TRANSIENT EXPRESSION OF S-100 BY MELANOTROPES OF THE RAT PITUITARY INTERMEDIATE LOBE DURING DEVELOPMENT

S-100, an acidic calcium-binding protein, is co-localized with vimenti n in glial-like cells in the adult rat pituitary intermediate lobe. S- 100 and melanotrope markers were not co-localized in the adult. During development, S-100 and vimentin were not co-localized but appeared in cells with different morphological characteristics. S-100 was co-loca lized with POMC mRNA and beta-endorphin during prenatal time and the f irst three postnatal weeks. This was demonstrated by double-label immu nohistochemistry, using combinations of antisera against S-100, viment in and beta-endorphin, and in situ hybridization histochemistry for PO MC mRNA combined with immunohistochemistry for S-100. In the second an d third weeks of postnatal development, S-100 was observed in fewer me lanotropes and more frequently in stellate cells, which also expressed vimentin. Thus, 5-100 appeared to be transiently expressed in melanot ropes during prenatal and early postnatal development. S-1OD serves as a neurotrophic and glial maturation factor in the CNS. Since S-100 ex pression in melanotropes coincides with the onset of dopaminergic inne rvation and morphological changes in glial-like cells of the lobe, it could have similar functions in the rat pituitary intermediate lobe.