Blockage of depolarization-induced mitogenesis in CNS neurons by 5-fluoro-2′-deoxyuridine

Experiments designed to provide further evidence, at the basic metabolic level, that true mitogenesis and mitotic activity are being induced in CNS neurons in response to sustained ionic depolarization were conducted. The ability of 5-fluoro-2′-deoxyuridine (FUdR), a well-studied inhibitor of normal mitogenesis in naturally proliferating cells, to block induction of DNA synthesis (and subsequent nuclear division) in culture-matured neurons depolarized with ouabain was ascertained, as well as the ability of exogenously supplied thymidine to permit effective bypass of such blockage. Observations of the sequence of intracellular morphological changes induced by ouabain were also made, along with a determination of the alterations in this sequence introduced by FUdR. The results indicate that ouabain-mediated depolarization rapidly induces and/or activates the key mitogenic enzyme thymidylate synthetase in the mitotically quiescent neurons, along with all other mitogenesis-specific enzymes required for DNA synthesis and nuclear division. A probable mechanism by which such mitogenic induction may proceed is elaborated. The early morphological changes observed correlate well with the early time sequence of mitogenic metabolic events, while development of the latter changes appears to be dependent upon the progress of mitogenesis activity. The results support the possibility that CNS neurons of adult origin may also be induced to initiate normal mitogenesis by appropriately imposed depolarization treatments.