Differential modulation of glutamate metabolizing enzymes in mouse and chick cultured glial cells by insulin

The effect of physiological concentrations of insulin (2 and 20 ng/ml) on glutamine synthetase (GS) and glutamate dehydrogenase (GDH) activities were compared in mouse and chick glial cells in culture. Addition of insulin to serum-containing medium increased the level of GS and GDH activities in glial cells prepared from 14-15-day-old embryonic mice. A similar but less pronounced effect was observed with glia derived from newborn mouse brain. In absence of serum, addition of insulin had no effect on the tested enzymes. The effects of insulin on enzymatic activities of glial cells from 14-15-day-old embryonic chick brain hemispheres were, in contrast, quite different. A significant decrease of GS activity was induced by the hormone, only in the absence of serum. Conversely, the presence of serum enhanced an inhibitory effect of insulin toward chick GDH. The different effects of insulin and the different serum dependence observed for the mammalian and the avian model could reflect fundamental chemical differences between both species as indicated by immunoelectrophoretic analysis. However, it can be concluded that insulin may be a physiological factor regulating glial maturation and amino acid neurotransmitter metabolism in the central nervous system.