[Embryonic pineal organ of Lacerta vivipara J. II. Electron microscopic study of 3H-5-hydroxytryptophan (3H-5-HTP) incorporation in the secretory rudimentary photoreceptor cells (SRP). The gradient of biochemical differentiation (author's transl)].

As the biosynthesis of indoleamines in Lacerta vivipara embryos from stage 36 to 40 is concerned, our ultrastructural radioautographic studies reveal a selective incorporation and metabolism of 3H-5-HTP in one of the two "sensory" cell types, the Secretory Rudimentary Photoreceptor cells (SRP). Specific radioautographic reactions are constantly for the most part located on the dense secretory granules which are stored in the basal processes of the SRP and originate in the Golgi complex. During ontogenesis, the amount of autoradiographically demonstrable tritiated indoleamines and the number of dense secretory granules increase at the same rate. The combination of electron microscopic and radioautographic studies shows that, during ontogenesis, a close relation exists between the cytological differentiation of the SRP and their capacity to synthesize and store indoleamines.