Open AccessSensitization of trigeminal brainstem pathways in a model for tear deficient dry eye
Author(s) -
Mostafeezur Rahman,
Keiichiro Okamoto,
Roby C. Thompson,
Ayano Katagiri,
David A. Bereiter
Publication year - 2015
Publication title -
pain
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.524
H-Index - 258
eISSN - 1872-6623
pISSN - 0304-3959
DOI - 10.1097/j.pain.0000000000000135
Subject(s) - brainstem , hypertonic saline , sensitization , medicine , trigeminal nerve , spinal trigeminal nucleus , anesthesia , saline , ophthalmology , nociception , receptor , immunology
Chronic dry eye disease (DE) is associated with an unstable tear film and symptoms of ocular discomfort. The characteristics of symptoms suggest a key role for central neural processing; however, little is known about central neuroplasticity and DE. We used a model for tear deficient DE and assessed effects on eye blink behavior, orbicularis oculi muscle activity (OOemg), and trigeminal brainstem neural activity in male rats. Ocular-responsive neurons were recorded at the interpolaris/caudalis transition (Vi/Vc) and Vc/upper cervical cord (Vc/C1) regions under isoflurane, whereas OOemg activity was recorded under urethane. Spontaneous tear volume was reduced by ∼50% at 14 days after exorbital gland removal. Hypertonic saline-evoked eye blink behavior in awake rats was enhanced throughout the 14 days after surgery. Saline-evoked neural activity at the Vi/Vc transition and in superficial and deep laminae at the Vc/C1 region was greatly enhanced in DE rats. Neurons from DE rats classified as wide dynamic range displayed enlarged convergent periorbital receptive fields consistent with central sensitization. Saline-evoked OOemg activity was markedly enhanced in DE rats compared with controls. Synaptic blockade at the Vi/Vc transition or the Vc/C1 region greatly reduced hypertonic saline-evoked OOemg activity in DE and sham rats. These results indicated that persistent tear deficiency caused sensitization of ocular-responsive neurons at multiple regions of the caudal trigeminal brainstem and enhanced OOemg activity. Central sensitization of ocular-related brainstem circuits is a significant factor in DE and likely contributes to the apparent weak correlation between peripheral signs of tear dysfunction and symptoms of irritation.