Sexual dimorphism of glial fibrillary acidic protein (GFAP) immunoreactivity in the rat interpeduncular nucleus

The intensity of immunostaining for the glial fibrillary acidic protein (GF AP) is outstandingly high in the interpeduncular nucleus. This nucleus was compared in males and females for its GFAP immunoreaction. Immunohistochemi stry was carried out on free floating vibratome slices and evaluated by sur face densitometry. While in males the reactions were similar, females showed individual variat ions. Since the interpeduncular nucleus is a hormonally inactive brain area where gonadal hormones do not induce plastic synaptic changes, it is concl uded that concerning this astroglial marker a sexual dimorphism exists also outside the "endocrine brain".