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Lors d’un stress, l’activation de l’axe hypothalamo-hypophyso-surrénalien (HHS) conduit à une augmentation de la production de glucocorticoïdes (tel que la corticostérone) par les glandes surrénales. Le rôle de la corticotropin-releasing hormone (CRH), à l’origine de l’activation de l’axe HHS, est encore méconnu. En effet, les récepteurs à la CRH sont présents aussi bien au niveau du système nerveux central (SNC), notamment au niveau du cervelet, qu’au niveau du système immunitaire (SI). Cela suggère donc une action directe possible de cette hormone sur ces deux systèmes. Au cours de ce projet, nous avons étudié les régulations des SNC et SI lors d’un stress, et plus particulièrement le rôle de la CRH et de ses récepteurs dans ces régulations. Suite à des injections chroniques de corticostérone, mimant un stress, nous avons observé une altération des fonctions locomotrices qui semble être reversée lorsque le CRH-R1 est inhibé avec un antagoniste. Ces premiers résultats permettent de mettre en avant un éventuel rôle de la CRH dans la régulation des fonctions motrices au niveau du cervelet en conditions de stress. En parallèle, d’autres études in vitro réalisées sur des splénocytes murins stimulés avec de la CRH ont montré une diminution de la viabilité des lymphocytes B (LB). Suite à ces résultats, nous avons caractérisé pour la première fois la présence de récepteurs à la CRH sur cette population de LB murins. Ces résultats montrent l’importance de la CRH dans les régulations des SNC et SI en condition de stress et le rôle de cette hormone dans les interactions entre les deux systèmes / In stress conditions, the Hypothalamo-Pituitary-Adrenal (HPA) axis activation leads to an overproduction of glucocorticoïds (such as corticosterone in rodent) by adrenal glands and this activation is well characterized. However, various questions remain about the precise role of corticotropin-releasing hormone (CRH), which is at the beginning of the HPA activation. Indeed, CRH receptors are presents both in central nervous system (CNS), especially in cerebellum, and in immune system (IS). This suggest a possible direct action of this hormone on both system. In this project, we studied the regulations on CNS and IS in stress conditions and more particularly the CRH role and these receptors in these regulations. After chronic corticsterone injections, to mimic a stress, we observed a locomotor alteration which seems to be inverted when CRH-R1 were inhibited with an antagonist. These first results show an possible CRH role in locomotor regulation in cerebellum under stress condition. In parallel, others in vitro studies performed on murine splenocytes stimulated with CRH showed a B lymphocyte (LB) viability decrease. Furthermore, we are the first to characterise the CRH receptors on murine LB. This work show the CRH importance in CNS and IS regulations under stress conditions and its role in interactions between the two systems

Introduction: Central cholinergic system plays a key role in control of different brain functions such as learning, memory, attention, locomotion and rewards. Disrupted integrity, regulation or capacity of cholinergic signalling is closely connected with cognitive symptoms of several neurodegenerative and neuropsychiatric diseases, as Alzheimer disease, Parkinson disease, attention deficit hyperactivity disorder (ADHD), depression, schizophrenia and increased distractibility. The major neurotransmitter of cholinergic neurons is acetylcholine (ACh) and regulation of ACh levels is main pharmacotherapeutic approach to the treatment of diseases associated with central cholinergic system. The aim of the thesis was to study the changes of central cholinergic neurotransmission with respect to various aspects of modulation of ACh levels in the brain by controlling its release through M4 muscarinic receptors (MR), its hydrolysis by acetylcholinesterase (AChE) or butyrylcholinesterase (BChE) and after hydrolysis in the synapse, regulation of the uptake of metabolite choline by high affinity choline transporter (CHT). Methods: Here we used telemetry to measure locomotor activity and body temperature in mice with selective deletion of M4 MR (M4KO) and their wild type (M4WT) controls under the basal conditions...

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

The stress response is an evolutionarily conserved mechanism critical for survival that requires orchestration of different systems in the body. Corticotropin-releasing hormone (CRH) neurons of the hypothalamic paraventricular nucleus (PVN) represent the final common pathway leading to HPA axis activation in response to stress. Noradrenergic inputs to CRH neurons in the PVN provide a powerful drive to activate the HPA axis. Previous anatomical studies have shown that noradrenergic afferents synapse directly on CRH neurons, but electrophysiological analyses indicate that the noradrenergic activation of CRH neurons is mediated primarily by the stimulation of presynaptic glutamatergic neurons. Here, using whole cell patch clamp recordings in identified CRH neurons, I demonstrate that norepinephrine (NE) stimulates excitatory synaptic inputs by activating postsynaptic α1 adrenergic receptors in CRH neurons and inducing the release of the retrograde messenger nitric oxide, which drives upstream glutamate neurons to elicit spike-dependent synaptic glutamate release onto the CRH neurons. Notably, the NE effect is dependent on ATP transmission and astrocytic function, suggesting that astrocytes serve as an intermediary in the retrograde activation of glutamateregic synaptic inputs to the CRH neurons. In addition, I also show that the NE-induced excitation of CRH neurons is stress-status sensitive and corticosterone dependent, in that stress-induced corticosterone causes internalization of membrane α1 adrenergic receptors to desensitize the CRH neurons to NE. Taken together, my findings provide evidence that NE excites CRH neurons in a stress state-dependent manner by a retrograde NO stimulation of local glutamate circuits that is dependent on glial activation. This retrograde trans-neuronal-glial regulation of excitatory synaptic inputs to CRH neurons by NE provides a mechanism for the NE activation of the HPA axis in the early stage of stress response. The stress-/corticosterone-induced desensitization of CRH neurons to NE modulation by the internalization of α1 adrenergic receptors confers a stress state-dependent resistance of the CRH neurons to repeated noradrenergic activation, which provides a mechanism for the negative feedback regulation of the CRH neurons and the HPA axis by stress and glucocorticoids, and a means to restore neuroendocrine homeostasis after stress exposure. / acase@tulane.edu

The neuropeptides arginine-vasotocin (AVT) and corticotropin-releasing hormone (CRH) are involved in the hypothalamic-pituitary-interrenal (HPI) axis. During stress, the HPI axis is activated and cortisol is released into the blood. In addition to their role in the HPI axis, AVT and CRH also have behavioural effects. The roles of AVT and CRH in stress responses and agonistic behaviour were studied in this thesis, using two different models. In the first model, two strains of rainbow trout (Onchorhynchus mykiss) divergent in stress-induced release of cortisol were investigated. This was done by observing behaviour and stress responses under different conditions. These strains were found to have divergent stress coping strategies based on the observed behaviour and levels of plasma cortisol. This divergence in behaviour could be associated with the CRH system, since the mRNA levels of CRH differed between the strains during stress. However, no differences between strains were observed in AVT or its receptor expressions. In the second model, non-selected rainbow trout were paired and the effect of intracerebroventricular (icv) injections of an active substance (AVT, CRH or the CRH related peptide Urotensin-I (UI)) on fights for dominance was investigated. One fish of the pair received the active substance icv and the other received saline icv. Fish receiving AVT became subordinate in accordance with the suggestion that AVT attenuates aggression in territorial vertebrates. Fish receiving CRH became subordinate whereas UI showed no effect on fights for dominance. Further, both CRH and UI induced an anxiety-related behaviour similar to non-ambulatory motor activity in rats. In addition, CRH appeared to affect the dopaminergic and serotonergic systems. In this thesis, it is suggested that CRH is involved in the behavioural modulation of the stress coping strategies in teleost fish. Further, AVT and CRH seem to act inhibitory on aggressive behaviour.

Measures of temperament including exit velocity (EV) and pen score (PEN) and were compared over 3 repeated observations (60-d interval) of yearling Brahman bulls (initial BW = 320 ± 4 kg; n = 66). Exit velocity measures were correlated; EV1 to EV2 (r = 0.32, P = 0.01), EV1 to EV3 (r = 0.31, P = 0.02), and EV2 to EV3 (r = 0.47, P < 0.001). Both EV and PEN were correlated with serum cortisol (CS) within Time 1 and Time 3; EV1 to CS1 (r = .26, P = 0.04), PEN1 to CS1 (r = 0.29, P = 0.02), and EV3 to CS3 (r = 0.44, P < 0.001). Two-year old Brahman heifer were given an ACTH challenge. The calm (C) and temperamental (T) groups consisted of 6 slow (EV=1.05 ± 0.05 m/sec) and 6 fast (EV = 3.14 ± 0.22 m/sec) heifers. Prior to ACTH challenge, T heifers had elevated CS (T = 48.97 ± 3.42, C = 29.60 ± 5.46 ng/mL). Basal CS was higher (P < 0.001) in T heifers (18.20 ± 2.63, C = 4.30 ± 0.58 ng/mL). Following ACTH (0.1 IU ACTH per kg BW) area under the response curve (AUC) was greater (P = 0.07) in C heifers (T = 69.08 ± 10.69, C = 95.87 ± 7.24 ng·h/mL). After declining below basal concentrations, CS in T heifers were again greater (P = 0.02) than in C heifers. The same heifers were subjected to a CRH challenge (0.1 µg bCRH per kg BW). Prior to CRH area under the ACTH curve was greater (P = 0.025) in T heifers (T = 385.72 ± 49.97, C = 239.24 ± 24.04 pg·h/mL). Basal ACTH did not differ (P = 0.10) between temperament groups. Area under the ACTH response curve was greater (P = 0.057) in C heifers (C = 66.72 ± 10.65, T = 38.11 ± 6.44 pg·h/mL). These data demonstrate that cattle with poor temperament exhibit increased stress responsiveness to handling, increased baseline adrenal function but not increased basal pituitary function, and a muted responsiveness to pharmacological stimulus. Thus functional characteristics of the HPA axis vary with animal temperament.

H ιδιοπαθής θρομβοπενική πορφύρα είναι ένα αυτοάνοσο νόσημα που χαρακτηρίζεται από χαμηλό αριθμό αιμοπεταλίων και αιμορραγίες. Επιπλέον αυτή η ασθένεια κατηγοριοποιείται σε οξεία (όταν διαρκεί λιγότερο από έξι μήνες) και χρόνια μορφή. Η λεπτίνη είναι μια ορμόνη/κυτταροκίνη που παράγεται από τα αδιποκύτταρα και ρυθμίζει την όρεξη και τον μεταβολισμό. Ως κυτταροκίνη η λεπτίνη προάγει την Th1 απόκριση και παίζει πολύ σημαντικό ρόλο στα αυτοάνοσα νοσήματα όπως έχει παρατηρηθεί σε πολλά μοντέλα ζώων. Στην εργασία αυτή μελετήσαμε τον ρόλο της λεπτίνης στην παιδική ιδιοπαθή θρομβοπενική πορφύρα (ΙΘΠ). Από τα πειράματά μας διαπιστώσαμε ότι τα επίπεδα της λεπτίνης συσχετίζονται αρνητικά με τον αριθμό των αιμοπεταλίων των ασθενών. Επιπλέον αποδείξαμε ότι στην ασθένεια που μελετήσαμε η λεπτίνη έχει αντί-φλεγμονώδη ρόλο αφού επάγει την έκφραση της IL-10 από το μονοκύτταρα Το μόριο της εκλυτικής ορμόνης της κορτικοτροπίνης (CRH) εκφράζεται κυρίως στον υποθάλαμο και ενεργοποιεί μέσω του άξονα υποθάλαμος-υπόφυση-επινεφρίδια τα γλυκοκορτικοειδή τα οποία έχουν ανοσοκατασταλτική δράση. Η CRH που εντοπίζεται στην περιφέρεια έχει αντιθέτως προ-φλεγμονώδη δράση. Εμείς μετρήσαμε τα επίπεδα της CRH στο πλάσμα υγιώς και ασθενών δοτών και παρατηρήσαμε ότι στους υγιείς δότες η CRH έχει την ικανότητα να ρυθμίζει αρνητικά την έκφραση της λεπτίνης. Ο έλεγχος όμως αυτός χάνεται στους ασθενείς με αποτέλεσμα τα επίπεδα τα λεπτίνης αυξάνονται στον ορό τους / Ιdiopathic thrombocytopenic purpura is an autoimmune disease characterized by a low platelet count and bleeding. Moreover this disorder is classified as acute (of six month or less duration) or chronic. Leptin is an adipocyte-derived hormone/cytokine that regulates food intake and basal metabolism. As a cytokine leptin promotes T helper 1 (TH1)-cell differentiation and can modulate the onset and progression of autoimmune responses in several animal models of disease. Here, we review the role of leptin in childhood idiopathic thrombopenic purpura (ITP). We found that leptin levels negatively correlated with platelet numbersand also that it plays an active anti-inflammatory role by promoting IL-10 secretion by monocytes. Corticotropin-Releasing Hormone (CRH) CRH, the hypothalamic component of the hypothalamic-pituitary,adrenal axis, attenuates inflammation through stimulation of glucocorticoid release, whereas peripherally expressed CRH acts as a proinflammatory mediator. We measured CRH levels in the plasma of children suffering from ITP and in the plasma of the paediatric controls, and we found that in controls CRH down-regulates leptin’s expression but not in patients.

Exercise is widely recognized for its role in the health management and prevention of several chronic diseases. Exercise is considered as a stimulus in the form of physical stress to which a group of anatomical structures in the human body responds by generating a stress response that enables certain physiological modifications essential for restoring systemic homeostasis. A major component of the response is produced through the complex hypothalamic-pituitary-adrenal (HPA) axis mechanism that results in the release of cortisol which then intercedes with the effects of the stimulus. To investigate how cortisol helps the body adapt to this physical stress it is necessary to gain deep insight into the cortisol response mechanism. However, this is a complex mechanism, so to better understand the mechanics and to be able to analyze complex data, mathematical models are used. Various mathematical models have already been developed that describe different metabolic responses to exercise but to date, to my knowledge, none of these existing models has illustrated the HPA axis response mechanism, particularly cortisol response to physical exercise. Therefore, I have developed a mathematical model that describes cortisol variations on a normal day in the absence of any form of stress and on the day of exercise. The developed cortisol response model could fit simulation to experimental data and also passed the χ2- statistical test. Additionally, the model has been validated on different cortisol experimental data with satisfying results. At last, considering the positive outcome of this mathematical model, it could be used as a groundwork for developing a comprehensive model which can describe other metabolic processes response to exercise such as glucose metabolism together with the cortisol response mechanism in the future.

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