Brainstem Trigeminal Mechanisms of Orofacial Pain

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Abstract One of the most common causes of chronic pain, is orofacial pain which has a prevalence of 10-15% in the adult population which increases with age and is more common in women with a significant societal impact. Individuals who experience orofacial pain often do so with no obvious underlying tissue damage. This suggests that their pain is likely due to dysfunction in central pain processing circuitry. We have identified a knockout mouse (Prrxl1 KO) that has chronic orofacial pain, which we will utilize to better understand the neural mechanisms underlying the condition as a necessary step towards targeted therapeutic interventions. Prrxl1 KO mice lack the typical patterning associated with whisker inputs in the trigeminal system. Our preliminary results have revelated that Prrxl1 KO mice posses a facial hyperalgesia and a somatic hypoaglgesia while also displaying excessive facial grooming and feeding issues consistent with a chronic trigeminally medicated orofacial pain. In the first aim we will characterize the behavioral issues experience by the Prrxl1 KO mice via probing with von Frey elements, utilization of a Peltier device and direct applied pressure to the face in Prrxl1KO mice, barrelless mice (which lack cortical patterning) and wild-type animals. Additional home-cage videography will allow for facial grimace and grooming measurements. Responses in the absence and the presence of an analgesic will be compared. The second aim will focus on neurophysiological responses from single neurons in the principle sensory nucleus of the trigeminal (PrV) and the spinal trigeminal nucleus (SpV) in response to mechanical and thermal stimuli to begin to elucidate the neural circuitry underlying orofacial pain.