Bright light produces Fos-positive neurons in caudal trigeminal brainstem

Neuroscience. 2009 Jun 2;160(4):858-64. doi: 10.1016/j.neuroscience.2009.03.003. Epub 2009 Mar 11.


Excessive discomfort after exposure to bright light often occurs after ocular injury and during headache. Although the trigeminal nerve is necessary for light-evoked discomfort, the mechanisms underlying this phenomenon, often referred to generally as photophobia, are not well defined. Quantitative Fos-like immunoreactivity (Fos-LI) was used to determine the pattern of neuronal activation in the caudal brainstem after bright light stimulation and, secondly, whether a neurovascular mechanism within the eye contributes to this response. Under barbiturate anesthesia, male rats were exposed to low (1 x 10(4) lx) or high intensity (2 x 10(4) lx) light delivered from a thermal neutral source for 30 min (30 s ON, 30 s OFF) and allowed to survive for 90 min. Intensity-dependent increases in Fos-LI were seen in laminae I-II at the trigeminal caudalis/cervical cord junction region (Vc/C1) and nucleus tractus solitarius (NTS). Fos-LI also increased at the trigeminal interpolaris/caudalis transition (Vi/Vc(vl)) and dorsal paratrigeminal (dPa5) regions independent of intensity. Intravitreal injection of norepinephrine greatly reduced light-evoked Fos-LI at the Vc/C1, dPa5 and NTS, but not at the Vi/Vc transition. Lidocaine applied to the ocular surface had no effect on Fos-LI produced in trigeminal brainstem regions. These results suggested that multiple regions of the caudal trigeminal brainstem complex integrate light-related sensory information. Fos-LI produced at the dPa5 and NTS, coupled with norepinephrine-induced inhibition, was consistent with the hypothesis that light-evoked activation of trigeminal brainstem neurons involves an intraocular neurovascular mechanism with little contribution from neurons that supply the ocular surface.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Biomarkers / analysis
  • Biomarkers / metabolism
  • Headache / etiology
  • Headache / metabolism
  • Headache / physiopathology*
  • Immunohistochemistry
  • Male
  • Neurons / metabolism
  • Neurons / radiation effects*
  • Norepinephrine / pharmacology
  • Photophobia / metabolism
  • Photophobia / physiopathology*
  • Posterior Horn Cells / metabolism
  • Posterior Horn Cells / radiation effects
  • Proto-Oncogene Proteins c-fos / metabolism
  • Proto-Oncogene Proteins c-fos / radiation effects*
  • Rats
  • Rats, Sprague-Dawley
  • Retinal Artery / drug effects
  • Retinal Artery / physiology
  • Solitary Nucleus / metabolism
  • Solitary Nucleus / physiopathology
  • Substantia Gelatinosa / metabolism
  • Substantia Gelatinosa / physiopathology
  • Trigeminal Caudal Nucleus / metabolism
  • Trigeminal Caudal Nucleus / physiopathology*


  • Biomarkers
  • Proto-Oncogene Proteins c-fos
  • Norepinephrine