Premium
Trigeminal interpolaris/caudalis transition neurons mediate reflex lacrimation evoked by bright light in the rat
Author(s) -
Okamoto Keiichiro,
Tashiro Akimasa,
Thompson Randall,
Nishida Yasuhiro,
Bereiter David A.
Publication year - 2012
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1111/j.1460-9568.2012.08272.x
Subject(s) - chemistry , reflex , trigeminal nerve , stimulation , trigeminal ganglion , spinal trigeminal nucleus , neuroscience , anatomy , inhibitory postsynaptic potential , sensory system , nociception , medicine , biology , receptor , biochemistry
Abnormal sensitivity to bright light can cause discomfort or pain and evoke protective reflexes such as lacrimation. Although the trigeminal nerve is probably involved, the mechanism linking luminance to somatic sensory nerve activity remains uncertain. This study determined the effect of bright light on second‐order ocular neurons at the ventral trigeminal interpolaris/caudalis transition (Vi/Vc) region, a major termination zone for trigeminal sensory fibers that innervate the eye. Most Vi/Vc neurons (80.9%) identified by responses to mechanical stimulation of the ocular surface also encoded bright light intensity. Light‐evoked neural activity displayed a long latency to activation (> 10 s) and required transmission through the trigeminal root ganglion. Light‐evoked neural activity was inhibited by intravitreal injection of phenylephrine or l ‐ N G ‐nitro‐arginine methyl ester (L‐NAME), suggesting a mechanism coupled to vascular events within the eye. Laser Doppler flowmetry revealed rapid light‐evoked increases in ocular blood flow that occurred prior to the increase in Vi/Vc neural activity. Synaptic blockade of the Vi/Vc region by cobalt chloride prevented light‐evoked increases in tear volume, whereas blockade at the more caudal spinomedullary junction (Vc/C1) had no effect. In summary, Vi/Vc neurons encoded bright light intensity and were inhibited by drugs that alter blood flow to the eye. These results support the hypothesis that light‐responsive neurons at the Vi/Vc transition region are critical for ocular‐specific functions such as reflex lacrimation, whereas neurons at the caudal Vc/C1 junction region probably serve other aspects of ocular nociception.