Stability of neuron number in cortical barrels of aging mice.

The question of whether age-related neuron loss occurs in the cerebral cortex of rodents, as it apparently does in humans, has not been directly answered by previous studies. The barrel, a discrete morphological and functional unit in rodent somatosensory cortex, is a favorable system in which to address the problem of neuron loss during senescence. The numerical density and absolute number of neurons as well as barrel volume were determined from a computer-assisted three-dimensional reconstruction of thick (100 microns) and semithin (1 micron) sections through a single barrel, C3, from inbred mice (C57Bl/6NNia) at 4, 12, 22, 26, 30, and 33 months of age. The number and density of neuron and glial cells and the volume of the barrel did not change significantly with age. These data indicate that neuron loss is not a universal phenomenon in senescence and that there may be significant species differences in the aging of laboratory rodents and humans.