Distribution of glial fibrillary acidic protein-immunopositive structures in the brain of the domestic chicken (Gallus domesticus).

The present study is the first comprehensive mapping of glial fibrillary acidic protein (GFAP)-immunopositive structures in the avian brain. Two main types of GFAP-immunopositive elements were observed: (1) nonbranching fibers, occasionally twisted or varicose, and (2) star-shaped cells. Long immunostained fibers originate from the lateral ventricle to form three bundles. Fibers of the dorsal group, emanating from the dorsal/lateral corner of the ventricle, course in lateral, anterior, and ventral directions forming a semidome, which separates the outer pallial (lateral cortical) regions from the underlying striatal mass. The middle group of fibers is directed anteriorly and laterally corresponding to the laminae frontales superior and suprema. The ventral fiber bundle is conical and traverses the lobus parolfactorius, crossing also the lamina medullaris dorsalis (the latter consisting mainly of star-shaped cells). The hippocampus, septum, and hypothalamus also contain straight radial fibers. In some areas, given their variable orientation, the fibers cannot be regarded as merely persisting radial glia. In the telencephalon, the nuclei basalis, accumbens, ectostriatum, paleostriatum primitivum, and the ventral paleostriatum are particularly rich in GFAP-positive cells, whereas the neostriatum, hyperstriatum, and paleostriatum augmentatum are almost devoid of GFAP labelling. Certain nuclei of the thalamus and the lower brainstem are conspicuous by their low levels of GFAP immunoreactivity. The Bergmann glia were GFAP-immunonegative.