Infraorbital Nerve Constriction Research Articles

Blockage of the fractalkine pathway reduces hyperalgesia and prevents morphological glial alterations-Comparison between inflammatory and neuropathic orofacial pain in male rats.

This study aimed to evaluate the effects of inhibitors of the fractalkine pathway in hyperalgesia in inflammatory and neuropathic orofacial pain in male rats and the morphological changes in microglia and satellite glial cells (SGCs). Rats were submitted to zymosan-induced arthritis of the temporomandibular joint or infraorbital nerve constriction, and treated intrathecally with a P2 X7 antagonist, a cathepsin S inhibitor or a p-38 mitogen-activated protein kinase (MAPK) inhibitor. Mechanical hyperalgesia was evaluated 4 and 6 h following arthritis induction or 7 and 14 days following nerve ligation. The expression of the receptor CX3 CR1 , phospho-p-38 MAPK, ionized calcium-binding adapter molecule-1 (Iba-1), and glutamine synthetase and the morphological changes in microglia and SGCs were evaluated by confocal microscopy. In both inflammatory and neuropathic models, untreated animals presented a higher expression of CX3 CR1 and developed hyperalgesia and up-regulation of phospho-p-38 MAPK, which was prevented by all drugs (p < .05). The number of microglial processes endpoints and the total branch length were lower in the untreated animals, but the overall immunolabeling of Iba-1 was altered only in neuropathic rats (p < .05). The mean area of SGCs per neuron was significantly altered only in the inflammatory model (p < .05). All morphological alterations were reverted by modulating the fractalkine pathway (p < .05). In conclusion, the blockage of the fractalkine pathway seemed to be a possible therapeutic strategy for inflammatory and neuropathic orofacial pain, reducing mechanical hyperalgesia by impairing the phosphorylation of p-38 MAPK and reverting morphological alterations in microglia and SGCs.

GFAP-NpHR mediated optogenetic inhibition of trigeminal nucleus caudalis attenuates hypersensitive behaviors and thalamic discharge attributed to infraorbital nerve constriction injury

The significance of hyperactive astrocytes in neuropathic pain is crucial. However, the association between medullary astrocytes and trigeminal neuralgia (TN)-related pain processing is unclear. Here, we examined how optogenetic inhibition of medullary astrocytes in the trigeminal nucleus caudalis (TNC) regulates pain hypersensitivity in an infraorbital nerve (ION) constricted TN model. We used adult Sprague Dawley rats subjected to infraorbital nerve (ION) constriction to mimic TN symptoms, with naive and sham rats serving as controls. For in vivo optogenetic manipulations, rats stereotaxically received AAV8-GFAP-eNpHR3.0-mCherry or AAV8-GFAP-mCherry at the trigeminal nucleus caudalis (TNC). Open field, von Frey, air puff, and acetone tests measured pain behavioral flexibility. In vivo thalamic recordings were obtained simultaneously with optogenetic manipulation in the TNC. Orofacial hyperalgesia and thalamic hyperexcitability were both accompanied by medullary astrocyte hyperactivity, marked by upregulated GFAP. The yellow laser-driven inhibition of TNC astrocytes markedly improved behavioral responses and regulated thalamic neuronal responses. Halorhodopsin-mediated inhibition in medullary astrocytes may modify the nociceptive input transmitted through the trigeminothalamic tract and pain perception. Taken together, these findings imply that this subpopulation in the TNC and its thalamic connections play a significant role in regulating the trigeminal pain circuitry, which might aid in the identification of new therapeutic measures in TN management.Graphical

Mechanistic contribution of CaV3.2 calcium channels to trigeminal neuralgia pathophysiology not clarified

Trigeminal neuralgia (TN) is a rare, yet debilitating trigeminal pain disorder, with jolts of supramaximal-debilitating pain in one or more of the three trigeminal branches. Familial TN is now recognized, with a recent report describing several human genetic polymorphisms. One affected gene is the voltage-gated calcium channel, CaV3.2 (CACNA1H), with 19 polymorphisms first described. A recent study in PAIN by Gambeta-et-al (DOI:10.1097/j.pain.0000000000002651) is entitled "CaV3.2 calcium channels contribute to trigeminal neuralgia ". Here, I call into question their claim. My main arguments are 1)-3): 1) Gambeta-et-al studied 4/19 mutations reported in heterologous cellular expression, with two mutations showing gain-of-function of CaV3.2, two mutations not showing gain-of-function. Therefore the exemplary picks of familial TN-associated CaV3.2 mutations do not show a uniform change of channel function, such as gain-of-function. 2) In Gambeta-et-al, one gain-of-function mutation, CaV3.2(G563R) was directed to mouse trigeminal ganglion (TG) neurons, and their resulting hyperexcitability was demonstrated. A critical control of a non-gain-of-function channel was not included here, it was unclear whether neurons were separated by sex, and human sensory neurons were not used. Importantly, it is not clear that TG neurons are the critical cellular site of CaV3.2 mutations. 3) Gambeta-et-al used CaV3.2-/- pan-null knockout mice. Human TN-associated CaV3.2 mutations were not over-expressed. They used a infraorbital nerve constriction injury and measured facial heat hyperalgesia. CaV3.2-/- show a pain phenotype similar to control, yet are not affected by a CaV3-inhibitory compound, Z944. My argument is that when starting with TN-associated human mutations, use of a trigeminal neuropathic pain model is of limited value, and that human mutations have to be expressed against a mouse null background. Re thermal cue, Gambeta-et-al failed to study cold-evoked pain which is a TN clinical hallmark. Thus, Gambeta-et-al's 2022 PAIN-paper offers little new mechanistic evidence why CaV3.2 polymorphisms are associated with trigeminal neuralgia.

Mechanistic contribution of CaV3.2 calcium channels to trigeminal neuralgia pathophysiology not clarified.

Trigeminal neuralgia (TN) is a rare, yet debilitating trigeminal pain disorder, with jolts of supramaximal-debilitating pain in one or more of the three trigeminal branches. Familial TN is now recognized, with a recent report describing several human genetic polymorphisms. One affected gene is the voltage-gated calcium channel, CaV3.2 ( CACNA1H), with 19 polymorphisms first described. A recent study in PAIN by Gambeta-et-al (DOI:10.1097/j.pain.0000000000002651) is entitled " CaV3.2 calcium channels contribute to trigeminal neuralgia ". Here, I call into question their claim. My main arguments are 1)-3): 1) Gambeta-et-al studied 4/19 mutations reported in heterologous cellular expression, with two mutations showing gain-of-function of CaV3.2, two mutations not showing gain-of-function. Therefore the exemplary picks of familial TN-associated CaV3.2 mutations do not show a uniform change of channel function, such as gain-of-function. 2) In Gambeta-et-al, one gain-of-function mutation, CaV3.2(G563R) was directed to mouse trigeminal ganglion (TG) neurons, and their resulting hyperexcitability was demonstrated. A critical control of a non-gain-of-function channel was not included here, it was unclear whether neurons were separated by sex, and human sensory neurons were not used. Importantly, it is not clear that TG neurons are the critical cellular site of CaV3.2 mutations. 3) Gambeta-et-al used CaV3.2-/- pan-null knockout mice. Human TN-associated CaV3.2 mutations were not over-expressed. They used a infraorbital nerve constriction injury and measured facial heat hyperalgesia. CaV3.2-/- show a pain phenotype similar to control, yet are not affected by a CaV3-inhibitory compound, Z944. My argument is that when starting with TN-associated human mutations, use of a trigeminal neuropathic pain model is of limited value, and that human mutations have to be expressed against a mouse null background. Re thermal cue, Gambeta-et-al failed to study cold-evoked pain which is a TN clinical hallmark. Thus, Gambeta-et-al's 2022 PAIN-paper offers little new mechanistic evidence why CaV3.2 polymorphisms are associated with trigeminal neuralgia.

Analgesic Effect of Tranilast in an Animal Model of Neuropathic Pain and Its Role in the Regulation of Tetrahydrobiopterin Synthesis.

Trigeminal neuralgia is unilateral, lancinating, episodic pain that can be provoked by routine activities. Anticonvulsants, such as carbamazepine, are the drugs of choice; however, these possess side-effects. Microvascular decompression is the most effective surgical technique with a higher success rate, although occasionally causes adverse effects. The potential treatment for this type of pain remains unmet. Increased tetrahydrobiopterin (BH4) levels have been reported in association with axonal injury. This study aimed to evaluate the effect of tranilast on relieving neuropathic pain in animal models and analyze the changes in BH4 synthesis. Neuropathic pain was induced via infraorbital nerve constriction. Tranilast, carbamazepine, or saline was injected intraperitoneally to assess the rat’s post-intervention pain response. In the von Frey’s test, the tranilast and carbamazepine groups showed significant changes in the head withdrawal threshold in the ipsilateral whisker pad area. The motor coordination test showed no changes in the tranilast group, whereas the carbamazepine group showed decreased performance, indicating impaired motor coordination. Trigeminal ganglion tissues were used for the PCR array analysis of genes that regulate the BH4 pathway. Downregulation of the sepiapterin reductase (Spr) and aldoketo reductase (Akr) genes after tranilast injection was observed compared to the pain model. These findings suggest that tranilast effectively treats neuropathic pain.

Pain Relief in a Trigeminal Neuralgia Model via Optogenetic Inhibition on Trigeminal Ganglion Itself With Flexible Optic Fiber Cannula.

The trigeminal ganglion (TG) is the primary site of aberration in trigeminal neuralgia (TN), and hence a crucial site where afferent input can be modulated. Here, we postulated that inhibiting TG via optogenetics using flexible optic cannula would diminish brainstem trigeminal nucleus caudalis (TNC) neuronal activity and pain behavior in TN rat model. Infraorbital nerve constriction was employed to induce TN in female Sprague-Dawley rats, while naive and sham rats served as controls. TG-directed microinjections of AAV virus containing either the optogenetic or null vector were delivered to rats in each group. In vivo electrophysiological responses were obtained from the ventral posteromedial nucleus (VPm) of the thalamus with simultaneous TG optogenetic stimulation using flexible optic cannula as well the effects on behavioral responses were investigated. Recordings in TN rats revealed a decrease in burst firing activity during yellow laser driven inhibition on TG, as well as considerably improved behavioral responses. In contrast, we noticed persistent hypersensitivity and increased tonic firing with blue laser stimulation which indicates that TG inhibition can synchronize trigeminal pain signal transmission in a TN animal model. The potential of an optogenetic approach in TG itself with flexible optic fiber to directly disrupt the trigeminal pain circuitry delivers fundamental underpinnings toward its prospective as a trigeminal neuralgia management.

Peripherally Administered Botulinum Toxin Type A Localizes Bilaterally in Trigeminal Ganglia of Animal Model.

Peripheral nerve injury leads to sensory ganglion hyperexcitation, which increases neurotransmitter release and neuropathic pain. Botulinum toxin type A (BoNT/A) regulates pain transmission by reducing neurotransmitter release, thereby attenuating neuropathic pain. Despite multiple studies on the use of BoNT/A for managing neuropathic pain in the orofacial region, its exact mechanism of transport remains unclear. In this study, we investigated the effects of BoNT/A in managing neuropathic pain in two different animal models and its transport mechanism in the trigeminal nerve. Intraperitoneal administration of cisplatin induced bilateral neuropathic pain in the orofacial region, reducing the head withdrawal threshold to mechanical stimulation. Unilateral infraorbital nerve constriction (IONC) also reduced the ipsilateral head withdrawal threshold to mechanical stimulation. Unilateral peripheral administration of BoNT/A to the rat whisker pad attenuated cisplatin-induced pain behavior bilaterally. Furthermore, contralateral peripheral administration of BoNT/A attenuated neuropathy-induced behavior caused by IONC. We also noted the presence of BoNT/A in the blood using the mouse bioassay. In addition, the Alexa Fluor-488-labeled C-terminal half of the heavy chain of BoNT/A (BoNT/A-Hc) was localized in the neurons of the bilateral trigeminal ganglia following its unilateral administration. These findings suggest that axonal and hematogenous transport are involved in the therapeutic effects of peripherally administered BoNT/A in the orofacial region.

Blockade of kappa opioid receptors reduces mechanical hyperalgesia and anxiety-like behavior in a rat model of trigeminal neuropathic pain

It has been shown that kappa opioid receptor (KOR) antagonists, such as nor-binaltorphimine (nor-BNI), have antinociceptive effects in some pain models that affect the trigeminal system. Also, its anxiolytic-like effect has been extensively demonstrated in the literature. The present study aimed to investigate the systemic, local, and central effect of nor-BNI on trigeminal neuropathic pain using the infraorbital nerve constriction model (CCI-ION), as well as to evaluate its effect on anxiety-like behavior associated with this model. Animals received nor-BNI systemically; in the trigeminal ganglion (TG); in the subarachnoid space to target the spinal trigeminal nucleus caudalis (Sp5C) or in the central amygdala (CeA) 14 days after CCI-ION surgery. Systemic administration of nor-BNI caused a significant reduction of facial mechanical hyperalgesia and promoted an anxiolytic-like effect, which was detected in the elevated plus-maze and the light-dark transition tests. When administered in the TG or CeA, the KOR antagonist was able to reduce facial mechanical hyperalgesia induced by CCI-ION, but without changing the anxiety-like behavior. Moreover, no change was observed on nociception and anxiety-like behavior after nor-BNI injection into the Sp5C. The present study demonstrated antinociceptive and anxiolytic-like effects of nor-BNI in a model of trigeminal neuropathic pain. The antinociceptive effect seems to be dissociated from the anxiolytic-like effect, at both the sites involved and at the dose need to achieve the effect. In conclusion, the kappa opioid system may represent a promising target to be explored for the control of trigeminal pain and associated anxiety. However, further studies are necessary to better elucidate its functioning and modulatory role in chronic trigeminal pain states.

Stimulating GABAergic Neurons in the Nucleus Accumbens Core Alters the Trigeminal Neuropathic Pain Responses in a Rat Model of Infraorbital Nerve Injury.

The nucleus accumbens core (NAcc) is an important component of brain reward circuitry, but studies have revealed its involvement in pain circuitry also. However, its effect on trigeminal neuralgia (TN) and the mechanism underlying it are yet to be fully understood. Therefore, this study aimed to examine the outcomes of optogenetic stimulation of NAcc GABAergic neurons in an animal model of TN. Animals were allocated into TN, sham, and control groups. TN was generated by infraorbital nerve constriction and the optogenetic virus was injected into the NAcc. In vivo extracellular recordings were acquired from the ventral posteromedial nucleus of the thalamus. Alterations of behavioral responses during stimulation “ON” and “OFF” conditions were evaluated. In vivo microdialysis was performed in the NAcc of TN and sham animals. During optogenetic stimulation, electrophysiological recordings revealed a reduction of both tonic and burst firing activity in TN animals, and significantly improved behavioral responses were observed as well. Microdialysis coupled with liquid chromatography/tandem mass spectrometry analysis revealed significant alterations in extracellular concentration levels of GABA, glutamate, acetylcholine, dopamine, and citrulline in NAcc upon optic stimulation. In fine, our results suggested that NAcc stimulation could modulate the transmission of trigeminal pain signals in the TN animal model.

Optogenetic stimulation of the motor cortex alleviates neuropathic pain in rats of infraorbital nerve injury with/without CGRP knock-down

BackgroundPrevious studies have reported that electrical stimulation of the motor cortex is effective in reducing trigeminal neuropathic pain; however, the effects of optical motor cortex stimulation remain unclear.ObjectiveThe present study aimed to investigate whether optical stimulation of the primary motor cortex can modulate chronic neuropathic pain in rats with infraorbital nerve constriction injury.MethodsAnimals were randomly divided into a trigeminal neuralgia group, a sham group, and a control group. Trigeminal neuropathic pain was generated via constriction of the infraorbital nerve and animals were treated via selective inhibition of calcitonin gene-related peptide in the trigeminal ganglion. We assessed alterations in behavioral responses in the pre-stimulation, stimulation, and post-stimulation conditions. In vivo extracellular recordings were obtained from the ventral posteromedial nucleus of the thalamus, and viral and α-CGRP expression were investigated in the primary motor cortex and trigeminal ganglion, respectively.ResultsWe found that optogenetic stimulation significantly improved pain behaviors in the trigeminal neuralgia animals and it provided more significant improvement with inhibited α-CGRP state than active α-CGRP state. Electrophysiological recordings revealed decreases in abnormal thalamic firing during the stimulation-on condition.ConclusionOur findings suggest that optical motor cortex stimulation can alleviate pain behaviors in a rat model of trigeminal neuropathic pain. Transmission of trigeminal pain signals can be modulated via knock-down of α-CGRP and optical motor cortex stimulation.

IL-10 and CXCL2 in trigeminal ganglia in neuropathic pain

Many trigeminal neuropathic pain patients suffer severe chronic pain. The neuropathic pain might be related with cross-excitation of the neighboring neurons and satellite glial cells (SGCs) in the sensory ganglia and increasing the pain signals from the peripheral tissue to the central nervous system. We induced trigeminal neuropathic pain by infraorbital nerve constriction injury (IONC) in Sprague-Dawley rats. We tested cytokine (CXCL2 and IL-10) levels in trigeminal ganglia (TGs) after trigeminal neuropathic pain induction, and the effect of direct injection of the anti-CXCL2 and recombinant IL-10 into TG. We found that IONC induced pain behavior. Additionally, IONC induced satellite glial cell activation in TG and cytokine levels of TGs were changed after IONC. CXCL2 levels increased on day 1 of neuropathic pain induction and decreased gradually, with IL-10 levels showing the opposite trend. Recombinant IL-10 or anti-CXCL2 injection into TG decreased pain behavior. Our results show that IL-10 or anti-CXCL2 are therapy options for neuropathic pain.

Anxiety- but not depressive-like behaviors are related to facial hyperalgesia in a model of trigeminal neuropathic pain in rats

Trigeminal neuralgia (TN) is a painful condition characterized by excruciating facial pain, which has a serious impact on quality of life. Depression and anxiety have been commonly associated with TN, but clinical studies report that these comorbidities are frequently underdiagnosed and undertreated in TN patients. Herein it was investigated if rats submitted to the infraorbital nerve constriction (CION), a model of trigeminal neuropathic pain, would display anxiety- and depressive-like behaviors in addition to the facial sensory changes in different time points after the nerve injury. CION rats developed facial heat hyperalgesia on day 5 after the nerve injury, but at this time point the time spent and the number of entries on open arms in the elevated plus maze (EPM) and the time spent on the lit compartment of light-dark transition test (LDT) was not statistically significant between SHAM and CION groups, suggesting that 5 days after CION animals do not display anxiety-like behavior. On the other hand, around 50% of CION rats developed mechanical allodynia on day 15 postsurgery and the analysis of the time spent and the number of entries on open arms on EPM and the time spent on lit compartment of LDT revealed that only CION-allodynic animals displayed anxiety-like behavior when compared to the SHAM group. The depressive-like behavior was assessed by measuring the time of immobility on the forced swim test (FST) and sucrose preference (SP) in rats previously tested for heat (day 5) and mechanical allodynia (days 15, 30 and 45) induced by CION. The evaluation of immobility time on FST and sucrose preference consumption revealed that both CION rats did not displayed depressive- and anhedonic-like behavior at any time point evaluated. Altogether, these results demonstrate that trigeminal neuropathic pain in rats leads to the development of anxiety-, but not depressive-like behavior, suggesting that the CION model represents a methodology that allows the study of drugs targeting both pain and anxiety.

EXPERIMENTAL TRIGEMINAL NEURALGIA OF INFRAORBITAL NERVE CAUSES MORPHOLOGICAL PERIPHERICAL CHANGES

The Trigeminal Neuralgia (TN) is a chronic disease and the most common and severe neuropathy in head and neck, that causes suffering and decrease the life quality of pacients and almost always it conducts to alodinia. It is characterized by shoots of pain in the trigeminal nerve region. It is believed that the trigeminal pain etiology is related of lesions in trigeminal nerve branches as demyelization. Neuronal injury conduct to neuroplasticity changes fallowed by central and peripheral sensitization, In addition, it is still unclear how morphological changes in the trigeminal pathway behave after a neuronal injury and its relationship with nociceptive response. The aim of this study was to evaluate the peripheral morphological changes in the trigeminal pathway in model of neuralgia of infraorbital nerve in rats. Eighteen male Wistar rats (180–220 g), originating from the Central Animal Facility of the Federal University of Ceará ‐ Brazil, kept at 22 °C, by day/night cycle ‐ 12/12 h, with water and food ad libitum were used. The rats were divided into 3 groups: control (C), Trigeminal Neuralgia (TN) and TN Sham. The TN was induced by infraorbital nerve (ION) constriction model, through a loose ligature on the rostral portion of the nerve. It was performed the measurement of nociceptive threshold using an electronic an algesimeter (Von Frey) twice per week, on days 0, 3, 7, 10, 14, 18 and 21 after TN surgery. The animals were euthanized and the ION, and vibrissal skin were collected. Immunofluorescence analysis was performed using the anti‐MBP and DAPI antibody in nerve and anti‐PGP9.5 and DAPI in vibrissal skin. Images of immunofluorescence were capture in a confocal microscopy and quantified the intensity of marking using the ImageJ software. Statistical analysis was performed by mean ± SEM of the measures recorded, by Student t test or ANOVA analyze, followed by Tukey or Games Howell pos‐hoc test, based on Levene's homogeneity teste, both with significance level p&lt;0.05 using SPSS 20.0 software. In the analysis of the nociceptive threshold for 21 days post‐induction (Figure 1A), it was verified that the TN group showed a very reduced nociceptive threshold in relation to Control and TN Sham groups (p&lt;0.0001) and no significance between Control and TN Sham groups (p=0.989), that confirms the presence of neuropathic pain. When we analyzed the anti‐MBP markers on ION, a significant increase in MPB expression was identified in the TN group (p&lt;0.0001) indicating a significant axonal lesion with a response of nerve through a MPB production (Figure 2A and 2C). In addition, we observed through DAPI marker on ION, that there is a probable large migration of macrophages the nerve (FIGURE 2B and 2C), that is essential to signalization to MBP Schwann cells production. As a consequence of this alterations, we found too, a reduction number of nervous endings in vibrissal skin, shown by the marker PGP9.5 expression (p&lt;0.0001) (FIGURE 1B and 1C). Thus, we conclude that the trigeminal neuralgia caused by peripheral injury conduct a loss of nervous terminations with a reaction of nerve to a possible repair, that could be a cause of a peripheral sensitization, reducing the nociceptive threshold. Thus, we hypothesize that a possible failure in remyelination, axonal loss and degeneration of the fibers and nerve endings, leading to nerve conduction failure of the nociceptive signals, leading to hypersensitivity.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Facial hyperalgesia due to direct action of endothelin-1 in the trigeminal ganglion of mice.

This study assessed the ability of endothelin-1 (ET-1) to evoke heat hyperalgesia when injected directly into the trigeminal ganglia (TG) of mice and determined the receptors implicated in this effect. The effects of TG ETA and ETB receptor blockade on alleviation of heat hyperalgesia in a model of trigeminal neuropathic pain induced by infraorbital nerve constriction (CION) were also examined. Naive mice received an intraganglionar (i.g.) injection of ET-1 (0.3-3 pmol) or the selective ETB R agonist sarafotoxin S6c (3-30 pmol), and response latencies to ipsilateral heat stimulation were assessed before the treatment and at 1-h intervals up to 5 h after the treatment. Heat hyperalgesia induced by i.g. ET-1 or CION was assessed after i.g. injections of ETA R and ETB R antagonists (BQ-123 and BQ-788, respectively, each at 0.5 nmol). Intraganglionar ET-1 or sarafotoxin S6c injection induced heat hyperalgesia lasting 4 and 2 h, respectively. Heat hyperalgesia induced by ET-1 was attenuated by i.g. BQ-123 or BQ-788. On day 5 after CION, i.g. BQ-788 injection produced a more robust antihyperalgesic effect compared with BQ-123. ET-1 injection into the TG promotes ETA R/ETB R-mediated facial heat hyperalgesia, and both receptors are clearly implicated in CION-induced hyperalgesia in the murine TG system.

Botulinum neurotoxin type A alleviates mechanical hypersensitivity associated with infraorbital nerve constriction injury in rats

We investigated the effect of botulinum neurotoxin type A (BoNT-A) on mechanical allodynia and hyperalgesia associated with infraorbital nerve constriction (ION-CCI) in rats. ION-CCI rats received a subcutaneous BoNT-A injection into the whisker pad area on day 7 postoperatively and underwent pain assessment on days 14 and 21 postoperatively. Rats were assigned to one of four treatment groups (n=5 each): ION-CCI+BoNT-A 20pg (low-dose group), ION-CCI+BoNT-A 200pg (high-dose group), ION-CCI+saline, and Sham. Mechanical allodynia and hyperalgesia were evaluated preoperatively (baseline) and on days 7, 14, and 21 postoperatively. After noxious mechanical stimulation of whisker pad skin, the number and distribution pattern of the phosphorylated extracellular signal-regulated kinase (pERK)-immunoreactive (IR) neurons were analyzed in the trigeminal spinal subnucleus caudalis (Vc) and upper cervical spinal cord (C1-C2). On day 21, nocifensive behavior was attenuated by high-dose but not low-dose BoNT-A administration. In addition, after noxious mechanical stimulation of whisker pad skin, the numbers of pERK-IR cells in the superficial laminae of Vc and C1-C2 were significantly lower in the high-dose BoNT-A group than in the ION-CCI+saline group. The present findings suggest that, by suppressing Vc neuronal activity, high-dose intradermal injection of BoNT-A at the site of ION innervation alleviates mechanical facial allodynia and hyperalgesia associated with ION-CCI.

Vitamin B complex attenuated heat hyperalgesia following infraorbital nerve constriction in rats and reduced capsaicin in vivo and in vitro effects

Vitamins of the B complex attenuate some neuropathic pain sensory aspects in various animal models and in patients, but the mechanisms underlying their effects remain to be elucidated. Herein it was investigated if the treatment with a vitamin B complex (VBC) reduces heat hyperalgesia in rats submitted to infraorbital nerve constriction and the possibility that TRPV1 receptors represent a target for B vitamins. In the present study, the VBC refers to a combination of vitamins B1, B6 and B12 at low- (18, 18 and 1.8mg/kg, respectively) or high- (180, 180 and 18mg/kg, respectively) doses. Acute treatment of rats with either the low- or the high-doses combination reduced heat hyperalgesia after nerve injury, but the high-doses combination resulted in a long-lasting effect. Repeated treatment with the low-dose combination reduced heat hyperalgesia on day four after nerve injury and showed a synergist effect with a single injection of carbamazepine (3 or 10mg/kg), which per se failed to modify the heat threshold. In naïve rats, acute treatment with the high-dose of VBC or B1 and B12 vitamins independently reduced heat hyperalgesia evoked by capsaicin (3µg into the upper lip). Moreover, the VBC, as well as, each one of the B vitamins independently reduced the capsaicin-induced calcium responses in HEK 293 cells transiently transfected with the human TRPV1 channels. Altogether, these results indicate that B vitamins can be useful to control heat hyperalgesia associated with trigeminal neuropathic pain and that modulation of TRPV1 receptors may contribute to their anti-hyperalgesic effects.

Contribution and interaction of kinin receptors and dynorphin A in a model of trigeminal neuropathic pain in mice

Infraorbital nerve constriction (CION) causes hypersensitivity to facial mechanical, heat and cold stimulation in rats and mice and is a reliable model to study trigeminal neuropathic pain. In this model there is evidence that mechanisms operated by kinin B1 and B2 receptors contribute to heat hyperalgesia in both rats and mice. Herein we further explored this issue and assessed the role of kinin receptors in mechanical hyperalgesia after CION. Swiss and C57Bl/6 mice that underwent CION or sham surgery or dynorphin A (1–17) administration were repeatedly submitted to application of either heat stimuli to the snout or mechanical stimuli to the forehead. Treatment of the animals on the fifth day after CION surgery with DALBK (B1 receptor antagonist) or HOE-140 (B2 receptor antagonist), both at 0.01–1μmol/kg (i.p.), effectively reduced CION-induced mechanical hyperalgesia. Knockout mice for kinin B1, B2 or B1/B2 receptors did not develop heat or mechanical hyperalgesia in response to CION. Subarachnoid dynorphin A (1–17) delivery (15nmol/5μL) also resulted in orofacial heat hyperalgesia, which was attenuated by post-treatment with DALBK (1 and 3μmol/kg, i.p.), but was not affected by HOE-140. Additionally, treatment with an anti-dynorphin A antiserum (200μg/5μL, s.a.) reduced CION-induced heat hyperalgesia for up to 2h. These results suggest that both kinin B1 and B2 receptors are relevant in orofacial sensory nociceptive changes induced by CION. Furthermore, they also indicate that dynorphin A could stimulate kinin receptors and this effect seems to contribute to the maintenance of trigeminal neuropathic pain.

NO‐ting a putative mechanism by which anti‐migraine drugs mitigate trigeminal neuropathic pain

<scp>NO</scp>‐ting a putative mechanism by which anti‐migraine drugs mitigate trigeminal neuropathic pain

Dural neurogenic inflammation induced by neuropathic pain is specific to cranial region

Up to now, dural neurogenic inflammation (DNI) has been studied primarily as a part of migraine pain pathophysiology. A recent study from our laboratory demonstrated the occurrence of DNI in response to peripheral trigeminal nerve injury. In this report, we characterize the occurrence of DNI after different peripheral nerve injuries in and outside of the trigeminal region. We have used the infraorbital nerve constriction injury model (IoNC) as a model of trigeminal neuropathic pain. Greater occipital nerve constriction injury (GoNC), partial transection of the sciatic nerve (ScNT) and sciatic nerve constriction injury (SCI) were employed to characterize the occurrence of DNI in response to nerve injury outside of the trigeminal region. DNI was measured as colorimetric absorbance of Evans blue plasma protein complexes. In addition, cellular inflammatory response in dural tissue was histologically examined in IoNC and SCI models. In comparison to the strong DNI evoked by IoNC, a smaller but significant DNI has been observed following the GoNC. However, DNI has not been observed either in cranial or in lumbar dura following ScNT and SCI. Histological evidence has demonstrated a dural proinflammatory cell infiltration in the IoNC model, which is in contrast to the SCI model. Inflammatory cell types (lymphocytes, plasma cells, and monocytes) have indicated the presence of sterile cellular inflammatory response in the IoNC model. To our knowledge, this is the first observation that the DNI evoked by peripheral neuropathic pain is specific to the trigeminal area and the adjacent occipital area. DNI after peripheral nerve injury consists of both plasma protein extravasation and proinflammatory cell infiltration.

P.1.h.006 Anti-allodynic effects of agomelatine combined with gabapentin in neuropathic rats with infraorbital nerve constriction

Agomelatine is a new antidepressant with an innovative pharmacological profile. It is a potent melatonergic agonist (MT1 and MT2) and also has 5-HT2c antagonist properties. Agometatine's efficacy in treating major depressive disorder (MDD) was first described in a placebo-controlled, dose-ranging study with paroxetine as a validator. In a recent placebo-controlled study, 212 MDD patients were randomly assigned double-blind to receive placebo or agomelatine 25 and 50 mg/day. There was a significant advantage for agomelatine after 6 weeks according to scores on the Hamilton Depression Rating Scale (HAM-D) (P = 0.026) and the Clinical Global Impression Severity (P = 0.017), with an improved response rate (P = 0.03). Robust evidence of agomelatine's efficacy in severe depression comes from analysis of a patient subgroup with baseline HAM-D scores >25. Analysis of pooled data from three different trials confirmed this observation and suggested that the agomelatine-placebo difference tends to increase with the severity of depression. Results suggest favorable tolerabitity of agomelatine compared with a serotonin and noradrenaline reuptake inhibitor, and agomelatine is associated with less sexual side effects that are troublesome with some antidepressants. As predicted from its pharmacological profile, agomelatine improves sleep quality without associated daytime drowsiness. Agomelatine was also shown not to induce a discontinuation syndrome. Agomelatine may fill the gap in the current therapeutic armamentarium by combining efficacy with a favorable tolerability profile and additional clinical benefits.