Bright light produces Fos-positive neurons in caudal trigeminal brainstem

• Published in: Neuroscience 2009-06, Vol.160 (4), p.858-864
• Main Authors: Okamoto, K, Thompson, R, Tashiro, A, Chang, Z, Bereiter, D.A
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Biomarkers - analysis; Biomarkers - metabolism; Fos; Fundamental and applied biological sciences. Psychology; Headache - etiology; Headache - metabolism; Headache - physiopathology; Immunohistochemistry; Male; Neurology; Neurons - metabolism; Neurons - radiation effects; Norepinephrine - pharmacology; pain; photophobia; 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; rat; 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; trigeminal subnucleus caudalis; Vertebrates: nervous system and sense organs
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/j.neuroscience.2009.03.003

Abstract 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.