Axonal-growth-associated intracellular molecule in the rat central nervous system recognized by the monoclonal antibody 5H.

In order to discover molecules involved in axonal outgrowth during development of the central nervous system (CNS), monoclonal antibodies (MAbs) were raised against homogenates of the early postnatal rat cerebral cortex. A novel MAb, 5H, was obtained which recognizes a developmentally regulated antigen in the CNS. In the cerebral cortex of postnatal (PN) day 0-6 rats, 5H-immunoreactive punctate or fiber-like processes were observed. In the PN day 12 cortex, 5H immunostaining was mostly present as puncta. The expression of the 5H antigens decreased in the second PN week and completely disappeared from the cortex of rats older than PN day 18. In the hippocampal region, 5H immunoreactivity exhibited similar developmental changes, but with a more prolonged period of expression of the antigen (up to 5 weeks postnatally). They were also absent from the hippocampus of the adult rat. Similar developmental changes were also observed in the other CNS regions, but the only region in the adult CNS that showed 5H immunoreactivity was the olfactory bulb, in which synaptic turnover normally occurs even in the adult. Immunoelectron microscopy revealed that 5H immunoreactivity was localized to the cytoplasm of neuronal processes, including synaptic boutons. The expression of the 5H antigen in neurons cultured from rat cerebral cortex obtained from embryonic day 16 to PN day 6 was mostly restricted to neurite tips, including growth cones. These results suggest that the MAb 5H antigen is associated with axonal outgrowth during early development in the CNS.