Localization of Biogenic Amines by Fluorescence Microscopy

Abstract

The first fluorescence microscopic localization of catecholamines was reported by Eränkö (1955), who observed a yellow fluorescence of striking intensity in the adrenal medullae of several mammalian species after fixation of the organs in aqueous formaldehyde solutions. The identification of other storage sites for catecholamines and for other biogenic amines by fluorescence microscopy had to await the introduction of tissue processing methods that avoided diffusion of the amines. In 1961 two research groups independently applied the technique of freezing, freeze-drying, and treatment of tissue blocks with formaldehyde vapor: Hillarp and his colleagues demonstrated the histochemical localization of catecholamines in central and peripheral adrenergic nerve terminals (Falck and Torp, 1961; Carlsson et al., 1962; Falck, 1962), while Lagunoff et al. (1961) demonstrated fluorescence of what appeared to be histamine in rat mast cells, although the situation was complicated by the presence of 5-hydroxytryptamine. The latter workers commented on the possibility that both catecholamines and 5-hydroxytryptamine formed fluorescent derivatives after reaction with formaldehyde. The plethora of subsequent publications concerning the adrenergic innervation of central and peripheral tissues is largely attributable to the enthusiasm of the colleagues and students of the late Prof. Hillarp, and has led to a profound clarification of the nature of adrenergic innervation, as well as providing the basis for the electron microscopic study of adrenergic neurons and other monoaminergic systems.