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

The lasting effects of a 9-day neonatal exposure to vasopressin and oxytocin were examined in the rat to discover if peptide administration results in organizational effects. When tested in young adulthood, brain growth, not body growth, appeared to be impaired. Basal and challenge tests of urine production, carried out to see the development of the hormonal antidiuretic function of vasopressin, revealed no lasting changes, and therefore did not confirm earlier findings of an induced mild polyurea. Behavioral testing of learning by making use of a one-trial step-through paradigm with a 24-h retention trial-a test that is sensitive to vasopressin-did not show impairments. Open field tests, however, showed enhanced emotionality in the vasopressin-treated females, as well as an initially increased ambulation in the males, and increased grooming in both sexes, the latter also having been reported to be 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 organizational development of the rat brain. It remains to be established whether this is an effect obtained through changes in the general peripheral physiology or a reflection of plasticity phenomena at the level of central vasopressin neurotransmission.