Horn Sclerosis Research Articles

Artery of Uchimura: origin and evolution of identification of the vascular supply to the hippocampus.

In 1928, neuroscientist Yushi Uchimura (1897-1980) published a landmark study detailing the hippocampal vasculature. Working in Walther Spielmeyer's Munich laboratory (1925-1927), Uchimura sought evidence for a vascular theory of Ammon's horn sclerosis (AHS). He described an artery supplying the vulnerable sector of the hippocampus, where pathognomonic changes of AHS were noted, and characterized the artery as particularly susceptible to circulatory disturbances. Discovery of this artery led to new concepts and new terminology pertaining to the hippocampus. In addition to having a distinguished career in psychiatry and academia (including a position as University of Tokyo dean), Uchimura was, before attending medical school, one of Japan's best baseball pitchers; he was eventually named Nippon Professional Baseball Organization commissioner and inducted into the Japan Baseball Hall of Fame. Uchimura's description of hippocampal vasculature, which is still subject to debate after nearly a century, brought international attention to AHS and epilepsy and showed the hippocampal vasculature to be variable and vulnerable; important considerations for later neurosurgeons in the development of selective mesial temporal surgery. Prominent figures in neurosurgery have since developed classification systems for the hippocampal vasculature in which the artery of Uchimura remains central. Perhaps no other brain artery has been the nexus for such intense investigation and debate about its association to structure, function, disease, and treatment methodology.

Increased expression of GABAA receptor subunits associated with tonic inhibition in patients with temporal lobe epilepsy.

Epilepsy animal models indicate pronounced changes in the expression and rearrangement of GABAA receptor subunits in the hippocampus and in para-hippocampal areas, including widespread downregulation of the subunits α5 and δ, and upregulation of α4, subunits that mediate tonic inhibition of GABA. In this case–control study, we investigated changes in the expression of subunits α4, α5 and δ in hippocampal specimens of drug resistant temporal lobe epilepsy patients who underwent epilepsy surgery. Using in situ hybridization, immunohistochemistry and α5-specific receptor autoradiography, we characterized expression of the receptor subunits in specimens from patients with and without Ammon’s horn sclerosis compared to post-mortem controls. Expression of the α5-subunit was abundant throughout all subfields of the hippocampus, including the dentate gyrus, sectors CA1 and CA3, the subiculum and pre- and parasubiculum. Significant but weaker expression was detected for subunits α4 and δ notably in the granule cell/molecular layer of control specimens, but was faint in the other parts of the hippocampus. Expression of all three subunits was similarly altered in sclerotic and non-sclerotic specimens. Respective mRNA levels were increased by about 50–80% in the granule cell layer compared with post-mortem controls. Subunit α5 mRNA levels and immunoreactivities were also increased in the sector CA3 and in the subiculum. Autoradiography for α5-containing receptors using [3H]L-655,708 as ligand showed significantly increased binding in the molecular layer of the dentate gyrus in non-sclerotic specimens. Increased expression of the α5 and δ subunits is in contrast to the previously observed downregulation of these subunits in different epilepsy models, whereas increased expression of α4 in temporal lobe epilepsy patients is consistent with that in the rodent models. Our findings indicate increased tonic inhibition likely representing an endogenous anticonvulsive mechanism in temporal lobe epilepsy.

Seven-Tesla MRI of Hippocampal Sclerosis: An In Vivo Feasibility Study With Histological Correlations.

Temporal lobe epilepsy (TLE) is the most frequent form of focal epilepsy in adults. Because approximately half of these patients develop drug resistance, epilepsy surgery designed to remove the epileptogenic zone is an excellent option in selected patients. Histopathological analyses of hippocampal specimens in TLE patients revealed 4 types of Ammon's horn sclerosis, which are correlated with long-term epileptological outcome. The aim of this study was the correlation of noninvasive, high-resolution, morphological magnetic resonance imaging (MRI) at an ultra-high-field (7 T) of the hippocampus in TLE patients with histopathological findings. High-resolution, T2-weighted FSE MRI in 14 patients with drug-resistant temporal lobe epilepsy was performed on a 7 T Magnetom using a 32-channel coil. Four independent investigators assessed the delineation and semiquantitative evaluation of volume, signal intensity, internal architecture, and overall grading of the hippocampal subfields CA1-4, as well as the presence of the dentate granule cell layer (DGCL), on MRI scans. Results were compared with semiquantitative evaluation of neuronal loss and astrogliosis in the histological sections of the surgical specimens. Seven-tesla MR examinations were evaluable in 13 cases. Volume loss and signal intensity, as well as overall grading, showed a strong correlation between MRI and histology in individual CA regions. Furthermore, sensitivity and specificity values up to 100% were found for the detection of pathology in the CA subfields. The prediction of Ammon's horn sclerosis type was correct in up to 12 of 13 cases, whereas the dentate gyrus could not be delineated on MRI. High-resolution, ultra-high-field MRI is a promising tool for the detection of subtle changes in the hippocampus in patients with temporal lobe epilepsy. Large cohorts will be necessary to confirm the predictive value of 7 T MRI in the preoperative evaluation of TLE patients.

Epilepsy, Ammon’s horn sclerosis, and Camille Bouchet

ABSTRACTIncreasing interest into the relationship between Ammon’s horn sclerosis (hippocampal sclerosis) and epilepsy seems to have developed after 1880 when Sommer’s paper appeared. Bouchet and Cazauvieilh had published the original description of the hippocampal anatomical abnormality in 1825 while attempting to locate the cerebral sites of origin of epilepsy and insanity. However, they offered no interpretation of the significance of the structural change. What has sometimes not been noticed in the subsequent literature is that, after a further investigation, in 1853, Bouchet described the change in 18 of 43 additional brains from persons with epilepsy. Despite this frequency of occurrence of the hippocampal abnormality, he concluded that epileptic seizures had no single site of origin in the brain. Before most of his contemporaries and their successors, he began to propose the idea that all epileptic seizures were symptoms of various, though mostly cerebral, disorders. In doing this, he tended to be reluctant to accept the view that epilepsy was a disease in its own right.

Hippocampal sclerosis: pathogenesis, clinical features, diagnosis, and treatment

Hippocampal sclerosis, also known as Ammon horn sclerosis or mesial temporal sclerosis, is usually associated with intractable epilepsy and characterized by specific patterns of neuronal loss and gliosis in the medial temporal lobe structures. Hippocampal sclerosis manifests clinically as epilepsy, often intractable epilepsy; in most cases, this condition is surgically treatable. As the most common histological diagnosis in adult patients subjected to epilepsy surgery, hippocampal sclerosis is characterized by complex pathogenesis and requires a multidisciplinary approach to its diagnosis and treatment. This article reviews the pathologic features, natural history, pathogenesis, and electroclinical and MRI signs of hippocampal sclerosis.

Neuropsychological outcome after epilepsy surgery in patients with bilateral Ammon's horn sclerosis.

The purpose of this study was to retrospectively assess the objective and subjective neuropsychological outcome after epilepsy surgery in patients with bilateral Ammon's horn sclerosis (AHS). Memory and executive functions were evaluated at baseline and at follow-up in 11 surgically treated patients and compared with 8 pharmacologically treated patients with temporal lobe epilepsy and bilateral AHS. The median follow-up duration was 16 months in the surgically treated patients and 80.5 months in the pharmacologically treated group. Subjective outcome was evaluated by questionnaires and included mood, quality of life, subjective memory, and activities of daily living. At the follow-up assessment, 82% of the surgically treated patients as opposed to 0% of the nonsurgery patients were seizure free. In the surgical group, nonverbal memory performance did not change significantly in any patient after surgery, but there was a floor effect in 55% of the surgical patients. Regarding verbal memory, 9% of the surgical patients improved while 73% declined, despite severe impairments already evident at baseline. In the nonsurgery control group, 13% of the patients declined in nonverbal memory (floor effect in 63%) and 25% declined in verbal memory (floor effect in 25%) at follow-up. None of the controls improved at follow-up. Executive functions remained unchanged on an impaired level in both groups. At follow-up, the patient groups did not differ significantly with respect to mood, quality of life, subjective memory, or activities of daily living. However, in most aspects, surgically treated patients reported a slightly better subjective outcome than pharmacologically treated patients and a significantly improved quality of life. These results suggest that beyond benefits concerning seizure control, surgically treated patients with bilateral AHS, despite already poor baseline performance, are still at risk for severe postoperative decline in memory. In the light of predominantly minor benefits on a subjective level, the findings put the overall outcome of epilepsy surgery in bilateral AHS patients into perspective.

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.

Temporal lobe surgery in Germany from 1988 to 2008: diverse trends in etiological subgroups

In the epilepsy community, there is talk that the number of classical patients with early onset temporal lobe epilepsy (TLE) and Ammon's horn sclerosis (AHS) is decreasing. This is counterintuitive, considering the success story of epilepsy surgery, improved diagnostic methods and the current recommendation of early admission to surgery. In order to recognize trends, the development of temporal lobe surgery over 20years in three major German epilepsy centers was reviewed. Age at surgery and duration of epilepsy, which was differentiated according to histopathology (AHS, developmental, tumor, vascular), year of surgery and center, were evaluated in a cohort of 2812 patients from three German epilepsy centers who underwent temporal lobe surgery between 1988 and 2008. The analysis was carried out for the pooled cohort as well as for each center separately. Of all patients, 52% showed AHS. Compared with other pathologies, the AHS group had the earliest epilepsy onset and the longest duration of epilepsy. Across five time epochs, the diagnosis of AHS increased in the first epoch, remaining constant thereafter. Contrary to the trends in other pathologies, in the AHS group the mean age of patients at surgery increased by 7years and the duration of epilepsy until surgery increased by 5years. This trend could be replicated in all three centers. As initially hypothesized for all groups, age and duration of epilepsy in other pathology groups remained constant or indicated earlier submission to surgery. During the first few years studied, most probably due to progress in brain imaging, the proportion of patients with AHS increased. However, despite stable numbers over time, and contrary to the trends in other pathology groups, age and duration of epilepsy in mesial TLE with AHS (mTLE+AHS) increased over time. This supports the hypothesis of a decreasing incidence of AHS. This trend is discussed with respect to disease-modifying factors which have changed the incidence of classical mTLE+AHS or, alternatively, to recent developments in antiepileptic drug treatment, the appraisal of surgery and economic incentives for treatment options other than surgery.

Disorganization of neocortical lamination in focal cortical dysplasia is brain-region dependent: evidence from layer-specific marker expression

BackgroundFocal cortical dysplasias (FCD) are local disturbances of neocortical architecture and a common cause of pharmaco-resistant focal epilepsy. Little is known about the pathomechanisms leading to architectural abnormalities associated with FCD.ResultsIn the present study we compared 52 FCD cases originating from the frontal or temporal lobe with or without Ammon’s horn sclerosis (AHS) with regard to structural and molecular differences. We applied layer-specific (ER81, RORß, SMI32, TLE4) and interneuron (calbindin, parvalbumin) markers by means of immunohistochemistry, in situ hybridization (ISH), and real time RT-PCR and correlated our findings with clinical parameters. We found that: (1) Structural abnormalities were most prominent in layers III-VI including changed morphology of individual neurons or dispersion, blurring and thinning of layers. These alterations were most pronounced in isolated frontal FCD, whereas the most homogeneous group was FCD IIIa. (2) Numbers of calbindin- and parvalbumin-positive interneurons varied considerably within the different FCD groups, but were not generally reduced. A significant decrease was only found for calbindin-positive interneurons in frontal FCD, and for parvalbumin-positive interneurons in FCD IIIa. (3) Interestingly, FCD IIIa presented with significant changes in the numbers of calbindin- or TLE4-positive neurons when compared to isolated FCD or controls. (4) Correlations between clinical and cellular parameters strongly depended on FCD localisation and age of the patients.ConclusionsIn summary, our data suggest that late cortical development is disturbed in FCD, yet most likely by different causes depending on brain region, FCD type and FCD severity.

Surgical pathology of epilepsy‐associated non‐neoplastic cerebral lesions: A brief introduction with special reference to hippocampal sclerosis and focal cortical dysplasia

Among epilepsy-associated non-neoplastic lesions, mesial temporal lobe epilepsy with hippocampal sclerosis (mTLE-HS) and malformation of cortical development (MCD), including focal cortical dysplasia (FCD), are the two most frequent causes of drug-resistant focal epilepsies, constituting about 50% of all surgical pathology of epilepsy. Several distinct histological patterns have been historically recognized in both HS and FCD, and several studies have tried to perform clinicopathological correlations. However, results have been controversial, particularly in terms of post-surgical seizure outcome. Recently, the International League Against Epilepsy constituted a Task Forces of Neuropathology and FCD within the Commission on Diagnostic Methods, to establish an international consensus of histological classification of HS and FCD, respectively, based on agreement with the recognition of the importance of defining a histopathological classification system that reliably has some clinicopathological correlation. Such consensus classifications are likely to facilitate future clinicopathological studies. Meanwhile, we reviewed the neuropathology of 41 surgical cases of mTLE, and confirmed three type/patterns of HS along with no HS, based on the qualitative evaluation of the distribution and severity of neuronal loss and gliosis within hippocampal formation, that is, HS type 1 (61%) equivalent to "classical" Ammon's horn sclerosis, HS type 2 (2%) representing CA1 sclerosis, HS type 3 (17%) equivalent to end folium sclerosis, and no HS (19%). Furthermore, we performed a neuropathological comparative study on mTLE-HS and dementia-associated HS (d-HS) in the elderly, and confirmed that neuropathological features differ between mTLE-HS and d-HS in the distribution of hippocampal neuronal loss and gliosis, morphology of reactive astrocytes and their protein expression, and presence of concomitant neurodegenerative changes, particularly Alzheimer type and TDP-43 pathologies. These differences may account, at least in part, for the difference in pathogenesis and epileptogenicity of HS in mTLE and senile dementia. However, the etiology and pathogenesis of most epileptogenic lesions are yet to be elucidated.

Outcome after epilepsy surgery in patients with MRI features of bilateral ammon's horn sclerosis

In refractory temporal lobe epilepsy with unilateral ammon's horn sclerosis (uAHS) resective epilepsy surgery is an established treatment option whereas little evidence exists about the consequences of unilateral hippocampal resection in patients with bilateral ammon's horn sclerosis (bAHS). The aim of this study was to evaluate the post-surgical outcome of patients with bAHS after selective amygdalo-hippocampectomy (SAH) in comparison to uAHS patients. For this purpose, all bAHS and uAHS patients, identified at our center between 2003 and 2009 were analyzed retrospectively. Thirty-one bAHS patients and 291 uAHS patients were identified. Only 55% of the bAHS, but 80% of the uAHS patients were referred for formal pre-surgical diagnostics (p=0.001). Eleven bAHS and 127 uAHS patients underwent SAH. There was no difference in seizure-free outcome (Engel IA) at 12 months (bAHS 82% vs. 69%, p=0.40) and 24 months follow up (bAHS 57% vs. 60%, p=0.80). None of the bAHS patients became globally amnesic post-surgically. The favorable outcome in these highly selected bAHS patients suggests that bAHS patients may have a fair chance of becoming seizure-free after SAH. However, due to the large number of bAHS patients not undergoing formal presurgical evaluation, the results cannot be extrapolated to bAHS patients in general.

Mechanisms underlying blood–brain barrier dysfunction in brain pathology and epileptogenesis: Role of astroglia

Astrocytes are increasingly recognized as equal partners to neurons, also contributing to neurologic disorders such as epilepsy. Activated astrocytes are a common hallmark in patients with mesial temporal lobe epilepsy and Ammon's horn sclerosis. Blood-brain barrier (BBB) opening during status epilepticus has short-term proepileptic effects, as the ionic composition of serum interferes with neuronal excitability. In the long run, astrocytic uptake of albumin induces transforming growth factor β (TGFβ)-mediated signaling cascades, leading to changes in astrocytic properties. Down-regulation of astrocytic inward rectifier K(+) channels and altered surface expression of the water channel, aquaporin 4 results in disturbances in spatial K(+) buffering, thereby rendering the tissue more seizure prone. The expression of astrocytic gap junctional proteins connexin 43 (Cx43) and connexin 30 (Cx30) is altered in epilepsy, and changes in gap junctional communication were found in sclerotic hippocampal tissue in animal models of epilepsy. Although gap junctional communication might exert both proepileptic and antiepileptic effects, double knock out of Cx43 and Cx30 resulted in occurrence of spontaneous epileptiform events. Seizures are associated with massive increases in cerebral blood flow in order to cover the increased energy demand. Hemodynamic responses at the microcirculation level are mediated by astrocyte-pericyte interactions, sharing common mechanisms with spatial K(+) buffering. Although many of the astrocytic mechanisms involving spatial K(+) buffering, nitric oxide, adenosine, and metabotropic glutamate receptor (mGluR)-mediated signalling are altered in epilepsy, little is known how these alterations affect neurovascular coupling. In conclusion, astrocytic activation preceding alterations in neuronal function might critically contribute to epileptogenesis. Therefore, astrocytes represent a promising new target for the development of antiepileptic drugs.

Hyperpolarization-activated cation current Ih of dentate gyrus granule cells is upregulated in human and rat temporal lobe epilepsy

The hyperpolarization-activated cation current Ih is an important regulator of neuronal excitability and may contribute to the properties of the dentate gyrus granule (DGG) cells, which constitute the input site of the canonical hippocampal circuit. Here, we investigated changes in Ih in DGG cells in human temporal lobe epilepsy (TLE) and the rat pilocarpine model of TLE using the patch-clamp technique. Messenger-RNA (mRNA) expression of Ih-conducting HCN1, 2 and 4 isoforms was determined using semi-quantitative in-situ hybridization. Ih density was ∼1.8-fold greater in DGG cells of TLE patients with Ammon’s horn sclerosis (AHS) as compared to patients without AHS. The magnitude of somatodendritic Ih was enhanced also in DGG cells in epileptic rats, most robustly during the latent phase after status epilepticus and prior to the occurrence of spontaneous epileptic seizures. During the chronic phase, Ih was increased ∼1.7-fold. This increase of Ih was paralleled by an increase in HCN1 and HCN4 mRNA expression, whereas HCN2 expression was unchanged. Our data demonstrate an epilepsy-associated upregulation of Ih likely due to increased HCN1 and HCN4 expression, which indicate plasticity of Ih during epileptogenesis and which may contribute to a compensatory decrease in neuronal excitability of DGG cells.

Increased membrane shedding – indicated by an elevation of CD133-enriched membrane particles – into the CSF in partial epilepsy

Recent analyses provided evidence that human adult cerebrospinal fluid (CSF) in addition to soluble proteins also contains membrane particles that moreover carry the somatic stem cell marker CD133. The significance of CD133 as a potential marker of cellular proliferation, including neurogenesis, remains unresolved. As adult neurogenesis has been implicated to be induced by epileptic seizures this study investigated whether patients with partial epilepsy show a varying amount of membrane-associated CD133 in CSF as compared to healthy adults. CSF samples of 34 partial epilepsy patients were analyzed and compared to 61 healthy controls. Following sequential centrifugation up to 200,000 g quantitative immunoblotting was performed using a mouse monoclonal antibody. Antigen-antibody complexes were detected using enhanced chemiluminescence, and visualized and quantified digitally. The overall amount of membrane particle-associated CD133 was significantly increased in epilepsy patients compared to healthy controls (9.6±2.9 ng of bound CD133 antibody versus 7.4±3.8 ng; p<0.01). There were no differences according to etiology of epilepsy (cryptogenic, neoplasia, dysplasia, ammon's horn sclerosis, and others). Dichotomization of the patients according to temporal versus extratemporal foci revealed a significant increase of membrane particle-associated CD133 in patients with temporal lobe epilepsy (10.88±3.3 ng of bound CD133 antibody versus 8.35±3.48 ng; p<0.05). The increased amount of membrane particle-associated CD133 in the CSF of patients with partial epilepsy contributes to the ongoing debate of the source of these particles potentially emerging from subventricular zone astrocytes serving as neural stem cells. As neurogenesis in adults is related to the hippocampus, the significance of the increase of membrane particle-associated CD133 especially in temporal lobe epilepsy needs further clinical correlation.

Glutamate decarboxylase67 is expressed in hippocampal mossy fibers of temporal lobe epilepsy patients

Recently, expression of glutamate decarboxylase-67 (GAD67), a key enzyme of GABA synthesis, was detected in the otherwise glutamatergic mossy fibers of the rat hippocampus. Synthesis of the enzyme was markedly enhanced after experimentally induced status epilepticus. Here, we investigated the expression of GAD67 protein and mRNA in 44 hippocampal specimens from patients with mesial temporal lobe epilepsy (TLE) using double immunofluorescence histochemistry, immunoblotting, and in situ hybridization. Both in specimens with (n = 37) and without (n = 7) hippocampal sclerosis, GAD67 was highly coexpressed with dynorphin in terminal areas of mossy fibers, including the dentate hilus and the stratum lucidum of sector CA3. In the cases with Ammon's horn sclerosis, also the inner molecular layer of the dentate gyrus contained strong staining for GAD67 immunoreactivity, indicating labeling of mossy fiber terminals that specifically sprout into this area. Double immunofluorescence revealed the colocalization of GAD67 immunoreactivity with the mossy fiber marker dynorphin. The extent of colabeling correlated with the number of seizures experienced by the patients. Furthermore, GAD67 mRNA was found in granule cells of the dentate gyrus. Levels, both of GAD67 mRNA and of GAD67 immunoreactivity were similar in sclerotic and nonsclerotic specimens and appeared to be increased compared to post mortem controls. Provided that the strong expression of GAD67 results in synthesis of GABA in hippocampal mossy fibers this may represent a self-protecting mechanism in TLE. In addition GAD67 expression also may result in conversion of excessive intracellular glutamate to nontoxic GABA within mossy fiber terminals.

Components of neuronal chloride transport in rat and human neocortex

Considerable evidence indicates disturbances in the ionic gradient of GABAA receptor-mediated inhibition of neurones in human epileptogenic tissues. Two contending mechanisms have been proposed, reduced outward and increased inward Cl⁻ transporters. We investigated the properties of Cl⁻ transport in human and rat neocortical neurones (layer II/III) using intracellular recordings in slices of cortical tissue. We measured the alterations in reversal potential of the pharmacologically isolated inhibitory postsynaptic potential mediated by GABAA receptors (IPSPA) to estimate the ionic gradient and kinetics of Cl⁻ efflux after Cl⁻ injections before and during application of selected blockers of Cl⁻ routes (furosemide, bumetanide, 9-anthracene carboxylic acid and Cs+). Neurones from human epileptogenic cortex exhibited a fairly depolarized reversal potential of GABAA receptor-mediated inhibition (EIPSP-A) of -61.9 ± 8.3 mV. In about half of the neurones, the EIPSP-A averaged -55.2 ± 5.7 mV, in the other half, 68.6 ± 2.3 mV, similar to rat neurones (-68.9 ± 2.6 mV). After injections of Cl⁻, IPSPA recovered in human neurones with an average time constant (τ) of 19.0 ± 9.6 s (rat neurones: 7.2 ± 2.4 s). We calculated Cl⁻ extrusion rates (1/τ) via individual routes from the τ values obtained in different experimental conditions, revealing that, for example, the K+-coupled Cl⁻ transporter KCC2 comprises 45.3% of the total rate in rat neurones. In human neurones, the total rate of Cl⁻ extrusion was 63.9% smaller, and rates via KCC2, the Na+-K+-2Cl⁻ transporter NKCC1 and the voltage-gatedCl− channelClCwere smaller than in rat neurones by 80.0%, 61.7% and 79.9%, respectively. The rate via anion exchangers conversely was 14.4% larger in human than in rat neurones. We propose that (i) KCC2 is the major route of Cl⁻ extrusion in cortical neurones, (ii) reduced KCC2 is the initial step of disturbed Cl⁻ regulation and (iii) reductions in KCC2 contribute to depolarizing EIPSP-A of neurones in human epileptogenic neocortex.

Granule cell dispersion in temporal lobe epilepsy is associated with changes in dendritic orientation and spine distribution

Granule cell dispersion is a characteristic feature of Ammon's horn sclerosis in temporal lobe epilepsy. It was recently shown that granule cell dispersion is associated with decreased expression of the extracellular matrix protein Reelin. Reelin controls neuronal lamination and the differentiation of dendrites and spines. Here, we studied dendritic orientation and the distribution of dendritic spines on granule cells in surgical specimens of patients suffering from temporal lobe epilepsy. In this material, we compared granule cells in dentate areas showing granule cell dispersion with granule cells in areas exhibiting a normal, densely packed granule cell layer. Granule cells (GC) were Golgi-stained and analyzed using a computer-based camera lucida system and were categorized as being located proximal or distal to the hilus (GCprox, GCdist). We found that GCprox in a densely packed granule cell layer exhibited a mainly vertically oriented dendritic arbor with a small bifurcation angle (17°) between branching dendrites. In contrast, GCdist in a densely packed granular layer showed a wider bifurcation angle (35°), suggesting a widening of the dendritic field during the migratory process to superficial positions. Granule cells in the dispersed granule cell layer showed an even wider bifurcation angle of their apical dendrites (GCprox: 40°; GCdist: 58°) and also exhibited recurrent basal dendrites. Spine density on dendrites of GCprox in dispersed areas was increased compared to GCprox in the normal, compact granule cell layer. In contrast, dendrites of GCdist extending into the molecular layer showed a reduced spine density in dispersed areas. The results are discussed in view of other findings on neuronal reorganization in the epileptic dentate gyrus.

The function of hyperpolarization-activated channels in human dentate gyrus granule cells

The function of hyperpolarization-activated channels in human dentate gyrus granule cells

Neuroanatomical substrates for recurrent epileptic limbic seizures

Epilepsy is a neurological disorder characterized by the recurrence of spontaneous, unprovoked epileptic seizures. Mesial temporal lobe epilepsy (more briefly, MTLE) is a very common form of epilepsy which is featured by the occurrence of focal limbic seizures, and associated to a specific neuropathological alteration, the so-called Ammon’s horn sclerosis, whose main features are a selective loss of the CA1 and CA3/4 section of the Ammon’s horn (CA, from Latin Cornu Ammonis, abbreviated as CA), a selective cell loss of inhibitory interneurons in the hilus of the dentate gyrus (DG), and the abnormal sprouting of granule cells mossy fibers (the so called mossy fiber sprouting, MFS). The onset of spontaneous seizures (SRS) is the hallmark of a good model of epilepsy. For temporal lobe epilepsy (TLE), the most used models consist in administering systemically chemoconvulsants inducing limbic status epilepticus (i.e. seizures lasting for more than 30’, SE) and evaluating the occurrence of SRS. However, in these models, the widespread involvement of different structures which complicates the interpretation of experimental findings: limbic seizures and status epilepticus (SE) can be triggered by focal infusion of chemoconvulsants within anterior piriform cortex (abbreviated as APC) This brain region is densely innervated by noradrenergic fibers arising from the locus coeruleus (LC), and we recently showed that a lesion of LC (induced by a selective neurotoxin, DSP-4, i.p.), induces SE. LC plays a critical role in modulating several models of seizures, and it plays a critical role in plastic mechanisms and neuroprotection in the brain. Thus, we compared the group DSP-4+bicuculline and cyclothiazide+bicuculline, to evaluate whether the focal SE evoked from the APC is capable of inducing SRS and AHS, and whether LC plays a significant role in this phenomena. We found that: the loss of LC induced: (i)a higher incidence of SRS; (ii) cell loss in the hippocampal DG hilus and CA3 (iii)the loss of parvalbumin-positive neurons. In conclusion, our study confirms that focal induction of SE from the APC represents a good model of TLE, and that NE released from the fibers originating from the LC plays a significant role both in the hippocampal damage occurring after SE, and in the incidence of SRS.

Mitochondrial dysfunction in neurological disorders with epileptic phenotypes

A broad variety of mutations of the mitochondrial DNA or nuclear genes that lead to the impairment of mitochondrial respiratory chain or mitochondrial ATP synthesis have been associated with epileptic phenotypes. Additionally, evidence for an impaired mitochondrial function in seizure focus of patients with temporal lobe epilepsy and Ammon's horn sclerosis, as well as, animal models of temporal lobe epilepsy has been accumulated. This implies a direct pathogenic role of mitochondrial dysfunction in the process of epileptogenesis and seizure generation in certain forms of epilepsy.