Presence of serotonin in the palate just prior to shelf elevation

Since serotonin and its antagonists affect shelf rotation in mouse embryo culture, experiments were carried out to determine whether a serotonergic system is present in the palate. Employing [³H]5-HT, day-14·5 embryos incorporated the monoamine into palates. Active uptake of [³H]5-HT was shown since excised palates incorporated 9-fold more radioactivity at 37°C than at 4°C. Synthesis of palatal serotonin was measured. Embryos were cultured in the presence of the serotonin precursor, [³H]5-HTP, and radioactive 5-HT was monitored in the palate by thin-layer chromatography. Furthermore, excised palates were incubated with [³H]5-HTP and radioactive 5-HT was measured. Incorporation was linear for about 6 h. In addition, another radioactive compound was detected which had the same Rf as the methylated derivative, 5-methoxytryptamine. Synthesis of this compound was appreciable, about 30% of that of serotonin. Levels of serotonin in the palate were measured by high pressure liquid chromatography. Palates at day 14·5 of gestation contained 0·40 ng serotonin/ mg protein, which was greater than that of tongue (0·33), body (0·14) but less than that of brain (3 09). Serotonin in palate and other embryonic tissues increased with time of development. Dopamine levels in the palate and other tissues were also determined. The distribution of serotonin in the palate was analyzed by culturing day-14-5 embryos in the presence of [³H]5-HTP, and after aldehyde fixation, paraffin embedment and sectioning, autoradiography was performed. Grains were observed throughout the palate in cells of regions 2 and 3, internal mesenchyme, tooth germ, and epithelium. Surprisingly, the pterygopalatine nerve, maxillary nerve and pterygopalatine ganglion contained an appreciable concentration of grains. Thus, the presence of serotonin in the palate is consistent with the neurotransmitter playing a role in shelf elevation.