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 Ca 2+-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.