GFAP immunoreactive structures in the hypothalamo-hypophyseal axis of the teleost Diplodus sargus.

The glial fibrillary acidic protein (GFAP) is the characteristic cytoskeletal protein of astroglia. It is a reliable molecular marker for all astroglial cells and shows also considerable stability in its antigenic characteristics across vertebrate phylogeny. The study of astroglial cells in the hypothalamo-hypophyseal axis of the teleost fishes is particularly significant because in these vertebrates there is no distinct portal system. The adenohypophysis, unlike the other vertebrates, is directly innervated by neurosecretory fibres and the pituicytes, typical astroglial cells of the neurohypophysis, may have an active role in the release of neurohormones. We report the occurrence and distribution of GFAP immunoreactive structures in the hypothalamo-hypophyseal axis of the teleost Diplodus sargus. For this study was used a polyclonal anti-cow GFAP antiserum (DAKO): deparaffined, dehydrated sections were immunostained using the ABC technique and the Immunogold technique was applied for the ultrastructural immunodetection. GFAP-immunoreactive fibres appeared particularly organized in bundles close to the ventricles and the hypophyseal stalk. These fibres were generally thin but they appeared more thick and numerous in the hypophyseal stalk where we observed as they were projected from hypothalamus towards neurohypophysis. Thin and isolated GFAP-immunoreactive fibres, corrisponding to the pituicytic processes, were found in the all neurohypophysis where was possible also to observe the pituicytic cellular bodies immunostained. This evidence was also confirmed by ultrastructural immunodetection: the gold particles appeared on the cellular body and on the long processes of the pituicytes of Dark type.