Appearance of catecholamine-synthesizing enzymes during development of rat sympathetic nervous system: Possible role of tissue environment

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Abstract
When and at what site in their migration cells derived from the neural crest differentiate into sympathetic neuroblasts was studied in rat embryos. Immunocytochemical detection, within the cells, of the enzymes catalyzing catecholamine biosynthesis- tyrosine hydroxylase [TH; tyrosine 3-monooxygenase, L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating), EC 1.14.16.2] dopamine-.beta.-hydroxylase [DBH; 3,4-dihydroxyphenylethylamine, ascorbate:oxygen oxidoreductase (.beta.-hydroxylating), EC 1.14.17.1] was used. As a marker of prospective adrenal medullary cells, the enzyme phenylethanolamine N-methyltransferase (PNMT; S-adenosyl-L-methionine:phenylethanolamine N-methyltransferase, EC 2.1.1.28) was studied. TH and DBH, not detected in the neural crest, appear almost simultaneously in cells of the thoracic sympathetic ganglia in 11 day old embryos and in abdominal and lumbar ganglia 1-2 days later, thereby exhibiting a characteristic rostral-caudal gradient of differentiation. Cells stained for TH and DBH are seen in the gut wall from day 11-day 14 but not thereafter. Cells stained for TH and DBH appear in the adrenal anlage at day 15. PNMT is not detected in the adrenal until day 17 of development, and is present only in the sympathoblasts in contact with the adrenal cortex. Treatment of pregnant rats with dexamethasone failed to accelerate the appearance of PNMT in the embryo or to initiate its expression in cells of other sympathetic organs. Neural crest cells apparently express a noradrenergic phenotype only after leaving the neural crest. These cells are labile with respect to their neurotransmitter and are capable of transformation in response to environmental stimuli.

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