Central trigeminal mechanisms in ocular pain

[unreadable] DESCRIPTION (provided by applicant): The overall goal of this project is to understand how persistent inflammation alters the properties of trigeminal brainstem neurons that process sensory signals from the ocular surface. Chronic ocular inflammation is a common clinical complaint that if not adequately managed can lead to abnormalities of the ocular surface and even loss of vision. It is well established that chronic inflammation induces long-term changes in spinal cord neurons; however, similar studies have not been extended to the trigeminal brainstem complex that displays unique properties different from the spinal cord. Sensory input from the ocular surface is processed at the rostral and caudal poles of trigeminal subnucleus caudalis: the rostral trigeminal subnucleus interpolaris/caudalis (Vi/Vc) transition and the caudal trigeminal subnucleus caudalis/cervical cord (Vc/C1) junction regions. As a result of new findings during the current grant period proposed studies will test two main hypotheses regarding the mechanisms underlying modulation of neurons at the Vi/Vc transition and Vc/C1 junction regions during persistent ocular inflammation. Aim 1 tests the hypothesis that modulation of Vi/Vc transition and Vc/C1 junction neurons after ocular inflammation involves time dependent alterations in GABAergic inhibitory mechanisms. GABA may act through local circuit neurons or intersubnuclear connections between the rostral Vi/Vc and caudal Vc/C1 junction regions. Contributions from GABAA and GABAB receptors are assessed. Aim 2 tests the hypothesis that prostaglandin E2, a major pro-inflammatory agent in severe conjunctivitis, contributes to the development as well as maintenance of long-term changes in trigeminal brainstem neurons after ocular inflammation. Emphasis is directed at inhibition of cyclooxygenase and specific receptor subtypes prostaglandins. These studies rely on electrophysiological approaches to test the behavior of single neurons that process sensory input from the ocular surface. Corroborative lines of evidence are provided by microdialysis sampling, immunocytochemistry and western blots. These studies will provide a better understanding of the effects of persistent inflammation on central brain circuits necessary for maintenance of the ocular surface and, more generally, for processing pain-related signals from craniofacial tissues. [unreadable] [unreadable]