Histological and ablation studies on the relation of the subcommissural organ and rostral midbrain to sodium and water metabolism

Fourteen mature male rats were fed a sodium‐deficient diet for six weeks. After three weeks on the diet, electrical ablations were made in the region of the subcommissural organ. During the six‐week period measurements were made of water intake, urine output, and urinary sodium output. A second group of five one‐month‐old male rats was given the sodium‐deficient diet and seven litter‐mates a control diet. Five months later, the adrenals and subcommissural organs were studied histologically. The results obtained indicate that: (1) subcommissural organ ablation does not change urinary sodium excretion; (2) sodium deprivation, although producing significant changes in the width of the adrenal zona glomerulosa, does not affect the periodic acid‐Schiff reactive material in the subcommissural organ; (3) complete subcommissural organ ablation is associated with decreased urine output and water intake; (4) partial subcommissural organ ablation combined with destruction of structures in and around the rostral periaqueductal gray matter and adjacent diencephalon is associated with increased urine output and water intake; (5) lesions which failed to involve significantly the aforementioned areas are associated with no change in urine output or water intake.