Project Summary: Trigeminal neuropathic pain is a debilitating condition and represents a challenge to clinicians because such pain is often refractory to currently available therapies. The brain neural circuit mechanism underlying this type of pain remains poorly understood. We will address the knowledge gap in this project. The objective of this project is to dissect a novel neural circuit for the modulation of trigeminal neuropathic pain. In my preliminary study, using a revolutionary approach called “Targeted Recombination in Active Populations (TRAP)”, I identify that neurons in the anterior paraventricular thalamic nucleus (aPVT) are markedly activated by chronic constriction injury of the infraorbital nerve (CCI-ION). By anterograde and retrograde viral tracing, I show that the TRAPed aPVT neurons directly project to anterior cingulate cortex (ACC). Moreover, I found that optogenetic excitation of the TRAPed aPVT neurons enhances CCI-ION-induced trigeminal neuropathic pain and optogenetic silencing of the aPVT neurons attenuates such pain. My preliminary results suggest that aPVT neurons and their projection to ACC could be involved in the modulation of trigeminal neuropathic pain. In this project, I will further interrogate the role of aPVT-ACC pathway in trigeminal pain modulation. My hypothesis is that specific manipulation of aPVT-ACC pathway can modulate trigeminal neuropathic pain in an activity- dependent manner: Specific activation of aPVT-ACC pathway enhances trigeminal neuropathic pain through increasing neuronal activity in the ACC; oppositely, specific inhibition of aPVT-ACC pathway produces pain relief by decreasing neuronal activity in the ACC. To address this central hypothesis, I will use multidisciplinary approaches to conduct the following studies in two specific aims. In Aim 1, I will determine the role of aPVT-ACC pathway in trigeminal pain modulation by investigating the effect of optogenetic manipulation of this pathway on CCI-ION-induced trigeminal neuropathic pain. Both evoked and spontaneous pain behaviors will be measured with von Frey test and real-time place preference assay, respectively. In Aim 2, I will characterize aPVT-ACC pathway-mediated regulation of neuronal activity in the ACC during trigeminal neuropathic pain using miniatured microscope-based in vivo calcium imaging in freely moving mice. Collectively, I expect to show that the aPVT- ACC pathway is critical for trigeminal pain modulation. The proposed research is significant since it will advance our understanding of brain neural circuitry for pain modulation. The proposed studies are innovative since these studies will reveal a previously unrecognized neural circuit that underlies trigeminal pain modulation.