A modification of the histochemical fluorescence method for the improved localization of 5-hydroxytryptamine

Summary By using a modified formaldehyde gas treatment, it has been possible to improve the histochemical fluorescence method for the demonstration of 5-hydroxytryptamine. A certain improvement of the localization of catecholamines has also been obtained.The modified histochemical procedure involves a primary treatment with a formaldehyde gas of a humidity which does not cause any noticeable diffusion. After this it is possible to retreat the tissue specimen with a formaldehyde gas of higher humidity resulting in increased yields of the final fluorescent compounds. In spite of this improvement of the formaldehyde gas technique for the demonstration of 5-hydroxytryptamine, it cannot be considered as sensitive as that for catecholamines. The reasons for this are discussed.