Delayed ontogenesis of histamine in the hypothalamus of the homozygous Brattleboro rat.

The ontogenetic development of histamine was studied in the diabetes insipidus rat to clarify the possible interference between the lack of vasopressin and the development of histaminergic systems in the hypothalamus. Rat pups were decapitated at different ages between the 2nd and 38th postnatal days. In addition to homozygous Brattleboro (diabetes insipidus) rats, Long Evans controls and heterozygous animals were studied. In all three genotypes hypothalamic histamine was almost equal during the first 6 postnatal days. In homozygous Brattleboro rats the period of most rapid increase occurred between days 14 to 26, which was significantly later than in Long Evans rats. In the remainder of the brain no such difference was seen. On the contrary, histamine values were highest in the youngest animals. It remains to be elucidated whether the delayed ontogenesis is causally related to vasopressin deficiency and what is the underlying mechanism.