Nerve injury and mouse models. A, The LG muscle of Cx3cr1^GFP/+::Ccr2^RFP/+ dual-heterozygous mice was injected with Fast Blue to retrogradely label one pool of axotomized MNs. Then, the tibial or sciatic nerve was transected and the proximal stump either ligated to prevent regeneration or aligned to the distal stump with fibrin glue to allow regeneration. Spinal cords were analyzed 3 d to 8 weeks after injury. B–E, 2D projections of confocal image stacks through the 50 μm section thickness showing the four fluorescent signals analyzed: Fast Blue MNs (B), CX3CR1-GFP⁺ microglia (C), CCR2-RFP⁺ infiltrating myeloid cells (D), and VGLUT1-immunofluorescence (E). This spinal cord was processed 14 d after sciatic nerve transection. Solid yellow line indicates the spinal cord edge. Dotted line indicates the gray matter. Cyan line indicates the approximate boundary of the sciatic and nonsciatic motor pools. GFP⁺ microgliosis is visible in the dorsal and ventral horns ipsilateral to the nerve injury. Ventrally microglia accumulate around the axotomized sciatic motor pools. Infiltrating RFP⁺ myeloid cells accumulate preferentially within the area of ventral microgliosis with little evidence of CCR2-RFP cells in the dorsal horn or the contralateral side. The sciatic motor pool region also shows depleted VGLUT1-immunoreactive punctae ipsilateral to the nerve injury side. Scale bars: B, 100 μm. C–E, Same magnification.