Evaluation des effets de l'inflammation combinée à une exposition chronique et combinée à des agents toxiques issus de l'environnement pendant la période périnatale : un potentiel facteur étiologique des pathologies dégénératives ?

Chronic exposure to environmental toxic agents, such as heavy metals, pesticides or cyanotoxins, is increasingly reported to be a sporadic factor in motor neuron degenerative diseases (MNDs). However, little is known about the roles of these toxins in the etiology of MNDs following early exposure (e.g., during pre- and post-natal developmental periods). These developmental stages are known to be critical periods of brain development during which highly regulated process disturbances can negatively affect the fundamental structure of the brain. Such changes can lead to the development of selective vulnerabilities to neurodegeneration and ultimately be responsible for late-onset neurodegenerative diseases such as MNDs s. Given the increasing amount of epidemiological, clinical and experimental evidence reinforcing the link between exposure to environmental toxic substances and the late onset of MNDs, it is essential to implement experimental studies closer to actual exposure conditions. For example, early exposure to cocktails of substances that are toxic to the environment, at low doses, may induce or predispose individuals to MNDs later in life. This thesis project focused on a behavioural study in mice following a perinatal exposure to a mixture of various environmental toxic substances at low doses (Glufosinate ammonium (GLA), β-N-methylamino-L-alanine (BMAA) and Glyphosate (GLY)), to see if they can act synergistically and precipitate the appearance of symptoms of MNDs later in life. We also checked whether the mixture induces more damage than each compound individually. Based on this hypothesis and in line with “exposome” notion, it was also assessed the importance of an asymptomatic inflammatory sensitization during pregnancy in combination with post-natal exposure to pollutants of interest. Our data revealed that a maternal exposure to this cocktail induces disturbances in motor and anxiety behaviours in offspring, from adolescence to aging. Interestingly, these impairments have not been observed when individuals were exposed to each compound separately. In addition, we were able to show that an exposure to a single risk factor such as prenatal immune sensitization to low dose of LPS is not sufficient to induce early and long lasting behavioural changes in offspring's. However, we demonstrated that this asymptomatic inflammatory sensitization associated to subsequent low doses xenobiotic exposure, act in synergy to affect behaviour in offspring's. Thus, these complementary studies have led to the demonstration of the importance of considering multi-exposure in the characterization of molecules with a neurotoxic potential in the short, medium and long term.L'exposition chronique à des agents toxiques issus de l'environnement, tels que les métaux lourds, les pesticides ou les cyanotoxines, est de plus en plus rapportée comme étant un potentiel facteur sporadique des maladies dégénératives des motoneurones (MDMs). Cependant, peu de choses sont connues quant aux rôles de ces toxines dans l'étiologie des MDMs suite à une exposition précoce (ex : durant les périodes pré et post-natales du développement). Ces stades développementaux sont connus pour être des périodes critiques du développement cérébral durant lesquels des perturbations de processus fortement régulés peuvent avoir un impact négatif sur la structure fondamentale du cerveau. De telles modifications peuvent conduire au développement de vulnérabilités sélectives à la neurodégénérescence et être finalement responsables de maladies neurodégénératives à déclenchement tardif telles que les MDMs. Compte tenu du nombre croissant de preuves épidémiologiques, cliniques et expérimentales renforçant le lien entre l'exposition à des substances toxiques de l'environnement et l'apparition tardive des MDMs, il est primordial de mettre en œuvre des études expérimentales plus en adéquation avec la réalité. Par exemple, il s'agit d'étudier l'exposition précoce à des cocktails de substances toxiques pour l'environnement, à de faibles doses, pouvant induire ou prédisposer des individus aux MDMs plus tard dans la vie. Ce projet de thèse s'est focalisé sur l'étude comportementale chez la souris suite à une exposition périnatale à un mélange de différentes substances toxiques pour l'environnement à faibles doses (Glufosinate d'Ammonium (GLA), β -N-méthylamino-L-alanine (BMAA) et Glyphosate (GLY)), afin de vérifier si ces derniers peuvent agir en synergie et précipiter l'apparition des symptômes des MDMs plus tard dans la vie. Nous avons également vérifié si le mélange induit plus de dommages que chaque composé pris individuellement. Dans le cadre d'une hypothèse en adéquation avec la notion d'exposome, il a également été évaluer l'importance et l'impact d'une sensibilisation inflammatoire asymptomatique pendant la gestation a été évaluer en association à une exposition post natale aux polluants d'intérêts. Nos données révèlent qu'une exposition maternelle à au cocktail induit des perturbations des comportements moteur et anxieux chez la descendance, depuis l'adolescence ce maintenant au cours du vieillissement, ce qui n'est pas le cas lors d'une exposition aux composé pris individuellement. De plus, nous avons pu montrer que l'exposition à un seul facteur de risque (sensibilisation maternelle à de faible dose de LPS) n'était pas suffisante pour induire des modifications précoces, perdurant au cours du vieillissement, du comportement chez la descendance. Cependant, une sensibilisation inflammatoire asymptomatique associé à l'exposition ultérieur à de faibles doses de xénobiotiques, induit des effets synergiques sur le comportement des petits. Ainsi, l'ensemble de ce travail a conduit à la démonstration de l'importance de considérer la multi exposition dans la caractérisation de molécules au potentiel neurotoxique à court, moyen et long terme

Dopamine synthesis during neuroinflammation: A focus on tetrahydrobiopterin

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3Rs-based optimization of mice behavioral testing: The habituation/dishabituation olfactory test

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Decrease in Operant Responding Under Obesogenic Diet Exposure is not Related to Deficits in Incentive or Hedonic Processes

OBJECTIVE: A growing body of evidence suggests that obesity could result from alterations in reward processing. In rodent models, chronic exposure to an obesogenic diet leads to blunted dopamine signaling and related incentive responding. This study aimed to determine which reward-related behavioral dimensions are actually impacted by obesogenic diet exposure. METHODS: Mice were chronically exposed to an obesogenic diet. Incentive and hedonic processes were tested through operant conditioning and licking microstructures, respectively. In parallel, mesolimbic dopamine transmission was assessed using microdialysis. RESULTS: Prolonged high-fat (HF) diet exposure led to blunted mesolimbic dopamine release, paralleled by a decrease in operant responding in all schedules tested. HF-fed and control animals similarly decreased their operant responding in an effort-based choice task, and HF-fed animals displayed an overall lower calorie intake in this task. Analysis of the licking microstructures during consumption of a freely accessible reward suggested a decrease in basal hunger and a potentiation of gastrointestinal inhibition in HF-fed animals, without changes in hedonic reactivity. CONCLUSIONS: These results suggest that the decrease in operant responding under prolonged HF diet exposure is mainly driven by decrease in hunger as well as stronger postingestive negative feedback mechanisms, rather than by a decrease in incentive or hedonic responses

Respective roles of the distinct populations of Medium Spiny Neurons of the Nucleus Accumbens in reward processing

National audienceThe nucleus accumbens (NAc) is a major structure that plays a key role in action selection and execution as well as reward processing and reward-dependent learning. It is largely composed of GABAergic Medium Spiny Neurons (MSN) that are divided into two distinct subpopulations, those expressing the dopamine D1 receptor (D1R; dMSNs), and those expressing the D2 receptor (D2R; iMSNs). Based on the model of the dorsal striatum, it has been proposed that dMSNs and iMSNs of the NAc play antagonistic effects on reward processing, but their respective roles are still largely debated (Carvalho Poyraz et al. 2016; Soares-Cunha et al. 2016). Herein, we aimed at deeper exploring the implication of these two populations of MSNs of the NAc core on various components of reward processing. Using operant conditioning tasks and pharmacogenetic approaches we show that activation of iMSNs decreases motivation to obtain a food reward but increases food consumption, while inhibition had the opposite effect, with no impact on hedonic reactivity. Interestingly, in vivo electrophysiology experiments in anesthetized animals revealed that the increased iMSN excitability boosts the activity of dopaminergic VTA neurons. Surprisingly, we observed that both inhibition and activation of dMSNs led to a decrease in performance in motivational tasks, likely related to a strong modulation of consummatory processes. Our data shed light on the complex function of dMSNs and iMSNs of the NAc core in reward processing and highlight differential effects on consummatory vs. motivational processes

Vulnerability of the nucleus accumbens neuronal network to developmental n-3 PUFA deficiency: consequences on the reward and motivation system

PosterVarious, though distinct psychiatric disorders, such as Schizophrenia, bipolar disorder or major depression are associated with a dysfunction of the reward system linked to an alteration of dopamine transmission. Furthermore, these pathologies are also accompanied by changes in lipid metabolism and in particular a decrease in the brain content n-3 polyunsaturated fatty acid (PUFA) in the nervous system. However, the implication of brain lipid composition in the etiology of psychiatric endophenotypes has been overlooked. The aim of this study was to investigate a potential causal link between n-3 PUFA deficiency and deficits in reward processing. Using operant conditioning tasks in mice, we showed that developmental n-3 PUFA deficiency leads to a selective motivational deficit at adulthood that is reversed by n-3 PUFA supplementation starting at birth. In parallel, we showed that n-3 PUFA deficiency leads to alterations in electrophysiological properties of medium spiny neurons (MSNs) in the nucleus accumbens, main actors for motivational processes. MSNs from the direct pathway (dMSNs) displayed a decrease in excitability paralleled with an increase of inhibitory input onto these neurons. Using pharmacogenetic and transgenic approaches, we showed that 1) alterations in dMSNs directly results from increased inhibitory input from MSNs of the indirect pathway (iMSNs), called lateral inhibition and 2) rescuing appropriate PUFA levels in D2R-expressing neurons selectively (including iMSNs), was sufficient to reverse both alterations in electrophysiological properties of dMSNs and motivational deficit observed in n-3 PUFA deficient mice

Perinatal Exposure to the Cyanotoxin β-N-Méthylamino-l-Alanine (BMAA) Results in Long-Lasting Behavioral Changes in Offspring—Potential Involvement of DNA Damage and Oxidative Stress

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Vulnerability of the nucleus accumbens neuronal network to developmental n-3 PUFA deficiency: consequences on the reward and motivation system

National audienceVarious, though distinct psychiatric disorders, such as Schizophrenia, bipolar disorder or major depression are associated with a dysfunction of the reward system linked to an alteration of dopamine transmission. Furthermore, these pathologies are also accompanied by changes in lipid metabolism and in particular a decrease in the brain content n-3 polyunsaturated fatty acid (PUFA) in the nervous system. However, the implication of brain lipid composition in the etiology of psychiatric endophenotypes has been overlooked. The aim of this study was to investigate a potential causal link between n-3 PUFA deficiency and deficits in reward processing. Using operant conditioning tasks in mice, we showed that developmental n-3 PUFA deficiency leads to a selective motivational deficit at adulthood that is reversed by n-3 PUFA supplementation starting at birth. In parallel, we showed that n-3 PUFA deficiency leads to alterations in electrophysiological properties of medium spiny neurons (MSNs) in the nucleus accumbens, main actors for motivational processes. MSNs from the direct pathway (dMSNs) displayed a decrease in excitability paralleled with an increase of inhibitory input onto these neurons. Using pharmacogenetic and transgenic approaches, we showed that 1) alterations in dMSNs directly results from increased inhibitory input from MSNs of the indirect pathway (iMSNs), called lateral inhibition and 2) rescuing appropriate PUFA levels in D2R-expressing neurons selectively (including iMSNs), was sufficient to reverse both alterations in electrophysiological properties of dMSNs and motivational deficit observed in n-3 PUFA deficient mice

Exploring the effects of tetrahydrobiopterin on motivation, dopamine release and acute inflammation in mice

Inflammation can affect mesodopaminergic system and mediates depressive symptoms related to motivation and locomotion. Precisely, pro-inflammatory cytokines can alter dopamine synthesis and thus availability. Tetrahydrobiopterin (BH4) is the mandatory co-factor for phenylalanine and tyrosine hydroxylase activities and therefore essential for dopamine synthesis. Interestingly, inflammation can decrease BH4 by acting on its synthesis and degradation. So, lower BH4 level could participate to the dopaminergic and motivational deficits that occur frequently in chronic inflammatory conditions. Despite its importance, the effects of BH4 administration on dopamine synthesis and related behaviors have been poorly characterized. We hypothesized that BH4 administration can improve dopaminergic function and motivational processes and could be used to counteract inflammation-induced alterations. We first demonstrated that peripheral administration of BH4 (50mg/kg;intraperitoneally) was sufficient to double BH4 brain content within 3h. Using in-situ brain perfusion, we found that the brain uptake clearance (Clup) of BH4 was approximately 0.08μl/g/sec, consistent with a modest transfer across the blood brain barrier. BH4 injection neither changed the expression of main enzymes involved in BH4 and DA synthesis nor total striatal dopamine content. However, using in vivo microdialysis in freely moving mice, we showed that BH4 administration induced a slight increase in dopamine release in the nucleus accumbens during food presentation and a higher amphetamine-induced DA release (3mg/kg). Furthermore, BH4 injection increased motivation in a progressive ratio task in operant conditioning without affecting sucrose consumption and anhedonia. Surprisingly, BH4 injection led to a moderate decrease in spontaneous locomotion and to a blunted locomotor sensitization after second exposure to amphetamine. Last, BH4 injection reduced brain pro-inflammatory cytokines expression in an acute inflammation model induced by lLipopolysaccharide injection (830μg/kg). Here, we showed that increased BH4 content leads to increased dopamine release and motivation, and reduces the proinflammatory response to an acute inflammatory challenge. This suggests that BH4 could be a promising treatment for behavioral deficits related to dopaminergic disturbances related to inflammatory condition

Tetrahydrobiopterin administration facilitates amphetamine-induced dopamine release and motivation in mice

Dopamine (DA) is a critical neurotransmitter involved in motivational processes. Tetrahydrobiopterin (BH4) is an essential cofactor for tyrosine hydroxylase, the rate-limiting enzyme in DA synthesis. Decreases in BH4 levels are observed in several DA-related neuropsychiatric diseases involving impairment in motivation. Yet, whether BH4 could be used to treat motivational deficits has not been comprehensively investigated. To investigate the effects of exogenous BH4 administration on the dopaminergic system and related behaviors, we acutely injected mice with BH4 (50 mg/kg). Passage of BH4 through the blood brain barrier and accumulation in brain was measured using the in situ brain perfusion technique. DA release was then recorded using in-vivo micro-dialysis and motivation was evaluated through operant conditioning paradigms in basal condition and after an amphetamine (AMPH) injection. First, we showed that BH4 crosses the blood-brain barrier and that an acute peripheral injection of BH4 is sufficient to increase the concentrations of biopterins in the brain, without affecting BH4- and DA-related protein expression. Second, we report that this increase in BH4 enhanced AMPH-stimulated DA release in the nucleus accumbens. Finally, we found that BH4-induced DA release led to improved performance of a motivational task. Altogether, these findings suggest that BH4, through its action on the dopaminergic tone, could be used as a motivational enhancer.Impact de la composition lipidique membranaire sur la transmission dopaminergique dépendante du récepteur D2 et la motivationProgram Initiative d’Excellenc