Developmental changes in 5-hydroxytryptamine immunoreactivity of sympathetic cells.

5-Hydroxytryptamine was demonstrated immunohistochemically in developing sympathetic chain ganglia, adrenal medullae and retroperitoneal paraganglionic tissue. Initially, all catecholamine-synthesizing cells were immunoreactive to 5-hydroxytryptamine, but during the maturation some sympathetic cell types lose this property. In the ganglia, small intensely fluorescent cells retain their 5-hydroxytryptamine content throughout maturation. This property is expressed transitionally in some neonatal principal neurons, but can be triggered even in adult neurons, e.g. after loading with L-tryptophan. In the adrenal medulla, immunoreactivity to 5-hydroxytryptamine is carried over to the adrenaline-synthesizing cells, while in the main retroperitoneal paraganglion it is observed in both adrenaline and noradrenaline cells. These results suggest that initial expression of 5-hydroxytryptamine immunoreactivity is coupled to the onset of catecholamine synthesis, but is regulated differently in each mature sympathetic organ.