Vasopressin gene is expressed at low levels in the hypothalamus of the Brattleboro rat.

The Brattleboro rat carries as a recessive trait the inability to synthesize hypothalamic vasopressin and its related neurophysin but is able to synthesize oxytocin and its neurophysin. Brattleboro rats homozygous for this trait have no immunologically detectable circulating vasopressin and manifest a complete syndrome of diabetes insipidus, which is corrected with vasopressin replacement therapy. Such a defect could be due to absence of the gene encoding vasopressin, the presence of an abnormal gene, or a variety of transcriptional or posttranscriptional abnormalities. We report here that the hypothalamus of the Brattleboro rat contains detectable, although markedly reduced, levels of an mRNA indistinguishable in size with and similar in sequence to authentic vasopressin mRNA. Corresponding levels of oxytocin mRNA were the same in Brattleboro and normal rat hypothalami. These findings indicate that the Brattleboro rat expresses a vasopressin gene, but at a reduced level.