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Macrophage and microglial cell response after common peroneal nerve cut and crush in C57BL/6J mice
1Department of Anatomy, Faculty of Medicine, National University of Singapore.
Abstract:
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.
Insights
This study on nerve injury in mice found that macrophage recruitment and microglial activation occur rapidly after injury, not delayed as previously suggested. Immune cell activity correlates with nerve degeneration, not regeneration.
Area of Science:
- Neuroscience
- Immunology
- Regenerative Medicine
Background:
- Peripheral nerve injury triggers immune responses involving macrophages and microglial cells.
- Previous research suggested delayed nerve regeneration in C57BL/6J mice, potentially linked to immune cell timing.
- Understanding immune cell dynamics is crucial for nerve repair strategies.
Purpose of the Study:
- To investigate the temporal dynamics of macrophage recruitment and microglial activation following peripheral nerve injury (common peroneal nerve cut or crush) in mice.
- To correlate immune cell responses with nerve fiber regeneration and degeneration.
- To clarify the role of immune cells in nerve repair in C57BL/6J mice.
Main Methods:
- Utilized Mac-1 immunohistochemistry to detect macrophages and microglial cells.
- Examined nerve injury models involving common peroneal nerve cut or crush in 86 C57BL/6J mice.
- Assessed immune cell presence in peripheral nerve fibers, dorsal root ganglia, and spinal cord segments at various time points post-injury.
Main Results:
- Macrophage recruitment and microglial activation were observed shortly after nerve injury, peaking at 5 days post-operation.
- Immune cell activity declined after the initial peak but showed reactivation between 20-30 days, possibly due to degenerating fibers.
- No significant immune cell reaction was noted during the primary nerve fiber regeneration phase.
Conclusions:
- Macrophage recruitment and microglial activation following peripheral nerve injury are rapid events, not delayed.
- Immune cell responses appear linked to nerve degeneration rather than active regeneration.
- Findings challenge previous notions of delayed immune responses in C57BL/6J mice nerve repair.