Comparison between two types of behavioral variables of non-evoked facial pain after chronic constriction injury to the rat infraorbital nerve.

Objective: Chronic constriction injury to the rat infraorbital nerve (IoN-CCI) was reported to induce asymmetric face grooming directed to the territory of the injured nerve, and localized mechanical allodynia. The model has been used for pharmacologic testing; responsiveness to mechanical stimulation has been used as outcome measure, but face grooming behavior was not studied in this context.

Methods: Face grooming data from a series of four experiments using the IoN-CCI model were retrospectively analyzed, and two types of face grooming were identified: on the one hand, isolated face grooming (i.e., face grooming that is neither preceded nor followed by body grooming); and on the other hand, face grooming during body grooming (i.e., face grooming that is part of more general body grooming behavior).

Results: In all four experiments, amount of isolated face grooming was found to be significantly increased after IoN-CCI. In contrast, the amount of face grooming during body grooming was not significantly altered after IoN-CCI in any of the four experiments.

Conclusions: The amount of isolated face grooming is a more sensitive outcome measure of neuropathic pain than is the total amount of face grooming, which includes face grooming during body grooming.