The development of nicotinic responses in the rat adrenal medulla was examined at various ages from 1 to 50 days of age by testing the ability of nicotine (10 mg/kg, s.c.) to deplete catecholamines and induce tyrosine hydroxylase. 2. Catecholamines were depleted 25% 3 h after injection of nicotine at all ages tested, but the degree of tyrosine hydroxylase induction 24 h after nicotine increased with age. 3. These data indicate that functional nicotinic receptors are present in the neonatal adrenal medulla before the development of functional splanchnic innervation, but that the development of the ability to induce tyrosine hydroxylase is not coupled directly to the development of secretory mechanisms. 4. The long-term effects of a single dose of nicotine (10 mg/kg, s.c.) administered to one day old rats were also examined. 5. After the short-term catecholamine depletion caused by nicotine, there were persistent elevations of catecholamines and tyrosine hydroxylase until 23 days of age; however, dopamine beta-hydroxylase remained elevated into young adulthood. 6. These data indicate that neonatal nicotine administration can produce long-term changes in adrenal catecholamine biosynthetic enzymes.
