Ontogenesis of serotonergic systems in rat brain.

It was shown that the concentration of brain 5-HT rises slowly, reaching mature values by 80 days of age, while the catabolic product of 5-HT, i.e., 5-HIAA, drops from a high perinatal value to lower values by adulthood. This is indicated of poorly developed storage mechanisms at this early period in life. It was also shown that MAO develops at a rapid rate, acquiring mature values by 20 days. The activity of MAO towards substrates develops at different rates, although the general pattern of development is the same.