Segmental, Axonal, and Demyelinative Lesions in the Trigeminal System Produce Neuropathic Pain
Chronic pain (CP) is among the most disabling and costly afflictions in North America, Europe, and Australia (IASP, 2003). Chronic pain afflicts approximately 2.3 million or 20% of the population of the State of Ohio (Buenaventura et al. 2003) and includes trigeminal neuralgia (TN) and other neuropathic pain (NP) states that are enigmatic. To determine whether proximal more than distal demyelinating lesions produce NP, we studied the effect of glycerol injected into the trigeminal root and identical chronic constrictive injury (CCI) to the infraorbital nerve (ION) in the orbit. Psychometric testing was performed with von Frey monofilaments and a pin prior to and after surgery to determine any change in pain behavioral responses from baseline presurgical behavioral testing. The 50% glycerol injection into trigeminal root caused statistically significant facial pain behavioral responses to tactile stimulation. Ultrastructural study revealed loss of large myelinated axons, ephapsis, degeneration and segmental, axonal, demyelination. The glycerol root injection is a reproducible animal model for the study of pain in the trigeminal system. The double CCI to orbital ION showed no statistically significant effect on pain behavior. In a third study, forty-four male Sprague-Dawley rats received a partial ION ligature with pstchometric behavioral testing before and after surgical manipulation with sham and normal controls. At weekly intervals after surgery the animals were studied with light and electron microscopy. The ION, trigeminal ganglia, and brainstem were evaluated for structural and inflammatory changes with Galanin (GAL). Microscopy showed segmental, axonal, demyelinative lesions and degeneration. The immunocytochemistry with GAL showed significant expression in the affected ION, ganglia and brainstem with similar changes on the normal side. The GAL upregulation was accompanied by a significant increase in aversive pain behavior. These two models will be studied with neuroimaging techniques, pharmacologic and surgical manipulations in animals and patients.
School:University of Toledo Health Science Campus
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:demyelinative axonal trigeminal neuropathic pain model
Date of Publication:01/01/2005