Effect of age and enrichment on certain brain dimensions in Brattleboro rats deficient in vasopressin

As a sequel to our first report in the series of studies on the brains of Brattleboro rats, measurements in caudal diencephalon, subcortical telencephalon, hippocampus, and pyriform cortex were made in three groups each of male heterozygous and homozygous Brattleboro rats. One group raised in standard conditions was killed at 60 days of age, another raised in standard conditions was killed at 90 days of age, and a third group raised in standard conditions for 60 days was killed at 90 days of age after 30 days of enrichment. Comparing 60- and 90-day-old standard condition animals, the heterozygous rats showed a significant increase in height of the caudal diencephalon. Comparing 90-day-old enriched animals with the 90-day-old standard group, significant increases occurred in 8 of 12 comparisons. In comparing the two types of Brattleboro rats, heterozygous rats had significantly greater brain dimensions than homozygous rats in width of the diencephalon in the 60-day-old standard group, and in witth of the telencephalon in both the 90-day-old standard and enriched groups. Differences in brain measures between heterozygous and homozygous Brattleboro rats tended to increase with age. Enrichment appeared to prevent this age-related increase in the difference between brain dimensions in the two types of Brattleboro rat. The same pattern was reflected in body weight differences, and it may be due to a greater anabolic response to enrichment in homozygous rats than in heterozygous rats. We suggest that brain abnormalities associated with congenital absence of vasopressin increase with age, and may be ameliorated by repetitive arousal as occurs in enrichment.