No description available.

No description available.

This thesis focuses on elucidating the electrical mechanisms underlying excitation of small intestinal and colonic smooth muscle initiated by interstitial cells of Cajal (ICC). All the ICC subtypes are involved in the orchestration, generation, and/or transmission of electrical signals to smooth muscle to pace gut motor patterns. Some ICC types have intrinsic activity leading to omnipresent rhythmic changes in smooth muscle excitability; others respond to stimuli, inducing pacemaker activity as required. Together they orchestrate motor patterns such as propulsion and segmentation, essential functions of the gut. To study ICC electrophysiology, I utilized patch clamping to record ion channel currents from single intestinal ICC and sharp microelectrodes to record colonic smooth muscle membrane potentials. I have made several discoveries contributing to our understanding of ICC electrophysiology. Firstly, my research increased our understanding of the properties of intrinsic pace-maker activity. I showed that maxi Cl– channels from small intestinal ICC make a significant contribution to slow wave depolarization triggered by intracellular calcium. Secondly, I showed that colonic intramuscular ICC (ICC-IM) selectively express KV7.5 channels, which are suppressed by cholinergic agonists, meaning that excitatory stimuli triggering acetylcholine release deactivate KV7.5 channels, leading to increased excitability. Thirdly, I have shown that the bile acid chenodeoxycholic acid and the nitric oxide donor sodium ni-troprusside both induce pacemaker activity, rhythmic transient depolarisations in mouse colonic muscle, which led to the hypothesis that nitrergic nerves are involved in generating inducible myenteric plexus ICC (ICC-MP) pacemaker activity. It is only when ICC are suitably stimulated by intracellular processes such as rhythmic Ca2+ transients or extracellular signalling from neurotransmitters or small molecules, that ICC produce membrane potential rhythmicity, required for generation of intrinsic slow waves, low-frequency rhythmic transient depolarisations and transmission of excitation into the muscle. / Thesis / Doctor of Philosophy (PhD) / The gut is essential for digestion and absorption of food. The gut has special cells called interstitial cells of Cajal (ICC), which control the contractions of the gut muscle. ICC are pacemaker cells, like those that pace heart beats. To pace gut muscle contractions, ICC generate electrical signals which cause the muscle to contract in an organized rhythmic manner, which promotes mixing or propulsion of gut contents, called motility. I used tiny electrodes to record electrical activity from ICC or gut muscle, to improve our understanding of how ICC pacemaker activity controls motility. My research characterised ion channels, which are microscopic protein pores that allow cells to make electrical currents, that enable generation of pacemaker signals by ICC. I also investigated activation of ICC electrical activity that causes propulsive colonic motility. This will hopefully lead to treatment improvements for patients with motility disorders in the future.

Los receptores cys-loop pertenecen a la familia de canales iónicos pentaméricos activados por ligandos (pLGICs). Se expresan ampliamente en el sistema nervioso, donde ejercen un rol vital en la comunicación neuronal. Están involucrados en los procesos de aprendizaje, memoria, movimiento, entre otros. Se han asociado alteraciones en la funcionalidad de estos receptores con una gran variedad de desórdenes neurológicos, tales como enfermedad de Alzheimer, enfermedad de Parkinson, epilepsia, síndromes miasténicos, esquizofrenia y depresión. Por ello, los receptores cys-loop son importantes blancos farmacológicos. En consecuencia, consideramos que el conocimiento de los mecanismos moleculares que conducen a su activación y disfunción es de suma relevancia. Los receptores Cys-loop están formados por un dominio extracelular, que contiene los sitios de unión de agonista, y un dominio transmembrana, que forma el poro iónico. La interfase entre ambos dominios, llamada región de acoplamiento, desempeña un rol clave en la propagación de los cambios conformacionales que se inician con la unión del agonista en la región extracelular y culminan con la apertura del poro iónico a nivel transmembranal. En este trabajo de Tesis Doctoral estudiamos dos regiones claves en el proceso de activación de los receptores Cys-loop: el sitio de unión de agonista, donde comienza la respuesta, y la interfase entre los dominios extracelular y transmembrana o región de acoplamiento. Utilizamos receptores homopentaméricos que por estar compuestos por cinco subunidades iguales, poseen cinco sitios de unión de agonista y cinco regiones de acoplamiento idénticas. Los receptores homoméricos surgieron más tempranamente en la escala evolutiva por lo que presentan características estructurales y funcionales comunes a todos los miembros Cys-loop, y son, por lo tanto, modelos útiles para el estudio de los receptores de esta familia. En el Capítulo I de esta Tesis determinamos el número de regiones de acoplamiento necesario para la activación de los receptores Cys-loop y su relación con los sitios de unión de agonista. Para ello, utilizamos como modelo de receptor homopentamérico al receptor quimérico a7-5HT3A, compuesto por secuencias del receptor a7 en su dominio extracelular y secuencias del receptor 5-HT3A en su dominio transmembrana, el que ha sido ampliamente utilizado como modelo de a7. Para conocer la contribución de cada una de las cinco regiones de acoplamiento a la estabilidad de canal abierto del receptor a7-5HT3A, empleamos nuestra estrategia experimental denominada electrical fingerprinting. Según esta estrategia, co-transfectamos células con una subunidad conteniendo la región de acoplamiento activa y otra subunidad conteniendo la región de acoplamiento inactiva, una de ellas conteniendo además mutaciones reporteras de conductancia. De esta forma, logramos expresar en membrana receptores con distinto número de regiones de acoplamiento funcionales que son identificados mediante registros de patch-clamp de canal único. Gracias a la presencia de las mutaciones reporteras de conductancia, la medición de la amplitud de cada apertura nos permitió conocer la estequiometria del receptor, es decir, el número de subunidades con región de acoplamiento funcional que tiene el receptor pentamérico que dio origen a esa apertura. Determinamos la duración de los eventos de apertura provenientes de receptores con distinto número de regiones de acoplamiento funcionales, que constituye una medida de la estabilidad de canal abierto. Encontramos que cada región de acoplamiento contribuye en forma independiente y simétrica a la estabilidad del canal abierto y que son necesarias las cinco regiones de acoplamiento funcionales para lograr la óptima activación del receptor. Demostramos además que la presencia de una sola región de acoplamiento funcional en el pentámero es suficiente para lograr la activación pero no permite mantener el canal abierto en su tiempo óptimo. Además generamos receptores a7-5HT3A mutantes, que contenían distinto número de sitios de unión de agonista y regiones de acoplamiento funcionales. Esta estrategia nos permitió establecer los requisitos estructurales mínimos que logran la activación del receptor, así como también los requerimientos estructurales que conducen a la máxima estabilidad del estado abierto. Encontramos que el receptor es capaz de responder al agonista mediante la ocupación de un único sitio si este se encuentra formado por dos subunidades con regiones de acoplamiento funcionales. Sin embargo, para lograr la óptima activación y duración máxima del canal abierto, el receptor modelo utilizado requiere de tres sitios de unión de agonista funcionales y sus cinco regiones de acoplamiento intactas. En el Capítulo II, estudiamos la activación del receptor neuronal a7 en condiciones de sub-ocupación de sus cinco sitios de unión de agonista. Este receptor se localiza principalmente en sitios distantes a los sitios de síntesis y liberación de acetilcolina (ACh), por lo que la ACh, o su producto colina, deben difundir y unirse a receptores a7 distantes. Este mecanismo colinérgico no sináptico predice que el grado de ocupación de los receptores a7 sería bajo en condiciones fisiológicas. Para estudiar la activación del receptor a7 en condiciones de sub-ocupación de sus sitios de agonista, realizamos ensayos electrofisiológicos y medimos la duración del canal abierto de receptores individuales que presentan un único sitio de unión de agonista funcional, y la comparamos con la de receptores que tienen sus cinco sitios funcionales. Para conocer el número de sitios de unión de agonista funcionales empleamos nuevamente la estrategia electrical fingerprinting. Esta estrategia requiere la medición exacta de la amplitud. Teniendo en cuenta que los receptores a7 presentan aperturas de duración breve que no permiten la resolución de su máxima amplitud, los estudios electrofisiológicos se realizaron sobre receptores a7 mutados o en presencia de potenciadores que aumentan la duración del canal abierto. En este trabajo, demostramos que la estabilidad del canal abierto de receptores a7 que presentan un único sitio de unión de agonista funcional es la misma que la de los receptores que presentan sus cinco sitios disponibles. Por otro lado, cuando reemplazamos el dominio transmembrana del receptor a7 por el del receptor 5-HT3A, encontramos que la duración del canal abierto se incrementa al aumentar el número de sitios ocupados por agonista. Este resultado demuestra por primera vez que el dominio extracelular no es el único determinante de la relación entre ocupación y estabilidad del canal abierto. Por lo tanto, en este trabajo demostramos la capacidad del receptor a7 de activarse y producir respuestas máximas con la ocupación de un solo sitio de unión de agonista, propiedad que es única y exclusiva de este receptor dentro de todos los miembros de la familia de receptores Cys-loop. Este resultado posee además relevancia fisiológica dado que esta propiedad le permitiría al receptor adaptarse al mecanismo de transmisión no sináptico. En su conjunto, los resultados que surgen de esta Tesis revelan una novedosa relación funcional entre dos dominios estructurales de estos receptores, el sitio de unión de agonista y la región de acoplamiento, y, además, contribuyen al conocimiento general del mecanismo de activación de los receptores de la familia Cys-loop. / Cys-loop receptors belong to the family of pentameric ligand-gated ion channels (pLGICs). They are widely expressed in the nervous system, where they exert a vital role in neuronal communication. They are involved in learning, memory, movement processes, among others. Functional disorders of these receptors have been associated with several neurological disorders, such as Alzheimer's disease, Parkinson's disease, epilepsy, myasthenic syndromes, schizophrenia and depression. Because Cys-loop receptors are important pharmacological targets for the development of therapies, the knowledge of the molecular mechanisms leading to activation and dysfunction of these receptors is of great importance. Cys-loop receptors contain an extracellular domain that carries the agonist binding sites and a transmembrane region that forms the ion pore. The interface between both domains, named as the coupling region, plays a key role in the propagation of the conformational changes from the binding site at the extracellular domain to the pore, located at the transmembrane region. In this Thesis, we studied two key regions that are essential for the activation process of Cys-loop receptors: the agonist binding site, where the response begins, and the interface between the extracellular and transmembrane domains or coupling region. We used homopentameric receptors that contain five identical subunits, and therefore five identical agonist binding sites and coupling regions. Because homomeric receptors appeared earlier on the evolutionary scale, they present structural and functional features that are common to all Cys-loop members, and are therefore useful models for the study of this receptor family. In Chapter I of this Thesis we studied the number of coupling regions necessary for Cys-loop receptor activation and evaluated the functional relationship of this domain with the agonist binding sites. To this end, we used a model of homopentameric receptor, the a7-5HT3A chimeric receptor, which contains a7 sequences in the extracellular domain and 5-HT3A sequences in the transmembrane domain. To determine the contribution of each of the five coupling regions to the stability of the open channel, we used our experimental strategy which is called electrical fingerprinting. For this strategy, cells were co-transfected with a subunit with an active coupling region and another subunit with an inactive coupling region, one of which carrying reporter conductance mutations, to generate receptors with different number of functional coupling regions. Next, we performed single-channel recordings to identify functional receptors using the patch-clamp technique. Due to the introduction of reporter conductance mutations, the measurement of the amplitude of each opening event allowed us to know receptor stoichiometry, i.e., the number of subunits with functional coupling region present in the pentameric receptor which originated the event. We measured open channel duration of receptors with different numbers of functional coupling regions, which indicates the open channel stability. We found that each coupling region contributes independently and symmetrically to open channel stability. We showed that five coupling regions are necessary to achieve optimal receptor activation and that the presence of only one functional coupling region is sufficient for receptor activation, but with reduced open channel duration. Furthermore, we constructed a7-5HT3A mutant receptors, containing different number of agonist binding sites and functional coupling regions. This strategy allowed us to establish the minimum structural requirements for receptor activation as well as the structural requirements for maximal open channel stability. We found that a7-5HT3A receptors are capable of responding to agonist by occupying a single agonist binding site, only if this site is formed by two subunits carrying functional coupling regions. However, to achieve optimal activation and maximal open channel duration, the model receptor requires three functional agonist binding sites and five functional coupling regions. In Chapter II, we studied a7 neuronal receptor activation under sub-occupancy conditions of its five agonist binding sites. In the brain, this receptor is mainly located at distant sites from the sites of synthesis and release of acetylcholine (ACh), so ACh, or its product choline, diffuse to bind distant a7 receptors. This non-synaptic cholinergic mechanism predicts that the degree of a7 receptor occupancy is low under physiological conditions. To study a7 activation under sub-occupancy conditions we performed single-channel recordings and measured open channel duration of receptors with only one functional agonist binding site, and compared it with that of receptors containing their five intact agonist binding sites. To know the number of agonist binding sites, we employed again the electrical fingerprinting strategy. This strategy requires accurate measurement of open channel amplitude. Because the brief duration of a7 opening events do not allow full amplitude resolution, single-channel recordings were performed in either a7 mutant receptors or in the presence of potentiators that increase open channel duration. In this work, we demonstrated that open channel stability of receptors with a single agonist binding site is the same as that of receptors containing five functional sites. Moreover, when we replaced the transmembrane domain of a7 receptors by that of 5-HT3A receptor, we found that open channel lifetime increases as the number of sites occupied by agonist increases. This result shows for the first time that the extracellular domain is not the only determinant of the relationship between occupancy and open channel stability. Therefore, in this work we demonstrated the ability of a7 receptor for activation and eliciting maximal responses with occupancy of only one agonist binding site, a property that is unique for a7 among all members of the Cys-loop family. This result has a physiological relevance since this property would allow a7 receptors to adapt to their non-synaptic mechanism. Taken together, the results that emerge from this Thesis reveal a novel functional relationship between two structural domains, the agonist binding site and the coupling region, and contribute to the general knowledge of the activation mechanism of Cys-loop receptors.

Yes / Sublethal carbon monoxide (CO) exposure is frequently associated with myocardial arrhythmias, and our recent studies have demonstrated that these may be attributable to modulation of cardiac Na+ channels, causing an increase in the late current and an inhibition of the peak current. Using a recombinant expression system, we demonstrate that CO inhibits peak human Nav1.5 current amplitude without activation of the late Na+ current observed in native tissue. Inhibition was associated with a hyperpolarizing shift in the steady-state inactivation properties of the channels and was unaffected by modification of channel gating induced by anemone toxin (rATX-II). Systematic pharmacological assessment indicated that no recognized CO-sensitive intracellular signaling pathways appeared to mediate CO inhibition of Nav1.5. Inhibition was, however, markedly suppressed by inhibition of NO formation, but NO donors did not mimic or occlude channel inhibition by CO, indicating that NO alone did not account for the actions of CO. Exposure of cells to DTT immediately before CO exposure also dramatically reduced the magnitude of current inhibition. Similarly, L-cysteine and N-ethylmaleimide significantly attenuated the inhibition caused by CO. In the presence of DTT and the NO inhibitor Nω-nitro-L-arginine methyl ester hydrochloride, the ability of CO to inhibit Nav1.5 was almost fully prevented. Our data indicate that inhibition of peak Na+ current (which can lead to Brugada syndrome-like arrhythmias) occurs via a mechanism distinct from induction of the late current, requires NO formation, and is dependent on channel redox state. / This work was supported by the British Heart Foundation

No / T-type Ca2+ channels are a distinct family of low voltage-activated Ca2+ channels which serve many roles in different tissues. Several studies have implicated them, for example, in the adaptive responses to chronic hypoxia in the cardiovascular and endocrine systems. Hydrogen sulfide (H2S) was more recently discovered as an important signalling molecule involved in many functions, including O2 sensing. Since ion channels are emerging as an important family of target proteins for modulation by H2S, and both T-type Ca2+ channels and H2S are involved in cellular responses to hypoxia, we have investigated whether recombinant and native T-type Ca2+ channels are a target for modulation by H2S. Using patch-clamp electrophysiology, we demonstrate that the H2S donor, NaHS, selectively inhibits Cav3.2 T-type Ca2+ channels heterologously expressed in HEK293 cells, whilst Cav3.1 and Cav3.3 channels were unaffected. Sensitivity of Cav3.2 channels to H2S required the presence of the redox-sensitive extracellular residue H191, which is also required for tonic binding of Zn2+ to this channel. Chelation of Zn2+ using TPEN prevented channel inhibition by H2S. H2S also selectively inhibited native T-type channels (primarily Cav3.2) in sensory dorsal root ganglion neurons. Our data demonstrate a novel target for H2S regulation, the T-type Ca2+ channel Cav3.2. Results have important implications for the proposed pro-nociceptive effects of this gasotransmitter. Implications for the control of cellular responses to hypoxia await further study.

The bi-directional dc/dc converter is a very popular and effective tool for alternative energy applications. One way it can be utilized is to charge and discharge batteries used in residential solar energy systems. In the day, excess power from the PV panels is used to charge the batteries. During the night, the charged batteries will power the dc bus for loads in the house such as home appliances. The dual active bridge (DAB) converter is very useful because of its high power capability and efficiency. Its symmetry is effective in transferring power in both directions. However, the DAB converter has drawbacks in the start-up stage. These drawbacks in boost mode include high in-rush current during start-up, and the fact that the high side voltage cannot be lower than the low side voltage. A popular existing method to alleviate this problem is the use of an active clamp and a flyback transformer in the circuit topology to charge the high side before the converter is switched into normal boost operation. The active clamp not only helps eliminate the transient spike caused by the transformer leakage, but also continues to be used during steady state. However, this method introduces a new current spike occurring when the converter transitions from start-up mode to boost mode. To alleviate this new setback, an additional transitional stage is proposed to significantly reduce the current spike without the use of any additional components. The converter is current-fed on the low side, and voltage-fed on the high side. A simple phase shift control is used in buck mode and PWM control is used during the boost mode for both the start-up mode and the normal boost operation. This thesis discusses the performance results of a 48-400 V dc/dc converter with 1000 W power output. / Master of Science

Yes / The fate of secretory and membrane proteins that mislocalize to the cytosol is decided by a collaboration between cochaperone SGTA (small, glutamine-rich, tetratricopeptide repeat protein alpha) and the BAG6 complex, whose operation relies on multiple transient and subtly discriminated interactions with diverse binding partners. These include chaperones, membrane-targeting proteins and ubiquitination enzymes. Recently a direct interaction was discovered between SGTA and the proteasome, mediated by the intrinsic proteasomal ubiquitin receptor Rpn13. Here, we structurally and biophysically characterize this binding and identify a region of the Rpn13 C-terminal domain that is necessary and sufficient to facilitate it. We show that the contact occurs through a carboxylate clamp-mediated molecular recognition event with the TPR domain of SGTA, and provide evidence that the interaction can mediate the association of Rpn13 and SGTA in a cellular context. / RLI was supported by MRC New Investigator Research Grant: G0900936. RLI and SH are funded by BBSRC grants: BB/L006952/1 and BB/L006510/1 respectively. RLI is funded by BBSRC grant: BB/N006267/1. AT is funded by BBSRC grant: BB/J014567/1. ILT was the recipient of a Wellcome Trust Vacation Scholarship 2015. NMR experiments were performed at the Centre for Biomolecular Spectroscopy, King’s College London, established with a Capital Award from the Wellcome Trust

With a higher power rating and broader application, Gallium nitride (GaN) is a promising next-generation power switch. The current four GaN HEMTs in paralleled phase leg that can block 400 V and conduct 200 A current is very beneficial, thus making the protection method on a GaN phase leg an urgent topic. This thesis starts with an overview of shortcircuit robustness among silicon (Si), silicon carbide (SiC) and GaN devices. An approximately safe operation area (SOA) for a GaN power switch will also be determined. The various common shortcircuit protection methods are mentioned. Additionally, current research on a GaN semiconductor is summarized. Among all of the protection methods, desaturation detection is selected and analyzed through simulation and then implemented in a parallel enhancement-mode high-electron-mobility transistor (E-HEMT) GaN phase leg. With this desaturation detection feature, the GaN E-HEMT can be turned off as quickly as 200 ns, and in the worst case, 500 ns, during a shortcircuit test. The phase leg survived a series of shortcircuit tests with shortcircuit protection. For the proposed protection scheme, the best-case reaction time (200 ns) is similar to others in the literature, while the shortcircuit peak current and peak energy are higher. The worst-case performance of this design is limited by both the gate driver and the device shortcircuit robustness. Due to the fast switching speed of the GaN HEMT, the false turn-on phenomenon caused by the Miller effect can be a problem. A shoot through may occur with one switch false turn on. The Miller clamp is added to the phase leg to improve its reliability. After the hardware was implemented, the Miller clamp was tested and verified through a double pulse test (DPT). Compared to the phase leg without the Miller clamp, the gate is better protected from gate voltage overshoot and undershoot. The switching loss is reduced by 20 percent by using a new gate driver IC with higher current driving capability. The degradation effect of GaN power switches in different shortcircuit pulses was also studied. The device passes through the shortcircuit tests, but any degradation effect that may change its parameters and influence its normal operation characteristic need to be addressed. Several GaN devices were selected and characterized after several shortcircuit tests to observe any degradation effect caused by the shortcircuit. The degradation test results reveal a "recovery effect" of the GaN HEMT used in this project. The parameter variations on threshold voltage and on-resistance recover to the original state, several hours after the shortcircuit test. The test results match with the conclusion drawn in degradation test conducts by other research groups that the parameter variation during shortcircuit test is negligible. Also, repetitively fast shortcircuit tests on the GaN HEMT show that the shortcircuit protection limit for this device under 400 V bus should be limited to 300 ns. / Master of Science / A phase leg consists of two power switches: a top switch and a bottom switch. As a result of a wrong gate signal or the Miller effect, shoot through problems may occur that lead to a shortcircuit current running through the channel. The excessive heat brought by the shortcircuit current will kill the device if not turned off in time. The failure of the phase leg may also have a hazardous impact on the rest of the system. To improve the overall system stability, a shortcircuit protection feature can be added on the gate-drive level. The shortcircuit protection turns off the device when it runs into shortcircuit mode, and before device failure. In this thesis, desaturation detection is selected to implement on a paralleled Gallium nitride (GaN) phase leg based on the device characteristic and configuration. Desaturation detection takes the device under test (DUT) as a current sensing component. By sensing the voltage across the DUT, the desaturation detection decides whether the DUT is operating under shortcircuit. If it is, a signal is sent to the gate driver to turn off the DUT when high voltage is sensed. A series of shortcircuit tests were conducted to verify the function of shortcircuit protection. A Miller clamp is also implemented and tested on the same phase leg to prevent a false turn on problem and to protect the gate. Both the Miller clamp and desaturation v detection features are tested on the same phase leg. The GaN devices survive the shortcircuit tests, with shortcircuit protection times between 200 ns to 500 ns. The design is successfully validated. Along with the implemented protection features, device degradation and shortcircuit robustness tests are also included in this work. The test results show that 300 ns shortcircuit time under 400 V bus is a safe turn off goal for this device.

Dans le domaine du neurométabolisme, un modèle indique que la leptine excite directement les neurones pro-opiomélanocortine (POMC) dans le noyau arqué de l'hypothalamus (ARC) pour stimuler l'appétit. Cependant, cette notion a été récemment remise en question suivant, entre autres, des évidences que les neurones POMC sont très hétérogènes. De plus, certains neurones POMC existent dans l'aire rétrochiasmatique (RCA) et la réponse des neurones POMC à la leptine chez les femelles reste incertaine. Par conséquent, il est nécessaire de mieux définir les effets de la leptine sur les neurones POMC de l'ARC et du RCA chez les mâles et les femelles. Dans cette thèse, nous avons cherché à étudier les effets de la leptine sur les propriétés électrophysiologiques des neurones POMC dans l'ARC (POMC$^\mathsf{ARC}$) et le RCA (POMC$^\mathsf{RCA}$) de souris mâles et femelles. Nous avons utilisé l'électrophysiologie de type patch-clamp sur cellules entières pour enregistrer l'activité électrique des neurones POMC$^\mathsf{ARC}$ et POMC$^\mathsf{RCA}$ à même des tranches de cerveau de souris POMC-CreERt2::tdTomato qui expriment la protéine fluorescente Tdtomato dans les neurones POMC adultes exclusivement. Nous avons également étudié si le cycle œstral affecte la réponse des neurones POMC à la leptine chez des souris femelles. L'application de leptine a induit des effets excitateurs et inhibiteurs sur des sous-populations de neurones POMC chez les mâles et les femelles. Il est intéressant de noter que la réponse des neurones POMC$^\mathsf{ARC}$ et POMC$^\mathsf{RCA}$ à la leptine était similaire. De plus, bien que la majorité des neurones POMC provenant de souris femelles ne répondaient pas à la leptine, les réponses des neurones POMC à la leptine entre les mâles et les femelles n'étaient pas statistiquement différentes. Il n'y avait aucune différence dans le pourcentage de neurones POMC à travers les différentes étapes du cycle œstral. Nos résultats révèlent une diversité sous-estimée dans la réponse des neurones POMC à la leptine qui semble exister de manière similaire entre les mâles et les femelles. L'analyse des diverses réponses des neurones POMC à la leptine pourrait être essentielle pour comprendre le rôle de cette population hétérogène dans l'intégration des signaux métaboliques pour réguler l'équilibre énergétique et d'autres fonctions dans des conditions physiologiques et pathologiques, tel que l'obésité. / In the field of neurometabolism, a prevalent model states that leptin directly excites pro-opiomelanocortin (POMC) neurons in the arcuate nucleus of the hypothalamus (ARC) to regulate feeding. However, this notion has been recently challenged by evidence that POMC neurons are greatly heterogeneous. In addition, some POMC neurons exist in the retrochiasmatic area (RCA). Furthermore, the response of female POMC neurons to leptin remains unclear. Therefore, there is a need to better define the effects of leptin on hypothalamic POMC neurons of the ARC and RCA in both males and females. In this thesis, we aimed to study the effects of leptin on the electrical properties of POMC neurons in the ARC (POMC$^\mathsf{ARC}$) and the RCA (POMC$^\mathsf{RCA}$) of male and female mice. We used whole-cell patch clamp electrophysiology to record POMC$^\mathsf{ARC}$ and POMC$^\mathsf{RCA}$ neurons from brain slices of POMC-CreERt2::tdTomato mice which express the fluorescent protein Tdtomato in adult POMC neurons exclusively. We also investigated whether the estrous cycle affects the response of POMC neurons to leptin by analyzing vaginal smears. Bath application of leptin induced excitatory and inhibitory effects on a subset of male and female POMC$^\mathsf{ARC}$ and POMC$^\mathsf{RCA}$ neurons. Interestingly, the responsiveness of POMC$^\mathsf{ARC}$ and POMC$^\mathsf{RCA}$ neurons to leptin was similar. Moreover, although the majority of female POMC neurons were nonresponsive to leptin, the responses of POMC neurons to leptin between males and females were not statistically different. Upon inspection, there were no differences in the percentage of female leptin-responsive POMC neurons across the different stages of the estrous cycle. Our results reveal an underappreciated diversity in the response of POMC neurons to leptin which appear to exist similarly in males and females. Analyzing the diverse responses of POMC neurons to leptin could be key for understanding the role of this heterogeneous population in integrating metabolic signals to regulate energy balance and other functions under physiological and pathological conditions, especially, obesity.