PROJECT SUMMARY/ABSTRACT Pain has a major impact on the quality of life, remains difficult to alleviate, and has contributed to the over- prescription of opioid analgesics that is often linked to the recent epidemic of addiction and mortality. Clinical pain results from inappropriate signaling from the somatosensory system, caused by changes in activity of peripheral sensory neurons and/or central processing of this input. Molar teeth are richly innervated by specialized somatosensory neurons, yet we only notice tooth sensation when injury or inflammation trigger intense toothache. This transformation of innocuous dental sensation to exquisite pain underlies the most common form of orofacial pain. Here I will address the roles, responses, and molecular mechanisms of sensory neurons innervating teeth in health and inflammation in order to expose both tooth-specific and common pain mechanisms, and spur new ideas for development and testing of non-opioid analgesics to alleviate pain. The overall objective of this application is to determine the cellular and molecular mechanisms responsible for tooth sensation (mentored phase) and address how sensory input from the teeth may be transformed to drive pain (independent phase). Powerful, cutting-edge approaches will be leveraged to develop a new and comprehensive view of the physiological roles of tooth-innervating trigeminal sensory neurons. To achieve this goal, Dr. Joshua Emrick will work with a mentoring team including Dr. Nicholas Ryba (primary mentor), Dr. Mark Hoon (co-mentor), and Drs. Alexander Chesler and Jennifer L. Gibbs (collaborators). In Aim 1, Dr. Emrick will explore the function of the tooth-innervating neurons by studying their central connectivity and manipulating them with optogenetics. To this end, standard nocifensive assays as well as orofacial feature categorization using machine learning will be used to evaluate pain responses. In Aim 2, Dr. Emrick will determine how trigeminal neurons respond to stimulation of teeth using an in vivo calcium imaging platform. In combination, these studies will reveal new information about tooth sensation, provide a tractable model for understanding pain, and a strategy for developing targeted clinical pain therapies. Importantly, the proposed training will support Dr. Emrick’s career development in his transition into independence as a dentist-scientist.