Estradiol promotes cell shape changes and glial fibrillary acidic protein redistribution in hypothalamic astrocytes in vitro: a neuronal-mediated effect.

We have previously shown that in hypothalamic mixed neuronal-glial cultures both astrocytic shape and distribution of glial fibrillary acidic protein (GFAP) are modified by estradiol. In the present study, we have investigated whether or not the presence of neurons is necessary for these hormonal effects. In mixed neuronal-glial hypothalamic cultures the proportion of process-bearing GFAP-immunoreactive cells was significantly increased after treatment for 30 min with 10(-12) M 17 beta estradiol. This effect was present for at least 1 day and was reverted by incubating the cells in estradiol-free medium. Estradiol incubation resulted in a progressive differentiation of GFAP-immunoreactive cells from a flattened epithelioid morphology to bipolar, radial, and stellate shapes. This effect was not observed in pure hypothalamic glial cultures. Furthermore, incubation of hypothalamic glial cells with medium conditioned by estradiol-treated mixed hypothalamic cultures did not affect the shape of GFAP-immunoreactive astrocytes. In contrast, addition of hypothalamic neurons, but not cerebellar neurons or fibroblasts, to established hypothalamic glial cultures affected the development of estradiol sensitivity in astrocytes. These results indicate that estradiol induction of shape changes in hypothalamic astrocytes is not only dependent on the presence of hypothalamic neurons, but that physical contact between astrocytes and neurons is necessary for the manifestation of the effect of this hormone.

Ontogeny of insulin-like growth factor I, its receptor, and its binding proteins in the rat hypothalamus.

A role for the insulin-like growth factors (IGFs) in brain growth and differentiation has recently been suggested. In previous studies on fetal hypothalamic cells we found a trophic influence of IGF-I on in vitro survival and differentiation of both neurons and glia. We have now investigated the expression of IGF-I, its receptor and its binding proteins in the rat hypothalamus to determine whether endogenous IGF-I might serve as a trophic factor during development of this brain area. Both IGF-I receptors and IGF-I binding proteins showed marked developmental stage-dependent variations. Thus, IGF-I receptors as measured by both binding and cross-linking techniques, were highest during fetal life and steadily decreased thereafter to reach low adult levels. Changes in receptor numbers rather than in its affinity constant accounted for the differences seen in binding activity during development. In addition, we found 3 different IGF-I binding proteins (IGFBPs) of apparent Mr of 24, 29 and 32 kDa respectively, whose levels also showed a specific developmental pattern. Highest levels of the 29 and 32 kDA IGFBPs were found in fetal and early postnatal life, whereas levels of the 24 kDa form were highest in young adults. Changes in the concentration of IGFBPs rather than in their affinities for IGF-I accounted for the different binding capacities found. Using a specific IGF-I radioimmunoassay we found that IGF-I-like immunoreactivity (IGF-I-li) levels had no direct correlation with developmental stage. IGF-I-li levels oscillated with no apparent trend throughout development of the hypothalamus.(ABSTRACT TRUNCATED AT 250 WORDS)