Age related changes in neuron number in the mouse red nucleus.

The red nucleus of the ASH/TO stain mouse brain was examined at 6, 22, 25, 28 and 31 months of age using quantitative histological techniques. Three types of neurons, large, medium and small, were identified on grounds of size and structural characteristics. The number of large neurons remained constant from 6 to 25 months of age before declining from 385 +/- 24 at 25 months to 126 +/- 12 at 31 months. The number of medium neurons remained constant from 6 to 31 months of age with an overall mean of 1139. The number of small neurons showed a slight decline at 31 months of age. The nuclear diameter of large neurons increased from 14.7 microns at 25 months to 15.6 microns at 28 months and this increase in diameter was statistically significant. The nuclear diameter of neither medium (mean 12.0 microns) nor small neurons (mean 9.6 microns) varied significantly with age.