A morphometric study of blood vessel, neuron and glial cell distribution in young and old rat brain.

The distribution of blood vessels, neurons and glial cells through the depth of the cortex in young and old rats has been investigated using semi-automatic quantitative morphometry. Toluidine blue stained semithin sections cut perpendicularly to the surface of the brain and spanning pia to white matter were analysed. There was a strong correlation between the distribution of blood vessels and neurons (P less than 0.001), with peaks in numerical density (Na) occurring at histological layers IV and VI. This correlation was not altered with age. Glial cell distribution was not correlated with either vessel or neuron distribution, but may be related to areas of high synaptic density. In the older animals (90 weeks) blood vessel Na and surface area to volume ratio (Sv) were significantly increased as was glial Na. Neuron Na was unaltered. These changes and the significant decrease in cortical thickness also found are consistent with neuronal loss in ageing and especially, preferential loss at layer IV.