Expression of phenylethanolamine N-methyltransferase in sympathetic neurons and extraadrenal chromaffin tissue of chick embryos in vivo and in vitro.

Previous studies suggested the existence of two populations of cells in the mammalian sympathetic nervous system which differ in their ability to express phenylethanolamine N-methyltransferase (PNMT), the enzyme which specifically subserves the biosynthesis of epinephrine: (1) sympathoblasts and their progeny, the noradrenergic sympathetic neurons (PNMT negative); and (2) phaeochromoblasts , the precursors of the adrenergic cells of the adrenal gland and extra-adrenal chromaffin tissue (PNMT-positive). We sought to determine whether similar differences between sympathoblasts and phaeochromoblasts exist in other classes of vertebrate embryos. Using immunohistochemical and biochemical techniques to assay PNMT in sympathetic organs, we have found that chick embryo paravertebral ganglia contain PNMT activity both in vivo and in vitro. In vitro PNMT immunostaining was detected in principal neurons as well as in small process bearing neurons similar to mammalian SIF cells. In vivo, cells containing PNMT were seen not only in the adrenal gland, but also in other sympathetic structures such as the extra-adrenal chromaffin tissue and, unexpectedly, also in some cells of the kidney. Tyrosine hydroxylase, the first enzyme of the catecholamine (CA) biosynthetic pathway, was found in the same cells which could be stained with PNMT antibodies as well as in the sympathetic ganglia. Thus, we conclude that in contrast to the rat, chick sympathoblasts share with phaeochromoblasts the property of expressing all the CA enzymes, including PNMT.