Differential expression of glutamate and GABA-A receptor subunit mRNA in cortical dysplasia.
ABSTRACT Focal cortical dysplasia is characterized by disorganized cortical lamination, dysplastic and heterotopic neurons, and an association with epilepsy. The contribution that dysplastic and heterotopic neurons make to epileptogenesis in focal cortical dysplasia is unknown and the phenotype of these cells may be distinct. The authors hypothesized that the expression of genes encoding glutamatergic (glutamate [GluR] and N-methyl-D-aspartate NMDA receptors [NR]) and gamma-aminobutyric acid A receptor (GABA(A)R) subunits is distinct in dysplastic and heterotopic neurons and that changes in receptor gene expression could be defined in a cell-specific pattern.
Single immunohistochemically labeled dysplastic and heterotopic neurons were microdissected from human focal cortical dysplasia specimens obtained during epilepsy surgery. Pyramidal neurons were microdissected from postmortem control cortex and from temporal cortex without dysplasia resected during temporal lobectomy. Poly (A) messenger RNA (mRNA) from single neurons was amplified, radiolabeled, and used to probe complementary DNA (cDNA) arrays containing GluR(1-6), NR(1A,1B), NR(2A-D), and GABA(A)Ralpha(1-6), and -Rbeta(1-3) subunit cDNAS: The relative hybridization intensities of each mRNA-cDNA hybrid were quantified by phosphorimaging.
GluR, NR, and GABA(A)R subunit mRNA expression did not differ between control neurons and nondysplastic epilepsy specimens. Expression of GluR(4), NR(2B), and NR(2C) subunit mRNA was increased, and NR(2A) and GABA(A)Rbeta(1) subunit mRNA was decreased in dysplastic compared with pyramidal and heterotopic neurons. In contrast, GABA(A)Ralpha(1), -Ralpha(2), and -Rbeta(2) as well as GluR(1) mRNA levels were reduced in both dysplastic and heterotopic neurons.
Differential expression of GluR, NR, and GABA(A)R mRNA in dysplastic and heterotopic neurons demonstrates cell specific gene transcription changes in focal cortical dysplasia. These results suggest that dysplastic and heterotopic neurons may be pharmacologically distinct and make differential contributions epileptogenesis in focal cortical dysplasia.
- SourceAvailable from: João Pereira Leite
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- "They found changes in GABA A receptors with reorganization of specific receptor subtypes in some cells and interneurons. In addition, Crino et al. (2001) found different patterns of GABA A receptor subunit expression in cortical dysplasia. Using immunohistochemistry, the authors observed a decrease in the expression of the b1 subunit in dysplastic neurons compared with pyramidal and heterotopic neurons. "
ABSTRACT: Temporal lobe epilepsy (TLE) is the most common form of partial epilepsy and affects 40% of the patients. Seizures arising from the mesial temporal lobe structures (i.e., amygdala and hippocampus) are common, whereas neocortical seizures are rare. In recent years, many studies aimed to identify the pattern of gene expression of neurotransmitters involved in molecular mechanisms of epilepsy. We used real-time PCR to quantify the expression of GABA(A) (subunits α1, β1, β2) and NMDA (subunits NR1, NR2A, and NR2B) receptor genes in amygdalae of 27 patients with TLE and 14 amygdalae from autopsy controls. The NR1 subunit was increased in patients with epilepsy when compared with controls. No differences were found in expression of NMDA subunits NR2A and NR2B or in α1, β1, and β2 subunits of GABA(A) receptors. Our results suggest that the NR1 subunit of NMDA receptors is involved in the amygdala hyperexcitability in some of the patients with TLE.Hippocampus 01/2012; 22(1):92-7. DOI:10.1002/hipo.20863
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- "Previous studies of GABA A receptor expression and function in focal cortical dysplasia have produced varying results. Single-cell PCR studies of dysplastic and heterotopic neurons in resected tissue from older children and adults with FCD revealed a reduction in α 1 subunit mRNA (Crino et al., 2001). However, in an immunohistochemical study which included two adults with cortical dysplasia, no difference in α 1 immunoreactivity was identified (Loup et al., 2000). "
ABSTRACT: Expression of the protein subunits that make up the γ-aminobutyric acid (GABA)(A) receptor pentamer is known to change during postnatal brain development in animal models. In the present study, analysis of cortical GABA(A) subunit expression was performed in control human tissue obtained from infancy through adolescence, and was compared to that from similarly aged children with intractable focal epilepsy. Twenty frozen pediatric control and 25 epileptic neocortical specimens were collected. The membrane fractions were isolated and subjected to quantitative western blot analysis. Subunit expression was correlated with clinical factors including age, pathology, and medication exposure. In control cortical samples, α₁ and γ₂ GABA(A) receptor subunits exhibited low expression in infancy, which increased over the first several years of life and then stabilized through adolescence. In contrast, α₄ subunit expression was higher in infants than in older children. The level of the chloride transporter KCC2 increased markedly with age, whereas that of NKCC1 decreased. These patterns were absent in the children with epilepsy, both in those with focal cortical dysplasia and in those with cortical gliosis. Although there was marked variability in GABA(A) receptor subunit expression among the children with epilepsy, identifiable patterns of subunit expression were found in each individual child. Maturation of cortical GABA(A) receptor subunit expression continues over the first several years of postnatal human development. Intractable focal epilepsy in children is associated with disruption of this normal developmental pattern. These findings have significant implications for the treatment of children with medications that modulate GABA(A) receptor function.Epilepsia 08/2010; 51(8):1456-67. DOI:10.1111/j.1528-1167.2009.02491.x
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- "Whatever the underlying cause for focal MCD, there are clear neurochemical changes that occur as secondary or corollary effects in relation to the pathologic defect. For example, several studies have demonstrated alterations in glutamate [N-methyl-D-aspartate (NMDA), a-amino-3- hydroxyl-5-methyl-4-isoxazole-propionate (AMPA), and mGlu receptors] and/or c-aminobutyric acid (GABA) receptor subunits in focal cortical dysplasia (Crino et al., 2001; Aronica et al., 2003; Andre et al., 2004). Translational interpretation of these results has proven to be complex . "
ABSTRACT: Focal malformations of cortical development are highly associated with intractable epilepsy in children and adults. Most patients with focal cortical malformations and epilepsy will require epilepsy surgery. Recent studies have provided new insights into the developmental pathogenesis of cortical malformations specifically relating to alterations in cell signaling though the mammalian target of rapamycin (mTOR) pathway. Focal cortical dysplasias, hemimegalencephaly, and tubers in tuberous sclerosis complex all exhibit evidence for hyperactive mTOR signaling, suggesting that these disorders form a spectrum of malformations or "TORopathies" characterized by disorganized cortical lamination, cytomegaly, and intractable seizures. Alterations in mTOR activity in focal brain malformations provide a potential pathogenic pathway to investigate for gene mutations and to exploit for animal models. Most importantly, however, if select focal cortical malformations result from enhanced mTOR signaling, new therapeutic antiepileptic compounds, such as rapamycin, can be designed and tested that specifically target mTOR signaling.Epilepsia 10/2009; 50 Suppl 9:3-8. DOI:10.1111/j.1528-1167.2009.02289.x