Effects of neonatal melatonin administration on the extra-hypothalamic regions in rat brains: Effects on the serotonergic system

The effects of 100 mu g melatonin injection at postnatal day 5 (PD 5) on th e development of the central serotonergic systems in male and female rats w ere investigated. The contents of serotonin (5-HT) and 5-hydroxy-3-indolace tic acid (5-HIAA) were measured in several extra-hypothalamic regions at 3, 10 and 42 weeks of age. The neonatal melatonin administration increased bo th 5-HT and 5-HIAA levels in the striatum throughout the examined period. I n the hippocampus, an increase in 5-HIAA contents by neonatal melatonin adm inistration was found at 3 weeks but not 10 or 42 weeks of age. There were no significant differences in the effects of melatonin between male and fem ale rats. These results indicated that exogenous melatonin administration d uring the early neonatal period influenced the development of the serotoner gic systems in extrahypothalamic regions including the hippocampus and the striatum.