Fipronil é um inseticida fenilpirazol de amplo espectro, desenvolvido para inibir seletivamente receptores GABA associados a canais de cloreto de insetos; tanto em Medicina Veterinária, como em Agricultura tem sido utilizado para o controle de pragas. Embora vários estudos procurem compreender os mecanismos da toxicidade neuronal dos praguicidas em mamíferos, há poucos relacionados aos efeitos neurocomportamentais. Assim, o presente estudo investigou os efeitos da exposição prolongada de ratos ao fipronil, observando-se alguns comportamentos ligados ao sistema GABAérgico, como atividade no campo aberto, no labirinto em cruz elevado (LCE), bem como na convulsão induzida por picrotoxina e pentilenotetrazol; avaliou-se ainda os níveis cerebrais de alguns neurotransmissores, como GABA, dopamina, noradrenalina, serotonina e seus respectivos metabólitos. Além disso, foram realizadas análises anátomo-histopatológicas em fígado, cérebro e rins dos animais. Ratos Wistar receberam, por via intragástrica (gavage), durante 28 dias um dos seguintes tratamentos: fipronil (0,1; 1,0 ou 10,0 mg/Kg/dia) ou água destilada 1 mL/Kg/dia. Após uma hora da última administração do fipronil ou água destilada, os ratos tiveram seu comportamento avaliado no campo aberto e no LCE com auxílio do sistema computadorizado EthoVision®. Observou-se no campo aberto apenas redução significante do nº de levantamentos nos animais tratados com 10,0 mg/Kg de fipronil, quando comparados com os ratos do grupo controle. No LCE, a exposição prolongada de ratos ao fipronil nas doses de 1,0 e 10,0 mg/Kg provocou redução na distância percorrida pelos animais e o tempo de permanência dos animais nos braços abertos, além de aumentar o tempo de permanência nos braços fechados. Para o cálculo da dose convulsivante mínima, seguiu-se o mesmo protocolo de tratamento, sendo observada diminuição significante na dose de picrotoxina e de pentilenotetrazol necessária para a indução da convulsão em animais tratados com 10,0 mg/Kg fipronil. A determinação dos níveis de neurotransmissores e seus respectivos metabólitos mostrou aumento dos níveis de dopamina no córtex frontal de ratos tratados com 10,0 mg/Kg de fipronil, redução nos níveis de GABA no striatum de ratos tratados com 1,0 mg/Kg de fipronil. Em relação à serotonina houve aumento de seus níveis no córtex frontal de ratos tratados com 1,0 mg/Kg e seu metabólito, ácido 5 (5HIAA), foi observado redução de seus níveis no córtex frontal de ratos tratados com 0,1 e 1,0 mg/kg p.c. de fipronil. No striatum também houve redução de seus níveis em ratos tratados com 0,1 e 1,0 mg/Kg de fipronil. O estudo anátomo-histopatológico revelou que a exposição prolongada ao fipronil pode causar hepatotoxicidade, caracterizada por aumento dos pesos absoluto e relativo do fígado e tumefação celular de hepatócitos. Em conclusão, os resultados mostraram que a exposição de ratos por 28 dias, via gavage, ao fipronil pode causar efeitos comportamentais relacionados a alterações em sistemas centrais de neurotransmissão e também hepatotoxicidade. / Fipronil is a phenylpyrazole insecticide with broad spectrum, developed to selectively inhibit insect GABA-gated chloride channels; both in Veterinary Medicine, and in Agriculture it has been used for the control of nuisances. Although several studies try to understand the mechanism of neuronal toxicity of pesticide in mammalian, there are few studies related to neurobehavioral effects. Thus, the present study investigated the effects of fipronil long term exposure in rats, being observed some behaviors connected to GABAergic system, as activity in open field, in elevated plus maze (EPM), as well as in the seizures induced by picrotoxinin and pentylenotetrazole. In addition, this study determinated the brain levels of some neurotransmitter as GABA, dopamine, noradrenaline, serotonin and metabolic levels and investigated liver, brain and kidney damage. Wistar rats received by intragastric (gavage) way during 28 days one of this treatment: fipronil (0,1, 1,0 or 10,0 mg/Kg) or distilled water; the rats behavior were evaluated in open field and elevated plus maze apparatus with system computer EthoVision®. There was a significant reduction of rearing in open field in rats treated with 10,0 mg/Kg of fipronil when compared with control rats. In the EPM, there was a decrease of distance moved in open arms and increase of time spent in closed arms to rats treated with 1,0 and 10,0 mg/Kg of fipronil when compared to control. It was still noticed the reduction in the time spent in open arms EPM in rats treated with 1,0 and 10,0 mg/Kg of fipronil when compared to control group. To calculate the minimum convulsant dose, was used the same treatment protocol and it was observed a significant reduction in picrotoxinin and pentylenotetrazole necessary dose to induction of seizure in animals treated with fipronil 10,0 mg/Kg. The level determination of neurotransmitters and their metabolites, it was observed the dopamine increasing in forebrain from fipronil treated rats by 10,0 mg/Kg. GABA levels decreased in fipronil treated rats striatum by 1,0 mg/Kg. Serotonin neurotransmitter was increased in fipronil treated rats forebrain by 1,0 mg/Kg to and its metabolite, 5HIAA, it was observed a levels decrease in fipronil forebrain treated rats by 0,1 e 1,0 mg/kg. There was decrease of 5HIAA levels in fipronil treated rats striatum by 0,1 e 1,0 mg/Kg. According to organ analyses, it was observed dose-response liver damage such as swelling liver cells. In conclusion, the data showed that fipronil administered in rats by 28 days caused behavioral effects related to central neurotransmitter alterations and hepatotoxicity.

A hipóxia mantida de curta duração (HM) está associada a alterações cardiorrespiratórias e ao desencadeamento de processo inflamatório em humanos e modelos experimentais. Ademais, há evidências de que a HM pode alterar a transmissão sináptica na região do Núcleo do Trato Solitários (NTS). No presente estudo, utilizamos a minociclina, um inibidor da ativação microglial e antiinflamatório, para avaliar a influência da inflamação desencadeada pela HM sobre a neurotransmissão glutamatérgica nos neurônios do NTS que enviam projeções para a região ventrolateral da medula (NTS-VLM). A hipótese geral do nosso estudo foi a seguinte: a HM induz processo inflamatório no tronco encefálico, o qual contribui para o aumento da neurotransmissão glutamatérgica em neurônios NTS-VLM, colaborando para a elevação da pressão arterial média (PAM) observada nestes ratos. Embora tenhamos observado aumento da pressão arterial média em ambos os grupos de ratos tratados com veículo (solução salina + água destilada, ip) ou minociclina [(30mg/Kg ip por 3 dias) submetidos a 24h de HM (FiO2 0.1) em relação aos seus respectivos grupos controle (FiO2 0,28), o aumento da MAP foi menor nos ratos previamente tratados com minociclina. Os registros eletrofisiológicos utilizando a técnica de whole cell patch-clamp mostraram que a HM não produziu alterações nas propriedades ativas e passivas dos neurônios NTS-VLM. No entanto, os neurônios de ratos submetidos a HM apresentaram aumento nas correntes glutamatérgicas espontâneas e evocadas pelo estímulo do trato solitário. Esse grupo de animais também apresentou aumento no número de microgliais na região do NTS. As alterações mencionadas foram atenuadas pelo tratamento prévio com minociclina. Concluímos que a inflamação induzida pela HM contribui para o aumento da neurotransmissão glutamatérgica nos neurônios NTS-VLM o qual poderia estar relacionado com a hipertensão arterial observada nestes ratos. / Short-term Sustained hypoxia (SH) is associated with cardiorespiratory changes and inflammatory process in humans and experimental models. There is also evidence that SH can change the synaptic transmission in the nucleus tractus solitarius (NTS) region. Here we use the minocycline, an anti-inflammatory and microglial inhibitor, to evaluate the role of inflammation triggered by SH on the excitatory neurotransmission in the NTS neurons sending projections to the ventrolateral medulla (NTS-VLM). We hypothesized that SH induces brainstem inflammatory process, which may contribute to increase in excitatory neurotransmission and excitability of the NTS-VLM neurons, collaborating to the high blood pressure observed on these rats. Although we have observed increased MAP in both groups of rats treated with vehicle (saline + distilled water, i.p) or minociclina [(30mg/Kg i.p for 3 days) submitted to 24h of SH (FiO2 0.1) in relation to their respective control groups (FiO2 0.28), the MAP increase was lower in rats treated with minociclina. The whole cell patch-clamp recordings showed that SH produced no changes in active properties of NTS neurons. However, neurons of rats submitted SH presented an increase in the glutamatergic neurotransmission and the number of microglial at the NTS region. These increases were prevented in the groups previously treated with minociclina. We conclude that inflammation induced by SH contributes to the increased excitatory neurotransmission in NTS-VLM neurons that could be associated to high blood pressure observed in these rats.

La polarité et l'efficacité de la transmission GABAergique dépendent de la concentration intra-neuronale en chlore. Dans les neurones matures, le co-transporteur K+/Cl- KCC2 maintient la concentration intracellulaire en chlore à un niveau bas, permettant ainsi une réponse inhibitrice du GABA. En plus de son rôle dans la transmission GABAergique, KCC2 régule aussi l'efficacité de la transmission glutamatergique en contrôlant la spinogenèse, l'exocytose et la dynamique membranaire des récepteurs AMPA. Du fait de son importance aux synapses excitatrices et inhibitrices, il est crucial de comprendre les mécanismes qui régulent l'expression membranaire et la fonction de KCC2. La régulation de KCC2 par l'activité glutamatergique excitatrice ayant été bien caractérisée, il reste à déterminer si l'expression et la fonction de KCC2 sont régulées par l'activité inhibitrice GABAergique. Pendant ma thèse, j'ai montré que KCC2 est en effet directement régulé par la transmission GABAergique. J'ai trouvé que l'activation aigue des RGABAA confine KCC2 dans la membrane alors que le blocage des RGABAA augmente la dynamique membranaire et l'internalisation du transporteur. Les mécanismes moléculaires impliquent le chlore comme messager secondaire, la kinase WNK1 et la phosphorylation de KCC2 sur des résidus thréonines clés. J'ai ensuite pu montrer que cette régulation à un impact aux synapses inhibitrice et excitatrice. Mon travail propose un mécanisme nouveau de la régulation de l'homéostasie du chlore par l'inhibition GABAergique. Ainsi les neurones peuvent compenser une augmentation ou une diminution en chlore neuronale par une adaptation rapide de KCC2 à la surface cellulaire. / The polarity and efficacy of GABAergic neurotransmission depends on the intraneuronal chloride concentration. In mature neurons chloride extrusion by the K+/Cl- co-transporter KCC2 permits an inhibitory influx upon activation of GABAA receptors. In addition to its role in GABAergic transmission, KCC2 regulates also glutamatergic transmission in an ion-independent manner by controlling spinogenesis and AMPAR exocytosis and membrane diffusion in dendritic spines. Knowing its pivotal role at central synapses, it is of particular importance to understand the cellular and molecular mechanisms underlying its regulation. While regulation of KCC2 by neuronal excitation is well documented, it is still unknown whether neuronal inhibition itself can regulate the transporter’s membrane expression and/or activity. During my PhD I was able to demonstrate a direct regulation of KCC2 membrane diffusion and stability by GABAA receptor-mediated inhibition and I characterized the underlying signaling cascade. I found that activation of GABAAR decreased KCC2 lateral diffusion while GABAAR blockade led to increased membrane dynamics and internalization of the transporter. I could show that KCC2 regulation by neuronal inhibition requires chloride as second intracellular messenger and chloride-sensing WNK1 kinase that directly phosphorylate KCC2 on key Threonine residues. This regulation has a functional impact at both excitatory and inhibitory synapses. My work reports a novel and rapid mechanism of control of chloride homeostasis by GABAA receptor-mediated inhibition that allows maintaining the polarity and activity of GABAA receptors constant.

The serotonergic and cholinergic systems are jointly involved in regulating sleep but this balance is theorized to be disturbed in depressed individuals (Janowsky 1972, Jouvet 1972). One potential cause of disturbed neurotransmission is genetic predisposition. The G(-1019) allele of the 5-HT1A receptor predicts an increased risk for depression compared to the wild-type C(-1019) allele. The goal of this study was to use pharmacological probes in normal controls to model the serotonergic/cholinergic imbalance of depression and its associated abnormalities in sleep structure while controlling for 5-HT1A receptor genotype. Seventeen healthy female participants homozygous for either C (n=11) or G (n=6) alleles, age 18-27 years were tested on four non-consecutive nights. Participants were given galantamine (an anti-acetylcholinesterase), buspirone (a serotonergic agonist), both drugs together, or placebos before sleeping. Buspirone suppressed tonic REM: there was a significant increase in REM latency (p<0.001). Galantamine increased tonic REM sleep, leading to more time spent in stage REM (p<0.001) and shorter REM latency (p<0.01). Galantamine and buspirone given together tended to negate the effects of each other on REM sleep measures but disrupted sleep more than either drug alone, showing lower SE and N3% and increased awakenings, Wake% and N1% (p<0.019). There was no main effect of genotype nor was there a significant multivariate interaction between genotype and drug condition. These findings are partially consistent with the literature about sleep in depression, notably short REM latency, higher percentage of total sleep time spent in REM, and increased sleep fragmentation. The C/G mutation in the 5-HT1A receptor does not appear to cause noticeable differences in the sleep patterns of healthy young females.

Dopamine is an important neurotransmitter in the brain, where it plays a regulatory role in the coordination of movement and cognition by acting through two classes of G protein-coupled receptors to modulate synaptic activity. In addition, it has been shown these two receptor classes can exhibit synergistic or antagonistic effects on neurotransmission. However, while the pharmacology of the mammalian dopamine receptors have been characterized in some detail, less is known about the molecular pathways that act downstream of the receptors. As in mammals, the soil nematode Caenorhabditis elegans uses two classes of dopamine receptors to control neural activity and thus can serve as a genetic tool to identify the molecular mechanisms through which dopamine receptors exert their effects on neurotransmission. To identify novel components of mammalian dopamine signaling pathways, we conducted a genetic screen for C. elegans mutants defective in exogenous dopamine response. We screened 31,000 mutagenized haploid genomes and recovered seven mutants. Five of these mutants were in previously-identified dopamine signaling genes, including those encoding the Ga proteins GOA-1 (ortholog of human Gao) and EGL-30 (ortholog of human Gaq), the diacylglycerol kinase DGK-1 (ortholog of human DGK0), and the dopamine receptor DOP-3 (ortholog of human D2-like receptor). In addition to these known components, we identified mutations in the glutamate-gated cation channel subunit GLR-1 (ortholog of human AMPA receptor subunits) and the class A acetycholinesterase ACE-1 (ortholog of human acetylcholinesterase). Behavioral analysis of these mutants demonstrates that dopamine signaling controls acetylcholine release by modulating the excitability of the cholinergic motor neurons in C. elegans through two antagonistic dopamine receptor signaling pathways, and that this antagonism occurs within a single cell. In addition, a mutation in the putative Rab GTPase activating protein TBC-4 was identified, which may suggest a role for this Rab GAP in synaptic vesicle trafficking. Subsequent behavioral and genetic analyses of mutants in synaptic vesicular trafficking components implicate RAB-3-mediated vesicular trafficking in DOP-3 receptor signaling. These results together suggest a possible mechanism for the regulation of dopamine receptor signaling by vesicular trafficking components in the cholinergic motor neurons of C. elegans.

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No / Most inhibitory signals are mediated via γ-aminobutyric acid (GABA) receptors whereas glutamate receptors mediate most excitatory signals (Trends Neurosci 14:515–519, 1991; Annu Rev Neurosci 17:31–108, 1994). Many factors influence the regulation of excitatory and inhibitory synaptic inputs on a given neuron. One important factor is the subtype of neurotransmitter receptor present not only at the correct location to receive the appropriate signals but also their abundance at synapses (Pharmacol Rev 51: 7–61, 1999; Cold Spring Harb Perspect Biol 3, 2011). GABAB receptors are G-protein-coupled receptors and different subunits dimerise to form a functional receptor. GABAB receptor subunits are widely expressed in the brain and by assembling different isoform combinations and accessory proteins they produce variety of physiological and pharmacological profiles in mediating both inhibitory and excitatory neurotransmission. This chapter will describe the understanding of the molecular mechanisms underlying GABAB receptor regulation of glutamate and GABAA receptors and how they modulate excitatory and inhibitory neurotransmission.

Le cervelet est une structure cérébrale impliquée dans la régulation motrice. Dans le cortex cerebelleux, les informations sensorimotrices sont transmises par les cellules en grain. Mon travail de thèse démontre que les connections synaptiques de ces neurones ont des propriétés hétérogènes. D’une synapse à l’autre, j’ai pu observer des variations d’ultrastructure, de composition moléculaire et de fonctionnement au cours de trains de potentiels d’action à haute fréquence. Plus particulièrement, j’ai caractérisé les propriétés de « plasticité à court terme » des synapses unitaires des cellules en grain : 1) Elles sont très différentes d’une synapse à l’autre et peuvent être classées en différentes sous-catégories. 2) Certaines catégories de fonctionnement synaptique reposent sur l’expression de molécules telles que la Synapsine2. 3) La réponse d’un neurone post-synaptique à de hautes fréquences de stimulation dépend de la nature de la synapse activée. / Cerebellum is a brain structure involved in motor regulation and motor learning. In the cerebellar cortex, sensorimotor information is transmitted by granule cells. During my PhD, I demonstrated that the properties of individual granule cell synaptic connections are highly heterogeneous. From one synapse to another, I observed ultrastructural, molecular and functional variability at unitary contacts. More precisely, I assessed the properties of short term plasticity at individual synapses during high frequency trains of stimulation :1) Short term plasticities are highly heterogeneous from one synapse to another and can be classified in sub-categories.2) Some categories of short-term plasticity profiles relie on the expression of molecules such as Synapsin2.3) The response of post-synaptic neuron to high-frequency inputs is dependent on the nature of the activated synaptic contact.

Le système endocannabinoïde (SEC) a récemment émergé comme un important modulateurde la prise alimentaire et de la balance énergétique. Les récepteurs cannabinoïdes de type 1(récepteurs CB1) et ses ligands endogènes, le 2-arachidonoyl-glycérol (2-AG) et l’anandamide(AEA), sont largement présents au sein du cerveau ainsi qu’au niveau des organespériphériques impliqués dans la régulation du métabolisme énergétique, tels que le foie, letissu adipeux, les muscles squelettiques, le pancréas et le tractus gastro-intestinal. Lastimulation pharmacologique des récepteurs CB1 conduit généralement à une augmentation dela prise et du stockage énergétique, tandis que les antagonistes CB1 exercent les effets opposéschez l’animal ainsi que chez l’homme. De surcroît, des corrélations ont été établies entre unesur régulation pathologique du SEC et les troubles métaboliques.Pourtant, plusieurs preuves indiquent que la relation entre le SEC et le métabolismeénergétique pourrait être plus complexe, probablement à cause de la multiplicité des sites oùle SEC peut agir à travers l’organisme. L’objectif général de ce travail de thèse fut dedisséquer les différents mécanismes par lesquels le SEC régule la prise alimentaire etl’équilibre énergétique. Le premier Chapitre de cette thèse détaille les mécanismes neuronauxmodulant l’équilibre énergétique chez les mammifères. Dans le Chapitre II, nous analysonsles différents types neuronaux cérébraux responsables de l’impact de la signalisation desrécepteurs CB1 sur la prise alimentaire stimulée. Dans le Chapitre III, nous proposons que leblocage pharmacologique des récepteurs CB1 exerce un effet anorexigène en agissant sur lesneurones périphériques sympathiques. Enfin, au cours du Chapitre IV nous disséquons le rôlepossible des récepteurs CB1 sur la balance énergétique.Les antagonistes CB1 ont été montrés comme n’exerçant que des effets anorexigènestransitoires, ceux-ci disparaissant après quelques semaines de traitement chez l’animal etquelques mois chez des patients obèses. De plus, les agonistes CB1 résultent en des effets biphasiques typiques. En effet, des doses faibles à modérées augmentent la prise alimentairechez l’animal tandis que de fortes doses diminuent les comportements d’ingestion. Lesrécepteurs CB1 sont exprimés sur différentes populations neuronales, dont les neuronesGABAergiques et glutamatergiques corticaux. Puisque l’activation des récepteurs CB1 induitgénéralement une réduction de la libération des neurotransmetteurs, il est probable que leseffets manifestement contradictoires des manipulations pharmacologiques soient dus à cetteexpression différentielle des récepteurs CB1. En combinant les approches pharmacologiqueset génétiques, nous avons montré que les récepteurs CB1 localisés au niveau du striatumventral sont associés à une action hypophagique via une inhibition de la transmissionGABAergique. Au contraire, les récepteurs CB1 cérébraux modulant les transmissionsexcitatrices sous-tendent l’effet orexigène bien connu des cannabinoïdes (Chapitre II).L’injection aiguë de l’antagoniste CB1, le SR141716 (Rimonabant) a un puissant effetanorexigène dans des conditions de prise alimentaire stimulée, telles que l’hyperphagieinduite par le jeûne. Néanmoins, la nature de cet effet (centrale versus périphérique) ainsi queles circuits neuronaux impliqués sont encore objets d’investigations. Dans le Chapitre III,nous mettons en évidence que l’hypophagie induite par le Rimonabant est indépendante d’unemodulation des transmissions GABAergique, glutamatergique corticale ou sérotoninergiquepar les récepteurs CB1 dans le cerveau, aussi bien que d’actions intrinsèques des récepteursCB1 au niveau de différents noyaux hypothalamiques. En fait, le Rimonabant inhibe la prisealimentaire stimulée en potentialisant directement l’activité du système périphériquesympathique.En ce qui concerne les fonctions métaboliques du SEC, il n’est actuellement pas encoreclairement établi si ce sont les récepteurs CB1 exprimés sur les neurones ou ceux localisés surles organes métaboliques périphériques qui jouent un rôle majeur dans le contrôle du stockageet de la consommation énergétique dans des conditions physiologiques ou pathologiques.Dans ce scenario, au Chapitre IV, nous montrons que les récepteurs CB1 neuronaux jouent unrôle clé dans le développement de l’obésité induite par la diète. Les souris mutantesconditionnelles caractérisées par une délétion des récepteurs CB1 au niveau des neurones duprosencéphale et des neurones périphériques sympathiques (connus pour contrôler la prisealimentaire et le poids corporel) mais pas au niveau des organes périphériques, exhibent unphénotype de type mince ainsi qu’une résistance à l’obésité induite par la diète. Ce phénotyperésulte d’une augmentation de l’oxydation des lipides et de la thermogenèse associée à unediminution de l’absorption énergétique due à une potentialisation de l’activité sympathique.Dans le Chapitre V, nous discutons de la signalisation neuronale des récepteurs CB1 commeune clé déterminante de l’action du SEC sur l’équilibre énergétique. Nous proposons que lesrécepteurs CB1 exercent un contrôle bimodal sur le comportement alimentaire et régulent lesdépenses énergétiques ainsi que l’activité du système nerveux sympathique. Les différencesentre le rôle des agonistes endogènes versus exogènes des récepteurs CB1, mais aussi entre lesagonistes versus antagonistes suggèrent que ces récepteurs pourraient bénéficier de propriétéspharmacologiques particulières à la signalisation du type cellulaire impliqué. / The endocannabinoid system (ECS) has recently emerged as an important modulator of foodintake and energy balance. Cannabinoid type-1 (CB1) receptor and endogenous ligands, 2-arachidonoyl-glycerol (2-AG) and anandamide (AEA), are largely present in the brain and inperipheral organs involved in the regulation of energy metabolism, such as liver, adiposetissue, skeletal muscle, pancreas and GI tract. Pharmacological CB1 stimulation generallyleads to an increase in energy intake and storage, whereas CB1 antagonists exert the oppositeeffects in both animals and humans. Furthermore, there is evidence of correlations betweenpathological ECS up-regulation and metabolic diseases.However, several pieces of evidence indicate that the relationship between the ECS andenergy intake and metabolism might be more complex than previously believed, likely due tothe different sites where the ECS could act in the body. The general aim of this Thesis workwas to dissect the different mechanisms through which the ECS regulates food intake andenergy balance. The first Chapter of this Thesis is an overview of the neuronal mechanismsregulating energy balance in mammals. In Chapter II, we analysed the brain neuronal typesresponsible of the impact of CB1 signalling on stimulated food intake. Chapter III, reveals thatthe pharmacological blockade of CB1 exerts anorectic effect acting at peripheral sympatheticneurons. Then (chapter IV) we dissected the possible impact of neuronal CB1 onto energybalance.CB1 antagonists were shown to exert only transient anorectic effects, which disappear afterfew weeks of treatment in animals and few months in obese patients. Furthermore, CB1agonists show typical biphasic effects, with low-to-moderate doses increasing food intake inanimals, and high doses decreasing ingestive behaviour. CB1 is expressed in many differentneuronal populations, including GABAergic and cortical glutamatergic neurons. As thegeneral effect of CB1 activation is a reduction of neurotransmitter release, it is possible thatthese apparently discrepant effects of pharmacological manipulations are due to thedifferential expression of the receptor. By using combined pharmacological and geneticapproaches we found that ventral striatal CB1 receptors are endowed with a hypophagicimpact through inhibition of GABAergic transmission. Conversely, brain CB1 receptorsmodulating excitatory transmission mediate the well-known orexigenic effects ofcannabinoids (Chapter II).The acute injection of CB1 antagonist SR141716 (Rimonabant) has an important anorecticeffect in condition of stimulated food intake, such as fasting-induced hyperphagia. However,the nature of this effect (central versus peripheral) as well as the neuronal circuits involved isstill matter of investigation. In Chapter III we show that rimonabant-induced hypophagia isindependent from CB1 modulation of GABAergic, cortical glutamatergic and serotoninergictransmission in the brain, as well as intrinsic actions of CB1 in different hypothalamic nuclei.In fact, rimonabant inhibits stimulated food intake by directly enhancing peripheralsympathetic actions.In relationship to metabolic functions of the ECS, it is not yet clear whether CB1 receptorsexpressed on neurons or on peripheral metabolic organs play a major role in the control ofenergy storage and consumption in both physiological and pathological conditions. In thisscenario, in Chapter IV, we show that neuronal CB1 receptors play a key role in thedevelopment of diet-induced obesity. Conditional mutant mice lacking CB1 expression inforebrain neurons and sympathetic peripheral neurons, known to control food intake and bodyweight, but not in peripheral organs, displayed a lean phenotype and resistance to diet-inducedobesity. This phenotype results from an increase in lipids oxidation and thermogenesis and adecrease in energy absorption due to an increase of the sympathetic tone.As discussed in the Chapter V, neuronal CB1 signalling is a key determinant of the ECSaction on energy balance, by exerting a bimodal control of feeding behaviour and byregulating energy expenditure and sympathetic nervous system activity. The differencesbetween the role of endogenous versus exogenous CB1 agonists, as well as between agonistsversus antagonists suggest that this receptor may have different pharmacological propertiesaccording to the cell type-specific signalling involved.