This study is another in a series of investigations attempting to define the changes in the brain as a consequence of environmental manipulation. Cortical depth and neuron size measurements were taken on brains of rats from enriched (ECT) and impoverished (IC) environments.
Celloidin embedded, 10 fi, transverse sections of formalin fixed rat brains were stained with thionin. Ten representative sections from each brain were taken, utilizing subcortical landmarks to insure uniform sampling. Cortical depths were measured on microslide projected drawings beginning at the midline and proceeding laterally. The number of readings per hemisphere ranged from 41 to 46. The greatest increases in depth were found in the sections from the posterior commissure landmark. At this position the increases in four regions, proceeding medially to laterally, were as follows: A, 5.2% ( p < 0.001); B, 6.3% ( p < 0.001); C, 3.2% (p < 0.01); D, 1.6% (NS).
Perikarya and nuclear size measurements were taken with a planimeter on microa m projected outlines. The cortex was divided into upper, middle and lower levels, and within each third, cell size increases were noted, with the outer third showing the greatest increases. The ECT perikarya were greater than the IC by 17.7% ( p < 0.001) in the upper level, by 7.2% (p < 0.05) in the middle level, and by 11.6% (p < 0.01) in the lower level.