Direct evidence that complex experience increases capillary branching and surface area in visual cortex of young rats

Rats housed in complex environments with toys and other rats generate new synapses, and the expanding neuropil tends to spread apart existing blood vessels. Previous work demonstrated that weanling rats kept in complex environments had more closely packed capillaries, suggesting that new capillaries had sprouted into the newly added neuropil. The present study directly investigates the issue of new branching by using india ink perfusions of weanling rats kept for 30 days in a complex environment (EC), paired in standard caging (SC), or individual cages (IC) to examine the density of capillary branch points and the capillary surface area per unit tissue volume. EC rats had a greater density of branch points than the SC and IC littermates, a finding consistent with increased capillary sprouting. Capillary surface area per unit tissue volume and the number of branch points per unit of capillary surface area were also higher for EC rats. This suggests that blood vessels of EC rats branch off more often than those of animals kept in more standard conditions, and provides further evidence that complex experience can increase angiogenesis in cerebral cortex of postweanling rats.