Lipopolysaccharide-induced Trigeminal Ganglion Nerve Fiber Damage is Associated with Autophagy Inhibition

Objective This study aimed to determine whether lipopolysaccharide(LPS)induces the loss of corneal nerve fibers in cultured trigeminal ganglion(TG)cells,and the underlying mechanism of LPS-induced TG neurite damage.Methods TG neurons were isolated from C57BL/6 mice,and the cell viability and purity were maintained for up to 7 days.Then,they were treated with LPS(1µg/mL)or the autophagy regulator(autophibib and rapamycin)alone or in combination for 48 h,and the length of neurites in TG cells was examined by the immunofluorescence staining of the neuron-specific proteinβ3-tubulin.Afterwards,the molecular mechanisms by which LPS induces TG neuron damage were explored.Results The immunofluorescence staining revealed that the average length of neurites in TG cells significantly decreased after LPS treatment.Importantly,LPS induced the impairment of autophagic flux in TG cells,which was evidenced by the increase in the accumulation of LC3 and p62 proteins.The pharmacological inhibition of autophagy by autophinib dramatically reduced the length of TG neurites.However,the rapamycin-induced activation of autophagy significantly lessened the effect of LPS on the degeneration of TG neurites.Conclusion LPS-induced autophagy inhibition contributes to the loss of TG neurites.

Facial pain induces the alteration of transient receptor potential vanilloid receptor 1 expression in rat trigeminal ganglion

Objective To investigate the involvement of transient receptor potential vanilloid receptor 1 （TRPV1） in the facial inflammatory pain in relation to thermal hyperalgesia and cold pain sensation. Methods Facial inflammatory pain model was developed by subcutaneous injection of turpentine oil （TO） into rat facial area. Head withdrawal thermal latency （HWTL） and head withdrawal cold latency （HWCL） were measured once a day for 21 d after TO treatment using thermal and cold measurement apparatus. The immunohistochemical staining, cell-size frequency analysis and the survey of average optical density （OD） value were used to observe the changes of TRPV1 expression in the neurons of the trigeminal ganglion （TG）, peripheral nerve fibers in the vibrissal pad, and central projection processes in the trigeminal sensory nuclei caudalis （Vc） on day 3, 5, 7, 14, and 21 after TO injection. Results HWTL and HWCL decreased significantly from day 1 to day 14 after TO injection with the lowest value on day 5 and day 3, respectively, and both recovered on day 21. The number of TRPV1-labeled neurons increased remarkably from day 1 to day 14 with a peak on day 7, and returned back to the normal level on day 21. In control rats, only small and medium-sized TG neurons were immunoreactive （IR） to TRPV1, and the TRPV1-IR terminals were abundant in both the vibrissal pad and the Vc. Within 2 weeks of inflammation, the expression of TRPV1 in small and medium-sized TG neurons increased obviously. Also the TRPV1 stained terminals and fibers appeared more frequent and denser in both the vibrissal pad skin and throughout laminae Ⅰ and the outer zone of laminae Ⅱ （Ⅱo） of Vc. Conclusion Facial inflammatory pain could induce hyperalgesia to noxious heat and cold stimuli, and result in increase of the numbers of TRPV1 positive TG neurons and the peripheral and central terminals of TG. These results suggest that the phenotypic changes of TRPV1 expression in small and medium-sized TG neurons and terminals might play an important role in the development and maintenance of TO-induced inflammatory thermal hyperalgesia and cold pain sensation.

Changes in P2Y purinoreceptor-mediated intracellular calcium signal pathways results in inositol-1, 4, 5-triphosphate-sensitive calcium stores in rat small trigeminal ganglion neurons

BACKGROUND： Most of the currently available information on purinergic receptors （P2Rs） involved in pain transmission is based on results obtained in dorsal root ganglion or the spinal cord. However, the mechanism of P2Rs in trigeminal neuralgia remains unclear. OBJECTIVE： To investigate changes in the P2R-mediated calcium signaling pathway in nociceptive trigemJnal ganglion neurons. DESIGN, TIME AND SETTING： In vitro experiments were conducted at the Patch-Clamp Laboratory of Comprehensive Experiment Center of Anhui Medical University, China from September 2008 to June 2009. MATERIALS： Thapsigargin, caffeine, suramin, and adenosine 5＇-triphosphate were purchased from Sigma, USA. METHODS： Using Fura-2-based microfluorimetry, intracellular calcium concentration （[Ca^2＋]i） was measured in freshly isolated adult rat small trigeminal ganglion neurons before and after drug application. MAIN OUTCOME MEASURES： Fluorescent intensities were expressed as the ratio F340/F380 to observe [Ca^2＋]i changes. RESULTS： In normal extracellular solution and Ca^2＋-free solution, application of thapsigargin （1 μmol/L）, a sarcoplasmic reticulum Ca^2＋ pump adenosine 5＇-triphosphate inhibitor, as well as caffeine （20 mmol/L）, a ryanodine receptor agonist, triggered [Ca^2＋]i increase in small trigeminal ganglion neurons. A similar response was induced by application of adenosine 5＇-triphosphate （100 μmol/L）. In Ca^2＋-free conditions, adenosine 5＇-triphosphate-induced [Ca^2＋]i transients in small trigeminal ganglion neurons were inhibited in cells pre-treated with thapsigargin （P 〈 0.01）, but not by caffeine （P 〉 0.05）. In normal, extracellular solution, adenosine 5＇-triphosphate-induced [Ca^2＋]i transients in small trigeminal ganglion neurons were partly inhibited in cells pre-treated with thapsigargin （P 〈 0.05）. CONCLUSION： Inositol-1,4, 5-triphosphate （IP3）- and ryanodine-sensitive Ca^2＋ stores exist in rat nociceptive trigeminal ganglion neurons. Two pathways are involved in the purinoreceptor-mediated [Ca^2＋]i rise observed in nociceptive trigeminal ganglion neurons. One pathway involves the metabotropic P2Y receptors, which are associated with the IP3 sensitive Ca^2＋store, and the second pathway is coupled to ionotropic P2X receptors that induce the Ca^2＋ influx.

Effects of Phorbol-12,13-dibuterate on Sodium Currents and Potassium Currents in Rat Trigeminal Ganglion Neurons

The effects of phorbol-12,13-dibuterate （PDBu） on total sodium current （INa-total）, tetrodotoxin-resistant sodium current （INa-TFXr）, 4-AP-sensitive potassium current （IA） and TEA-sensitive potassium current （IK） in trigeminal ganglion （TG） neurons were investigated. Whole-cell patch clamp techniques were used to record ion currents in cultured TG neurons of rats. Results revealed that 0.5μmol/L PDBu reduced the amplitude of INa-total by （38.3±4.5）% （n=6, P〈0.05）, but neither the G-V curve （control： V0.5 =-17.1±4.3 mV, k=7.4±1.3; PDBu： V0.5=-15.9±5.9 mV, k=5.9±1.4; n=6, P〉0.05） nor the inactivation rate constant （control： 3.6±0.9 ms; PDBu： 3.6±0.8 ms; n=6, P〉0.05） was altered. 0.5 μmol/L PDBu could significantly increase the amplitude of INa-TFXr by （37.2± 3.2）% （n=9, P〈0.05） without affecting the G-V curve （control： V0.5=-14.7±6.0 mV, k=6.9± 1.4; PDBu： V0.5=- 11.1±5.3 mV, k=8.1± 1.5; n=5, P〉0.05 ） or the inactivation rate constant （control： 4.6±0.6 ms; PDBu： 4.2±0.5 ms; n=5, P〉0.05）. 0.5 μmol/L PDBu inhibited IK by （15.6±5.0） % （n=16, P〈0.05）, and V0.5 was significantly altered from - 4.7±1.4 mV to -7.9 ±1.8 mV （n=16, P〈0.05）. IA was not significantly affected by PDBu, 0.5μmol/L PDBu decreased IA by only （0.3±3.2）% （n=5, P〉0.05）. It was concluded that PDBu inhibited INa-total ：.but enhanced INa-TFXr, and inhibited IK without affecting IA. These data suggested that the activation of PKC pathway could exert the actions.

Chlorogenic acid alters the voltage-gated potassium channel currents of trigeminal ganglion neurons

Chlorogenic acid（5-caffeoylquinic acid, CGA） is a phenolic compound that is found ubiquitously in plants, fruits and vegetables and is formed via the esterification of caffeic acid and quinic acid. In addition to its notable biological functions against cardiovascular diseases, type-2 diabetes and inflammatory conditions, CGA was recently hypothesized to be an alternative for the treatment of neurological diseases such as Alzheimer＇s disease and neuropathic pain disorders. However, its mechanism of action is unclear.Voltage-gated potassium channel（Kv） is a crucial factor in the electro-physiological processes of sensory neurons. Kv has also been identified as a potential therapeutic target for inflammation and neuropathic pain disorders. In this study, we analysed the effects of CGA on the two main subtypes of Kv in trigeminal ganglion neurons, namely, the IK,Aand IK,Vchannels. Trigeminal ganglion（TRG）neurons were acutely disassociated from the rat TRG, and two different doses of CGA（0.2 and 1 mmol·L21） were applied to the cells.Whole-cell patch-clamp recordings were performed to observe alterations in the activation and inactivation properties of the IK,Aand IK,Vchannels. The results demonstrated that 0.2 mmol·L21CGA decreased the peak current density of IK,A. Both 0.2 mmol·L21and1 mmol·L21CGA also caused a significant reduction in the activation and inactivation thresholds of IK,Aand IK,V. CGA exhibited a strong effect on the activation and inactivation velocities of IK,Aand IK,V. These findings provide novel evidence explaining the biological effects of CGA, especially regarding its neurological effects.

Effect of Interleukin-1β on I_A and I_K Currents in Cultured Murine Trigeminal Ganglion Neurons

To investigate the effect of intedeukin-1β （IL-1β） on IA and IK currents in cultured murine trigeminal ganglion （TG） neurons, whole-cell patch clamp technique was used to record the IA and IK currents before and after 20 ng/mL IL-1β perfusion. Our results showed that 20 ng/mL IL-1β inhibited IA currents （18.3±10.7）% （n=6, P〈0.05）. IL-1β at 20 ng/mL had no effect on G-V curve of IA but moved the H-infinity curve V0.5 from -36.6±6. 1 mV to-42.4±5.2 mV （n=5, P〈0.01）. However, 20 ng/mL IL-1β had effect on neither the amplitude nor the G-V curve of IK. IL-1β was found to selectively inhibit IA current in TG neurons and the effect may contribute to hyperalgesia under various inflammatory conditions.

Cannabinoids Increase Mechanosensitivity of Trigeminal Ganglion Neurons Innervating the Inner Walls of Rat Anterior Chambers via Activation of TRPA1

Our previous study found that some trigeminal ganglion（TG） nerve endings in the inner walls of rat anterior chambers were mechanosensitive, and transient receptor potential ankyrin 1（TRPA1） was an essential mechanosensitive channel in the membrane. To address the effect of cannabinoids on the mechanosensitive TG nerve endings in the inner walls of anterior chambers of rat eye, we investigated the effect of the（R）-（＋）-WIN55, 212-2 mesylate salt（WIN）, a synthetic cannabinoid on their cell bodies in vitro. Rat TG neurons innervating the inner walls of the anterior chambers were labeled by 1,1＇-dilinoleyl-3,3,3＇,3＇-tetramethylindocarbocyanine, 4-chlorobenzenesulfona（FAST Di I）. Whole cell patch clamp was performed to record the currents induced by drugs and mechanical stimulation. Mechanical stimulation was applied to the neurons by buffer ejection. WIN evoked inward currents via TRPA1 activation in FAST Di I-labeled TG neurons. WIN enhanced mechanosensitive currents via TRPA1 activation in FAST Di I-labeled TG neurons. Our results indicate that cannabinoids can enhance the mechanosensitivity of TG endings in the inner walls of anterior chambers of rat eye via TRPA1 activation.

Regulatory effects of anandamide on intracellular Ca^(2+) concentration increase in trigeminal ganglion neurons

Activation of cannabinoid receptor type 1 on presynaptic neurons is postulated to suppress neu- ~ ~ ~ 2＋ ~ ~ 2＋ rotransmlsslon by decreasing Ca reflux through high voltage-gated Ca channels. However, recent studies suggest that cannabinoids which activate cannabinoid receptor type 1 can increase neurotransmitter release by enhancing Ca2＋ influx in vitro. The aim of the present study was to investigate the modulation of intracellular Ca2＋ concentration by the cannabinoid receptor type 1 agonist anandamide, and its underlying mechanisms. Using whole cell voltage-damp and calcium imaging in cultured trigeminal ganglion neurons, we found that anandamide directly caused Ca2＋ influx in a dose-dependent manner, which then triggered an increase of intracellular Ca2＋ concentration. The cyclic adenosine and guanosine monophosphate-dependent protein kinase systems, but not the protein kinase C system, were involved in the increased intracellular Ca2＋concentration by anandamide. This result showed that anandamide increased intracellu- lar Ca2＋ concentration and inhibited high voltage-gated Ca2＋ channels through different signal transduction pathways.

Inhibitory effects of synthetic cannabinoid WIN55,212-2 on nicotine-activated currents in rat trigeminal ganglion neurons

Cannabinoid and nicotinic acetylcholine receptors are strongly associated with algesia. Previous studies in our laboratory have reported inhibitory effects of synthetic cannabinoid WIN55, 212-2 on nicotine-activated currents （Inic）, but the underlying mechanisms remain poorly understood. The present study used whole-cell patch clamp techniques to investigate the modulatory effects of synthetic cannabinoid WIN55, 212-2 on Inic in cultured rat trigeminal ganglion neurons. The results revealed several major findings： WIN55, 212-2 inhibited Inic in rat trigeminal ganglion neurons. In addition, when WIN55, 212-2 （3 μmol/L） was applied simultaneously with nicotine （100 μmol/L）, the inhibition of WIN55, 212-2 on Inic was reversible, concentration-dependent and voltage-independent This effect was not mediated by CB1, CB2 or VR1 receptors; neither the selective CB1 receptor antagonist AM281, CB2 receptor antagonist AM630 nor VR1 receptor antagonist capsazepine reduced the inhibitory effect of WIN55, 212-2. Further, the inhibition of nicotinic responses by WIN55, 212-2 was not sensitive to the membrane permeable cyclic adenosine monophosphate （cAMP） analog 8-Br-cAMP. The G-protein inhibitor GDP-I3-S （1 mmol/L） did not block the inhibitory effects of WIN55, 212-2 on/n^c, excluding the involvement of G-protein mediation. The results suggested that WIN55, 212-2 inhibits/n^o directly via the neuronal nicotinic acetylcholine receptor, and that this inhibition is non-competitive. WIN55, 212-2 did not act as an open channel blocker of the neuronal nicotinic acetylcholine receptor, and did not affect the desensitization of Into. The results suggest that nicotine receptors may be physically plugged from outside the membrane by drugs containing WIN55, 212-2.

Inhibition of 5-HT_3 Receptors-activated Currents by Cannabinoids in Rat Trigeminal Ganglion Neurons

This study investigated the modulatory effect of synthetic cannabinoids WIN55,212-2 on 5-HT3 receptor-activated currents (I5-HT3) in cultured rat trigeminal ganglion (TG) neurons using whole-cell patch clamp technique. The results showed that: (1) The majority of examined neurons (78.70%) were sensitive to 5-HT (3–300 μmol/L). 5-HT induced inward currents in a concentration-dependent manner and the currents were blocked by ICS 205-930 (1 μmol/L), a selective antagonist of the 5-HT3 receptor; (2) Pre-application of WIN55,212-2 (0.01–1 μmol/L) significantly inhibited I5-HT3 reversibly in concentration-dependent and voltage-independent manners. The concentra-tion-response curve of 5-HT3 receptor was shifted downward by WIN55,212-2 without any change of the threshold value. The EC50 values of two curves were very close (17.5±4.5) mmol/L vs. (15.2±4.5) mmol/L and WIN55,212-2 decreased the maximal amplitude of I5-HT3 by (48.65±4.15)%; (3) Neither AM281, a selective CB1 receptor antagonist, nor AM630, a selective CB2 receptor antagonist reversed the inhibition of I5-HT3 by WIN55,212-2; (4) When WIN55,212-2 was given from 15 to 120 s before 5-HT application, inhibitory effect was gradually increased and the maximal inhibition took place at 90 s, and the inhibition remained at the same level after 90 s. We are led to concluded that-WIN55,212-2 inhibited I5-HT3 significantly and neither CB1 receptor antagonist nor CB2 receptor antagonist could reverse the inhibition of I5-HT3 by WIN55,212-2. Moreover, WIN55,212-2 is not an open channel blocker (OCB) of 5-HT3 receptor. WIN55,212-2 significantly inhibited 5-HT-activated currents in a non-competitive manner. The inhibition of I5-HT3 by WIN55,212-2 is probably new one of peripheral analgesic mechanisms of WIN55,212-2, but the mechanism by which WIN55,212-2 inhibits I5-HT3 warrants further investigation.

Histochemical Observation of Nitric Oxide Synthase in Trigeminal Ganglion of Rats with Experimental Pulpitis

Summary: In order to understand the roles of nitric oxide (NO) in pulpalgia and pulpitis, the histochemistry of nitric oxide synthase (NOS) in the neurons of trigeminal ganglion in experimental pulpitis rat and human inflammatory dental pulp tissues were histochemically studied by NADPH diaphorase (NADPH D) techniques. Results showed that NADPH D positive neurons were scattered in rat trigeminal ganglions, but the sizes of positive neurons were not changed. None of NOS positive fibers was found in human normal and inflammatory dental pulp tissues. The results suggested that NOS in trigeminal ganglion might play an important role in sensory transmission and regulation of pulpalgia. The absence of NOS positive nerves in human pulp suggested that NO may not be related to inflammatory stimulation and transmission in dental pulp tissues.

Effects of WIN 55,212-2 on I_K Current in Cultured Trigeminal Ganglion Neurons of Rat

Summary: To investigate the effects of WIN 55,212-2 on I K in cultured rat trigeminal ganglion (TG) neurons, whole-cell patch clamp techniques were used to record the I K before and after WIN 55,212-2 perfusion at different concentrations. 30 μmol/L WIN 55,212-2 markedly (35 7 %± 7 3 %, P<0.01, n=8) inhibited I K currents, and the currents were partially recovered after washing. 30 μmol/L WIN 55,212-2 also induced a significant depolarizing shift in conductance-voltage parameters (control: V 0 5=10 43 ± 4.25 mV, k=16 27±3 86; WIN 55,212-2: V 0.5=24.71±3.91 mV, k =16.69±2.75; n = 8, P<0.01 for V 0.5). 0.01 μmol/L WIN 55,212-2 slightly (27.0 %± 7.9 %, P<0.05, n=7) increased I K currents, but had no significant change in conductance–voltage parameters (control: V 0.5=10.74±5.27 mV, k=17.33±2.96; WIN 55,212-2: V 0.5=11.06±2.05 mV, k=19.69±6.60; n=7, P>0.05 for V 0.5 and k). These results suggested that WIN 55,212-2 has dual action, which might be through different receptors.

Optimal duration of percutaneous microballoon compression for treatment of trigeminal nerve injury

Percutaneous microballoon compression of the trigeminal ganglion is a brand new operative technique for the treatment of trigeminal neuralgia. However, it is unclear how the procedure mediates pain relief, and there are no standardized criteria, such as compression pressure, com- pression time or balloon shape, for the procedure. In this study, percutaneous microballoon compression was performed on the rabbit trigeminal ganglion at a mean inflation pressure of 1,005 ＋ 150 mmHg for 2 or 5 minutes. At 1, 7 and 14 days after percutaneous microballoon compression, the large-diameter myelinated nerves displayed axonal swelling, rupture and demy- elination under the electron microscope. Fragmentation of myelin and formation of digestion chambers were more evident after 5 minutes of compression. Image analyzer results showed that the diameter of trigeminal ganglion cells remained unaltered after compression. These experi- mental findings indicate that a 2-minute period of compression can suppress pain transduction. Immunohistochemical staining revealed that vascular endothelial growth factor expression in the ganglion cells and axons was significantly increased 7 days after trigeminal ganglion compression, however, the changes were similar after 2-minute compression and 5-minute compression. The upregulated expression of vascular endothelial growth factor in the ganglion cells after percu- taneous microballoon compression can promote the repair of the injured nerve. These findings suggest that long-term compression is ideal for patients with recurrent trigeminal neuralgia.

Expression of hNav1.8 sodium channel protein in affected nerves of patients with trigeminal neuralgia

Objective: To explore the pathogenesis of trigeminal neuralgia (TN) and to provide a new target for the drug treatment of TN by studying the expression of tetrodotoxin-resistant hNav1. 8 sodium channel protein in affected nerves of patients with TN. Methods: Twelve affected inferior alveolar nerves were obtained from patients with idiopathic TN, to whom the drug therapy was not effective. As negative control, one nonnal inferior alveolar nerve was obtained from patients who accepted the combined radical neck dissection with glossectomy and mandibulectomy. One muscle sample was obtained as normal control. One dorsal root ganglion from rat was as positive control. These tissues and prepared hNav1. 8 antibody were conducted immunohistochemistry response. Results: hNav1.8 channel protein was expresses in all the 12 specimens of the affected nerves of patients with TN, but not in the muscle sample and the normal inferior alveolar nerve. Conclusion: The abnormal expression of hNav1. 8 channel protein in the affected nerves of patients with TN may play an important role in the pathogenesis of TN.

ATP对大鼠三叉神经节小直径神经元胞内钙浓度的调制作用及其机制

目的探讨神经递质ATP通过何种途径引起大鼠三叉神经节(trigeminal ganglion,TG)小直径神经元胞内钙离子浓度升高。方法在急性分离的TG神经元上,应用钙离子成像技术检测胞内游离Ca2+浓度([Ca2+]i)的变化。结果在大鼠TG小直径神经元中,ATP(100μmol·L-1),thap-sigargin(1μmol·L-1,内质网钙泵抑制剂)和咖啡因(20mmol·L-1,内质网钙离子通道开放剂)在正常细胞外液和去除细胞外Ca2+的情况下,均能够引起细胞[Ca2+]i升高。在细胞外无Ca2+条件下,thapsigargin能够可逆地抑制ATP引起细胞内[Ca2+]i升高(n=8,P<0.01),而咖啡因对ATP引起的细胞内[Ca2+]i升高无影响(n=6,P>0.05)。然而在正常外液中,thapsigargin不能完全抑制ATP引起的细胞内[Ca2+]i升高,不过ATP引起的细胞内[Ca2+]i升高的幅度明显地低于thapsigargin处理前(n=7,P<0.05)。结论在大鼠TG小直径神经元中,存在有IP3敏感钙库和Ryanod-ine敏感钙库。ATP可通过激动P2Y受体引起IP3敏感钙库的Ca2+释放,也可通过激动P2X受体引起细胞外钙内流。

Electroacupuncture at Fengchi(GB20) inhibits calcitonin gene-related peptide expression in the trigeminovascular system of a rat model of migraine

Most migraine patients suffer from cutaneous allodynia; however, the underlying mechanisms are unclear. Calcitonin gene-related peptide（CGRP） plays an important role in the pathophysiology of migraine, and it is therefore, a potential therapeutic target for treating the pain. In the present study, a rat model of conscious migraine, induced by repeated electrical stimulation of the superior sagittal sinus, was established and treated with electroacupuncture at Fengchi（GB20）（depth of 2–3 mm, frequency of 2/15 Hz, intensity of 0.5–1.0 m A, 15 minutes/day, for 7 consecutive days）. Electroacupuncture at GB20 significantly alleviated the decrease in hind paw and facial withdrawal thresholds and significantly lessened the increase in the levels of CGRP in the trigeminal ganglion, trigeminal nucleus caudalis and ventroposterior medial thalamic nucleus in rats with migraine. No CGRP-positive cells were detected in the trigeminal nucleus caudalis or ventroposterior medial thalamic nucleus by immunofluorescence. Our findings suggest that electroacupuncture treatment ameliorates migraine pain and associated cutaneous allodynia by modulating the trigeminovascular system ascending pathway, at least in part by inhibiting CGRP expression in the trigeminal ganglion.

Current advances in orthodontic pain

Orthodontic pain is an inflammatory pain that is initiated by orthodontic force-induced vascular occlusion followed by a cascade of inflammatory responses, including vascular changes, the recruitment of inflammatory and immune cells, and the release of neurogenic and pro-inflammatory mediators. Ultimately, endogenous analgesic mechanisms check the inflammatory response and the sensation of pain subsides. The orthodontic pain signal, once received by periodontal sensory endings, reaches the sensory cortex for pain perception through three-order neurons： the trigeminal neuron at the trigeminal ganglia, the trigeminal nucleus caudalis at the medulla oblongata and the ventroposterior nucleus at the thalamus. Many brain areas participate in the emotion, cognition and memory of orthodontic pain, including the insular cortex, amygdala, hippocampus, locus coeruleus and hypothalamus. A built-in analgesic neural pathway--periaqueductal grey and dorsal raphe---has an important role in alleviating orthodontic pain. Currently, several treatment modalities have been applied for the relief of orthodontic pain, including pharmacological, mechanical and behavioural approaches and low-level laser therapy. The effectiveness of nonsteroidal anti- inflammatory drugs for pain relief has been validated, but its effects on tooth movement are controversial. However, more studies are needed to verify the effectiveness of other modalities. Furthermore, gene therapy is a novel, viable and promising modality for alleviatin~ orthodontic oain in the future.

Flunarizine inhibits sensory neuron excitability by blocking voltage-gated Na＋ and Ca2＋ currents in trigeminal ganglion neurons

Background Although flunarizine has been widely used for migraine prophylaxis with clear success, the mechanisms of its actions in migraine prophylaxis are not completely understood. The aim of this study was to investigate the effects of flunarizine on tetrodotoxin-resistant Na＋ channels and high-voltage activated Ca2＋ channels of acutely isolated mouse trigeminal ganglion neurons. Methods Sodium currents and calcium currents in trigeminal ganglion neurons were monitored using whole-cell patch-clamp recordings. Paired Student＇s t test was used as appropriate to evaluate the statistical significance of differences between two group means. Results Both tetrodotoxin-resistant sodium currents and high-voltage activated calcium currents were blocked by flunarizine in a concentration-dependent manner with the concentration producing half-maximal current block values of 2.89 μmol/L and 2.73 μmol/L, respectively. The steady-state inactivation curves of tetrodotoxin-resistant sodium currents and high-voltage activated calcium currents were shifted towards more hyperpolarizing potentials after exposure to flunarizine. Furthermore, the actions of flunarizine in blocking tetrodotoxin-resistant sodium currents and high-voltage activated calcium currents were use-dependent, with effects enhanced at higher rates of channel activation. Conclusion Blockades of these currents might help explain the peripheral mechanism underlying the preventive effect of flunarizine on migraine attacks.

TLR8 in the Trigeminal Ganglion Contributes to the Maintenance of Trigeminal Neuropathic Pain in Mice

Trigeminal neuropathic pain(TNP)is a significant health problem but the involved mechanism has not been completely elucidated.Toll-like receptors(TLRs)have recently been demonstrated to be expressed in the dorsal root ganglion and involved in chronic pain.Here,we show that TLR8 was persistently increased in the trigeminal ganglion(TG)neurons in model of TNP induced by partial infraorbital nerve ligation(pIONL).In addition,deletion or knockdown of Tlr8 in the TG attenuated pIONL-induced mechanical allodynia,reduced the activation of ERK and p38-MAPK,and decreased the expression of pro-inflammatory cytokines in the TG.Furthermore,intra-TG injection of the TLR8 agonist VTX-2337 induced pain hypersensitivity.VTX-2337 also increased the intracellular Ca^(2+)concentration,induced the activation of ERK and p38,and increased the expression of pro-inflammatory cytokines in the TG.These data indicate that TLR8 contributes to the maintenance of TNP through increasing MAPK-mediated neuroinflammation.Targeting TLR8 signaling may be effective for the treatment of TNP.

P2X_3 , but not P2X_1 , Receptors Mediate ATP-activated Current in Neurons Innervating Tooth-pulp

Summary： We developed a method that allows us to label nociceptive neurons innervating tooth-pulp in rat trigeminal ganglion neurons using a retrograde fluorescence-tracing method, to re- cord ATP-activated current in freshly isolated fluorescence-labeled neurons and to conduct single cell immunohistochemical staining for P2X1 and P2X3 subunits in the same neuron. Three types of ATP-activated current in these neurons （F, I and S） were recorded. The cells exhibiting the type F current mainly showed positive staining for P2X3, but negative staining for P2X1. The results provide direct and convincing evidence at the level of single native nociceptive neurons for correlation of the characteristics of ATP-activated currents with their composition of P2Xl and P2X3 subunits and cell size. The results also suggest that the P2X3, but not P2X1, is the main subunit that mediates the fast ATP-activated current in nociceptive neurons.