Effects of melatonin on maturational indices of the brain in rats.

In order to investigate the effects of the pineal indole melatonin upon the brain maturation, groups of 40 Wistar rats were treated (for 6 days) either with melatonin (100 micrograms/0.1 ml) or with diluent alone (0.1 ml). The brain development was investigated by following the weight, total lipids as well as the water content of the brain in rats of 12, 30, 40 days or of adult age. Whether in rats of 12 days of age, melatonin produced no significant effects on brain maturation, beginning with the 30th day of age, it increases the weight, total lipids as well as the water content of the brain. It is concluded that, since these effects are opposite to those reported for the pineal hormone arginine vasotocin, not only as aspect but also in the age of their appearance, the maturation of the rat brain could be under a double tonic control, one inhibitory (the fetal and neonatal pineal arginine vasotocin) and another stimulatory (the postnatal pineal melatonin).