Year of Publication

2014

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Medicine

Department

Physiology

First Advisor

Dr. Karin N. Westlund High

Abstract

Approximately 22% of the United States population suffers from a chronic orofacial pain condition. One such condition is known as trigeminal neuropathic pain frequently reported as continuous aching and burning pain, often accompanied by intermittent electrical shock-like sensations. Dental procedures or trauma are known causes of peripheral trigeminal nerve injury and inflammation. Patients who have this type of facial pain also suffer from emotional distress. For these reasons, trigeminal neuropathic pain needs to be studied in more detail to improve the understanding of the etiology and maintenance of this condition, as well as to develop effective treatment strategies. The first experiment was focused on characterizing the behavioral aspects of the Trigeminal Inflammatory Compression (TIC) mouse model. The findings determined that the TIC injury model induced mechanical and cold hypersensitivity that persist at least 21 weeks. This orofacial, neuropathic pain condition was accompanied by anxiety- and depressive-like behaviors at week 8 post injury. The TIC injury mouse model’s chronicity and development of psychosocial impairments demonstrated its usefulness as a facial pain model. The second experiment used the mouse TIC injury model to test the ability of pioglitazone (PIO), a PPARγ agonist used clinically for treatment of diabetes, on alleviating trigeminal pain. A single low dose of PIO had no effect, but a higher dose attenuated facial pain. The third experiment determined that combining ineffective low doses of PIO and D-cycloserine (DCS) produced a potentiated anti-allodynic response of these drugs and attenuated the anxiety associated with the TIC injury. Ex vivo studies revealed that cortical mitochondrial dysfunction occurred after the TIC injury but could be reversed by the combination of DCS/PIO which improves mitochondrial function. Overall, the present studies determined that the novel mouse TIC injury model is a clinically relevant facial neuropathic pain model. The results suggest that PPARγ and brain mitochondria may represent new molecular targets for the treatment of trigeminal neuropathic pain. These studies support the future “repurposing” of PIO and DCS as well as the combination of the two drugs for this new use in patients with trigeminal neuropathic pain.

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