EAAT4-eGFP BAC reporter transgenic adult mice were used to detect EAAT4 gene expression in individual cells of cerebral cortex, and eGFP fluorescence was measured to compare EAAT4 promoter activity in different cells. Most eGFP+ cells were neurons; only rare GFAP+ profiles were eGFP+. About 10% of NeuN+ cells was eGFP+, and the percentage of NeuN/eGFP co-localization varied from 2 to 20% of NeuN+ cells throughout cortical layers: layers I and II-III showed the highest values of co-localization, layer IV the lowest. The intensity of eGFP fluorescence did not exhibit laminar variations. Finally, we observed that EAAT4 promoter activity in cortical neurons was 10% of that measured in cerebellar Purkinje cells, i.e., the cells displaying the highest intensity in the CNS. These results extend our knowledge on EAAT4 expression in the cerebral cortex of adult mice, and suggest that the role of EAAT4 in cortical glutamatergic transmission may be more important than previously thought.
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