Introduction. While opioid medications are commonly prescribed for management of neuropathic pain (NP), long-term use has been associated with increased risk for overdose, drug interactions and addiction. New strategies are necessary to better manage chronic pain, thereby reducing need for opioid medications and their associated adverse consequences. N-acetyl-L-cysteine (NAC), an over-the-counter supplement, has shown promise in the treatment of psychiatric and addictive disorders. In addition, NAC has shown promise for reducing physiological signs of NP in laboratory rat models, prompting this study. Purpose. The present study was an open-label clinical trial of NAC as an adjuvant to opioid treatment for poorly controlled, chronic NP. It examined whether 1200 mg NAC twice daily for 4 weeks was associated with: lower ratings of patient-reported pain; reductions in PRN opioid medication for breakthrough pain; and improvements in physical and mental health quality of life (QoL). The study also examined whether appraisal of pain impacts response to medication. Method. Participants were N=28 chronic NP patients who consented to study participation. This consisted of 2 baseline assessments, 4 weeks of NAC and 1 post-trial follow-up visit. The majority (N=17) dropped out or were excluded during baseline. Of the remaining participants, N = 11 started the study medication and N=10 completed the study, with daily recordings of pain severity ratings and use of PRN opioid medication. Small sample size limited analyses to qualitative case reviews and effect sizes. Results. Over 90% of participants receiving NAC completed the study. Case review found varied results. While 4 of 10 participants showed decrease in average pain ratings during NAC, estimated effect sizes for the whole sample were small, bordering on negligible (ω² from .003 to .027) as were those for PRN opioids (Partial Eta-Squared=.0003). Effect size for mental health QoL was medium (Cohen's d=.421). Conclusions. With N=10, findings must be interpreted with caution. Nonetheless, the study found some albeit small evidence supporting NAC for improving mental health QoL and pain ratings. Several participants reported improvements in pain and mental health domains while taking NAC. NAC was well tolerated with minimal side effects. Lessons from this study will inform design and implementation of future NAC studies.

Les douleurs chroniques et notamment les douleurs neuropathiques sont particulièrement difficiles à traiter par les solutions thérapeutiques actuellement disponibles. Par conséquent, il existe un besoin crucial de découvrir et d'exploiter de nouveaux concepts d'antalgiques afin de traiter ce type de douleurs. Parmi les différentes pistes possibles, le système glutamatergique semble particulièrement intéressant puisque le glutamate est le principal neurotransmetteur propageant l'information douloureuse. Notre hypothèse est que l'activation du récepteur mGlu4 spinal inhiberait la neurotransmission glutamatergique et réduirait donc l'excès de douleur observé lors de douleurs chroniques. Grâce notamment au développement du premier agoniste orthostérique sélectif de mGlu4, nous avons mis en évidence que le récepteur mGlu4 n'altère pas la perception de la douleur aiguë mais qu'il influe, au contraire, sur l'aspect pathologique de la douleur en inhibant l'allodynie et l'hyperalgie mécanique ou thermique présentes lors de douleurs chroniques. Nous montrons que la modulation de l'hypersensibilité par mGlu4 semble provenir de sa capacité à inhiber la transmission glutamatergique via un couplage négatif avec les canaux calciques de type N au niveau de la couche II de la moelle épinière et plus particulièrement au niveau des fibres exprimant le transporteur vésiculaire VGLUT3. L'ensemble de nos résultats permettent de valider le récepteur mGlu4 spinal comme une cible thérapeutique potentielle pour le traitement des douleurs chroniques. En effet, les agonistes de mGlu4 pourraient être des antalgiques puissants et sélectifs des douleurs pathologiques. / Chronic pain and in particular neuropathic pain are particularly difficult to treat by therapeutic options currently available. Therefore, it is a crucial to develop new concepts of analgesics to treat this type of pain. Among the various possibilities, targeting the glutamatergic system seems to be particularly interesting since glutamate is the main neurotransmitter propagating the pain information. Our hypothesis is that the activation of spinal mGlu4 receptor would inhibit the spinal glutamatergic neurotransmission and would thus reduce the excess of pain observed in chronic pain.Thanks to the development of the first orthosteric agonist selective for mGlu4 and the use of transgenic animals, we demonstrated that mGlu4 receptor does not alter the perception of acute pain but that it does affect the pathological aspect of pain by inhibiting the allodynia and the hyperalgesia (mechanical and thermal) usually observed in chronic pain. We show that the mGlu4 modulation of the hypersensitivity seems to result from the ability of the receptor to inhibit the glutamatergic transmission through a negative coupling with N-type calcium channels in the lamina II of the spinal cord and especially at the level of fibers expressing the vesicular transporter VGLUT3. Taken together, our results validate spinal mGlu4 as a potential therapeutic target for the treatment of chronic pain. Indeed, mGlu4 agonists could be potent and selective painkillers of pathological pain.

A dor neuropática é uma condição debilitante causada por danos no sistema nervoso somatossensorial, como lesões dos nervos periféricos. As células do sistema imune, em particular os monócitos/macrófagos, desempenham um papel fundamental no desenvolvimento deste processo. Embora diversos estudos sugiram o envolvimento dessas células na medula espinal e gânglio da raiz dorsal (GRD) após a indução da neuropatia, a caracterização funcional e fenotípica, bem como a origem dessas células nesses órgãos, ainda não está esclarecida. Na medula espinal, estudos recentes têm demonstrado que apesar da massiva ativação e proliferação da micróglia residente, não há recrutamento de células mielóides para esse tecido após a indução da neuropatia, divergindo dos dados anteriormente descritos na literatura. Diante desses estudos controversos, iniciamos nosso trabalho demonstrando que possivelmente as células mielóides não são capazes de ultrapassar a barreira hematoencefálica e infiltrar na medula espinal após a indução da neuropatia periférica pelo modelo de SNI e assim, a ativação microglial ocorre de maneira independente do infiltrado dessas células neste tecido. No que se refere aos GRDs, trabalhos anteriores demonstram que há um aumento dos marcadores de ativação de macrófagos nesse tecido após a lesão periférica. Com isso, nós caracterizamos as subpopulações de monócitos/macrófagos presentes no GRD e identificamos, células CX3CR1+ e células CCR2+. De maneira interessante, ao isolarmos as células CX3CR1+ observamos que esse subtipo celular possa ser as principais células responsáveis pela produção dos mediadores inflamatórios no GRD após indução de SNI, enquanto as células CCR2+ parecem contribuir apenas de maneira parcial para a produção de IL-1? e TNF-? neste tecido, uma vez que a expressão desses mediadores não foi totalmente suprimida na ausência desse subtipo celular. Por fim, investigamos a origem desses subtipos de monócitos presentes no GRD. Por meio da parabiose entre animais wild type e GFP+, observamos que embora haja um pequeno aumento de células GFP+ no GRD de animais lesionados, essas células não são macrófagos. Corroborando com esses dados, ao realizarmos a parabiose de animais wild type com animais CX3CR1GFP/+CCR2RFP/+ não observamos presença de células CX3CR1 ou CCR2 no GRD após SNI. Em conjunto, nossos dados demonstram que existem duas subpopulações de monócitos no GRD, sendo uma delas residente e contribuindo de maneira efetiva para a produção dos mediadores inflamatórios locais e outra população de células CCR2+ que podem ter um papel mais relevante no sítio da lesão e assim, a exacerbação da inflamação local pode interferir indiretamente, na ativação das células presentes nos GRDs, bem como na produção dos mediadores inflamatórios no tecido, que vão contribuir para o desenvolvimento da dor neuropática. / Neuropathic pain is a debilitating disease due to severe damage to the nervous system, induced by peripheral nerve injury. The cells of the immune system, especially monocytes/macrophages, played a critical role in these process. Several projects have been suggested the role of these cells in the spinal cord and dorsal root ganglia (DRG) after neuropathic pain induction, but the functional and phenotypic characterization, as well as the source of cells, is still unclear. In the spinal cord, recent studies have shown that although massive activation and proliferation of the microglial occurred, there is no recruitment of myeloid cells to this tissue after the neuropathic pain induction, but this is contrary to previous findings in the literature. Based on this controversial studies, we first showed that myeloid cells are not able to overcome the blood-brain barrier and infiltrate in the spinal cord after the peripheral nerve injury by SNI model and thus, the microglial activation occurs independent of the infiltration of these cells in this tissue. With regard to DRGs, previous work has shown that there is an increase in the activation markers of macrophages after peripheral nerve injury.Thus, we characterized the subpopulations of monocytes/macrophages in the DRG and we identified CX3CR1+ and CCR2+ cells. Interestingly, when isolating the CX3CR1+ cells, we observed that this cell subtype may be the main cells responsible for the production of inflammatory mediators in the DRG after SNI induction, whereas CCR2+ cells appear to contribute only partially to the production of IL-1? and TNF-? in this tissue, since the expression of these mediators was not completely suppressed in the absence of this cellular subtype. Finally, we investigated the origin of these monocyte subtypes present in the DRG. Through parabiosis between wild type and GFP+ animals, we observed that although there is a small increase of GFP+ cells in the DRG of injured animals, these cells are not macrophages. Corroborating with these data, when performing the wild type parabiosis with CX3CR1GFP /+ CCR2RFP/+ animals, we did not observe the presence of CX3CR1 or CCR2 cells in the GRD after SNI. Finally, our data demonstrate that there are two subpopulations of monocytes in the DRG, one of them residing and contributing effectively to the production of local inflammatory mediators and another population of CCR2 cells that may have a more relevant role at the lesion site and thus, the exacerbation of local inflammation may indirectly interfere, in the activation of the cells present in the DRGs, as well as in the production of inflammatory mediators in the tissue, which will contribute to the development of neuropathic pain.

A dor neuropática atinge cerca de 6 a 10% da população global e estima-se o seu aumento nos próximos anos. Essa síndrome não tem cura e afeta consideravelmente a qualidade de vida das pessoas por ela acometidas. Os medicamentos utilizados atualmente para o seu tratamento, como antidepressivos, anticonvulsivantes, opióides, dentre outros, não proporcionam um resultado satisfatório pelo fato de não reduzirem consideravelmente os sintomas e/ou por terem muitos efeitos colaterais. Pesquisas recentes mostram que o receptor sigma-1 pode ser utilizado no tratamento da dor neuropática. Verificou-se na literatura uma nova série de pirimidinas que são capazes de se ligar ao receptor sigma-1, atuando como seus antagonistas, sendo potenciais alvos para a produção de fármacos que podem ser utilizados no tratamento da dor neuropática. Então, estudos de Relações Quantitativas Estrutura-Atividade (QSAR) foram realizados utilizando os métodos de Mínimos Quadrados Parciais (PLS) e Redes Neurais Artificiais (ANN) para prever a atividade biológica dessa série de pirimidinas. Os resultados obtidos se mostraram satisfatórios tanto para o método de PLS (r2 = 0,877, q2 = 0,800 e r2teste = 0,738), quanto para o método de ANN (r2trein = 0,734, r2val = 0,753 e r2teste = 0,676), mostrando que o conjunto de compostos antagonistas do receptor Sigma-1 pode ser descrito tanto de forma linear quanto de forma não-linear. / Neuropathic pain affects about 6 to 10% of the global population and it is estimated to increase in the coming years. This syndrome has no cure and considerably affects the life quality of people affected by it. Medications currently used for its treatment, such as antidepressants, anticonvulsants, opioids, among others, do not provide a satisfactory result because they do not significantly reduce the symptoms and/or have many side effects. Recent research shows that the sigma-1 receptor can be used in the treatment of the neuropathic pain. A new series of pyrimidines have been found in the literature, which are capable of binding to the sigma-1 receptor, acting as its antagonists, and have been synthesized as potential targets that can be used in the treatment of the neuropathic pain. Therefore, Quantitative Structure-Activity Relationships (QSAR) were performed using Partial Least Squares (PLS) and Artificial Neural Networks (ANN) methods to predict the biological activity of this series of pyrimidines. Through the mathematical models obtained by PLS (r2 = 0.877, q2 = 0.800 and r2test = 0.738) and ANN (r2trein = 0.734, r2val = 0.753 and r2test = 0.676) methods, it was showed that they were able to predict the biological activity of the studied pyrimidines.

A dor neuropática (dor devido à lesão no tecido nervoso) é uma condição debilitante, com alta incidência na população mundial. O tratamento dessa condição dolorosa ainda é um grande desafio na clínica devido às ações limitadas dos fármacos atualmente disponíveis e seus consequentes efeitos colaterais. O uso de substâncias com potencial antioxidante no tratamento da dor neuropática vem sendo amplamente discutido devido à participação das espécies reativas de oxigênio e de nitrogênio nessa condição dolorosa. O ácido ascórbico (vitamina C) e o !-tocoferol (vitamina E) representam potentes antioxidantes, os quais são adquiridos por custo relativamente baixo, são bem aceitos pela população, muito utilizados como suplemento alimentar, e parecem possuir algum efeito analgésico, embora esse último efeito tenha ainda muitas questões especulativas e que necessita esclarecimentos. Por estes motivos, o objetivo deste estudo foi avaliar o efeito das vitaminas C e E, administradas isoladas ou juntas, sobre parâmetros nociceptivos, oxidativos e nitrosativos, e proteínas de sinalização intracelular em ratos com constrição no nervo isquiático (CCI, do inglês chronic constriction injury), um modelo de dor neuropática. Após aprovação pelo comitê de ética no uso de animal da UFRGS (#23352), ratos Wistar machos, com idade de 60 dias, foram divididos em 3 grupos experimentais: controle (ratos que não sofreram intervenção cirúrgica), sham (ratos que tiveram o nervo isquiático direito apenas exposto) e CCI (ratos que tiveram o nervo isquiático exposto e esse recebeu 4 amarraduras em seu tronco comum). Cada grupo experimental foi dividido em subgrupos que receberam administração de veículo (salina ou água de beber acrescidas de Tween 80 a 1%), vitamina C (30 mg/kg/dia), vitamina E (15 mg/kg/dia) ou coadministração de vitaminas C+E nas mesmas doses. As administrações foram intraperitoneal ou por via oral, por período de 3 e 10 dias. Os parâmetros nociceptivos utilizados para avaliar sensibilidade mecânica, sensibilidade térmica e recuperação funcional do nervo foram os testes de von Frey eletrônico, teste da placa quente e do índice funcional do isquiático (IFI), respectivamente. Para avaliar o efeito antinociceptivo da administração i.p. dos tratamentos, os parâmetros nociceptivos foram mensurados antes do procedimento cirúrgico, e aos 3, 5, 7 e 10 dias após a lesão nervosa. Ao final dos períodos de 3 e 10 dias, os animais foram mortos por decapitação, e foi coletado plasma, para determinação de indicadores de função hepática e renal (alanina aminotransferase, aspartato aminotransferase, gama GT, bilirrubina e creatinina); fígado, para determinação da morfologia dos hepatócitos e parâmetros oxidativos (hidroperóxidos lipídicos, Glutationa-s-transferase - GST, e capacidade antioxidante total - TAC); nervo isquiático lesionado, para determinação de parâmetros oxidativos (hidroperóxidos lipídicos e TAC); e o segmento lombossacral da medula espinal, para determinação de parâmetros oxidativos (formação de ânion superóxido - SAG, e valores de peróxido de hidrogênio, hidroperóxidos lipídicos, tióis totais, ácido ascórbico e TAC) e nitrosativos (metabólitos do óxido nítrico - NO). O segmento da medula espinal foi usado ainda para determinar a expressão das proteínas de sinalização p38 fosforilada (p-p38), Akt e Akt fosforilada (p-Akt) e do transportador de vitamina C dependente de sódio do tipo 2 (SVCT-2). Foi avaliada ainda, mediante determinação de parâmetros nociceptivos, a duração do efeito antinociceptivo da vitamina C, vitamina E ou vitaminas C+E após o tratamento, o efeito antinociceptivo das vitaminas C+E administradas por via oral, e a coadministração de vitaminas C+E (via oral) concomitante à gabapentina (i.p.), fármaco normalmente utilizado no tratamento de dor neuropática. Os dados de sensibilidade térmica e mecânica foram analisados por ANOVA de medidas repetidas, seguida pelo pós-teste de Tukey. Os demais parâmetros foram avaliados por ANOVA de duas vias (fatores: lesão e tratamento), seguida do pós-teste de Tukey. Os resultados mostraram que vitamina C, vitamina E e vitaminas C+E atenuaram a nocicepção e provocou melhora no IFI tanto aos 3 como aos 10 dias, e que a coadministração das vitaminas induziu efeito antinociceptivo maior do que as mesmas administradas isoladamente em ratos com CCI. O efeito antinociceptivo das vitaminas C+E foi similar, tanto após administração i.p. quanto oral. Também foi observado que o efeito antinociceptivo das vitaminas C, E e C+E durou por várias horas após o término do período de administração de 3 e 10 dias. O uso de vitaminas C+E+gabapentina provocou efeito antinociceptivo maior do que o uso de gabapentina isoladamente. Não foram observadas alterações nos indicadores de função hepática e renal, na morfologia dos hepatócitos e nos parâmetros oxidativos avaliados no tecido hepático. No nervo isquiático lesionado, embora não houve alterações significativas, observou-se acréscimo de 38% na TAC e diminuição de 45% nos hidroperóxidos lipídicos nos animais que receberam vitaminas, comparado aos valores obtidos nos ratos tratados com veículo. Na medula espinal, a administração das vitaminas preveniu a redução nos valores de tióis totais e o aumento na SAG, comparado ao grupo CCI tratado com veículo. Ainda comparado ao grupo veículo, as vitaminas preveniram o aumento nos metabólitos do NO e nos hidroperóxidos lipídicos. A administração de vitaminas C+E também preveniu a redução significativa na expressão do transportador SVCT-2, o aumento nas expressões das proteínas p-p38, p-Akt e Akt, e o aumento no valor do ácido ascórbico, comparado aos ratos CCI que receberam veículo. A administração das vitaminas e a CCI não provocaram alterações significativas na TAC e nos valores de peróxido de hidrogênio na medula espinal. Assim, os resultados mostram que vitamina C, vitamina E e vitaminas C+E, nas doses aqui estudadas, atenuam a dor neuropática e modificam parâmetros oxidativo e nitrosativo, e de sinalização celular, alterados pela CCI. A administração dessas vitaminas não parece provocar toxicidade ao organismo, e poderiam ser uma alternativa como coadjuvante a medicações clássicas usadas no tratamento de condições de dor neuropática. Porém, é necessária a realização de estudos complementares em humanos, dada às diferenças nas respostas à dor em ratos e humanos. / Neuropathic pain (pain due to nerve tissue injury) is a debilitating condition, with a high incidence in the world population. The treatment of this painful condition is still a great challenge in the clinic due to the limited actions of the currently available drugs and their consequent side effects. The use of substances with antioxidant potential in the treatment of neuropathic pain has been widely discussed due to the participation of reactive oxygen and nitrogen species in this painful condition. Ascorbic acid (vitamin C) and !-tocopherol (vitamin E) are potent antioxidants, which are obtained by relatively low cost, are well accepted by patients, are widely used as a food supplement, and appear to have some analgesic effect, although this last effect still has many speculative issues and needs clarification. For these reasons, the aim of this study was to evaluate the effect of vitamins C and E, administered alone or together, on nociceptive, oxidative and nitrosative parameters and intracellular signaling proteins in rats with chronic constriction injury (CCI), a model of neuropathic pain. After approval by the ethics committee on animal use of UFRGS (#23352), male Wistar rats, aged 60 days, were divided into 3 groups: control (rats that did not undergo surgery), sham (rats whose right sciatic nerve was only exposed) and CCI (rats whose sciatic nerve was exposed and received 4 ligations in their common trunk). Each experimental group was divided into subgroups that received vehicle injection (saline or drinking water plus Tween 80, 1%), vitamin C (30 mg/kg/day), vitamin E (15 mg/kg/day) or co-administration of vitamins C+E in the same doses. The administrations were by intraperitoneal or oral route, for a period of 3 and 10 days. The nociceptive parameters used to evaluate mechanical sensitivity, thermal sensitivity and nerve functional recovery were the electronic von Frey test, the hot plate test and the sciatic functional index (SFI), respectively. To evaluate the antinociceptive effect of ip administration of vitamin C, vitamin E or vitamins C+E, nociceptive parameters were measured before the surgical procedure and at 3, 5, 7 and 10 days following nerve injury. At the end of the 3 and 10 day periods, the animals were killed by decapitation, and plasma was collected for determination of hepatic and renal function indicators (aspartate aminotransferase, alanine aminotransferase, gamma-GT , bilirubin and creatinine); liver, for determination of hepatocyte morphology and oxidative parameters (lipid hydroperoxides, Glutathione-s-transferase - GST, and total antioxidant capacity - TAC); injured sciatic nerve for determination of oxidative parameters (lipid hydroperoxides and TAC); and the lumbosacral segment of the spinal cord for determination of oxidative (superoxide anion formation - SAG, and values of hydrogen peroxide, lipid hydroperoxides, total thiols, ascorbic acid and TAC) and nitrosative (nitric oxide metabolites - NO) parameters. The spinal cord segment was also used to determine the expression of signaling proteins phosphorylated p38 (p-p38), Akt and phosphorylated Akt (p-Akt), and sodium-dependent vitamin C transporter type 2 (SVCT-2). In addition, it was assessed the duration of the antinociceptive effect of vitamin C, vitamin E or vitamins C+E after end of the treatment, the antinociceptive effect of vitamins C+E by oral route, and the antinociceptive effect of co-administration of vitamins C+E (oral route) concomitant with gabapentin (ip), a drug normally used in the treatment of neuropathic pain. Thermal and mechanical sensitivity data were analyzed by repeated measures ANOVA, followed by Tukey’s post-test. The other parameters were evaluated by two-way ANOVA (factors: injury and treatment), followed by Tukey's post-test. The results showed that vitamin C, vitamin E and C+E vitamins attenuated nociception and improved SFI at both 3 and 10 days, and that a greater antinociceptive effect was induced when vitamins were co-administered than when they were given alone in CCI rats. The antinociceptive effect of vitamins C+E was similar after ip and oral administration. It was also observed that the antinociceptive effect of vitamins C, E and C+E lasted for several hours after the end of the administration period of 3 and 10 days. The use of C+E vitamins+gabapentin caused greater antinociceptive effect than the use of gabapentin alone. . No changes were observed in hepatic and renal function indicators, hepatocyte morphology, and oxidative parameters evaluated in the hepatic tissue. Despite no significant, the injured sciatic nerve showed increase (38%) in TAC and reduction (45%) in lipid hydroperoxides in vitamins-treated CCI rats, compared to rats that received vehicle. In spinal cord, the vitamin administration prevented the reduction in total thiol values and the increase in SAG in CCI animals, compared to vehicle-treated CCI rats. Also compared to vehicletreated CCI rats, the vitamins prevented the increase in NO metabolites and lipid hydroperoxides. The use of vitamins C+E also prevented the significant reduction in SVCT-2 transporter expression, the increase in p-p38, p-Akt, and Akt expressions, and the increase in ascorbic acid levels, compared to CCI rats that received vehicle. Vitamins and CCI did not induce significant changes in TAC and hydrogen peroxide values in the spinal cord. Thus, the results show that vitamins C, E and C+E, in doses used, attenuated neuropathic pain and changed oxidative, nitrosative and cellular signaling parameters modified by CCI. In addition, the use of vitamins does not appear to induce toxicity to the body and could be an alternative as adjuvant to classical medications used in the treatment of neuropathic pain conditions. However, further studies in humans are needed, given the differences in pain responses in rats and humans.

La douleur neuropathique est un syndrome secondaire à une maladie ou à une lésion affectant le système nerveux somatosensoriel. Environ 30% des patients souffrant de douleurs neuropathiques présentent des troubles de l’humeur. Les causes biologiques de ces comorbidités ne sont pas clairement établies. Grâce à l’utilisation d’un modèle murin de douleur neuropathique, nous avons cherché à comprendre l’apparition des conséquences émotionnelles de cette douleur. Pour cela, nous avons cherché à identifier des régions cérébrales impliquées dans les différentes composantes et conséquences de la douleur ainsi que les modifications moléculaires y prenant place. Nous avons mis en évidence une ségrégation corticale de la douleur avec l’intégration de la composante sensorielle par le cortex insulaire postérieur d’une part et l’intégration de la composante aversive et des conséquences émotionnelles par le cortex cingulaire antérieur d’autre part. Nous avons ensuite montré l’implication de la protéine MKP-1 dans l’expression des comportements de type anxiodépressif dans notre modèle. / Neuropathic pain is defined as a pain caused by a lesion or disease of the somatosensory nervous system. Around 30% of neuropathic pain patients develop mood disorders. The biologic bases of these comorbidities are not clearly established. Using a murine model of neuropathic pain, we tried to understand the emotional consequences of neuropathic pain. Thus, we identified cerebral regions involved in the different components of pain and molecular modifications taking place in these regions. We showed a cortical separation of the pain experience with on one hand the integration of the sensory component of pain in the posterior insular cortex and on the other hand the integration of the aversive component and the emotional consequences of pain in the anterior cingulate cortex (ACC). Looking at the molecular modifications in the ACC, we showed that MKP-1, a protein able to dephosphorylate the MAPK, is involved in the development of pain-related mood disorders in our model of neuropathic pain.

A lesão do nervo alveolar inferior (NAI) está relacionada à prática odontológica. Estudos demonstram que a laserterapia promove a regeneração do nervo e analgesia. Usando o modelo de esmagamento do NAI associado à laserterapia avaliamos a reparação nervosa e a nocicepção dos animais antes da lesão, e após o tratamento. Vimos que o laser reverteu o comportamento hipernociceptivo e que a modulação de receptores para glutamato, de neurotrofinas, do receptor de potencial transiente vanilóide do subtipo 1, da substância p e do peptídeo relacionado ao gene da calcitonina atuam neste processo. Adicionalmente, o laser alterou o microambiente da lesão modulando proteínas, como laminina, proteína mielínica zero e neurofilamentos, promovendo a regeneração do nervo; por microscopia eletrônica mostramos esta regeneração, evidenciada pelo aumento no número de fibras nervosas e da espessura da bainha de mielina no nervo do grupo tratado em relação ao grupo operado. Em conjunto, os resultados obtidos contribuem para reforçar o uso terapêutico do laser. / The inferior alveolar nerve injury (IAN) is related to dental practice. Studies have shown that LLLT promotes nerve regeneration and analgesia. Using IAN crush model associated with laser therapy we evaluated nerve repair and nociception of animals before injury and after treatment. We have seen that the laser reversed hipernociceptive behavior and modulation of glutamate receptors, neurotrophins, the transient potential vanilloid receptor subtype 1, substance P and calcitonin gene-related peptide act in this process. Additionally, the laser alter the microenvironment of the lesion modulating proteins such as laminin, myelin protein zero and neurofilaments, promoting nerve regeneration; electron microscopy showed this regeneration, evidenced by the increase in the number of nerve fibers and the thickness of the myelin sheath in nerve treated group compared to the surgery group. Together, these results contribute to enhance the therapeutic use of the laser.

Neuropathic pain affects up to 50% of the 29 million diabetic patients in the United States. Neuropathic pain in diabetes manifests as a disease of the peripheral and central nervous systems. The prevalence of type 2 diabetes is far greater than type 1 (90%), yet the overwhelming focus on type 1 models this has left the mechanisms of pain in type 2 diabetes largely unknown. Therefore I aimed to improve the current mechanistic understanding of pain associated with type 2 diabetes using two preclinical rodent models: Zucker Diabetic Fatty rats and db/db mice. In addition, I highlight the translational importance of simultaneous measurement of evoked/sensory and non-evoked/affective pain-related behaviors in preclinical models. This work is the first to show a measure of motivational-affective pain in a model of type 2 diabetes. I used methodological approaches including: (1) immunohistochemical and calcium imaging to assess stimulus-evoked sensitization; (2) measurement nociceptive behaviors and evoked sensory thresholds as well as pain affect using novel mechanical conflict avoidance and conditioned place preference/aversion assays; (3) pharmacological and genetic manipulation of methylglyoxal, TRPA1, AC1, and PPARγ. I hypothesized that the thiazolidinedione class of peroxisome proliferator-activated receptor gamma (PPARγ) agonists would reduce neuropathic pain-like behavior and spinal neuron sensitization in traumatic nerve injury and type 2 diabetes. As PPARγ is a nuclear receptor, and already targeted clinically to promote cellular insulin sensitization to reduce hyperglycemia, sustained changes in gene expression are widely believed to be the mechanism of pain reduction. In two separate research aims, I challenged this view and tested whether the PPARγ agonist pioglitazone would (1) rapidly alleviate neuropathic pain through a non-genomic mechanism and (2) reduce painful sensitization in nociceptive and neuropathic pain models independent from lowering blood glucose. I aimed to investigate the contribution of the glucose metabolite methylglyoxal to painful type 2 diabetes. I tested the hypothesis that methylglyoxal produces nociceptive, evoked, and affective pain that is dependent on activation of the sensory neuron cation channel TRPA1 and the secondary messenger enzyme AC1. I also tested whether pioglitazone or the novel methylglyoxal scavenging peptide GERP10 could alleviate painful type 2 diabetes.

L’amygdale est une structure du système nerveux central impliquée dans l’intégration des émotions comme la peur et l’anxiété. Des études ont également montré que l’amygdale peut moduler de façon positive ou négative la douleur par le biais des projections de son noyau de sortie, le noyau central de l’amygdale (CeA), sur les structures impliquées dans les contrôles nociceptifs descendants. Le complexe basolatéral de l’amygdale (BLA), placé en amont du noyau central, est intimement connecté à ce dernier et peut ainsi réguler son fonctionnement. Les données obtenues au cours de ma thèse ont montré l’existence d’un contrôle tonique amygdalien de la nociception et de la douleur, directement dépendant de l’équilibre entre l’excitation et l’inhibition au sein de la structure. Ainsi la modulation de l’une ou l’autre des neurotransmission influence directement la sortie douloureuse, chez des animaux sains ou neuropathiques. Par ailleurs, nous nous sommes également intéressés à l’étude précise du mode d’action d’une molécule anxiolytique non benzodiazépinique, l’étifoxine (EFX), et à son effet sur le comportement douloureux. Les résultats des injections d’EFX dans le BLA indiquent qu’elle induit une action analgésique chez les animaux neuropathiques, mais ne modifie pas les seuils de sensibilité des animaux sains. Cette action analgésique est dépendante de l’effet indirect neurostéroïdogène de l’EFX. Ceci, associé au fait que l’EFX ne présente pas ou peu d’effets secondaires, en fait une molécule particulièrement intéressante pour un traitement alternatif des douleurs neuropathiques. Dans une dernière partie, nous avons cherché à observer les mécanismes en jeu au niveau cellulaire lorsque l’EFX est appliquée sur les neurones du BLA. Ainsi, nous avons montré que l’EFX potentialise l’inhibition au sein de la structure, via trois mécanismes indépendants ; l’augmentation de la fréquence des courants post-synaptiques inhibiteurs miniatures (mCPSIs), l’augmentation de leur amplitude, et l’augmentation de leur constante de déactivation. Ces deux derniers effets sont dépendants de l’action neurostéroïdogène de l’EFX, tandis que l’effet sur la fréquence des mCPSIs est du à l’action de l’EFX sur le récepteur GABAA. Les résultats de ma thèse ont ainsi permis de montrer l’existence d’un contrôle tonique amygdalien de la douleur, dans le cadre d’animaux neuropathiques, mais également de la nociception, chez des animaux sains. Par ailleurs, la place du complexe basolatéral de l’amygdale, souvent peu prise en compte dans les études sur la douleur, a été redéfinie. Ce complexe doit être pris en considération dans le circuit de la douleur et son rôle de pilote du noyau central de l’amygdale ne doit pas être négligé. / The amygdala is a major control center of the emotions, but also integrates sensory, especially nociceptive information. Cortical afferents to the amygdala largely target its basolateral complex. The basolateral amygdala (BLA) then projects to the central amygdala nucleus, which in turn projects densely to the periaqueductal gray and thus can drive a behavioural output via the spinal cord. Data obtained during my thesis have shown that the balance between excitation and inhibition in the BLA triggers an tonic control of pain. Therefore modulating one of the neurotransmission directly influences the pain threshold of control or nociceptive mice. My thesis work also focused on the functioning of an anxiolytic and non benzodiazepinic drug ; Etifoxin (EFX). This molecule as a positive modulator of GABAA receptors and indirectly by increasing the synthesis of neurosteroids, also known as strong modulator of these receptors. In our team, we already showed that EFX has anti-nociceptive effects when injected intraperitonealy in rats. Here we wanted to determine the action of EFX on pain descending control drive by BLA. We showed that EFX infusion in the BLA seems to be anti-nociceptive, inducing a recover of the pre-cuff mechanical threshold level. We also used a patch-clamp approach to study directly in vitro the modulation of the inhibitory synaptic transmission produced by EFX. We showed that EFX potentiate the inhibition in BLA neurons via different and complementary mechanisms. These potentiating effects are mostly dependent of a neurosteroidogenesis increase.

It is widely accepted that the unique painful and non-painful sensations in neuropathic pain are the result of particular mechanisms, and that specific management strategies for neuropathic pain should be applied to tackle them. Ideally, the treatment of chronic pain should be directed at eliminating the cause of pain, but in reality this is rarely possible. The management of chronic pain is therefore often limited to reducing the intensity of such pain and associated symptoms. Pain is essentially a subjective phenomenon described with patient-specific symptoms and expressed with a certain intensity. It therefore makes sense to examine the value of verbal descriptors and pain qualities as a basis for distinguishing neuropathic pain from other types of chronic pain. Work by Dubuisson and Melzack (1976) and later by Boureau et al. (1990) supported anecdotal opinion that key words might be discriminatory for neuropathic pain. In the last 5 years, much research has been undertaken to develop screening tools for this purpose. These tools are based on verbal pain description with, or without, limited bedside testing. This paper reviews the strengths and weaknesses of such tools.