The Experts below are selected from a list of 180 Experts worldwide ranked by ideXlab platform
Beulah Leitch - One of the best experts on this subject based on the ideXlab platform.
-
The impact of silencing feed-forward parvalbumin-expressing inhibitory interneurons in the cortico-thalamocortical network on seizure generation and behaviour.
Neurobiology of disease, 2019Co-Authors: Sandesh Panthi, Beulah LeitchAbstract:Abstract Feed-forward inhibition (FFI) is an essential mechanism within the brain, to regulate neuronal firing and prevent runaway excitation. In the cortico-thalamocortical (CTC) network, fast spiking parvalbumin-expressing (PV+) inhibitory interneurons regulate the firing of pyramidal cells in the cortex and relay neurons in the thalamus. PV+ interneuron dysfunction has been implicated in several neurological disorders, including epilepsy. Previously, we demonstrated that loss of excitatory AMPA-receptors, specifically at synapses on PV+ interneurons in CTC feedforward microcircuits, occurs in the Stargazer Mouse model of absence epilepsy. These mice present with absence seizures characterized by spike and wave discharges (SWDs) on electroencephalogram (EEG) and concomitant behavioural arrest, similar to childhood absence epilepsy. The aim of the current study was to investigate the impact of loss of FFI within the CTC on absence seizure generation and behaviour using new Designer Receptor Exclusively Activated by Designer Drug (DREADD) technology. We crossed PV-Cre mice with Cre-dependent hM4Di DREADD strains of mice, which allowed Cre-recombinase-mediated restricted expression of inhibitory Gi-DREADDs in PV+ interneurons. We then tested the impact of global and focal (within the CTC network) silencing of PV+ interneurons. CNO mediated silencing of all PV+ interneurons by intraperitoneal injection caused the impairment of motor control, decreased locomotion and increased anxiety in a dose-dependent manner. Such silencing generated pathological oscillations similar to absence-like seizures. Focal silencing of PV+ interneurons within cortical or thalamic feedforward microcircuits, induced SWD-like oscillations and associated behavioural arrest. Epileptiform activity on EEG appeared significantly sooner after focal injection compared to peripheral injection of CNO. However, the mean duration of each oscillatory burst and spike frequency was similar, irrespective of mode of CNO delivery. No significant changes were observed in vehicle-treated or non-DREADD wild-type control animals. These data suggest that dysfunctional feed-forward inhibition in CTC microcircuits may be an important target for future therapy strategies for some patients with absence seizures. Additionally, silencing of PV+ interneurons in other brain regions may contribute to anxiety related neurological and psychiatric disorders.
-
Cortical expression of AMPA receptors during postnatal development in a genetic model of absence epilepsy.
International journal of developmental neuroscience : the official journal of the International Society for Developmental Neuroscience, 2018Co-Authors: Nadia Kafui Adotevi, Beulah LeitchAbstract:Abstract Childhood absence epilepsy has been associated with poor academic performance, behavioural difficulties, as well as increased risk of physical injury in some affected children. The frequent episodes of ‘absence’ arise from corticothalamocortical network dysfunction, with multifactorial mechanisms potentially involved in genetically different patients. Aberrations in glutamatergic neurotransmission has been implicated in some seizure models, and we have recently reported that reduced cortical AMPA receptor (AMPAR) expression (predominantly GluA4- containing AMPARs) in parvalbumin-containing (PV+) inhibitory interneurons, could underlie seizure generation in the Stargazer mutant Mouse. In the present study, we investigate AMPA receptor subunit changes occurring during postnatal development in the Stargazer Mouse, to determine when these changes occur relative to seizure onset and thus could be contributory to seizure generation. Using quantitative western blotting, we analysed the expression of AMPAR GluA1-4 subunits in the somatosensory cortex at three critical time points; two before seizure onset (postnatal days (PN) 7–9 and 13–15), and one at seizure onset (PN17–18) in Stargazers. We report that compared to their non-epileptic littermates, in the Stargazer somatosensory cortex, there was a significant reduction in expression of AMPARs containing GluA1, 3 and 4 subunits prior to seizure onset, whereas reduction in expression of GluA2-AMPARs appears to be a post-seizure event. Thus, while loss of GluA4-containing AMPARs (likely GluA1/4 and GluA3/4) may be linked to seizure induction, the loss of GluA2-containing AMPARs is a secondary post-seizure mechanism, which is most likely involved in seizure maintenance.
-
Postnatal expression of thalamic GABAA receptor subunits in the Stargazer Mouse model of absence epilepsy.
Neuroreport, 2017Co-Authors: Steve Seo, Beulah LeitchAbstract:Absence seizures are known to originate from disruptions within the corticothalamocortical network; however, the precise underlying cellular and molecular mechanisms that induce hypersynchronicity and hyperexcitability are debated and likely to be complex and multifactorial. Recent studies implicate impaired thalamic GABAergic inhibition as a common feature in multiple animal models of absence epilepsy, including the well-established Stargazer Mouse model. Recently, we demonstrated region-specific increases in the whole tissue and synaptic levels of GABAA receptor (GABAAR) subunits α1 and β2, within the ventral posterior region of the thalamus in adult epileptic Stargazer mice compared with nonepileptic control littermates. The objective of this study was to investigate whether such changes in GABAAR subunits α1 and β2 can be observed before the initiation of seizures, which occur around postnatal (PN) days 16-18 in Stargazers. Semiquantitative western blotting was used to analyze the relative tissue level expression of GABAAR α1 and β2 subunits in the thalamus of juvenile Stargazer mice compared with their nonepileptic control littermates at three different time points before the initiation of seizures. We show that there is a statistically significant increase in the expression of α1 and β2 subunits in the thalamus of Stargazer mice, at the PN7-9 stage, compared with the control littermates, but not at PN10-12 and PN13-15 stages. These results suggest that an aberrant expression of GABAAR subunits α1 and β2 in the Stargazers does not occur immediately before seizure onset and therefore is unlikely to directly contribute to the initiation of absence seizures.
-
NMDA Receptor Expression in the Thalamus of the Stargazer Model of Absence Epilepsy
Scientific Reports, 2017Co-Authors: Z. Barad, D. R. Grattan, Beulah LeitchAbstract:In the Stargazer Mouse model of absence epilepsy, altered corticothalamic excitation of reticular thalamic nucleus (RTN) neurons has been suggested to contribute to abnormal synchronicity in the corticothalamic-thalamocortical circuit, leading to spike-wave discharges, the hallmark of absence seizures. AMPA receptor expression and function are decreased in Stargazer RTN, due to a mutation of AMPAR auxiliary subunit stargazin. It is unresolved and debated, however, if decreased excitation of RTN is compatible with epileptogenesis. We tested the hypothesis that relative NMDAR expression may be increased in RTN and/or thalamic synapses in Stargazers using Western blot on dissected thalamic nuclei and biochemically isolated synapses, as well as immunogold cytochemistry in RTN. Expression of main NMDAR subunits was variable in Stargazer RTN and relay thalamus; however, mean expression values were not statistically significantly different compared to controls. Furthermore, no systematic changes in synaptic NMDAR levels could be detected in Stargazer thalamus. In contrast, AMPAR subunits were markedly decreased in both nucleus-specific and synaptic preparations. Thus, defective AMPAR trafficking in Stargazer thalamus does not appear to lead to a ubiquitous compensatory increase in total and synaptic NMDAR expression, suggesting that elevated NMDAR function is not mediated by changes in protein expression in Stargazer mice.
-
Alterations in AMPA receptor subunit expression in cortical inhibitory interneurons in the epileptic Stargazer mutant Mouse.
Neuroscience, 2016Co-Authors: Nadia Kafui Adotevi, Beulah LeitchAbstract:Absence seizures arise from disturbances within the corticothalamocortical network, however the precise cellular and molecular mechanisms underlying seizure generation arising from different genetic backgrounds are not fully understood. While recent experimental evidence suggests that changes in inhibitory microcircuits in the cortex may contribute to generation of the hallmark spike-wave discharges, it is still unclear if altered cortical inhibition is a result of interneuron dysfunction due to compromised glutamatergic excitation and/or changes in cortical interneuron number. The Stargazer Mouse model of absence epilepsy presents with a genetic deficit in stargazin, which is predominantly expressed in cortical parvalbumin-positive (PV+) interneurons, and involved in the trafficking of glutamatergic AMPA receptors. Hence, in this study we examine changes in (1) the subunit-specific expression of AMPA receptors which could potentially result in a loss of excitation onto cortical PV+ interneurons, and (2) PV+ neuron density that could additionally impair cortical inhibition. Using Western blot analysis we found subunit-specific alterations in AMPA receptor expression in the Stargazer somatosensory cortex. Further analysis using confocal fluorescence microscopy revealed that although there are no changes in cortical PV+ interneuron number, there is a predominant loss of GluA1 and 4 containing AMPA receptors in PV+ neurons in Stargazers compared to non-epileptic controls. Taken together, these data suggest that the loss of AMPA receptors in PV+ neurons could impair their feed-forward inhibitory output, ultimately altering cortical network oscillations, and contribute to seizure generation in Stargazers. As such the feed-forward inhibitory interneurons could be potential targets for future therapeutic intervention for some absence epilepsy patients.
Z. Barad - One of the best experts on this subject based on the ideXlab platform.
-
NMDA Receptor Expression in the Thalamus of the Stargazer Model of Absence Epilepsy
Scientific Reports, 2017Co-Authors: Z. Barad, D. R. Grattan, Beulah LeitchAbstract:In the Stargazer Mouse model of absence epilepsy, altered corticothalamic excitation of reticular thalamic nucleus (RTN) neurons has been suggested to contribute to abnormal synchronicity in the corticothalamic-thalamocortical circuit, leading to spike-wave discharges, the hallmark of absence seizures. AMPA receptor expression and function are decreased in Stargazer RTN, due to a mutation of AMPAR auxiliary subunit stargazin. It is unresolved and debated, however, if decreased excitation of RTN is compatible with epileptogenesis. We tested the hypothesis that relative NMDAR expression may be increased in RTN and/or thalamic synapses in Stargazers using Western blot on dissected thalamic nuclei and biochemically isolated synapses, as well as immunogold cytochemistry in RTN. Expression of main NMDAR subunits was variable in Stargazer RTN and relay thalamus; however, mean expression values were not statistically significantly different compared to controls. Furthermore, no systematic changes in synaptic NMDAR levels could be detected in Stargazer thalamus. In contrast, AMPAR subunits were markedly decreased in both nucleus-specific and synaptic preparations. Thus, defective AMPAR trafficking in Stargazer thalamus does not appear to lead to a ubiquitous compensatory increase in total and synaptic NMDAR expression, suggesting that elevated NMDAR function is not mediated by changes in protein expression in Stargazer mice.
-
Changes in the GRIP 1&2 scaffolding proteins in the cerebellum of the ataxic Stargazer Mouse.
Brain research, 2013Co-Authors: M. Trotman, Z. Barad, Diane Guévremont, Joanna M. Williams, Beulah LeitchAbstract:Glutamate receptor-interacting proteins (GRIP1&2) and protein-interacting with C kinase-1 (PICK1) are synaptic scaffold proteins associated with the stabilization and recycling of synaptic GluA2-, 3- and 4c-containing α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs). PICK1-mediated phosphorylation of GluA serine880 uncouples GRIP1&2 leading to AMPAR endocytosis, important in mediating forms of synaptic plasticity underlying learning and memory. Ataxic and epileptic Stargazer mice possess a mutation in the CACNG2 gene encoding the transmembrane AMPAR-regulatory protein (TARP)-γ2 (stargazin). TARPs are AMPAR-auxiliary subunits required for efficient AMPAR trafficking to synapses. Stargazin is abundantly expressed in the cerebellum and its loss results in severe deficits in AMPAR trafficking to cerebellar synapses, particularly at granule cell (GC) synapses, leading to the ataxic phenotype of Stargazers. However, how the stargazin mutation impacts on the expression of other AMPAR-interacting scaffold proteins is unknown. This study shows a significant increase in GRIP1&2, but not PICK1, levels in whole tissue and synapse-enriched extracts from Stargazer cerebella. Post-embedding immunogold-cytochemistry electron microscopy showed GRIP1&2 levels were unchanged at mossy fiber-GC synapses in Stargazers, which are silent due to virtual total absence of synaptic and extrasynaptic GluA2/3-AMPARs. These results indicate that loss of synaptic AMPARs at this excitatory synapse does not affect GRIP1&2 expression within the postsynaptic region of mossy fiber-GC synapses. Interestingly, increased GRIP and reduced GluA2-AMPARexpression also occur in cerebella of autistic patients. Further research establishing the role of elevated cerebellar GRIP1&2 in Stargazers may help identify common cellular mechanisms in the comorbid disorders ataxia, epilepsy and autism leading to more effective treatment strategies.
-
Selective loss of AMPA receptors at corticothalamic synapses in the epileptic Stargazer Mouse
Neuroscience, 2012Co-Authors: Z. Barad, Olga Shevtsova, Gordon W. Arbuthnott, Beulah LeitchAbstract:Absence seizures are common in the Stargazer mutant Mouse. The mutation underlying the epileptic phenotype in Stargazers is a defect in the gene encoding the normal expression of the protein stargazin. Stargazin is involved in the membrane trafficking and synaptic targeting of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) at excitatory glutamatergic synapses. Thus, the genetic defect in the Stargazer results in a loss of AMPARs and consequently, excitation at glutamatergic synapses. Absence seizures are known to arise in thalamocortical networks. In the present study we show for the first time, using Western blot analysis and quantitative immunogold cytochemistry, that in the epileptic Stargazer Mouse, there is a global loss of AMPAR protein in nucleus reticularis (RTN) and a selective loss of AMPARs at corticothalamic synapses in inhibitory neurons of the RTN thalamus. In contrast, there is no significant loss of AMPARs at corticothalamic synapses in excitatory relay neurons in the thalamic ventral posterior (VP) region. The findings of this study thus provide cellular and molecular evidence for a selective regional loss of synaptic AMPAR within the RTN that could account for the loss of function at these inhibitory neuron synapses, which has previously been reported from electrophysiological studies. The specific loss of AMPARs at RTN but not relay synapses in the thalamus of the Stargazer, could contribute to the absence epilepsy phenotype by altering thalamocortical network oscillations. This is supported by recent evidence that loss of glutamate receptor subunit 4 (GluA4) (the predominant AMPAR-subtype in the thalamus), also leads to a specific reduction in strength in the cortico-RTN pathway and enhanced thalamocortical oscillations, in the Gria4−/− model of absence epilepsy. Thus further study of thalamic changes in these models could be important for future development of drugs targeted to absence epilepsy.
Olga Shevtsova - One of the best experts on this subject based on the ideXlab platform.
-
Selective loss of AMPA receptors at corticothalamic synapses in the epileptic Stargazer Mouse
Neuroscience, 2012Co-Authors: Z. Barad, Olga Shevtsova, Gordon W. Arbuthnott, Beulah LeitchAbstract:Absence seizures are common in the Stargazer mutant Mouse. The mutation underlying the epileptic phenotype in Stargazers is a defect in the gene encoding the normal expression of the protein stargazin. Stargazin is involved in the membrane trafficking and synaptic targeting of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) at excitatory glutamatergic synapses. Thus, the genetic defect in the Stargazer results in a loss of AMPARs and consequently, excitation at glutamatergic synapses. Absence seizures are known to arise in thalamocortical networks. In the present study we show for the first time, using Western blot analysis and quantitative immunogold cytochemistry, that in the epileptic Stargazer Mouse, there is a global loss of AMPAR protein in nucleus reticularis (RTN) and a selective loss of AMPARs at corticothalamic synapses in inhibitory neurons of the RTN thalamus. In contrast, there is no significant loss of AMPARs at corticothalamic synapses in excitatory relay neurons in the thalamic ventral posterior (VP) region. The findings of this study thus provide cellular and molecular evidence for a selective regional loss of synaptic AMPAR within the RTN that could account for the loss of function at these inhibitory neuron synapses, which has previously been reported from electrophysiological studies. The specific loss of AMPARs at RTN but not relay synapses in the thalamus of the Stargazer, could contribute to the absence epilepsy phenotype by altering thalamocortical network oscillations. This is supported by recent evidence that loss of glutamate receptor subunit 4 (GluA4) (the predominant AMPAR-subtype in the thalamus), also leads to a specific reduction in strength in the cortico-RTN pathway and enhanced thalamocortical oscillations, in the Gria4−/− model of absence epilepsy. Thus further study of thalamic changes in these models could be important for future development of drugs targeted to absence epilepsy.
-
Selective loss of AMPA receptor subunits at inhibitory neuron synapses in the cerebellum of the ataxic Stargazer Mouse.
Brain research, 2011Co-Authors: Olga Shevtsova, Beulah LeitchAbstract:Abstract AMPA receptor subunits (GluA1–4) are trafficked to membrane synaptic sites by transmembrane AMPA receptor regulatory proteins (TARPs). In the Stargazer mutant Mouse, expression of TARP-γ2 (stargazin) is severely reduced, resulting in cerebellar ataxia. Stargazer granule cells (GCs) have a complete loss of functional AMPARs, as γ2 is their main TARP; hence mossy fiber (MF)–GC synapses are silent. The aim of the current study was to investigate how the stargazin deficit affects expression levels of AMPAR subunits at output synapses from GC parallel fibers (PF) onto inhibitory neurons in the molecular layer. Cerebella from male litter-pairs of Stargazer and control mice were analyzed by post-embedding immunogold-microscopy. Levels of GluA2/3 and GluA4 were evaluated by measuring relative density of immunogold at PF–Purkinje cell (PF–PC) and PF–interneuron (PF–In) synapses respectively. In total, 100 synapses were analyzed in each pair of Stargazer and control littermates. GluA2/3 and GluA4 expression was significantly reduced throughout the Stargazer cerebellar cortex. GluA2/3 levels were reduced by 52% (p
-
Loss of calcium channels in the cerebellum of the ataxic and epileptic Stargazer mutant Mouse
Brain research, 2009Co-Authors: Beulah Leitch, Olga Shevtsova, Diane Guévremont, Joanna M. WilliamsAbstract:Abstract The Stargazer Mouse displays cerebellar ataxia and absence epilepsy as a result of a single, recessive mutation on chromosome 15 which silences the expression of the voltage-dependent calcium channel (VDCC) subunit γ2, termed stargazin. Stargazin is the predominant γ-subunit expressed in the cerebellum and is essential for correct assembly and trafficking of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate-subtype of glutamate receptors (AMPARs) to postsynaptic membranes. As a functional association between AMPARs and VDCCs has been reported, and loss of stargazin results in a loss of AMPA receptors at cerebellar synapses, we investigated whether the loss of stargazin might also change the expression levels of calcium channels at cerebellar synapses. We present data showing that the stargazin mutation affects the expression of postsynaptic L-type Cav1.2 (α1C-class) but not presynaptic P/Q-type Cav2.1 (α1A-class) calcium channel proteins at cerebellar synapses. Both Western blot and immunogold analyses demonstrated a significant reduction in the levels of L-type calcium channel Cav1.2 at Stargazer cerebellar synapses compared to their non-ataxic littermates. This is in contrast to Stargazer hippocampal synapses where no differences were detected in Cav1.2 and 2.1 levels compared to controls, likely due to compensation by subunit γ8. The loss of L-type calcium channel Cav1.2 at Stargazer cerebellar synapses suggests that stargazin mutation may contribute to the loss of VDCCs at postsynaptic sites. It is therefore possible that stargazin is involved in the trafficking of both AMPARs and VDCCs or in the formation of a functional AMPA receptor–calcium channel complex in the postsynaptic membrane.
Steve Seo - One of the best experts on this subject based on the ideXlab platform.
-
Postnatal expression of thalamic GABAA receptor subunits in the Stargazer Mouse model of absence epilepsy.
Neuroreport, 2017Co-Authors: Steve Seo, Beulah LeitchAbstract:Absence seizures are known to originate from disruptions within the corticothalamocortical network; however, the precise underlying cellular and molecular mechanisms that induce hypersynchronicity and hyperexcitability are debated and likely to be complex and multifactorial. Recent studies implicate impaired thalamic GABAergic inhibition as a common feature in multiple animal models of absence epilepsy, including the well-established Stargazer Mouse model. Recently, we demonstrated region-specific increases in the whole tissue and synaptic levels of GABAA receptor (GABAAR) subunits α1 and β2, within the ventral posterior region of the thalamus in adult epileptic Stargazer mice compared with nonepileptic control littermates. The objective of this study was to investigate whether such changes in GABAAR subunits α1 and β2 can be observed before the initiation of seizures, which occur around postnatal (PN) days 16-18 in Stargazers. Semiquantitative western blotting was used to analyze the relative tissue level expression of GABAAR α1 and β2 subunits in the thalamus of juvenile Stargazer mice compared with their nonepileptic control littermates at three different time points before the initiation of seizures. We show that there is a statistically significant increase in the expression of α1 and β2 subunits in the thalamus of Stargazer mice, at the PN7-9 stage, compared with the control littermates, but not at PN10-12 and PN13-15 stages. These results suggest that an aberrant expression of GABAAR subunits α1 and β2 in the Stargazers does not occur immediately before seizure onset and therefore is unlikely to directly contribute to the initiation of absence seizures.
-
altered thalamic gabaa receptor subunit expression in the Stargazer Mouse model of absence epilepsy
Epilepsia, 2014Co-Authors: Steve Seo, Beulah LeitchAbstract:Summary Purpose Absence seizures, also known as petit mal seizures, arise from disruptions within the cortico-thalamocortical network. Interconnected circuits within the thalamus consisting of inhibitory neurons of the reticular thalamic nucleus (RTN) and excitatory relay neurons of the ventral posterior (VP) complex, generate normal intrathalamic oscillatory activity. The degree of synchrony in this network determines whether normal (spindle) or pathologic (spike wave) oscillations occur; however, the cellular and molecular mechanisms underlying absence seizures are complex and multifactorial and currently are not fully understood. Recent experimental evidence from rodent models suggests that regional alterations in γ-aminobutyric acid (GABA)ergic inhibition may underlie hypersynchronous oscillations featured in absence seizures. The aim of the current study was to investigate whether region-specific differences in GABAA receptor (GABAAR) subunit expression occur in the VP and RTN thalamic regions in the Stargazer Mouse model of absence epilepsy where the primary deficit is in α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) expression. Methods Immunofluorescence confocal microscopy and semiquantitative Western blot analysis were used to investigate region-specific changes in GABAAR subunits in the thalamus of the Stargazer Mouse model of absence epilepsy to determine whether changes in GABAergic inhibition could contribute to the mechanisms underlying seizures in this model of absence epilepsy. Key Findings Immunofluorescence confocal microscopy revealed that GABAAR α1 and β2 subunits are predominantly expressed in the VP, whereas α3 and β3 subunits are localized primarily in the RTN. Semiquantitative Western blot analysis of VP and RTN samples from epileptic Stargazers and their nonepileptic littermates showed that GABAAR α1 and β2 subunit expression levels in the VP were significantly increased (α1: 33%, β2: 96%) in epileptic Stargazers, whereas α3 and β3 subunits in the RTN were unchanged in the epileptic mice compared to nonepileptic control littermates. Significance These findings suggest that region-specific differences in GABAAR subunits in the thalamus of epileptic mice, specifically up-regulation of GABAARs in the thalamic relay neurons of the VP, may contribute to generation of hypersynchronous thalamocortical activity in absence seizures. Understanding region-specific differences in GABAAR subunit expression could help elucidate some of the cellular and molecular mechanisms underlying absence seizures and thereby identify targets by which drugs can modulate the frequency and severity of epileptic seizures. Ultimately, this information could be crucial for the development of more specific and effective therapeutic drugs for treatment of this form of epilepsy.
-
Altered thalamic GABAA‐receptor subunit expression in the Stargazer Mouse model of absence epilepsy
Epilepsia, 2014Co-Authors: Steve Seo, Beulah LeitchAbstract:Summary Purpose Absence seizures, also known as petit mal seizures, arise from disruptions within the cortico-thalamocortical network. Interconnected circuits within the thalamus consisting of inhibitory neurons of the reticular thalamic nucleus (RTN) and excitatory relay neurons of the ventral posterior (VP) complex, generate normal intrathalamic oscillatory activity. The degree of synchrony in this network determines whether normal (spindle) or pathologic (spike wave) oscillations occur; however, the cellular and molecular mechanisms underlying absence seizures are complex and multifactorial and currently are not fully understood. Recent experimental evidence from rodent models suggests that regional alterations in γ-aminobutyric acid (GABA)ergic inhibition may underlie hypersynchronous oscillations featured in absence seizures. The aim of the current study was to investigate whether region-specific differences in GABAA receptor (GABAAR) subunit expression occur in the VP and RTN thalamic regions in the Stargazer Mouse model of absence epilepsy where the primary deficit is in α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) expression. Methods Immunofluorescence confocal microscopy and semiquantitative Western blot analysis were used to investigate region-specific changes in GABAAR subunits in the thalamus of the Stargazer Mouse model of absence epilepsy to determine whether changes in GABAergic inhibition could contribute to the mechanisms underlying seizures in this model of absence epilepsy. Key Findings Immunofluorescence confocal microscopy revealed that GABAAR α1 and β2 subunits are predominantly expressed in the VP, whereas α3 and β3 subunits are localized primarily in the RTN. Semiquantitative Western blot analysis of VP and RTN samples from epileptic Stargazers and their nonepileptic littermates showed that GABAAR α1 and β2 subunit expression levels in the VP were significantly increased (α1: 33%, β2: 96%) in epileptic Stargazers, whereas α3 and β3 subunits in the RTN were unchanged in the epileptic mice compared to nonepileptic control littermates. Significance These findings suggest that region-specific differences in GABAAR subunits in the thalamus of epileptic mice, specifically up-regulation of GABAARs in the thalamic relay neurons of the VP, may contribute to generation of hypersynchronous thalamocortical activity in absence seizures. Understanding region-specific differences in GABAAR subunit expression could help elucidate some of the cellular and molecular mechanisms underlying absence seizures and thereby identify targets by which drugs can modulate the frequency and severity of epileptic seizures. Ultimately, this information could be crucial for the development of more specific and effective therapeutic drugs for treatment of this form of epilepsy.
Terence J. O'brien - One of the best experts on this subject based on the ideXlab platform.
-
Genetic absence epilepsy rats from Strasbourg have increased corticothalamic expression of stargazin.
Neurobiology of disease, 2008Co-Authors: Kim L. Powell, Mervyn Kyi, Christopher A. Reid, Lucia Paradiso, Giovanna M. D'abaco, Andrew H. Kaye, Simon J. Foote, Terence J. O'brienAbstract:Stargazin is membrane bound protein involved in trafficking, synapse anchoring and biophysical modulation of AMPA receptors. A quantitative trait locus in chromosome 7 containing the stargazin gene has been identified as controlling the frequency and duration of absence seizures in the Genetic Absence Epilepsy Rats from Strasbourg (GAERS). Furthermore, mutations in this gene result in the Stargazer Mouse that displays an absence epilepsy phenotype. GAERS stargazin mRNA expression is increased 1.8 fold in the somatosensory cortex and by 1.3 fold in the thalamus. The changes were present before and after the onset of absence seizures indicating that increases are not a secondary consequence of the seizures. Stargazin protein expression was also significantly increased in the somatosensory cortex after the onset of spontaneous seizures. The results are of significant importance beyond the GAERS model, as they are the first to show that an increase in stargazin expression may be pro-epileptic.