Correlation between water intake and dendritic branching in homozygous Brattleboro rats: A Golgi study

This report is the fourth in a series on the brains of three groups of male Brattleboro rats. The present study concerns only homozygous Brattleboro rats. One group raised in standard environmental 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 environmental enrichment. Water intake (measured between 33 and 40 days of age) was compared with the number of branching segments on basal dendrites of pyramidal neurons in the upper layers of the parietal and occipital cortices. A significant negative correlation between water intake and the number of dendritic branching segments per primary branch was found in both parietal and occipital cortices in the 90-day-old standard condition group. In contrast, the 90-day-old enriched group showed a significant positive correlation between water intake and segments per primary branch in the parietal cortex, and a similar but nonsignificant response to enrichment in the occipital cortex. These results may reflect a cumulative effect of the congenital absence of vasopressin which is apparent by 90 days of age and which is modified by environmental enrichment. In the light of our previous data linking vasopressin and dendritic branching, we speculate that the neuropeptide, oxytocin, may be a physiologic correlate linking the behavioral parameter (water intake) and the anatomic parameter (dendritic branching) in homozygous Brattleboro rats.