Fig. 3. Morphologic alterations produced by chronic constriction injury. Morphology of the sham control infraorbital nerve (ION): The cytoarchitecture of the ION in the surgical sham control group is shown in nerve cross sections. Axons stained for neurofilament 200 by immunofluorescence (green ) are surrounded by myelin sheaths (white arrow ) stained for myelin protein zero (red ). Inset : Hematoxylin and eosin (H&E) staining shows the normal structure of a fascicle of the ION fiber. Each myelinated nerve fiber axon is densely stained and encircled by the lighter Schwann cell myelin sheath ring (black arrows ) (A ). Morphology after ION chronic constriction injury (CCI): Most MPZ-stained myelin sheaths have lost their circular morphology and axonal staining in the center of their structure (i.e. , the immunopositive structures [red ] wrapping around the axons [green ] have collapsed). Axons are seen scattered in the endoneurium without myelin sheaths or with a few wraps of a damaged myelin sheath (white arrows ). Inset : Myelin sheath in infraorbital nerve disrupted by ligation shown 5 weeks after surgery (black arrows ). Bars = 10 μm (B ) ION size distribution: The histogram shows the infraorbital nerve myelinated axon fiber size distribution and changes after constriction injury (C ).