DISTRIBUTION OF B-50[GAP-43) MESSENGER-RNA AND PROTEIN IN THE NORMAL ADULT HUMAN SPINAL-CORD

B-50(GAP-43) is a phosphoprotein mainly found in the nervous system wh ich plays a major role in neurite growth during development and regene ration as well as in synaptic remodelling. In the mature intact centra l nervous system, intense B-50 immunoreactivity (B50-IR) can still be detected in regions which maintain residual capacity for structural re -organization. B-50 expression has been studied extensively in laborat ory animals; however, its distribution and regulation in the human spi nal cord is largely unknown. As a first step to analyze lesion-induced structural alterations, we investigated the distribution of B-50 prot ein and mRNA in the normal adult human spinal cord and dorsal root gan glia. Intense B-50-IR was localized to the superficial laminae of the dorsal horn at all segmental levels, the intermediolateral nucleus at thoracic levels and Onuf's nucleus at sacral levels. Scattered neurons , particularly in the ventral horn of lumbar and sacral segmental leve ls (and occasionally also in Clarke's nucleus) displayed intense B-50- IR in close apposition to the perikaryal and proximal dendritic surfac es. Nonradioactive in situ hybridization indicated that B-50 mRNA coul d also be detected in neurons of the ventral horn and also in the inte rmediolateral nucleus. The distribution of B-50 mRNA and protein in th e normal human spinal cord shows a marked similarity to that reported in experimental animals, including the selective labelling of Onuf's n ucleus. However, the strong B-50-IR on the surface of some large anter ior horn motor neurons has not been observed in other mammals. This fi nding might reflect a particular state of readiness for synaptic plast icity.