[Serotoninergic innervation of the paraventricular organ in chick embryo and chick; histofluorescence and autoradiography study optic and electron microscopy].

Fluorescence microscopy (Falck and Hillarp technique) of 11th day old chick embryo shows aminergic neurons and processes in the paraventricular organ area. Administration of tritiated amines permits us to observe uptake and storage of serotonin only as early as the 10th day; this suggests a very early hypothalamic serotoninergic nervous system differentiation.