No description available.

Despite the lack of robust clinical response, treatment strategies for cancer-induced depression (CID) are currently limited to those developed for non-cancer-related depression. The work presented in this dissertation conceptualizes CID as a pathophysiologically distinct form of depression. To investigate CID at the most basic level, we first developed a preclinical model that was validated by comparison to an established model of stress-induced depressive-like behaviours. The positive control model was developed by chronically treating female BALB/c mice with oral corticosterone (CORT). The CID model was developed using subcutaneous inoculation with 4T1 mammary carcinoma cells. Anhedonia, behavioural despair, and dendritic atrophy in the medial prefrontal cortex (mPFC) were observed in both models. Similar to many human cancer cell lines, 4T1 cells were shown to secrete significant amounts of glutamate, which was markedly attenuated using the system xc- inhibitor sulfasalazine (SSZ). In CID mice, oral treatment with SSZ was at least as effective as fluoxetine, a popular clinical antidepressant, at preventing depressive-like behaviours. This effect was primarily attributable to intact SSZ, rather than its anti-inflammatory metabolite. RNA-sequencing was performed on hippocampal samples from CID and CORT animals. Analysis of differential expressed genes (DEGs) revealed significant overlap between the two models. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways and biological process gene ontologies (GO:BP) terms related to ion homeostasis and neuronal communication were enriched for both models. CID was associated with additional DEGs that were not identified in the CORT model. These DEGs were enriched in KEGG pathways and GO:BP terms related to neuronal development, intracellular signalling cascade, learning, and memory. These studies suggest that CID may involve a distinct aetiology, and that glutamate secretion by cancer cells presents a viable target for antidepressant treatment. The development of mechanism-based therapeutics for CID will dramatically improve the quality of life for cancer patients. / Thesis / Doctor of Philosophy (PhD) / Cancer patients are at a high risk of developing depression. In addition to the psychological stress caused by a cancer diagnosis, there is evidence that cancer causes depression through biological pathways. To investigate these pathways, a mouse model of cancer-induced depression (CID) was developed. This model showed comparable behavioural and structural brain deficits to those observed in a stress model of depression. Cancer cells secrete elevated levels of glutamate, a signalling molecule that is involved in depression. In CID mice, inhibiting glutamate release had an antidepressant effect similar to that of fluoxetine, a standard clinical antidepressant. A genetic analysis on brain samples from the CID model revealed significant overlap with the stress model of depression. CID mice had additional changes relevant to learning, memory, and brain cell development that were not detected in the stress model. A better understanding of CID will lead to better treatment strategies developed specifically for cancer patients.

No description available.

Patients with MDD demonstrate impairments in various components of affective processing, which are believed to persist in the remitted phase of the illness and are believed to underlie the vulnerability for future relapse. Despite advances in neuropsychiatry, the neuroanatomical site of action of various treatment modalities remains unclear, leaving clinicians without an algorithm to guide optimal treatment selection for individual patients. This thesis sought to characterize differences in brain activation during affective processing between MDD treatment responders (RS) and non-responders (NR) by combining clinical and neuroimaging variables in a repeat-measure functional magnetic resonance imaging (fMRI) investigation. We induced increases in positive and negative affect using visual stimuli under fMRI conditions in 21 MDD subjects and 18 healthy controls (HC). Based on previous neuroimaging investigations and preclinical animal data, we hypothesized that increased activation of the amygdala and the pregenual cingulate during negative affect induction (NAI), and decreased activity of the ventral striatum during positive affect induction (PAI), would differentiate ultimate NR from RS. Following the first scan, treatment with fluoxetine and olanzapine was initiated in the MDD group, with follow-up scans at one- and six-weeks thereafter. We hypothesized that decreases in depressive symptoms would be associated with decreased activation of the ventromedial prefrontal cortex (PFC) and amygdala during NAI and increased activation of the hippocampus during PAI. Eleven MDD subjects met criteria for clinical remission at study endpoint. Based on trait differences between MDD and HC, we hypothesized that differences observed during NAI would be limited to brain regions involved in regulation of the affective state, including the dorsolateral PFC and the anterior midcingulate cortex. The results of the analyses confirmed the a-prior hypotheses and additionally demonstrated differential activation of the insular, medial temporal, and premotor cortex during repeat PAI and NAI between HC, RS, and NR. These findings provide: i) a neuroanatomical target of successful antidepressant therapy during PAI/NAI; ii) a differential effect of depressive symptoms and dispositional affect on brain activation during PAI/NAI; and iii) an a-prior method to differentiate RS from NR, and iv) demonstrate the need for additional treatment to prevent relapse in the remitted state.

Le trouble du déficit de l’attention avec ou sans hyperactivité (TDAH) est de plus en plus reconnu chez l'adulte. Les psychostimulants représentent la première ligne de traitement, mais ceux-ci ne sont parfois pas tolérés, peuvent être contrindiqués ou ne pas être efficaces. Les médicaments non stimulants constituent une alternative mais ont été insuffisamment explorés. Cette thèse présente un essai clinique randomisé contrôlé de 30 sujets souffrant de TDAH qui ont reçu soit la duloxétine 60 mg par jour ou le placebo pendant une période de 6 semaines. Le Conners’ Adult ADHD Rating Scale (CAARS) et le Clinical Global Impression scale (CGI) ont été utilisés pour mesurer la sévérité des symptômes et l'amélioration clinique. Le Hamilton Anxiety Rating Scale (HARS) et le Hamilton Depression Rating Scale (HDRS) ont été choisis pour vérifier l'impact sur la symptomatologie anxio-dépressive. Les résultats démontrent que les sujets ayant reçu la duloxétine avait un score au CGI-Severity (CGI-S) inférieur au groupe contrôle à 6 semaines de traitement et une amélioration plus importante au CGI-Improvement (CGI-I). Ce groupe démontre également des diminutions supérieures des scores à plusieurs sous-échelles du CAARS. Aucun effet n'a été observé sur le HARS et le HDRS. Le taux de retrait du bras duloxetine remet par contre en question la dose initiale choisie dans ce protocole. La duloxétine semble donc une option prometteuse dans le traitement du TDAH chez l'adulte et la réplication des données cliniques serait la prochaine étape pour confirmer ces résultats. / Attention-deficit/hyperactivity disorder (ADHD) is increasingly recognized in adults. Stimulants are first-line treatment options but can be ineffective, poorly tolerated or contraindicated in some patients. For these patients, non-stimulants can be an interesting option; however, this heterogeneous class has been insufficiently studied. This thesis presents the results of a pilot study. In this randomized controlled clinical trial, thirty adults with ADHD received either placebo or duloxetine 60 mg daily for 6 weeks. The Conners’ Adult ADHD Rating Scale (CAARS) and the Clinical Global Impression scale (CGI) were chosen to assess symptom severity and clinical improvement. The Hamilton Anxiety Rating Scale (HARS) and the Hamilton Depression Rating Scale (HDRS) were used to measure the effect on anxiety and depressive symptoms. In summary, the duloxetine group showed a lower score on CGI-Severity at week 6, greater improvement on CGI-Improvement and greater decreases on multiple subscales of the CAARS. There was no treatment group effect on HDRS or HARS scores. Tolerability was an issue with participants in the duloxetine group and the dose titration schedule chosen in this study should be revised. This is the first clinical trial of duloxetine in adults with ADHD. This medication seams to improve symptoms in this condition but further studies are required to replicate these findings in larger samples of ADHD adults.

Diversos estudos têm sugerido uma ação anti-inflamatória para o antidepressivo amitriptilina; a presente investigação pretende analisar os mecanismos envolvidos com esta resposta. Mais especificamente, o objetivo do presente estudo é avaliar os efeitos da amitriptilina sobre a resposta inflamatória induzida pela carragenina em ratos e investigar os prováveis mecanismos relacionados a estes efeitos. Num primeiro momento, utilizando-se o modelo do edema de pata induzido pela carragenina, avaliamos o efeito anti-inflamatório da amitriptilina após administração em diferentes doses e intervalos de tempo, isto é, de forma aguda ou em múltiplas doses, por diferentes vias de administração. Verificamos que o tratamento com amitriptilina 10mg/kg, administrada a cada tempo de meia-vida de eliminação, produziu redução significante do edema de pata nos diversos tempos avaliados. Não houve reversão deste efeito anti-inflamatório quando os animais foram pré-tratados com um antagonista de receptores de glicocorticoides (RU-486); houve potencialização do efeito anti-inflamatório pelo pré-tratamento com antagonista de receptores alfa-1-adrenérgicos (prazosina). A administração de amitriptilina juntamente com um inibidor inespecífico de síntese de óxido nítrico (L-NAME) levou a uma potencialização do efeito anti-inflamatório avaliado pelo modelo do edema de pata; produziu, ainda, uma redução significante na concentração de leucócitos e no número total de leucócitos do exsudato peritoneal induzido por carragenina e uma redução significante do total de nitratos circulantes, quando comparados aos animais do grupo controle. Este efeito anti-inflamatório avaliado pelo edema de pata não foi revertido pela administração de um precursor da síntese de NO. O tratamento com amitriptilina ou L-NAME isoladamente ou em conjunto não produziu alterações significantes na expressão das moléculas de adesão ICAM-1, PECAM-1, L-selectina e MAC-1 por leucócitos do sangue periférico. Quando avaliamos o comportamento dos leucócitos por microscopia intravital, observamos que a amitriptilina produziu uma redução significante no rolamento, adesão e transmigração de leucócitos avaliados em condição inflamatória. A administração de amitriptilina isoladamente ou em conjunto com L-NAME também mostrou produzir redução significante nos níveis de IL-1beta e TNF-alfa no soro de ratos. Podemos assim concluir que a amitriptilina apresentou um efeito anti-inflamatório na maioria dos modelos avaliados. Os mecanismos parecem envolver a participação dos receptores alfa-1-adrenérgicos, a inibição da NOS - com consequente redução na síntese de NO e das ações próinflamatórias a ele associadas - e a diminuição nos níveis das citocinas IL-1beta e TNF-alfa. Considerando-se a teoria que implica a depressão como um fenômeno inflamatório, a compreensão dos mecanismos envolvidos no efeito anti-inflamatório da amitriptilina poderia contribuir nas investigações envolvendo esta teoria / Several studies have suggested an anti-inflammatory action to the antidepressant amitriptyline; the present investigation intend to analyze the mechanisms involved in this response. More specifically, the objective of the present study is to evaluate the effects of amitriptyline in the carrageenan-induced inflammatory response and investigate the possible mechanisms related to these effects. At first, with the carrageenan-induced paw edema model, we evaluated the anti-inflammatory effect of amitriptyline administrated in different doses, intervals, acute or chronically, by different routes of administration. We verified that amitriptyline 10mg/kg, administrated each elimination half-life, produced a significant reduction on paw edema in several times evaluated. It was not reverted with the pretreatment with an glicocorticoid antagonist (RU-486); it was potentiated with the pretreatment with an alpha-1- antagonist (prazosin). The co-administration of amitriptyline and an unspecific inhibitor of nitric oxide synthesis (L-NAME) produced a potentialization of the anti-inflammatory effect, evaluated in the paw edema model, a decrease in the leukocyte concentration and total number in the carrageenan-induced peritoneal exsudate and a significant reduction in the total serum nitrate, when compared to the control group. This anti-inflammatory effect evaluated by the paw edema was not reverted with a NO precursor administration. The only amitriptyline or L-NAME treatment didnt produce significant alterations in the adhesion molecules expression ICAM-1, PECAM-1, L-selectin e MAC-1 by leukocytes of the peripheral blood. When the leukocyte behavior was evaluated by intravital microscopy, we verified that amitriptyline produced significant reduction in the rolling, adhesion and transmigration of leukocytes evaluate in inflammatory condition. Amitriptyline and/or L-NAME administration produced a significant reduction on IL-1beta and TNF-alpha levels in rats serum. We may conclude that amitriptyline presented an anti-inflammatory effect in the most models evaluated. Mechanisms seem to involve alpha-1-adrenergic receptors, NOS inhibition - and consequent reduction in NO synthesis and its proinflammmatory actions - and reduction on cytokines IL-1beta and TNF-alpha levels. Considering the theory that implicates depression as an inflammatory phenomenon, the comprehension of the anti-inflammatory effects of amitriptyline could contribute in the investigations about this theory

Les antidépresseurs ISRS (inhibiteurs sélectifs de la recapture de sérotonine) sont parmi les plus prescrits pour traiter les épisodes dépressifs majeurs. Cependant, leur efficacité n’est pas optimale. En effet, ils montrent un long délai d’action, de nombreux effets indésirables et sont inefficaces pour une proportion non négligeable de patients. La dépression étant actuellement un enjeu de santé publique majeur, il est donc nécessaire de développer de nouvelles molécules possédant un meilleur profil thérapeutique. Récemment, un intérêt croissant a été porté sur le récepteur 5-HT3, notamment depuis le développement de la vortioxétine, ISRS de nouvelle génération ayant des propriétés antagonistes pour ce récepteur localisé dans les zones cérébrales contrôlant l’humeur. Le but de ce travail de thèse a été d’étudier le rôle du récepteur 5-HT3 dans la réponse aux antidépresseurs, ainsi que dans la physiopathologie de la dépression. Dans ce cadre, nous avons utilisé une approche génétique, en caractérisant un modèle de souris knockout (KO) dont le gène de la sous-unité 3A du récepteur 5-HT3 a été invalidé. Le phénotype de ces animaux et leurs contrôles de type sauvage (Wild-Type, WT) a tout d’abord été évalué dans des tests comportementaux de screening de molécules anxiolytiques et antidépressives, puis leur réponse à des traitements aigus d’ISRS a été mesurée par ces mêmes approches. L’effet de traitements antidépresseurs chroniques a quant à lui été évalué par une technique d’électrophysiologie in vitro. Enfin, les souris ont été soumises au modèle du stress de défaite sociale chronique (CSDS), afin de déterminer le rôle du récepteur 5-HT3 dans la réponse au stress. En conditions basales, le turn-over de la sérotonine est diminué chez les souris 5-HT3 KO par rapport aux souris WT. Cet effet est accompagné par une augmentation de l’expression génique des récepteurs 5-HT1A et de leur couplage aux protéines G au niveau du noyau raphé dorsal (NRD) des souris KO par rapport aux WT. Au niveau comportemental, les souris KO 5-HT3 montrent un phénotype apparenté à celui induit par un anxiolytique et par un antidépresseur. Lorsqu’elles reçoivent une injection de citalopram, un ISRS sélectif, les souris 5-HT3 KO ne se comportent pas différemment de leurs contrôles WT dans les tests de screening des antidépresseurs. Cependant, dans ces mêmes tests, l’effet de la fluoxétine, ISRS possédant des propriétés antagonistes pour le récepteur 5-HT3, est perdu chez les souris 5-HT3 KO. Le traitement chronique par le citalopram (20 mg/kg/j) induit une désensibilisation similaire des autorécepteurs 5-HT1A localisés sur les neurones sérotoninergiques du NRD chez les animaux WT et KO. Dans les mêmes conditions, mais en utilisant une dose de citalopram plus faible (5 mg/kg/j), la désensibilisation des autorécepteurs 5-HT1A est plus forte chez les animaux KO que chez les WT, confortant ainsi l’effet potentialisateur de l’invalidation des récepteurs 5-HT3 dans l’efficacité thérapeutique des ISRS. Afin de disséquer le rôle des récepteurs 5-HT3 dans la réponse au stress chronique, le CSDS a fait l’objet d’une validation avec l’agomélatine, antidépresseur de nouvelle génération. Ce stress a engendré des altérations de la mémoire à long terme, en lien avec des modifications de l’expression génique de l’exon IV du BDNF et d’enzymes de régulation épigénétique. Ces effets délétères du stress ont été traités efficacement par l’agomélatine (50 mg/kg/j) en injection chronique, mais cette molécule n’a cependant pas modifié les effets du CSDS sur les phénotypes de type anxieux et dépressifs observés après le stress. Nous avons montré que le CSDS augmentait l’expression génique de la sous-unité 3A du récepteur 5-HT3 dans différentes structures cérébrales des souris WT. De plus, les altérations de l’expression génique de CamkIIa et SOD1 induites par le stress dans le cortex préfrontal des souris WT n’ont pas été retrouvées chez les souris 5-HT3 KO (...) / SSRI (selective serotonin reuptake inhibitor) antidepressants are among the most prescribed drugs to treat major depression. However, their efficacy is not optimal yet. Indeed, they possess a long delay of action, various side effects and show not efficacy in some patients. As depression is currently a global burden, there is a great need for new molecules with a better therapeutic efficacy. Recently, an increased attention has been taking to 5-HT3 receptors, notably since the development of vortioxetine, a new generation SSRI that antagonizes this receptor. The aim of the study was to assess the role of 5-HT3 receptor in the antidepressant response and the physiopathology of depression. In this context, we used a genetic approach, by characterizing a knockout (KO) mice model lacking the 3A subunit of the 5-HT3 receptor. Their phenotype and the one of wild-type (WT) control mice was first evaluated in behavioral tests widely used for antidepressant and anxiolytic drugs screening, then following acute SSRI treatments. Effect of chronic SSRI administration was assessed by in vitro electrophysiology. Finally, mice were submitted to the chronic social defeat stress (CSDS) model, to determine the role of 5-HT3 receptor in stress response. In basal conditions, 5-HT turnover was decreased in 5-HT3 KO mice compared with WT mice. This effect was accompanied by an increase in the 5-HT1A receptor gene expression and their coupling to G proteins at the dorsal raphe nucleus (DRN) level. 5-HT3 KO mice displayed anxiolytic-like and antidepressive-like phenotype. When injected with citalopram, a very selective SSRI, 5-HT3 KO mice behaved similarly as WT mice in antidepressant screening tests. However, in the same tests, the effect of fluoxetine, a SSRI that possesses 5-HT3 receptor antagonist properties, was blunted in 5-HT3 KO mice. Chronic treatment with citalopram (20 mg/kg/d) induced in WT and KO mice a similar desensitization of 5-HT1A autoreceptors located on DRN 5-HT neurons. In the same conditions, but using a lower citalopram dose (5 mg/kg/d), 5-HT1A autoreceptor desensitization was higher in 5-HT3 KO mice than in WT mice, thus reinforcing the potentiating effect of the 5-HT3 receptor in the SSRI efficacy. In order to assess the role of 5-HT3 receptor in chronic stress response, CSDS paradigm was validated using agomelatine, a new generation antidepressant drug. This stress model provoked long term memory alterations, linked with modifications in hippocampal mRNA levels of BDNF exon IV and epigenetic modifying enzymes. These deleterious stress effects were prevented by chronic agomelatine treatment (50 mg/kg/d), but this molecule did not modify the stress-induced anxious- and depressive-like phenotypes. We showed that subunit 3A gene expression was increased in various WT mice brain structures subjected to CSDS. Moreover, stress-induced modifications of CamkIIa and SOD1 gene expression in the prefrontal cortex of WT mice were not present in KO mice. Genetic invalidation of 5-HT3 receptor blocked the effects of social stress in some behavioral tests (splash test, saccharine preference test) and on body weight gain. Taken altogether, these data show that 5-HT3 receptor plays an important role in anxiety- and depression-related behaviors. Moreover, invalidation of this receptor increased the effect of a low dose chronic SSRI treatment, and blunted the effect of a SSRI targeting 5-HT3 receptor. These results highlight the interest of this receptor in the development of innovating therapies to treat anxio-depressive disorders. Finally, the reduced sensitivity of 5-HT3 KO mice to chronic stress suggests an involvement of this receptor in stress-related behaviors and depression physiopathology.

Les astrocytes joueraient un rôle central dans la physiopathologie des troubles anxio-dépressifs et dans l’activité thérapeutique des antidépresseurs. En effet, différentes études in vitro suggèrent que les inhibiteurs sélectifs de recapture de la sérotonine (ISRS) stimulent la synthèse de substances neuroactives par ces cellules gliales nécessaires à la prolifération, la maturation et la survie neuronale mais également au maintien de la plasticité synaptique. Le Brain-derived neurotrophic factor (BDNF) fait partie de ces substances mais son origine, notamment astrocytaire, doit encore être démontrée dans les systèmes intégrés tel que l’animal vivant. A partir de ce constat, dans une première partie de ce travail de thèse, nous avons donc voulu préciser si les astrocytes constituent une source cellulaire participant à la synthèse et/ou à la libération de BDNF en réponse à l’administration prolongée d’un ISRS, la fluoxétine d’une part chez des souris naïves et d’autre part chez des souris exposées à la corticostérone pendant plusieurs semaines (modèle « CORT »). Pour cela, nous avons utilisé une stratégie de transfection virale induisant la surexpression de BDNF spécifiquement dans les astrocytes de l'hippocampe. Nos résultats mettent en lumière que cette surexpression provoque des effets de types anxiolytiques-antidépresseurs dépendant de la neurogenèse hippocampique chez des souris naïves soumises au test d’hypophagie induite par la nouveauté mais pas dans le modèle CORT. Nous avons également mis en évidence que le BDNF pouvait agir en retour sur les cellules qui l’ont libéré pour renforcer le réseau astrocytaire (mécanisme autocrine) mais également sur les neurones sérotoninergiques pré-synaptiques (mécanisme paracrine) pour exercer un frein sur la libération de sérotonine dans l’hippocampe. Différents arguments de la littérature suggèrent d’ailleurs que ce dernier mécanisme pourrait être favorable à l’activité anxiolytique de la fluoxétine tel que nous l’avons observé dans ce travail. Sachant que les astrocytes expriment à leur surface, une grande variété de récepteurs sérotoninergiques, nous nous sommes ensuite intéressé à la possibilité que le sous-type de récepteur 5-HT2A pourrait être un élément clé dans la synthèse et/ou la libération de BDNF et de ce fait moduler la réponse au stress et celle à la fluoxétine. Lors de cette seconde étude nous avons appliqué une approche génétique utilisant des souris mutées, privées de manière constitutive du récepteur 5-HT2A (5-HT2A-/-). A l’opposé de la surexpression de BDNF dans les astrocytes, nous avons montré que les souris 5-HT2A-/- sont plus sensibles au stress, modélisé par l’exposition chronique à la corticostérone, et semblent résistantes à la fluoxétine comparées aux souris 5-HT2A+/+. Afin de préciser le mécanisme pouvant rendre compte de ces observations, nous avons mis en évidence que l’inactivation du récepteur 5-HT2A s’accompagne d’une hypersensibilité du frein inhibiteur exercé par les autorécepteurs 5-HT1A somatodendritiques sur le tonus sérotoninergique. / Growing evidence demonstrates that astrocytes could play a crucial role in the pathophysiologies of anxiety and depression as well as in the therapeutic activity of antidepressant drugs. Indeed, in vitro studies suggest that the selective serotonin reuptake inhibitors (SSRIs) stimulate the synthesis of neuroactive substances by these glial cells which are necessary for the proliferation and maturation of neuronal progenitors but also for the maintenance of the neuronal survival. Brain-derived neurotrophic factor (BDNF) is one of these substances, but its cellular origin has yet to be demonstrated in embedded systems such as living animals. In this context, the first part of this thesis was aimed at clarifying whether astrocytes constitute a source of BDNF in response to the chronic administration of the SSRI, fluoxetine, in both naive and anxio-depressive mice exposed to corticosterone (" CORT" model). In this prospect, we used a novel and efficient gene transfer strategy inducing BDNF overexpression specifically in the astrocytes of the hippocampus. Our results indicated that BDNF overexpression produced anxiolytic-/antidepressant-like activity in the novelty suppressed feeding paradigm in relation with the stimulation of hippocampal neurogenesis in naive mice but not in the CORT model. We also showed that BDNF could act on astrocytes themselves (autocrine mechanism) to improve the hippocampal astrocytic network but also on the pre-synaptic serotonergic nerve terminals (paracrine mechanism) to limit the local serotonin release. Different arguments from the literature suggest that the latter mechanism may be favorable to an anxiolytic-like activity of fluoxetine. Given that astrocytes express at the surface a variety of serotonin receptors, we then raised the possibility that the 5-HT2A receptor subtype may be a key element in the synthesis and/or release of BDNF and thereby modulating the vulnerability to depression and/or the response of fluoxetine. In the second part of this thesis, a genetic approach with mutant mice constitutively lacking the 5-HT2A receptor (5-HT2A-/-) was applied. In contrast to Lenti-BDNF mice, we showed that 5-HT2A-/- mice were more prone to develop anxio-depressive-like symptoms in response to the chronic exposure to corticosterone. Moreover, these mutants were resistant to the chronic administration of fluoxetine compared to 5-HT2A+/+ wild type mice. In order to clarify the mechanism underpinning these observations, we demonstrated that the inactivation of the 5-HT2A receptor was associated with a hypersensitivity of a negative feedback exerted by the somatodendritic 5-HT1A autoreceptors on serotonergic tone.Together these data suggest that astrocytes act in concert with neurons to regulate mood and antidepressant drug response, notably through the synthesis and/or release of BDNF following the activation of the 5-HT2A receptor. More generally, our results illustrate the concept of the tripartite synapse in which the bidirectional communication between astrocytes and monoaminergic neurons would be essential in the regulation of higher brain functions.

Les inhibiteurs sélectifs de recapture de la sérotonine (ISRS), agonistes indirects des récepteurs de la sérotonine (5-HT), ont un début d'effet antidépresseur retardé de plusieurs semaines. Des travaux antérieurs suggèrent que le récepteur 5-HT4 de la sérotonine serait une cible directe pour traiter la dépression et un nouvel espoir pour traiter plus rapidement ces pathologies anxio-dépressives. Toutefois, l'hypothèse « 5-HT4 » doit encore être validée dans des modèles animaux d'anxiété/dépression. Les questions posées étaient : la stimulation des récepteurs 5-HT4 centraux est-elle nécessaire aux effets comportementaux des ISRS ? la neurogenèse hippocampique adulte contribue-t-elle à ces effets ? En utilisant le modèle de stress chronique à la corticostérone (CORT) chez la souris, nous avons évalué les effets sur ces paramètres d’un traitement chronique avec un agoniste du récepteur 5-HT4 (RS67333, 1,5 mg/kg/jour pendant 4 semaines) comparé à un traitement à la fluoxétine (18 mg/kg/jour). Nous avons ensuite utilisé ce modèle murin combiné à l’ablation de la neurogenèse hippocampique par rayons-X afin d’examiner si la neurogenèse est nécessaire aux effets comportementaux d’un traitement subchronique (7 jours) ou chronique (28 jours) avec le RS67333. Nous avons également évalué le blocage des effets de la fluoxétine par un antagoniste du récepteur 5-HT4 (GR125487, 1 mg/kg/jour). Le traitement chronique avec RS67333, comme celui de la fluoxétine, induit une activité anxiolytique/antidépressive et stimule la neurogenèse hippocampique adulte. Cependant, contrairement à la fluoxétine , les effets anxiolytiques du RS67333 sont déjà présents après 7 jours de traitement, sans nécessité l’activation de la neurogenèse. Le traitement chronique avec le GR125487 empêche les deux effets anxiolytique/antidépresseur et neurogènique de la fluoxétine, indiquant que l'activation du récepteur 5-HT4 est nécessaire à ces effets de l’ISRS. Nous avons ensuite cherché à savoir si le court délai d’action antidépresseur du RS67333 peut être prédit par l'expression d'un biomarqueur périphérique. Des données de la littérature indiquent que la cascade de signalisation de β-arrestine 1 (impliquée dans la désensibilisation et l’internalisation du récepteur 5-HT4) serait un biomarqueur potentiel pré-clinique/clinique des états dépressifs et des effets d’un traitement antidépresseur. À cette fin, nous avons développé une nouvelle méthode d’évaluation des taux de protéines circulantes grâce à une analyse par immunoblot des leucocytes (PBMC) isolés à partir du sang total de souris. Les taux de β-arrestine 1 sont diminués dans les leucocytes des souris pré-traitées à la CORT. Il faut 7 jours de traitement avec le RS67333, mais 28 jours avec la fluoxétine chez ces animaux pour restaurer un taux de β-arrestine 1 comparable à celui des animaux contrôles. Ces résultats suggèrent que le taux sanguin de β-arrestine 1 est un biomarqueur de la rapidité de la réponse antidépressive. Enfin, l'activation du récepteur 5-HT4 dans le cerveau peut représenter une approche thérapeutique innovante d’apparition pour traiter plus rapidement des symptômes dépressifs associés à l’anxiété. / Selective serotonin reuptake inhibitors (SSRIs) display a delayed onset of action of several weeks. Past work demonstrated evidence that the 5-HT4 receptor may be a direct target for treating depression and a new hope for fast acting antidepressant treatment. However, the 5-HT4 hypothesis still needs to be validated in models of anxiety/depression.We decided to investigate whether 5-HT4 receptor stimulation was necessary for the effects of SSRIs in a mouse model of anxiety/depression and whether hippocampal neurogenesis contributed to these effects. Using the mouse corticosterone model of anxiety/depression, we assessed whether chronic treatment with a 5-HT4 receptor agonist (RS67333, 1.5 mg/kg/day) had effects on anxiety and depression-related behaviors as well as on hippocampal neurogenesis in comparison to chronic fluoxetine treatment (18 mg/kg/day). Then, using our model combined with ablation of hippocampal neurogenesis, we investigated whether neurogenesis was necessary for the behavioral effects of subchronic (7-days) or chronic (28-days) RS67333 treatment. We also assessed whether a 5-HT4 receptor antagonist, (GR125487, 1 mg/kg/day) could prevent the behavioral and neurogenic effects of fluoxetine. Chronic treatment with RS67333, similar to fluoxetine, induced anxiolytic/antidepressant-like activity and stimulated adult hippocampal neurogenesis. However, unlike fluoxetine, the anxiolytic effects of RS67333 were already present after 7 days and did not require hippocampal neurogenesis. Chronic treatment with GR125487 prevented both anxiolytic/antidepressant-like and neurogenic effects of fluoxetine, indicating that 5-HT4 receptor activation is necessary for these effects of SSRIs. We then explored whether the fast onset of action of the 5-HT4 receptor agonist RS67333 could be predicted by expression of a peripheral biomarker. The β-arrestin-signaling cascade which is involved in 5-HT4 receptor desensitization and internalization, has recently gained attention as a potential pre-clinical/clinical bridging biomarker for depressive states and treatment effects. To this end, we developed a new method to assess levels of circulating proteins through immunoblot analyses of mouse PBMCs isolated from whole blood of anesthetized animals. While we did not detect any change in β-arrestin 1 in mouse leukocytes after 7 days of fluoxetine in corticosterone-treated animals, a short term treatment with RS67333, restored the level of this protein to control levels. In fluoxetine-treated animals, a restoration was only observed in the corticosterone model after a longer exposure. These results suggest that blood levels of β-arrestin 1 may be a useful biomarker to predict antidepressant/anxiolytic activities. Finally, the activation of 5-HT4 receptors in the brain may represent an innovative and rapid onset therapeutic approach to treat depression with comorbid anxiety.

Major depressive disorder (MDD) is a heritable and highly debilitating condition with antidepressants, first-line treatment, demonstrating low to modest response rates. No current biological mechanism substantially explains MDD but both neurostructural and neurochemical pathways have been suggested. Further explication of these may aid in identifying subgroups of MDD that are better defined by their aetiology. Specifically, genetic stratification provides an array of tools to do this, including the intermediate phenotype approach which was applied in this thesis. This thesis explores genetic overlap with regional brain volume and MDD and the genetic and non-genetic components of antidepressant response. The first study utilised the most recent published data from ENIGMA (Enhancing Neuroimaging Genetics through Meta-analysis) Consortium's genome-wide association study (GWAS) of regional brain volume to examine shared genetic architecture between seven subcortical brain volumes and intracranial volume (ICV) and MDD. This was explored using linkage disequilibrium score regression (LDSC), polygenic risk scoring (PRS) techniques, Mendelian randomisation (MR) analysis and BUHMBOX (Breaking Up Heterogeneous Mixture Based On Cross-locus correlations). Results indicated that hippocampal volume was positively genetically correlated with MDD (rg= 0.46, P= 0.02), although this did not survive multiple comparison testing. Additionally, there was evidence for genetic subgrouping in Generation Scotland: Scottish Family Health Study (GS:SFHS) MDD cases (P=0.00281), however, this was not replicated in two other independent samples. This study does not support a shared architecture for regional brain volumes and MDD, however, provided some evidence that hippocampal volume and MDD may share genetic architecture in a subgroup of individuals, albeit the genetic correlation did not survive multiple testing correction and genetic subgroup heterogeneity was not replicated. To explore antidepressant treatment resistance, the second study utilised prescription data in (GS:SFHS) to define a measure of (a) treatment resistance (TR) and (b) stages of resistance (SR) by inferring antidepressant switching as non-response. GWAS were conducted separately for TR in GS:SFHS and the GENDEP (Genome-based Therapeutic Drugs for Depression) study and then meta-analysed (meta-analysis n=4,213, cases=358). For SR, a GWAS on GS:SFHS only was performed (n=3,452). Additionally, gene-set enrichment, polygenic risk scoring (PRS) and genetic correlation analysis were conducted. No significant locus, gene or gene-set was associated with TR or SR, however power analysis indicated that this analysis was underpowered. Pedigree-based correlations identified genetic overlap with psychological distress, schizotypy and mood disorder traits. Finally, the role of neuroticism, psychological resilience and coping styles in antidepressant resistance was investigated. Univariate, moderation and mediation models were applied using logistic regression and structural equation modelling techniques. In univariate models, neuroticism and emotion-orientated coping demonstrated significant negative association with antidepressant resistance, whereas resilience, task-orientated and avoidance-orientated coping demonstrated significant positive association. No moderation of the association between neuroticism and TR was detected and no mediating effect of coping styles was found. However, resilience was found to partially mediate the association between neuroticism and TR. Whilst the first study does not indicate a genetic overlap between regional brain volumes and MDD, it demonstrates the utility of the intermediate approach in complex disease. Antidepressant resistance was associated with neuroticism both genetically and phenotypically, indicating its role as an intermediate phenotype. Nonetheless, larger sample sizes are needed to adequately address the components of antidepressant resistance. Further work in antidepressant non-response may help to identify biological mechanisms responsible in MDD pathology and help stratify individuals into more tractable groups.