AVP and diabetes insipidus: Hom Brattleboro rats develop diabetes insipidus due to the absence of AVP-mediated water reabsorption at the level of the kidney (Valtin and Schroeder, 1964), and symptoms are evident before play onset: increased plasma osmolarity is present at 10-14 d of age, and polydipsia develops between 15 and 16 d of age (Dlouhá et al., 1982; Zelena et al., 2009).