A comparative study of the dentate gyrus in hippocampal sclerosis in epilepsy and dementia

Repurposing dimethyl fumarate as an antiepileptogenic and disease-modifying treatment for drug-resistant epilepsy

BACKGROUND

Epilepsy affects over 65 million people worldwide and significantly burdens patients, caregivers, and society. Drug-resistant epilepsy occurs in approximately 30% of patients and growing evidence indicates that oxidative stress contributes to the development of such epilepsies. Activation of the Nrf2 pathway, which is involved in cellular defense, offers a potential strategy for reducing oxidative stress and epilepsy treatment. Dimethyl fumarate (DMF), an Nrf2 activator, exhibits antioxidant and anti-inflammatory effects and is used to treat multiple sclerosis.

METHODS

The expression of Nrf2 and its related genes in vehicle or DMF treated rats were determined via RT-PCR and Western blot analysis. Neuronal cell death was evaluated by immunohistochemical staining. The effects of DMF in preventing the onset of epilepsy and modifying the disease were investigated in the kainic acid-induced status epilepticus model of temporal lobe epilepsy in rats. The open field, elevated plus maze and T-Maze spontaneous alteration tests were used for behavioral assessments.

RESULTS

We demonstrate that administration of DMF following status epilepticus increased Nrf2 activity, attenuated status epilepticus-induced neuronal cell death, and decreased seizure frequency and the total number of seizures compared to vehicle-treated animals. Moreover, DMF treatment reversed epilepsy-induced behavioral deficits in the treated rats. Moreover, DMF treatment even when initiated well after the diagnosis of epilepsy, reduced symptomatic seizures long after the drug was eliminated from the body.

CONCLUSIONS

Taken together, these findings suggest that DMF, through the activation of Nrf2, has the potential to serve as a therapeutic target for preventing epileptogenesis and modifying epilepsy.

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.

Neuropathology of Dementia Disorders

PURPOSE OF REVIEW

This article provides an overview of the neuropathology of common age-related dementing disorders, focusing on the pathologies that underlie Alzheimer disease (AD) and related dementias, including Lewy body dementias, frontotemporal dementia, vascular dementia, limbic-predominant age-related transactive response DNA-binding protein 43 (TDP-43) encephalopathy (LATE), and mixed-etiology dementias. This article also discusses the underlying proteinopathies of neurodegenerative diseases (eg, amyloid-β, paired helical filament tau, α-synuclein, and TDP-43 pathology) and vascular pathologies, including tissue injury (eg, infarcts, hemorrhages) with or without vessel disease.

RECENT FINDINGS

New criteria for AD pathologic diagnosis highlight amyloid-β as the sine qua non of AD; they require molecular markers of amyloid and establish a minimum threshold of Braak neurofibrillary tangle stage 3. Pathologic diagnosis is separated from clinical disease (ie, pathologic diagnosis no longer requires dementia). TDP-43 pathology, a major pathology in a frontotemporal dementia subtype, was found as a central pathology in LATE, a newly named amnestic disorder. Multiple pathologies (often co-occurring with AD) contribute to dementia and add complexity to the clinical picture. Conversely, Lewy body, LATE, and vascular dementias often have accompanying AD pathology. Pathology and biomarker studies highlight subclinical pathologies in older people without cognitive impairment. This resilience to brain pathology is common and is known as cognitive reserve.

SUMMARY

The pathologies of dementia in aging are most commonly amyloid, tangles, Lewy bodies, TDP-43, hippocampal sclerosis, and vascular pathologies. These pathologies often co-occur (mixed pathologies), which may make specific clinical diagnoses difficult. In addition, dementia-related pathologies are often subclinical, suggesting varying levels of resilience in older people.

Mechanisms Involved in Epileptogenesis in Alzheimer's Disease and Their Therapeutic Implications

Epilepsy and Alzheimer's disease (AD) incidence increases with age. There are reciprocal relationships between epilepsy and AD. Epilepsy is a risk factor for AD and, in turn, AD is an independent risk factor for developing epilepsy in old age, and abnormal AD biomarkers in PET and/or CSF are frequently found in late-onset epilepsies of unknown etiology. Accordingly, epilepsy and AD share pathophysiological processes, including neuronal hyperexcitability and an early excitatory-inhibitory dysregulation, leading to dysfunction in the inhibitory GABAergic and excitatory glutamatergic systems. Moreover, both β-amyloid and tau protein aggregates, the anatomopathological hallmarks of AD, have proepileptic effects. Finally, these aggregates have been found in the resection material of refractory temporal lobe epilepsies, suggesting that epilepsy leads to amyloid and tau aggregates. Some epileptic syndromes, such as medial temporal lobe epilepsy, share structural and functional neuroimaging findings with AD, leading to overlapping symptomatology, such as episodic memory deficits and toxic synergistic effects. In this respect, the existence of epileptiform activity and electroclinical seizures in AD appears to accelerate the progression of cognitive decline, and the presence of cognitive decline is much more prevalent in epileptic patients than in elderly patients without epilepsy. Notwithstanding their clinical significance, the diagnosis of clinical seizures in AD is a challenge. Most are focal and manifest with an altered level of consciousness without motor symptoms, and are often interpreted as cognitive fluctuations. Finally, despite the frequent association of epilepsy and AD dementia, there is a lack of clinical trials to guide the use of antiseizure medications (ASMs). There is also a potential role for ASMs to be used as disease-modifying drugs in AD.

Neuropathology of the temporal lobe

Neuropathological examination of the temporal lobe provides a better understanding and management of a wide spectrum of diseases. We focused on inflammatory diseases, epilepsy, and neurodegenerative diseases, and highlighted how the temporal lobe is particularly involved in those conditions. Although all these diseases are not specific or restricted to the temporal lobe, the temporal lobe is a key structure to understand their pathophysiology. The main histological lesions, immunohistochemical markers, and molecular alterations relevant for the neuropathological diagnostic reasoning are presented in relation to epidemiology, clinical presentation, and radiological findings. The inflammatory diseases section addressed infectious encephalitides and auto-immune encephalitides. The epilepsy section addressed (i) susceptibility of the temporal lobe to epileptogenesis, (ii) epilepsy-associated hippocampal sclerosis, (iii) malformations of cortical development, (iv) changes secondary to epilepsy, (v) long-term epilepsy-associated tumors, (vi) vascular malformations, and (vii) the absence of histological lesion in some epilepsy surgery samples. The neurodegenerative diseases section addressed (i) Alzheimer's disease, (ii) the spectrum of frontotemporal lobar degeneration, (iii) limbic-predominant age-related TDP-43 encephalopathy, and (iv) α-synucleinopathies. Finally, inflammatory diseases, epilepsy, and neurodegenerative diseases are considered as interdependent as some pathophysiological processes cross the boundaries of this classification.

Resveratrol prevents long-term structural hippocampal alterations and modulates interneuron organization in an animal model of ASD

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder characterized by impairments in both communication and social interaction, besides repetitive or stereotyped behavior. Although the etiology is unknown, environmental factors such as valproic acid (VPA) increase the risk of ASD onset. Resveratrol (RSV), a neuroprotective molecule, has been shown to counteract the effects of intrauterine exposure to VPA. We aimed to evaluate histological parameters related to hippocampal morphology and to the distribution of parvalbumin- (PV), calbindin- (CB), and somatostatin-positive (SOM) interneurons sub-populations, in addition to evaluate the total/phosphorylation levels of PTEN, AKT, GSK3β and total CK2 in the animal model of autism induced by VPA, as well as addressing the potential protective effect of RSV. On postnatal day 120, histological analysis showed a loss in total neurons in the dentate gyrus (DG) and decreased CB+ neurons in DG and CA1 in VPA animals, both prevented by RSV. In addition, PV+ neurons were diminished in CA1, CA2, and CA3, and SOM+ were interestingly increased in DG (prevented by RSV) and decreased in CA1 and CA2. A hippocampal lesion similar to sclerosis was also observed in the samples from the VPA group. Besides that, VPA reduced AKT and PTEN immunocontent, and VPA increased CK2 immunocontent. Thus, this work demonstrated long-term effects of prenatal exposure to ASD in different sub-populations of interneurons, structural damage of hippocampus, and also alteration in proteins associated with pivotal cell signaling pathways, highlighting the role of RSV as a tool for understanding the pathophysiology of ASD.

Activity-Dependent Reconnection of Adult-Born Dentate Granule Cells in a Mouse Model of Frontotemporal Dementia

Frontotemporal dementia (FTD) is characterized by neuronal loss in the frontal and temporal lobes of the brain. Here, we provide the first evidence of striking morphological alterations in dentate granule cells (DGCs) of FTD patients and in a mouse model of the disease, Tau^VLW mice. Taking advantage of the fact that the hippocampal dentate gyrus (DG) gives rise to newborn DGCs throughout the lifetime in rodents, we used RGB retroviruses to study the temporary course of these alterations in newborn DGCs of female Tau^VLW mice. In addition, retroviruses that encode either PSD95:GFP or Syn:GFP revealed striking alterations in the afferent and efferent connectivity of newborn Tau^VLW DGCs, and monosynaptic retrograde rabies virus tracing showed that these cells are disconnected from distal brain regions and local sources of excitatory innervation. However, the same cells exhibited a predominance of local inhibitory innervation. Accordingly, the expression of presynaptic and postsynaptic markers of inhibitory synapses was markedly increased in the DG of Tau^VLW mice and FTD patients. Moreover, an increased number of neuropeptide Y-positive interneurons in the DG correlated with a reduced number of activated egr-1⁺ DGCs in Tau^VLW mice. Finally, we tested the therapeutic potential of environmental enrichment and chemoactivation to reverse these alterations in mice. Both strategies reversed the morphological alterations of newborn DGCs and partially restored their connectivity in a mouse model of the disease. Moreover, our data point to remarkable morphological similarities between the DGCs of Tau^VLW mice and FTD patients.SIGNIFICANCE STATEMENT We show, for the first time to our knowledge, that the population of dentate granule cells is disconnected from other regions of the brain in the neurodegenerative disease frontotemporal dementia (FTD). These alterations were observed in FTD patients and in a mouse model of this disease. Moreover, we tested the therapeutic potential of two strategies, environmental enrichment and chemoactivation, to stimulate the activity of these neurons in mice. We found that some of the alterations were reversed by these therapeutic interventions.

The relevance of hippocampal subfield integrity and clock drawing test performance for the diagnosis of Alzheimer's disease and mild cognitive impairment

OBJECTIVES

The clock drawing test (CDT) is one of the worldwide most used screening tests for Alzheimer's disease (AD). MRI studies have identified temporo-parietal regions being involved in CDT impairment. However, the contributions of specific hippocampal subfields and adjacent extrahippocampal structures to CDT performance in AD and mild cognitive impairment (MCI) have not been investigated so far. It is unclear whether morphological alterations or CDT score, or a combination of both, are able to predict AD.

METHODS

38 AD patients, 38 MCI individuals and 31 healthy controls underwent neuropsychological assessment and MRI at 3 Tesla. FreeSurfer 5.3 was used to perform hippocampal parcellation. We used a collection of statistical methods to better understand the relationship between CDT and hippocampal formation. We also tested the clinical feasibility of this relationship when predicting AD.

RESULTS

Impaired CDT performance in AD was associated with widespread atrophy of the cornu ammonis, presubiculum, and subiculum, whereas MCI subjects showed CDT-related alterations of the CA4-dentate gyrus and subiculum. CDT correlates in AD and MCI showed regional and quantitative overlap. Importantly, CDT score was the best predictor of AD.

CONCLUSIONS

Our findings lend support for an involvement of different hippocampal subfields in impaired CDT performance in AD and MCI. CDT seems to be more efficient than subfield imaging for predicting AD.

Neuropathologic features of the hippocampus and amygdala in cats with familial spontaneous epilepsy

OBJECTIVE To investigate epilepsy-related neuropathologic changes in cats of a familial spontaneous epileptic strain (ie, familial spontaneous epileptic cats [FSECs]). ANIMALS 6 FSECs, 9 age-matched unrelated healthy control cats, and 2 nonaffected (without clinical seizures)dams and 1 nonaffected sire of FSECs. PROCEDURES Immunohistochemical analyses were used to evaluate hippocampal sclerosis, amygdaloid sclerosis, mossy fiber sprouting, and granule cell pathological changes. Values were compared between FSECs and control cats. RESULTS Significantly fewer neurons without gliosis were detected in the third subregion of the cornu ammonis (CA) of the dorsal and ventral aspects of the hippocampus as well as the central nucleus of the amygdala in FSECs versus control cats. Gliosis without neuronal loss was also observed in the CA4 subregion of the ventral aspect of the hippocampus. No changes in mossy fiber sprouting and granule cell pathological changes were detected. Moreover, similar changes were observed in the dams and sire without clinical seizures, although to a lesser extent. CONCLUSIONS AND CLINICAL RELEVANCE Findings suggested that the lower numbers of neurons in the CA3 subregion of the hippocampus and the central nucleus of the amygdala were endophenotypes of familial spontaneous epilepsy in cats. In contrast to results of other veterinary medicine reports, severe epilepsy-related neuropathologic changes (eg, hippocampal sclerosis, amygdaloid sclerosis, mossy fiber sprouting, and granule cell pathological changes) were not detected in FSECs. Despite the use of a small number of cats with infrequent seizures, these findings contributed new insights on the pathophysiologic mechanisms of genetic-related epilepsy in cats.

Anatomy Based Networks and Topology Alteration in Seizure-Related Cognitive Outcomes

Epilepsy is a paroxysmal neurological disorder characterized by recurrent and unprovoked seizures affecting approximately 50 million people worldwide. Cognitive dysfunction induced by seizures is a severe comorbidity of epilepsy and epilepsy syndromes and reduces patients’ quality of life. Seizures, along with accompanying histopathological and pathophysiological changes, are associated with cognitive comorbidities. Advances in imaging technology and computing allow anatomical and topological changes in neural networks to be visualized. Anatomical components including the hippocampus, amygdala, cortex, corpus callosum (CC), cerebellum and white matter (WM) are the fundamental components of seizure- and cognition-related topological networks. Damage to these structures and their substructures results in worsening of epilepsy symptoms and cognitive dysfunction. In this review article, we survey structural, network changes and topological alteration in different regions of the brain and in different epilepsy and epileptic syndromes, and discuss what these changes may mean for cognitive outcomes related to these disease states.

Hippocampal sclerosis, hippocampal neuron loss patterns and TDP-43 in the aged population

Hippocampal neuron loss is a common neuropathological feature in old age with various underlying etiologies. Hippocampal sclerosis of aging (HS-Aging) is neuropathologically characterized by severe CA1 neuronal loss and frequent presence of transactive response DNA-binding protein of 43 kDa (TDP-43) aggregations. Its etiology is unclear and currently no standardized approaches to measure HS-Aging exist. We developed a semi-quantitative protocol, which captures various hippocampal neuron loss patterns, and compared their occurrence in the context of HS-Aging, TDP-43, vascular and tau pathology in 672 brains (TDP-43 staining n = 642/672, 96%) donated for the population-based Cambridge City over-75s Cohort and the Cognitive Function and Ageing Study. HS-Aging was first evaluated independently from the protocol using the most common criteria defined in literature, and then described in detail through examination of neuron loss patterns and associated pathologies. 34 (5%) cases were identified, with a maximum of five pyramidal neurons in each of over half CA1 fields-of-view (x200 magnification), no vascular damage, no neuron loss in CA2-CA4, but consistent TDP-43 neuronal solid inclusions and neurites. We also report focal CA1 neuron loss with vascular pathology to affect predominantly CA1 bordering CA2 (Fisher's exact, P = 0.009), whereas neuron loss in the subicular end of CA1 was associated with TDP-43 inclusions (Fisher's exact, P < 0.001) and high Braak stage (Fisher's exact, P = 0.001). Hippocampal neuron loss in CA4-CA2 was not associated with TDP-43. We conclude that hippocampal neuron loss patterns are associated with different etiologies within CA1, and propose that these patterns can be used to form objective criteria for HS-Aging diagnosis. Finally, based on our results we hypothesize that neuron loss leading to HS-Aging starts from the subicular end of CA1 when it is associated with TDP-43 pathology, and that this neurodegenerative process is likely to be significantly more common than "end-stage" HS-Aging only.

Endogenous opiates and behavior: 2014

This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants). This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants).

Oestradiol Regulates Neuropeptide Y Release and Gene Coupling with the GABAergic and Glutamatergic Synapses in the Adult Female Rat Dentate Gyrus

Neuropeptide Y (NPY) is an endogenous modulator of neuronal activity affecting both GABAergic and glutamatergic transmission. Previously, we found that oestradiol modifies the number of NPY immunoreactive neurones in the hippocampal dentate gyrus. In the present study, we investigated which oestrogen receptor type is responsible for these changes in the number of NPY-positive neurones. Furthermore, we determined the effects of oestrogen receptor activation on NPY release. Finally, we examined the contribution of oestrogen toward the remodelling of the GABAergic and glutamatergic gene networks in terms of coupling with Npy gene expression in ovariectomised rats. We found that activation of either oestrogen receptor type (ERα or ERβ) increases the number of NPY-immunopositive neurones and enhances NPY release in the dentate gyrus. We also found that, compared to oestrogen-lacking ovariectomised rats, oestrogen replacement increases the probability of synergistic/antagonistic coupling between the Npy and GABAergic synapse genes, whereas the glutamatergic synapse genes are less likely to be coupled with Npy under similar conditions. The data together suggest that oestrogens play a critical role in the regulation of NPY system activity and are also involved in the coupling/uncoupling of the Npy gene with the GABAergic and glutamatergic synapses in the female rat dentate gyrus.

Network dysfunction in α-synuclein transgenic mice and human Lewy body dementia

Objective

Dementia with Lewy bodies (DLB) is associated with the accumulation of wild‐type human α‐synuclein (SYN) in neurons and with prominent slowing of brain oscillations on electroencephalography (EEG). However, it remains uncertain whether the EEG abnormalities are actually caused by SYN.

Methods

To determine whether SYN can cause neural network abnormalities, we performed EEG recordings and analyzed the expression of neuronal activity‐dependent gene products in SYN transgenic mice. We also carried out comparative analyses in humans with DLB.

Results

We demonstrate that neuronal expression of SYN in transgenic mice causes a left shift in spectral power that closely resembles the EEG slowing observed in DLB patients. Surprisingly, SYN mice also had seizures and showed molecular hippocampal alterations indicative of aberrant network excitability, including calbindin depletion in the dentate gyrus. In postmortem brain tissues from DLB patients, we found reduced levels of calbindin mRNA in the dentate gyrus. Furthermore, nearly one quarter of DLB patients showed myoclonus, a clinical sign of aberrant network excitability that was associated with an earlier age of onset of cognitive impairments. In SYN mice, partial suppression of epileptiform activity did not alter their shift in spectral power. Furthermore, epileptiform activity in human amyloid precursor protein transgenic mice was not associated with a left shift in spectral power.

Interpretation

We conclude that neuronal accumulation of SYN slows brain oscillations and, in parallel, causes aberrant network excitability that can escalate into seizure activity. The potential role of aberrant network excitability in DLB merits further investigation.

Comorbidities in Neurology: Is adenosine the common link?

Comorbidities in Neurology represent a major conceptual and therapeutic challenge. For example, temporal lobe epilepsy (TLE) is a syndrome comprised of epileptic seizures and comorbid symptoms including memory and psychiatric impairment, depression, and sleep dysfunction. Similarly, Alzheimer's disease (AD), Parkinson's disease (PD), and Amyotrophic Lateral Sclerosis (ALS) are accompanied by various degrees of memory dysfunction. Patients with AD have an increased likelihood for seizures, whereas all four conditions share certain aspects of psychosis, depression, and sleep dysfunction. This remarkable overlap suggests common pathophysiological mechanisms, which include synaptic dysfunction and synaptotoxicity, as well as glial activation and astrogliosis. Astrogliosis is linked to synapse function via the tripartite synapse, but astrocytes also control the availability of gliotransmitters and adenosine. Here we will specifically focus on the 'adenosine hypothesis of comorbidities' implying that astrocyte activation, via overexpression of adenosine kinase (ADK), induces a deficiency in the homeostatic tone of adenosine. We present evidence from patient-derived samples showing astrogliosis and overexpression of ADK as common pathological hallmark of epilepsy, AD, PD, and ALS. We discuss a transgenic 'comorbidity model', in which brain-wide overexpression of ADK and resulting adenosine deficiency produces a comorbid spectrum of seizures, altered dopaminergic function, attentional impairment, and deficits in cognitive domains and sleep regulation. We conclude that dysfunction of adenosine signaling is common in neurological conditions, that adenosine dysfunction can explain co-morbid phenotypes, and that therapeutic adenosine augmentation might be effective for the treatment of comorbid symptoms in multiple neurological conditions.

Revisiting hippocampal sclerosis in mesial temporal lobe epilepsy according to the "two-hit" hypothesis

Hippocampal sclerosis (HS) is the most common neuropathological pattern observed in pharmacoresistant epilepsy and represents a critical feature in mesial temporal lobe epilepsy syndrome. However, its pathophysiological mechanisms and neuropathological consequences on seizures remain mostly unresolved. The new international classification of hippocampal sclerosis aims at standardizing its description to allow comparisons between different clinical studies. However, several aspects are not considered in this classification (granule cell dispersion, sprouting, glial modifications…). In this chapter, we discuss these different features associated with hippocampal sclerosis in perspective with the "two-hit" hypothesis and propose mechanisms that could be involved in the modulation of some specific neuropathological aspects like early life stress, hyperthermic seizures, brain lesions or hormonal modifications.

Review: Hippocampal sclerosis in epilepsy: a neuropathology review

Hippocampal sclerosis (HS) is a common pathology encountered in mesial temporal lobe epilepsy (MTLE) as well as other epilepsy syndromes and in both surgical and post-mortem practice. The 2013 International League Against Epilepsy (ILAE) classification segregates HS into typical (type 1) and atypical (type 2 and 3) groups, based on the histological patterns of subfield neuronal loss and gliosis. In addition, granule cell reorganization and alterations of interneuronal populations, neuropeptide fibre networks and mossy fibre sprouting are distinctive features of HS associated with epilepsies; they can be useful diagnostic aids to discriminate from other causes of HS, as well as highlighting potential mechanisms of hippocampal epileptogenesis. The cause of HS remains elusive and may be multifactorial; the contribution of febrile seizures, genetic susceptibility, inflammatory and neurodevelopmental factors are discussed. Post-mortem based research in HS, as an addition to studies on surgical samples, has the added advantage of enabling the study of the wider network changes associated with HS, the long-term effects of epilepsy on the pathology and associated comorbidities. It is likely that HS is heterogeneous in aspects of its cause, epileptogenetic mechanisms, network alterations and response to medical and surgical treatments. Future neuropathological studies will contribute to better recognition and understanding of these clinical and patho-aetiological subtypes of HS.

Angiotensin II and its receptor in activated microglia enhanced neuronal loss and cognitive impairment following pilocarpine-induced status epilepticus

Neuroinflammation plays a role in the pathology of epilepsy and in cognitive impairment. Angiotensin II (AII) and the angiotensin receptor type 1 (AT1) have been shown to regulate seizure susceptibility in different models of epilepsy. Inhibition of AT1 attenuates neuroinflammatory responses in different neurological diseases. In the present study, we showed that the protein expression of AII and AT1 was increased in activated microglia following lithium pilocarpine-induced status epilepticus (SE) in rats. Furthermore, the AT1 receptor antagonist, losartan, significantly inhibited SE-induced cognitive impairment and microglia-mediated inflammation. Losartan also prevented SE induced neuronal loss in the hippocampus and exerted neuroprotection. These data suggest that losartan improves SE-induced cognitive impairment by suppressing microglia mediated inflammatory responses and attenuating hippocampal neuronal loss. Overall, our findings provide a possible therapeutic strategy for the treatment of cognitive impairment in epilepsy.