The Relationship Of Pain And The Changes Of Microcirculation And GDNF In Trigeminal Nerve

Objective: To study the changes of the pain-related behaviours, microcirculationbed and glial cell line-derived neurotrophic factor(GDNF) in Sprague Dauley rat modelof idiopathic trigeminal neuralgia-like, for exploring the machanism and therapy oftrigeminal neuralgia.Methods:1. Animal modelAll of60male SD rats were randomly divided into3groups (operative groups,sham-operative groups and control groups).1) In the operative groups (27), a chronic constriction injury (CCI) was producedby placing loose chromic gut ligatures around the right infraorbital nerve (ION). Ratswere anesthetized with10%chloral hydrate intraperitoneal. The incision (1cm) wasmade along the right side of the gingival buccal groove closed to maxillary first molarunder direct visual control in the fixed rat, followed by ligatures of ION with2chromicguts (4-0,2mm intervals). The incision was closed in layers using nylon sutures (4-0).2) In the sham-operative groups (27), the right infraorbital nerve was only exposedusing the same procedure without ligation.3) In the control groups (6), the right infraorbital nerve was not subject to anytreatment.The behavioral reactions and the mechanical response threshold (pain threshold)of the3groups were recorded at different time after operation.2. Perfusion with Indian inkRats were anesthetized with10%chloral hydrate intraperitoneal by intraperitonealinjection in different time. Cardiovascular system was perfused with saline,4%paraformaldehyde and5%gelatin-ink in order. The trigeminal nerve ganglion and ION were obtained. The changes of microcirculation in each group were observed by usingHE staining, focus overlap and specimen transparent.3. Immunohistochemical stainThe trigeminal ganglion was obtained. The GDNF expression in each group wasanalyzed with immunohistochemical staining.4. Statistical analysisThe experimental data were analyzed with Zerene Stacker1.02, Image-Pro Plus6.0and SPSS13.0.Results:1. An allodynia to mechanical stimulation in the territory of ligated ION wasfound from the2nd week after operation. There was a significant difference (P<0.01) inpain threshold, compared with the pre-operation, sham-operative groups and controlgroups. Low-intensity mechanical sensory input resulted in hyper-responsiveness. Thethresholds started to increase gradually from the6th week and reached the original levelon10-12th week after operation.2. On the2nd week after operation, obvious demyelination and damages werefound in the fibers of the ION. On the6th week after operation, the degeneration of thefibers reduced. On the12th week after operation, the injured nerve almost recovered tonormal.3. The epineurial vessels of the ION ran along the nerve’s long axis and gave offbranches, distributing along nerve bundle to enter into endoneurium. The microvascularnumber of microcirculation bed in operative groups reduces compared with thesham-operative groups and the control groups. The microcirculation of the trigeminalnerve in the operative group was slightly different in different time.4. The cells expressing GDNF markedly increased in operative groups comparedwith the sham-operative groups and the control groups (P<0.01), and had a change indifferent time. The expression of GDNF showed no obvious difference in thesham-operative groups and the control groups (P>0.05).Conclusion:1. CCI-ION is able to establishment the trigeminal neuralgia-like animal model.The abnormal pain threshold related to partial demyelination of the ION. This modelimitates successfully the clinical trigeminal neuralgia caused by nerve constriction,which could be easily produced with a high success rate. The model provides afoundation for studying mechanism and treatment of trigeminal neuralgia. 2. Microcirculatory regulation in the ION mainly depends on the epineurial andperineurial arterioles. The microcirculation of trigeminal nerve may play an importantrole in trigeminal neuralgia. The ION being oppressed for long time can causemicrocirculation trauma, which may lead to demyelination of the trigeminal nerve.3. The expression of GDNF in trigeminal ganglion increases, and changes withtime. GDNF plays a role in regulation of pain by promoting restoration and regenerationof nerve fibers.