Axo-somatic inhibition of projection neurons in the lateral nucleus of amygdala in human temporal lobe epilepsy: an ultrastructural study

Effectiveness of deep brain stimulation on refractory aggression in pediatric patients with autism and severe intellectual disability: meta-analytic review

Some patients with autism and severe intellectual disability may experience uncontrolled aggression, causing serious injury or harm to others, and the therapeutic ineffectiveness of traditional pharmacological and behavioral treatment may aggravate symptoms. Deep brain stimulation (DBS) has been tested in patients with little evidence in children and adolescents. Therefore, we analyzed the efficacy and safety of DBS in refractory aggression in pediatric subjects with autism (ASD) and severe intelligence deficit (ID).Methods A meta-analytic review of Web of Science (WOS) and Scopus articles, following Prisma criteria. A total of 555 articles were identified, but after applying the inclusion criteria, only 18 were analyzed. The review of the registries and the extraction of information was performed by 2 independent groups, to reduce the evaluator's bias. For the description of the results, pediatric patients with ASD or ID present in each registry, with an application of specialized scales (Overt aggression scale, OAS, and THE modified version of the OAS, MOAS) pre and post-DBS, with a clinical follow-up of at least 12 months, were considered valid. Clinical improvement was calculated using tests of aggressiveness. In each registry with available data and then pooling the means of all patients in the OAS and MOAS, the effect size of DBS (overall and per study) was estimated. Finally, the adapted NOS scale was applied to rate the studies' quality and level of bias.Results In the studies analyzed, 65/100 were pediatric patients, with a mean age of 16.8 years. Most of the studies were conducted in South America and Europe. In all teams, aggressive behavior was intractable, but only 9 groups (53/65) applied specialized scales to measure aggressiveness, and of these, only 51 subjects had a follow-up of at least 12 months. Thus, in 48/51 a clinical improvement of patients was estimated (94.2%), with a considerable overall effect size (OAS: d = 4.32; MOAS: d = 1.46). However, adverse effects and complications were found in 13/65 subjects undergoing DBS. The brain target with the most evidence and the fewest side effects was the posteromedial hypothalamic nuclei (pHypN). Finally, applying the adapted NOS scale, quality, and bias, only 9 studies show the best indicators.Conclusion An optimal level of efficacy was found in only half of the publications. This is mainly due to design errors and irrelevant information in the reports. We believe that DBS in intractable aggressiveness in children and adolescents with ASD and severe ID can be safe and effective if working groups apply rigorous criteria for patient selection, interdisciplinary assessments, objective scales for aggressiveness, and known surgical targets.

Clinical Correlation of Altered Molecular Signatures in Epileptic Human Hippocampus and Amygdala

Widespread alterations in the expression of various genes could contribute to the pathogenesis of epilepsy. The expression levels of various genes, including major inhibitory and excitatory receptors, ion channels, cell type-specific markers, and excitatory amino acid transporters, were assessed and compared between the human epileptic hippocampus and amygdala, and findings from autopsy controls. Moreover, the potential correlation between molecular alterations in epileptic brain tissues and the clinical characteristics of patients undergoing epilepsy surgery was evaluated. Our findings revealed significant and complex changes in the expression of several key regulatory genes in both the hippocampus and amygdala of patients with intractable epilepsy. The expression changes in various genes differed considerably between the epileptic hippocampus and amygdala. Different correlation patterns were observed between changes in gene expression and clinical characteristics, depending on whether the patients were considered as a whole or were subdivided. Altered molecular signatures in different groups of epileptic patients, defined within a given category, could be viewed as diagnostic biomarkers. Distinct patterns of molecular changes that distinguish these groups from each other appear to be associated with epilepsy-specific functional consequences.

Loss of PV interneurons in the BLA contributes to altered network and behavioral states in chronically epileptic mice

Psychiatric disorders, including anxiety and depression, are highly comorbid in people with epilepsy. However, the mechanisms mediating the shared pathophysiology are currently unknown. There is considerable evidence implicating the basolateral amygdala (BLA) in the network communication of anxiety and fear, a process demonstrated to involve parvalbumin-positive (PV) interneurons. The loss of PV interneurons has been well described in the hippocampus of chronically epileptic mice and in postmortem human tissue of patients with temporal lobe epilepsy (TLE). We hypothesize that a loss of PV interneurons in the BLA may contribute to comorbid mood disorders in epilepsy. To test this hypothesis, we employed a ventral intrahippocampal kainic acid (vIHKA) model of chronic epilepsy in mice, which exhibits profound behavioral deficits associated with chronic epilepsy. We demonstrate a loss of PV interneurons and dysfunction of remaining PV interneurons in the BLA of chronically epileptic mice. Further, we demonstrate altered principal neuron function and impaired coordination of BLA network and behavioral states in chronically epileptic mice. To determine whether these altered network and behavioral states were due to the loss of PV interneurons, we ablated a similar percentage of PV interneurons observed in chronically epileptic mice by stereotaxically injecting AAV-Flex-DTA into the BLA of PV-Cre mice. Loss of PV interneurons in the BLA is sufficient to alter behavioral states, inducing deficits in fear learning and recall of fear memories. These data suggest that compromised inhibition in the BLA in chronically epileptic mice contributes to behavioral deficits, suggesting a novel mechanism contributing to comorbid anxiety and epilepsy.

Significance Statement

Psychiatric illnesses and epilepsy are highly comorbid and negatively impact the quality of life of people with epilepsy. The pathophysiological mechanisms mediating the bidirectional relationship between mood disorders and epilepsy remain unknown and, therefore, treatment options remain inadequate. Here we demonstrate a novel mechanism, involving the loss of PV interneurons in the BLA, leading to a corruption of network and behavioral states in mice. These findings pinpoint a critical node and demonstrate a novel cellular and circuit mechanism involved in the comorbidity of psychiatric illnesses and epilepsy.

Parvalbumin Role in Epilepsy and Psychiatric Comorbidities: From Mechanism to Intervention

Parvalbumin is a calcium-binding protein present in inhibitory interneurons that play an essential role in regulating many physiological processes, such as intracellular signaling and synaptic transmission. Changes in parvalbumin expression are deeply related to epilepsy, which is considered one of the most disabling neuropathologies. Epilepsy is a complex multi-factor group of disorders characterized by periods of hypersynchronous activity and hyperexcitability within brain networks. In this scenario, inhibitory neurotransmission dysfunction in modulating excitatory transmission related to the loss of subsets of parvalbumin-expressing inhibitory interneuron may have a prominent role in disrupted excitability. Some studies also reported that parvalbumin-positive interneurons altered function might contribute to psychiatric comorbidities associated with epilepsy, such as depression, anxiety, and psychosis. Understanding the epileptogenic process and comorbidities associated with epilepsy have significantly advanced through preclinical and clinical investigation. In this review, evidence from parvalbumin altered function in epilepsy and associated psychiatric comorbidities were explored with a translational perspective. Some advances in potential therapeutic interventions are highlighted, from current antiepileptic and neuroprotective drugs to cutting edge modulation of parvalbumin subpopulations using optogenetics, designer receptors exclusively activated by designer drugs (DREADD) techniques, transcranial magnetic stimulation, genome engineering, and cell grafting. Creating new perspectives on mechanisms and therapeutic strategies is valuable for understanding the pathophysiology of epilepsy and its psychiatric comorbidities and improving efficiency in clinical intervention.

Alterations in GABAA Receptor Subunit Expression in the Amygdala and Entorhinal Cortex in Human Temporal Lobe Epilepsy

The amygdala has long been implicated in the pathophysiology of human temporal lobe epilepsy (TLE). The different nuclei of this complex structure are interconnected and share reciprocal connections with the hippocampus and other brain structures, partly via the entorhinal cortex. Expression of GABAA receptor subunits α1, α2, α3, α5, β2, β2/3, and γ2 was evaluated by immunohistochemistry in amygdala specimens and the entorhinal cortex of 12 TLE patients and 12 autopsy controls. A substantial decrease in the expression of α1, α2, α3, and β2/3 subunits was found in TLE cases, accompanied by an increase of γ2 subunit expression in many nuclei. In the entorhinal cortex, the expression of all GABAA receptor subunits was decreased except for the α1 subunit, which was increased on cellular somata. The overall reduction in α subunit expression may lead to decreased sensitivity to GABA and its ligands and compromise phasic inhibition, whereas upregulation of the γ2 subunit might influence clustering and kinetics of receptors and impair tonic inhibition. The description of these alterations in the human amygdala is important for the understanding of network changes in TLE as well as the development of subunit-specific therapeutic agents for the treatment of this disease.

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.

Directional spread of activity in synaptic networks of the human lateral amygdala

Spontaneous epileptiform activity has previously been observed in lateral amygdala (LA) slices derived from patients with intractable-temporal lobe epilepsy. The present study aimed to characterize intranuclear LA synaptic connectivity and to test the hypothesis that differences in the spread of flow of neuronal activity may relate to spontaneous epileptiform activity occurrence. Electrical activity was evoked through electrical microstimulation in acute human brain slices containing the LA, signals were recorded as local field potentials combined with fast optical imaging of voltage-sensitive dye fluorescence. Sites of stimulation and recording were systematically varied. Following recordings, slices were anatomically reconstructed using two-dimensional unitary slices as a reference for coronal and parasagittal planes. Local spatial patterns and spread of activity were assessed by incorporating the coordinates of electrical and optical recording sites into the respective unitary slice. A preferential directional spread of evoked electrical signals was observed from ventral to dorsal, rostral to caudal and medial to lateral regions in the LA. No differences in spread of evoked activity were observed between spontaneously and non-spontaneously active LA slices, i.e. basic properties of evoked synaptic responses were similar in the two functional types of LA slices, including input-output relationship, and paired-pulse depression. These results indicate a directed propagation of synaptic signals within the human LA in spontaneously active epileptic slices. We suggest that the lack of differences in local and in systemic information processing has to be found in confined epileptiform circuits within the amygdala likely involving well-known "epileptic neurons".

Expression of neuropeptide Y1 receptors in the amygdala and hippocampus and anxiety-like behavior associated with Ammon's horn sclerosis following intrahippocampal kainate injection in C57BL/6J mice

Damage to the amygdala is often linked to Ammon's horn sclerosis (AHS) in surgical specimens of patients suffering from temporal lobe epilepsy (TLE). Moreover, amygdalar pathology is thought to contribute to the development of anxiety symptoms frequently found in TLE. The neuropeptide Y (NPY) Y1 receptor is critical in the regulation of anxiety-related behavior and epileptiform activity in TLE. Therefore, intrahippocampal kainate (KA) injection was performed to induce AHS-associated TLE and to investigate behavioral and cytoarchitectural changes that occur in the amygdala related to Y1 receptor expression. Status epilepticus was induced by intrahippocampal KA injection in C57BL/6J mice. Anxiety-like behavior was assessed using the elevated plus maze (EPM). Pathology of hippocampus and amygdala (volume loss and gliosis) was examined in KA-injected and saline-injected controls. Y1 receptor expression was measured using immunohistochemistry and ELISA. Animal injected with KA showed increased anxiety-like behaviors and reduced risk assessment in the EPM test compared with saline-injected controls. In the ipsilateral hippocampus of KA-injected animals, CA1 ablation, granule cell dispersion, and volume reduction were accompanied by astrogliosis indicating the development of AHS. In the amygdala, a significant decrease in the volume of nuclei and numbers of neurons was observed in the ipsilateral lateral, basolateral, and central amygdalar nuclei, which was accompanied by astrogliosis. In addition, a decrease in Y1 receptor-expressing cells in the ipsilateral CA1 and CA3 sectors of the hippocampus, ipsilateral and contralateral granule cell layer of the dentate gyrus, and ipsilateral central nucleus of the amygdala was found, consistent with a reduction in Y1 receptor protein levels. Our results suggest that plastic changes in hippocampal and/or amygdalar Y1 receptor expression may negatively impact anxiety levels. Moreover, intrahippocampal KA injection can induce amygdalar damage suggesting that AHS-associated amygdala damage may contribute to behavioral alterations seen in patients with TLE.

The best-laid plans go oft awry: synaptogenic growth factor signaling in neuropsychiatric disease

Growth factors play important roles in synapse formation. Mouse models of neuropsychiatric diseases suggest that defects in synaptogenic growth factors, their receptors, and signaling pathways can lead to disordered neural development and various behavioral phenotypes, including anxiety, memory problems, and social deficits. Genetic association studies in humans have found evidence for similar relationships between growth factor signaling pathways and neuropsychiatric phenotypes. Accumulating data suggest that dysfunction in neuronal circuitry, caused by defects in growth factor-mediated synapse formation, contributes to the susceptibility to multiple neuropsychiatric diseases, including epilepsy, autism, and disorders of thought and mood (e.g., schizophrenia and bipolar disorder, respectively). In this review, we will focus on how specific synaptogenic growth factors and their downstream signaling pathways might be involved in the development of neuropsychiatric diseases.

DBS in the basolateral amygdala improves symptoms of autism and related self-injurious behavior: a case report and hypothesis on the pathogenesis of the disorder

We treated a 13-year-old boy for life-threatening self-injurious behavior (SIB) and severe Kanner's autism with deep brain stimulation (DBS) in the amygdaloid complex as well as in the supra-amygdaloid projection system. Two DBS-electrodes were placed in both structures of each hemisphere. The stimulation contacts targeted the paralaminar, the basolateral (BL), the central amygdala as well as the supra-amygdaloid projection system. DBS was applied to each of these structures, but only stimulation of the BL part proved effective in improving SIB and core symptoms of the autism spectrum in the emotional, social, and even cognitive domains over a follow up of now 24 months. These results, which have been gained for the first time in a patient, support hypotheses, according to which the amygdala may be pivotal in the pathogeneses of autism and point to the special relevance of the BL part.

Interictal-like network activity and receptor expression in the epileptic human lateral amygdala

While the amygdala is considered to play a critical role in temporal lobe epilepsy, conclusions on underlying pathophysiological mechanisms have been derived largely from experimental animal studies. Therefore, the present study aimed to characterize synaptic network interactions, focusing on spontaneous interictal-like activity, and the expression profile of transmitter receptors in the human lateral amygdala in relation to temporal lobe epilepsy. Electrophysiological recordings, obtained intra-operatively in vivo in patients with medically intractable temporal lobe epilepsy, revealed the existence of interictal activity in amygdala and hippocampus. For in vitro analyses, slices were prepared from surgically resected specimens, and sections from individual specimens were used for electrophysiological recordings, receptor autoradiographic analyses and histological visualization of major amygdaloid nuclei for verification of recording sites. In the lateral amygdala, interictal-like activity appeared as spontaneous slow rhythmic field potentials at an average frequency of 0.39 Hz, which occurred at different sites with various degrees of synchronization in 33.3% of the tested slices. Pharmacological blockade of glutamate α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors, but not N-methyl-D-aspartate receptors, abolished interictal-like activity, while the γ-aminobutyric acid A-type receptor antagonist bicuculline resulted in a dampening of activity, followed by highly synchronous patterns of slow rhythmic activity during washout. Receptor autoradiographic analysis revealed significantly higher α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, kainate, metabotropic glutamate type 2/3, muscarinic type 2 and adrenoceptor α(1) densities, whereas muscarinergic type 3 and serotonergic type 1A receptor densities were lower in the lateral amygdala from epileptic patients in comparison to autopsy controls. Concerning γ-aminobutyric acid A-type receptors, agonist binding was unaltered whereas antagonist binding sites were downregulated in the epileptic lateral amygdala, suggesting an altered high/low-affinity state ratio and concomitant reduced pool of total γ-aminobutyric acid A-type receptors. Together these data indicate an abnormal pattern of receptor densities and synaptic function in the lateral nucleus of the amygdala in epileptic patients, involving critical alterations in glutamate and γ-aminobutyric acid receptors, which may give rise to domains of spontaneous interictal discharges contributing to seizure activity in the amygdala.

Astrocytes in the amygdala

The amygdala has received considerable attention because of its established role in specific behaviors and disorders such as anxiety, depression, and autism. Studies have revealed that the amygdala is a complex and dynamic brain region that is highly connected with other areas of the brain. Previous works have focused on neurons, demonstrating that the amygdala in rodents is highly plastic and sexually dimorphic. However, our more recent work explores sex differences in nonneuronal cells, joining a rich literature concerning glia in the amygdala. Prior investigation of glia in the amygdala can generally be divided into disease-related and hormone-related categories, with both areas of research producing interesting findings concerning glia in this important brain region. Despite a wide range of research topics, the collected findings make it clear that glia in the amygdala are sensitive and plastic cells that respond and develop in a highly region specific manner.

Doublecortin-expressing cells persist in the associative cerebral cortex and amygdala in aged nonhuman primates

A novel population of cells that express typical immature neuronal markers including doublecortin (DCX+) has been recently identified throughout the adult cerebral cortex of relatively large mammals (guinea pig, rabbit, cat, monkey and human). These cells are more common in the associative relative to primary cortical areas and appear to develop into interneurons including type II nitrinergic neurons. Here we further describe these cells in the cerebral cortex and amygdala, in comparison with DCX+ cells in the hippocampal dentate gyrus, in three age groups of rhesus monkeys: young adult (12.3 ± 0.2 years, n = 3), mid-age (21.2 ± 1.9 years, n = 3) and aged (31.3 ± 1.8 years, n = 4). DCX+ cells with a heterogeneous morphology persisted in layers II/III primarily over the associative cortex and amygdala in all groups (including in two old animals with cerebral amyloid pathology), showing a parallel decline in cell density with age across regions. In contrast to the cortex and amygdala, DCX+ cells in the subgranular zone diminished in the mid-age and aged groups. DCX+ cortical cells might arrange as long tangential migratory chains in the mid-age and aged animals, with apparently distorted cell clusters seen in the aged group. Cortical DCX+ cells colocalized commonly with polysialylated neural cell adhesion molecule and partially with neuron-specific nuclear protein and γ-aminobutyric acid, suggesting a potential differentiation of these cells into interneuron phenotype. These data suggest a life-long role for immature interneuron-like cells in the associative cerebral cortex and amygdala in nonhuman primates.

Positive correlation between the density of neuropeptide y positive neurons in the amygdala and parameters of self-reported anxiety and depression in mesiotemporal lobe epilepsy patients

BACKGROUND

Neuropeptide Y (NPY) has been implicated in depression, anxiety, and memory. Expression of human NPY and the number of NPY-positive neurons in the rodent amygdala correlate with anxiety and stress-related behavior. Increased NPY expression in the epileptic brain is supposed to represent an adaptive mechanism counteracting epilepsy-related hyperexcitability. We attempted to investigate whether NPY-positive neurons in the human amygdala are involved in these processes.

METHODS

In 34 adult epileptic patients undergoing temporal lobe surgery for seizure control, the density of NPY-positive neurons was assessed in the basal, lateral, and accessory-basal amygdala nuclei. Cell counts were related to self-reported depression, anxiety, quality of life, clinical parameters (onset and duration of epilepsy, seizure frequency), antiepileptic medication, and amygdala and hippocampal magnetic resonance imaging volumetric measures.

RESULTS

Densities of NPY-positive basolateral amygdala neurons showed significant positive correlations with depression and anxiety scores, and they were negatively correlated with lamotrigine dosage. In contrast, NPY cell counts showed no relation to clinical factors or amygdalar and hippocampal volumes.

CONCLUSIONS

The results point to a role of amygdalar NPY in negative emotion and might reflect state processes at least in patients with temporal lobe epilepsy. Correlations with common clinical parameters of epilepsy were not found. The question of a disease-related reduction of the density of NPY-positive amygdalar neurons in temporal lobe epilepsy requires further investigation.

Ultrastructural and functional characterization of satellitosis in the human lateral amygdala associated with Ammon's horn sclerosis

The amygdala displays neuronal cell loss and gliosis in human temporal lobe epilepsy (TLE). Therefore, we investigated a certain type of gliosis, called satellitosis, in the lateral amygdala (LA) of TLE patients with Ammon's horn sclerosis (AHS, n = 15) and non-AHS (n = 12), and in autopsy controls. Satellite cells were quantified using light and electron microscopy at the somata of Nissl-stained and glutamic acid decarboxylase-negative projection neurons, and their functional properties were studied using electrophysiology. Non-AHS cases suffered from ganglioglioma, cortical dysplasia, Sturge-Weber syndrome, astrocytoma WHO III-IV, Rasmussen's encephalitis, cerebral infarction and perinatal brain damage. TLE cases with AHS had a more prominent satellitosis as compared to non-AHS and/or autopsy cases, which correlated with epilepsy duration but not age. At ultrastructural level, the predominant type of satellite cells occurring in both AHS and non-AHS cases displayed a dark cytoplasm and an irregularly shaped dark nucleus, whereas perineuronal glial cells with a light cytoplasm and light oval nucleus were much rarer. Satellite cells expressed time- and voltage-dependent transmembrane currents as revealed by patch-clamp recordings typical for 'complex' glia, although only 44% of satellite cells were immunostained for the chondroitin sulfate proteoglycan NG2. Together, the perineuronal cells described here were a heterogenous cell population regarding their NG2 expression, although they resembled NG2 cells rather than bona fide oligodendrocytes and astrocytes based on their ultrastructural and electrophysiological characteristics. Thus, perineuronal satellitosis as studied in the LA seems to be a hallmark of AHS-associated TLE pathology in patients suffering from intractable epilepsy.

Pathology and pathophysiology of the amygdala in epileptogenesis and epilepsy

Acute brain insults, such as traumatic brain injury, status epilepticus, or stroke are common etiologies for the development of epilepsy, including temporal lobe epilepsy (TLE), which is often refractory to drug therapy. The mechanisms by which a brain injury can lead to epilepsy are poorly understood. It is well recognized that excessive glutamatergic activity plays a major role in the initial pathological and pathophysiological damage. This initial damage is followed by a latent period, during which there is no seizure activity, yet a number of pathophysiological and structural alterations are taking place in key brain regions, that culminate in the expression of epilepsy. The process by which affected/injured neurons that have survived the acute insult, along with well-preserved neurons are progressively forming hyperexcitable, epileptic neuronal networks has been termed epileptogenesis. Understanding the mechanisms of epileptogenesis is crucial for the development of therapeutic interventions that will prevent the manifestation of epilepsy after a brain injury, or reduce its severity. The amygdala, a temporal lobe structure that is most well known for its central role in emotional behavior, also plays a key role in epileptogenesis and epilepsy. In this article, we review the current knowledge on the pathology of the amygdala associated with epileptogenesis and/or epilepsy in TLE patients, and in animal models of TLE. In addition, because a derangement in the balance between glutamatergic and GABAergic synaptic transmission is a salient feature of hyperexcitable, epileptic neuronal circuits, we also review the information available on the role of the glutamatergic and GABAergic systems in epileptogenesis and epilepsy in the amygdala.