Stability of neuron number in the subthalamic and entopeduncular nuclei of the ageing mouse brain.

The subthalamic and entopeduncular nuclei of mice aged 6, 15, 25, 28 and 31 months were examined in parasagittal 6 microns sections using quantitative histological techniques. The mean number of neurons in the subthalamic (overall mean 5366) and entopeduncular (overall mean 1101) nuclei did not vary significantly with age. The number of sections containing the subthalamic nucleus increased progressively in number with age with the increase beginning between 15 and 25 months. The increase in size of the nucleus was accompanied by a decrease in neuron packing density. No similar changes were observed in the entopeduncular nucleus despite its close anatomical and functional relationships to the subthalamic nucleus.