Increases in cortical depth and glia numbers in rats subjected to enriched environment

Abstract We have previously reported anatomical and chemical changes in the cerebral cortex of rats living in an enriched, stimulating environment. The present study includes additional histological measures such as more extensive depth measures, differential cell counts, and cell size measurements. Celloidin‐embedded, thionin‐stained sections of the visual cortex from environmentally enriched rats and their impoverished littermates were measured. Two methods for calculating cortical depths were used: one, with an ocular micrometer taking eight measures lateral to the elevation in the corpus callosum on each hemisphere; two, on enlarged photographs taking 51 measurements 2 mm apart on each hemisphere. With the ocular micrometer method the cortical depth of the enriched brains was 6.4% greater than the depth of the impoverished cortex. On the enlarged photographs the more medial depths in the enriched rats showed greater increases than the lateral depths. Overlapping photomicrographs were made of a medial cortical area 1.00 mm by 0.75 mm on each transverse section and were combined into one composite picture for each animal. Differential cell counts from the composite pictures were determined independently by two technicians. Results indicate a 14% (p<0.01) increase in glia among the enriched rats. No significant differences between enriched and impoverished groups were found in the perikarya and nuclear circumferences as measured with a planimeter from camera lucida drawings.