Enhanced expression of microtubule-associated protein 2 in large neurons of cortical dysplasia

Expression of TRPC3 in cortical lesions from patients with focal cortical dysplasia

Focal cortical dysplasia (FCD) is one of the main causes of medically intractable epilepsy. Some studies have reported that transient receptor potential canonical channel 3 (TRPC3) may play an important role in the occurrence of seizures. In this study, we investigated the expression patterns of TRPC3 in different types of FCD. Forty-five FCD specimens and 12 control samples from autopsies were used in our study. Western blotting, immunohistochemistry, and immunofluorescence staining were employed to detect protein expression and distribution. The amount of TRPC3 protein was markedly elevated in the FCD group. The immunohistochemistry results revealed that TRPC3 staining was strong in the malformed cells and microcolumns. Most of the TRPC3-positive cells were colabeled with glutamatergic and GABAergic markers. The overexpression and altered cellular distribution of TRPC3 in the FCD samples suggest that TRPC3 may be related to epileptogenesis in FCD.

Infantile tauopathies: Hemimegalencephaly; tuberous sclerosis complex; focal cortical dysplasia 2; ganglioglioma

Tau is a normal microtubule-associated protein; mutations to phosphorylated or acetylated forms are neurotoxic. In many dementias of adult life tauopathies cause neuronal degeneration. Four developmental disorders of the fetal and infant brain are presented, each of which exhibits up-regulation of tau. Microtubules are cytoskeletal structures that provide the strands of mitotic spindles and specify cellular polarity, growth, lineage, differentiation, migration and axonal transport of molecules. Phosphorylated tau is abnormal in immature as in mature neurons. Several malformations are demonstrated in which upregulated tau may be important in pathogenesis. All produce highly epileptogenic cortical foci. The prototype infantile tauopathy is (1) hemimegalencephaly (HME); normal tau is degraded by a mutant AKT3 or AKT1 gene as the aetiology of focal somatic mosaicism in the periventricular neuroepithelium. HME may be isolated or associated with neurocutaneous syndromes, particularly epidermal naevus syndromes, also due to somatic mutations. Other tauopathies of early life include: (2) tuberous sclerosis complex; (3) focal cortical dysplasia type 2b (FCD2b); and (4) ganglioglioma, a tumor with dysplastic neurons and neoplastic glial cells. Pathological tau in these infantile cases alters cellular growth and architecture, synaptic function and tissue organization, but does not cause neuronal loss. All infantile tauopathies are defined neuropathologically as a tetrad of (1) dysmorphic and megalocytic neurons; (2) activation of the mTOR signaling pathway; (3) post-zygotic somatic mosaicism; and (4) upregulation of phosphorylated tau. HME and FCD2b may be the same disorder with different timing of the somatic mutation in the mitotic cycles of the neuroepithelium. HME and FCD2b may be the same disorder with different timing of the somatic mutation in the mitotic cycles of the neuroepithelium. Tauopathies must be considered in infantile neurological disease and no longer restricted to adult dementias. The mTOR inhibitor everolimus, already demonstrated to be effective in TSC, also may be a potential treatment in other infantile tauopathies.

Adenosine kinase expression in cortical dysplasia with balloon cells: analysis of developmental lineage of cell types

Focal cortical dysplasia type IIB (FCDIIB) is a developmental malformation of the cerebral cortex that is associated with pharmacoresistant epilepsy. Overexpression of adenosine kinase (ADK) has been regarded as a pathologic hallmark of epilepsy. We hypothesized that the epileptogenic mechanisms underlying FCDIIB are related to abnormal ADK expression. We used immunohistochemistry to examine the expression of ADK and of heterogeneous cell population markers of astrocytes (glial fibrillary acidic protein), immature glia (vimentin), immature neurons (neuronal class III beta-tubulin, TUJ1), multipotential progenitor cells (nestin), mature neurons (microtubule-associated protein 2), and antiapoptotic gene products (Bcl-2) in surgically resected human epileptic cortical specimens from FCDIIB patients (n = 20). Expression patterns were compared with those in normal autopsy (n = 6) and surgical control (n = 6) brain samples. Balloon cells in FCDII lesions were immunoreactive for ADK (77%) and balloon cells expressing the different cell markers expressing different degrees of ADK. Adenosine kinase expression assessed by Western blot and enzymatic activity were also greater in FCD versus control samples. These results suggest that upregulation of ADK is a common pathologic component of FCDIIB. Adenosine kinase might, therefore, be a target in the treatment of epilepsy associated with FCD.

Clinical neuropathology practice guide 5-2013: markers of neuronal maturation

This review surveys immunocytochemical and histochemical markers of neuronal lineage for application to tissue sections of fetal and neonatal brain. They determine maturation of individual nerve cells as the tissue progresses to mature architecture. From a developmental perspective, neuronal markers are all about timing. These diverse cellular labels may be classified in two ways: 1) time of onset of expression (early; intermediate; late); 2) labeling of subcellular structures or metabolic functions (nucleoproteins; synaptic vesicle proteins; enolases; cytoskeletal elements; calcium-binding; nucleic acids; mitochondria). Apart from these positive markers of maturation, other negative markers are expressed in primitive neuroepithelial cells and early stages of neuroblast maturation, but no longer are demonstrated after initial stages of maturation. These examinations are relevant for studies of normal neuroembryology at the cellular level. In fetal and perinatal neuropathology they provide control criteria for application to malformations of the brain, inborn metabolic disorders and acquired fetal insults in which neuroblastic maturation may be altered. Disorders, in which cells differentiate abnormally, as in tuberous sclerosis and hemimegalencephaly, pose another yet aspect of mixed cellular lineage. The measurement in living patients, especially neonates, of serum and CSF levels of enolases, chromogranins and S-100 proteins as biomarkers of brain damage may potentially be correlated with their corresponding tissue markers at autopsy in infants who do not survive. The neuropathological markers here described can be performed in ordinary hospital laboratories, not just research facilities, and offer another dimension of diagnostic precision in interpreting abnormally developed fetal and postnatal brains.

Focal cortical dysplasia

Focal cortical dysplasias are among the most common causes of intractable epilepsy in children. As the neuropathology of these conditions has been better clarified, the nomenclature has undergone numerous revisions. Their recognition has grown with the use of neuroimaging, and recent advances in imaging technology will further improve detection. Clinical, electroencephalographic, and imaging findings are often diagnostic, so it is imperative for the clinician to recognize the characteristic patterns. Treatment for developmental and behavioral disability remains largely symptomatic, and epilepsy medications are often ineffective. Epilepsy surgery, however, can be successful in selected patients. The basic science underlying the development of focal cortical dysplasias may lead to novel therapeutic approaches in the future.

Glycine transporter-1 expression in the rat model of cortical dysplasia

OBJECTIVE

Glycine transporter-1 (GLYT1) is an early marker of neural development and involved in the excitatory transmission in cortex. The study was designed to investigate the expression of GLYT1 in different parts of the brain by immunohistochemistry in the rat cortical dysplasia model.

METHODS

On postnatal day 0, one freeze lesion was carried out on ten rats between bregma and lambda on the skull in the right hemisphere for 5 seconds. Six weeks later, rats were transcardially perfused with fixative and then their brains were removed for both hamotoxylin-eosine (H&E) staining for histopathology and immunohistochemistry staining for glial fibrillary acidic protein (GFAP) for astrocytic activity and GLYT1 in the cortical dysplastic region and other rostral brain regions involving epileptogenesis such as hippocampus, pyriform cortex, amygdala, thalamus and substantia nigra.

RESULTS

GFAP immunoreactivity showed clusters of glial cells in the area of the microgyrus. Dense GLYT1 expression was localized to superficial layer of microgyric cortex and around the microgyrus. GLYT1 immunoreactivity was not detected in the other rostral regions.

DISCUSSION

GLYT1 stained superficial structures might correspond to immature neuron and higher concentrations of GLYT1 around microgyrus might be correlated with increased excitatory mechanisms in these regions.

Pathophysiological mechanisms of focal cortical dysplasia: a critical review of human tissue studies and animal models

Cortical dysplasia (CD, also known as malformations of cortical development) are the pathological substrates in a large percentage of patients with pharmacoresistant epilepsy who may be amenable to surgical treatment. Therefore, research on the mechanisms of dysplastic lesion formation and epileptogenicity is of paramount importance for the prevention, detection, and treatment of CD-induced epilepsy. The purpose of this review is to discuss and critically evaluate the current state and results of human tissue experimentation (focusing on reported results of studies done on neocortical dysplastic tissue resected from patients with pharmacoresistant epilepsy), and to discuss some of the concerns related to research that uses surgically resected epileptic human tissue. The use of better animal models of CD as a tool toward the better understanding of the mechanisms of pathogenesis, epileptogenesis, and epileptogenicity of dysplastic lesions will be reviewed from the perspective of their usefulness in a model of translational research that should ultimately result in better diagnostic and therapeutic techniques of CD.

Expression of neural stem cell surface marker CD133 in balloon cells of human focal cortical dysplasia

PURPOSE

Focal cortical dysplasia (CD) is characterized by the presence of dysmorphic neurons, laminar and columnar disorganization. A few patients with CD have balloon cells intermixed with dysmorphic neurons. The cellular characteristics of balloon cells remain unknown. This study was intended to determine further the cellular characteristics of balloon cells.

METHODS

Neocortical tissue resected from five patients with medically intractable focal epilepsy due to CD was studied. The presence of balloon cells (large opalescent cells with eccentric nuclei) was confirmed in all five patients by using cresylecht violet staining. Immunocytochemistry used antibodies against markers of pluripotential stem cells (CD133), multipotential progenitor cells (nestin), antiapoptotic gene products (Bcl-2), immature neurons (beta-tubulin 3, TUJ1), immature glia (vimentin), mature neurons (MAP2 and NeuN), and astrocytes (glial fibrillary acidic protein; GFAP).

RESULTS

Balloon cells (BCs) were found to be immunoreactive to Bcl-2 (46%), vimentin (41%), Nestin (28%), CD133 (28%), MAP2 (27%), GFAP (14%), and TUJ1 (10%). An extremely small number of BCs were immunopositive for NeuN. Confocal double labeling showed that balloon cells were dually immunopositive for CD133/nestin; CD133/GFAP; CD133/Bcl-2, and nestin/GFAP.

CONCLUSIONS

These results show that balloon cells are heterogeneous cell populations expressing cell-surface markers for pluripotential stem cells and proteins for multipotent progenitors, or immature neurons/glia. The presence of stem cell/progenitor markers in the balloon cells could be due to a persistent postnatal neurogenesis or early embryonic insult that resulted in arrest of proliferation/differentiation at their early stages. Additionally, the coexpression of Bcl-2 in CD133-positive balloon cells suggests that a resistance to programmed cell death may be involved in the pathogenesis of cortical dysplasia.

Aberrant neuronal-glial differentiation in Taylor-type focal cortical dysplasia (type IIA/B)

Focal cortical dysplasia (FCD) type IIA/B (Taylor type) is a malformation of cortical development characterized by laminar disorganization and dysplastic neurons. FCD IIA and FCD IIB denote subtypes in which balloon cells are absent or present, respectively. The etiology of FCD IIA/B is unknown, but previous studies suggest that its pathogenesis may involve aberrant, mixed neuronal-glial differentiation. To investigate whether aberrant differentiation is a consistent phenotype in FCD IIA/B, we studied a panel of neuronal and glial marker antigens in a series of 15 FCD IIB cases, and 2 FCD IIA cases. Double-labeling immunofluorescence and confocal imaging revealed that different combinations of neuronal and glial antigens were co-expressed by individual cells in all cases of FCD IIA/B, but not in control cases of epilepsy due to other causes. Co-expression of neuronal and glial markers was most common in balloon cells, but was also observed in dysplastic neurons. The relative expression of neuronal and glial antigens varied over a broad range. Microtubule-associated protein 1B, an immature neuronal marker, was more frequently co-expressed with glial antigens than were mature neuronal markers, such as neuronal nuclear antigen. Our results indicate that aberrant neuronal-glial differentiation is a consistent and robust phenotype in FCD IIA/B, and support the hypothesis that developmental defects of neuronal and glial fate specification play an important role in its pathogenesis.

Activated remodeling and N-methyl-D-aspartate (NMDA) receptors in cortical dysplasia

Cortical dysplasia is now recognized as one of the major etiologies causing intractable epilepsy in childhood. Dysplastic cortex displays cortical dyslamination, which is often associated with dysmorphic large neurons and less frequently with balloon cells. The dysmorphic large neurons are commonly located in the subcortical white matter and cerebral cortex, with enlarged nuclei with a single prominent nucleolus and showing aberrant cytoskeletal changes. I have shown that dysmorphic large neurons have several immature types of cytoskeletal proteins, such as the low-molecular-weight form of microtubule-associated protein 2 (MAP2) and MAP1B, which are involved in the outgrowth and modeling of neuronal processes in the immature brain. I have also reported that dysmorphic large neurons also have enhanced gene expression of growth-associated protein GAP43, which is a phosphoprotein enriched at presynaptic nerve terminals and is thought to be involved in axonal outgrowth and plasticity in synaptic connections. Finally, I have shown that the N-methyl-D-aspartate acid (NMDA) receptor R1 gene is up-regulated in the dysmorphic large neurons and nearly normal-sized neurons located in the dysplastic cortex. This evidence suggests that growth of neuronal processes and activated excitatory synaptic remodeling exist in the epileptic conditions of cortical dysplasia.

Pathologic features of dysplasia and accompanying alterations observed in surgical specimens from patients with intractable epilepsy

Malformations caused by abnormalities of cortical development, or cortical dysplasias, were examined in surgical specimens from 108 patients with medically intractable epilepsy to determine the scope of histopathologic changes. The relevance of the clinical findings was also evaluated. Various types and degrees of dysplastic features were observed in various combinations, including architectural abnormalities, an increased number of neurons in the molecular layer and/or cortical layer II, neuronal clustering, an increased number of satellite oligodendrocytes, abnormal gyration, single and/or aggregates of heterotopic neurons in the white matter, and the appearance of cytologically abnormal cells, such as giant or dysmorphic neurons and balloon cells. In the temporal lobe specimens, microdysgenesis (corresponding to mild malformations caused by abnormalities of cortical development and type IA/B focal cortical dysplasias) was more frequently observed than Taylor-type focal cortical dysplasia (type IIA/B), whereas in the frontal lobe specimens, the frequency of occurrence of both types was even. The ages at seizure onset and surgery of patients with the latter type were significantly lower than those of patients with the former. On the other hand, prominent astrocytosis in the cortex and white matter was evident in all cases, and many corpora amylacea and neurofibrillary tangle-like inclusions were observed in a subset of cases. An ultrastructural investigation revealed dilatation of the postsynaptic dendritic spines and shafts in the cortex and features indicating the occurrence in the white matter of demyelination followed by remyelination. Thus, with regard to the epileptogenic lesions, although dysplastic changes constitute the pathogenetic basis, the overlapping subsequent degenerative processes involving synapses, dendrites, and axons might contribute to the development of epileptogenic processes. Astrocytes might also actively participate in the development of the pathogenesis of epilepsy.

High molecular weight microtubule-associated protein 2 over-expression in neuronal migration disorders caused by N-methyl-D-aspartate receptor activation in hamsters

To evaluate the neuronal cytoarchitectural changes in neuronal migration disorders, the immunohistochemical expression of microtubule-associated proteins (MAPs) was analyzed using the experimental model induced by ibotenate in newborn hamsters. The cortical lesions observed after intracerebral ibotenate injections strongly resembled the following neuronal migration disorders: (1) microgyria; (2) focal subcortical heterotopia; (3) focal subependymal heterotopia; and (4) leptomeningeal glioneuronal heterotopia. Microgyria and leptomeningeal glioneuronal heterotopia had MAP2 (HM-2: high and low-molecular-weight forms of MAP2) immunoreactive dendritic processes or neuronal elements. The high molecular weight isoform of MAP2 (AP-20), which is more characteristic of mature neurons, showed enhanced expression in neurons of focal subcortical or subependymal heterotopia, although MAP1B (AA6: early form of MAP) immunoreactive elements were not detected in these heterotopic areas. We conclude that high molecular weight isoform of MAP2 is closely associated with cytoarchitectural repair and remodeling of neuronal processes, resulting in neuronal heterotopia after NMDA receptor activation.

Malformations of cortical development: burdens and insights from important causes of human epilepsy

Malformations of cortical development (MCD) are important causes of chronic epilepsy in human beings. A blanket term, MCD encompasses many varied developmental disorders with diverse clinical manifestations in patients that neurologists, paediatricians, and learning disability psychiatrists will encounter. Advances in imaging and genetics have led to a significant increase in our understanding of MCD, which has in turn enriched our knowledge of human epileptogenesis and normal brain development and function. In this review, I discuss some of the most common or enlightening MCD: focal cortical dysplasia, periventricular heterotopia, polymicrogyria, band heterotopia and lissencephaly, dysembryoplastic neuroepithelial tumours, and microdysgenesis. Clinical and imaging features, genetic aetiologies, treatments, and the insights that have resulted from MCD study are covered. The burden of epilepsy due to MCD is significant and there is still much to learn about MCD.

Gene expression profile analyses of cortical dysplasia by cDNA arrays

Cortical dysplasia (CD) is a well-recognized cause of intractable epilepsy, especially in children and is characterized histologically by derangements in cortical development and organization. The objective of this study was to expand the current knowledge of altered gene expression in CD as a first step towards in the identification of additional genes operative in the evolution of CD. Surgical specimens were obtained from eight patients (4 males and 4 females; age range 2-38 years; mean 15 years) with a pathologic diagnosis of CD. Nondysplastic temporal neocortex was obtained from a 2-year-old boy with intractable epilepsy and medial temporal lobe ganglioglioma. After total RNA isolation from frozen brain tissues, we carried out gene expression profiling using a cDNA expression array. Differences in gene expressions between CD and the nondysplastic neocortex were confirmed by semi-quantitative conventional reverse transcription-PCR. Three genes (recombination activating gene 1 (RAG1), heat shock 60 kDa protein 1 (HSP-60), and transforming growth factor beta1 (TGF beta1)) were found to be up-regulated more than two-fold in CD, whereas four genes (phosphoinositide-3-kinase regulatory subunit polypeptide 1 [p85 alpha] (PI3K), frizzled homolog 2 [Drosophila], Bcl-2/adenovirus E1B 19 kDa interacting protein (NIP3), and glia maturation factor beta (GMF beta)) were down-regulated to less than 50% of their normal levels. Interestingly, the majority of genes showing altered expression were associated with apoptosis. Our study demonstrates diverse changes in gene expression in CD. However, it remains to be shown which of these are causally related to the evolution of CD.

Neurotrophin receptor immunoreactivity in severe cerebral cortical dysplasia

PURPOSE

Cerebral cortical dysplasia (CD) is one of the important causes of intractable epilepsies and characterized histologically by disorganized cortical lamination and cytomegalic dysplastic neurons. Although it has been suggested that neurotrophins play an important role in differentiation, growth, and survival of developmental neurons, their pathogenetic role in CD has rarely been investigated.

METHODS

To know the pathogenetic role of various neurotrophins on dysplastic neurons, immunohistochemical staining was performed using antibodies against NGFRp75, trkA, trkB, and trkC in surgical specimens of 20 patients with CD.

RESULTS

TrkB and trkC were strongly expressed in dysplastic neurons of severe CD, and NGFRp75 was also expressed in some dysplastic neurons.

CONCLUSIONS

It is known that brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) contribute to the differentiation of neuronal precursor cells, dendritic and axonal arborization, synaptic plasticity, and cellular hyperexcitability, so increased expression of trkB and trkC may have a critical pathogenetic role in cytoskeletal abnormalities and epileptogenicity in dysplastic neurons of CD.

Hippocampal neuronal apoptosis in type 1 diabetes

Duration-related cognitive impairment is an increasingly recognized complication of type 1 diabetes. To explore potential underlying mechanisms, we examined hippocampal abnormalities in the spontaneously type 1 diabetic BB/W rat. As a functional assay of cognition, the Morris water maze test showed significantly prolonged latencies in 8-month diabetic rats not present at 2 months of diabetes. These abnormalities were associated with DNA fragmentation, positive TUNEL staining, elevated Bax/Bcl-x(L) ratio, increased caspase 3 activities and decreased neuronal densities in diabetic hippocampi. These changes were not caused by hypoglycemic episodes or reduced weight in diabetic animals. To explore potential mechanisms responsible for the apoptosis, we examined the expression of the IGF system. Western blotting and in situ hybridization revealed significant reductions in the expression of IGF-I, IGF-II, IGF-IR and IR preceding (2 months) and accompanying (8 months) the functional cognitive impairments and the apoptotic neuronal loss in hippocampus. These data suggest that a duration-related apoptosis-induced neuronal loss occurs in type 1 diabetes associated with cognitive impairment. The data also suggest that this is at least in part related to impaired insulin and/or IGF activities.

A review of gene expression patterns in the malformed brain

Major advances in the identification of genes expressed in malformation-associated epileptic disorders have been made. Some of these changes reflect the complex gene interactions necessary for proper neurodevelopment, whereas others suggest specific synaptic aberrations that could result in a hyperexcitable, and ultimately, epileptic condition. Here we review reported changes in gene expression associated with a malformed brain, with particular emphasis on how these changes provide clues to seizure genesis.

Nestin expression in ganglioglioma

It has been suggested that gangliogliomas represent a neoplastic transformation of a dysplastic focus or heterotopia. Other theories propose that gangliogliomas arise from multipotent stem cells with the ability to differentiate along glial and neuronal cell lines. Our goal was to characterize the expression of nestin, a neuroepithelial precursor/stem cell antigen, in gangliogliomas along with other pathological and clinical features of this entity. The clinical and operative features of 18 recent cases meeting the histological criteria for ganglioglioma were reviewed. The expression of nestin, microtubule-associated protein 2 (MAP2), neurofilament, and glial fibrillary acidic protein (GFAP) was assessed by immunohistochemistry and confocal scanning laser microscopy. Abundant MAP2- and nestin-positive neuronal cells were found by immunohistochemistry in all 18 gangliogliomas. GFAP staining was found in reactive and lesional astrocytes but not in cells of neuronal morphology. Confocal microscopy demonstrated colocalization of nestin and MAP2 in select neuronal cells. The true lineage of gangliogliomas remains controversial. Our findings confirm the presence of cells within these lesions that harbor a persistent stem cell cytoskeletal protein (nestin). Further insight into the cytoskeletal derangement of nestin-positive neuronal cells may shed further light on the pathogenesis of gangliogliomas and its associated epilepsy.

Drug resistance in epilepsy: expression of drug resistance proteins in common causes of refractory epilepsy

Epilepsy is resistant to drug treatment in about one-third of cases, but the mechanisms underlying this drug resistance are not understood. In cancer, drug resistance has been studied extensively. Amongst the various resistance mechanisms, overexpression of drug resistance proteins, such as multi-drug resistance gene-1 P-glycoprotein (MDR1) and multidrug resistance-associated protein 1 (MRP1), has been shown to correlate with cellular resistance to anticancer drugs. Previous studies in human epilepsy have shown that MDR1 and MRP1 may also be overexpressed in brain tissue from patients with refractory epilepsy; expression has been shown in glia and neurones, which do not normally express these proteins. We examined expression of MDR1 and MRP1 in refractory epilepsy from three common causes, dysembryoplastic neuroepithelial tumours (DNTs; eight cases), focal cortical dysplasia (FCD; 14 cases) and hippocampal sclerosis (HS; eight cases). Expression was studied immunohistochemically in lesional tissue from therapeutic resections and compared with expression in histologically normal adjacent tissue. With the most sensitive antibodies, in all eight DNT cases, reactive astrocytes within tumour nodules expressed MDR1 and MRP1. In five of eight HS cases, reactive astrocytes within the gliotic hippocampus expressed MDR1 and MRP1. Of 14 cases of FCD, MDR1 and MRP1 expression was noted in reactive astrocytes in all cases. In five FCD cases, MRP1 expression was also noted in dysplastic neurones. In FCD and DNTs, accentuation of reactivity was noted around lesional vessels. Immunoreactivity was always more frequent and intense in lesional reactive astrocytes than in glial fibrillary acidic protein-positive reactive astrocytes in adjacent histologically normal tissue. MDR1 is able to transport some antiepileptic drugs (AEDs), and MRP1 may also do so. The overexpression of these drug resistance proteins in tissue from patients with refractory epilepsy suggests one possible mechanism for drug resistance in patients with these pathologies. We propose that overexpressed resistance proteins lower the interstitial concentration of AEDs in the vicinity of the epileptogenic pathology and thereby render the epilepsy caused by these pathologies resistant to treatment with AEDs.

Nestin expression in cortical dysplasia

OBJECT

It is recognized that cortical dysplasia (CD) is associated with an increased incidence of glioneuronal neoplasms. Among hypothetical considerations, there is the possibility that CD and other neuronal migration abnormalities harbor dysmature cells with the potential to give rise to glioneuronal neoplasms. Such cells, if present, would be reasonably expected to display immature features. The goal of the present study was to characterize the expression of nestin, a neuroepithelial precursor/stem cell antigen, in CD, along with other pathological and clinical features of this entity.

METHODS

Clinical and surgical features of 10 recent cases meeting the histological criteria for CD were reviewed. Expressions of nestin, MAP2, neurofilament, and glial fibrillary acidic protein (GFAP) were assessed using immunohistochemical analysis and confocal scanning laser microscopy. Immunoreactivity for both glial and neuronal antigens as well as nestin was found in a select group of cells within regions of CD. Immunohistochemical and confocal microscopic findings demonstrated that these cells with neuronal or ambiguous features are a mixed population, some of which are dysmature neurons (positive for nestin and MAP2), whereas others are astrocytic (positive for nestin and GFAP).

CONCLUSIONS

Further insight into the nature of nestin-positive neurons may shed light on the cause and pathogenesis of the associated glioneuronal tumors and the accompanying chronic seizures.

Staging of cytoskeletal and beta-amyloid changes in human isocortex reveals biphasic synaptic protein response during progression of Alzheimer's disease

We have examined the relationships between dementia, loss of synaptic proteins, changes in the cytoskeleton, and deposition of beta-amyloid plaques in the neocortex in a clinicopathologically staged epidemiological cohort using a combination of biochemical and morphometric techniques. We report that loss of synaptic proteins is a late-stage phenomenon, occurring only at Braak stages 5 and 6, or at moderate to severe clinical grades of dementia. Loss of synaptic proteins was seen only after the emergence of the full spectrum of tau and beta-amyloid pathology in the neocortex at stage 4, but not in the presence of beta-amyloid plaques alone. Contrary to previous studies, we report increases in the levels of synaptophysin, syntaxin, and SNAP-25 at stage 3 and of alpha-synuclein and MAP2 at stage 4. Minimal and mild clinical grades of dementia were associated with either unchanged or elevated levels of synaptic proteins in the neocortex. Progressive aggregation of paired helical filament (PHF)-tau protein could be detected biochemically from stage 2 onwards, and this was earliest change relative to the normal aging background defined by Braak stage 1 that we were able to detect in the neocortex. These results are consistent with the possibility that failure of axonal transport associated with early aggregation of tau protein elicits a transient adaptive synaptic response to partial de-afferentation that may be mediated by trophic factors. This early abnormality in cytoskeletal function may contribute directly to the earliest clinically detectable stages of dementia.

Mechanisms underlying epileptogenesis in cortical malformations

The presence of developmental cortical malformations is associated with epileptogenesis and other neurological disorders. In recent years, animal models specific to certain malformations have been developed to study the underlying epileptogenic mechanisms. Teratogens (chemical, thermal or radiation) applied during cortical neuroblast division and migration result in lissencephaly and focal cortical dysplasia. Animals with these malformations have a lowered seizure threshold as well as histopathologies typical of those found in human dysgenic brains. Alterations that may promote epileptogenesis have been identified in lissencephalic brains, such as increased numbers of bursting types of neurons, and abnormal connections between hippocampus, subcortical heterotopia, and neocortex. A distinct set of pathological properties is present in animal models of 4-layered microgyria, induced with cortical lesions made during late stages of cortical neuroblast migration. Hyperexcitability has been demonstrated in cortex adjacent to the microgyrus (paramicrogyral zone) in in vitro slice preparations. A number of observations suggest that cellular differentiation is delayed in microgyric brains. Other studies show increases in postsynaptic glutamate receptors and decreases in GABA(A) receptors in microgyric cortex. These alterations could promote epileptogenesis, depending on which cell types have the altered receptors. The microgyrus lacks thalamic afferents from sensory relay nuclei, that instead appear to project to the paramicrogyral region, thereby increasing excitatory connectivity within this epileptogenic zone. These studies have provided a necessary first step in understanding molecular and cellular mechanisms of epileptogenesis associated with cortical malformations.

Focal cortical dysplasia: a neuropathological and developmental perspective

Focal cortical dysplasia (FCD) is a rare, sporadic disorder which is a recognised cause of chronic epilepsy. It is proposed to result from disordered neuronal migration and differentiation and has characteristic histological features which include disturbed cortical lamination, large abnormal neurons and the presence of large balloon cells with glassy eosinophilic cytoplasm and pleomorphic eccentric nuclei. These latter express both glial and neuronal markers indicative of abnormal neuroglial differentiation. In this paper we review the current literature on the neuropathology of FCD and discuss potential mechanisms. We focus on growth factors, signalling pathways and candidate genes with known roles in Drosophila and vertebrate brain development that could be responsible for the developmental brain changes seen in FCD. At issue are the factors that influence cell fate and differentiation and which regulate neural migration. Some of the molecular pathways, such as those involving the Notch and the Wnt pathways have particularly important roles in neuroglial differentiation in vertebrates, and these are proposed as potential candidates.

Cellular and molecular basis of cerebral dysgenesis

Maldevelopment of the cerebral cortex, cortical dysgenesis (CD), may be associated with epilepsy, mental retardation (MR), and focal or widespread neurologic deficits. The histologic hallmark of CD is disrupted cytoarchitecture, including disorganized lamination, malpositioned neurons with respect to their normal radial orientation, abnormal dendritic arborization, and heterotopic neurons within the white matter. Seizures in these patients are particularly difficult to control with conventional anti-epileptic drugs (AEDs) and may require epilepsy surgery to remove these abnormal foci. Focal CD has been reported in up to 30% of epilepsy surgery specimens and are believed to provide the central pathologic substrate responsible for seizures in these patients. How and why CD results in epileptiform activity is unknown. Advances in understanding the pathogenesis of some types of CD have occurred recently with the cloning genes responsible for a few types of X-linked and autosomal CD. This review will outline the major subtypes of CD, the pathologic findings, and the molecular etiologies for a variety of CD. We will also address recent experimental advances in studying the pathogenesis of CD.

Hypoxia-induced ABR change and heat shock protein expression in the pontine auditory pathway of young rabbits

The auditory brainstem response (ABR) was compared with the immunohistochemical expression of heat shock protein (HSP-72) and microtubule-associated protein 2 (MAP-2) of the brainstem auditory pathway in young rabbits subjected to hypoxic stress. Severe hypoxia for 2 h produced significant prolongation and decreased amplitude of the later component of ABR. HSP-72 expression was distinctly increased in the cochlear nucleus, but there was less induction in the inferior colliculus under severe hypoxia. MAP-2 immunostaining of neuropiles in the inferior collicular nucleus was decreased slightly after severe-long hypoxia, but cytoplasmic staining did not change. The present ABR change, which was produced by brainstem hypoxia-ischemia and acidosis, may be due to the neural cytoarchitectural derangement and less induction of stress proteins in the upper brainstem.