# Role of Descending Pain Modulation System in Orofacial Pain

> **NIH NIH F30** · OREGON HEALTH & SCIENCE UNIVERSITY · 2020 · $51,320

## Abstract

PROJECT SUMMARY
TMD is a prevalent, but poorly understood condition that can be difficult to treat. Many patients with
chronic TMD have pain that continues after injury resolution or no obvious underlying tissue damage.
Their pain is thus most likely due to dysfunction in central pain processing circuitry. Nociception is the
transmission of information about harmful stimuli from the peripheral tissues to the central nervous
system. Nociceptive signals are actively regulated by descending pain-modulatory systems, which can
either dampen of enhance nociceptive transmission. The rostral ventromedial medulla (RVM) is a major
output of the best-studied pain-modulation circuit. RVM modulates nociceptive transmission via two
classes of cells, termed “ON-cells” and “OFF-cells.” A third class of cells in RVM, referred to as “NEUTRAL
cells,” have no apparent function in pain-modulation. The net effect of RVM output on nociceptive
processing in the dorsal horn of the spinal cord has been studied extensively, and shown to be altered in
states of persistent pain. However, the changes in ON- and OFF cells, the output of the descending
control from RVM, during orofacial inflammation have not been determined.
The goal of this proposal is to determine how orofacial inflammation changes the outputs of RVM ON- and
OFF-cells. Specifically a masseter muscle inflammation model of myogenous TMD in the rat will be used
to achieve this goal. Changes in cell firing evoked by innocuous and noxious mechanical stimulation of
orofacial tissues will be quantified using in vivo electrophysiology to test the hypothesis that the force
required to elicit an RVM neuronal response will be decreased in animals with masseter inflammation, at
the site of inflammation as well as at distant locations (Specific Aim 1). Additionally, light leads to changes
in a subset of RVM cells. If the proportion and responsiveness of light sensitive RVM cells increases in
states of persistent pain, then light could facilitate pain transmission through RVM. Thus, this project will
test the hypothesis that orofacial inflammation will increase light responsiveness of RVM (Specific Aim 2).
This work will contribute significantly to our understanding of the neural circuitry changes underlying
chronic TMD.

## Key facts

- **NIH application ID:** 9978811
- **Project number:** 5F30DE027584-04
- **Recipient organization:** OREGON HEALTH & SCIENCE UNIVERSITY
- **Principal Investigator:** Gwen Hryciw
- **Activity code:** F30 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $51,320
- **Award type:** 5
- **Project period:** 2017-09-01 → 2023-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9978811

## Citation

> US National Institutes of Health, RePORTER application 9978811, Role of Descending Pain Modulation System in Orofacial Pain (5F30DE027584-04). Retrieved via AI Analytics 2026-05-27 from https://api.ai-analytics.org/grant/nih/9978811. Licensed CC0.

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