The rôle of neurohumours in early embryogenesis. : I. Serotonin content of developing embryos of sea urchin and loach

Abstract

Serotonin (5-hydroxytryptamine, 5-HT) is shown to be present in early embryos of Deuterostomia, in the sea urchin Strongylocentrotus dröbachiensis, and in a teleost—the loach Misgurnus fossilis. 5-HT is found in mature unfertilized eggs of S. dröbachiensis’, soon after fertilization the concentration of this substance rises sharply, while the first four cleavage divisions are accompanied by rhythmical rises in 5-HT content. In the early blastula 5-HT concentration is low, it rises somewhat in the mid- and late blastula and at the beginning of gastrulation, dropping again in the late gastrula to zero. Pluteus formation is accompanied by the resumption of 5-HT synthesis. 5-HT seems to appear in the loach eggs within the first minutes of fertilization. The first three cleavage divisions are accompanied by sharp fluctuations of 5-HT content, although no distinct synchrony could be found between the 5-HT rises and divisions in this case. Up to the stage of the late blastula no 5-HT is found. Two high 5-HT peaks are observed during gastrulation. From this and earlier work the suggestion is put forward that 5-HT is a universal participant in the processes of early embryogenesis both in Protostomia and Deuterostomia. The elucidation of the rôle of this embryonic hormone requires further investigation.