Increase in thickness of cerebral cortex in response to environmental enrichment in brattleboro rats deficient in vasopressin

Changes in cortical thickness were observed in male Brattleboro rats killed at 60 and 90 days of age from standard environmental conditions, and at 90 days of age after 30 days in an enriched condition. When 60- and 90-day-old standard animals were compared, both homozygous Brattleboro rats with diabetes insipidus and also heterozygous nondiabetic rats showed reduction in cortical thickness with age. When 90-day-old enriched animals were compared with the 90-day-old standard group: the homozygous rats with enrichment showed statistically significant thickening in frontal, parietal, and occipital cortices, and the heterozygous rats showed statistically significant thickening with enrichment in parietal and occipital regions. In both heterozygous and homozygous Brattleboro rats the most significant increases were in the occipital cortex. These results are in general agreement with previously reported developmental and enrichment studies in the normal Long-Evans strain of rats, with an important difference: both heterozygous and homozygous animals showed greater and more generalized response to enrichment. We speculate that this greater responsiveness to environmentally induced cortical thickening in the Brattleboro rats is due to increased arousal, and it may be related to alterations in norepinephrine concentration and/or turnover associated with absence of, or abnormalities in, vasopressin in the brain.