Differential neurophysin immunoreactivities in solitary magnocellular neurons of the homozygous Brattleboro rat indicate an altered neurophysin moiety.

In the homozygous Brattleboro rat (di/di) a single base deletion in the vasopressin (VP) gene causes diabetes insipidus, resulting in the synthesis of a VP precursor with a different C-terminus. We reported previously that a small number of post-mitotic VP neurons in di/di rats undergo a switch to a heterozygous phenotype, suggesting the existence of VP mRNAs with a restored reading frame coding for a normal VP precursor. In the present study we report that the increase in the number of these revertant cells declines after 79 weeks of age. Furthermore, we provide evidence that the neurophysin (NP) moiety in solitary neurons is different from normal NP. Comparing the immunoreactivities of two different NP antibodies we deduced that the restoration of the reading frame may take place downstream of the deletion between amino acids 75 and 93 of the VP-NP.