To begin, carry a single mouse from the housing to the test room in a covered plastic cage without bedding material. Place the cage in front of a video camera. Then place a mirror to view the mouse's face when its back is toward the camera.
Record the mouse's behavior for 10 minutes. After recording, clean the observation cage before recording the next animal. Have an observer blind to the experimental conditions to analyze the recorded behavior of the mouse.
Note each face grooming episode during the 10-minute recording. Make a distinction between isolated face grooming and face grooming behaviors during body grooming. Determine the number of face grooming episodes with a four-second cutoff criterion.
The time between grooming actions of less than four seconds is defined as a pause within a single episode. A time greater than four seconds is defined as a full interruption of grooming actions between two episodes. Place the mouse tail in a soft silicone clamp and attach the clamp magnetically to a metal plate on the table.
Place a three-walled plastic holder over the mouse so that only the head protrudes from the container. Place a weight on top of the holder to keep it in place. Use a graded series of four von Frey hairs to apply force to the mouse.
Habituate the mouse to the restrainer and reaching movements for 10 minutes. When the mouse is relaxed, slowly apply the lightest von Frey hair within the infraorbital nerve territory near the center of the vibrissae until it bends. Score the mouse response to the stimulation into one of the following categories.
Calculate the mean score for ipsilateral responses to the four von Frey hairs, then calculate mean scores for the contralateral sides. Distal infraorbital nerve chronic constriction injury mice exhibited a significant postoperative increase in isolated face grooming time and episodes, peaking in the first week and then gradually decreasing, remaining elevated for six weeks. Initially, distal infraorbital nerve chronic constriction injury mice showed almost complete unresponsiveness to mechanical stimulation, which, during subsequent weeks, transformed into hyperresponsiveness lasting for six weeks.
A slight increase in responsiveness to contralateral mechanical stimulation was also observed.
