Aging in the rat medial nucleus of the trapezoid body. II. Electron microscopy.

The medial nucleus of the trapezoid body (MTB), the largest cell group of the rat superior olivary complex, was studied ultrastructurally in five groups of rats ranging in age from 2 to 33 months. Relatively little aging pigment (lipofuscin) accumulates intraneuronally, even in rats aged 33 months. The heaviest accumulation of age pigment is in glial and perivascular cells of the MTB. In rats aged 24-33 months, there is evidence of axonal and dendritic degeneration in the MTB neuropil. Aged rats also show evidence of degeneration of nerve endings. This includes the loss of calycine axosomatic terminals synapsing with MTB principal cells. All of the ultrastructural changes observed in the MTB gradually increase in frequency with advancing age.