Induction by Hydrocortisone of Glutamine Synthetase in Mouse Primary Astrocyte Cultures

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Abstract
Glutamine synthetase activity was investigated in developing primary astroglial cultures established from newborn mouse cerebral hemispheres. Between the 2nd and 4th wk of culture, there was little change in activity under our standard culturing conditions; when hydrocortisone (10 .mu.M) was added to the cultures for 48 h, the enzyme activity increased 2- to 4-fold, depending upon the age of the culture, with maximum response in 2 wk old cultures. The addition of dibutyryl cAMP (dBcAMP) to the culture medium caused morphological differentiation of the astroglial cells but eliminated the response of the cells to hydrocortisone. Culturing in elevated serum levels, which delays morphological differentiation and inhibits astroglial cytodifferentiation after exposure to dBcAMP, shifted the time of maximal response to hydrocortisone from 2-3 wk and prevented the abolishment of glutamine synthetase induction by dBcAMP. The induction of glutamine synthetase by hydrocortisone was prevented by actinomycin D (0.5 .mu.g/ml), indicating its dependence upon RNA and protein synthesis. Hydrocortisone apparently induces glutamine synthetase in neural tissues but does not require intact tissues for the induction.