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Updated: Jun 15, 2026
04:39
In-Vivo Calcium Imaging of Sensory Neurons in the Rat Trigeminal Ganglion
Published on: February 9, 2024
Bright light activates a trigeminal nociceptive pathway.
Keiichiro Okamoto1, Akimasa Tashiro, Zheng Chang
1Department of Diagnostic and Biological Sciences, University of Minnesota School of Dentistry, 18-214 Moos Tower, 515 Delaware St. SE, Minneapolis, MN 55455, USA.
Pain
|March 9, 2010
Summary
Bright light triggers eye pain through a newly discovered reflex circuit. This pathway involves intraocular mechanisms and increased parasympathetic nerve activity, explaining how light intensity affects trigeminal nerve responses.
Area of Science:
- Neuroscience
- Ophthalmology
- Sensory Physiology
Background:
- Bright light exposure can induce ocular discomfort and pain.
- The precise neural mechanisms linking light intensity to trigeminal nerve activation remain unclear.
Purpose of the Study:
- To elucidate the novel reflex circuit responsible for bright light-induced excitation of nociceptive neurons.
- To identify the intraocular and neural pathways involved in transmitting light signals to the trigeminal system.
Main Methods:
- Investigated light-evoked activity in trigeminal subnucleus caudalis (Vc/C1) neurons.
- Utilized lidocaine microinjections in the eye, trigeminal root ganglion (TRG), and superior salivatory nucleus.
- Administered vasoconstrictors (norepinephrine, phenylephrine) and atropine.
- Blocked the olivary pretectal nucleus to assess accessory visual pathway involvement.
Main Results:
- Vc/C1 neurons exhibited light intensity-dependent responses with a significant delay.
- Intraocular lidocaine and TRG blockade abolished light responses, indicating an intraocular origin and TRG transmission.
- Vasoconstrictor microinjections into the eye, but not the TRG, blocked light-evoked activity.
- Parasympathetic outflow via the superior salivatory nucleus and accessory visual input through the olivary pretectal nucleus were critical.
Conclusions:
- Bright light activates trigeminal nerve activity via a novel intraocular reflex circuit.
- This circuit involves luminance detection, increased parasympathetic outflow to the eye, and transmission through the TRG.
- The findings provide a mechanistic link between light exposure and trigeminal nociception.
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