Increased Capsaicin Receptor TRPV1 in the Peritoneum of Women With Chronic Pelvic Pain

Objective: To investigate the expression of capsaicin receptor [transient receptor potential vanilloid type-1 (TRPV1)] in the peritoneum of women with chronic pelvic pain (CPP). Methods: A case-control study was conducted on 25 women with CPP and 10 controls. Samples of the rectouterine excavation (2 cm 2) were obtained by laparoscopy, fixed in 4% formaldehyde, and underwent immunohistochemistry analysis using rabbit anti-TRPV1 (1:400) polyclonal antibodies and anti-protein gene product 9.5 (PGP 9.5) (1:2000) as a neuronal marker. Ten sequential images of high magnification fields ( x 40) were captured from each slide and the area identified with the antibody was calculated with Kontron V2.0 software. Results: Immunoreactivity to TRPV1 was sparsely detected in the nervous tissue and epithelium of endometriotic lesions. The percent area of immunoreactivity for TRPV1 [expressed as median (range)] was greater in specimens from women with CPP, 1.02% (0.54 to 2.93), than from women without the disease, 0.14% (0.07 to 1.12) (P<0.0001). This greater expression was not secondary to an increase in neuronal fibers because there was also a significant difference in the percent area TRPV1:PGP 9.5 ratio between women with CPP, 1.18 (0.26 to 4.63), and controls, 0.15 (0.06 to 0.95) (P = 0.0003). Discussion: TRPV1 may play an important role in the maintenance and perpetuation of symptoms in women with CPP. In view of the immunoreactivity detected for TRPV1, the endometriotic lesion may have the ability to interfere with nociception or with the inflammatory peritoneal environment in women with CPP. Further Studies are needed to elucidate the participation of TRPV1 in CPP and its association with endometriosis.

TRPV1 Expression on Peritoneal Endometriosis Foci is Associated With Chronic Pelvic Pain

Objective: To investigate the expression of capsaicin receptor (transient receptor potential vanilloid type 1 [TRPV1]) in the peritoneal endometriosis foci of women with and without chronic pelvic pain (CPP). Methods: A case-control study was conducted on 49 women with endometriosis who underwent laparoscopy, 28 of whom had CPP and 21 without CPP. Samples from peritoneum of the rectouterine excavation (2 cm(2)) were obtained by laparoscopy, fixed in 4% formaldehyde, and underwent immunohistochemistry analysis using rabbit anti-TRPV1 (1:400) polyclonal antibody. Results: Image analysis revealed that the immunoreactivity for TRPV1 was more frequent in specimens (endometriosis foci) from women with CPP (n = 15 of 28, 53.6%), compared to samples from the endometriosis foci of women without CPP (n = 6 of 21, 28.6%; P = .04). There was no correlation with duration, intensity of pain, or stage of the disease (endometriosis). Discussion: The present study shows that TRPV1 expression in peritoneal endometriosis foci is related to CPP in women. However, this association is not related to the endometriosis stage. In view of the immunoreactivity for TRPV1 observed here, we believe that some endometriotic lesions may provide a scenario for TRPV1 to be tonically active and this activity may contribute to the underlying pathology of CPP.

Inflammatory mediators involved in the nociceptive and oedematogenic responses induced by Tityus serrulatus scorpion venom injected into rat paws.

The present study investigated the role of kinins, prostaglandins (PGs) and nitric oxide (NO) in mechanical hypernociception, Spontaneous nociception and paw oedema after intraplantar (ipl) injection of Tityus serrulatus venom (Tsv) in male Wistar rats. Tsv was ipl-injected in doses of 0.01-10 mu g/paw. Pre-treatment (30 min prior) with DALBK (100 nmol/paw) and icatibant (10 nmol/paw), B1 and B2 selective kinin receptor antagonists, L-NAME (50 mg/kg, i.p., a non-selective nitric oxide synthase inhibitor) or celecoxib, selective COX-2 inhibitor, was given 1 h prior per os (5 mg/kg, p.o.), significantly reduced the hypernociceptive response (Von Frey method), the spontaneous nociception (determined by counting the number of flinches) and paw oedema (plethysmometer method) induced by Tsv at doses of 1.0 and 10 mu g/paw for both nociceptive and oedematogenic responses, respectively. Nevertheless, indomethacin (5 mg/kg, i.p.. 30 min prior) was ineffective in altering all of these events. The results of the present study show that Tsv, injected ipl into the rat paw, causes a dose-dependent paw oedema, mechanical hypernociception and flinches (a characteristic biphasic response) in which kinins and NO are substantially involved. Although celecoxib was effective against the oedema and pain caused by Tsv, COX-2 does not seem to be involved in the inflammatory response caused by Tsv. (C) 2008 Elsevier Ltd. All rights reserved.

Role of the spinal cord heme oxygenase-carbon monoxide-cGMP pathway in the nociceptive response of rats

The aim of the present study was to investigate the role of the spinal cord heme oxygenase (HO)-carbon monoxide (CO)-soluble guanylate cyclase (sGC)-cGMP pathway in nociceptive response of rats to the formalin experimental nociceptive model. Animals were handled and adapted to the experimental environment for a few days before the formalin test was applied. For the formalin test 50 mu l of a 1% formalin solution was injected subcutaneously in the dorsal surface of the right hind paw. Following injections, animals were observed for I h and flinching behavior was measured as the nociceptive response. Thirty min before the test, rats were pretreated with intrathecal injections with the HO inhibitor, zinc deuteroporphyrin 2,4-bis glycol (ZnDPBG) or heme-lysinate, which is known to induce the HO pathway. Control animals were treated with vehicles. We observed a significant increase in nociceptive response of rats treated with ZnDPBG, and a drastic reduction of flinching nociceptive behavioral response in the heme-lysinate treated animals. Furthermore, the HO pathway seems to act via cGMP, since methylene blue (a sGC inhibitor) prevented the reduction of flinching nociceptive behavioral response caused by heme-lysinate. These findings strongly indicate that the HO pathway plays a spinal antinociceptive role during the formalin test, acting via cGMP. (C) 2007 Elsevier B.V. All rights reserved.

Effects of short-term acetaminophen and celecoxib treatment on orthodontic tooth movement and neuronal activation in rat

Non-steroidal anti-inflammatory drugs (NSAIDs) have been used for pain relief in orthodontics, but clinical studies reported that they may reduce tooth movement (TM). By other side, TM seems to activate brain structures related to nociception, but the effects of NSAIDs in this activation have not been studied yet. We analyzed the effect of short-term treatment with acetaminophen or celecoxib in the separation of rat upper incisors, as well as in neuronal activation of the spinal trigeminal nucleus, following tooth movement. Thirty rats (400-420 g) were pretreated through oral gavage (1 ml/dose)with acetaminophen (200 mg/kg), celecoxib (50 mg/kg) or vehicle (carboxymethylcellulose 0.4%). After 30 min, they received an activated (30 g) orthodontic appliance for TM. In controls, this appliance was immediately removed after its introduction. Rats received ground food, and every 12 h, one of the drugs or vehicle. After 48 h, they were anesthetized, maxilla was radiographed, and were perfused with 4% paraformaldehyde. Brains were further processed for Fos immunohistochemistry. TM induced incisor distalization (p < 0.05) and neuronal activation of the spinal trigeminal nucleus. Treatment with both drugs did not affect tooth movement, but reduced c-fos expression in the caudalis subnucleus. No changes in c-fos expression were seen in the oralis and interpolaris subnuclei. We conclude that neither celecoxib nor acetaminophen seems to affect tooth movement, when used for 2 days, but both drugs are able to reduce the activation of brain structures related to nociception. Short-term treatment with celecoxib, thus, may be a therapeutic alternative to acetaminophen when the latter is contra indicated. (C) 2009 Elsevier Inc. All rights reserved.

Rapid maxillary expansion causes neuronal activation in brain structures of rats

A correlation between pain sensation and neuronal c-fos expression has been analyzed following experimental rapid maxillar expansion (RME). Adult male Wistar rats were anaesthetized and divided into three groups: animals that received an orthodontic apparatus, which was immediately removed after the insertion (control), animals that received an inactivated orthodontic apparatus (without force), and animals that received an orthodontic apparatus previously activated (140 g force). After 6, 24, 48, or 72 h, the animals were re-anaesthetized, and perfused with 4% paraformaldehyde. The brains were removed, fixed, and sections containing brain structures related to nociception were processed for Fos protein immunohistochemistry (IHC). The insertion of the orthodontic apparatus with 140 g was able to cause RME that could be seen by radiography. The IHC results showed that the number of activated neurons in the different nuclei changed according to the duration of appliance insertion and followed a temporal pattern similar to that of sensations described in clinics. The animals that received the orthodontic apparatus without force did not show RME but a smaller c-fos expression in the same brain structures. In conclusion, we demonstrate that orthodontic force used for palate disjunction activates brain structures that are related to nociception, and that this activation is related to the pain sensation described during orthodontic treatment. (c) 2008 Elsevier Inc. All rights reserved.

The effect of musculoskeletal pain on motor activity and control

Aberrant movement patterns and postures are obvious to clinicians managing patients with musculoskeletal pain. However, some changes in motor function that occur in the presence of pain are less apparent. Clinical and basic science investigations have provided evidence of the effects of nociception on aspects of motor function. Both increases and decreases in muscle activity have been shown, along with alterations in neuronal control mechanisms, proprioception, and local muscle morphology. Various models have been proposed in an attempt to provide an explanation for some of these changes. These include the vicious cycle and pain adaptation models. Recent research has seen the emergence of a new model in which patterns of muscle activation and recruitment are altered in the presence of pain (neuromuscular activation model). These changes seem to particularly affect the ability of muscles to perform synergistic functions related to maintaining joint stability and control. These changes are believed to persist into the period of chronicity. This review shows current knowledge of the effect of musculoskeletal pain on the motor system and presents the various proposed models, in addition to other shown effects not covered by these models. The relevance of these models to both acute and chronic pain is considered. It is apparent that people experiencing musculoskeletal pain exhibit complex motor responses that may show some variation with the time course of the disorder. (C) 2001 by the American Pain Society.

Cutaneous lesions sensory impairment recovery and nerve regeneration in leprosy patients

It is important to understand the mechanisms that enable peripheral neurons to regenerate after nerve injury in order to identify methods of improving this regeneration. Therefore, we studied nerve regeneration and sensory impairment recovery in the cutaneous lesions of leprosy patients (LPs) before and after treatment with multidrug therapy (MDT). The skin lesion sensory test results were compared to the histopathological and immunohistochemical protein gene product (PGP) 9.5 and the p75 nerve growth factor receptors (NGFr) findings. The cutaneous neural occupation ratio (CNOR) was evaluated for both neural markers. Thermal and pain sensations were the most frequently affected functions at the first visit and the most frequently recovered functions after MDT. The presence of a high cutaneous nerve damage index did not prevent the recovery of any type of sensory function. The CNOR was calculated for each biopsy, according to the presence of PGP and NGFr-immunostained fibres and it was not significantly different before or after the MDT. We observed a variable influence of MDT in the recovery from sensory impairment in the cutaneous lesions of LPs. Nociception and cold thermosensation were the most recovered sensations. The recovery of sensation in the skin lesions appeared to be associated with subsiding inflammation rather than with the regenerative activity of nerve fibres.

Consensus paper: the role of the cerebellum in perceptual processes.

Various lines of evidence accumulated over the past 30 years indicate that the cerebellum, long recognized as essential for motor control, also has considerable influence on perceptual processes. In this paper, we bring together experts from psychology and neuroscience, with the aim of providing a succinct but comprehensive overview of key findings related to the involvement of the cerebellum in sensory perception. The contributions cover such topics as anatomical and functional connectivity, evolutionary and comparative perspectives, visual and auditory processing, biological motion perception, nociception, self-motion, timing, predictive processing, and perceptual sequencing. While no single explanation has yet emerged concerning the role of the cerebellum in perceptual processes, this consensus paper summarizes the impressive empirical evidence on this problem and highlights diversities as well as commonalities between existing hypotheses. In addition to work with healthy individuals and patients with cerebellar disorders, it is also apparent that several neurological conditions in which perceptual disturbances occur, including autism and schizophrenia, are associated with cerebellar pathology. A better understanding of the involvement of the cerebellum in perceptual processes will thus likely be important for identifying and treating perceptual deficits that may at present go unnoticed and untreated. This paper provides a useful framework for further debate and empirical investigations into the influence of the cerebellum on sensory perception.

Endogenous angiotensinergic system in neurons of rat and human trigeminal ganglia.

To clarify the role of Angiotensin II (Ang II) in the sensory system and especially in the trigeminal ganglia, we studied the expression of angiotensinogen (Ang-N)-, renin-, angiotensin converting enzyme (ACE)- and cathepsin D-mRNA, and the presence of Ang II and substance P in the rat and human trigeminal ganglia. The rat trigeminal ganglia expressed substantial amounts of Ang-N- and ACE mRNA as determined by quantitative real time PCR. Renin mRNA was untraceable in rat samples. Cathepsin D was detected in the rat trigeminal ganglia indicating the possibility of existence of pathways alternative to renin for Ang I formation. In situ hybridization in rat trigeminal ganglia revealed expression of Ang-N mRNA in the cytoplasm of numerous neurons. By using immunocytochemistry, a number of neurons and their processes in both the rat and human trigeminal ganglia were stained for Ang II. Post in situ hybridization immunocytochemistry reveals that in the rat trigeminal ganglia some, but not all Ang-N mRNA-positive neurons marked for Ang II. In some neurons Substance P was found colocalized with Ang II. Angiotensins from rat trigeminal ganglia were quantitated by radioimmunoassay with and without prior separation by high performance liquid chromatography. Immunoreactive angiotensin II (ir-Ang II) was consistently present and the sum of true Ang II (1-8) octapeptide and its specifically measured metabolites were found to account for it. Radioimmunological and immunocytochemical evidence of ir-Ang II in neuronal tissue is compatible with Ang II as a neurotransmitter. In conclusion, these results suggest that Ang II could be produced locally in the neurons of rat trigeminal ganglia. The localization and colocalization of neuronal Ang II with Substance P in the trigeminal ganglia neurons may be the basis for a participation and function of Ang II in the regulation of nociception and migraine pathology.

C/EBPbeta couples dopamine signalling to substance P precursor gene expression in striatal neurones.

Dopamine-induced changes in striatal gene expression are thought to play an important role in drug addiction and compulsive behaviour. In this study we report that dopamine induces the expression of the transcription factor CCAAT/Enhancer Binding Protein beta (C/EBP)-beta in primary cultures of striatal neurones. We identified the preprotachykinin-A (PPT-A) gene coding for substance P and neurokinin-A as a potential target gene of C/EBPbeta. We demonstrated that C/EBPbeta physically interacts with an element of the PPT-A promoter, thereby facilitating substance P precursor gene transcription. The regulation of PPT-A gene by C/EBPbeta could subserve many important physiological processes involving substance P, such as nociception, neurogenic inflammation and addiction. Given that substance P is known to increase dopamine signalling in the striatum and, in turn, dopamine increases substance P expression in medium spiny neurones, our results implicate C/EBPbeta in a positive feedback loop, changes of which might contribute to the development of drug addiction.

Nedd4-2 ubiquitin ligase: a contributor to experimental neuropathic pain?

Background: Neuropathic pain is associated with altered expression of voltage-gated sodium channels (VGSCs) leading to peripheral nerve hyperexcitability. Interestingly, in cell expression systems, the ubiquitin ligase Nedd4-2 regulates the cell membrane density of the most abundant peripheral and pain-related VGSC, namely Nav1.7, and decreases its sodium current. Yet nothing is known about the involvement of Nedd4-2 in nociception and chronic pain. Therefore, the goal of this study is (i) to characterize Nedd4-2 and Nav1.7 expression in an experimental model of neuropathic pain (ii) to design by viral vector-mediated gene therapy an approach to depict the implication of Nedd4-2 in chronic pain. Methods: Western Blot and immunohistochemistry experiments detecting Nav1.7 and Nedd4-2 were performed in rodent DRGs 7 days after spared nerve injury (SNI). For the viral vector-mediated gene therapy, a recombinant Adeno-Associated Virus (rAAV2/6) was generated expressing the Nedd4-2 gene. Intrathecal injection of rAAV2/6 was followed 2 weeks after by the SNI surgery. Data are expressed in mean ± SEM, n = 4 in each condition. Results: Immunofluorescence on DRGs neurons reveals a decreased number of positive Nedd4-2 cells in the SNI model (27.0 ± 1.2%) versus sham group (43.4 ± 3.5%; p <0.005), as well as an increase in positive Nav1.7 cells in SNI (50.1 ± 2.9%) versus Sham (41.6 ± 1.8%; p <0.05). The change of Nedd4-2 expression was confirmed by western-blot analysis. In addition, we show that Nedd4-2 and Nav1.7 are largely expressed in overlapping cell populations, chiefly colocalizing with markers of small nociceptive neurons. Furthermore, we report that intrathecal injection of rAAV is able to counteract the reduction of Nedd4-2 expression in SNI animals. Conclusion: Our results indicate that Nedd4-2 is mainly expressed in nociceptors and downregulated after nerve injury. Moreover, our data suggest that the reduction of Nedd4-2, after nerve injury, may modulate Nav1.7 activity and contribute to hyperexcitability in neuropathic pain. A normal level of Nedd4-2 can be restored using a viral vector and we will further assess its functional effect on pain sensitivity.

Regulation of Nav1.7 and Nav1.8 voltage-gated sodium channels by Nedd4-2 and β-subunits and its implication in neuropathic pain

In mammals, the presence of excitable cells in muscles, heart and nervous system is crucial and allows fast conduction of numerous biological information over long distances through the generation of action potentials (AP). Voltage-gated sodium channels (Navs) are key players in the generation and propagation of AP as they are responsible for the rising phase of the AP. Navs are heteromeric proteins composed of a large pore-forming a-subunit (Nav) and smaller ß-auxiliary subunits. There are ten genes encoding for Navl.l to Nav1.9 and NaX channels, each possessing its own specific biophysical properties. The excitable cells express differential combinations of Navs isoforms, generating a distinct electrophysiological signature. Noteworthy, only when anchored at the membrane are Navs functional and are participating in sodium conductance. In addition to the intrinsic properties of Navs, numerous regulatory proteins influence the sodium current. Some proteins will enhance stabilization of membrane Navs while others will favour internalization. Maintaining equilibrium between the two is of crucial importance for controlling cellular excitability. The E3 ubiquitin ligase Nedd4-2 is a well-characterized enzyme that negatively regulates the turnover of many membrane proteins including Navs. On the other hand, ß-subunits are known since long to stabilize Navs membrane anchoring. Peripheral neuropathic pain is a disabling condition resulting from nerve injury. It is characterized by the dysregulation of Navs expressed in dorsal root ganglion (DRG) sensory neurons as highlighted in different animal models of neuropathic pain. Among Navs, Nav1.7 and Nav1.8 are abundantly and specifically expressed in DRG sensory neurons and have been recurrently incriminated in nociception and neuropathic pain development. Using the spared nerve injury (SNI) experimental model of neuropathic pain in mice, I observed a specific reduction of Nedd4-2 in DRG sensory neurons. This decrease subsequently led to an upregulation of Nav1.7 and Nav1.8 protein and current, in the axon and the DRG neurons, respectively, and was sufficient to generate neuropathic pain-associated hyperexcitability. Knocking out Nedd4-2 specifically in nociceptive neurons led to the same increase of Nav1.7 and Nav1.8 concomitantly with an increased thermal sensitivity in mice. Conversely, rescuing Nedd4-2 downregulation using viral vector transfer attenuated neuropathic pain mechanical hypersensitivity. This study demonstrates the significant role of Nedd4-2 in regulating cellular excitability in vivo and its involvement in neuropathic pain development. The role of ß-subunits in neuropathic pain was already demonstrated in our research group. Because of their stabilization role, the increase of ßl, ß2 and ß3 subunits in DRGs after SNI led to increased Navs anchored at the membrane. Here, I report a novel mechanism of regulation of a-subunits by ß- subunits in vitro; ßl and ß3-subunits modulate the glycosylation pattern of Nav1.7, which might account for stabilization of its membrane expression. This opens new perspectives for investigation Navs state of glycosylation in ß-subunits dependent diseases, such as in neuropathic pain. - Chez les mammifères, la présence de cellules excitables dans les muscles, le coeur et le système nerveux est cruciale; elle permet la conduction rapide de nombreuses informations sur de longues distances grâce à la génération de potentiels d'action (PA). Les canaux sodiques voltage-dépendants (Navs) sont des participants importants dans la génération et la propagation des PA car ils sont responsables de la phase initiale de dépolarisation du PA. Les Navs sont des protéines hétéromériques composées d'une grande sous-unité a (formant le pore du canal) et de petites sous-unités ß accompagnatrices. Il existe dix gènes qui codent pour les canaux sodiques, du Nav 1.1 au Nav 1.9 ainsi que NaX, chacun possédant des propriétés biophysiques spécifiques. Les cellules excitables expriment différentes combinaisons des différents isoformes de Navs, qui engendrent une signature électrophysiologique distincte. Les Navs ne sont fonctionnels et ne participent à la conductibilité du Na+, que s'ils sont ancrés à la membrane plasmique. En plus des propriétés intrinsèques des Navs, de nombreuses protéines régulatrices influencent également le courant sodique. Certaines protéines vont favoriser l'ancrage et la stabilisation des Navs exprimés à la membrane, alors que d'autres vont plutôt favoriser leur internalisation. Maintenir l'équilibre des deux processus est crucial pour contrôler l'excitabilité cellulaire. Dans ce contexte, Nedd4-2, de la famille des E3 ubiquitin ligase, est une enzyme bien caractérisée qui régule l'internalisation de nombreuses protéines, notamment celle des Navs. Inversement, les sous-unités ß sont connues depuis longtemps pour stabiliser l'ancrage des Navs à la membrane. La douleur neuropathique périphérique est une condition débilitante résultant d'une atteinte à un nerf. Elle est caractérisée par la dérégulation des Navs exprimés dans les neurones sensoriels du ganglion spinal (DRG). Ceci a été démontré à de multiples occasions dans divers modèles animaux de douleur neuropathique. Parmi les Navs, Nav1.7 et Nav1.8 sont abondamment et spécifiquement exprimés dans les neurones sensoriels des DRG et ont été impliqués de façon récurrente dans le développement de la douleur neuropathique. En utilisant le modèle animal de douleur neuropathique d'épargne du nerf sural (spared nerve injury, SNI) chez la souris, j'ai observé une réduction spécifique des Nedd4-2 dans les neurones sensoriels du DRG. Cette diminution avait pour conséquence l'augmentation de l'expression des protéines et des courants de Nav 1.7 et Nav 1.8, respectivement dans l'axone et les neurones du DRG, et était donc suffisante pour créer l'hyperexcitabilité associée à la douleur neuropathique. L'invalidation pour le gène codant pour Nedd4-2 dans une lignée de souris génétiquement modifiées a conduit à de similaires augmentations de Nav1.7 et Nav1.8, parallèlement à une augmentation à la sensibilité thermique. A l'opposé, rétablir une expression normale de Nedd4-2 en utilisant un vecteur viral a eu pour effet de contrecarrer le développement de l'hypersensibilité mécanique lié à ce modèle de douleur neuropathique. Cette étude démontre le rôle important de Nedd4-2 dans la régulation de l'excitabilité cellulaire in vivo et son implication dans le développement des douleurs neuropathiques. Le rôle des sous-unités ß dans les douleurs neuropathiques a déjà été démontré dans notre groupe de recherche. A cause de leur rôle stabilisateur, l'augmentation des sous-unités ßl, ß2 et ß3 dans les DRG après SNI, conduit à une augmentation des Navs ancrés à la membrane. Dans mon travail de thèse, j'ai observé un nouveau mécanisme de régulation des sous-unités a par les sous-unités ß in vitro. Les sous-unités ßl et ß3 régulent l'état de glycosylation du canal Nav1.7, et stabilisent son expression membranaire. Ceci ouvre de nouvelles perspectives dans l'investigation de l'état de glycosylation des Navs dans des maladies impliquant les sous-unités ß, notamment les douleurs neuropathiques.

Intraneuronal angiotensinergic system in rat and human dorsal root ganglia.

To elucidate the local formation of angiotensin II (Ang II) in the neurons of sensory dorsal root ganglia (DRG), we studied the expression of angiotensinogen (Ang-N)-, renin-, angiotensin converting enzyme (ACE)- and cathepsin D-mRNA, and the presence of protein renin, Ang II, Substance P and calcitonin gene-related peptide (CGRP) in the rat and human thoracic DRG. Quantitative real time PCR (qRT-PCR) studies revealed that rat DRG expressed substantial amounts of Ang-N- and ACE mRNA, while renin mRNA as well as the protein renin were untraceable. Cathepsin D-mRNA and cathepsin D-protein were detected in the rat DRG indicating the possibility of existence of pathways alternative to renin for Ang I formation. Angiotensin peptides were successfully detected with high performance liquid chromatography and radioimmunoassay in human DRG extracts. In situ hybridization in rat DRG confirmed additionally expression of Ang-N mRNA in the cytoplasm of numerous neurons. Intracellular Ang II staining could be shown in number of neurons and their processes in both the rat and human DRG. Interestingly we observed neuronal processes with angiotensinergic synapses en passant, colocalized with synaptophysin, within the DRG. In the DRG, we also identified by qRT-PCR, expression of Ang II receptor AT(1A) and AT(2)-mRNA while AT(1B)-mRNA was not traceable. In some neurons Substance P and CGRP were found colocalized with Ang II. The intracellular localization and colocalization of Ang II with Substance P and CGRP in the DRG neurons may indicate a participation and function of Ang II in the regulation of nociception. In conclusion, these results suggest that Ang II may be produced locally in the neurons of rat and human DRG and act as a neurotransmitter.

ACID-SENSING ION CHANNELS: functional and molecular characterization in putative nociceptors, and modulation by nerve injury and serine protease

Résumé Les canaux ioniques ASICs (acid-sensing ion channels) appartiennent à la famille des canaux ENaC/Degenerin. Pour l'instant, quatre gènes (1 à 4) ont été clonés dont certains présentent des variants d'épissage. Leur activation par une acidification rapide du milieu extracellulaire génère un courant entrant transitoire essentiellement sodique accompagné pour certains types d'ASICs d'une phase soutenue. Les ASICs sont exprimés dans le système nerveux, central (SNC) et périphérique (SNP). On leur attribue un rôle dans l'apprentissage, la mémoire et l'ischémie cérébrale au niveau central ainsi que dans la nociception (douleur aiguë et inflammatoire) et la méchanotransduction au niveau périphérique. Toutefois, les données sont parfois contradictoires. Certaines études suggèrent qu'ils sont des senseurs primordiaux impliqués dans la détection de l'acidification et la douleur. D'autres études suggèrent plutôt qu'ils ont un rôle modulateur inhibiteur dans la douleur. De plus, le fait que leur activation génère majoritairement un courant transitoire alors que les fibres nerveuses impliquées dans la douleur répondent à un stimulus nocif avec une adaptation lente suggère que leurs propriétés doivent être modulés par des molécules endogènes. Dans une première partie de ma thèse, nous avons abordé la question de l'expression fonctionnelle des ASICs dans les neurones sensoriels primaires afférents du rat adulte pour clarifier le rôle des ASICs dans les neurones sensoriels. Nous avons caractérisé leurs propriétés biophysiques et pharmacologiques par la technique du patch-clamp en configuration « whole-cell ». Nous avons pu démontrer que près de 60% des neurones sensoriels de petit diamètre expriment des courants ASICs. Nous avons mis en évidence trois types de courant ASIC dans ces neurones. Les types 1 et 3 ont des propriétés compatibles avec un rôle de senseur du pH alors que le type 2 est majoritairement activé par des pH inférieurs à pH6. Le type 1 est médié par des homomers de la sous-unité ASIC1 a qui sont perméables aux Ca2+. Nous avons étudié leur co-expression avec des marqueurs des nocicepteurs ainsi que la possibilité d'induire une activité neuronale suite à une acidification qui soit dépendante des ASICs. Le but était d'associer un type de courant ASIC avec une fonction potentielle dans les neurones sensoriels. Une majorité des neurones exprimant les courants ASIC co-expriment des marqueurs des nocicepteurs. Toutefois, une plus grande proportion des neurones exprimant le type 1 n'est pas associée à la nociception par rapport aux types 2 et 3. Nous avons montré qu'il est possible d'induire des potentiels d'actions suite à une acidification. La probabilité d'induction est proportionnelle à la densité des courants ASIC et à l'acidité de la stimulation. Puis, nous avons utilisé cette classification comme un outil pour appréhender les potentielles modulations fonctionnelles des ASICs dans un model de neuropathie (spared nerve injury). Cette approche fut complétée par des expériences de «quantitative RT-PCR ». En situation de neuropathie, les courants ASIC sont dramatiquement changés au niveau de leur expression fonctionnelle et transcriptionnelle dans les neurones lésés ainsi que non-lésés. Dans une deuxième partie de ma thèse, suite au test de différentes substances sécrétées lors de l'inflammation et l'ischémie sur les propriétés des ASICs, nous avons caractérisé en détail la modulation des propriétés des courants ASICs notamment ASIC1 par les sérines protéases dans des systèmes d'expression recombinants ainsi que dans des neurones d'hippocampe. Nous avons montré que l'exposition aux sérine-protéases décale la dépendance au pH de l'activation ainsi que la « steady-state inactivation »des ASICs -1a et -1b vers des valeurs plus acidiques. Ainsi, l'exposition aux serine protéases conduit à une diminution du courant quand l'acidification a lieu à partir d'un pH7.4 et conduit à une augmentation du courant quand l'acidification alleu à partir d'un pH7. Nous avons aussi montré que cette régulation a lieu des les neurones d'hippocampe. Nos résultats dans les neurones sensoriels suggèrent que certains courants ASICs sont impliqués dans la transduction de l'acidification et de la douleur ainsi que dans une des phases du processus conduisant à la neuropathie. Une partie des courants de type 1 perméables au Ca 2+ peuvent être impliqués dans la neurosécrétion. La modulation par les sérines protéases pourrait expliquer qu'en situation d'acidose les canaux ASICs soient toujours activables. Résumé grand publique Les neurones sont les principales cellules du système nerveux. Le système nerveux est formé par le système nerveux central - principalement le cerveau, le cervelet et la moelle épinière - et le système nerveux périphérique -principalement les nerfs et les neurones sensoriels. Grâce à leur nombreux "bras" (les neurites), les neurones sont connectés entre eux, formant un véritable réseau de communication qui s'étend dans tout le corps. L'information se propage sous forme d'un phénomène électrique, l'influx nerveux (ou potentiels d'actions). A la base des phénomènes électriques dans les neurones il y a ce que l'on appelle les canaux ioniques. Un canal ionique est une sorte de tunnel qui traverse l'enveloppe qui entoure les cellules (la membrane) et par lequel passent les ions. La plupart de ces canaux sont normalement fermés et nécessitent d'être activés pour s'ouvrire et générer un influx nerveux. Les canaux ASICs sont activés par l'acidification et sont exprimés dans tout le système nerveux. Cette acidification a lieu notamment lors d'une attaque cérébrale (ischémie cérébrale) ou lors de l'inflammation. Les expériences sur les animaux ont montré que les canaux ASICs avaient entre autre un rôle dans la mort des neurones lors d'une attaque cérébrale et dans la douleur inflammatoire. Lors de ma thèse je me suis intéressé au rôle des ASICs dans la douleur et à l'influence des substances produites pendant l'inflammation sur leur activation par l'acidification. J'ai ainsi pu montrer chez le rat que la majorité des neurones sensoriels impliqués dans la douleur ont des canaux ASICs et que l'activation de ces canaux induit des potentiels d'action. Nous avons opéré des rats pour qu'ils présentent les symptômes d'une maladie chronique appelée neuropathie. La neuropathie se caractérise par une plus grande sensibilité à la douleur. Les rats neuropathiques présentent des changements de leurs canaux ASICs suggérant que ces canaux ont une peut-être un rôle dans la genèse ou les symptômes de cette maladie. J'ai aussi montré in vitro qu'un type d'enryme produit lors de l'inflammation et l'ischémie change les propriétés des ASICs. Ces résultats confirment un rôle des ASICs dans la douleur suggérant notamment un rôle jusque là encore non étudié dans la douleur neuropathique. De plus, ces résultats mettent en évidence une régulation des ASICs qui pourrait être importante si elle se confirmait in vivo de part les différents rôles des ASICs. Abstract Acid-sensing ion channels (ASICs) are members of the ENaC/Degenerin superfamily of ion channels. Their activation by a rapid extracellular acidification generates a transient and for some ASIC types also a sustained current mainly mediated by Na+. ASICs are expressed in the central (CNS) and in the peripheral (PNS) nervous system. In the CNS, ASICs have a putative role in learning, memory and in neuronal death after cerebral ischemia. In the PNS, ASICs have a putative role in nociception (acute and inflammatory pain) and in mechanotransduction. However, studies on ASIC function are somewhat controversial. Some studies suggest a crucial role of ASICs in transduction of acidification and in pain whereas other studies suggest rather a modulatory inhibitory role of ASICs in pain. Moreover, the basic property of ASICs, that they are activated only transiently is irreconcilable with the well-known property of nociception that the firing of nociceptive fibers demonstrated very little adaptation. Endogenous molecules may exist that can modulate ASIC properties. In a first part of my thesis, we addressed the question of the functional expression of ASICs in adult rat dorsal root ganglion (DRG) neurons. Our goal was to elucidate ASIC roles in DRG neurons. We characterized biophysical and pharmacological properties of ASIC currents using the patch-clamp technique in the whole-cell configuration. We observed that around 60% of small-diameter sensory neurons express ASICs currents. We described in these neurons three ASIC current types. Types 1 and 3 have properties compatible with a role of pH-sensor whereas type 2 is mainly activated by pH lower than pH6. Type 1 is mediated by ASIC1a homomultimers which are permeable to Ca 2+. We studied ASIC co-expression with nociceptor markers. The goal was to associate an ASIC current type with a potential function in sensory neurons. Most neurons expressing ASIC currents co-expressed nociceptor markers. However, a higher proportion of the neurons expressing type 1 was not associated with nociception compared to type 2 and -3. We completed this approach with current-clamp measurements of acidification-induced action potentials (APs). We showed that activation of ASICs in small-diameter neurons can induce APs. The probability of AP induction is positively correlated with the ASIC current density and the acidity of stimulation. Then, we used this classification as a tool to characterize the potential functional modulation of ASICs in the spared nerve injury model of neuropathy. This approach was completed by quantitative RT-PCR experiments. ASICs current expression was dramatically changed at the functional and transcriptional level in injured and non-injured small-diameter DRG neurons. In a second part of my thesis, following an initial screening of the effect of various substances secreted during inflammation and ischemia on ASIC current properties, we characterized in detail the modulation of ASICs, in particular of ASIC1 by serine proteases in a recombinant expression system as well as in hippocampal neurons. We showed that protease exposure shifts the pH dependence of ASIC1 activation and steady-state inactivation to more acidic pH. As a consequence, protease exposure leads to a decrease in the current response if ASIC1 is activated by a pH drop from pH 7.4. If, however, acidification occurs from a basal pH of 7, protease-exposed ASIC1a shows higher activity than untreated ASIC1a. We provided evidence that this bi-directional regulation of ASIC1a function also occurs in hippocampal neurons. Our results in DRG neurons suggest that some ASIC currents are involved in the transduction of peripheral acidification and pain. Furthermore, ASICs may participate to the processes leading to neuropathy. Some Ca 2+-permeable type 1 currents may be involved in neurosecretion. ASIC modulation by serine proteases may be physiologically relevant, allowing ASIC activation under sustained slightly acidic conditions.