Glutamine synthetase in the avian diencephalon

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Abstract
Glutamine synthetase (GS) activities are high in the nucleus rotundus of the avian diencephalon in late embryos and hatched chicks. The nucleus rotundus is known to be one component of a visual pathway in birds involving also the neural retina, the optic tectum and the cerebral ectostriatum. Since previous studies have shown that the retina, tectum and ectostriatum have high GS activities as well, the enzyme is considered to be clearly associated in some measure, although not exclusively, with processes subserving vision. Some of the possible normal functions for GS at specific neural sites are discussed.Hydrocortisone promotes GS levels in vitro in the embryonic diencephalon, just as GS activities are increased with this steroid in cultures of embryonic retina, tectum and cerebrum. The effects of steroid on GS in the diencephalon appear to be general and not restricted to the nucleus rotundus or the visual pathway.