Comparative investigations of glutaminase development in cerebral cortex of chick embryo and in primary cultures of neurons and glial cells.

Glutaminase activity was determined in pure cultures of neurons, glial cells and in mixed cultures obtained from chick embryo brain. The development of this enzyme was observed periodically over time and compared to its evolution in corresponding cerebral hemispheres during embryonic and postnatal development. The specific activity of brain glutaminase increased between the twelfth and sixteenth day of embryogenesis. A similar increase was observed in cultures of neuroblasts during the corresponding period of time, although the activity in culture was about one-third lower than in vivo. In contrast to neurons, there was no significant increase of glutaminase activity in glial cells before the fifteenth day of culture. The enzyme level in glial cells between the thirteenth and fifteenth days of culture was approximately 25% of that in 7- and 8-day-old neurons. The different development of glutaminase activity in neurons and glial cells was demonstrated in both pure and mixed cultures. The results support the hypothesis that there is a glutamine shunt from glial cells to neurons.