MILD SUSTAINED EFFECTS OF NEONATAL VASOPRESSIN AND OXYTOCIN TREATMENTON BRAIN GROWTH AND BEHAVIOR OF THE RAT

The lasting effects of a 9-day neonatal exposure to vasopressin and ox ytocin were examined in the rat to discover if peptide administration results in organizational effects. When tested in young adulthood, bra in growth, not body growth, appeared to be impaired. Basal and challen ge tests of urine production, carried out to see the development of th e hormonal antidiuretic function of vasopressin, revealed no lasting c hanges, and therefore did not confirm earlier findings of an induced m ild polyurea. Behavioral testing of learning by making use of a one-tr ial step-through paradigm with a 24-h retention trial-a test that is s ensitive to vasopressin-did not show impairments. Open field tests, ho wever, showed enhanced emotionality in the vasopressin-treated females , as well as an initially increased ambulation in the males, and incre ased grooming in both sexes, the latter also having been reported to b e induced by vasopressin administration in the septal areas. Oxytocin treatment did not produce lasting changes. Our conclusion, therefore, is that peripherally circulating vasopressin can affect the organizati onal development of the rat brain. It remains to be established whethe r this is an effect obtained through changes in the general peripheral physiology or a reflection of plasticity phenomena at the level of ce ntral vasopressin neurotransmission.