Vasotocin involvement in the maturation of the rat brain.

In order to investigate the effects of arginine vasotocin (AVT), (a pineal nonapeptide hormone) on the brain maturation, the sleep-wake cycle, the day of eyelids opening and the total brain lipids level were followed up in new-born rats receiving daily (between day 2 and 8 of life) 100 ng of synthetic AVT, arginine-vasopressin (AVP), oxytocin (OT) or 0.1 ml saline solution. While AVP and OT had no effect, AVT induced: 1) an increase in the amount of active sleep (AS); 2) a decrease in the brain weight and the total brain lipids, and 3) a delay in the eyelids opening. These findings demonstrate that chronic administration of AVT induces a delay in the brain maturation of the new-born rats. Association of low brain lipids with a high percentage of AS is a very useful index of brain maturation. It is suggested that the drop in the endogenous brain levels of AVT below a critical threshold might represent a hormonal signal for triggering the beginning of brain maturation in mammals.