Impact of perinatal stress in rodents : behavioral assessment and mechanisms of action

Les enfants ayant subi des perturbations périnatales, telles qu’un stress prénatal ou une naissance prématurée, sont exposés in utero et/ou lors de la période néonatale à un environnement sensoriel particulièrement agressif. Celui-ci peut affecter le développement cérébral de l’enfant et sa santé à long terme. Ce travail de thèse vise à comprendre l’effet de perturbations périnatales sur les différentes composantes de la douleur (sensori-discriminative, émotionnelle, comportementale et cognitive), et de déterminer les mécanismes moléculaires responsables des altérations constatées au niveau phénotypique. En particulier, nous avons pu démontrer un dysfonctionnement majeur et durable de la signalisation ocytocinergique suite à un stress périnatal, associé à des troubles de la régulation de l’homéostasie chlorure, altérant l’intégrité fonctionnelle des contrôles inhibiteurs. Ce travail a ainsi permis d’identifier l’ocytocine comme un acteur clé de l’apparition de divers troubles comportementaux associés à une douleur comme l’anxiété chronique ou les troubles des interactions sociales.Early life adverse events such as prenatal stress or prematurity are known to affect brain development and its function at a later age. In particular, in utero and/or neonatal exposition to a stressful environment increases the risk to develop chronic pain and associated behavioral comorbidities accross the lifespan. The goal of this PhD thesis was to better understand the consequences of early life stress on the different components of pain (sensory-discriminative, emotional, behavioral and cognitive), and to decipher the molecular mecanisms underlying the observed behavioral alterations. Notably, we demonstrated a long-lasting impairment of oxytocinergic signaling following early life stress, associated with chloride homeostasis dysregulation, suggesting alterations in the functional integrity of inhibitory controls. This work led to the identification of oxytocin as a critical determinant in the emergence of the abnormal sensoriality and emotionality following early life stress

Overexpression of chloride importer NKCC1 contributes to the sensory-affective and sociability phenotype of rats following neonatal maternal separation

International audienceBackground: Early life stress is known to affect the development of the nervous system and its function at a later age. It increases the risk to develop psychiatric disorders as well as chronic pain and its associated affective comorbidities across the lifespan. GABAergic inhibition is important for the regulation of central function and related behaviors, including nociception, anxiety or social interactions, and requires low intracellular chloride levels. Of particular interest, the oxytocinergic (OTergic) system exerts potent anxiolytic, analgesic and pro-social properties and is known to be involved in the regulation of chloride homeostasis and to be impaired following early life stress.Methods: We used behavioral measures to evaluate anxiety, social interactions and pain responses in a rat model of neonatal maternal separation (NMS). Using quantitative PCR, we investigated whether NMS was associated with alterations in the expression of chloride transporters in the cerebrum and spinal cord. Finally, we evaluated the contribution of OTergic signaling and neuro-inflammatory processes in the observed phenotype.Results: NMS animals displayed a long-lasting upregulation of chloride importer Na-K-Cl cotransporter type 1 (NKCC1) expression in the cerebrum and spinal cord. Neonatal administration of the NKCC1 inhibitor bumetanide or oxytocin successfully normalized the anxiety-like symptoms and the lack of social preference observed in NMS animals. Phenotypic alterations were associated with a pro-inflammatory state which could contribute to NKCC1 upregulation.Conclusions: This work suggests that an impaired chloride homeostasis, linked to oxytocin signaling dysfunction and to neuro-inflammatory processes, could contribute to the sensori-affective phenotype following NMS

Long-lasting analgesic and neuroprotective action of the non-benzodiazepine anxiolytic etifoxine in a mouse model of neuropathic pain.

International audienceNeuropathic pain is frequently associated with anxiety and major depressive disorders, which considerably impact the overall patient experience. Favoring GABAergic inhibition through the pain matrix has emerged as a promising strategy to restore proper processing of nociceptive and affective information in neuropathic pain states. In this context, the non-benzodiazepine anxiolytic etifoxine (EFX), known to amplify GABAergic inhibition through positive modulation of GABAA receptors and neurosteroidogenesis, presents several advantages. Therefore, we sought to investigate the preclinical therapeutic potential of EFX on the somatosensory and affective components of neuropathic pain. Here, we used a murine model in which neuropathic pain was induced by the implantation of a compressive cuff around the sciatic nerve (mononeuropathy). We showed that the intraperitoneal EFX treatment for five consecutive days (50 mg/kg) relieved mechanical allodynia in a sustained manner. Besides its effect on evoked mechanical hypersensitivity, EFX also alleviated aversiveness of ongoing pain as well as anxiodepressive-like consequences of neuropathic pain following cuff-induced mononeuropathy. This effect was also seen 12 weeks after induction of the neuropathy when allodynia was no longer present. Analgesic and neuroprotective actions of EFX were also seen by the absence of neuropathic pain symptoms if a second sciatic nerve constriction injury was applied to the contralateral hindpaw. Mass spectrometry analysis revealed a normalization of brainstem serotonin levels in EFX-treated animals and an increase in norepinephrine. This study suggests that EFX presents promising therapeutic potential for the relief of both somatosensory and affective consequences of neuropathic pain, a beneficial effect that is likely to involve monoamine descending controls

Cholecalciferol (Vitamin D3) Reduces Rat Neuropathic Pain by Modulating Opioid Signaling

International audienceThe impact of vitamin D on sensory function, including pain processing, has been receiving increasing attention. Indeed, vitamin D deficiency is associated with various chronic pain conditions, and several lines of evidence indicate that vitamin D supplementation may trigger pain relief. However, the underlying mechanisms of action remain poorly understood. We used inflammatory and non-inflammatory rat models of chronic pain to evaluate the benefits of vitamin D3 (cholecalciferol) on pain symptoms. We found that cholecalciferol supplementation improved mechanical nociceptive thresholds in monoarthritic animals and reduced mechanical hyperalgesia and cold allodynia in a model of mononeuropathy. Transcriptomic analysis of cerebrum, dorsal root ganglia and spinal cord tissues indicate that cholecalciferol supplementation induces a massive gene dysregulation which, in the cerebrum, is associated with opioid signaling (23 genes), nociception (14), and allodynia (8), and, in the dorsal root ganglia, with axonal guidance (37 genes), and nociception (17). Among the identified cerebral dysregulated nociception-, allodynia-and opioid-associated genes, 21 can be associated with vitamin D metabolism. However, it appears that their expression is modulated by intermediate regulators such as diverse protein kinases and not, as expected, by the vitamin D receptor. Overall, several genes-Oxt, Pdyn, Penk, Pomc, Pth, Tac1, Tgfb1-encoding for peptides/hormones stand out as top candidates to explain the therapeutic benefit of vitamin D3 supplementation. Further studies are now warranted to detail the precise mechanisms of action but also the most favourable doses and time windows for pain relief

Pharmacological rescue of nociceptive hypersensitivity and oxytocin analgesia impairment in a rat model of neonatal maternal separation

International audienc

Identification of bacterial lipopeptides as key players in IBS

International audienceObjectives Clinical studies revealed that early-life adverse events contribute to the development of IBS in adulthood. The aim of our study was to investigate the relationship between prenatal stress (PS), gut microbiota and visceral hypersensitivity with a focus on bacterial lipopeptides containing γ-aminobutyric acid (GABA). Design We developed a model of PS in mice and evaluated, in adult offspring, visceral hypersensitivity to colorectal distension (CRD), colon inflammation, barrier function and gut microbiota taxonomy. We quantified the production of lipopeptides containing GABA by mass spectrometry in a specific strain of bacteria decreased in PS, in PS mouse colons, and in faeces of patients with IBS and healthy volunteers (HVs). Finally, we assessed their effect on PS-induced visceral hypersensitivity. Results Prenatally stressed mice of both sexes presented visceral hypersensitivity, no overt colon inflammation or barrier dysfunction but a gut microbiota dysbiosis. The dysbiosis was distinguished by a decreased abundance of Ligilactobacillus murinus , in both sexes, inversely correlated with visceral hypersensitivity to CRD in mice. An isolate from this bacterial species produced several lipopeptides containing GABA including C14AsnGABA. Interestingly, intracolonic treatment with C14AsnGABA decreased the visceral sensitivity of PS mice to CRD. The concentration of C16LeuGABA, a lipopeptide which inhibited sensory neurons activation, was decreased in faeces of patients with IBS compared with HVs. Conclusion PS impacts the gut microbiota composition and metabolic function in adulthood. The reduced capacity of the gut microbiota to produce GABA lipopeptides could be one of the mechanisms linking PS and visceral hypersensitivity in adulthood