Uncovering spinal circuits recruited by descending facilitation

Stress is a well-known risk factor for pain and its chronification, though the mechanisms remain poorly understood. One possibility is that stress disrupts endogenous pain modulation networks, particularly the rostral ventromedial medulla (RVM), which sends descending projections to the spinal cord to bidirectionally regulate nociceptive processing. A hallmark of chronic pain is the enhancement of descending facilitation from the RVM, establishing a pro-nociceptive state. Mu opioid receptor (MOR)-expressing neurons in the RVM (RVMMOR) are thought to play a key role in this facilitation, as silencing these neurons alleviates chronic pain. However, the specific spinal neurons receiving input from these descending RVMMOR neurons remain largely uncharacterized. One hypothesis is that RVMMOR projections primarily target spinal inhibitory neurons, leading to disinhibition and increased excitatory output from projection neurons. Identifying these postsynaptic targets is critical for understanding spinal pain processing and developing targeted interventions. To address this gap, I have developed a novel ex vivo platform for imaging the targets of descending modulation, providing the first population-level identification of spinal neurons engaged by descending facilitation. Additionally, our group has identified transcriptomically distinct spinal neuron populations conserved from mouse to human. These conserved cell types will allow my findings in mouse to be rapidly translated to humans with high confidence. Leveraging these cutting-edge tools, I will test the central hypothesis that under normal conditions, RVMMOR neurons project to inhibitory spinal networks and that chronic stress amplifies this descending facilitation, leading to pathological activation of nociceptive circuits. This proposal will provide training in advanced neuroscience techniques, including spatial transcriptomics, multiphoton imaging, and computational analysis. In Aim 1 (K99), I will use chemogenetics and two-photon calcium imaging to identify spinal neurons activated by descending RVMMOR neurons. In Aim 2 (K99), I will apply transsynaptic viral tracing to construct an input-defined transcriptomic map of descending pain facilitation in the spinal dorsal horn. In Aim 3 (R00), I will investigate how repeated psychological stress alters the functional and genetic landscape of spinal neurons using the approaches developed in Aims 1 and 2. This proposal includes professional development activities, such as formal coursework in bioinformatics and mentorship from leading experts in pain neuroscience. The outcomes of these studies will identify unique markers for spinal neurons activated by descending facilitation. Using these markers, I aim to develop novel therapeutics that selectively silence pro-nociceptive neurons while avoiding reward pathways associated with addiction. Collectively, the training outlined in this proposal will help me to develop a cutting edge research program that will effectively launch my career as an independent investigator studying descending modulation of nociception. Project Number: 1K99NS146440-01 | Fiscal Year: 2026 | NIH Institute/Center: National Institute of Neurological Disorders and Stroke (NINDS) | Principal Investigator: Harrison Stratton | Institution: UNIVERSITY OF PITTSBURGH AT PITTSBURGH, PITTSBURGH, PA | Award Amount: $129,330 | Activity Code: K99 | Study Section: Special Emphasis Panel[ZRG1 IVBH-G (55)] View on NIH RePORTER: https://reporter.nih.gov/project-details/11281780