A Model of Chronic Temporal Lobe Epilepsy Presenting Constantly Rhythmic and Robust Spontaneous Seizures, Co-morbidities and Hippocampal Neuropathology

Marked differences in the effects of levetiracetam and its analogue brivaracetam on microglial, astrocytic, and neuronal density in the rat model of kainic acid-induced temporal lobe epilepsy

Efficient treatment of temporal lobe epilepsy (TLE) remains challenging due to limited understanding of cellular and network changes and the interference of novel antiepileptic drugs (AEDs) with tissue reorganisation. This study compared the effects of brivaracetam and levetiracetam on histological alterations in key brain regions of the epileptic circuitry, namely, the hippocampus, amygdala, piriform cortex (PC), endopiriform nucleus (EPN) and paraventricular thalamic nucleus (PVT), using the kainic acid (KA) rat model of TLE. Male Wistar rats were assigned to sham-operated (SHAM), epileptic (EPI), brivaracetam- (BRV-EPI) and levetiracetam-treated (LEV-EPI) epileptic groups. Epileptic groups received KA in the right lateral ventricle, which induced status epilepticus followed by a 3-week recovery and latent period. Rats then underwent 3 weeks of oral brivaracetam, levetiracetam or placebo treatment with continuous video monitoring for seizure analysis. Subsequently, triple fluorescent immunolabeling assessed microglial, astrocytic, and neuronal changes. The results showed a drastic increase in microglia density in the EPI and BRV-EPI groups compared to control and LEV-EPI. The BRV-EPI group displayed a significantly higher microglia density than SHAM and EPI groups in the right CA1, CA3 and left CA1 regions, bilateral amygdalae, EPN, PVT and left PC. Astrocyte density was significantly elevated in hippocampal regions of the BRV-EPI group, while neuronal density decreased. Furthermore, brivaracetam did not reduce seizure activity in this disease phase. Significance: Brivaracetam treatment increased microglial activation under epileptic conditions in vivo in all examined brain-regions participating in the epileptic circuitry, in contrast to the effects of levetiracetam, highlighting differences in AED-induced histological alterations.

Cell-specific extracellular vesicle-encapsulated exogenous GABA controls seizures in epilepsy

BACKGROUND

Epilepsy affects ∼60 million people worldwide. Most antiseizure medications in the market act on voltage-gated sodium or calcium channels, indirectly modulating neurotransmitter GABA or glutamate levels or multiple targets. Earlier studies made significant efforts to directly deliver GABA into the brain with varied success. Herein, we have hypothesized to directly deliver exogenous GABA to the brain with epilepsy through extracellular vesicles (EVs) from human GABA-producing cells and their progenitors as EVs largely mimic their parent cell composition.

METHODS

Human neural stem cells (NSCs), medial ganglionic eminence (MGE) cells, and GABAergic interneurons (INs) were generated from induced pluripotent stem cells (iPSCs) and characterized. EVs were isolated from NSCs, MGE cells, and INs and characterized for size and distribution, morphological features, and molecular markers. Exogenous GABA was passively loaded to the isolated EVs as a zwitterion at physiological pH, and the encapsulated dose of GABA was quantified. Epilepsy was developed through status epilepticus induction in Fisher rats by administration of repeated low doses of kainic acid. The extent of the seizures was measured for 10 h/ day for 3-6 months by video recording and its evaluation for stage III, IV and V seizures as per Racine scale. EVs from INs, MGE cells, and NSCs encapsulated with exogenous GABA were sequentially tested in the 4th, 5th, and 6th months by intranasal administration in the rats with epilepsy for detailed seizure, behavioral and synapse analysis. In separate experiments, several controls including exogenic GABA alone and EVs from INs and MGE cells were evaluated for seizure-controlling ability.

RESULTS

Exogenic GABA could enter the brain through EVs. Treatment with EVs from INs and MGE cells encapsulated with GABA significantly reduced total seizures, stage V seizures, and total time spent in seizure activity. EVs from NSCs encapsulated with GABA demonstrated limited seizure control. Exogenic GABA alone and EVs from INs and MGE cells individually failed to control seizures. Further, exogenic GABA with EVs from MGE cells improved depressive behavior while partially improving memory functions. Co-localization studies confirmed exogenous GABA with presynaptic vesicles in the hippocampus, indicating the interaction of exogenous GABA in the brain with epilepsy.

CONCLUSION

For the first time, the study demonstrated that exogenous GABA could be delivered to the brain through brain cell-derived EVs, which could regulate seizures in temporal lobe epilepsy. It is identified that the cellular origin of EVs plays a vital role in seizure control with exogenous GABA.

Differential Regulation of Wnt/β-catenin Signaling in Acute and Chronic Epilepsy in Repeated Low Dose Lithium-Pilocarpine Rat Model of Status Epilepticus

Epilepsy is a chronic neurological complication characterized by unprovoked seizure episodes due to the imbalance between excitatory and inhibitory neurons. The epileptogenesis process has been reported to be involved in chronic epilepsy however, the mechanism underlying epileptogenesis remains unclear. Recent studies have shown the possible involvement of Wnt/β-catenin signaling in the neurogenesis and neuronal reorganization in epileptogenesis. In this study, we used repeated low dose lithium-pilocarpine model of status epilepsy (SE) to study the involvement of Wnt/β-catenin signaling at acute and chronic stages post SE induction. The acute study ranged from day 0 to day 28 post SE induction and the chronic study ranged from day 0 to day 56 post SE induction. Several neurobehavioral parameters and seizure score and seizure frequency was analysed until the end of the study. The proteins involved in the regulation of Wnt/β-catenin signaling and downstream cascading were analysed using western blot and quantitative real-time PCR analysis. The Wnt/β-catenin pathway was found inactive in acute SE, while the same was found activated at the chronic stage. Our findings suggest that the activated Wnt/β-catenin signaling in chronic epilepsy might be the possible mechanism underlying epileptogenesis as indicated by increased neuronal count, increased synaptic density, astrogliosis and apoptosis in chronic epilepsy. These findings can help target the Wnt/β-catenin pathway differentially depending upon the type of epilepsy. The acute stage characterized by SE can be improved by targeting GSK-3β levels and the chronic stage characterized by temporal lobe epilepsy can be improved by targeting β-catenin and disheveled proteins.

Neuroprotective Effect of Exogenous Galectin-1 in Status Epilepticus

Intrahippocampal pilocarpine microinjection (H-PILO) induces status epilepticus (SE) that can lead to spontaneous recurrent seizures (SRS) and neurodegeneration in rodents. Studies using animal models have indicated that lectins mediate a variety of biological activities with neuronal benefits, especially galectin-1 (GAL-1), which has been identified as an effective neuroprotective compound. GAL-1 is associated with the regulation of cell adhesion, proliferation, programmed cell death, and immune responses, as well as attenuating neuroinflammation. Here, we administrated GAL-1 to Wistar rats and evaluated the severity of the SE, neurodegenerative and inflammatory patterns in the hippocampal formation. Administration of GAL-1 caused a reduction in the number of class 2 and 4 seizures, indicating a decrease in seizure severity. Furthermore, we observed a reduction in inflammation and neurodegeneration 24 h and 15 days after SE. Overall, these results suggest that GAL-1 has a neuroprotective effect in the early stage of epileptogenesis and provides new insights into the roles of exogenous lectins in temporal lobe epilepsy (TLE).

Grafted hPSC-derived GABA-ergic interneurons regulate seizures and specific cognitive function in temporal lobe epilepsy

Interneuron loss/dysfunction contributes to spontaneous recurrent seizures (SRS) in chronic temporal lobe epilepsy (TLE), and interneuron grafting into the epileptic hippocampus reduces SRS and improves cognitive function. This study investigated whether graft-derived gamma-aminobutyric acid positive (GABA-ergic) interneurons directly regulate SRS and cognitive function in a rat model of chronic TLE. Human pluripotent stem cell-derived medial ganglionic eminence-like GABA-ergic progenitors, engineered to express hM4D(Gi), a designer receptor exclusively activated by designer drugs (DREADDs) through CRISPR/Cas9 technology, were grafted into hippocampi of chronically epileptic rats to facilitate the subsequent silencing of graft-derived interneurons. Such grafting substantially reduced SRS and improved hippocampus-dependent cognitive function. Remarkably, silencing of graft-derived interneurons with a designer drug increased SRS and induced location memory impairment but did not affect pattern separation function. Deactivation of DREADDs restored both SRS control and object location memory function. Thus, transplanted GABA-ergic interneurons could directly regulate SRS and specific cognitive functions in TLE.

Differences in Evolution of Epileptic Seizures and Topographical Distribution of Tissue Damage in Selected Limbic Structures Between Male and Female Rats Submitted to the Pilocarpine Model

Epidemiological evidence shows that clinical features and comorbidities in temporal lobe epilepsy (TLE) may have different manifestations depending on the sex of patients. However, little is known about how sex-related mechanisms can interfere with the processes underlying the epileptic phenomenon. The findings of this study show that male rats with epilepsy in the pilocarpine model have longer-lasting and more severe epileptic seizures, while female rats have a higher frequency of epileptic seizures and a greater number of seizure clusters. Significant sex-linked pathological changes were also observed: epileptic brains of male and female rats showed differences in mass reduction of 41.8% in the amygdala and 18.2% in the olfactory bulb, while loss of neuronal cells was present in the hippocampus (12.3%), amygdala (18.1%), and olfactory bulb (7.5%). Another important sex-related finding was the changes in non-neuronal cells with increments for the hippocampus (36.1%), amygdala (14.7%), and olfactory bulb (37%). Taken together, our study suggests that these neuropathological changes may underlie the differences in the clinical features of epileptic seizures observed in male and female rats.

Neferine, an Alkaloid from Lotus Seed Embryos, Exerts Antiseizure and Neuroprotective Effects in a Kainic Acid-Induced Seizure Model in Rats

Current anti-seizure drugs fail to control approximately 30% of epilepsies. Therefore, there is a need to develop more effective anti-seizure drugs, and medicinal plants provide an attractive source for new compounds. This study aimed to evaluate the possible anti-seizure and neuroprotective effects of neferine, an alkaloid from the lotus seed embryos of Nelumbo nucifera, in a kainic acid (KA)-induced seizure rat model and its underlying mechanisms. Rats were intraperitoneally (i.p.) administrated neferine (10 and 50 mg/kg) 30 min before KA injection (15 mg/kg, i.p.). Neferine pretreatment increased seizure latency and reduced seizure scores, prevented glutamate elevation and neuronal loss, and increased presynaptic protein synaptophysin and postsynaptic density protein 95 expression in the hippocampi of rats with KA. Neferine pretreatment also decreased glial cell activation and proinflammatory cytokine (interleukin-1β, interleukin-6, tumor necrosis factor-α) expression in the hippocampi of rats with KA. In addition, NOD-like receptor 3 (NLRP3) inflammasome, caspase-1, and interleukin-18 expression levels were decreased in the hippocampi of seizure rats pretreated with neferine. These results indicated that neferine reduced seizure severity, exerted neuroprotective effects, and ameliorated neuroinflammation in the hippocampi of KA-treated rats, possibly by inhibiting NLRP3 inflammasome activation and decreasing inflammatory cytokine secretion. Our findings highlight the potential of neferine as a therapeutic option in the treatment of epilepsy.

Long-term development of dynamic changes in neurovascular coupling after acute temporal lobe epilepsy

Epilepsy is an abnormal brain state that may be induced by synchronous neuronal activation and also abnormalities in energy metabolism or the oxygen supply vascular system. Neurovascular coupling (NVC), the relationship between neuron, capillary, and penetrating artery, remains unexplored on a fine-scale with respect to the pathology process after acute temporal lobe epilepsy (TLE). Here we use two-photon microscopy (TPM) to provide high temporal-spatial resolution imaging to identify changes in NVC during spontaneous and electro-stimulated (ES) states in awake mice. Implantation of a long-term craniotomy window allowed TPM recording of the pathological development after the acute Kainic Acid temporal lobe epilepsy model. Our results provide direct evidence that the capillary and penetrating artery are not correlated to rhythmic neuronal activity during acute epilepsy. During the CSD period, NVC shows a strong correlation. We demonstrate that NVC exhibits nonlinear dynamics after status epilepticus. Furthermore, the vascular correlation to neuronal signals in spontaneous and ES states shows dynamic changes which correlate to the evolution after acute TLE. Understanding NVC in all TLE stages, from the acute through the TLE pathological development, may provide new therapeutic pathways.

Animal Models of Epilepsy: A Phenotype-oriented Review

Epilepsy is a serious neurological disorder characterized by abnormal, recurrent, and synchronous discharges in the brain. Long-term recurrent seizure attacks can cause serious damage to brain function, which is usually observed in patients with temporal lobe epilepsy. Controlling seizure attacks is vital for the treatment and prognosis of epilepsy. Animal models, such as the kindling model, which was the most widely used model in the past, allow the understanding of the potential epileptogenic mechanisms and selection of antiepileptic drugs. In recent years, various animal models of epilepsy have been established to mimic different seizure types, without clear merits and demerits. Accordingly, this review provides a summary of the views mentioned above, aiming to provide a reference for animal model selection.

The Discordance between Network Excitability and Cognitive Performance Following Vigabatrin Treatment during Epileptogenesis

Vigabatrin (VGB), a potent selective γ-aminobutyric acid transaminase (GABA-T) inhibitor, is an approved non-traditional anti-seizure drug for patients with intractable epilepsy. Nevertheless, its effect on epileptogenesis, and whether this effect is correlated with post-epileptogenic cognitive function remain unclear. Based on lithium-pilocarpine-induced seizure modeling, we evaluated the effect of VGB on epileptogenesis and neuronal damage following status epilepticus in Sprague-Dawley rats. Cognitive evaluations were performed with the aid of inhibitory avoidance testing. We found that VGB could interrupt epileptogenesis by reducing spontaneous recurrent seizures, hippocampal neuronal damage, and chronic mossy fiber sprouting. Nevertheless, VGB did not help with the retention of cognitive performance. Our findings suggest that further research into the role of VGB in epileptogenesis and the treatment of epilepsy in clinical practice is warranted.

Envisioning the role of inwardly rectifying potassium (Kir) channel in epilepsy

Epilepsy is a devastating neurological disorder characterized by recurrent seizures attributed to the disruption of the dynamic excitatory and inhibitory balance in the brain. Epilepsy has emerged as a global health concern affecting about 70 million people worldwide. Despite recent advances in pre-clinical and clinical research, its etiopathogenesis remains obscure, and there are still no treatment strategies modifying disease progression. Although the precise molecular mechanisms underlying epileptogenesis have not been clarified yet, the role of ion channels as regulators of cellular excitability has increasingly gained attention. In this regard, emerging evidence highlights the potential implication of inwardly rectifying potassium (Kir) channels in epileptogenesis. Kir channels consist of seven different subfamilies (Kir1-Kir7), and they are highly expressed in both neuronal and glial cells in the central nervous system. These channels control the cell volume and excitability. In this review, we discuss preclinical and clinical evidence on the role of the several subfamilies of Kir channels in epileptogenesis, aiming to shed more light on the pathogenesis of this disorder and pave the way for future novel therapeutic approaches.

Cognitive Impairment and Mossy Fiber Sprouting in a Rat Model of Drug-Resistant Epilepsy Induced by Lithium-Pilocarpine

BACKGROUND

The mossy fiber sprouting (MFS) in the dentate gyrus is a common pathological change of epilepsy. Previous studies suggested that it is associated with drug-resistant epilepsy, and mossy cells control spontaneous seizures and spatial memory.

METHODS

We investigated the correlations among cognitive impairment, MFS, seizure frequency and drug resistance in a rat model of epilepsy induced by lithium-pilocarpine. Phenytoin and phenobarbital were used to screen drug resistance. Cognitive function and MFS were detected through the novel object recognition (NOR) test, Morris water maze (MWM) test and Timm staining.

RESULTS

The results showed that object memory and spatial memory functions were both significantly impaired in rats with epilepsy, and only spatial memory impairment was more severe in rats with drug-resistant epilepsy. More frequent spontaneous seizures and more obvious MFS were observed in the drug-resistant rats. The seizure frequency was significantly associated with the MWM performance but not with the NOR performance in rats with epilepsy. The degree of MFS was significantly associated with seizure frequency and spatial memory function.

CONCLUSION

Taken together, these correlations among drug resistance, seizure frequency, spatial memory impairment and MFS suggested the possibility of a common pathological mechanism. More studies are needed to clarify the underlying mechanism behind these correlations and the detailed role of MFS in epilepsy. The mechanism of mossy cell change may be an important target for the treatment of seizures, drug resistance and cognitive dysfunction in patients with epilepsy.

Combination of Matching Responsive Stimulations of Hippocampus and Subiculum for Effective Seizure Suppression in Temporal Lobe Epilepsy

Responsive neural stimulation (RNS) is considered a promising neural modulation therapy for refractory epilepsy. Combined stimulation on different targets may hold great promise for improving the efficacy of seizure control since neural activity changed dynamically within associated brain targets in the epileptic network. Three major issues need to be further explored to achieve better efficacy of combined stimulation: (1) which nodes within the epileptogenic network should be chosen as stimulation targets? (2) What stimulus frequency should be delivered to different targets? and (3) Could the efficacy of RNS for seizure control be optimized by combined different stimulation targets together? In our current study, Granger causality (GC) method was applied to analyze epileptogenic networks for finding key targets of RNS. Single target stimulation (100 μA amplitude, 300 μs pulse width, 5s duration, biphasic, charge-balanced) with high frequency (130 Hz, HFS) or low frequency (5 Hz, LFS) was firstly delivered by our lab designed RNS systems to CA3, CA1, subiculum (SUB) of hippocampi, and anterior nucleus of thalamus (ANT). The efficacy of combined stimulation with different groups of frequencies was finally assessed to find out better combined key targets with optimal stimulus frequency. Our results showed that stimulation individually delivered to SUB and CA1 could shorten the average duration of seizures. Different stimulation frequencies impacted the efficacy of seizure control, as HFS delivered to CA1 and LFS delivered to SUB, respectively, were more effective for shortening the average duration of electrographic seizure in Sprague-Dawley rats (n = 3). Moreover, the synchronous stimulation of HFS in CA1 combined with LFS in SUB reduced the duration of discharge significantly in rats (n = 6). The combination of responsive stimulation at different targets may be an inspiration to optimize stimulation therapy for epilepsy.

miR-106b-5p upregulation is associated with microglial activation and inflammation in the mouse hippocampus following status epilepticus

To investigate the association of miR-106b-5p with neuroinflammation and microglial activation in a status epilepticus (SE) mouse model. We examined changes in the expression of microRNA-106b-5p (miRNA-106b-5p), repulsive guidance molecule A (RGMa), triggering receptor expressed on myeloid cells 2 (TREM2), and the microglia-related markers interleukin (IL)-1β, IL-4, IL-6, IL-10, inducible nitric oxide synthase (iNOS), and arginase-1 (Arg-1) in the mouse hippocampus of the lithium-pilocarpine-induced SE mouse model. Eighty-four female C57BL/6 mice were randomly divided into a normal control group (n = 12), and six SE groups (n = 12/group), which were monitored at 6 h and at 1, 3, 7, 14, and 21 days (d) post-SE induction. Unlike in the dentate gyrus, immunohistochemical staining revealed prominent neuronal swelling at 6 h, significant neuronal loss and apoptosis on day 3, and recovery by day 14 in the hippocampal cornu ammonis (CA)1 and CA3 pyramidal cells in SE mice. We noted elevated levels of miRNA-106b-5p and all microglia-related markers, which peaked at 3 days post-SE, except IL-4, which peaked at 7 days post-SE, indicating inflammation and microglial activation. RGMa and TREM2 levels decreased at 6 h post-SE. All markers but miRNA-106b-5p, RGMa, and TREM2 returned to baseline levels at 21 days post-SE. Dual luciferase reporter gene assay showed that microRNA-106b-5p can interact with RGMa. We observed that miR-106b-5p level increased while both RGMa and TREM2 levels decreased post-SE and showed associations with microglial activation and inflammation in the mouse hippocampus, suggesting their potential as SE therapeutic targets.

Increased ATP release and CD73-mediated adenosine A2A receptor activation mediate convulsion-associated neuronal damage and hippocampal dysfunction

Extracellular ATP is a danger signal to the brain and contributes to neurodegeneration in animal models of Alzheimer's disease through its extracellular catabolism by CD73 to generate adenosine, bolstering the activation of adenosine A_2A receptors (A_2AR). Convulsive activity leads to increased ATP release, with the resulting morphological alterations being eliminated by A_2AR blockade. However, it is not known if upon convulsions there is a CD73-mediated coupling between ATP release and A_2AR overactivation, causing neurodegeneration. We now show that kainate-induced convulsions trigger a parallel increase of ATP release and of CD73 and A_2AR densities in synapses and astrocytes of the mouse hippocampus. Notably, the genetic deletion of CD73 attenuates neuronal degeneration but has no impact on astrocytic modifications in the hippocampus upon kainate-induced convulsions. Furthermore, kainate-induced convulsions cause a parallel deterioration of hippocampal long-term potentiation (LTP) and hippocampal-dependent memory performance, which is eliminated by knocking out CD73. This demonstrates the key role of the ATP release/CD73/A_2AR pathway to selectively control synaptic dysfunction and neurodegeneration following an acute brain insult, paving the way to consider CD73 as a new therapeutic target to prevent neuronal damage upon acute brain damage.

Diurnal burden of spontaneous seizures in early epileptogenesis in the post-kainic acid rat model of epilepsy

Patients with epilepsy can experience diurnal seizure patterns. However, few studies in rodent models of temporal lobe epilepsy (TLE) routinely quantify the diurnal pattern of spontaneous recurrent seizures (SRS), and those that have conducted such assessments used small groups. This study thus aimed to define whether there was a diurnal pattern of SRS in the early phases of epileptogenesis in a large cohort (n = 40) of post-kainic acid (KA)-induced status epilepticus (SE) male Sprague Dawley rats. Rats were monitored by continuous 24/7 video-EEG in two-week epochs up to 6 weeks post-KA-induced SE. The total number of SRS by 6 weeks post-SE correlated to body weight at the time of SE insult (R2  = .1465, P = .0143). The total number of spontaneous behavioral and electrographic seizures, seizure severity, and seizure burden was recorded during lights ON (light) or lights OFF (dark) phases. All measures significantly increased with time post-SE; we detected significantly more seizures during the lights OFF phase of the post-SE monitoring periods. Moreover, a subset of rats demonstrated marked seizure preference in the lights OFF phase. Our study confirms that a diurnal pattern of SRS is variably detectable in early epileptogenesis in this model of TLE.

Impact of Stress on Epilepsy: Focus on Neuroinflammation-A Mini Review

Epilepsy, one of the most common neurological disorders worldwide, is characterized by recurrent seizures and subsequent brain damage. Despite strong evidence supporting a deleterious impact on seizure occurrence and outcome severity, stress is an overlooked component in people with epilepsy. With regard to stressor duration and timing, acute stress can be protective in epileptogenesis, while chronic stress often promotes seizure occurrence in epilepsy patients. Preclinical research suggests that chronic stress promotes neuroinflammation and leads to a depressive state. Depression is the most common psychiatric comorbidity in people with epilepsy, resulting in a poor quality of life. Here, we summarize studies investigating acute and chronic stress as a seizure trigger and an important factor that worsens epilepsy outcomes and psychiatric comorbidities. Mechanistic insight into the impact of stress on epilepsy may create a window of opportunity for future interventions targeting neuroinflammation-related disorders.

d-Serine Intervention In The Medial Entorhinal Area Alters TLE-Related Pathology In CA1 Hippocampus Via The Temporoammonic Pathway

Entrainment of the hippocampus by the medial entorhinal area (MEA) in Temporal Lobe Epilepsy (TLE), the most common type of drug-resistant epilepsy in adults, is believed to be mediated primarily through the perforant pathway (PP), which connects stellate cells in layer (L) II of the MEA with granule cells of the dentate gyrus (DG) to drive the hippocampal tri-synaptic circuit. Using immunohistochemistry, high-resolution confocal microscopy and the rat pilocarpine model of TLE, we show here that the lesser known temporoammonic pathway (TAP) plays a significant role in transferring MEA pathology to the CA1 region of the hippocampus independently of the PP. The pathology observed was region-specific and restricted primarily to the CA1c subfield of the hippocampus. As shown previously, daily intracranial infusion of d-serine (100 μm), an antagonist of GluN3-containing triheteromeric N-Methyl d-aspartate receptors (t-NMDARs), into the MEA prevented loss of LIII neurons and epileptogenesis. This intervention in the MEA led to the rescue of hippocampal CA1 neurons that would have otherwise perished in the epileptic animals, and down regulation of the expression of astrocytes and microglia thereby mitigating the effects of neuroinflammation. Interestingly, these changes were not observed to a similar extent in other regions of vulnerability like the hilus, DG or CA3, suggesting that the pathology manifest in CA1 is driven predominantly through the TAP. This work highlights TAP's role in the entrainment of the hippocampus and identifies specific areas for therapeutic intervention in dealing with TLE.

An update on the rod microglia variant in experimental and clinical brain injury and disease

Contemporary microglia morphologies include ramified, activated and amoeboid, with the morphology of microglia considered highly coupled to the cellular function. Rod microglia are an additional activated microglia variant observed in the ageing, injured and diseased brain. Rod microglia were reported frequently in the early 1900s by neuropathologists in post-mortem cases of general paresis, Alzheimer's disease and encephalitis, and then remained largely ignored for almost 100 years. Recent reports have renewed interest in rod microglia, most notably after experimental traumatic brain injury. Rod microglia are formed by the narrowing of the soma and retraction of planar processes, which results in the appearance of an elongated, rod-shaped cell. Rod microglia are most commonly observed in the cortex, aligned perpendicular to the dural surface and adjacent to neuronal processes; in the hippocampus, they are aligned perpendicular to hippocampal layers. Furthermore, rod microglia form trains with one another, apical end to basal end. By replicating the process of sketching microscopic observation, rod microglia are re-defined by circumnutation around the long axis. In this update, we summarize the rod microglia variant in clinical and experimental literature and advocate for investigation into mechanisms of rod microglia origin and function.

Pro-inflammatory cytokines, but not brain- and extracellular matrix-derived proteins, are increased in the plasma following electrically induced kindling of seizures

Background

The aim of the study was to evaluate the brain-derived proteins, extracellular matrix-derived protein and cytokines as potential peripheral biomarkers of different susceptibility to seizure development in an animal model of epilepsy evoked by chronic focal electrical stimulation of the brain.

Methods

The plasma levels of IL-1β (interleukin 1β), IL-6 (interleukin 6), UCH-L1 (ubiquitin C-terminal hydrolase 1), MMP-9 (matrix metalloproteinase 9), and GFAP (glial fibrillary acidic protein) were assessed. The peripheral concentrations of the selected proteins were analyzed according to the status of kindling and seizure severity parameters. In our study, increased concentrations of plasma IL-1β and IL-6 were observed in rats subjected to hippocampal kindling compared to sham-operated rats.

Results

Animals that developed tonic–clonic seizures after the last stimulation had higher plasma concentrations of IL-1β and IL-6 than sham-operated rats and rats that did not develop seizure. Elevated levels of IL-1β and IL-6 were observed in rats that presented more severe seizures after the last five stimulations compared to sham-operated animals. A correlation between plasma IL-1β and IL-6 concentrations was also found. On the other hand, the plasma levels of the brain-derived proteins UCH-L1, MMP-9, and GFAP were unaffected by kindling status and seizure severity parameters.

Conclusions

The plasma concentrations of IL-1β and IL-6 may have potential utility as peripheral biomarkers of immune system activation in the course of epilepsy and translational potential for future clinical use. Surprisingly, markers of cell and nerve ending damage (GFAP, UCH-L1 and MMP-9) may have limited utility.

Hippocampal Neural Stem Cell Grafting after Status Epilepticus Alleviates Chronic Epilepsy and Abnormal Plasticity, and Maintains Better Memory and Mood Function

Hippocampal damage after status epilepticus (SE) leads to multiple epileptogenic changes, which lead to chronic temporal lobe epilepsy (TLE). Morbidities such as spontaneous recurrent seizures (SRS) and memory and mood impairments are seen in a significant fraction of SE survivors despite the administration of antiepileptic drugs after SE. We examined the efficacy of bilateral intra-hippocampal grafting of neural stem/progenitor cells (NSCs) derived from the embryonic day 19 rat hippocampi, six days after SE for restraining SE-induced SRS, memory, and mood impairments in the chronic phase. Grafting of NSCs curtailed the progression of SRS at 3-5 months post-SE and reduced the frequency and severity of SRS activity when examined at eight months post-SE. Reduced SRS activity was also associated with improved memory function. Graft-derived cells migrated into different hippocampal cell layers, differentiated into GABA-ergic interneurons, astrocytes, and oligodendrocytes. Significant percentages of graft-derived cells also expressed beneficial neurotrophic factors such as the fibroblast growth factor-2, brain-derived neurotrophic factor, insulin-like growth factor-1 and glial cell line-derived neurotrophic factor. NSC grafting protected neuropeptide Y- and parvalbumin-positive host interneurons, diminished the abnormal migration of newly born neurons, and rescued the reelin+ interneurons in the dentate gyrus. Besides, grafting led to the maintenance of a higher level of normal neurogenesis in the chronic phase after SE and diminished aberrant mossy fiber sprouting in the dentate gyrus. Thus, intrahippocampal grafting of hippocampal NSCs shortly after SE considerably curbed the progression of epileptogenic processes and SRS, which eventually resulted in less severe chronic epilepsy devoid of significant cognitive and mood impairments.

The Paradox of Astroglial Ca2 + Signals at the Interface of Excitation and Inhibition

Astroglial networks constitute a non-neuronal communication system in the brain and are acknowledged modulators of synaptic plasticity. A sophisticated set of transmitter receptors in combination with distinct secretion mechanisms enables astrocytes to sense and modulate synaptic transmission. This integrative function evolved around intracellular Ca²⁺ signals, by and large considered as the main indicator of astrocyte activity. Regular brain physiology meticulously relies on the constant reciprocity of excitation and inhibition (E/I). Astrocytes are metabolically, physically, and functionally associated to the E/I convergence. Metabolically, astrocytes provide glutamine, the precursor of both major neurotransmitters governing E/I in the central nervous system (CNS): glutamate and γ-aminobutyric acid (GABA). Perisynaptic astroglial processes are structurally and functionally associated with the respective circuits throughout the CNS. Astonishingly, in astrocytes, glutamatergic as well as GABAergic inputs elicit similar rises in intracellular Ca²⁺ that in turn can trigger the release of glutamate and GABA as well. Paradoxically, as gliotransmitters, these two molecules can thus strengthen, weaken or even reverse the input signal. Therefore, the net impact on neuronal network function is often convoluted and cannot be simply predicted by the nature of the stimulus itself. In this review, we highlight the ambiguity of astrocytes on discriminating and affecting synaptic activity in physiological and pathological state. Indeed, aberrant astroglial Ca²⁺ signaling is a key aspect of pathological conditions exhibiting compromised network excitability, such as epilepsy. Here, we gather recent evidence on the complexity of astroglial Ca²⁺ signals in health and disease, challenging the traditional, neuro-centric concept of segregating E/I, in favor of a non-binary, mutually dependent perspective on glutamatergic and GABAergic transmission.

Neural Activities in Multiple Rat Brain Regions in Lithium-Pilocarpine-Induced Status Epilepticus Model

To clarify the different regional brain electroencephalogram (EEG) activities and biochemical responses in seizure and epilepsy models, we assessed the EEG and c-Fos immunolabeling characteristics in a lithium-pilocarpine-induced status epilepticus (SE) model and pentylenetetrazol (PTZ)-induced seizure model. The regional brain activities were evaluated by EEG and c-Fos immunolabeling. ZnT3 immunostaining was performed to observe hippocampal mossy fiber sprouting (MFS) within 7 days after the induction of SE in the lithium-pilocarpine model. The EEG recordings showed distinctive features of activation in different brain areas. With the aggravation of the behavioral manifestations of the seizures, the frequency and amplitude of the discharges on EEG gradually increased. SE was eventually induced and sustained. The labeling of c-Fos was enhanced in the cortex and hippocampal CA1, CA3, and dentate gyrus (DG); however, compared to the PTZ-induced seizure model, c-Fos staining could only be observed in the striatum and thalamus in the lithium-pilocarpine-induced epilepsy model. In each brain region, prominent c-Fos labeling was observed 2 h and 4 h after the induction of SE or seizures and diminished at 24 h. During the lithium-pilocarpine-induced chronic epilepsy phase after SE induction, MFS was observed 7 days after SE and was accompanied by the dynamic evolution of epileptic EEG activities. These findings validated the lithium-pilocarpine-induced SE model as an epilepsy model with a specific spatial-temporal profile of neural activation. The EEG characteristics and c-Fos expression patterns differ from those presented in a previous study using a PTZ-induced seizure model. Hippocampal mossy fiber spouting might be associated with spontaneous seizures during the chronic phase and can be detected at least within 1 week by ZnT3 staining after stimulation.

Intranasally Administered Human MSC-Derived Extracellular Vesicles Pervasively Incorporate into Neurons and Microglia in both Intact and Status Epilepticus Injured Forebrain

Extracellular vesicles (EVs) derived from human bone marrow mesenchymal stem cells (hMSCs) have great promise as biologics to treat neurological and neurodegenerative conditions due to their robust antiinflammatory and neuroprotective properties. Besides, intranasal (IN) administration of EVs has caught much attention because the procedure is noninvasive, amenable for repetitive dispensation, and leads to a quick penetration of EVs into multiple regions of the forebrain. Nonetheless, it is unknown whether brain injury-induced signals are essential for the entry of IN-administered EVs into different brain regions. Therefore, in this study, we investigated the distribution of IN-administered hMSC-derived EVs into neurons and microglia in the intact and status epilepticus (SE) injured rat forebrain. Ten billion EVs labeled with PKH26 were dispensed unilaterally into the left nostril of naïve rats, and rats that experienced two hours of kainate-induced SE. Six hours later, PKH26 + EVs were quantified from multiple forebrain regions using serial brain sections processed for different neural cell markers and confocal microscopy. Remarkably, EVs were seen bilaterally in virtually all regions of intact and SE-injured forebrain. The percentage of neurons incorporating EVs were comparable for most forebrain regions. However, in animals that underwent SE, a higher percentage of neurons incorporated EVs in the hippocampal CA1 subfield and the entorhinal cortex, the regions that typically display neurodegeneration after SE. In contrast, the incorporation of EVs by microglia was highly comparable in every region of the forebrain measured. Thus, unilateral IN administration of EVs is efficient for delivering EVs bilaterally into neurons and microglia in multiple regions in the intact or injured forebrain. Furthermore, incorporation of EVs by neurons is higher in areas of brain injury, implying that injury-related signals likely play a role in targeting of EVs into neurons, which may be beneficial for EV therapy in various neurodegenerative conditions including traumatic brain injury, stroke, multiple sclerosis, and Alzheimer's disease.

Extracellular Vesicles in the Forebrain Display Reduced miR-346 and miR-331-3p in a Rat Model of Chronic Temporal Lobe Epilepsy

An initial precipitating injury in the brain, such as after status epilepticus (SE), evolves into chronic temporal lobe epilepsy (TLE). We investigated changes in the miRNA composition of extracellular vesicles (EVs) in the forebrain after the establishment of SE-induced chronic TLE. We induced SE in young Fischer 344 rats through graded intraperitoneal injections of kainic acid, which resulted in consistent spontaneous recurrent seizures at ~ 3 months post-SE. We isolated EVs from the entire forebrain of chronically epileptic rats and age-matched naïve control animals through an ultracentrifugation method and performed miRNA-sequencing studies to discern changes in the miRNA composition of forebrain-derived EVs in chronic epilepsy. EVs from both naïve and epileptic forebrains displayed spherical or cup-shaped morphology, a comparable size range, and CD63 expression but lacked the expression of a deep cellular marker GM130. However, miRNA-sequencing studies suggested downregulation of 3 miRNAs (miR-187-5p, miR-346, and miR-331-3p) and upregulation of 4 miRNAs (miR-490-5p, miR-376b-3p, miR-493-5p, and miR-124-5p) in EVs from epileptic forebrains with fold changes ranging from 1.5 to 2.4 (p < 0.0006; FDR < 0.05). By using geNorm and Normfinder software, we identified miR-487 and miR-221 as the best combination of reference genes for measurement of altered miRNAs found in the epileptic forebrain through qRT-PCR studies. The validation revealed that only miR-346 and miR-331-3p were significantly downregulated in EVs from the epileptic forebrain. The enrichment pathway analysis of these miRNAs showed an overrepresentation of signaling pathways that are linked to molecular mechanisms underlying chronic epilepsy, including GABA-ergic (miR-346 targets) and mTOR (miR-331-3p targets) systems. Thus, the packaging of two miRNAs into EVs in neural cells is considerably altered in chronic epilepsy. Functional studies on these two miRNAs may uncover their role in the pathophysiology and treatment of TLE.