Aging and the Meynert cells in rhesus monkey primary visual cortex.

We have assessed the effects of aging on the cell bodies of the large Meynert cells in layers V and VI of the rhesus monkey primary visual cortex by comparing the frequency, size, and cytology of these neurons in three young (5-6 years of age), one middle-aged (12 years of age), and four old monkeys (25-35 years of age). In the young monkeys there is an average of 20.8 Meynert cells beneath 1 mm2 of cortical surface, and in the old monkeys the value is 22.3 cells. The cell bodies of these large pyramidal cells do not become smaller with age, and surprisingly they accumulate only small amounts of lipofuscin. The conclusion is that in the rhesus monkey there is no loss of Meynert cells with age and that aging has little effect on the morphology of the cell bodies of these neurons.