Immunohistochemical localization of the catecholamine-synthesizing enzymes, substance P and enkephalin in the human fetal sympathetic ganglion.

The human fetal sympathetic ganglia were studied using the indirect peroxidase-antiperoxidase PAP method for immunocytochemical demonstration of three catecholamine-synthesizing enzymes, tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH) and phenylethanolamine-N-methyltransferase (PNMT) as well as the neuropeptides leucine (Leu5)-enkephalin and substance P. The neuroblasts of the ganglia showed intense peroxidase immunoreactivity for TH, moderate reaction to DBH, and no reaction to PNMT. The small intensely fluorescent (SIF) cells situated along the blood vessels also showed positive labelling for only two enzymes, TH and BDH. The immunocytochemical localization of these enzymes suggests that both neuroblasts and SIF cells synthesize noradrenalin. Neither the neuroblasts nor SIF cells showed a reaction to substance P, and only the SIF cells contained enkephalin-like immunoreactivity. The role of enkephalin in the noradrenalin-containing SIF cells is unknown, but may be related to neuromodulation of ganglionic transmission.