microglial activation and neuroinflammation response. The present study investigated the functional significance of GPNMB in epilepsy. A proven model of epilepsy was established by intraperitoneal injection of pilocarpine to male Sprague Dawley rats. Lentivirus vectors carrying GPNMB or GPNMB short hairpin RNA (shGPNMB) were injected into the hippocampus to induce overexpression or knockdown of GPNMB. GPNMB expression was significantly upregulated and overexpression of GPNMB in the hippocampus reduced seizure activity and neuronal loss after status epilepticus (SE). We here focused on the effects of GPNMB deficiency on neuronal injury and microglia polarization 28 days after SE. GPNMB knockdown accelerated neuronal damage in the hippocampus, evidenced by increased neuron loss and neuronal cell apoptosis. Following GPNMB knockdown, M1 polarization (iNOS) and secretion of pro-inflammatory cytokines IL-6, IL-1β, and TNF-α were increased, and M2 polarization (Arg1) and secretion of anti-inflammatory cytokines IL-4, IL-10, and TGF-β were decreased. BV2 cells were used to further confirm the regulatory role of GPNMB in modulating phenotypic transformations and inflammatory cytokine expressions in microglia. In conclusion, these results indicated that GPNMB suppressed epilepsy through repression of hippocampal neuroinflammation, suggesting that GPNMB might be considered the potential neurotherapeutic target for epilepsy management and play a protective role against epilepsy by modulating the polarization of microglia.

MiR-23b-3p Improves Brain Damage after Status Epilepticus by Reducing the Formation of Pathological High-Frequency Oscillations via Inhibition of cx43 in Rat Hippocampus

In order to investigate the effectiveness and safety of miR-23b-3p in anti-seizure activity and to elucidate the regulatory relationship between miR-23b-3p and Cx43 in the nervous system, we have established a lithium chloride-pilocarpine (PILO) status epilepticus (SE) model. Rats were randomly divided into the following groups: seizure control (PILO), valproate sodium (VPA+PILO), recombinant miR-23b-3p overexpression (miR+PILO), miR-23b-3p sponges (Sponges+PILO), and scramble sequence negative control (Scramble+PILO) (n = 6/group). After experiments, we got the following results. In the acute phase, the time required for rats to reach stage IV after PILO injection was significantly longer in VPA+PILO and miR+PILO. In the chronic phase after SE, the frequency of spontaneous recurrent seizures (SRSs) in VPA+PILO and miR+PILO was significantly reduced. At 10 min before seizure cessation, the average energy expression of fast ripples (FRs) in VPA+PILO and miR+PILO was significantly lower than in PILO. After 28 days of seizure, Cx43 expression in PILO was significantly increased, and Beclin1expression in all groups was significantly increased. After 28 days of SE,the number of synapses in the CA1 region of the hippocampus was significantly higher in the VPA+PILO and miR+PILO groups compared to that in the PILO group. After 28 days of SE ,hippocampal necrotic cells in the CA3 region were significantly lower in the VPA+PILO and miR+PILO groups compared to those in the PILO group. There were no significant differences in biochemical indicators among the experimental group rats 28 days after SE compared to the seizure control group. Based on the previous facts, we can reach the conclusion that MiR-23b-3p targets and blocks the expression of hippocampal Cx43 which can reduce the formation of pathological FRs, thereby alleviating the severity of seizures, improving seizure-induced brain damage.

Light-Driven Sodium Pump as a Potential Tool for the Control of Seizures in Epilepsy

The marine flavobacterium Krokinobactereikastus light-driven sodium pump (KR2) generates an outward sodium ion current under 530 nm light stimulation, representing a promising optogenetic tool for seizure control. However, the specifics of KR2 application to suppress epileptic activity have not yet been addressed. In the present study, we investigated the possibility of KR2 photostimulation to suppress epileptiform activity in mouse brain slices using the 4-aminopyrindine (4-AP) model. We injected the adeno-associated viral vector (AAV-PHP.eB-hSyn-KR2-YFP) containing the KR2 sodium pump gene enhanced with appropriate trafficking tags. KR2 expression was observed in the lateral entorhinal cortex and CA1 hippocampus. Using whole-cell patch clamp in mouse brain slices, we show that KR2, when stimulated with LED light, induces a substantial hyperpolarization of entorhinal neurons. However, continuous photostimulation of KR2 does not interrupt ictal discharges in mouse entorhinal cortex slices induced by a solution containing 4-AP. KR2-induced hyperpolarization strongly activates neuronal HCN channels. Consequently, turning off photostimulation resulted in HCN channel-mediated rebound depolarization accompanied by a transient increase in spontaneous network activity. Using low-frequency pulsed photostimulation, we induced the generation of short HCN channel-mediated discharges that occurred in response to the light stimulus being turned off; these discharges reliably interrupt ictal activity. Thus, low-frequency pulsed photostimulation of KR2 can be considered as a potential tool for controlling epileptic seizures.

Neuroprotective potential of topiramate, pregabalin and lacosamide combination in a rat model of acute SE and intractable epilepsy: Perspectives from electroencephalographic, neurobehavioral and regional degenerative analysis

The lithium-pilocarpine model is commonly used to recapitulate characteristics of human intractable focal epilepsy. In the current study, we explored the impact of topiramate (TPM) alone and in combination with pregabalin and lacosamide administration for 6 weeks on the evolution of spontaneous recurrent seizures (SRS) and disease-modifying potential on associated neuropsychiatric comorbidities. In addition, redox impairments and neurodegeneration in hippocampus regions vulnerable to temporal lobe epilepsy (TLE) were assessed by cresyl violet staining. Results revealed that acute electrophysiological (EEG) profiling of the ASD cocktail markedly halted sharp ictogenic spikes as well as altered dynamics of brain wave oscillations thus validating the need for polytherapy vs. monotherapy. In TLE animals, pharmacological intervention for 6 weeks with topiramate 10 mg/kg in combination with PREG and LAC at the dose of 20 mg/kg exhibited marked protection from SRS incidence, improved body weight, offensive aggression, anxiety-like behavior, cognitive impairments, and depressive-like behavior (p < 0.05). Moreover, combination therapy impeded redox impairments as evidenced by decreased MDA and AchE levels and increased activity of antioxidant SOD, GSH enzymes. Furthermore, polytherapy rescued animals from SE-induced neurodegeneration with increased neuronal density in CA1, CA3c, CA3ab, hilus, and granular cell layer (GCL) of the dentate gyrus. In conclusion, early polytherapy with topiramate in combination with pregabalin and lacosamide prompted synergy and prevented epileptogenesis with associated psychological and neuropathologic alterations.

Increasing adult neurogenesis protects mice from epilepsy

Neurogenesis occurs in the adult brain in the hippocampal dentate gyrus, an area that contains neurons which are vulnerable to insults and injury, such as severe seizures. Previous studies showed that increasing adult neurogenesis reduced neuronal damage after these seizures. Because the damage typically is followed by chronic life-long seizures (epilepsy), we asked if increasing adult neurogenesis would prevent epilepsy. Adult neurogenesis was selectively increased by deleting the pro-apoptotic gene Bax from Nestin-expressing progenitors. Tamoxifen was administered at 6 weeks of age to conditionally delete Bax in Nestin-CreERT2 Bax fl/fl mice. Six weeks after tamoxifen administration, severe seizures (status epilepticus; SE) were induced by injection of the convulsant pilocarpine. After mice developed epilepsy, seizure frequency was quantified for 3 weeks. Mice with increased adult neurogenesis exhibited fewer chronic seizures. Postictal depression was reduced also. These results were primarily in female mice, possibly because they were the more affected by Bax deletion than males, consistent with sex differences in Bax. The female mice with enhanced adult neurogenesis also showed less neuronal loss of hilar mossy cells and hilar somatostatin-expressing neurons than wild type females or males, which is notable because these two hilar cell types are implicated in epileptogenesis. The results suggest that selective Bax deletion to increase adult neurogenesis can reduce experimental epilepsy, and the effect shows a striking sex difference. The results are surprising in light of past studies showing that suppressing adult-born neurons can also reduce chronic seizures.

Development of spontaneous recurrent seizures accompanied with increased rates of interictal spikes and decreased hippocampal delta and theta activities following extended kindling in mice

Interictal epileptiform discharges refer to aberrant brain electrographic signals between seizures and feature intermittent interictal spikes (ISs), sharp waves, and/or abnormal rhythms. Recognition of these epileptiform activities by electroencephalographic (EEG) examinations greatly aids epilepsy diagnosis and localization of the seizure onset zone. ISs are a major form of interictal epileptiform discharges recognized in animal models of epilepsy. Progressive changes in IS waveforms, IS rates, and/or associated fast ripple oscillations have been shown to precede the development of spontaneous recurrent seizures (SRS) in various animal models. IS expressions in the kindling model of epilepsy have been demonstrated but IS changes during the course of SRS development in extended kindled animals remain to be detailed. We hence addressed this issue using a mouse model of kindling-induced SRS. Adult C57 black mice received twice daily hippocampal stimulations until SRS occurrence, with 24-h EEG monitoring performed following 50, 80, and ≥ 100 stimulations and after observation of SRS. In the stimulated hippocampus, increases in spontaneous ISs rates, but not in IS waveforms nor IS-associated fast ripples, along with decreased frequencies of hippocampal delta and theta rhythms, were observed before SRS onset. Comparable increases in IS rates were further observed in the unstimulated hippocampus, piriform cortex, and entorhinal cortex, but not in the unstimulated parietal cortex and dorsomedial thalamus. These data provide original evidence suggesting that increases in hippocampal IS rates, together with reductions in hippocampal delta and theta rhythms are closely associated with development of SRS in a rodent kindling model.

Molecular Genetics of Acquired Temporal Lobe Epilepsy

An epilepsy diagnosis reduces a patient's quality of life tremendously, and it is a fate shared by over 50 million people worldwide. Temporal lobe epilepsy (TLE) is largely considered a nongenetic or acquired form of epilepsy that develops in consequence of neuronal trauma by injury, malformations, inflammation, or a prolonged (febrile) seizure. Although extensive research has been conducted to understand the process of epileptogenesis, a therapeutic approach to stop its manifestation or to reliably cure the disease has yet to be developed. In this review, we briefly summarize the current literature predominately based on data from excitotoxic rodent models on the cellular events proposed to drive epileptogenesis and thoroughly discuss the major molecular pathways involved, with a focus on neurogenesis-related processes and transcription factors. Furthermore, recent investigations emphasized the role of the genetic background for the acquisition of epilepsy, including variants of neurodevelopmental genes. Mutations in associated transcription factors may have the potential to innately increase the vulnerability of the hippocampus to develop epilepsy following an injury-an emerging perspective on the epileptogenic process in acquired forms of epilepsy.

Time- and Region-Specific Selection of Reference Genes in the Rat Brain in the Lithium-Pilocarpine Model of Acquired Temporal Lobe Epilepsy

Reverse transcription followed by quantitative polymerase chain reaction (RT-qPCR) is a commonly used tool for gene expression analysis. The selection of stably expressed reference genes is required for accurate normalization. The aim of this study was to identify the optimal reference genes for RT-qPCR normalization in various brain regions of rats at different stages of the lithium-pilocarpine model of acquired epilepsy. We tested the expression stability of nine housekeeping genes commonly used as reference genes in brain research: Actb, Gapdh, B2m, Rpl13a, Sdha, Ppia, Hprt1, Pgk1, and Ywhaz. Based on four standard algorithms (geNorm, NormFinder, BestKeeper, and comparative delta-Ct), we found that after pilocarpine-induced status epilepticus, the stability of the tested reference genes varied significantly between brain regions and depended on time after epileptogenesis induction (3 and 7 days in the latent phase, and 2 months in the chronic phase of the model). Pgk1 and Ywhaz were the most stable, while Actb, Sdha, and B2m demonstrated the lowest stability in the analyzed brain areas. We revealed time- and region-specific changes in the mRNA expression of the housekeeping genes B2m, Actb, Sdha, Rpl13a, Gapdh, Hprt1, and Sdha. These changes were more pronounced in the hippocampal region during the latent phase of the model and are thought to be related to epileptogenesis. Thus, RT-qPCR analysis of mRNA expression in acquired epilepsy models requires careful selection of reference genes depending on the brain region and time of analysis. For the time course study of epileptogenesis in the rat lithium-pilocarpine model, we recommend the use of the Pgk1 and Ywhaz genes.

Saikosaponin D mitigate pilocarpine-induced astrocyte injury by regulating the NLRP3/caspase-1 signaling pathway

Studies have shown that saikosaponin D (SSD) has favorable neurotherapeutic effects. Therefore, the objective of this study was to explore the efficacy and possible molecular mechanisms of SSD on pilocarpine (PP)-induced astrocyte injury. Primary astrocytes were isolated from juvenile rats and identified using immunofluorescence. The cells were treated with PP and/or SSD for 6 h and 12 h, respectively, followed by measurement of their viability through 3-(4,5-dimethylthiazol)-2,5-diphenyl-tetrazolium bromide (MTT) assay. Next, quantitative real-time polymerase chain reaction (qRT-PCR) was used to measure the expression levels of Glial fibrillary acidic protein (GFAP), C3, S100 calcium binding protein A10 (S100a10), pentraxin 3 (Ptx3), toll-like receptor 4 (TLR4), and RAG in astrocytes after different treatments. Enzyme-linked immunosorbent assay and biochemical tests were utilized to evaluate the level of inflammatory factors [interleukin (IL)-1β, IL-6, and tumor necrosis factor alpha (TNF-α)] secreted by cells and the content of oxidative stress-related factors (malondialdehyde [MDA] and glutathione [GSH]) or enzyme activity (catalase [CAT] and glutathione peroxidase [GPX]) in cells. The JC-1 mitochondrial membrane potential (MMP) fluorescence probe was used to measure the MMP in astrocytes. Additionally, western blot was applied to test the expression of proteins related to the nod-like receptor protein 3 (NLRP3)/caspase-1 signaling pathway. PP treatment (1 mM) induced cell injury by significantly reducing the viability of astrocytes and expression of cellular markers. SSD treatment (4 μM) had no toxicity to astrocytes. Besides, SSD (4 μM) treatment could significantly up-regulate the cell viability and marker expression of PP-induced astrocytes. Furthermore, SSD could be employed to inhibit inflammation (reduce IL-1β, IL-6, and TNF-α levels) and oxidative stress (decrease MDA level, elevate GSH level, the activity of CAT and GPX), and ameliorate mitochondrial dysfunction (upregulate JC-1 ratio) in PP-induced astrocytes. Moreover, further mechanism exploration revealed that SSD treatment significantly reduced the activity of the NLRP3/caspase-1 signaling pathway activated by PP induction. SSD increased cell viability, inhibited inflammation and oxidative stress response, and ameliorated mitochondrial dysfunction in PP-induced astrocyte injury model, thus playing a neuroprotective role. The mechanism of SSD may be related to the inhibition of the NLRP3/caspase-1 inflammasome.

Current advances in rodent drug-resistant temporal lobe epilepsy models: Hints from laboratory studies

Anti-seizure drugs (ASDs) are the first choice for the treatment of epilepsy, but there is still one-third of patients with epilepsy (PWEs) who are resistant to two or more appropriately chosen ASDs, named drug-resistant epilepsy (DRE). Temporal lobe epilepsy (TLE), a common type of epilepsy usually associated with hippocampal sclerosis (HS), shares the highest proportion of drug resistance (approximately 70%). In view of the key role of the temporal lobe in memory, emotion, and other physiological functions, patients with drug-resistant temporal lobe epilepsy (DR-TLE) are often accompanied by serious complications, and surgical procedures also yield extra considerations. The exact mechanisms for the genesis of DR-TLE remain unillustrated, which makes it hard to manage patients with DR-TLE in clinical practice. Animal models of DR-TLE play an irreplaceable role in both understanding the mechanism and searching for new therapeutic strategies or drugs. In this review article, we systematically summarized different types of current DR-TLE models, and then recent advances in mechanism investigations obtained in these models were presented, especially with the development of advanced experimental techniques and tools. We are deeply encouraged that novel strategies show great therapeutic potential in those DR-TLE models. Based on the big steps reached from the bench, a new light has been shed on the precise management of DR-TLE.

Disruption of TLE epileptiform activity retarded the seizure and reduced pathological HFOs

In temporal lobe epilepsy (TLE), the epileptogenic zones, such as the temporal lobe structure, could generate pathological high-frequency oscillations (pHFOs, 250-500 Hz) before the ictal period. These pHFOs have also been observed during the process of seizures in both TLE patients and animals, exhibiting a critical role as promising biomarkers for TLE seizures. TLE seizures could be modulated via regulating the neural excitability in epileptogenic zones, for that TLE is primarily associated with the excitation-inhibition imbalance. However, whether these kinds of modulations could also impact the pHFOs characteristics during TLE seizures is still unclear. For this purpose, we pharmaco-genetically inhibited the principal cells (PCs) in the mouse CA3 region and tracked the difference in the behavioral and electrophysiological features during LiCl-pilocarpine-induced TLE seizure between the hM4Di+CNO (experimental) mice and mCherry+CNO (control) mice. Delayed latency, decreased averaged duration, and reduced counts of the generalized seizure were observed in the experimental mice. Besides, the electrophysiological characteristics, such as the firing rate of PCs and the count of pHFO, exhibited significant decline in the CA3 and CA1 regions. During TLE seizure, there existed strong phase-coupling between pHFO and PCs spike timing in the control mice, while it was abolished in the experimental mice. In addition, we also found that the counts of pHFO were significantly associated with the behavioral features, indicating the close relationships within them. Collectively, our findings suggested that alterations in pHFO and the retardation of seizures may be attributed to disruptions in neuronal excitability, and the variations of electrophysiological features were related to seizure severity during TLE seizures. These results provide valuable insights into the role of pHFOs in TLE and shed light on the underlying mechanisms involved.

Changes in the Dentate Gyrus Gene Expression Profile Induced by Levetiracetam Treatment in Rats with Mesial Temporal Lobe Epilepsy

Temporal lobe epilepsy (TLE) is one of the most common forms of focal epilepsy. Levetiracetam (LEV) is an antiepileptic drug whose mechanism of action at the genetic level has not been fully described. Therefore, the aim of the present work was to evaluate the relevant gene expression changes in the dentate gyrus (DG) of LEV-treated rats with pilocarpine-induced TLE. Whole-transcriptome microarrays were used to obtain the differential genetic profiles of control (CTRL), epileptic (EPI), and EPI rats treated for one week with LEV (EPI + LEV). Quantitative RT-qPCR was used to evaluate the RNA levels of the genes of interest. According to the results of the EPI vs. CTRL analysis, 685 genes were differentially expressed, 355 of which were underexpressed and 330 of which were overexpressed. According to the analysis of the EPI + LEV vs. EPI groups, 675 genes were differentially expressed, 477 of which were downregulated and 198 of which were upregulated. A total of 94 genes whose expression was altered by epilepsy and modified by LEV were identified. The RT-qPCR confirmed that LEV treatment reversed the increased expression of Hgf mRNA and decreased the expression of the Efcab1, Adam8, Slc24a1, and Serpinb1a genes in the DG. These results indicate that LEV could be involved in nonclassical mechanisms involved in Ca2+ homeostasis and the regulation of the mTOR pathway through Efcab1, Hgf, SLC24a1, Adam8, and Serpinb1a, contributing to reduced hyperexcitability in TLE patients.

Highly dynamic inflammatory and excitability transcriptional profiles in hippocampal CA1 following status epilepticus

Transient brain insults including status epilepticus (SE) can initiate a process termed 'epileptogenesis' that results in chronic temporal lobe epilepsy. As a consequence, the entire tri-synaptic circuit of the hippocampus is fundamentally impaired. A key role in epileptogenesis has been attributed to the CA1 region as the last relay station in the hippocampal circuit and as site of aberrant plasticity, e.g. mediated by acquired channelopathies. The transcriptional profiles of the distinct hippocampal neurons are highly dynamic during epileptogenesis. Here, we aimed to elucidate the early SE-elicited mRNA signature changes and the respective upstream regulatory cascades in CA1. RNA sequencing of CA1 was performed in the mouse pilocarpine-induced SE model at multiple time points ranging from 6 to 72 h after the initial insult. Bioinformatics was used to decipher altered gene expression, signalling cascades and their corresponding cell type profiles. Robust transcriptomic changes were detected at 6 h after SE and at subsequent time points during early epileptogenesis. Major differentially expressed mRNAs encoded primarily immediate early and excitability-related gene products, as well as genes encoding immune signalling factors. Binding sites for the transcription factors Nfkb1, Spi1, Irf8, and two Runx family members, were enriched within promoters of differentially expressed genes related to major inflammatory processes, whereas the transcriptional repressors Suz12, Nfe2l2 and Rest were associated with hyperexcitability and GABA / glutamate receptor activity. CA1 quickly responds to SE by inducing transcription of genes linked to inflammation and excitation stress. Transcription factors mediating this transcriptomic switch represent targets for new highly selected, cell type and time window-specific anti-epileptogenic strategies.

MiR-324-5p inhibition after intrahippocampal kainic acid-induced status epilepticus does not prevent epileptogenesis in mice

Background

Acquired epilepsies are caused by an initial brain insult that is followed by epileptogenesis and finally the development of spontaneous recurrent seizures. The mechanisms underlying epileptogenesis are not fully understood. MicroRNAs regulate mRNA translation and stability and are frequently implicated in epilepsy. For example, antagonism of a specific microRNA, miR-324-5p, before brain insult and in a model of chronic epilepsy decreases seizure susceptibility and frequency, respectively. Here, we tested whether antagonism of miR-324-5p during epileptogenesis inhibits the development of epilepsy.

Methods

We used the intrahippocampal kainic acid (IHpKa) model to initiate epileptogenesis in male wild type C57BL/6 J mice aged 6-8 weeks. Twenty-four hours after IHpKa, we administered a miR-324-5p or scrambled control antagomir intracerebroventricularly and implanted cortical surface electrodes for EEG monitoring. EEG data was collected for 28 days and analyzed for seizure frequency and duration, interictal spike activity, and EEG power. Brains were collected for histological analysis.

Results

Histological analysis of brain tissue showed that IHpKa caused characteristic hippocampal damage in most mice regardless of treatment. Antagomir treatment did not affect latency to, frequency, or duration of spontaneous recurrent seizures or interictal spike activity but did alter the temporal development of frequency band-specific EEG power.

Conclusion

These results suggest that miR-324-5p inhibition during epileptogenesis induced by status epilepticus does not convey anti-epileptogenic effects despite having subtle effects on EEG frequency bands. Our results highlight the importance of timing of intervention across epilepsy development and suggest that miR-324-5p may act primarily as a proconvulsant rather than a pro-epileptogenic regulator.

IRAK-M Ablation Promotes Status Epilepticus-Induced Neuroinflammation via Activating M1 Microglia and Impairing Excitatory Synaptic Function

Epilepsy is one of the most common neurological disorders. The pro-epileptic and antiepileptic roles of microglia have recently garnered significant attention. Interleukin-1 receptor-associated kinase (IRAK)-M, an important kinase in the innate immune response, is mainly expressed in microglia and acts as a negative regulator of the TLR4 signaling pathway that mediates the anti-inflammatory effect. However, whether IRAK-M exerts a protective role in epileptogenesis as well as the molecular and cellular mechanisms underlying these processes are yet to be elucidated. An epilepsy mouse model induced by pilocarpine was used in this study. Real-time quantitative polymerase chain reaction and western blot analysis were used to analyze mRNA and protein expression levels, respectively. Whole-cell voltage-clamp recordings were employed to evaluate the glutamatergic synaptic transmission in hippocampal neurons. Immunofluorescence was utilized to show the glial cell activation and neuronal loss. Furthermore, the proportion of microglia was analyzed using flow cytometry. Seizure dynamics influenced the expression of IRAK-M. Its knockout dramatically exacerbated the seizures and the pathology in epilepsy and increased the N-methyl-d-aspartate receptor (NMDAR) expression, thereby enhancing glutamatergic synaptic transmission in hippocampal CA1 pyramidal neurons in mice. Furthermore, IRAK-M deficiency augmented hippocampal neuronal loss via a possible mechanism of NMDAR-mediated excitotoxicity. IRAK-M deletion promotes microglia toward the M1 phenotype, which resulted in high levels of proinflammatory cytokines and was accompanied by a visible increase in the expressions of key microglial polarization-related proteins, including p-STAT1, TRAF6, and SOCS1. The findings demonstrate that IRAK-M dysfunction contributes to the progression of epilepsy by increasing M1 microglial polarization and glutamatergic synaptic transmission. This is possibly related to NMDARs, particularly Grin2A and Grin2B, which suggests that IRAK-M could serve as a novel therapeutic target for the direct alleviation of epilepsy.

Nicotinic Acetylcholine Receptor Dysfunction in Addiction and in Some Neurodegenerative and Neuropsychiatric Diseases

The cholinergic system plays an essential role in brain development, physiology, and pathophysiology. Herein, we review how specific alterations in this system, through genetic mutations or abnormal receptor function, can lead to aberrant neural circuitry that triggers disease. The review focuses on the nicotinic acetylcholine receptor (nAChR) and its role in addiction and in neurodegenerative and neuropsychiatric diseases and epilepsy. Cholinergic dysfunction is associated with inflammatory processes mainly through the involvement of α7 nAChRs expressed in brain and in peripheral immune cells. Evidence suggests that these neuroinflammatory processes trigger and aggravate pathological states. We discuss the preclinical evidence demonstrating the therapeutic potential of nAChR ligands in Alzheimer disease, Parkinson disease, schizophrenia spectrum disorders, and in autosomal dominant sleep-related hypermotor epilepsy. PubMed and Google Scholar bibliographic databases were searched with the keywords indicated below.

Ectopic expression of neuronal adenosine kinase, a biomarker in mesial temporal lobe epilepsy without hippocampal sclerosis

AIMS

Mesial temporal lobe epilepsy without hippocampal sclerosis (no-HS MTLE) refers to those MTLE patients who have neither magnetic resonance imaging (MRI) lesions nor definite pathological evidence of hippocampal sclerosis. They usually have resistance to antiepileptic drugs, difficulties in precise seizure location and poor surgical outcomes. Adenosine is a neuroprotective neuromodulator that acts as a seizure terminator in the brain. The role of adenosine in no-HS MTLE is still unclear. Further research to explore the aetiology and pathogenesis of no-HS MTLE may help to find new therapeutic targets.

METHODS

In surgically resected hippocampal specimens, we examined the maladaptive changes of the adenosine system of patients with no-HS MTLE. In order to better understand the dysregulation of the adenosine pathway in no-HS MTLE, we developed a rat model based on the induction of focal cortical lesions through a prenatal freeze injury.

RESULTS

We first examined the adenosine system in no-HS MTLE patients who lack hippocampal neuronal loss and found ectopic expression of the astrocytic adenosine metabolising enzyme adenosine kinase (ADK) in hippocampal pyramidal neurons, as well as downregulation of neuronal A1 receptors (A1 Rs) in the hippocampus. In the no-HS MTLE model rats, the transition of ADK from neuronal expression to an adult pattern of glial expression in the hippocampus was significantly delayed.

CONCLUSIONS

Ectopic expression of neuronal ADK might be a pathological hallmark of no-HS MTLE. Maladaptive changes in adenosine metabolism might be a novel target for therapeutic intervention in no-HS MTLE.

Dynamic effects of miR-20a-5p on hippocampal ripple energy after status epilepticus in rats

To determine the dynamic effects of miR-20a-5p on hippocampal ripple energy in rats after status epilepticus (SE). A lithium pilocarpine (LiCl-PILO)-induced rat model of status epilepticus (SE) was established, and the rats were divided into the normal control (Control, CTL), epileptic control (PILO), valproic acid (VPA + PILO), miR-20a-5p overexpression lentivirus vector (miR + PILO), sponges blocking lentivirus vector (Sponges + PILO), and scramble sequence negative control (Scramble + PILO) groups (n = 6). Electroencephalograms (EEGs) were used to analyze changes in hippocampal ripple energy before and after SE. Quantitative polymerase chain reaction (q-PCR) analysis showed that miR-20a-5p levels gradually increased after miR-20a-5p overexpression lentivirus vector injection into the lateral ventricle, and the miR-20a-5p levels were significantly higher than that in CTL group on days 7 and 36 (P < 0.001). The miR-20a-5p levels decreased significantly on days 7 and 36 after blocking by sponges lentivirus vector injected into the lateral ventricle (P < 0.001). After injection of PILO, the average ripple energy expression in each group gradually increased, and reached the peak before chloral hydrate injection (compared with 1 day before SE, P < 0.05). The ripple energy in the VPA + PILO and Sponges + PILO groups was significantly lower than that in the PILO group at 60 min and 70 min after PILO injection and before chloral hydrate injection (P < 0.05), and maintained lower until 2 h after chloral hydrate injection in VPA + PILO (P < 0.05). Compared with the VPA + PILO group, the mean ripple energy of the Sponges + PILO group had no difference at all time points (P ≥ 0.05). After SE, ripple distribution of space and energy is closely related to the occurrence of epilepsy. Inhibition of miR20a-5p expression can downregulate ripple oscillation energy during seizure.

Animal Models of Hypertension (ISIAH Rats), Catatonia (GC Rats), and Audiogenic Epilepsy (PM Rats) Developed by Breeding

Research into genetic and physiological mechanisms of widespread disorders such as arterial hypertension as well as neuropsychiatric and other human diseases is urgently needed in academic and practical medicine and in the field of biology. Nevertheless, such studies have many limitations and pose difficulties that can be overcome by using animal models. To date, for the purposes of creating animal models of human pathologies, several approaches have been used: pharmacological/chemical intervention; surgical procedures; genetic technologies for creating transgenic animals, knockouts, or knockdowns; and breeding. Although some of these approaches are good for certain research aims, they have many drawbacks, the greatest being a strong perturbation (in a biological system) that, along with the expected effect, exerts side effects in the study. Therefore, for investigating the pathogenesis of a disease, models obtained using genetic selection for a target trait are of high value as this approach allows for the creation of a model with a "natural" manifestation of the pathology. In this review, three rat models are described: ISIAH rats (arterial hypertension), GC rats (catatonia), and PM rats (audiogenic epilepsy), which are developed by breeding in the Laboratory of Evolutionary Genetics at the Institute of Cytology and Genetics (the Siberian Branch of the Russian Academy of Sciences).

Thalamocortical circuits in generalized epilepsy: Pathophysiologic mechanisms and therapeutic targets

Generalized epilepsy affects 24 million people globally; at least 25% of cases remain medically refractory. The thalamus, with widespread connections throughout the brain, plays a critical role in generalized epilepsy. The intrinsic properties of thalamic neurons and the synaptic connections between populations of neurons in the nucleus reticularis thalami and thalamocortical relay nuclei help generate different firing patterns that influence brain states. In particular, transitions from tonic firing to highly synchronized burst firing mode in thalamic neurons can cause seizures that rapidly generalize and cause altered awareness and unconsciousness. Here, we review the most recent advances in our understanding of how thalamic activity is regulated and discuss the gaps in our understanding of the mechanisms of generalized epilepsy syndromes. Elucidating the role of the thalamus in generalized epilepsy syndromes may lead to new opportunities to better treat pharmaco-resistant generalized epilepsy by thalamic modulation and dietary therapy.

(+)-Borneol exerts neuroprotective effects via suppressing the NF-κB pathway in the pilocarpine-induced epileptogenesis rat model

Neuroinflammation plays a crucial role in the development of epilepsy, and suppressing neuroinflammation can delay epileptogenesis. Recent reports have demonstrated that (+)-borneol has neuroprotective effects in several brain disorders by reducing neuroinflammation. However, its effects on epilepsy have not been reported. In this research, we first studied the effect of different doses of (+)-borneol (3, 6, and 12 mg/kg) on neuroinflammation in a pilocarpine model of epileptogenesis by detecting IL-1β, TNF-α, and COX-2 expression. We demonstrated that different doses of (+)-borneol decreased IL-1β, TNF-α, and COX-2 levels, with 12 mg/kg having the most substantial effect. Furthermore, we examined the effects of 12 mg/kg (+)-borneol on neuronal damage, glial cell activation, and apoptosis in the hippocampus at different time points (1, 3, and 7 days) after SE. We found that (+)-borneol significantly ameliorated neuronal injury, decreased glial cell activation, and attenuated apoptosis. We also found that (+)-borneol inhibited the NF-κB pathway activation induced by SE. In conclusion, our results indicated that (+)-borneol reduces neuroinflammation by inhibiting the NF-κB pathway activation, exerts neuroprotective effects, and may have an inhibitory effect in epileptogenesis.

PET Imaging and Neurohistochemistry Reveal that Curcumin Attenuates Brain Hypometabolism and Hippocampal Damage Induced by Status Epilepticus in Rats

Numerous preclinical studies provide evidence that curcumin, a polyphenolic phytochemical extracted from Curcuma longa (turmeric) has neuroprotective, anti-inflammatory and antioxidant properties against various neurological disorders. Curcumin neuroprotective effects have been reported in different animal models of epilepsy, but its potential effect attenuating brain glucose hypometabolism, considered as an early marker of epileptogenesis that occurs during the silent period following status epilepticus (SE), still has not been addressed. To this end, we used the lithium-pilocarpine rat model to induce SE. Curcumin was administered orally (300 mg/kg/day, for 17 days). Brain glucose metabolism was evaluated in vivo by 2-deoxy-2-[¹⁸F]Fluoro-D-Glucose ([¹⁸F]FDG) positron emission tomography (PET). In addition, hippocampal integrity, neurodegeneration, microglia-mediated neuroinflammation, and reactive astrogliosis were evaluated as markers of brain damage. SE resulted in brain glucose hypometabolism accompanied by body weight (BW) loss, hippocampal neuronal damage, and neuroinflammation. Curcumin did not reduce the latency time to the SE onset, nor the mortality rate associated with SE. Nevertheless, it reduced the number of seizures, and in the surviving rats, curcumin protected BW and attenuated the short-term glucose brain hypometabolism as well as the signs of neuronal damage and neuroinflammation induced by the SE. Overall, our results support the potential adaptogen-like effects of curcumin attenuating key features of SE-induced brain damage.

Thalidomide Attenuates Epileptogenesis and Seizures by Decreasing Brain Inflammation in Lithium Pilocarpine Rat Model

Thalidomide (TAL) has shown potential therapeutic effects in neurological diseases like epilepsy. Both clinical and preclinical studies show that TAL may act as an antiepileptic drug and as a possible treatment against disease development. However, the evidence for these effects is limited. Therefore, the antiepileptogenic and anti-inflammatory effects of TAL were evaluated herein. Sprague Dawley male rats were randomly allocated to one of five groups (n = 18 per group): control (C); status epilepticus (SE); SE-TAL (25 mg/kg); SE-TAL (50 mg/kg); and SE-topiramate (TOP; 60mg/kg). The lithium-pilocarpine model was used, and one day after SE induction the rats received pharmacological treatment for one week. The brain was obtained, and the hippocampus was micro-dissected 8, 18, and 28 days after SE. TNF-α, IL-6, and IL-1β concentrations were quantified. TOP and TAL (50 mg/kg) increased the latency to the first of many spontaneous recurrent seizures (SRS) and decreased SRS frequency, as well as decreasing TNF-α and IL-1β concentrations in the hippocampus. In conclusion, the results showed that both TAL (50 mg/kg) and TOP have anti-ictogenic and antiepileptogenic effects, possibly by decreasing neuroinflammation.

Evolution of interictal activity in models of mesial temporal lobe epilepsy

Interictal activity and seizures are the hallmarks of focal epileptic disorders (which include mesial temporal lobe epilepsy, MTLE) in humans and in animal models. Interictal activity, which is recorded with cortical and intracerebral EEG recordings, comprises spikes, sharp waves and high-frequency oscillations, and has been used in clinical practice to identify the epileptic zone. However, its relation with seizures remains debated. Moreover, it is unclear whether specific EEG changes in interictal activity occur during the time preceding the appearance of spontaneous seizures. This period, which is termed "latent", has been studied in rodent models of MTLE in which spontaneous seizures start to occur following an initial insult (most often a status epilepticus induced by convulsive drugs such as kainic acid or pilocarpine) and may mirror epileptogenesis, i.e., the process leading the brain to develop an enduring predisposition to seizure generation. Here, we will address this topic by reviewing experimental studies performed in MTLE models. Specifically, we will review data highlighting the dynamic changes in interictal spiking activity and high-frequency oscillations occurring during the latent period, and how optogenetic stimulation of specific cell populations can modulate them in the pilocarpine model. These findings indicate that interictal activity: (i) is heterogeneous in its EEG patterns and thus, presumably, in its underlying neuronal mechanisms; and (ii) can pinpoint to the epileptogenic processes occurring in focal epileptic disorders in animal models and, perhaps, in epileptic patients.

Nicotinic acetylcholine receptors and epilepsy

Despite recent advances in understanding the causes of epilepsy, especially the genetic, comprehending the biological mechanisms that lead to the epileptic phenotype remains difficult. A paradigmatic case is constituted by the epilepsies caused by altered neuronal nicotinic acetylcholine receptors (nAChRs), which exert complex physiological functions in mature as well as developing brain. The ascending cholinergic projections exert potent control of forebrain excitability, and wide evidence implicates nAChR dysregulation as both cause and effect of epileptiform activity. First, tonic-clonic seizures are triggered by administration of high doses of nicotinic agonists, whereas non-convulsive doses have kindling effects. Second, sleep-related epilepsy can be caused by mutations on genes encoding nAChR subunits widely expressed in the forebrain (CHRNA4, CHRNB2, CHRNA2). Third, in animal models of acquired epilepsy, complex time-dependent alterations in cholinergic innervation are observed following repeated seizures. Heteromeric nAChRs are central players in epileptogenesis. Evidence is wide for autosomal dominant sleep-related hypermotor epilepsy (ADSHE). Studies of ADSHE-linked nAChR subunits in expression systems suggest that the epileptogenic process is promoted by overactive receptors. Investigation in animal models of ADSHE indicates that expression of mutant nAChRs can lead to lifelong hyperexcitability by altering i) the function of GABAergic populations in the mature neocortex and thalamus, ii) synaptic architecture during synaptogenesis. Understanding the balance of the epileptogenic effects in adult and developing networks is essential to plan rational therapy at different ages. Combining this knowledge with a deeper understanding of the functional and pharmacological properties of individual mutations will advance precision and personalized medicine in nAChR-dependent epilepsy.

Beneficial Effects of Rosmarinic Acid In Vitro and In Vivo Models of Epileptiform Activity Induced by Pilocarpine

Epilepsy is characterized by a predisposition to generate recurrent and spontaneous seizures; it affects millions of people worldwide. Status epilepticus (SE) is a severe type of seizure. In this context, screening potential treatments is very important. In the present study, we evaluated the beneficial effects of rosmarinic acid (RA) in pilocarpine-induced in vitro and in vivo models of epileptiform activity. Using an in vitro model in combined entorhinal cortex-hippocampal from Wistar rats we evaluated the effects of RA (10 µg/mL) on the lactate release and a glucose fluorescent analogue, 2-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-2-deoxyglucose (2-NDBG), after incubation in high potassium aCSF supplemented or not with pilocarpine. In the in vivo model, SE was induced in male C57BL/6 mice by pilocarpine. At 1, 24, and 48 h after the end of SE mice were treated with RA (30 mg/kg/v.o.). We evaluated the neuromotor impairment by neuroscore tests and protein carbonyl levels in the cerebral cortex. In both in vitro models, RA was able to decrease the stimulated lactate release, while no effect on 2-NBDG uptake was found. RA has beneficial effects in models of epileptiform activity in vivo and in vitro. We found that RA treatment attenuated SE-induced neuromotor impairment at the 48 h timepoint. Moreover, post-SE treatment with RA decreased levels of protein carbonyls in the cerebral cortex of mice when compared to their vehicle-treated counterparts. Importantly, RA was effective in a model of SE which is relevant for the human condition. The present data add to the literature on the biological effects of RA, which could be a good candidate for add-on therapy in epilepsy.

Scoping review of disease-modifying effect of drugs in experimental epilepsy

Objective

Epilepsy affects ~50 million people worldwide causing significant medical, financial, and sociologic concerns for affected patients and their families. To date, treatment of epilepsy is primarily symptomatic management because few effective preventative or disease-modifying interventions exist. However, recent research has identified neurobiological mechanisms of epileptogenesis, providing new pharmacologic targets to investigate. The current scientific evidence remains scattered across multiple studies using different model and experimental designs. The review compiles different models of anti-epileptogenic investigation and highlights specific compounds with potential epileptogenesis-modifying experimental drugs. It provides a platform for standardization of future epilepsy research to allow a more robust compound analysis of compounds with potential for epilepsy prevention.

Methods

PubMed, Ovid MEDLINE, and Web of Science were searched from 2007 to 2021. Studies with murine models of epileptogenesis and explicitly detailed experimental procedures were included in the scoping review. In total, 51 articles were selected from 14,983 and then grouped by five core variables: (1) seizure frequency, (2) seizure severity, (3) spontaneous recurrent seizures (SRS), (4) seizure duration, and (5) mossy fiber sprouting (MFS). The variables were differentiated based on experimental models including methods of seizure induction, treatment schedule and timeline of data collection. Data was categorized by the five core variables and analyzed by converting original treatment values to units of percent of its respective control.

Results

Discrepancies in current epileptogenesis models significantly complicate inter-study comparison of potential anti-epileptogenic interventions. With our analysis, many compounds showed a potential to reduce epileptogenic characteristics defined by the five core variables. WIN55,212-2, aspirin, rapamycin, 1400W, and LEV + BQ788 were identified compounds with the potential of effective anti-epileptic properties.

Significance

Our review highlights the need for consistent methodology in epilepsy research and provides a novel approach for future research. Inconsistent experimental designs hinder study comparison, slowing the progression of treatments for epilepsy. If the research community can optimize and standardize parameters such as methods of seizure induction, administration schedule, sampling time, and aniMal models, more robust meta-analysis and collaborative research would follow. Additionally, some compounds such as rapamycin, WIN 55,212-2, aspirin, 1400W, and LEV + BQ788 showed anti-epileptogenic modulation across multiple variables. We believe they warrant further study both individually and synergistically.

A companion to the preclinical common data elements for phenotyping seizures and epilepsy in rodent models. A report of the TASK3-WG1C: Phenotyping working group of the ILAE/AES joint translational task force

Epilepsy is a heterogeneous disorder characterized by spontaneous seizures and behavioral comorbidities. The underlying mechanisms of seizures and epilepsy across various syndromes lead to diverse clinical presentation and features. Similarly, animal models of epilepsy arise from numerous dissimilar inciting events. Preclinical seizure and epilepsy models can be evoked through many different protocols, leaving the phenotypic reporting subject to diverse interpretations. Serendipity can also play an outsized role in uncovering novel drivers of seizures or epilepsy, with some investigators even stumbling into epilepsy research because of a new genetic cross or unintentional drug effect. The heightened emphasis on rigor and reproducibility in preclinical research, including that which is conducted for epilepsy, underscores the need for standardized phenotyping strategies. To address this goal as part of the TASK3-WG1C Working Group of the International League Against Epilepsy (ILAE)/American Epilepsy Society (AES) Joint Translational Task Force, we developed a case report form (CRF) to describe the common data elements (CDEs) necessary for the phenotyping of seizure-like behaviors in rodents. This companion manuscript describes the use of the proposed CDEs and CRF for the visual, behavioral phenotyping of seizure-like behaviors. These phenotyping CDEs and accompanying CRF can be used in parallel with video-electroencephalography (EEG) studies or as a first visual screen to determine whether a model manifests seizure-like behaviors before utilizing more specialized diagnostic tests, like video-EEG. Systematic logging of seizure-like behaviors may help identify models that could benefit from more specialized diagnostic tests to determine whether these are epileptic seizures, such as video-EEG.

Selective activation of the hypothalamic orexinergic but not melanin-concentrating hormone neurons following pilocarpine-induced seizures in rats

Introduction

Sleep disorders are common comorbidities in patients with temporal lobe epilepsy (TLE), but the underlying mechanisms remain poorly understood. Since the lateral hypothalamic (LH) and the perifornical orexinergic (ORX) and melanin-concentrating hormone (MCH) neurons are known to play opposing roles in the regulation of sleep and arousal, dysregulation of ORX and MCH neurons might contribute to the disturbance of sleep-wakefulness following epileptic seizures.

Methods

To test this hypothesis, rats were treated with lithium chloride and pilocarpine to induce status epilepticus (SE). Electroencephalogram (EEG) and electromyograph (EMG) were recorded for analysis of sleep-wake states before and 24 h after SE. Double-labeling immunohistochemistry of c-Fos and ORX or MCH was performed on brain sections from the epileptic and control rats. In addition, anterograde and retrograde tracers in combination with c-Fos immunohistochemistry were used to analyze the possible activation of the amygdala to ORX neural pathways following seizures.

Results

It was found that epileptic rats displayed prolonged wake phase and decreased non-rapid eye movement (NREM) and rapid eye movement (REM) phase compared to the control rats. Prominent neuronal activation was observed in the amygdala and the hypothalamus following seizures. Interestingly, in the LH and the perifornical nucleus, ORX but not MCH neurons were significantly activated (c-Fos+). Neural tracing showed that seizure-activated (c-Fos+) ORX neurons were closely contacted by axon terminals originating from neurons in the medial amygdala.

Discussion

These findings suggest that the spread of epileptic activity from amygdala to the hypothalamus causes selective activation of the wake-promoting ORX neurons but not sleep-promoting MCH neurons, which might contribute to the disturbance of sleep-wakefulness in TLE.

GABAA signaling, focal epileptiform synchronization and epileptogenesis

Under physiological conditions, neuronal network synchronization leads to different oscillatory EEG patterns that are associated with specific behavioral and cognitive functions. Excessive synchronization can, however, lead to focal or generalized epileptiform activities. It is indeed well established that in both epileptic patients and animal models, focal epileptiform EEG patterns are characterized by interictal and ictal (seizure) discharges. Over the last three decades, employing in vitro and in vivo recording techniques, several experimental studies have firmly identified a paradoxical role of GABA_A signaling in generating interictal discharges, and in initiating—and perhaps sustaining—focal seizures. Here, we will review these experiments and we will extend our appraisal to evidence suggesting that GABA_A signaling may also contribute to epileptogenesis, i.e., the development of plastic changes in brain excitability that leads to the chronic epileptic condition. Overall, we anticipate that this information should provide the rationale for developing new specific pharmacological treatments for patients presenting with focal epileptic disorders such as mesial temporal lobe epilepsy (MTLE).

Epilepsy Characteristics in Neurodevelopmental Disorders: Research from Patient Cohorts and Animal Models Focusing on Autism Spectrum Disorder

Epilepsy, a heterogeneous group of brain-related diseases, has continued to significantly burden society and families. Epilepsy comorbid with neurodevelopmental disorders (NDDs) is believed to occur due to multifaceted pathophysiological mechanisms involving disruptions in the excitation and inhibition (E/I) balance impeding widespread functional neuronal circuitry. Although the field has received much attention from the scientific community recently, the research has not yet translated into actionable therapeutics to completely cure epilepsy, particularly those comorbid with NDDs. In this review, we sought to elucidate the basic causes underlying epilepsy as well as those contributing to the association of epilepsy with NDDs. Comprehensive emphasis is put on some key neurodevelopmental genes implicated in epilepsy, such as MeCP2, SYNGAP1, FMR1, SHANK1-3 and TSC1, along with a few others, and the main electrophysiological and behavioral deficits are highlighted. For these genes, the progress made in developing appropriate and valid rodent models to accelerate basic research is also detailed. Further, we discuss the recent development in the therapeutic management of epilepsy and provide a briefing on the challenges and caveats in identifying and testing species-specific epilepsy models.

Spatio-Temporal Alterations in Synaptic Density During Epileptogenesis in the Rat Brain

Synaptic vesicle glycoprotein 2A (SV2A) is a transmembrane protein that binds levetiracetam and is involved in neurotransmission via an unknown mechanism. SV2A-immunoreactivity is reduced in animal models of epilepsy, and in postmortem hippocampi from patients with temporal lobe epilepsy. It is not known if other regions outside the hippocampus are affected in epilepsy, and whether SV2A is expression permanently reduced or regulated over time. In this study, we induced a generalized status epilepticus (SE) by systemic administration of lithium-pilocarpine to adult female rats. The brains from all animals experiencing SE were collected at different time points after the treatment. The radiotracer, [¹¹C]-UCB-J, binds to SV2A with high affinity, and has been used for in vivo imaging as an a-proxy marker for synaptic density. Here we determined the level of tritiated UCB-J binding by semiquantitative autoradiography in the cerebral cortex, hippocampus, thalamus, and hypothalamus, and in subregions of these. A prominent and highly significant reduction in SV2A binding capacity was observed over the first days after SE in the cerebral cortex and the hippocampus, but not in the thalamus and hypothalamus. The magnitude in reduction was larger and occurred earlier in the hippocampus and the piriform cortex, than in other cortical subregions. Interestingly, in all areas examined, the binding capacity returned to control levels 12 weeks after the SE comparable to the chronic phase. These data show that lithium-pilocarpine-induced epileptogenesis involves both loss and gain of synapses in the in a time-dependent manner.

Bilateral optogenetic activation of inhibitory cells favors ictogenesis

Mesial temporal lobe epilepsy (MTLE) is the most common type of focal refractory epilepsy and is characterized by recurring seizures that are often refractory to medication. Since parvalbumin-positive (PV) interneurons were recently shown to play significant roles in ictogenesis, we established here how bilateral optogenetic stimulation of these interneurons in the hippocampus CA3 regions modulates seizures, interictal spikes and high-frequency oscillations (HFOs; ripples: 80-200 Hz, fast ripples: 250-500 Hz) in the pilocarpine model of MTLE. Bilateral optogenetic stimulation of CA3 PV-positive interneurons at 8 Hz (lasting 30 s, every 2 min) was implemented in PV-ChR2 mice for 8 consecutive days starting on day 7 (n = 8) or on day 13 (n = 6) after pilocarpine-induced status epilepticus (SE). Seizure occurrence was higher in both day 7 and day 13 groups of PV-ChR2 mice during periods of optogenetic stimulation ("ON"), compared to when stimulation was not performed ("OFF") (day 7 group = p < 0.01, day 13 group = p < 0.01). In the PV-ChR2 day 13 group, rates of seizures (p < 0.05), of interictal spikes associated with fast ripples (p < 0.01), and of isolated fast ripples (p < 0.01) during optogenetic stimulations were significantly higher than in the PV-ChR2 day 7 group. Our findings reveal that bilateral activation of PV-interneurons in the hippocampus (leading to a presumptive increase in GABA signaling) favors ictogenesis. These effects may also mirror the neuropathological changes that occur over time after SE in this animal model.

Changes in Metabotropic Glutamate Receptor Gene Expression in Rat Brain in a Lithium-Pilocarpine Model of Temporal Lobe Epilepsy

Preventing epileptogenesis in people at risk is an unmet medical need. Metabotropic glutamate receptors (mGluRs) are promising targets for such therapy. However, drugs acting on mGluRs are not used in the clinic due to limited knowledge of the involvement of mGluRs in epileptogenesis. This study aimed to analyze the changes in gene expression of mGluR subtypes (1-5, 7, 8) in various rat brain regions in the latent and chronic phases of a lithium-pilocarpine model of epilepsy. For this study, multiplex test systems were selected and optimized to analyze mGluR gene expression using RT-qPCR. Region- and phase-specific changes in expression were revealed. During the latent phase, mGluR5 mRNA levels were increased in the dorsal and ventral hippocampus, and expression of group III genes was decreased in the hippocampus and temporal cortex, which could contribute to epileptogenesis. Most of the changes in expression detected in the latent stage were absent in the chronic stage, but mGluR8 mRNA production remained reduced in the hippocampus. Moreover, we found that gene expression of group II mGluRs was altered only in the chronic phase. The study deepened our understanding of the mechanisms of epileptogenesis and suggested that agonists of group III mGluRs are the most promising targets for preventing epilepsy.

MTEP, a Selective mGluR5 Antagonist, Had a Neuroprotective Effect but Did Not Prevent the Development of Spontaneous Recurrent Seizures and Behavioral Comorbidities in the Rat Lithium-Pilocarpine Model of Epilepsy

Metabotropic glutamate receptors (mGluRs) are expressed predominantly on neurons and glial cells and are involved in the modulation of a wide range of signal transduction cascades. Therefore, different subtypes of mGluRs are considered a promising target for the treatment of various brain diseases. Previous studies have demonstrated the seizure-induced upregulation of mGluR5; however, its functional significance is still unclear. In the present study, we aimed to clarify the effect of treatment with the selective mGluR5 antagonist 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]-pyridine (MTEP) on epileptogenesis and behavioral impairments in rats using the lithium–pilocarpine model. We found that the administration of MTEP during the latent phase of the model did not improve survival, prevent the development of epilepsy, or attenuate its manifestations in rats. However, MTEP treatment completely prevented neuronal loss and partially attenuated astrogliosis in the hippocampus. An increase in excitatory amino acid transporter 2 expression, which has been detected in treated rats, may prevent excitotoxicity and be a potential mechanism of neuroprotection. We also found that MTEP administration did not prevent the behavioral comorbidities such as depressive-like behavior, motor hyperactivity, reduction of exploratory behavior, and cognitive impairments typical in the lithium–pilocarpine model. Thus, despite the distinct neuroprotective effect, the MTEP treatment was ineffective in preventing epilepsy.

Dual targeting nanoparticles for epilepsy therapy

Dual-targeting nanoparticles containing D-T7 peptide and Tet1 peptide were designed for carrying lamotrigine (LTG) to cross the blood–brain barrier and further concentrate at the epilepsy lesions for treating epilepsy with high biosafety.

Impairments of Long-Term Synaptic Plasticity in the Hippocampus of Young Rats during the Latent Phase of the Lithium-Pilocarpine Model of Temporal Lobe Epilepsy

Status epilepticus (SE) causes persistent abnormalities in the functioning of neuronal networks, often resulting in worsening epileptic seizures. Many details of cellular and molecular mechanisms of seizure-induced changes are still unknown. The lithium–pilocarpine model of epilepsy in rats reproduces many features of human temporal lobe epilepsy. In this work, using the lithium–pilocarpine model in three-week-old rats, we examined the morphological and electrophysiological changes in the hippocampus within a week following pilocarpine-induced seizures. We found that almost a third of the neurons in the hippocampus and dentate gyrus died on the first day, but this was not accompanied by impaired synaptic plasticity at that time. A diminished long-term potentiation (LTP) was observed following three days, and the negative effect of SE on plasticity increased one week later, being accompanied by astrogliosis. The attenuation of LTP was caused by the weakening of N-methyl-D-aspartate receptor (NMDAR)-dependent signaling. NMDAR-current was more than two-fold weaker during high-frequency stimulation in the post-SE rats than in the control group. Application of glial transmitter D-serine, a coagonist of NMDARs, allows the enhancement of the NMDAR-dependent current and the restoration of LTP. These results suggest that the disorder of neuron–astrocyte interactions plays a critical role in the impairment of synaptic plasticity.

Sleep Disruption Worsens Seizures: Neuroinflammation as a Potential Mechanistic Link

Sleep disturbances, such as insomnia, obstructive sleep apnea, and daytime sleepiness, are common in people diagnosed with epilepsy. These disturbances can be attributed to nocturnal seizures, psychosocial factors, and/or the use of anti-epileptic drugs with sleep-modifying side effects. Epilepsy patients with poor sleep quality have intensified seizure frequency and disease progression compared to their well-rested counterparts. A better understanding of the complex relationship between sleep and epilepsy is needed, since approximately 20% of seizures and more than 90% of sudden unexpected deaths in epilepsy occur during sleep. Emerging studies suggest that neuroinflammation, (e.g., the CNS immune response characterized by the change in expression of inflammatory mediators and glial activation) may be a potential link between sleep deprivation and seizures. Here, we review the mechanisms by which sleep deprivation induces neuroinflammation and propose that neuroinflammation synergizes with seizure activity to worsen neurodegeneration in the epileptic brain. Additionally, we highlight the relevance of sleep interventions, often overlooked by physicians, to manage seizures, prevent epilepsy-related mortality, and improve quality of life.