Immunohistochemical demonstration of L-ornithine decarboxylase enzyme protein in different areas of the developing human brain.

L-Ornithine decarboxylase (ODC), the rate-limiting enzyme of polyamine biosynthesis and thus a unique marker of the proliferation and maturation processes, has been localized by means of immunohistochemistry in the human central nervous system. The enzyme protein has not only been found in the developing nervous system but also in the adult brain. The first immunopositive neuroblasts occurred in the 15th week of gravidity, whereas an increasing number of structures in the medulla oblongata and cerebellum showed ODC immunoreactivity in weeks 18-24 of gravidity. ODC immunoreactivity was revealed in multiple neurons and in the ependymal lining of ventricles. In the adult human brain ODC immunoreactivity was found in the hippocampus and in the spinal cord. In no case were immunoreactive glial cells observed.