Development of the hypothalamic 5-hydroxytryptamine system during ontogenesis in rats: uptake and release of 5-hydroxytryptamine in vitro.

The development of the hypothalamic 5-hydroxytryptamine system has been evaluated in vitro according to [3H]5-hydroxytryptamine uptake and release in fetuses (16-20th fetal day), neonates (9th postnatal day) and adults (45th day of life). At the 16th fetal day the hypothalamic neural elements were characterized by specific uptake of 5-hydroxytryptamine and its spontaneous release; the next day K+-stimulated Ca2+-dependent release appeared. By the 18th fetal day, the 5-hydroxytryptamine uptake doubled and was retained at this level both in older fetuses and in postnatal rats. The K+-stimulated release of [3H]5-hydroxytryptamine increased considerably during the perinatal period, reaching an adult level by the 9th postnatal day. These data indicate the sprouting of 5-hydroxytryptamine fibers to the hypothalamus and the maturation of their membrane mechanisms for the bidirectional transport of 5-hydroxytryptamine early during ontogenesis-to a significant extent before the 18th fetal day.