Assessing nociceptive sensitivity in mouse models of inflammatory and neuropathic trigeminal pain.

Chronic orofacial pain encompasses a range of debilitating conditions, however in contrast to other body regions, few animal models are available to investigate mechanisms and treatments in the trigeminal area. Particularly, there is a lack of reliable models and testing methods in mice. We have behaviourally tested C57BL/6 mice subjected to unilateral chronic constriction injury (CCI) of the infraorbital nerve (IoN) or unilateral injections of Complete Freunds Adjuvant (CFA) into the vibrissal pad region with the aid of von Frey filaments and air-puffs and the use of a newly designed restraining device. These models were validated by suppressing the pain responses with appropriate drugs. The IoN-CCI group showed significant hyperalgesia on the ipsilateral side in comparison to baseline values for up to 20 days post-CCI following von Frey and air-puff stimulation. Gabapentin (60mg/kg), but not saline, temporarily reversed the hyperalgesia. Animals that received a CFA injection showed hyperresponsivity to both von Frey and air-puff stimulation for up to 4 days post injection. These effects were transiently reversed with 3mg/kg i.p. morphine but not saline. Our study proposes a new restraining device for mice, and validates a behavioural testing procedure of several facial pain models in mice, allowing for reproducible and robust assessment of the effects of pain-related agents and treatments, or phenotyping of genetically modified animals.