The relationship between lipofuscin and neuromelanin in some sites of the nervous system of the horse.

Histochemical and cytochemical features of neuronal pigment in the spinal cord, and in the sympathetic and spinal ganglia of the adult horse have been studied. Light and electron microscopical observations revealed that lipofuscin pigment is present in the spinal ganglia and in the spinal cord, whereas in the sympathetic ganglia both lipofuscin and neuromelanin are present. The ultrastructural studies showed that lipofuscin granules exhibited a triphasic organization consisting of a matrix, a system of lamellae and one or more lipid vacuoles. Neuromelanin granules have structural features in common with lipofuscin-like granules, except the former types store a highly electron dense material on their matrix. The electron dense material has been identified as melanin by a modification of the Lillie ferrous sulfate reaction applied at the ultrastructural level. From the ultrastructural appearance and cytochemistry of the neuronal pigments in horse it is concluded that neuromelanin should be considered as melanized lipofuscin. The possibility that the different ratio of lipofuscin to melanin within the same granule is responsible for the peculiar reaction of certain neuromelanin granules to lipophilic dyes, the PAS reaction, a histochemical assay for melanin and exposure to ultraviolet light, is discussed.