title: Altered thalamic GABAA-receptor subunit expression in the stargazer mouse model of absence epilepsy.
abstract: OBJECTIVE
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Anatomy, Brain Health Research Centre, Otago School of Medical Sciences, University of Otago, Dunedin, New Zealand.
authors.forename: Steve
authors.initials: S
authors.lastname: Seo
authors.forename: Beulah
authors.initials: B
authors.lastname: Leitch
mesh_terms: D000818:Animals; D015220:Calcium Channels / Q000096:biosynthesis* / Q000235:genetics; D004195:Disease Models, Animal; D004832:Epilepsy, Absence / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D008297:Male; D051379:Mice; D021122:Protein Subunits / Q000096:biosynthesis / Q000235:genetics; D018079:Receptors, GABA / Q000096:biosynthesis* / Q000235:genetics; D011963:Receptors, GABA-A / Q000096:biosynthesis* / Q000235:genetics; D013788:Thalamus / Q000378:metabolism*; D020651:Ventral Thalamic Nuclei / Q000378:metabolism
chemical_list: C113940:Cacng2 protein, mouse; D015220:Calcium Channels; C546241:Gabra1 protein, mouse; C470436:Gabrb2 protein, mouse; D021122:Protein Subunits; D018079:Receptors, GABA; D011963:Receptors, GABA-A
keywords: Absence epilepsy; GABAA receptors; Immunofluorescence; Stargazer mouse; Thalamocortical network; Western blot