Fast non-genomic effects of progesterone-derived neurosteroids on nociceptive thresholds and pain symptoms

Abstract Fast Inhibitory controls mediated by glycine (GlyRs) and GABAA receptors (GABAARs) play an important role to prevent the apparition of pathological pain symptoms of allodynia and hyperalgesia. The use of positive allosteric modulators of these receptors, specifically expressed in the spinal cord, may represent an interesting strategy to limit or block pain expression. In this study, we have used stereoisomers of progesterone metabolites, acting only via non-genomic effects, in order to evaluate the contribution of GlyRs and GABAARs for the reduction of mechanical and thermal heat hypernociception. We show that 3a neurosteroids were particularly efficient to elevate nociceptive thresholds in naive animal. It also reduced mechanical allodynia and thermal heat hyperalgesia in the carrageenan model of inflammatory pain. This effect is likely to be mediated by GABAA receptors since 3b isomer was inefficient. More interestingly, 3a5b neurosteroid was only efficient on mechanical allodynia while having no effect on thermal heat hyperalgesia. We characterized these paradoxical effects of 3a5b neurosteroid using the strychnine and bicuculline models of allodynia. We clearly show that 3a5b neurosteroid exerts an antinociceptive effect via a positive allosteric modulation of GABAARs but, at the same time, is pronociceptive by reducing GlyR function. This illustrates the importance of the inhibitory amino acid receptor channels and their allosteric modulators in spinal pain processing. Moreover, our results indicate that neurosteroids, which are synthesized in the dorsal horn of the spinal cord and have limited side effects, may be of significant interest in order to treat pathological pain symptoms.

Antinociceptive action of oxytocin involves inhibition of potassium channel currents in lamina II neurons of the rat spinal cord

<p>Abstract</p> <p>Background</p> <p>Growing evidence in the literature shows that oxytocin (OT) has a strong spinal anti-nociceptive action. Oxytocinergic axons originating from a subpopulation of paraventricular hypothalamic neurons establish synaptic contacts with lamina II interneurons but little is known about the functional role of OT with respect to neuronal firing and excitability.</p> <p>Results</p> <p>Using the patch-clamp technique, we have recorded lamina II interneurons in acute transverse lumbar spinal cord slices of rats (15 to 30 days old) and analyzed the OT effects on action potential firing ability. In the current clamp mode, we found that bath application of a selective OT-receptor agonist (TGOT) reduced firing in the majority of lamina II interneurons exhibiting a bursting firing profile, but never in those exhibiting a single spike discharge upon depolarization. Interestingly, OT-induced reduction in spike frequency and increase of firing threshold were often observed, leading to a conversion of the firing profile from repetitive and delayed profiles into phasic ones and sometimes further into single spike profile. The observed effects following OT-receptor activation were completely abolished when the OT-receptor agonist was co-applied with a selective OT-receptor antagonist. In current and voltage clamp modes, we show that these changes in firing are strongly controlled by voltage-gated potassium currents. More precisely, transient I_Acurrents and delayed-rectifier currents were reduced in amplitude and transient I_Acurrent was predominantly inactivated after OT bath application.</p> <p>Conclusion</p> <p>This effect of OT on the firing profile of lamina II neurons is in good agreement with the antinociceptive and analgesic properties of OT described <it>in vivo</it>.</p

Long-lasting spinal oxytocin analgesia is ensured by the stimulation of allopregnanolone synthesis which potentiates GABA(A) receptor-mediated synaptic inhibition.

Hypothalamospinal control of spinal pain processing by oxytocin (OT) has received a lot of attention in recent years because of its potency to reduce pain symptoms in inflammatory and neuropathic conditions. However, cellular and molecular mechanisms underlying OT spinal antinociception are still poorly understood. In this study, we used biochemical, electrophysiological, and behavioral approaches to demonstrate that OT levels are elevated in the spinal cord of rats exhibiting pain symptoms, 24 h after the induction of inflammation with an intraplantar injection of λ-carrageenan. Using a selective OT receptor antagonist, we demonstrate that this elevated OT content is responsible for a tonic analgesia exerted on both mechanical and thermal modalities. This phenomenon appeared to be mediated by an OT receptor-mediated stimulation of neurosteroidogenesis, which leads to an increase in GABA(A) receptor-mediated synaptic inhibition in lamina II spinal cord neurons. We also provide evidence that this novel mechanism of OT-mediated spinal antinociception may be controlled by extracellular signal-related protein kinases, ERK1/2, after OT receptor activation. The oxytocinergic inhibitory control of spinal pain processing is emerging as an interesting target for future therapies since it recruits several molecular mechanisms, which are likely to exert a long-lasting analgesia through nongenomic and possibly genomic effects.journal articleresearch support, non-u.s. gov't2013 Oct 16importe

Abnormal nociception and opiate sensitivity of STOP null mice exhibiting elevated levels of the endogenous alkaloid morphine

<p>Abstract</p> <p>Background-</p> <p>Mice deficient for the stable tubule only peptide (STOP) display altered dopaminergic neurotransmission associated with severe behavioural defects including disorganized locomotor activity. Endogenous morphine, which is present in nervous tissues and synthesized from dopamine, may contribute to these behavioral alterations since it is thought to play a role in normal and pathological neurotransmission.</p> <p>Results-</p> <p>In this study, we showed that STOP null brain structures, including cortex, hippocampus, cerebellum and spinal cord, contain high endogenous morphine amounts. The presence of elevated levels of morphine was associated with the presence of a higher density of mu opioid receptor with a higher affinity for morphine in STOP null brains. Interestingly, STOP null mice exhibited significantly lower nociceptive thresholds to thermal and mechanical stimulations. They also had abnormal behavioural responses to the administration of exogenous morphine and naloxone. Low dose of morphine (1 mg/kg, i.p.) produced a significant mechanical antinociception in STOP null mice whereas it has no effect on wild-type mice. High concentration of naloxone (1 mg/kg) was pronociceptive for both mice strain, a lower concentration (0.1 mg/kg) was found to increase the mean mechanical nociceptive threshold only in the case of STOP null mice.</p> <p>Conclusions-</p> <p>Together, our data show that STOP null mice displayed elevated levels of endogenous morphine, as well as an increase of morphine receptor affinity and density in brain. This was correlated with hypernociception and impaired pharmacological sensitivity to mu opioid receptor ligands.</p

Pain, Parental Involvement, and Oxytocin in the Neonatal Intensive Care Unit

Preterm infants (PTI) typically experience many painful and stressful procedures or events during their first weeks of life in a neonatal intensive care unit, and these can profoundly impact subsequent brain development and function. Several protective interventions during this sensitive period stimulate the oxytocin system, reduce pain and stress, and improve brain development. This review provides an overview of the environmental risk factors experienced by PTI during hospitalization, with a focus on the effects of pain, and early maternal separation. We also describe the long-term adverse effects of the simultaneous experiences of pain and maternal separation, and the potential beneficial effects of maternal vocalizations, parental contact, and several related processes, which appear to be mediated by the oxytocin system

Pain, Parental Involvement, and Oxytocin in the Neonatal Intensive Care Unit

Preterm infants (PTI) typically experience many painful and stressful procedures or events during their first weeks of life in a neonatal intensive care unit, and these can profoundly impact subsequent brain development and function. Several protective interventions during this sensitive period stimulate the oxytocin system, reduce pain and stress, and improve brain development. This review provides an overview of the environmental risk factors experienced by PTI during hospitalization, with a focus on the effects of pain, and early maternal separation. We also describe the long-term adverse effects of the simultaneous experiences of pain and maternal separation, and the potential beneficial effects of maternal vocalizations, parental contact, and several related processes, which appear to be mediated by the oxytocin system

PONE_Etifoxine and type1 diabete

Data used to generate the article in Plos One 202

Etude préclinique du potentiel thérapeutique des stéroïdes neuroactifs endogènes dans les douleurs pathologiques

Les neurostéroïdes sont des stéroïdes synthétisés par les neurones et les cellules gliales dans le système nerveux à partir du cholestérol. Les neurostéroïdes, en particulier ceux réduits en position 3a comme l allopregnanolone peuvent réduire les symptômes douloureux s ils sont administrés de manière exogène. Dans le laboratoire, nous avons montré que leur effet antinociceptif pourrait passer, entre autre, par la potentialisation de l inhibition médiée par le récepteur GABAA dans la moelle épinière. Au cours de ce travail de thèse, j ai employé une stratégie visant à stimuler la neurostéroïdogénèse endogène. Pour cela, j ai utilisé l étifoxine (Stresam ), un anxiolytique non benzodiazépinique capable de stimuler la synthèse de neurostéroïdes en se liant à une protéine mitochondriale (appelée TSPO pour translocator protein ) favorisant la translocation du cholestérol.Dans un premier temps j ai caractérisé l effet analgésique de cette molécule dans plusieurs modèles de douleurs chroniques. Sur des animaux présentant des douleurs neuropathiques suite à une chimiothérapie ou à une compression du nerf sciatique, un traitement à l étifoxine réduit significativement les symptômes douloureux ou empêche complètement leur apparition, s il est administré avant l induction de la douleur. Un traitement curatif à l étifoxine réduit aussi les symptômes douloureux causés par une monoarthrite (inflammatoire du genou). Nous avons aussi montré que l effet observé était effectivement dû à la stimulation de la synthèse endogène de neurostéroïdes 3a-réduits et ceci, même en absence de source hormonale périphérique (gonadectomie, surrénalectomie).Dans une deuxième partie du travail, j ai mis en évidence de nouveaux mécanismes d action de l étifoxine capables d expliquer les effets analgésiques obtenus. Tout d abord, la réponse inflammatoire spinale qui s exprime par une augmentation de la production de cytokines pro-inflammatoires et l activation des microglies est réduite après le traitement. Cette action est corrélée avec une optimisation de l inhibition spinale portée par au moins trois mécanismes : la récupération d une désinhibition spinale glycinergique induite par la production locale de PGE2, potentialisation de l inhibition GABAergique et le rétablissement de l expression de l exporteur KCC2. Ce dernier mécanisme, comme les autres, rend parfaitement compte du rétablissement d une nociception spinale comparable aux animaux contrôle des animaux traités par l étifoxine.Dans la troisième partie de mon travail je me suis intéressée au mode d action de la vitamine D3 dont la structure est proche de celle des neurostéroïdes neuroactifs. Une supplémentation en vitamine D3 sous forme d aliments enrichis ou par administration orale réduits significativement les symptômes douloureux chez des rats monoarthritiques ou ayant une neuropathie induite par compression chronique du nerf sciatique. Les cibles moléculaires sont actuellement à l étude avec en particulier l action stimulatrice de la vitamine sur l hypothalamus et les contrôles inhibiteurs descendants impliquant l ocytocine et la pro-opiomélanocortine.En résumé, les travaux réalisés durant cette thèse ont permis de mettre en évidence le potentiel thérapeutique des neurostéroïdes endogènes dans le traitement des douleurs neuropathiques et inflammatoires chez l animal. L étifoxine et la vitamine D3 sont déjà prescrites en tant que médicaments en France et présentent des effets secondaires très minimes. Les nouvelles pistes thérapeutiques et les mécanismes d action décrits dans ce travail préclinique pourraient conduire rapidement à la mise en place d essais cliniques chez l homme, voire à une modification de la prise en charge des douleurs chroniquesNeurosteroids are synthesized by neurons and glial cells in the nervous system from cholesterol or by intermediate metabolites having crossed the blood brain barrier. 3a reduced neurosteroids (3aNS), such as allopregnanolone, display interesting analgesic properties, if administered exogenously. However, their use is limited by known side effects related to functional tolerance, sedation and possible physical dependence after cessation of the treatment. In the laboratory, we have adopted a strategy aimed at stimulating the production of 3aNS. To do so, we used etifoxine (Stresam ), a non-benzodiazepine anxiolytic which preferentially binds to a mitochondrial translocator protein (TSPO) and stimulates cholesterol metabolization into 3aNS.In the first part of this work, we characterized the analgesic effect of this molecule in several models of chronic pain. In animals exhibiting neuropathic pain symptoms resulting from a chemotherapy or a chronic nerve compression, etifoxine treatment significantly reduced the pain symptoms. When administered before the induction of pain, it completely prevented the appearance of the pain symptoms. Etifoxine also reduced inflammatory-driven pain symptoms caused by a knee monoarthritis. These analgesic effects were all attributed to the endogenous synthesis of 3aNS and persisted even in the absence of gonads and surrenals.In the second part of the work, we identified novel mechanisms of action explaining etifoxine analgesia. First, the overall spinal inflammatory response was reduced after the etifoxine treatment as attested by reduced expression of proinflammatory cytokines, COX2 and PGE2 levels. Moreover, activation of microglial cells seen in painful animals was not detected in etifoxine-treated animals. As a result, spinal inhibition was optimized by etifoxine treatment through a recovery from PGE2 induced glycinergic disinhibition, potentiation of GABAergic transmission and a possible re-establishment of normal chloride gradients controlled by the exporter KCC2. Together, spinal nociceptive processing of painful animals treated by etifoxine was not different to that seen in control (pain free) animals.In the last part of this work, we characterized the analgesic effects of vitamin D3, a secosteroid showing structural similarities to neurosteroids, in neuropathic and inflammatory pain models. Supplementation with vitamin D3 strongly reduced pain symptoms in rats suffering from knee monoarthritis or sciatic neuropathy. Molecular and cellular signaling explaining the beneficial effects of vitamin D3 are currently under investigation. In summary, this work helps highlight the therapeutic potential of endogenous neurosteroids in the treatment of inflammatory and neuropathic pain in animals. The etifoxine and vitamin D3 are already prescribed in France and have very little side effects. The new therapeutical approaches and the mechanisms of action described in this preclinical work could quickly lead to the development of clinical trials in humans or alternatively, help clinicians improve the current therapies.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Plasticité de la transmission synaptique inhibitrice dans le système nociceptif spinal de la souris

L'inhibition synaptique joue un rôle important dans la régulation de l'excitabilité des neurones. Dans la lamina II de la moelle épinière, l'équilibre entre les composantes excitatrices et inhibitrices va influencer le passage des informations nociceptives périphériques vers les structures supramédullaires. Dans mon travail de thèse, je me suis intéressé à la plasticité de la transmission synaptique dans la lamina II de souris. En utilisant la technique de patch clamp sur tranches aigues, j'ai dans un premier temps caractérisé la transmission synaptique inhibitrice puis mis en évidence une plasticité au cours du développement post-natal ainsi que suite à l'invalidation génétique d'une sous unité du récepteur de la glycine. Enfin, j'ai étudié la modulation positive à court et à long terme de la transmission synaptique inhibitrice par le contrôle descendant oxytocinergique responsable d'une diminution de l'hyperalgésie thermique et mécanique dans un modèle de douleur inflammatoire.The synaptic inhibition is important in the control of neurons excitability. In the spinal lamina II, the balance between inhibitory and excitatory components regulates the transmission of the peripheral nociceptive inputs to supraspinal structures. During my PhD, I worked on the plasticity of inhibitory synaptic transmission in lamina II of mouse. Using the patch-clamp technique on acute slices, I first characterized the inhibitory synaptic transmission and then its plasticity throughout the postnatal development as in a transgenic model where a subunit of the glycine receptor is knocked-out. At last, I studied the short and long lasting positive modulation of inhibitory synaptic transmission by the oxytocinergic descending pathway that produces an impairment of thermal and mechanical hyperalgesia in an inflammatory model of pain.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF