High histamine levels in specific hypothalamic nuclei of Brattleboro rats lacking vasopressin.

Histamine levels were determined in whole hypothalamus and specific hypothalamic nuclei of male 9-week-old homozygous Brattleboro rats lacking vasopressin and presenting the syndrome of diabetes insipidus (DI rats). These levels were compared to those in heterozygous Brattleboro rats with a partial deficit in vasopressin (HZ rats) and those in Long Evans control rats (LE rats). In whole hypothalamus, histamine levels in DI rats were higher than those found in HZ and LE rats. DI rats showed histamine levels higher than those present in LE rats in the nuclei supraopticus, paraventricularis and suprachiasmatis and in the area retrochiasmatica. Vasopressin replacement produced a selective decrease in histamine levels of DI rats, restricted to the area retrochiasmatica and nuclei supraopticus and paraventricularis. In contrast, vasopressin increased histamine levels in the area retrochiasmatica and eminentia mediana of HZ rats. In other areas normally rich in vasopressin such as the nucleus arcuatus and the eminentia mediana, the histamine content was not different among LE, HZ or DI rats. Our results suggest a physiological interaction between vasopressin and histamine systems in specific hypothalamic areas of the rat and support the hypothesis of a role of brain histamine on the central control of water balance.