Glutamine synthetase and energy metabolism enzymes in cultivated chick neurons and astrocytes: modulation by serum and hydrocortisone.

Primary cultures of astroglial cells and of neurons obtained from chick embryos were grown in culture medium with and without serum added. The expression of glutamine synthetase (GS) in the cultured nerve cells was investigated immunocytochemically and biochemically. The cellular localization of GS in cerebellar tissue sections and in cerebral cortex of chick embryos was investigated by immunohistochemical staining. In tissue sections the enzyme is only present in astrocytes and their processes; neurons and their structures do not express the enzyme. In contrast, in pure neuronal primary cultures, a high level of GS was detected by biochemical and immunochemical methods. Thus, our results clearly indicate the presence of GS in pure neuronal cell cultures and its absence in this type of cells in vivo. Removal of serum from the culture medium enhanced GS levels in primary astrocyte cultures, but was without effect on GS activity in neurons. Addition of calf serum to the culture medium induces a two-fold increase of cellular lactate dehydrogenase (LDH) activity in neurons by increasing specifically the M subunit containing isoenzymes. The sensitivity of chick astroglial cells and neurons toward the GS inducing effect of hydrocortisone and modulation of its effect by serum was also investigated. Differences in the sensitivity of the two types of nerve cells in culture toward the GS inducing effect of hydrocortisone, and the effect of serum could be demonstrated.