Macrophage and microglial cell response after common peroneal nerve cut and crush in C57BL/6J mice.

The present study using Mac-1 immunohistochemistry for the detection of macrophages and microglial cells, has investigated the signals for macrophage recruitment in the peripheral nerve fibres and dorsal root ganglia, and microglial cell activation in the dorsal and ventral horns of the spinal cord, at different periods after a right common peroneal (CP) nerve cut or crush in 86 C57BL/6J mice. Though a previous study has demonstrated a delayed regeneration of the peripheral sensory but not the motor fibres in this strain of mice, the present study could not demonstrate a corresponding delay in macrophage recruitment in the L4-L6 dorsal root ganglia and microglial cell activation in the dorsal and ventral horns of the corresponding segments of the spinal cord. In fact, macrophage recruitment and microglial cell activation appeared a short time after the nerve lesion and peaked at 5 days post-operation then subsequently declined. Microglial cells, however, became reactivated at 20-30 days after CP nerve cut, perhaps because of the presence of newly degenerated fibres. In contrast to the above observation, there was no exuberant macrophage recruitment or microglial cell reaction during the period when the majority of the regenerated fibres were detected in the distal segment of the crushed nerve.