Characterising subtypes of hippocampal sclerosis and reorganization: correlation with pre and postoperative memory deficit

Sex-specific effects of intermittent fasting on hippocampal neurogenesis via the gut-brain axis

Intermittent fasting (IF) is a widely used dietary strategy that has shown several advantageous impacts on general health and aging. IF has recently been linked to the control of neurogenesis, a crucial process for emotional control, memory, and learning, in the hippocampus. Nevertheless, there is little knowledge about the sex-specific impacts of IF on hippocampal neurogenesis and the related mechanisms, which were investigated in this study among both male and female rats, together with analyzing the involvement of the flora-gut-brain axis in facilitating these effects. Our findings show that IF favorably affects hippocampus neurogenesis in female mice relative to male mice, suggesting a sex-specific mechanism. In addition, IF influenced the diversity of the gut microbiota and decreased the synthesis of fructose-1-phosphate (F-1-P), which is believed together with fructose metabolism to be linked to neurological damage and cognitive decline. Collectively, these data indicate that the connection between the flora-gut-brain axis and hippocampus neurogenesis is significant.

Focused review: Clinico-neuropathological aspects of late onset epilepsies: Pathogenesis

The aim of the present study was to review the current knowledge on the neuropathological spectrum of late onset epilepsies. Several terms including 'neuropathology*' AND 'late onset epilepsy' (LOE) combined with distinct neuropathological diagnostic terms were used to search PubMed until November 15, 2023. We report on the relevance of definitional aspects of LOE with implications for the diagnostic spectrum of epilepsies. The neuropathological spectrum in patients with LOE is described and includes vascular lesions, low-grade neuroepithelial neoplasms and focal cortical dysplasias (FCD). Among the latter, the frequency of the FCD subtypes appears to differ between LOE patients and those with seizure onset at a younger age. Neurodegenerative neuropathological changes in the seizure foci of LOE patients require careful interdisciplinary interpretation with respect to the differential diagnosis of primary neurodegenerative changes or epilepsy-related changes. Innate and adaptive neuroinflammation represents an important cause of LOE with intriguing therapeutic options.

Postoperative seizure and memory outcome of temporal lobe epilepsy with hippocampal sclerosis: A systematic review

We conducted a systematic review and meta-analysis to evaluate postoperative seizure and memory outcomes of temporal lobe epilepsy with different hippocampal sclerosis (HS) subtypes classified by International League Against Epilepsy (ILAE) Consensus Guidelines in 2013. Following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) and MOOSE (Meta-Analysis of Observational Studies in Epidemiology) guidelines, we searched PubMed, Embase, Web of Science, and Cochrane Library from January 1, 2013 to August 6, 2023. Observational studies reporting seizure and memory outcomes among different HS subtypes were included. We used the Newcastle-Ottawa scale to assess the risk of bias and the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach to grade the quality of evidence. Seizure freedom and improved outcome (Engel 1 or ILAE class 1-2) ≥1 year after surgery were defined as the primary and secondary seizure outcome. A random-effects meta-analysis by DerSimonian and Laird method was performed to obtain pooled risk ratio (RRs) with 95% confidence interval (CIs). The memory impairment was narratively reviewed because of various evaluation tools. Fifteen cohort studies with 2485 patients were eligible for the meta-analysis of seizure outcome. Six cohorts with detailed information on postoperative memory outcome were included. The pooled RRs of seizure freedom, with moderate to substantial heterogeneity, were .98 (95% CI = .84-1.15) between HS type 2 and type 1, 1.11 (95% CI = .82-1.52) between type 3 and type 1, and .80 (95% CI = .62-1.03) between the no-HS and HS groups. No significant difference of improved outcome was found between different subtypes (p > .05). The quality of evidence was deemed to be low to very low according to GRADE. The long-term seizure outcome (≥5 years after surgery) and memory impairment remained controversial.

Hyperphosphorylated Tau in Mesial Temporal Lobe Epilepsy: a Neuropathological and Cognitive Study

Temporal lobe epilepsy (TLE) often courses with cognitive deficits, but its underlying neuronal basis remains unclear. Confluent data suggest that epilepsy share pathophysiological mechanisms with neurodegenerative diseases. However, as most studies analyze subjects 60 years old and older, it is challenging to rule out that neurodegenerative changes arise from age-related mechanisms rather than epilepsy in these individuals. To fill this gap, we conducted a neuropathological investigation of the hippocampal formation of 22 adults with mesial TLE and 20 age- and sex-matched controls (both younger than 60 years). Moreover, we interrogated the relationship between these neuropathological metrics and cognitive performance. Hippocampal formation extracted from patients with drug-resistant mesial TLE undergoing surgery and postmortem non-sclerotic hippocampal formation of clinically and neuropathologically controls underwent immunohistochemistry against amyloid β (Aβ), hyperphosphorylated tau (p-tau), and TAR DNA-binding protein-43 (TDP-43) proteins, followed by quantitative analysis. Patients underwent a comprehensive neuropsychological evaluation prior to surgery. TLE hippocampi showed a significantly higher burden of p-tau than controls, whereas Aβ deposits and abnormal inclusions of TDP-43 were absent in both groups. Patients with hippocampal sclerosis (HS) type 2 had higher immunostaining for p-tau than patients with HS type 1. In addition, p-tau burden was associated with impairment in attention tasks and seizures frequency. In this series of adults younger than 60 years-old, the increase of p-tau burden associated with higher frequency of seizures and attention impairment suggests the involvement of tau pathology as a potential contributor to cognitive deficits in mesial TLE.

Neuropathological Insights into Unexpected Cognitive Decline in Epilepsy

OBJECTIVE

Some patients unexpectedly display an unfavorable cognitive course after epilepsy surgery subsequent to any direct cognitive sequelae of the surgical treatment. Therefore, we conducted in-depth neuropathological examinations of resective specimens from corresponding patients to provide insights as to the underlying disease processes.

METHODS

In this study, cases with significant cognitive deterioration following a previous postoperative assessment were extracted from the neuropsychological database of a longstanding epilepsy surgical program. An extensive reanalysis of available specimens was performed using current, state-of-the-art neuropathological examinations. Patients without cognitive deterioration but matched in regard to basic pathologies served as controls.

RESULTS

Among the 355 operated patients who had undergone more than one postoperative neuropsychological examination, 30 (8%) showed significant cognitive decline in the period after surgery. Of the 24 patients with available specimens, 71% displayed further neuropathological changes in addition to the typical spectrum (ie, hippocampal sclerosis, focal cortical dysplasias, vascular lesions, and low-grade tumors), indicating (1) a secondary, putatively epilepsy-independent neurodegenerative disease process; (2) limbic inflammation; or (3) the enigmatic pathology pattern of "hippocampal gliosis" without segmental neurodegeneration. In the controls, the matched individual principal epilepsy-associated pathologies were not found in combination with the secondary pathology patterns of the study group.

INTERPRETATION

Our findings indicate that patients who unexpectedly displayed unfavorable cognitive development beyond any direct surgical effects show rare and very particular pathogenetic causes or parallel, presumably independent, neurodegenerative alterations. A multicenter collection of such cases would be appreciated to discern presurgical biomarkers that help with surgical decision-making. ANN NEUROL 2023;93:536-550.

Morphometric and microstructural characteristics of hippocampal subfields in mesial temporal lobe epilepsy and their correlates with mnemonic discrimination

Introduction

Pattern separation (PS) is a fundamental aspect of memory creation that defines the ability to transform similar memory representations into distinct ones, so they do not overlap when storing and retrieving them. Experimental evidence in animal models and the study of other human pathologies have demonstrated the role of the hippocampus in PS, in particular of the dentate gyrus (DG) and CA3. Patients with mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HE) commonly report mnemonic deficits that have been associated with failures in PS. However, the link between these impairments and the integrity of the hippocampal subfields in these patients has not yet been determined. The aim of this work is to explore the association between the ability to perform mnemonic functions and the integrity of hippocampal CA1, CA3, and DG in patients with unilateral MTLE-HE.

Method

To reach this goal we evaluated the memory of patients with an improved object mnemonic similarity test. We then analyzed the hippocampal complex structural and microstructural integrity using diffusion weighted imaging.

Results

Our results indicate that patients with unilateral MTLE-HE present alterations in both volume and microstructural properties at the level of the hippocampal subfields DG, CA1, CA3, and the subiculum, that sometimes depend on the lateralization of their epileptic focus. However, none of the specific changes was found to be directly related to the performance of the patients in a pattern separation task, which might indicate a contribution of various alterations to the mnemonic deficits or the key contribution of other structures to the function.

Discussion

we established for the first time the alterations in both the volume and the microstructure at the level of the hippocampal subfields in a group of unilateral MTLE patients. We observed that these changes are greater in the DG and CA1 at the macrostructural level, and in CA3 and CA1 in the microstructural level. None of these changes had a direct relation to the performance of the patients in a pattern separation task, which suggests a contribution of various alterations to the loss of function.

Neuroprotective Effect of Celastrus Paniculatus Seed Extract on Epilepsy and Epilepsy-associated Cognitive Deficits

Introduction

Cognitive deficit is one of the common comorbidity accompanying epilepsy. The present study evaluated the effect of Celastrus paniculatus seed extract on seizure severity and cognitive deficit following the pentylenetetrazole (PTZ)-induced chemical kindling model.

Methods

PTZ kindling model was developed by daily administration of the sub-convulsive dose of PTZ 30 mg/kg for four weeks. After four weeks of induction, the following treatment, namely sodium valproic acid (SVA) 200 mg/kg, C. paniculatus 500 mg\kg, pergolide 2 mg/kg, C. paniculatus (250 mg\kg)+ Pergolide (1 mg/kg), and C. paniculatus (250 mg\kg)+ SVA (100 mg/kg) were administered 30 minutes prior to PTZ (30 mg/kg) injection for a period of next 14 days. Neurobehavioral parameters, including superoxide dismutase (SOD), Catalase (CAT), glutathione (GSH), and dopamine levels were assessed and the Morris water maze test (MWM) and Grip strength test (GPS) were performed. Hematoxylin & Eosin (H&E) staining of hippocampal cornu ammonis (CA1), CA2, CA3, dentate gyrus (DG), and frontal cortex was performed.

Results

C. paniculatus (500 mg/kg) alone and in combination (C. paniculatus (250 mg\ kg)+ pergolide (1 mg/kg) and C. paniculatus (250 mg\kg)+ SVA (100 mg/kg)) significantly (P<0.05) reduced the seizure score, mean latency time, and distance traveled in the MWM. However, no significant effect was seen in GPS. Biochemical analysis showed elevated antioxidant markers, namely GSH, CAT, and SOD, and also elevated dopamine levels. C. paniculatus and its combination also significantly (P<0.05) protected against neuronal loss in the hippocampus and frontal cortex evidenced by H&E staining.

Conclusion

C. paniculatus alone and in combination with other agents may have the potential to treat epilepsy and associated cognitive deficits.

Serum neurofilament light and MRI predictors of cognitive decline in patients with secondary progressive multiple sclerosis: Analysis from the MS-STAT randomised controlled trial

BACKGROUND

Cognitive impairment affects 50%-75% of people with secondary progressive multiple sclerosis (PwSPMS). Improving our ability to predict cognitive decline may facilitate earlier intervention.

OBJECTIVE

The main aim of this study was to assess the relationship between longitudinal changes in cognition and baseline serum neurofilament light chain (sNfL) in PwSPMS. In a multi-modal analysis, MRI variables were additionally included to determine if sNfL has predictive utility beyond that already established through MRI.

METHODS

Participants from the MS-STAT trial underwent a detailed neuropsychological test battery at baseline, 12 and 24 months. Linear mixed models were used to assess the relationships between cognition, sNfL, T2 lesion volume (T2LV) and normalised regional brain volumes.

RESULTS

Median age and Expanded Disability Status Score (EDSS) were 51 and 6.0. Each doubling of baseline sNfL was associated with a 0.010 [0.003-0.017] point per month faster decline in WASI Full Scale IQ Z-score (p = 0.008), independent of T2LV and normalised regional volumes. In contrast, lower baseline volume of the transverse temporal gyrus was associated with poorer current cognitive performance (0.362 [0.026-0.698] point reduction per mL, p = 0.035), but not change in cognition. The results were supported by secondary analyses on individual cognitive components.

CONCLUSION

Elevated sNfL is associated with faster cognitive decline, independent of T2LV and regional normalised volumes.

Tauopathy and Epilepsy Comorbidities and Underlying Mechanisms

Tau is a microtubule-associated protein known to bind and promote assembly of microtubules in neurons under physiological conditions. However, under pathological conditions, aggregation of hyperphosphorylated tau causes neuronal toxicity, neurodegeneration, and resulting tauopathies like Alzheimer's disease (AD). Clinically, patients with tauopathies present with either dementia, movement disorders, or a combination of both. The deposition of hyperphosphorylated tau in the brain is also associated with epilepsy and network hyperexcitability in a variety of neurological diseases. Furthermore, pharmacological and genetic targeting of tau-based mechanisms can have anti-seizure effects. Suppressing tau phosphorylation decreases seizure activity in acquired epilepsy models while reducing or ablating tau attenuates network hyperexcitability in both Alzheimer's and epilepsy models. However, it remains unclear whether tauopathy and epilepsy comorbidities are mediated by convergent mechanisms occurring upstream of epileptogenesis and tau aggregation, by feedforward mechanisms between the two, or simply by coincident processes. In this review, we investigate the relationship between tauopathies and seizure disorders, including temporal lobe epilepsy (TLE), post-traumatic epilepsy (PTE), autism spectrum disorder (ASD), Dravet syndrome, Nodding syndrome, Niemann-Pick type C disease (NPC), Lafora disease, focal cortical dysplasia, and tuberous sclerosis complex. We also explore potential mechanisms implicating the role of tau kinases and phosphatases as well as the mammalian target of rapamycin (mTOR) in the promotion of co-pathology. Understanding the role of these co-pathologies could lead to new insights and therapies targeting both epileptogenic mechanisms and cognitive decline.

Verbal Learning and Longitudinal Hippocampal Network Connectivity in Temporal Lobe Epilepsy Surgery

Introduction

Learning new verbal information can be impaired in 20–40% of patients after mesial temporal lobe resection. In recent years, understanding epilepsy as a brain network disease, and investigating the relationship between large-scale resting networks and cognition has led to several advances. Aligned studies suggest that it is the integrity of the hippocampal connectivity with these large-scale networks what is relevant for cognition, with evidence showing a functional and structural heterogeneity along the long axis hippocampus bilaterally.

Objective

Our aim is to examine whether pre-operative resting-state connectivity along the long hippocampal axis is associated with verbal learning decline after anterior temporal lobe resection.

Methods

Thirty-one patients with epilepsy who underwent an anterior temporal lobe resection were pre-surgically scanned at 3-tesla, and pre/post-surgery evaluated for learning deficits using the Rey Auditory Verbal Learning Task (RAVLT). Eighteen controls matched by age, gender and handedness were also scanned and evaluated with the RAVLT. We studied the functional connectivity along the (anterior/posterior) long axis hippocampal subregions and resting-state functionally-defined brain networks involved in learning [executive (EXE), dorsal attention (DAN) and default-mode (DMN) networks]. Functional connectivity differences between the two groups of patients (learning intact or with learning decline) and controls were investigated with MANOVA and discriminant analysis.

Results

There were significant differences in the pattern of hippocampal connectivity among the groups. Regarding the anterior connectivity hippocampal pattern, our data showed an increase of connectivity in the pathological side with the DAN (p = 0.011) and the EXE (p = 0.008) when comparing learning-decline vs. learning-intact patients. Moreover, the non-pathological side showed an increase in the anterior connectivity pattern with the DAN (p = 0.027) between learning-decline vs. learning-intact patients. In contrast, the posterior hippocampus showed a reduction of connectivity in the learning-decline patients with the DMN, both in the pathological (p = 0.004) and the non-pathological sides (p = 0.036). Finally, the discriminant analysis based on the pre-operative connectivity pattern significantly differentiated the learning-decline patients from the other groups (p = 0.019).

Conclusion

Our findings reveal bilateral connectivity disruptions along the longitudinal axis of the hippocampi with resting-state networks, which could be key to identify those patients at risk of verbal learning decline after epilepsy surgery.

Epilepsy under the scope of ultra-high field MRI

Ultra-high field magnetic resonance imaging (UHF-MRI) is capable of unraveling anatomical structures in a submillimeter range. In addition, its high resonance regime allows the quantification of constitutive molecules in a spatially sensitive manner, a crucial capability for determining the extent and localization of a probable epileptogenic region or the severity of the epilepsy. The main technical challenges for data acquisition under UHF are to produce a strong, homogeneous transverse field, while keeping the tissue power deposition within the safe regulatory guidelines. The nonuniformities caused by destructive and constructive interferences at UHFs required new technologies to accelerate and increase yield regarding time spent and quality achieved. Image quality is the paramount contribution of UHF high-resolution imaging, which is capable to disclose fine details of the hippocampal formation and its surroundings and their changes in the course of epilepsy. Other sequences like diffusion tensor imaging (DTI) and multiecho susceptibility imaging at 7 T in vivo can assist the creation of normative atlases of the hippocampal subfields or the reconstruction of the highly arborized cerebral blood vessels. In our review, we specify the impact of these advanced relevant techniques onto the study of epilepsy. In this context, we focused onto high field high-resolution scanners and clinically-enriched decision-making. Studies on focal dysplasias correlating ex vivo high-resolution imaging with specific histological and ultrastructural patterns showed that white matter hyperintensities were related to a demyelination process and other alterations. Preliminary results correlating thick serial sections through bioptic epileptogenic tissue could extend the strategy to localize degenerated tissue sectors, correlate nature and extent of tissue loss with preoperative diagnosis and postoperative outcome. Finally, this protocol will provide the neurosurgeon with a detailed depiction of the removed pathologic tissue and possible adverse effects by the pathologic tissue left in situ. This article is part of the special issue "NEWroscience 2018".

Operative variations in temporal lobe epilepsy surgery and seizure and memory outcome in 226 patients suffering from hippocampal sclerosis

Objective: The aim of this retrospective cohort study was to assess seizure and memory outcomes following temporal lobe surgery in patients suffering from medically refractory temporal lobe epilepsy (TLE) and hippocampal sclerosis (HS).Methods: A retrospective monocentric data analysis was performed in consecutive patients who were operated on during 2002-2018. In the first decennium, standard temporal lobe resections (TLR) were predominately performed, and later, antero-temporal lobe resections (ATLR) were mainly performed. Seizure and memory outcomes over time were assessed according to ILAE/Engel classification and the Berlin Amnesia Test (BTA), respectively.Results: Altogether, 231 surgeries were performed on 226 patients (mean age, 40 years [range, 10-68 years]; male: female, 1:1.4; mean seizure duration, 25 years; and mean follow-up duration, 4.75 years [range, 1-16]). Recently, outcomes of 78.3% of the patients in the total cohort were classified as Engel class I, with 54.9% of patients being completely seizure free. The recent cohort of ATLR since 2012 showed significant more completely seizure-free patients than before 2012 (Engel IA 46.6% versus 67.7%, p < 0.0025, χ²), although the Kaplan Meier analysis of all patients favors TLR for better seizure outcome (61% ATLR vs 73% TLR seizure free after 5 yrs, log rank p < 0.001). Verbal memory improved significantly in non-dominant patients. Minor neurological complications were noted (permanent severe complications, 0.4%; temporary severe complications, 4.8%).Conclusion: Significant improvements in seizure and memory outcomes were observed over time, with surgical technique and seizure duration as important prognostic factors. Early admittance for surgery may favor an excellent seizure outcome in patients undergoing temporal lobe resection for HS.

Prognostic value of histopathologic pattern for long-term surgical outcomes of 198 patients with confirmed mesial temporal lobe epilepsy

Hippocampal sclerosis (HS) is the most common neuropathologic findings in patients with intractable temporal lobe epilepsy (TLE). The international league against epilepsy has proposed a new classification of HS based on pyramidal cell loss on different subfields to facilitate the study of HS pathology in patients after anterior temporal lobectomy (ATL), and the influence of these HS patterns on the prognosis of patients with TLE is contradictory. This study aims to investigate the relationship between different HS subtypes and postoperative seizure outcomes for intractable patients with TLE. From January 2008 to December 2018, we retrospectively reviewed 198 TLE patients with ATL surgery, and all patients had a complete preoperative evaluation, a specimen of hippocampal tissue after surgery, cognitive test after surgery, and more than 2 years of postoperative follow-up. The main findings were as follows: 1) temporal neocortical gray matter heterotopia were more common in the no-HS group; 2) HS type 1 was associated with a longer duration of epilepsy; 3) history of meningitis was the independent predictor of HS type 1; 4) no-HS patients experienced worse postoperative seizure outcomes than those with HS type1 and type 2, whereas no difference in seizure outcomes was obtained between HS type 1 and type 2; 5) no-HS patients were at increased risk for verbal memory decline after left hippocampal resection. The HS subtypes were associated with the prognosis of patients with TLE, and other variables were the predictors of different HS types. `Further study was to identify the HS subtypes by noninvasive evaluation to approve better postoperative outcomes.

Sublayer- and cell-type-specific neurodegenerative transcriptional trajectories in hippocampal sclerosis

Hippocampal sclerosis, the major neuropathological hallmark of temporal lobe epilepsy, is characterized by different patterns of neuronal loss. The mechanisms of cell-type-specific vulnerability and their progression and histopathological classification remain controversial. Using single-cell electrophysiology in vivo and immediate-early gene expression, we reveal that superficial CA1 pyramidal neurons are overactive in epileptic rodents. Bulk tissue and single-nucleus expression profiling disclose sublayer-specific transcriptomic signatures and robust microglial pro-inflammatory responses. Transcripts regulating neuronal processes such as voltage channels, synaptic signaling, and cell adhesion are deregulated differently by epilepsy across sublayers, whereas neurodegenerative signatures primarily involve superficial cells. Pseudotime analysis of gene expression in single nuclei and in situ validation reveal separated trajectories from health to epilepsy across cell types and identify a subset of superficial cells undergoing a later stage in neurodegeneration. Our findings indicate that sublayer- and cell-type-specific changes associated with selective CA1 neuronal damage contribute to progression of hippocampal sclerosis.

Validation of automatic MRI hippocampal subfield segmentation by histopathological evaluation in patients with temporal lobe epilepsy

OBJECTIVE

The present study validates the results of automated hippocampal subfield segmentation with histopathology in epilepsy patients undergoing epilepsy surgery.

METHODS

We performed an automated hippocampal subfield segmentation on presurgical three-dimensional, T1-weighted magnetization Prepared Rapid Acquisition of Gradient Echoes Magnetic Resonance Imaging (MRI) data of 25 patients with unilateral mesial temporal lobe epilepsy due to hippocampal sclerosis (HS), using Freesurfer Version 6.0. The resulting volumes of cornu ammonis (CA) subfields CA1, CA2/3, CA4 and the dentate gyrus (DG) were compared to the histopathological cell count.

RESULTS

We found a significant correlation between histopathology in subregion CA2 and automated segmentation of subregion CA1 (p = 0.0062), CA2/3 (p = 0.004), CA4 (p = 0.0062) and the DG (p = 0.0054), between histopathology in CA3 and automated segmentation of CA1 (p = 0.0132), CA2/3 (p = 0.0004), CA4 (p = 0.0032) and the DG (p = 0.0037), as well as between histopathology in the DG and automated segmentation of CA1 (p = 0.0115), CA2/3 (p < 0.0001), CA4 (p < 0.0001) and the DG (p = 0.0001). The histopathological finding of HS type 1 could correctly be classified in all cases on MRI.

SIGNIFICANCE

The present study shows significant correlations between histopathological evaluation and results of the automated segmentation of the hippocampus, thereby validating the automated segmentation method. As the differential involvement of different hippocampal subfields may be associated with clinical parameters and the outcome after epilepsy surgery, the automated segmentation is also promising for prognostic purposes.

The Antagonism of 5-HT6 Receptor Attenuates Current-Induced Spikes and Improves Long-Term Potentiation via the Regulation of M-Currents in a Pilocarpine-Induced Epilepsy Model

Recent studies have documented that reduced M-current promotes epileptogenesis and attenuates synaptic remodeling. Neurite growth is closely related to the level of 5-HT6 receptor (5-HT6R) in the central nervous system. However, little research is available regarding the relation between 5-HT6R and M-current and the role of 5-HT6R in M-current regulation. Herein, we found that the expression of 5-HT6R was notably increased and the expression of KNCQ2/3, the main components of the M channel, was decreased in a time-dependent manner in pilocarpine-induced chronic epileptic hippocampus. Interestingly, antagonism of 5-HT6R by SB271046 upregulated the expression of KCNQ2 but not KCNQ3. SB271046 greatly alleviated excitatory/inhibitory imbalance and improved the impaired LTP in the chronic epileptic hippocampus. Further mechanism exploration revealed that the above effects of SB271046 can be reversed by the M-channel inhibitor XE991, which also confirmed that SB271046 can indeed improve abnormal M current. These data indicate that the antagonism of 5-HT6R may decrease the excitability of hippocampal pyramidal neurons in chronic epileptic rats and improve the impaired long-term potentiation by upregulating the expression of KCNQ2 in the M-channel.

Betahistine, prevents kindling, ameliorates the behavioral comorbidities and neurodegeneration induced by pentylenetetrazole

A seizure may occur because of the imbalance between glutamate and gamma-aminobutyric acid (GABA). Recurrent seizures induce some cognitive problems, such as, depression, learning and memory deficits, and neurodegeneration. Histamine is an appropriate therapeutic target for epilepsy via its effect on regulating neurotransmitter release. Also, evidence indicates the effect of histamine on neuroprotection and alleviating cognitive disorders. An ideal antiepileptic drug is a substance, which has both anticonvulsant effects and decreases the comorbidities that are induced by repeated seizures. Betahistine dihydrochloride (betahistine) is a structural analog of histamine. It acts as histamine H1 receptor agonist and H3 receptor antagonist, which enhances histaminergic neuronal activities. In the present study, we examined the effect of betahistine administration on seizure scores, memory deficits, depression, and neuronal loss induced by pentylenetetrazole (PTZ). Eight- to ten-week-old BALB/c male mice (20-25 g) received betahistine, 1, and 10 mg/kg daily from 7 days before the onset of PTZ-induced kindling until the end of the establishment of the kindling. We found that betahistine prevented generalized tonic-clonic seizures induction and diminished forelimb clonic seizures intensity. Also, it decreased cell death in the hippocampus and cortex, ameliorated the memory deficit and depression induced by PTZ in the kindled animals. Altogether, these results indicate that pretreatment and repetitive administration with betahistine exerts antiepileptogenic and anticonvulsant activity. These findings might be due to the neuroprotective impact of betahistine in the hippocampus and cortex.

Microgliosis is associated with visual memory decline in patients with temporal lobe epilepsy and hippocampal sclerosis: A clinicopathologic study

Hippocampal sclerosis (HS) is characterized by neuronal loss and gliosis. The intensity and distribution of these histopathological findings over the Cornu Ammonis (CA) subfields are important for the classification of HS and prognostication of patients with temporal lobe epilepsy (TLE). Several studies have associated the neuronal density reduction in the hippocampus with cognitive decline in patients with TLE. The current study aimed at investigating whether the expression of glial proteins in sclerotic hippocampi is associated with presurgical memory performance of patients with TLE. Before amygdalohippocampectomy, patients were submitted to memory tests. Immunohistochemical and morphometric analyses with glial fibrillary acidic protein (GFAP) for astrogliosis and human leucocyte antigen DR (HLA-DR) for microgliosis were performed in paraffin-embedded HS and control hippocampi. Sclerotic hippocampi exhibited increased gliosis in comparison with controls. In patients with TLE, the area and intensity of staining for HLA-DR were associated with worse performance in the memory tests. Glial fibrillary acidic protein was neither associated nor correlated with memory test performance. Our data suggest association between microgliosis, but not astrogliosis, with visual memory decline in patients with TLE.

Modulatory Effect of Serotonergic System in Pentylenetetrazole-Induced Seizures and Associated Memory Deficit: Role of 5-HT1A and 5-HT2A/2C

Background and Purpose

Recent studies have recognised the memory deficit as one of the most common psychiatric issues in the patients with epilepsy, which severely affects the quality of life. Our previous studies have demonstrated the possible involvement of serotonergic system in the pathogenesis of epilepsy and associated memory deficit. The possible involvement of 5-HT_1A and 5-HT_2A/2C receptor has not been explored yet. Therefore, this study has been envisaged to explore the effect of 5-HT_1A and 5-HT_2A/2C receptor modulation on epilepsy and memory deficit in pentylenetetrazole-kindled mice.

Methods

In the present experimental approach, we examined the efficacy of modulation of 5-HT_1A and 5-HT_2A/2C receptor in pentylenetetrazole-induced kindling in male Swiss mice (n=75). Mice were kindled by sub-convulsive dose of pentylenetetrazole (35 mg/kg, intraperitoneal injection), at the interval of 48±2 hours). Successfully kindled animals were treated with 5-HT_1A and 5-HT_2A/2C receptor modulators. The effect of different treatments on seizure severity score and memory impairment was analysed.

Results

5-HT_1A receptor agonist improved the memory functions while seizure severity was not improved, and the opposite effect was observed with 5-HT_1A receptor antagonist. On the other hand, 5-HT_2A/2C receptor agonist significantly improved memory deficit as well as seizure severity in the kindled animals.

Conclusions

The outcome of the study indicates the possible involvement of 5-HT_2A/2C receptor in the pathogenesis of epilepsy and associated memory deficit, which can be further explored for its management.

Bcl-2/Bax ratio increase does not prevent apoptosis of glia and granular neurons in patients with temporal lobe epilepsy

Temporal lobe epilepsy (TLE) is usually associated with hippocampal sclerosis (HS), characterized by gliosis and neuronal loss, mainly in the cornus ammonis (CA). Regardless the type of HS, gliosis is associated with neuronal loss. Indeed, glial reactivation seems to induce both neuronal and glial apoptosis. Anti-apoptotic mechanisms are also activated in order to contain the cell death in chronic epilepsy. However, the role of the intrinsic apoptosis pathway in human TLE is unclear, mainly in relation to glial death. The purpose of this study was to evaluate the reactive gliosis areas in parallel with Bcl-2/Bax ratio and active caspase 3 immunoreactivity in hippocampi of TLE patients in comparison with control hippocampi. We also sought to investigate whether the levels of these markers were correlated with TLE clinical parameters. Paraffin-embedded sclerotic and control hippocampi were collected for immunohistochemical analyses of glial fibrillary acidic protein (GFAP), human leucocyte antigen DR (HLA-DR), neuronal nuclei protein (NeuN), Bax, Bcl-2 and active caspase 3. Sclerotic hippocampi presented higher immunoreactivity areas of GFAP and HLA-DR than controls, with similar values in HS types 1 and 2. Bcl-2 protein expression was increased in epileptic hippocampi, while Bax expression was similar to controls. Despite Bcl2/Bax ratio increase, granular neurons and glia exhibited active caspase 3 expression in TLE hippocampi, while controls did not show staining for the same marker. In conclusion, glial and neuronal death is increased in sclerotic hippocampi, independently of HS type, and co-localized with gliosis. Furthermore, Bcl-2/Bax ratio increase does not prevent expression of active caspase 3 by glia and granular neurons in TLE.

Reelin, tau phosphorylation and psychiatric complications in patients with hippocampal sclerosis and structural abnormalities in temporal lobe epilepsy

INTRODUCTION

Temporal lobe epilepsy (TLE) is the most common adult epileptic syndrome. About 30-70% of those cases have neuropsychiatric complications. More than 10% of patients have TLE because of focal cortical dysplasia (FCD) type IIIa.

OBJECTIVES

The objective of this study was to review the evidence of reelin (RELN) deficiency and tau phosphorylation role in the histopathological, neuropsychiatric, and hyperexcitability features in TLE because of dysplasia type IIIa.

METHODS

The current literature was reviewed using Cochrane, EMBASE, PROSPERO, MEDLINE, and PubMed from 1995 to July 2018. Articles of interest were reviewed by one investigator (RAM).

RESULTS

Reelin deficit is related to an abnormal migration of neurons in dentate gyrus, and its deficit causes dentate gyrus abnormalities, which in turn has been associated with memory deficits in patients with TLE. A decreased in the expression of RELN ribonucleic acid (RNA) was found in patients with TLE and dysplasia type IIIa compared with patients with TLE and isolated hippocampal sclerosis (HS). Reelin might affect the distribution and dynamic instability of microtubules within neurons in the cerebral cortex and their phosphorylation. Amyloid pathology, tauopathy, or phosphorylated tau (p-tau) overexpression has been reported in epileptic human brain and in animal models of epilepsy.

CONCLUSION

Reelin deficit may determine an abnormal cortical lamination and dentate gyrus dispersion and might be associated with an abnormal tau phosphorylation. These processes can be associated with an abnormal hyperexcitability, neuropsychiatric complications, and a myriad of typical histopathological features seen in patients with TLE because of dysplasia type IIIa.

Ultra-high field MRI of human hippocampi: Morphological and multiparametric differentiation of hippocampal sclerosis subtypes

The aim of the present study is to differentiate subtypes of hippocampal sclerosis (HS) using ex vivo ultra-high field magnetic resonance imaging (MRI). Included were 14 surgically resected hippocampi of patients with medically intractable temporal lobe epilepsy. The resected hippocampi were histologically categorized into subtypes of hippocampal sclerosis (HS type 1 (n = 10), HS type 2 (n = 2) and no-HS (n = 2)) and subsequently scanned on a preclinical 7T MRI acquiring T2-weighted morphology, relaxometry and diffusion tensor imaging. On the morphological images, the pyramidal cell layer (PCL) of the hippocampus was segmented and the following parameters were derived: T2 signal intensity, T1-, T2- and T2*-relaxation times, apparent diffusion coefficient (ADC), fractional anisotropy (FA) and mean diffusivity (MD). Furthermore, the area of the PCL was determined, as well as the parameter product which refers to the widths of the PCL parallel and perpendicular to the stratum moleculare. Spearman correlation coefficient was used to demonstrate relationships between MR-parameters and type of sclerosis. In comparison to no-HS specimens, the PCL was significantly narrower in HS type 1 and HS type 2 hippocampi. This narrowing affected the entire cornu ammonis sector (CA) 1 in HS type 1, while it was limited to the upper half of CA1 in direction to CA2 in HS type 2. The parameter product median increased from 0.43 to 1.67 and 2.91 mm2 for HS type 1, HS type 2 and no-HS, respectively. Correlation coefficients were significant for the PCL parameters product (0.73), area (0.71), T2*-time (-0.67), FA (0.65) and ADC (0.55). Our initial results suggest that HS type 1, HS type 2 and no-HS subtypes can be distinguished from each other using ex vivo UHF MRI based on T2-weighted morphologic images and the assessment of the parameter product. Upon clinical translation, UHF-MRI may provide a promising technique for the preoperative differentiation of HS subtypes in patients.

Hippocampal MRS and subfield volumetry at 7T detects dysfunction not specific to seizure focus

Ultra high-field 7T MRI offers sensitivity to localize hippocampal pathology in temporal lobe epilepsy (TLE), but has rarely been evaluated in patients with normal-appearing clinical MRI. We applied multimodal 7T MRI to assess if focal subfield atrophy and deviations in brain metabolites characterize epileptic hippocampi. Twelve pre-surgical TLE patients (7 MRI-negative) and age-matched healthy volunteers were scanned at 7T. Hippocampal subfields were manually segmented from 600μm isotropic resolution susceptibility-weighted images. Hippocampal metabolite spectra were acquired to determine absolute concentrations of glutamate, glutamine, myo-inositol, NAA, creatine and choline. We performed case-controls analyses, using permutation testing, to identify abnormalities in hippocampal imaging measures in individual patients, for evaluation against clinical evidence of seizure lateralisation and neuropsychological memory test scores. Volume analyses identified hippocampal subfield atrophy in 9/12 patients (75%), commonly affecting CA3. 7/8 patients had altered metabolite concentrations, most showing reduced glutamine levels (62.5%). However, neither volume nor metabolite deviations consistently lateralized the epileptogenic hippocampus. Rather, lower subiculum volumes and glutamine concentrations correlated with impaired verbal memory performance. Hippocampal subfield and metabolic abnormalities detected at 7T appear to reflect pathophysiological processes beyond epileptogenesis. Despite limited diagnostic contributions, these markers show promise to help elucidate mnemonic processing in TLE.