Immunocytochemical localization of tyrosine hydroxylase in the human fetal nervous system

The peroxidase-antiperoxidase (PAP) technique is used to determine the cellular localization of tyrosine hydroxylase in the human fetal nervous system. Antiserum to trypsin-treated tyrosine hydroxylase from the bovine adrenal medulla can be detected immunocytochemically in peripheral sympathetic neurons in the 8-mm (5-week) fetus, but can not be detected in the central nervous system until later stages of development. The cytological features and distribution of the neuronal perikarya and processes labeled for the enzyme are similar to those of the catecholaminergic neurons previously identified by histofluorescence. These findings indicate that specific neurons in the human fetus have at least one of the enzymes necessary for the biosynthesis of catecholamines and that cross-species reactivity exists between antiserum produced to the bovine tyrosine hydroxylase and human tissues.