By combining the histochemical fluorescence method for catecholamines (CA) and 5-hydroxytryptamine (5-HT) with electron microscopy it has been possible to study the ultrastructure of the central CA and 5-HT nerve cells of the locus coeruleus and the nuc. raphe dorsalis. The CA and the 5-HT nerve cells have the same ultrastructural characteristics: a well-developed granular reticulum and a peri-nuclearly situated, prominent Golgi apparatus which almost completely surrounds the nucleus. Agranular vesicles (300–500 Å in diameter) are found mainly in a perinuclear area in association with the Golgi apparatus. They are similar to the small agranular vesicles present in large numbers in the presynaptic bags. A few complex vesicles and granular vesicles (600–1200 Å in diameter) are noticed throughout the cytoplasm. No certain changes are observed in the different types of vesicles after treatment with reserpine or MAO inhibitors.
It is suggested that the agranular vesicles contain CA, since these vesicles are most numerous in a perinuclear area where the concentration of the amines are highest. In spite of the low number of agranular vesicles present as compared to the high number found in nerve terminals they might store at least a considerable part of the amines, since the amine concentrations are much lower (100–1000 X) in the nerve cells than in the terminals.