ENDOCRINE-DEPENDENT ACCUMULATION OF IGF-I BY HYPOTHALAMIC GLIA

TANYCYTES are specialized glial cells of the hypothalamus and median e minence. Immunoreactive insulin-like growth factor I (IGF-I) levels fl uctuate in tanycytes with the natural variations in sex steroids assoc iated with the ovarian cycle. To determine whether these changes are a s a result of differences in IGF-I accumulation, the peptide was label led with digoxigenin and injected into the lateral cerebral ventricle. Tanycyte-like cells specifically accumulated digoxigenin-labelled IGF -I. This accumulation was mediated by IGF-I receptors and showed marke d differences during the oestrous cycle, being low in the afternoon of pro-oestrus and high in the afternoon of oestrus. These results indic ate that the accumulation by tanycytes of IGF-I or IGF-I fragments cap able of receptor-mediated internalization is under endocrine control, suggesting that hypothalamic glia may be involved in neuroendocrine re gulation.