Bright light produces Fos-positive neurons in caudal trigeminal brainstem

K. Okamoto, R. Thompson, A. Tashiro, Z. Chang, D. A. Bereiter

Research output: Contribution to journalArticlepeer-review

74 Scopus citations


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 (1×104 lx) or high intensity (2×104 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/Vcvl) 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.

Original languageEnglish (US)
Pages (from-to)858-864
Number of pages7
Issue number4
StatePublished - Jun 2 2009

Bibliographical note

Funding Information:
This project was supported by NIH grant NS26137. The authors wish to thank D. F. Bereiter and J. Cioffi for excellent technical assistance.


  • Fos
  • pain
  • photophobia
  • rat
  • trigeminal subnucleus caudalis


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