Histochemical observations on rodent brain melanin

The presence or absence of melanin and neuromelanin in rodent brain was determined by means of light microscopic histochemistry. Melanin in melanocytes located in meninges and along cerebral capillaries occurred in abundance in C57 black mice and to a lesser extent in pigmented rats. Meningeal melanin bound cupric and ferrous ions, reduced ferricyanide, and appeared golden-brown in the bright field, light scattering in the dark field, and absorbant in the ultraviolet. Eleven aging albino rats were utilized to ascertain if the age related pigment, neuromelanin was present in neurons of the substantia nigra. Evidence of neuromelanin was not obtained as the cupric and ferrous ion uptake reactions were negative and neuromelanin could not be seen in the bright or dark field. Substantia nigra neurons did exhibit histochemical reactions for lipofuscin, however, as acid phosphatase positive, periodic acid-Schiff positive, and autofluorescent granules were demonstrated.