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M V Squier

Publications and source records attributed to M V Squier.

At least 19 recordsLinked to original sources
PubMed2002

Drug resistance in epilepsy: human epilepsy.

The basis of drug resistance in human epilepsy is not understood. Parallels with resistance in cancer suggest that drug resistance proteins may have a role. To examine this possibility, we have studied human brain tissue containing pathologies capable of causing refractory epilepsy. Using immunohistochemistry for P glycoprotein (Pgp) and multidrug resistance-associated protein 1 (MRP1), we examined both pathological tissue and control tissue. We demonstrate expression of Pgp and MRP1 in glia from cases of malformation of cortical development studied both before and after the onset of epilepsy, as well as in cases of hippocampal sclerosis and dysembryoplastic neuroepithelial tumours. In one particular type of malformation, we also demonstrate that dysplastic neurons express MRP1. The pattern of immunolabelling suggests overexpression is concentrated particularly around vessels in most of the pathologies. The timing shows that expression may be constitutive in some pathologies. These findings suggest that drug resistance proteins may contribute to drug resistance in refractory epilepsy.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2002

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.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

Multidrug-resistance protein 1 in focal cortical dysplasia.

Drug resistance in epilepsy is poorly understood. We used routine immunohistochemistry to assess overexpression of a multidrug-resistance protein in dysplastic neurons, glia, and around vessels in surgically resected epileptogenic human brain tissue. We showed non-tumoral overexpression of this multidrug-resistance protein, which might contribute to drug resistance in epilepsy caused by focal cortical dysplasia.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

Persistent reelin-expressing Cajal-Retzius cells in polymicrogyria.

Cajal-Retzius (CR) cells are early-developing cells important in mammalian corticogenesis. Reelin, a protein secreted by CR cells, is essential for completion of neuronal migration and cortical lamination. Lack of reelin causes the 'reeler' phenotype in mice and autosomal recessive lissencephaly with cerebellar hypoplasia in man. Focal increases in reelin and CR cells are associated with thickening and local invaginations of the marginal zone and microgyria in animal studies. It has been suggested that abnormalities of reelin expression may be involved in human polymicrogyria. We have studied CR cells and reelin expression in pathological sections of human polymicrogyria to explore this possibility. Occurrence, distribution, morphology and reelin expression in CR cells were studied in 12 cases of human polymicrogyria, ranging from 21 gestational weeks to 10 years of age. Findings were compared with age-matched controls. Large, reelin-positive CR-like cells were more numerous in the majority of the polymicrogyria cases and persisted for longer than usual, up to 10 years of age. The CR-like cells tended to cluster and were most frequent in fused molecular layers in the polymicrogyria. Reelin-expressing CR-like cells were also found in bridges between the molecular layer and overlying leptomeningeal heterotopia and within the heterotopia itself. Clusters of CR-like cells were also found in adjacent non-polymicrogyric cortex. No clusters were seen in the control subjects. Increased numbers of CR-like cells were seen in both familial and acquired cases. In contrast to previous reports, the findings show that large CR-like cells persisted for longer than usual, up to 10 years of age, and that they may continue to express reelin. Their maximal aggregation in regions of polymicrogyria and overlying leptomeningeal heterotopia suggest an association between the presence of these cells and polymicrogyria, which we interpret in the light of recent findings concerning the roles of reelin and its downstream signalling pathway in neuronal and glial developmental dynamics and post-developmental function.

Aging↗
PubMed2000

Sulcogyral variation in NMDA receptor 2A/B subunit immunoreactivity in human brain.

NMDA receptors (NR) are important in many neurological processes. Using a large series of human brain tissue, we show that the distribution of NR2A/B immunoreactivity varies according to position along a gyrus. For pyramidal neurons in laminae II and III, immunoreactivity is most marked at gyral crown and gyral lips, diminishes along sulcal wall, and is barely detectable in sulcal floor cortex. In contrast, in some cases, immunoreactivity in laminae V and VI pyramidal neurons shows the reverse pattern. Neurofilament and calretinin immunoreactivity do not show this phenomenon. The findings suggest novel functional regionalization at the sulcogyral level in normal human brain.

Adolescent↗
PubMed1999

Over-expression of P-glycoprotein in malformations of cortical development.

Drug resistance in epilepsy due to malformations of cortical development (MCD) is unexplained. P-glycoprotein is a mediator of drug resistance, and we propose that MCD lesions over-express P-glycoprotein. Because P-glycoprotein expression may be induced by some antiepileptic drugs (AEDs), we studied brain samples from MCD cases before the onset of seizures or treatment with AEDs. Sixteen MCD cases and 16 age-matched controls were examined using immunohistochemistry. Glial labelling, representing over-expression, was seen in 10 of 16 MCD samples and in two of 16 control samples (p = 0.003). Semiquantitative assessment showed many immunoreactive glia in five of 16 MCD and one of 16 controls. We conclude that there is constitutive over-expression of P-glycoprotein in many MCD.

ATP Binding Cassette Transporter, Subfamily B↗
PubMed1998

Normal in vivo skeletal muscle oxidative metabolism in sporadic inclusion body myositis assessed by 31P-magnetic resonance spectroscopy.

Sporadic inclusion body myositis (s-IBM) is a chronic inflammatory myopathy of unknown pathogenesis. The common findings of ragged red fibres, cytochrome c oxidase-negative fibres and multiple mitochondrial DNA deletions in the muscle of patients with s-IBM have suggested that a deficit of energy metabolism may be of pathogenic relevance. To test this hypothesis we used 31P magnetic resonance spectroscopy to assess in vivo skeletal muscle mitochondrial function in the calf muscles of 12 patients with definite s-IBM. Eleven patients showed multiple mitochondrial DNA deletions in skeletal muscle and 67% showed ragged red fibres and/or cytochrome c oxidase-negative fibres. T1-weighted MR images showed increased signal intensity in the calf muscle of all patients except one. The involvement of calf muscle was confirmed by 31P magnetic resonance spectroscopy of resting muscle, which disclosed abnormalities in metabolite ratios in all patients. However, muscle oxidative metabolism assessed during recovery from exercise was normal in patients with s-IBM, as maximum rates of mitochondrial ATP production and post-exercise ADP recovery rates were within the normal range in all cases. We conclude that muscle mitochondrial abnormalities are a secondary process and unlikely to play a significant role in the pathogenesis of s-IBM.

Adenosine Diphosphate↗
PubMed1997

Widespread neuronal ectopia associated with secondary defects in cerebrocortical chondroitin sulfate proteoglycans and basal lamina in MARCKS-deficient mice.

Mice deficient in MARCKS, a prominent neural substrate for protein kinase C (PKC), die before or shortly after birth. They exhibit high frequencies of exencephaly, universal agenesis of forebrain commissures, and abnormalities of cerebral cortical and retinal lamination. We show here that these mice have wide-spread and severe neuronal ectopia in the outer layers of the developing forebrain, manifested by the migration of clusters of developing neuroblasts through the basal lamina and often through the pial membrane and into the subarachnoid space. This abnormality became apparent by Embryonic Day (E) 13 or 14, shortly after the formation of the early marginal zone. MARCKS deficiency was associated with decreased staining for marginal zone chondroitin sulfate proteoglycans; this decrease was detectable earlier in development than the neuronal ectopia. Later in development, there was also marked disruption of the basal lamina at the pial-glial interface, as evidenced by gross abnormalities in laminin and reticulin staining; however, the basal lamina appeared normal at E9.5. These data indicate that MARCKS is required for the prevention of neuronal ectopia during development. Potential mechanisms responsible for the neuronal ectopia in the MARCKS-deficient mice include decreased expression or increased proteolytic destruction of basal lamina proteins and marginal zone chondroitin sulfate proteoglycans in the developing brain.

Animals↗
PubMed1997

Dystrobrevin deficiency at the sarcolemma of patients with muscular dystrophy.

Mutations in the genes encoding dystrophin or dystrophin-associated proteins are responsible for Duchenne muscular dystrophy or various forms of limb-girdle muscular dystrophies respectively. We have recently cloned the gene for the murine 87 kDa postsynaptic protein dystrobrevin, a dystrophin-associated protein. Anti-dystrobrevin antibodies stain the sarcolemma in normal skeletal muscle indicating that dystrobrevin co-localises with dystrophin and the dystrophin-associated protein complex. By contrast, dystrobrevin membrane staining is severely reduced in muscles of Duchenne muscular dystrophy patients, consistent with dystrobrevin being a dystrophin-associated protein. Interestingly, dystrobrevin staining at the sarcolemma is dramatically reduced in patients with limb-girdle muscular dystrophy arising from the loss of one or all of the sarcoglycan components. Normal dystrobrevin staining is observed in patients with other forms of limb-girdle muscular dystrophy where dystrophin and the rest of the dystrophin-associated protein complex are normally expressed and in other neuromuscular disorders. Our results show that dystrobrevin-deficiency is a generic feature of dystrophies linked to dystrophin and the dystrophin-associated proteins. This is the first indication that a cytoplasmic component of the dystrophin-associated protein complex may be involved in the pathogenesis of limb-girdle muscular dystrophy.

Cytoskeletal Proteins↗
PubMed1997

Apoptosis in the brains of infants suffering intrauterine cerebral injury.

This study addressed the hypothesis that in human infants severe in utero insults induce a significant proportion of brain cells to undergo apoptosis. Morphologic criteria were used to quantify apoptosis and necrosis in the cingulate gyrus of two groups of infants: six infants who died after severe birth asphyxia with hypoxic-ischemic encephalopathy, and six others who suffered unexpected and apparently sudden intrauterine death at or close to term. The fraction of apoptotic cells was much higher than basal levels determined in animal experiments, and within both groups increased in proportion to the severity of injury as determined by total cell death (p < 0.05). The mean fraction of apoptotic cells was similar in asphyxiated infants, 8.3% (95% confidence interval for the population, 3.7-12%), and in stillbirths, 6.7% (0.2-13.6%). In the asphyxiated group, 20.8% (11-30.6%) of cells were necrotic, but significantly less necrosis, 3% (0.4-5.6%), was seen in stillborn infants (p < 0.05). Cell death was apoptotic after birth asphyxia in 26% (1-51%) and 78% (41-100%) in stillborn infants. In situ end labeling studies confirmed the presence of DNA fragmentation in apoptotic cells. These results demonstrate that infants who die after intrauterine insults, both those with evidence of delayed cerebral injury after hypoxia-ischemia and those without, have a significant number of cells in the brain with the morphologic characteristics of apoptosis. They confirm that apoptosis contributes significantly to cerebral damage in the perinatal period.

Apoptosis↗
PubMed1997

Apoptosis and necrosis in the newborn piglet brain following transient cerebral hypoxia-ischaemia.

We have used a porcine model of global hypoxia-ischaemia to examine the mode and extent of cell damage to the newborn brain. Apoptosis and necrosis were observed in neurons and glial cells following transient cerebral hypoxic-ischaemic injury (HII) by haematoxylin and eosin staining and by in situ end labelling (ISEL). Quantitative neuropathological analysis of the cingulate gyrus, the hippocampus and the cerebellum showed that the degree of both apoptosis and necrosis increased with the severity of injury in these brain areas. The hippocampus and cerebellar cortex were particularly sensitive to HII. Furthermore, some cell types were more susceptible to a particular mode of cell death. In the cerebellum. Purkinje cells died by necrosis but never by apoptosis. In contrast, cerebellar granule cells were frequently apoptotic, but never necrotic. In the hippocampus, apoptosis occurred in the inner layer neurons of the dentate fascia and necrosis in the more mature outer layer neurons. This suggests that immature neurons may be more prone to apoptotic death while terminally differentiated neurons die by necrosis. Apoptosis but not necrosis was seen in cerebral white matter. This model may help to elucidate the factors that determine cell fate following HII and aid the development of cerebroprotective strategies.

Animals↗
PubMed1996

Neuropathology and pathogenesis of mitochondrial diseases.

The majority of patients with mitochondrial disease have significant neuropathology, with the most common features being spongiform degeneration, neuronal loss and gliosis. Although there is considerable overlap between different mitochondrial diseases, the nature and distribution of the lesions is sufficiently distinctive in some cases to suggest a specific diagnosis. On the other hand, a number of different defects in cerebral energy metabolism are associated with common patterns of neuropathology (e.g. Leigh syndrome), suggesting that there is a limited range of responses to this type of metabolic disturbance. There are many descriptions of neuropathological changes in patients with mitochondrial disease, but there has been remarkably little investigation of the underlying pathogenic mechanisms. Comparisons with other conditions of cerebral energy deprivation such as ischaemia/hypoxia and hypoglycaemia suggest a possible role for excitotoxicity initiated by excitatory amino acid neurotransmitters. An additional contributing factor may be peroxynitrite, which is formed from nitric oxide and the oxygen free radicals which accumulate with defects of the mitochondrial electron transport chain. Mitochondrial diseases are often characterized by episodes of neurological dysfunction precipitated by intercurrent illness. Depending on the severity of the metabolic abnormality, each of these episodes carries a risk of further neuronal death and the result is usually progressive accumulation of irreversible damage. The balance between reversible functional impairment and neuronal death during episodes of metabolic imbalance is determined by the effectiveness of various protective mechanisms which may act to limit the damage. These include protective metabolic shielding of neurons by astrocytes and suppression of electrical activity (and hence energy demands) by activation of ATP-gated ion channels. In addition, recent evidence suggests that lactic acid, the biochemical abnormality common to these conditions, may not be toxic at moderately high concentrations but may in fact be protective by reducing the sensitivity of neurons to excitotoxic mechanisms.

Brain↗
PubMed1996

Clinical associations and time of onset of cerebral white matter damage in very preterm babies.

Neuropathological examinations were carried out at necropsy on 83 very pre-term babies who died during their first hospital admission. Forty seven (57%) babies had evidence of cerebral damage-39 with ischaemic white matter damage. The time of onset of ischaemic lesions was thought to be prenatal in 12 cases (31%) and postnatal in a further 12 (31%). The exact timing of damage could not be determined in 15 (38%) cases. Maternal and neonatal case notes were reviewed to ascertain clinical associations of ischaemic white matter damage. There were no clear associations between adverse clinical factors and prenatal ischaemic white matter damage. In contrast, pre-eclampsia, intrauterine growth retardation, and delivery without labour were associated with postnatal damage as were neonatal sepsis, necrotising enterocolitis, and seizures. The absence of a clear association between the timing of adverse clinical factors and the timing of ischaemic cerebral damage suggests that cerebral damage in very preterm babies may result from a sequence of events rather than one specific insult.

Brain↗
PubMed1995

Specific inhibition of apoptosis after cerebral hypoxia-ischaemia by moderate post-insult hypothermia.

In piglets studied on the first day of life transient hypoxia-ischaemia caused an increase in the fractions of necrotic and apoptotic cells in the cingulate sulcus compared to sham-operated controls. In animals subjected to the same hypoxic-ischaemic insult but cooled to 34.9 degrees C (mean tympanic membrane temperature) for 12 hours commencing after resuscitation the fraction of cells undergoing necrosis was unchanged and comparable to that in animals which were not cooled. However, the fraction of apoptotic cells was reduced and was similar to that in sham-operated controls. Thus hypothermia specifically inhibited apoptosis. This result has implications for understanding the mechanisms of delayed cerebral injury and for the use of hypothermia as a neural rescue strategy in the developing brain.

Adenosine Triphosphate↗
PubMed1995

Ubiquitinated inclusions in inclusion-body myositis patients are immunoreactive for cathepsin D but not beta-amyloid.

The nature of the inclusions in the human muscle disease inclusion-body myositis (IBM) has been the subject of debate. Parallels with Alzheimer's disease have been drawn after these inclusions were found to be ubiquitinated, and immunoreactive with antibodies to beta-amyloid (A beta) and certain amyloid-associated proteins. We have used a battery of antibodies against A beta and associated proteins to immunostain muscle biopsies from patients with IBM. Although the inclusions are ubiquitinated, we could not show immunoreactivity for A beta or the associated proteins investigated. We did, however, find that the ubiquitinated inclusions colocalised with the lysosomal marker, cathepsin D.

Alzheimer Disease↗
PubMed1995

Muscle X-inactivation patterns and dystrophin expression in Duchenne muscular dystrophy carriers.

Muscle pathology, dystrophin expression and X-inactivation patterns were studied in the muscle of five asymptomatic females heterozygous for deletions in the dystrophin gene (non-manifesting carriers) and five symptomatic carriers (manifesting carriers). Muscle from the non-manifesting carriers showed an increase in the population of centrally nucleated fibres (9.0 +/- 2.8%; controls, 1.4 +/- 0.3%), frequent fibers with abnormally interrupted dystrophin staining (38 +/- 5%), and, in sections from three individuals, small numbers of dystrophin-negative fibers (1-4%). The amount of dystrophin measured by immunoblotting was reduced to 64 +/- 5% (P < 0.001 n = 5) of normal. The pattern of X-inactivation in muscle DNA was non-biased (50: 50-60: 40) in all cases. In the manifesting carriers both highly biased (90: 10) and non-biased patterns of X-inactivation were found, but no consistent relationship was apparent between the patterns of X-inactivation and the proportions of dystrophin-negative fibers. We conclude from studies of the non-manifesting carriers that the proportion of residual dystrophin is similar to the relative activation in muscle of the X-chromosome carrying the wild-type allele. Extreme bias of X-inactivation can be associated with early clinical symptoms and severe pathology. However, as non-manifesting and some manifesting adult carriers had identical patterns of X-inactivation, abnormalities in the distribution of dystrophin, as well as overall levels of expression, may be important for the development of myopathic pathology.

Adolescent↗