A procedure for measuring neuromelanin in neurocytes by a TV-image analyser

With the aid of a Robotron A6471 type TV-image analyser the number, total area, area of one granule and density features (sum, average of gray values and average gray value of one pigment granule) of melanin granules in neurocytes of the substantia nigra in 3-month-old and 3-year-old male rats were determined. The number of cells in sections of identical areas was similar in the young and old rats. A statistically non-significant difference between the two age cohorts in the proportion of neurocytes with and without melanin was found; 773 (48.1%) and 853 (51.8%), in the young rats and 1219 (65.1%) and 652 (34.8%) in the old ones. Within the melanin containing neurocytes, however, statistically conspicuous, age-related differences in the number, area and density features of melanin granules were discovered. The majority of the neurocytes in young rats contained numerous, small sized neuromelanin granules, whereas in the majority of the neurocytes of old rats smaller numbers of large sized, neuromelanin granules were detected.