Ultrastructure of neuromelanin granules in dog substantia nigra at different ages.

: The Authors study through ultrastructural observations the sequence of processes concerning the appearance and the depositing of the neuromelanic pigment in the neurons of dog mesencephalic substantia nigra nucleus at different ages. The results are as follows: in the one year old dog, in a low percentage of lysosome-like oval organelles, few masses, strongly electron-dense, appear on the matrix. In the five year old dog, these masses are deposited and increased in quantity inside many more organelles. In the specimens extracted from older dogs, these organelles, characterized moreover by the presence of lipidic globules, merging in groups, became larger and more irregular. The Authors discuss the results obtained with the ultrastructural observation, compared with those obtained with the optical methods.