Chromic gut suture placement and histological evidence of injury at the site of TIC. (A) Schematic illustration of the chromic gut suture placement between the infraorbital nerve and the maxillary bone. (B) During behavioral testing mice are held in a pair of cotton insulated lab gloves by one experimenter and another experimenter probes the mouse whisker pad with the calibrated von Frey filaments to determine the mechanical threshold. (C) A photomicroscopic image taken during surgery shows the anatomical relationship of the 2 mm segment of chromic gut suture inserted between the infraorbital nerve and the maxillary bone in the lower orbital cavity. (D) A photomicrograph showing the chromic gut suture adhered onto the infraorbital nerve as dissected at the end of the experimental time course (10 weeks). (E) H&E histological staining of a normal axon bundle from an animal in the sham group illustrating normal morphology with minimal spaces between axons and intact axonal myelin sheaths. (F) The histology of the infraorbital nerve at the site adjacent to the chromic gut suture indicates there was no overt damage to the nerve axons. The spaces between axons are enlarged indicating edema. The axonal myelin sheaths were intact. (G) Immunofluorescence for activated macrophage marker, CD68, was not detected in the infraorbital nerves from the sham group mice. (H) CD68 immunoreactive was evident throughout the axonal fascicles adjacent to the chromic gut suture indicating inflammatory infiltration.