Neurodevelopmental disorders as a cause of seizures: neuropathologic, genetic, and mechanistic considerations

This review will consider patterns of developmental neuropathologic abnormalities-malformations of cortical development (MCD)--encountered in infants (often with infantile spasms), children, and adults with intractable epilepsy. Treatment of epilepsy associated with some MCD, such as focal cortical dysplasia and tubers of tuberous sclerosis, may include cortical resection performed to remove the "dysplastic" region of cortex. In extreme situations (eg, hemimegalencephaly), hemispherectomy may be carried out on selected patients. Neuropathologic (including immunohistochemical) findings within these lesions will be considered. Other conditions that cause intractable epilepsy and often mental retardation, yet are not necessarily amenable to surgical treatment (eg, lissencephaly, periventricular nodular heterotopia, double cortex syndrome) will be discussed. Over the past 10 years there has been an explosion of information on the genetics of MCD. The genes responsible for many MCD (eg, TSC1, TSC2, LIS-1, DCX, FLN1) have been cloned and permit important mechanistic studies to be carried out with the purpose of understanding how mutations within these genes result in abnormal cortical cytoarchitecture and anomalous neuroglial differentiation. Finally, novel techniques allowing for analysis of patterns of gene expression within single cells, including neurons, is likely to provide answers to the most vexing and important question about these lesions: Why are they epileptogenic?

Co-localization of TSC1 and TSC2 gene products in tubers of patients with tuberous sclerosis

Two genes, mutations in which result in the phenotype of tuberous sclerosis (TSC), have recently been cloned. TSC2 on chromosome 16p13.3 encodes the protein tuberin, which appears to have growth regulating properties. TSC1 on chromosome 9q34 encodes hamartin which, as yet, has no specified cellular functions. Polyclonal antibodies were raised to synthetic peptides representing portions of tuberin and hamartin and used in immunoblots and immunohistochemical studies to localize the proteins in surgically resected neocortical tubers from four TSC patients. On Western blots of autopsy brain specimens, K-562 cell, and NT2 lysates, each antibody labelled a single band at the expected molecular weight. In immunohistochemical protocols on paraffin embedded tissue, antibodies to both tuberin and hamartin prominently labelled atypical and dysmorphic neuroglial cells that are a defining feature of TSC tubers. Some abnormal cells within cortical tuber sections were labelled with both tuberin and hamartin antisera. Our results suggest that tuberin and hamartin are both robustly expressed in similar populations of neuroglial cells of TSC tubers, even in the presence of TSC1 or TSC2 germline mutations. The roles of these gene products in normal and abnormal cortical development, tuber pathogenesis and the generation of seizures remain to be defined.

Stereotactic Radiosurgery of the Rete Mirabile in Swine: A Longitudinal Study of Histopathological Changes

OBJECTIVE:

Stereotactic radiosurgery is an established, effective treatment for brain arteriovenous malformations. The mechanisms of vessel occlusion in arteriovenous malformations has not been extensively evaluated. To better understand these mechanisms, we report histopathological changes in the swine rete mirabile after stereotactic radiosurgery.

METHODS:

Thirty-five swine were used, 15 as nonradiated controls and 20 as radiated. Two in the control group and five in the radiated group were sacrificed before the study endpoint. Tissue was obtained from 13 nonradiated (4 at 3 mo, 5 at 6 mo, 4 at 9 mo) and 15 radiated swine (2 at 3 mo, 3 at 6 mo, 10 at 9 mo) for histological, immunohistochemical, and morphometric analysis.

RESULTS:

Radiated vessels showed increasing intimal hyperplasia over the follow-up period. Histometrical analysis confirmed this with evidence of progressive luminal narrowing over the follow-up period. Immunohistochemical analysis showed intimal cells to be proliferating smooth muscle cells with surrounding extracellular collagen Type IV. Adventitial fibrosis composed of collagen Type IV was also seen with smooth muscle cells interspersed within the collagen matrix. The nonradiated animals showed no intimal hyperplasia or change in the appearance or size of the vessels over the same follow-up period. Adventitial fibrosis was minimal in the nonradiated animals.

CONCLUSION:

The vessels show an intimal response to radiation with progressive occlusion caused by migrating, proliferating smooth muscle cells, a likely source of the extracellular collagen in the intima. Cytokine mediated pathways likely produce these morphological changes. Future studies will be directed toward elucidating these underlying molecular mechanisms.

Neuropathologic Correlates of Activities of Daily Living in Alzheimer Disease

Functional status, reflected by measures of activities of daily living (ADLs), deteriorates as Alzheimer disease (AD) progresses. Decline in activities of daily living may be mediated by executive and frontal lobe dysfunction. The objective of this study was to examine the relationship between activities of daily living and pathologic burden in Alzheimer disease. Twenty two subjects with definite Alzheimer disease were selected from the UCLA ADRC neuropathology database. A total activities of daily living score was derived from the Retrospective Collateral Dementia Interview-Revised (RCDI-R) questionnaire, which was administered to caregivers of autopsied subjects included in the study. Neuritic plaque (NP) and neurofibrillary tangle (NFT) counts were performed for 8 brain regions. There was a significant positive correlation between total activities of daily living score (higher scores indicate more disability) and mean neuritic plaques and neurofibrillary tangle counts (r = 0.671, P = 0.001, and r = 0.542, P = 0.009, resp), as well as CA1 and prosubiculum neuritic plaques and neurofibrillary tangle counts, right and left orbital frontal neuritic plaques counts, and occipital neuritic plaques count. Total activities of daily living score did not correlate with age at death, age at symptom onset, dementia duration, gender, or education. Deteriorating activities of daily living in Alzheimer Disease subjects correlate with greater overall pathologic burden and possibly selectively with involvement of the medial temporal, occipital, and orbital frontal regions.

Status Epilepticus and Frequent Seizures: Incidence and Clinical Characteristics in Pediatric Epilepsy Surgery Patients

PURPOSE

The literature suggests that pediatric epilepsy surgery cases that present in status epilepticus (SE) are an unusual occurrence. However, this concept is based on case reports, and the incidence and clinical characteristics of these patients have not been systematically assessed.

METHODS

The cohort consisted of resective epilepsy surgery cases from 2000 to 2005 (n = 115), and they were classified as presenting with continuous SE requiring medical suppression therapy (n = 6) or intermittent SE (greater than 3 seizures/hour; n = 17). The SE categories were compared with extratemporal surgery patients without SE (non-SE; n = 64) for differences in clinical variables abstracted from the medical record.

RESULTS

Continuous SE was noted in 5% and intermittent SE in 15% of resective surgery cases, and all had extratemporal cortical involvement. Compared with continuous SE and non-SE cases, intermittent SE patients were younger at surgery with shorter duration of seizures, and had an increased incidence of active infantile spasms during video scalp EEG monitoring. Compared with non-SE cases, the continuous and intermittent SE groups required a larger number of antiepileptic medications presurgery and 6-months postsurgery, underwent hemispherectomy more frequently, and had an increased incidence of hemimegalencephaly and Rasmussen encephalitis and a lower occurrence of infarct/ischemia and infectious etiologies. Seizure control was over 71% up to 2 years postsurgery, and there were no differences between patient groups. Finally, seizure frequency per hour was greater in continuous SE cases compared with the intermittent SE group.

CONCLUSIONS

Children presenting with continuous or intermittent SE are not rare in pediatric epilepsy surgery centers, and such cases are more commonly associated with infantile spasms, Rasmussen's syndrome, and hemimegalencephaly pathologies. Seizure outcome after surgery was not altered in pediatric patients because they had presented with continuous or intermittent SE.

Contralateral hemimicrencephaly and clinical-pathological correlations in children with hemimegalencephaly

In paediatric epilepsy surgery patients with hemimegalencephaly (HME; n = 23), this study compared clinical, neuroimaging and pathologic features to discern potential mechanisms for suboptimal post-hemispherectomy developmental outcomes and structural pathogenesis. MRI measured affected and non-affected cerebral hemisphere volumes for HME and non-HME cases, including monozygotic twins where one sibling had HME. Staining against neuronal nuclei (NeuN) determined grey and white matter cell densities and sizes in HME and autopsy cases, including the non-affected side of a HME surgical/autopsy case. By MRI, the affected hemisphere was larger and the non-affected side smaller in HME compared with non-HME children. The affected HME side showed enlarged abnormal deep grey and white matter structures and/or T2-weighted hypointensity in the subcortical white matter in 75% of cases, suggestive of excessive pre-natal neurogenesis and heterotopias. Histopathological examination of the affected HME side revealed immature-appearing neurons in 70%, polymicrogyria (PMG) in 61% and balloon cells in 45% of cases. Compared with autopsy cases, in HME children NeuN cell densities on the affected side were increased in the molecular layer and upper cortex (+244 to +18%), decreased in lower cortical layers (-35%) and increased in the white matter (+139 to +149%). Deep grey matter MRI abnormalities and/or T2-weighted white matter hypointensity correlated with the presence of immature-appearing neurons and PMG on histopathology, decreased NeuN cell densities in lower cortical layers and a positive history of infantile spasms. Post-surgery seizure control was associated with decreased NeuN densities in the molecular layer. In young children with HME and epilepsy, these findings indicate that there are bilateral cerebral hemispheric abnormalities and contralateral hemimicrencephaly is a likely explanation for poorer post-surgery seizure control and cognitive outcomes. In addition, our findings support the hypothesis that HME pathogenesis probably involves somatic mutations that affect each developing cerebral hemisphere differently with more neurons than expected on the HME side.

Are cytomegalic neurons and balloon cells generators of epileptic activity in pediatric cortical dysplasia?

PURPOSE

Severe cortical dysplasia (CD) is characterized by the presence of cytomegalic neurons and balloon cells. These aberrant cells could participate in the generation of epileptic activity. The aim of this study was to morphologically and electrophysiologically characterize cells in pediatric CD tissue.

METHODS

We used infrared video-microscopy to visualize normal and abnormal-appearing cells. To characterize electrophysiological properties, we used whole-cell patch clamp recordings in tissue slices obtained from 42 cases of pediatric CD (ages 0.2-14 years). The pipette contained biocytin for determination of morphological features.

RESULTS

Approximately 25% of recorded cells displayed morphologic differences compared with normal-appearing pyramidal neurons, and were divided as follows: immature, misoriented, dysmorphic, cytomegalic, and balloon cells. Immature cells displayed electrophysiological membrane properties typical of developing neurons. Misoriented pyramidal neurons and pyramidal neurons with dysmorphic processes displayed properties similar to normal-appearing pyramidal neurons. In contrast, cytomegalic neurons and balloon cells displayed abnormal membrane properties. Balloon cells had a very high input resistance and lacked voltage-gated Na+ and Ca2+ currents. Cytomegalic neurons had a very high membrane capacitance, very low input resistance, and showed signs of hyperexcitability, as exemplified by the occurrence of repetitive, slowly inactivating Ca2+ spikes when depolarized.

CONCLUSIONS

We suggest that cytomegalic neurons but not balloon cells have the potential to be epileptic generators, although probably not instigators, in severe CD tissue.

Correlates of hippocampal neuron number in Alzheimer's disease and ischemic vascular dementia

The cornu ammonis 1 region of the hippocampus (CA1) sector of hippocampus is vulnerable to both Alzheimer's disease (AD)-type neurofibrillary degeneration and anoxia-ischemia. The objective of this article is to compare number and size of neurons in CA1 in AD versus ischemic vascular dementia. Unbiased stereological methods were used to estimate the number and volume of neurons in 28 autopsy-derived brain samples. For each case, the entire hippocampus from one cerebral hemisphere was sliced into 5mm slabs (5-7 slabs/case), cut into 50 microm sections, and stained with gallocyanine. Using the optical dissector, we systematically sampled the number and size of neurons throughout the extent of CA1 and CA2. The total number of neurons was significantly less in AD compared with ischemic vascular dementia (p < 0.02), but there was no significant difference in neuron size. The greatest loss of neurons was observed in two cases with combined AD and hippocampal sclerosis. Regardless of causative diagnosis, the number of CA1 neurons correlates with magnetic resonance imaging-derived hippocampal volume (r = 0.72; p < 0.001) and memory score (r = 0.62; p < 0.01). We conclude that although CA1 neuron loss is more consistently observed in AD than ischemic vascular dementia, severity of loss shows the expected correlation with structure and function across causative subtype. Reductions in magnetic resonance imaging-derived hippocampal volume reflect loss, rather than shrinkage, of CA1 neurons.

Pediatric Cortical Dysplasia: Correlations between Neuroimaging, Electrophysiology and Location of Cytomegalic Neurons and Balloon Cells and Glutamate/GABA Synaptic Circuits

Seizures in cortical dysplasia (CD) could be from cytomegalic neurons and balloon cells acting as epileptic 'pacemakers', or abnormal neurotransmission. This study examined these hypotheses using in vitro electrophysiological techniques to determine intrinsic membrane properties and spontaneous glutamatergic and GABAergic synaptic activity for normal-pyramidal neurons, cytomegalic neurons and balloon cells from 67 neocortical sites originating from 43 CD patients (ages 0.2-14 years). Magnetic resonance imaging (MRI), (18)fluoro-2-deoxyglucose positron emission tomography (FDG-PET) and electrocorticography graded cortical sample sites from least to worst CD abnormality. Results found that cytomegalic neurons and balloon cells were observed more frequently in areas of severe CD compared with mild or normal CD regions as assessed by FDG-PET/MRI. Cytomegalic neurons (but not balloon cells) correlated with the worst electrocorticography scores. Electrophysiological recordings demonstrated that cytomegalic and normal-pyramidal neurons displayed similar firing properties without intrinsic bursting. By contrast, balloon cells were electrically silent. Normal-pyramidal and cytomegalic neurons displayed decreased spontaneous glutamatergic synaptic activity in areas of severe FDG-PET/MRI abnormalities compared with normal regions, while GABAergic activity was unaltered. In CD, these findings indicate that cytomegalic neurons (but not balloon cells) might contribute to epileptogenesis, but are not likely to be 'pacemaker' cells capable of spontaneous paroxysmal depolarizations. Furthermore, there was more GABA relative to glutamate synaptic neurotransmission in areas of severe CD. Thus, in CD tissue alternate mechanisms of epileptogenesis should be considered, and we suggest that GABAergic synaptic circuits interacting with cytomegalic and normal-pyramidal neurons with immature receptor properties might contribute to seizure generation.

Brain deposition of beta-amyloid is a common pathologic feature in HIV positive patients

BACKGROUND

We planned to analyze the prevalence and distribution of beta-amyloid deposition in the HIV+ brain in the HAART era. Our working hypothesis is that long term survival, aging and the secondary effects of HAART may contribute to increased beta-amyloid accumulation in this patient population.

METHODS

Paraffin embedded archival brain autopsy tissues were assessed by immunocytochemistry for beta-amyloid. Detailed in-vivo neuro-behavioral assessments and ApoE genotyping were available for a subset of the studied population.

RESULTS

Immunoreactivity with the antibodies 4G8 and 6E10 was found predominantly in neuronal soma and dystrophic axonal processes. Extracellular, often perivascular plaques were also identified in many cases.

CONCLUSIONS

We propose that prolonged HAART and aging may contribute to an overall increase in amyloid deposition, potentially mediated by inhibition of insulin degradation enzyme (IDE) or disruption of the axonal transport of the amyloid precursor protein.

Surgery for symptomatic infant-onset epileptic encephalopathy with and without infantile spasms

Children undergoing surgery with infant-onset epilepsy were classified into those with medically refractory infantile spasms (IS), successfully treated IS, and no IS history, and the groups were compared for pre- and postsurgery clinical and Vineland Adaptive Behavior Scale (VABS) developmental quotients (DQ). Children without an IS history were older at surgery and had longer epilepsy durations than those with IS despite similar substrates, surgeries, and seizure frequencies. In all groups, better postsurgery VABS-DQ scores were associated with early surgical intervention indicating that infant-onset epilepsy patients with or without IS are at risk for seizure-induced encephalopathy.

Insulin signaling pathways in cortical dysplasia and TSC-tubers: tissue microarray analysis

To evaluate the possible roles of the Akt/PKB-mTOR-p70S6K-S6 and cap-dependent translation (eIF4G) pathways in the pathogenesis of tuberous sclerosis complex (TSC)-associated cortical tubers and focal cortical dysplasia (FCD), we performed qualitative and semiquantitative immunohistochemical evaluation on surgically resected corticectomy specimens to detect phosphorylated molecules as activated downstream targets of the signaling pathways. A tissue microarray paraffin block was constructed from 63 archival specimens of surgically resected TSC tubers, FCDs with balloon cells, cortical dysplasia without balloon cells, and histologically normal-appearing neocortex obtained from cases with Rasmussen encephalitis, cystic-gliotic encephalopathy, and temporal lobe epilepsy. Abnormal neuroglial cells were positive for phospho-S6 and phospho-eIF4G with various staining intensities in FCDs and TSC tubers. Both proteins were much less abundantly expressed in normal-appearing neocortex. Phospho-mTOR expression was observed in neurons in all groups. The expression of phospho-S6 and phospho-eIF4G was associated with dysplastic lesions (p < 0.05), and the cytoplasmic phospho-p70S6K expression was most specific for and abundant in TSC tubers and much less prominent in other groups (p < 0.01). These results suggest that constitutive activation of cytoplasmic p70S6K plays a pivotal role in the pathogenesis of TSC tubers and that FCDs possess a distinct mechanism for activation of S6 and eIF4G.

Cerebral hemispherectomy: hospital course, seizure, developmental, language, and motor outcomes

OBJECTIVE

To compare hemispherectomy patients with different pathologic substrates for hospital course, seizure, developmental, language, and motor outcomes.

METHODS

The authors compared hemispherectomy patients (n = 115) with hemimegalencephaly (HME; n = 16), hemispheric cortical dysplasia (hemi CD; n = 39), Rasmussen encephalitis (RE; n = 21), infarct/ischemia (n = 27), and other/miscellaneous (n = 12) for differences in operative management, postsurgery seizure control, and antiepilepsy drug (AED) usage. In addition, Vineland Adaptive Behavior Scale (VABS) developmental quotients (DQ), language, and motor assessments were performed pre- or postsurgery, or both.

RESULTS

Surgically, HME patients had the greatest perioperative blood loss, and the longest surgery time. Fewer HME patients were seizure free or not taking AEDs 1 to 5 years postsurgery, but the differences between pathologic groups were not significant. Postsurgery, 66% of HME patients had little or no language and worse motor scores in the paretic limbs. By contrast, 40 to 50% of hemi CD children showed near normal language and motor assessments, similar to RE and infarct/ischemia cases. VABS DQ scores showed +5 points or more improvement postsurgery in 57% of patients, and hemi CD (+12.7) and HME (+9.1) children showed the most progress compared with RE (+4.6) and infarct/ischemia (-0.6) cases. Postsurgery VABS DQ scores correlated with seizure duration, seizure control, and presurgery DQ scores.

CONCLUSIONS

The pathologic substrate predicted pre- and postsurgery differences in outcomes, with hemimegalencephaly (but not hemispheric cortical dysplasia) patients doing worse in several domains. Furthermore, shorter seizure durations, seizure control, and greater presurgery developmental quotients predicted better postsurgery developmental quotients in all patients, irrespective of pathology.

Human Cortical Dysplasia and Epilepsy: An Ontogenetic Hypothesis Based on Volumetric MRI and NeuN Neuronal Density and Size Measurements

In epilepsy patients with cortical dysplasia (CD), this study determined the probable ontogenetic timing of pathogenesis based on the number, location and appearance of neurons. Magnetic resonance imaging (MRI) determined gray and white matter volumes of affected and non-affected cerebral hemispheres, and gray and white matter neuronal-nuclear protein (NeuN) densities and sizes were assessed in epilepsy surgery patients (0.2-38 years) with CD (n = 25) and non-CD etiologies (n = 14), and compared with autopsy cases (n = 13; 0-33 years). Pathology group, seizure type and age at surgery were compared against MRI and NeuN data. CD patients demonstrated increased MRI cerebral (3%) and gray matter (8%) volumes of the affected compared with non-affected cerebral hemisphere, and increased layer 1 (131%), upper cortical (9-23%) and white matter (28-77%) NeuN densities compared with autopsy cases. Non-CD cases showed decreased cerebral volumes of the affected hemisphere (14-18%) without changes in NeuN densities. Compared with autopsy cases, in CD and non-CD patients, cortical neurons were hypertrophied. Patients with a history of infantile spasms had a 40% increase in the size of layer 1 neurons compared with cases without spasms. By age, regardless of pathology group, there were logarithmic increases in MRI cerebral and white matter volumes, logarithmic increases in the size of lower gray and superficial white matter neurons, and logarithmic decreases in gray and white matter neuronal densities. These results support the concept that there were more neurons than expected in layer 1, gray, and white matter of CD patients compared with non-CD and autopsy cases. In addition, the location and appearance of neurons are consistent with the hypothesis that CD is the consequence of abnormalities occurring late in corticoneurogenesis that involve excessive neurogenesis with retention of pre-plate cells in the molecular layer and subplate regions.

Five or More Acute Postoperative Seizures Predict Hospital Course and Long-term Seizure Control after Hemispherectomy

PURPOSE

Acute postoperative seizures (APOSs) are those that occur in the first 7 to 10 days after surgery, and previous studies in temporal lobe epilepsy patients support the notion that APOSs may foretell failure of long-term seizure control. It is unknown whether APOSs also predict seizure outcome or hospital course after hemispherectomy.

METHODS

Hemispherectomy patients (n = 114) were studied retrospectively and subdivided into the following groups: No APOSs, 1 to 5 APOSs, or >5 APOSs. Intensive care unit (ICU) nursing staff or family members reported and described the APOS events. APOS categories were compared with pre- and postsurgery clinical variables abstracted from the medical record.

RESULTS

APOSs occurred in 22.6% of hemispherectomy patients. Compared with the 0 and 1 to 5 APOS groups, patients with >5 APOS showed (a) longer seizure durations before surgery, (b) longer hospitalizations, (c) later oral food intake, (d) more frequent lumbar punctures, (e) worse seizure control at 0.5 and 1 year after surgery, (f) more antiepileptic drug (AED) use at 2 and 5 years after surgery, and (g) higher reoperation rate. No similar differences were found between the 0 and 1 to 5 APOS groups. The day of the APOS, whether the APOS was typical of preoperative seizures, and postsurgery scalp EEG did not predict long-term seizure control. APOS patients in the 1 to 5 and >5 groups had lower pre- and postsurgery Vineland developmental quotients compared with those without an APOS.

CONCLUSIONS

Hemispherectomy patients with >5 APOSs had a more prolonged and complicated hospital course and worse postsurgery seizure control, more AED use, and higher reoperation rate than did patients with 0 or 1 to 5 APOSs. Thus the number of APOSs was a predictor of postsurgery seizure control and can be used to counsel patients and families about prognosis after hemispherectomy.

Terminology and classification of the cortical dysplasias

BACKGROUND

There have been difficulties in achieving a uniform terminology in the literature regarding issues of classification with respect to focal cortical dysplasias (FCDs) associated with epilepsy.

OBJECTIVE

S: To review and refine the current terminology and classification issues of potential clinical relevance to epileptologists, neuroradiologists, and neuropathologists dealing with FCD.

METHODS

A panel discussion of epileptologists, neuropathologists, and neuroradiologists with special expertise in FCD was held.

RESULTS

The panel proposed 1) a specific terminology for the different types of abnormal cells encountered in the cerebral cortex of patients with FCD; 2) a reappraisal of the different histopathologic abnormalities usually subsumed under the term "microdysgenesis," and suggested that this terminology be abandoned; and 3) a more detailed yet straightforward classification of the various histopathologic features that usually are included under the heterogeneous term of "focal cortical dysplasia."

CONCLUSION

The panel hopes that these proposals will stimulate the debate toward more specific clinical, imaging, histopathologic, and prognostic correlations in patients with FCD associated with epilepsy.

New JC virus infection patterns by in situ polymerase chain reaction in brains of acquired immunodeficiency syndrome patients with progressive multifocal leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML), caused by the human polyomavirus JC (JCV), is an opportunistic infection of the central nervous system (CNS), the histopathological diagnosis of which can be made by routine staining. Very low copy numbers of JCV nucleic acid can be detected in paraffin sections by the specific and highly sensitive in situ polymerase chain reaction (in situ PCR). The authors evaluated JCV infection in 12 acquired immunodeficiency syndrome (AIDS) patients with PML by comparison of hematoxylin and eosin (H&E) staining, in situ hybridization (ISH), and in situ PCR. Phenotype of infected cells was determined by immunohistochemistry with antibodies against glial fibrillary acidic protein (GFAP) or cluster of differentiation 68 (CD68), focusing on cells containing low JC viral copy numbers, and on cell types that are normally not associated with papovavirus infection. The number of detectable JCV-positive oligodendrocytes increased markedly upon PCR amplification and hitherto unknown oligodendrocytic staining patterns were discernible: JCV DNA was detectable in both nucleus and cytoplasm, in cytoplasm only, and as ghost-cell silhouettes appearing as a membranous "rim" of staining product in some cells. The authors suggest that the staining patterns correspond to different stages of the viral replication cycle. Some human immunodeficiency virus (HIV)-type giant cells (HIV-GCs) were shown to contain JCV DNA, thus probably revealing a double infection. Macrophages and HIV-GCs showed staining in the cytoplasm and the nuclei, indicating that they not only may phagocytize JCV particles but may also be actively infected. CD68-positive GCs were occasionally noted to contain a complete JCV DNA-positive nucleus in their center, and were accordingly called JCV-type giant cells (JCV-GCs). Rarely, JCV DNA signals were noted in vascular endothelium. No JCV infection was detectable in lymphocytes, neurons, or in brain tissue of JCV-negative age-matched controls. The authors report new findings concerning inter- and intracellular JCV infection patterns in PML, possibly shedding new light on JCV susceptibility of different cell types in the brain of AIDS patients with PML.

NMDA Receptor Alterations in Neurons from Pediatric Cortical Dysplasia Tissue

The subunit composition of glutamate receptors affects their functional properties, and could contribute to abnormal electrophysiology in pediatric cortical dysplasia (CD). We examined electrophysiological responses and subunit assembly of N-methyl-D-aspartate (NMDA) receptors in acutely dissociated normal-appearing pyramidal and cytomegalic neurons from CD tissue and normal-appearing pyramidal neurons from non-CD tissue. In most cytomegalic and approximately 30% of normal-appearing pyramidal neurons from CD tissue, NMDA currents showed decreased Mg(2+) sensitivity compared with neurons from non-CD tissue. Ifenprodil had less effect in CD compared with non-CD neurons, indicating a functional loss of NR2B subunits. NMDA-evoked current density was decreased in cytomegalic compared with normal-appearing neurons. Single-cell reverse transcriptase polymerase chain reaction showed that all non-CD neurons expressed NR2B subunit mRNA. By comparison, 22% of pyramidal neurons in CD tissue lacked NR2B mRNA. Immunofluorescence showed a decrease in NR2B subunit expression in cytomegalic neurons and a subset of normal-appearing pyramidal neurons from CD tissue. Taken together, these results demonstrate the presence of NMDA receptors with altered subunit composition and Mg(2+) sensitivity that could contribute to functional abnormalities in CD.