Hormonal induction of glutamine synthetase in cultures of embryonic retina cells: requirement for neuron-glia contact interactions.

Cortisol induces glutamine synthetase (GS) in gliocytes of chick embryo neural retina. Using adherent cultures of retina cells we have demonstrated that responsiveness of the gliocytes to GS induction by the hormone requires contact with neurons. GS is not inducible in high-density cultures depleted of neurons and consisting only of gliocytes. In neuron-containing cultures, induced GS was detected immunohistochemically only in those gliocytes that were closely juxtaposed with clusters of neurons. Unlike the induction of GS, the expression of carbonic anhydrase-C (which does not require cortisol) persisted in these glia cells also in the absence of neurons. The nature and role of glia-neuron interactions in the hormonal induction of GS are briefly discussed.