Development of nitric oxide synthase in the avian retina

Nitric oxide is an important intercellular messenger in the central nervous system. Our previous work showed the presence of NADPH-diaphorase activity, that partially corresponded to nitric oxide synthase, in the chick embryo retina. In the present study, we have demonstrated the presence of nitric oxide synthase in the chick retina measuring the conversion of 3(H)arginine to 3(H)citrulline. We found that the enzyme is dependent on the presence of calcium, calmodulin and NADPH and is inhibited by the arginine analog L-NG-nitroarginine. The enzyme activity was higher at 8-day-old embryonic retinas, decreased at 13-14 days and attained minimal levels at 15 days up to the post-hatching period. Glutamate stimulated nitric oxide synthase activity approximately 4 fold, an effect that was blocked by the NMDA antagonist MK-801. The results indicate that the glutamate/nitric oxide system has important functions during retinal development.