Les neurones sérotoninergiques du noyau raphé Magnus dans le contrôle de la transmission nociceptive dans la corne dorsale de la moelle épinière : une étude optogénétique dans différents contextes pathophysiologiques

Pain is an unpleasant sensation and emotional experience elicited by potentially harmful stimulations to protect the integrity of the body. An endogenous mechanism involving the PAG-RVM modulatory system control pain sensation by filtering nociceptive inputs. A balance between both excitatory and inhibitory influences control nociceptive transmission and impairment in this balance leads to the development of pathological pain. In the present study, we used an optogenetic approach to specifically target serotoninergic neurons (5-HT) that projected to the dorsal horn of the spinal cord. We showed that these neurons exerted a tonic analgesic action through a decreased excitability of projection neurons of the dorsal horn of the spinal cord. This effect is gender independent. We also observed that 5-HT neurons are indirectly connected to projection neurons through local inhibitory interneurons. Then, we showed that 5-HT neurons of the RMg received descending inputs from the SST neurons of the ventro-lateral part of the periaqueductal gray (vlPAG) that exerted downward facilitation on pain transmission. Interestingly, we show that 5-HT inhibitory action is switched to an excitatory influence in a model of peripheral neuropathy due to a spinal chloride equilibrium shift. These results suggest that the same descending pathway can be both excitatory and inhibitory upon pathological conditions, providing crucial insights about long-term changes associated with chronic pain.La douleur est une sensation et une expérience émotionnelle désagréable résultant de stimulations potentiellement nuisibles pour protéger l'intégrité du corps. Un mécanisme endogène impliquant le système PAG-RVM, module la sensation de douleur en filtrant les entrées nociceptives. Un équilibre entre des influences excitatrices et inhibitrices contrôle la transmission nociceptive et une perturbation de cet équilibre conduit à l’installation de douleurs pathologiques. Dans ce travail, nous avons utilisé une approche optogénétique pour cibler spécifiquement les neurones sérotoninergiques (5-HT) du noyau du raphé Magnus (RMg) projetant sur la corne dorsale de la moelle épinière. Nous avons montré que ces neurones exerçaient une action analgésique tonique par une diminution de l'excitabilité des neurones de projection de la corne dorsale de la moelle épinière. Cet effet étant indépendant du sexe. Nous avons également observé que les neurones sérotoninergiques (5-HT) sont indirectement liés aux neurones de projection par l'intermédiaire d'interneurones inhibiteurs locaux. Puis, nous avons montré que les neurones sérotoninergiques (5-HT) du RMg recevaient des projections des neurones à somatostatine du ventro-latérale de la substance grise périaqueducale (vlPAG) exerçant une facilitation descendante de la transmission nociceptive. Fait intéressant, nous montrons que dans un modèle de neuropathie périphérique, l'action inhibitrice des neurones à sérotonine (5-HT) du RMg est transformée en influence excitatrice, aussi bien chez les mâles que les femelles, en raison d'un déplacement de l'équilibre du chlore au sein de la moelle épinière. Ces résultats suggèrent que la même voie descendante peut être à la fois excitatrice et inhibitrice dans des conditions pathologiques, révélant des informations cruciales sur les changements à long terme associés à la douleur chronique

Serotonergic neurons of the nucleus raphe Magnus in the control of nociceptive transmission in the dorsal horn of the spinal cord : an optogenetic study in different pathophysiological contexts

La douleur est une sensation et une expérience émotionnelle désagréable résultant de stimulations potentiellement nuisibles pour protéger l'intégrité du corps. Un mécanisme endogène impliquant le système PAG-RVM, module la sensation de douleur en filtrant les entrées nociceptives. Un équilibre entre des influences excitatrices et inhibitrices contrôle la transmission nociceptive et une perturbation de cet équilibre conduit à l’installation de douleurs pathologiques. Dans ce travail, nous avons utilisé une approche optogénétique pour cibler spécifiquement les neurones sérotoninergiques (5-HT) du noyau du raphé Magnus (RMg) projetant sur la corne dorsale de la moelle épinière. Nous avons montré que ces neurones exerçaient une action analgésique tonique par une diminution de l'excitabilité des neurones de projection de la corne dorsale de la moelle épinière. Cet effet étant indépendant du sexe. Nous avons également observé que les neurones sérotoninergiques (5-HT) sont indirectement liés aux neurones de projection par l'intermédiaire d'interneurones inhibiteurs locaux. Puis, nous avons montré que les neurones sérotoninergiques (5-HT) du RMg recevaient des projections des neurones à somatostatine du ventro-latérale de la substance grise périaqueducale (vlPAG) exerçant une facilitation descendante de la transmission nociceptive. Fait intéressant, nous montrons que dans un modèle de neuropathie périphérique, l'action inhibitrice des neurones à sérotonine (5-HT) du RMg est transformée en influence excitatrice, aussi bien chez les mâles que les femelles, en raison d'un déplacement de l'équilibre du chlore au sein de la moelle épinière. Ces résultats suggèrent que la même voie descendante peut être à la fois excitatrice et inhibitrice dans des conditions pathologiques, révélant des informations cruciales sur les changements à long terme associés à la douleur chronique.Pain is an unpleasant sensation and emotional experience elicited by potentially harmful stimulations to protect the integrity of the body. An endogenous mechanism involving the PAG-RVM modulatory system control pain sensation by filtering nociceptive inputs. A balance between both excitatory and inhibitory influences control nociceptive transmission and impairment in this balance leads to the development of pathological pain. In the present study, we used an optogenetic approach to specifically target serotoninergic neurons (5-HT) that projected to the dorsal horn of the spinal cord. We showed that these neurons exerted a tonic analgesic action through a decreased excitability of projection neurons of the dorsal horn of the spinal cord. This effect is gender independent. We also observed that 5-HT neurons are indirectly connected to projection neurons through local inhibitory interneurons. Then, we showed that 5-HT neurons of the RMg received descending inputs from the SST neurons of the ventro-lateral part of the periaqueductal gray (vlPAG) that exerted downward facilitation on pain transmission. Interestingly, we show that 5-HT inhibitory action is switched to an excitatory influence in a model of peripheral neuropathy due to a spinal chloride equilibrium shift. These results suggest that the same descending pathway can be both excitatory and inhibitory upon pathological conditions, providing crucial insights about long-term changes associated with chronic pain

Serotonergic neurons of the nucleus raphe Magnus in the control of nociceptive transmission in the dorsal horn of the spinal cord : an optogenetic study in different pathophysiological contexts

La douleur est une sensation et une expérience émotionnelle désagréable résultant de stimulations potentiellement nuisibles pour protéger l'intégrité du corps. Un mécanisme endogène impliquant le système PAG-RVM, module la sensation de douleur en filtrant les entrées nociceptives. Un équilibre entre des influences excitatrices et inhibitrices contrôle la transmission nociceptive et une perturbation de cet équilibre conduit à l’installation de douleurs pathologiques. Dans ce travail, nous avons utilisé une approche optogénétique pour cibler spécifiquement les neurones sérotoninergiques (5-HT) du noyau du raphé Magnus (RMg) projetant sur la corne dorsale de la moelle épinière. Nous avons montré que ces neurones exerçaient une action analgésique tonique par une diminution de l'excitabilité des neurones de projection de la corne dorsale de la moelle épinière. Cet effet étant indépendant du sexe. Nous avons également observé que les neurones sérotoninergiques (5-HT) sont indirectement liés aux neurones de projection par l'intermédiaire d'interneurones inhibiteurs locaux. Puis, nous avons montré que les neurones sérotoninergiques (5-HT) du RMg recevaient des projections des neurones à somatostatine du ventro-latérale de la substance grise périaqueducale (vlPAG) exerçant une facilitation descendante de la transmission nociceptive. Fait intéressant, nous montrons que dans un modèle de neuropathie périphérique, l'action inhibitrice des neurones à sérotonine (5-HT) du RMg est transformée en influence excitatrice, aussi bien chez les mâles que les femelles, en raison d'un déplacement de l'équilibre du chlore au sein de la moelle épinière. Ces résultats suggèrent que la même voie descendante peut être à la fois excitatrice et inhibitrice dans des conditions pathologiques, révélant des informations cruciales sur les changements à long terme associés à la douleur chronique.Pain is an unpleasant sensation and emotional experience elicited by potentially harmful stimulations to protect the integrity of the body. An endogenous mechanism involving the PAG-RVM modulatory system control pain sensation by filtering nociceptive inputs. A balance between both excitatory and inhibitory influences control nociceptive transmission and impairment in this balance leads to the development of pathological pain. In the present study, we used an optogenetic approach to specifically target serotoninergic neurons (5-HT) that projected to the dorsal horn of the spinal cord. We showed that these neurons exerted a tonic analgesic action through a decreased excitability of projection neurons of the dorsal horn of the spinal cord. This effect is gender independent. We also observed that 5-HT neurons are indirectly connected to projection neurons through local inhibitory interneurons. Then, we showed that 5-HT neurons of the RMg received descending inputs from the SST neurons of the ventro-lateral part of the periaqueductal gray (vlPAG) that exerted downward facilitation on pain transmission. Interestingly, we show that 5-HT inhibitory action is switched to an excitatory influence in a model of peripheral neuropathy due to a spinal chloride equilibrium shift. These results suggest that the same descending pathway can be both excitatory and inhibitory upon pathological conditions, providing crucial insights about long-term changes associated with chronic pain

Windup of Nociceptive Flexion Reflex Depends on Synaptic and Intrinsic Properties of Dorsal Horn Neurons in Adult Rats

Windup, a progressive increase in spinal response to repetitive stimulations of nociceptive peripheral fibers, is a useful model to study central sensitization to pain. Windup is expressed by neurons in both the dorsal and ventral horn of the spinal cord. In juvenile rats, it has been demonstrated both in vivo and in vitro that windup depends on calcium-dependent intrinsic properties and their modulation by synaptic components. However, the involvement of these two components in the adults remains controversial. In the present study, by means of electromyographic and extracellular recordings, we show that windup in adults, in vivo, depends on a synaptic balance between excitatory N-methyl-D-aspartate (NMDA) receptors and inhibitory glycinergic receptors. We also demonstrate the involvement of L-type calcium channels in both the dorsal and ventral horn of the spinal cord. These results indicate that windup in adults is similar to juvenile rats and that windup properties are the same regardless of the spinal network, i.e., sensory or motor

Neuropsychopharmacology

Behavioral phenotyping devices have been successfully used to build ethograms, but many aspects of behavior remain out of reach of available phenotyping systems. We now report on a novel device, which consists in an open-field platform resting on highly sensitive piezoelectric (electromechanical) pressure-sensors, with which we could detect the slightest movements (up to individual heart beats during rest) from freely moving rats and mice. The combination with video recordings and signal analysis based on time-frequency decomposition, clustering, and machine learning algorithms provided non-invasive access to previously overlooked behavioral components. The detection of shaking/shivering provided an original readout of fear, distinct from but complementary to behavioral freezing. Analyzing the dynamics of momentum in locomotion and grooming allowed to identify the signature of gait and neurodevelopmental pathological phenotypes. We believe that this device represents a significant progress and offers new opportunities for the awaited advance of behavioral phenotyping. © 2021, The Author(s), under exclusive licence to American College of Neuropsychopharmacology.Bordeaux Region Aquitaine Initiative for NeuroscienceInitiative d'excellence de l'Université de Bordeau

Detecting fine and elaborate movements with piezo sensors provides non-invasive access to overlooked behavioral components

International audienceBehavioral phenotyping devices have been successfully used to build ethograms, but many aspects of behavior remain out of reach of available phenotyping systems. We now report on a novel device, which consists in an open-field platform resting on highly sensitive piezoelectric (electromechanical) pressure-sensors, with which we could detect the slightest movements (up to individual heart beats during rest) from freely moving rats and mice. The combination with video recordings and signal analysis based on time-frequency decomposition, clustering, and machine learning algorithms provided non-invasive access to previously overlooked behavioral components. The detection of shaking/shivering provided an original readout of fear, distinct from but complementary to behavioral freezing. Analyzing the dynamics of momentum in locomotion and grooming allowed to identify the signature of gait and neurodevelopmental pathological phenotypes. We believe that this device represents a significant progress and offers new opportunities for the awaited advance of behavioral phenotyping

Switch of serotonergic descending inhibition into facilitation by a spinal chloride imbalance in neuropathic pain

International audienceDescending control from the brain to the spinal cord shapes our pain experience, ranging from powerful analgesia to extreme sensitivity. Increasing evidence from both preclinical and clinical studies points to an imbalance toward descending facilitation as a substrate of pathological pain, but the underlying mechanisms remain unknown. We used an optogenetic approach to manipulate serotonin (5-HT) neurons of the nucleus raphe magnus that project to the dorsal horn of the spinal cord. We found that 5-HT neurons exert an analgesic action in naïve mice that becomes proalgesic in an experimental model of neuropathic pain. We show that spinal KCC2 hypofunction turns this descending inhibitory control into paradoxical facilitation; KCC2 enhancers restored 5-HT–mediated descending inhibition and analgesia. Last, combining selective serotonin reuptake inhibitors (SSRIs) with a KCC2 enhancer yields effective analgesia against nerve injury–induced pain hypersensitivity. This uncovers a previously unidentified therapeutic path for SSRIs against neuropathic pain

Determination of reverse transcriptase inhibitor resistance mutations in HIV-1 infected children in Côte d’Ivoire

Treatment scale-up is leading to a progressive increase in HIV resistance to antiretrovirals, especially in children. To assess resistance to reverse transcriptase inhibitors (RTIs) in HIV-1 infected children in Côte d’Ivoire, genotypic resistance tests were performed and interpreted using the ANRS algorithm (www.hivfrenchresistance.org). Phylogenetic trees were created using BioEdit v7 and Mega7 software. The frequency of resistance to at least one RTI was 79%. It was 88% for nucleoside reverse transcriptase inhibitors (NRTIs), 71% for non-nucleoside reverse transcriptase inhibitors (NNRTIs), and 63% for both classes (NRTI + NNRTI). The frequency of resistance was 50% for the ZDV + 3TC + EFV combination, 42% for the ABC + 3TC + EFV combination, and 8% for the TDF + 3TC + EFV combination. Frequently encountered resistance mutations were for NRTIs: M184V (88%), TAMs (67%), T215F/I/V/Y (33%), and L74I/V (24%); for NNRTIs: K103N/S (74%), P225H (26%), and G190A/E/Q (24%). The synthesis of phylogenetic analyses showed the predominance of the viral subtype CRF02_AG (85%). These results show a high prevalence of resistance to RTIs in children infected with HIV-1. Hence the interest of a more accessible monitoring of viral load and genotypic resistance tests in HIV-1 infected children undergoing treatment in Côte d’Ivoire.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author