Preservation of hippocampal neuron numbers in aged rhesus monkeys

To investigate whether or not aging of nonhuman primates is accompanied by a region-specific neuron loss in the hippocampal formation, we used the optical fractionator technique to obtain stereological estimates of unilateral neuron numbers of the hippocampi of eight young (0-4 years) and five aged (18-31 years) male rhesus monkeys (Macaca mulatta). Our results show a preservation of neurons (mean x 10(3) S.D. x 10(3)) in the subiculum (young = 588 +/- 124, aged = 612 +/- 207), CA1 (young = 1051 +/- 249, aged = 1318 +/- 311), CA2 (young 100 +/- 18, aged = 113 +/- 12), CA3 (young = 478 +/- 125, aged = 509 +/- 139), hilus (young = 337 +/- 115, aged = 394 +/- 90), and dentate gyrus (young = 5550 +/- 1725, aged = 7799 +/- 2087) of the hippocampal formation. These results confirm a previous stereological study in rhesus monkeys, but are in conflict with data for humans, showing age-dependent region-specific alterations in the hippocampal formation. (C) 2002 Elsevier Science Inc. All rights reserved.