Neuromelanin in the substantia nigra of adult horses.

The structure and histochemical properties of neuromelanin in the Substantia nigra of the horse were studied by light and electron microscopy. Morphological, histochemical and cytochemical evidences showed the presence of a melanin component in some pigment granules, even if a large quantity of granules displayed only the properties of lipofuscins. Pigment formation in the neurons of the Substantia nigra of the horse may take place through the tyrosine-tyrosinase enzymatic pathway, as shown by positive Dopa-reaction. The results obtained were discussed in reference to the possible use of melanin as a marker for catecholaminergic neurons in the brainstem of the horse.