Ontogeny of glutamine synthetase in rat brain.

The developmental pattern of glutamine synthetase (GS) in rat brain has been studied with respect to that of the cells involved in the synthesis of the enzyme. GS activity is very low until day 13 after birth, rises sharply between days 13 and 15, and slowly thereafter. In contrast, more than half of the total number of protoplasmic astrocytes-the cells involved in synthesis of GS-are formed by day 12, following which the rate of proliferation declines considerably. GS is precociously inducible by cortisol in purified protoplasmic astrocytes, in organ cultures of 6-13 day rat brain and in the brains of cortisoladministered 12 day rats. These results and the temporal coincidence of the period of increase of GS with the onset of the function of adrenal cortex suggest that GS activity in the developing rat brain is under steroidal control.