Postnatal development of glial fibrillary acidic protein immunoreactivity in the hamster arcuate nucleus

The postnatal development (from 2 days to 1 year) of glial fibrillary acidic protein (GFAP) immunoreactive cells was studied in the arcuate nucleus of male hamsters. In the first postnatal week, GFAP immunoreactivity was observed in radial glial cells whose cell bodies were located in the ependymal layer. Cell processes of GFAP immunoreactive radial glia crossed the arcuate nucleus and reached the pial surface, where they formed a thin and incomplete external limiting membrane. During the second postnatal week, some immunoreactive cell bodies were also located far from the ependymal layer. Some of these cell bodies presented processes that made contact with the ependymal layer whereas others, probably corresponding to maturing astrocytes, did not show ventricular connections. In the third week, only astrocytes showed GFAP immunoreactive perikarya and their immunoreactive processes reached either the blood vessels to form end-feet, or the basal hypothalamic zone to form the glia limitans. In successive weeks, there was an increase of the amount of GFAP-immunoreactive profiles on the glia limitans and surrounding the arcuate nucleus blood vessels. After the 6th postnatal week we observed some GFAP-immunoreactive cells close to arcuate neurons. The number of these cells increased from the 8th postnatal week. From this age on GFAP immunoreactive astrocytic processes compartimentalized the arcuate nucleus defining several rows of aligned neurons. These results indicate that the cytoarchitectonic organization of GFAP immunoreactive elements and their relationship with neurons, blood vessels and pia is not completed until the first 8 weeks of postnatal life in the arcuate nucleus of the hamster.