Expression of Na+-K+-Cl- cotransporter in rat brain during development andits localization in mature astrocytes

Na+-K+-Cl- cotransporter has been proposed to play an important role in the regulation of intracellular Cl- concentration in neurons during developmen t. In this study, the expression pattern of the cotransporter in different regions of rat brain was examined at birth (PO), postnatal days 7 (P7), P14 , P21, and adult by Western blotting analysis. In cortex, thalamus, cerebel lum and striatum, the cotransporter expression level was low at PO and sign ificantly increased at P14 (P <0.05). The expression peaked at P21 and was maintained at the same level in adulthood. However, in hippocampus, a peak level of the cotransporter expression was detected in adult brain. The immu nocytochemistry study of adult rat brain revealed that an intense staining of the Na+-K+-Cl- cotransporter protein was observed in dendritic processes of CA1-CA3 hippocampal pyramidal neurons. In contrast, abundant immuno-rea ctive signals of the cotransporter were found in somata of thalamic nucleus . Immunofluorescence double staining demonstrates that the Na+-K+-Cl- cotra nsporter was expressed in astrocytes within cortex, corpus callosum, hippoc ampus and cerebellum. In addition, co-localization of the cotransporter and glial fibrillary acidic protein (GFAP), or with aquaporin 4, was found in perivascular astrocytes of cortical cortex and white matter. The results in dicate that a time-dependent expression of the Na+-K+-Cl- cotransporter pro tein occurs not only in cortex but also in hippocampus, striatum, thalamus and cerebellum. In addition, the cotransporter is expressed in astrocytes a nd perivascular astrocytes of adult rat brain. (C) 2001 Elsevier Science BY All ri-hts reserved.