Epilepsy-induced microarchitectural changes in the brain

Medullary Serotonergic Binding Deficits and Hippocampal Abnormalities in Sudden Infant Death Syndrome: One or Two Entities?

Sudden infant death syndrome (SIDS) is understood as a syndrome that presents with the common phenotype of sudden death but involves heterogenous biological causes. Many pathological findings have been consistently reported in SIDS, notably in areas of the brain known to play a role in autonomic control and arousal. Our laboratory has reported abnormalities in SIDS cases in medullary serotonin (5-HT) receptor 1A and within the dentate gyrus of the hippocampus. Unknown, however, is whether the medullary and hippocampal abnormalities coexist in the same SIDS cases, supporting a biological relationship of one abnormality with the other. In this study, we begin with an analysis of medullary 5-HT1A binding, as determined by receptor ligand autoradiography, in a combined cohort of published and unpublished SIDS (n = 86) and control (n = 22) cases. We report 5-HT1A binding abnormalities consistent with previously reported data, including lower age-adjusted mean binding in SIDS and age vs. diagnosis interactions. Utilizing this combined cohort of cases, we identified 41 SIDS cases with overlapping medullary 5-HT1A binding data and hippocampal assessment and statistically addressed the relationship between abnormalities at each site. Within this SIDS analytic cohort, we defined abnormal (low) medullary 5-HT1A binding as within the lowest quartile of binding adjusted for age and we examined three specific hippocampal findings previously identified as significantly more prevalent in SIDS compared to controls (granular cell bilamination, clusters of immature cells in the subgranular layer, and single ectopic cells in the molecular layer of the dentate gyrus). Our data did not find a strong statistical relationship between low medullary 5-HT1A binding and the presence of any of the hippocampal abnormalities examined. It did, however, identify a subset of SIDS (~25%) with both low medullary 5-HT1A binding and hippocampal abnormalities. The subset of SIDS cases with both low medullary 5-HT1A binding and single ectopic cells in the molecular layer was associated with prenatal smoking (p = 0.02), suggesting a role for the exposure in development of the two abnormalities. Overall, our data present novel information on the relationship between neuropathogical abnormalities in SIDS and support the heterogenous nature and overall complexity of SIDS pathogenesis.

Hippocampal Formation Maldevelopment and Sudden Unexpected Death across the Pediatric Age Spectrum

Sudden infant death syndrome (SIDS) and sudden unexplained death in childhood (SUDC) are defined as sudden death in a child remaining unexplained despite autopsy and death scene investigation. They are distinguished from each other by age criteria, i.e. with SIDS under 1 year and SUDC over 1 year. Our separate studies of SIDS and SUDC provide evidence of shared hippocampal abnormalities, specifically focal dentate bilamination, a lesion classically associated with temporal lobe epilepsy, across the 2 groups. In this study, we characterized the clinicopathologic features in a retrospective case series of 32 children with sudden death and hippocampal formation (HF) maldevelopment. The greatest frequency of deaths was between 3 weeks and 3 years (81%, 26/32). Dentate anomalies were found across the pediatric age spectrum, supporting a common vulnerability that defies the 1-year age cutoff between SIDS and SUDC. Twelve cases (38%) had seizures, including 7 only with febrile seizures. Subicular anomalies were found in cases over 1 year of age and were associated with increased risk of febrile seizures. Sudden death associated with HF maldevelopment reflects a complex interaction of intrinsic and extrinsic factors that lead to death at different pediatric ages, and may be analogous to sudden unexplained death in epilepsy.

Dentate gyrus abnormalities in sudden unexplained death in infants: morphological marker of underlying brain vulnerability

Sudden unexplained death in infants, including the sudden infant death syndrome, is likely due to heterogeneous causes that involve different intrinsic vulnerabilities and/or environmental factors. Neuropathologic research focuses upon the role of brain regions, particularly the brainstem, that regulate or modulate autonomic and respiratory control during sleep or transitions to waking. The hippocampus is a key component of the forebrain-limbic network that modulates autonomic/respiratory control via brainstem connections, but its role in sudden infant death has received little attention. We tested the hypothesis that a well-established marker of hippocampal pathology in temporal lobe epilepsy-focal granule cell bilamination in the dentate, a variant of granule cell dispersion-is associated with sudden unexplained death in infants. In a blinded study of hippocampal morphology in 153 infants with sudden and unexpected death autopsied in the San Diego County medical examiner's office, deaths were classified as unexplained or explained based upon autopsy and scene investigation. Focal granule cell bilamination was present in 41.2% (47/114) of the unexplained group compared to 7.7% (3/39) of the explained (control) group (p < 0.001). It was associated with a cluster of other dentate developmental abnormalities that reflect defective neuronal proliferation, migration, and/or survival. Dentate lesions in a large subset of infants with sudden unexplained death may represent a developmental vulnerability that leads to autonomic/respiratory instability or autonomic seizures, and sleep-related death when the infants are challenged with homeostatic stressors. Importantly, these lesions can be recognized in microscopic sections prepared in current forensic practice. Future research is needed to determine the relationship between hippocampal and previously reported brainstem pathology in sudden infant death.

An early decrease in cell proliferation after pentylenetetrazole-induced seizures

There are increasing data on the influence of seizures on neurogenesis in the adult brain. However, data on cell proliferation and differentiation during the early stages of kindling are scarce. We have used pentylenetetrazole (PTZ)-induced kindling to investigate the temporal profile of cytogenesis in the germinative zones of adult rat brain. For comparison, we also used a single PTZ-induced generalized tonic-clonic seizure. During kindling development, the density of 5-bromo-2'-deoxyuridine-positive cells demonstrated similar changes in all germinative zones: a dramatic decrease after the first subthreshold PTZ injection, and a gradual increase to the control level following repeated PTZ administration. On the contrary, a single PTZ-induced generalized tonic-clonic seizure was followed by an increase in the number of proliferating cells in both the dentate gyrus and the subventricular zone. These results may indicate the existence of global mechanisms affecting cellular proliferation in adult brain during seizures. Different temporal profiles of neuronal damage and proliferation changes suggest that neurodegeneration is unlikely to be a global proliferation-regulating factor. The data may contribute to better understanding of the initial phase of kindling development and epileptogenesis.

Mortality in individuals with autism, with and without epilepsy

Previous studies show higher mortality rates among individuals with autism than the general population. Comorbidity with epilepsy is an assumed, often ill-defined factor in the increased mortality rates of individuals with autism. Data from the Autism Tissue Program, a tissue donation program established to support biomedical research on autism, show that approximately one-third of its brain donors with autism also had epilepsy. Analysis of new data from the California State Department of Developmental Services is consistent with past reports showing that there is a higher than expected rate of mortality in individuals with autism and epilepsy than autism alone. Accurate, complete and accessible records on cause of death are necessary not just for brain research, but also for understanding risk factors that contribute to early death in individuals with autism spectrum disorders. Various national health care and state developmental disability agency initiatives to reduce risk of mortality are described.

Tumours arising in the setting of paediatric chronic epilepsy

BACKGROUND

Along with malformations of cortical development or cortical dysplasia, hippocampal sclerosis, and remote ischaemic damage, tumours are among the more commonly identifiable causes of medically intractable seizures in paediatric age patients. This study reviews one institution's 20 year experience with tumours arising in this clinical setting.

METHODS

Retrospective review of 129 paediatric patients [less than 19 years of age, 65 females (50.4%)] with tumours and medically intractable seizures encountered during a 20 year period of time (1989-2009). Using the most recent World Health Organization (WHO) classification of brain tumours, tumour type and grade were assessed.

RESULTS

The most common sites of origin included temporal lobe (n = 77, 59.7%), parietal lobe (n = 20, 15.5%), and frontal lobe (n = 15, 11.6%). WHO grade included 73 (56.6%) grade I tumours, 32 (24.8%) grade II tumours, and 18 (14%) grade I/II tumours. In six cases (4.7%), a WHO grade was not associated with mass. Tumour types included: ganglioglioma (n = 48, 37.2%), dysembryoplastic neuroepithelial tumour (n = 17, 13.2%), low grade astrocytoma (n = 15, 11.6%), low grade mixed glioma (n = 8, 6.2%), low grade oligodendroglioma (n = 5, 3.9%), meningioangiomatosis (n = 4, 3.1%) angiocentric glioma (n = 3, 2.3%), and dysembryoplastic neuroepithelial tumour/ganglioglioma composite tumour (n = 3, 2.3%). Less frequently observed lesions (n = 1 or 2) included pilocytic astrocytoma, protoplasmic astrocytoma, pleomorphic xanthoastrocytoma, and glioneuronal hamartoma. In 18 cases, distinction between low grade glioma and low grade glioneuronal tumour could not be definitively made. Coexisting malformation of cortical development/cortical dysplasia was noted in 29.8% of evaluable cases. In four tumours, coexistent hippocampal sclerosis was identified. Ki-67 labelling indices were less than 5% in all (n = 51) cases assessed. Of 25 tumours evaluated for chromosome 1p status, only one low grade mixed glioma demonstrated evidence of deletion; only one of 22 evaluated tumours (a low grade mixed glioma) showed evidence of chromosome 19q deletion.

CONCLUSION

Collectively, WHO grade I glioneuronal tumours account for slightly more than half of all neoplasms which cause intractable epilepsy in paediatric patients. A significant minority of tumours (n = 18, 14%) were difficult to definitively classify as glioma versus glioneuronal tumour, due to extent of sampling. Coexistent pathologies including malformation of cortical development/cortical dysplasia may be observed in a significant minority of tumours, suggesting a possible developmental origin for some tumours arising in this setting.

Coexistent pathology in chronic epilepsy patients with neoplasms

Neoplasms are a well-established cause of medically intractable or chronic epilepsy. Certain tumors, including gangliogliomas and dysembryoplastic neuroepithelial tumors, are well known to be associated with cortical dysplasia. This study retrospectively examines the incidence of coexistent pathology in patients with tumors and chronic epilepsy. This study is a retrospective review of 270 tumors arising in patients with medically intractable epilepsy encountered during a 20-year period (1989-2009). Coexistent pathology was noted in 50 of 270 (17.8%) patients, including 27 males (54%) with a mean age at surgery of 18 years (range 1-52 years). The vast majority of lesions (n=40) (80%) were located in the temporal lobe and less commonly in the parietal lobe (n=4) and the occipital lobe (n=3). Tumor diagnoses included ganglioglioma (n=29), dysembryoplastic neuroepithelial tumor (n=10), low-grade glial/glioneuronal neoplasm (n=5), low-grade astrocytoma (n=2), angiocentric glioma (n=1), low-grade mixed glioma (n=1), dysembryoplastic neuroepithelial tumor/ganglioglioma mixed tumor (n=1), and meningioangiomatosis (n=1). Forty-one (82%) tumors represented WHO grade-I neoplasms. Concomitant pathology included malformation of cortical development (cortical dysplasia) in 40 patients (80%) (Palmini et al type-I: n=37; Palmini et al type-II: n=3). Hamartias were identified in 10 patients (20%), hippocampal sclerosis in four patients (8%), and nodular heterotopia in one patient (2%). The true incidence of coexistent pathology (17.8% in this study) was likely underrepresented, given the limited extent of adjacent non-tumoral tissue sampling in cases of resected tumor. Coexistent pathology may account for the incidence of recurrent or residual epilepsy in patients who undergo tumor resection.

Altered expression of the small guanosine triphosphatase RhoA in human temporal lobe epilepsy

The small guanosine triphosphatase RhoA has recently been implicated in the pathogenesis of epilepsy in animals. In this study, we investigated the expression of RhoA in human epilepsy. Brain tissue samples from 40 patients with intractable epilepsy and 14 histologically normal temporal lobes from control patients were used to compare RhoA immunoreactivity using immunohistochemistry, immunofluorescent staining, and western blotting. Immunohistochemical staining and western blot analysis showed that RhoA immunoreactivity was increased in the patient group (p < 0.05). Immunofluorescent staining showed that RhoA was mainly expressed on cell membranes and in the cytoplasm. Our findings demonstrate that upregulation of RhoA immunoreactivity occurs in the brains of patients with intractable epilepsy.

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

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

Changes in individual and group spatial and verbal learning characteristics after anterior temporal lobectomy

PURPOSE

To evaluate the effects of anterior temporal lobectomy (ATL) on individual and group spatial and verbal learning and memory abilities as a function of side of surgery and seizure control outcome.

METHODS

We evaluated pre- and postsurgical learning and memory abilities of 75 left-hemisphere language dominant individuals who underwent ATL (33 left, 42 right) using the 8-trial Nonverbal Selective Reminding test and the 12-trial Verbal Selective Reminding test.

RESULTS

Reliable change index methods indicated that 40.5% of individuals who underwent right-ATL had a clinically significant decline in spatial memory, and 62.5% of individuals who underwent left-ATL had a significant reduction in verbal memory. Growth curve analyses indicated that both side of surgery and poor seizure outcome independently affected the learning slope in the best fitting models. Left-ATL reduced the slope, but did not affect the overall shape, of verbal learning across trials. On the other hand, poor seizure control outcome affected the slope of spatial learning regardless of the side of surgery.

DISCUSSION

Results demonstrate both individual and group declines in spatial memory and learning after ATL. Results suggest that individuals who undergo right-ATL should be counseled regarding the likelihood of a decline in spatial memory and learning abilities after ATL. Results also suggest that individuals with poor seizure control after ATL should be referred for rehabilitation services given the significant declines in spatial and verbal memory that occurred in our sample regardless of side of surgery.