Postnatal development of serotonin in adrenal medullary cells

The ontogeny of serotonin in the chromaffin cells of the adrenal medulla in rats from 1 to 48 days of age was studied using immunocytochemical and biochemical methods. Using indirect antibody enzyme PAP method on glycol methacrylate embedded sections, serotonin-immunostaining was evident as distinct granules in medullary cells already at one day of age. Serotonin was present in cells prior to complete maturation as was evident by immunostaining in medullary cells which had not yet migrated into a central medulla and in mitotic cells. However, no immunostaining was observed in the chromaffin precursor cells which were evident through 8 days of age or in ganglion cells. A progressive increase in the number of immunoreactive cells and the amount of serotonin-immunostaining per cell was observed between 1 and 12 days of age. After 12 days of age the serotonin-immunostaining appeared adultlike in distribution. Quantitative determination of the adrenal serotonin content by HPLC-EC substantiated the immunocytochemical observations. While serotonin was present at a concentration of approximately 10 mumoles/kg adrenal weight, the total content increased progressively with age (1.24 +/- 0.01 X 10(-11) moles at one day to 10.00 +/- 1.00 X 10(-11) moles at 48 days of age). Dopamine, norepinephrine and epinephrine were measured and also increase with age. In conclusion, like the catecholamines, serotonin is already present in adrenal medullary cells at day one neonatally and the indoleamine and catecholamines show essentially a parallel development.