The localization of catecholamine fluorescence to dog hypothalamic neuromelanin-bearing neurons.

By use of histochemical methods, a survey has been made of the localization of catecholamine to neuronal perikarya and processes in relation to neuromelanin accumulation in neuronal perikarya in the hypothalamus of dogs of various ages. Catecholamine was visualized in sections as a green fluorescence by means of the formaldehyde gasinduced fluorescence method of Falck and Hillarp. Neuromelanin, if also present in these sections, was identified on the basis of its characteristic optical properties as visualized through bright field, dark field and fluorescence microscopy. The study demonstrated a sequential replacement of temporally diminishing catecholamine fluorescence by accumulating neuromelanin within the same neuronal perikaryon wherein they were found to overlap during part of the 1st year of life. Catecholamine in processes in the perifornical region of the hypothalamus, where the neuromelanin-accumulating neurons were situated, was also diminished with age. If neuromelanin was extensively exposed to ultraviolet light, as required for viewing and for photography, the initially nonfluorescent pigment was converted to one which appeared fluorescent yellow. The larger and older accumulations of neuromelanin were more resistant to this induced alteration than the smaller and younger accumulations. These results support the concept that catecholamine contributes to the formation of neuromelanin although they do not exclude the possibility that the presence of both these substances in the same perikaryon is entirely coincidental.