Objective: 

Neuronal regeneration after spinal cord injury may be impeded by a glial scar, but its character and temporal development are still vague.

Methods: 

Triple-transgenic mice with labeled neurons and glial cells with different fluorescent proteins (axons/YFP, microglia [MG]/GFP, astrocytes/CFP) were imaged with two photon microscopy before and after laser-induced spinal cord lesions. The lesions were regularly re-inspected for up to one year. The initial laminectomy at spinal cord L4 and re-opening for re-inspections were performed under full volatile anaesthesia. The days after operation, the mice received buprenorphin.

Results: 

Within minutes after the lesion, MG sent their processes towards the lesion. During the next days, nearby MG cells migrated toward the lesion accumulating and staying there for about a week, then slowly diminishing during the next five months. Astrocytes started to extend processes to the lesion after two days. An astroglial reaction surrounding the lesion site was fully developed after a week and subsequently decreased within five months. Within hours after the lesion, dissected axons formed bulbous debris which was partly engulfed by MG processes. Occasionally, axonal sprouting was detected about three months after injury; they could cross the site of injury, when the glial accumulation had almost vanished.

Conclusions: 

Detailed knowledge of the temporal behavior of the main cell types involved in the reaction to spinal cord injury may provide valuable hints for a therapeutical approach to improve axonal survival and regeneration.