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Published on: March 28, 2025
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Brainstem pain-modulating neurons are sensitized to visual light in persistent inflammation
Gwen Hryciw1,2,3, Jennifer Wong3, Mary M Heinricher3,4
1School of Dentistry, Oregon Health & Science University, Portland, OR, USA.
Neurobiology of Pain (Cambridge, Mass.)
|January 6, 2023
Summary
Pain-modulating neurons respond to dim light, even in healthy individuals. In chronic pain, light exposure may decrease pain inhibition, contributing to photosensitivity and light aversion.
Area of Science:
- Neuroscience
- Pain Research
- Sensory Processing
Background:
- Chronic pain patients often experience heightened sensitivity to light (photosensitivity).
- The rostral ventromedial medulla (RVM) modulates pain and responds to light in male rats.
- Understanding light's effect on RVM neurons is key to explaining photosensitivity.
Purpose of the Study:
- To characterize RVM ON- and OFF-cell responses to varying light intensities in male and female rats.
- To investigate if persistent inflammation alters light-evoked RVM neuronal activity.
Main Methods:
- Recorded RVM ON- and OFF-cell firing rates in response to a range of light intensities (30–16,000 lx).
- Compared responses in naive animals versus those with induced persistent inflammation.
- Analyzed sex differences in light-evoked neuronal responses.
Main Results:
- Both ON- and OFF-cells responded to dim light (<1000 lx) in naive rats, with no sex differences in response thresholds.
- Persistent inflammation enhanced light-evoked suppression of OFF-cell activity.
- Light-evoked activation of ON-cells remained unchanged in inflammation.
Conclusions:
- Pain-modulating RVM neurons are sensitive to dim light under normal conditions.
- Light-evoked reduction in descending inhibition may contribute to pain and light aversion in chronic pain.
- Light acts as a distinct "top-down" regulatory input to the RVM, differing from somatic stimuli.
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