New Insights into GFAP Negative Astrocytes in Calbindin D28k Immunoreactive Astrocytes

Glial fibrillary acidic protein (GFAP) is commonly used as a specific marker for the identification of astrocytes. Nevertheless, it is known from the literature that astrocytes in situ in contrast to cultured astrocytes may feature lower levels of GFAP. In order to characterize the properties of GFAP in Calbindin D28k immunoreactive astrocytes, we use primary astrocyte cultures from cells of new-born mice. A double fluorescence immunocytochemical analysis reveals that GFAP in cultured Calbindin D28k astrocytes behaves differently depending on whether the medium contains foetal bovine serum (FBS) or not. The novelty in our study is, however, that a high percentage of Calbindin D28k cultured astrocytes in a medium with 10% FBS are GFAP negative. In addition, the study shows that Calbindin D28k astrocytes have (i) a different morphology and (ii) a higher concentration of Calbindin D28k in the nucleus than in the cytoplasm. The study provides new evidence that in order to fully understand the characteristics of astrocytes, astrocytes which are Calbindin D28k positive have to be investigated.