Ultrastructural heterogeneity of neuronal lipofuscin in the normal human cerebral cortex.

The ultrastructure of the age pigment in neurons of the normal human isocortex was investigated in seven autopsies and two biopsies. In the autopsies four cortical areas of Brodmann, viz. 6, 7, 11 and 17 were studied. The lipofuscin granules appear as complexes composed of lipid and pigment. These are characterized by their shape, frequency per neuron, the relative amount of pigment and lipid in the complexes, and the structure of the matrix. The neurons contain numerous varieties of lipopigment, six of which occur with great frequency and are designated as varieties 1-6. Variety 1 is found in pyramidal neurons and seems to be characteristic of long loop projectory neuronal systems. 2 is found in large non-pyramidal neurons. 3 is found in pyramidal and non-pyramidal neurons. 4, 5 and 6 are found in non-pyramidal neurons. The pigment matrix is linear in all six varieties of lipopigment. Short linear elements are present in varieties 1, 2 and 5. Long linear elements are found in varieties 3, 4, and 6. Circular whorled arrangements are found in 4. We think that these varieties of lipofuscin may signify metabolic and/or functional differences of the different types of neurons and may contribute to the biochemical classification of cortical neurons.