Mechanisms of macrophage recruitment in Wallerian degeneration.

Monocytes/macrophages are important effector cells in myelin removal during Wallerian degeneration. Experiments with the mouse mutant C57BL/Ola revealed prolonged axonal survival and reduced phagocytic cell recruitment after nerve transsection. In the present study, we compared the course of Wallerian degeneration in peripheral nerves of C57BL and C57BL/Ola mice in vivo and in vitro. In vivo experiments confirmed earlier investigations describing a delayed degeneration in the C57BL/Ola mutant compared with C57BL mice which were used as control animals without abnormal degeneration. Quite different results were seen in experiments in vitro: degenerating nerve segments of C57BL/Ola mice revealed pronounced axonal breakdown even in the absence of non-resident phagocytic cells. There was no difference in vitro compared with degenerating nerves from C57BL mice. The differences observed between the in vivo and in vitro situations suggest that axonal breakdown plays an important role in the initiation of macrophage recruitment to degenerating peripheral nerves.