Postnatal development of GFAP, connexin43 and connexin30 in cat visual cortex.

In cat visual cortex, neurons acquire progressively mature functional properties during the first postnatal months. The aim of this study was to analyze the development of astrocytes during this period. The patterns of expression of the glial fibrillary acidic protein (GFAP) as well as of two gap junction proteins expressed in astrocytes, connexin43 (Cx43) and connexin30 (Cx30), were investigated by immunohistochemistry and optical density measurements, in visual cortical areas 17 and 18 at four different ages: 2 weeks (postnatal days 12 to 15, P12-15), 1 month (P27-31), 2 months (P60-62) and beyond 1 year. Since visual experience is a key factor for neural development, the patterns of expression of these three proteins were studied both in normally-reared and monocularly deprived animals. Interestingly, the distribution of GFAP, Cx43 and Cx30 was found to change dramatically but independently of visual experience, during postnatal development, even beyond P60. During the first postnatal month, GFAP and Cx43 were mainly localized in the white matter underlying the visual cortical areas 17 and 18. Then, their distributions evolved similarly with a progressive decrease of their density in the white matter associated with an increase in the cortex. Connexin30 expression appeared only from the second postnatal month, strictly in the cortex and with a laminar distribution which was similar to that of Cx43 at the same age. In adults, a specific laminar distribution was observed, that was identical for GFAP, Cx43 and Cx30: their density was higher in layers II/III and V than in the other cortical layers.