Modulación de la transmisión sináptica inducida por IGF-I en neuronas piramidales de la corteza infralímbica y de barriles

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Medicina, Departamento de Anatomía, Histología y Neurociencia. Fecha de lectura: 25-10-2019Esta tesis tiene embargado el acceso al texto completo hasta el 25-04-2021IGF‐I es un péptido con funciones tróficas bien estudiadas. Sin embargo, su papel como neuromodulador es objeto de debate. Algunas investigaciones han estudiado la acción del IGFI sobre la transmisión sináptica tanto excitadora como inhibidora y sobre la excitabilidad neuronal. De hecho, IGF‐I afecta a la extensión de los campos receptivos, y reduce el umbral de generación de potenciales de acción en respuesta a estímulos en la corteza somatosensorial, además de aumentar de la actividad del electrocorticograma (ECG) en esta corteza. Se ha demostrado que, en la modulación de la transmisión sináptica, los astrocitos juegan un papel muy importante. Asimismo, estos pueden sintetizar IGF‐I y presentan en su membrana plasmática receptores de IGF‐I (IGF‐IR). Aquí se muestra que el IGF‐I incrementa la excitabilidad e induce una potenciación a corto plazo (STP) de las corrientes postsinápticas excitadoras (EPSC) en neuronas piramidales de capa 2/3 de la corteza de barriles del ratón. Sin embargo, IGF‐I genera una modulación dual del EPSC ya que se observa una depresión a largo plazo (LTD) presináptica del EPSC cuando la acción del IGF‐I es en ausencia de potenciales de acción o de incrementos de calcio citosólico postsináptico. Adicionalmente, también induce una LTD de las corrientes postsinápticas inhibidoras (IPSC). Aunque la potenciación del EPSC mediada por IGF‐I requiere la activación de los receptores de adenosina A1 y A2A y los receptores metabotrópicos de glutamato (mGluR) del grupo I, solo la activación de los A2A es necesaria para la depresión del EPSC y del IPSC. En adición, tanto la modulación dual del EPSC como del IPSC son dependientes de aumentos de calcio citosólito astrocitario. Por tanto, IGF‐I podría tener una funcionalidad en procesos de memoria asociativa tanto in vitro como in vivo al inducir metaplasticidad favoreciendo la plasticidad sináptica inducida por protocolos de Spike Timing dependent plasticity (STDP). Por otro lado, los niveles de IGF‐I se han relacionado con procesos emocionales, estando disminuidos en la corteza prefrontal medial (mPFC) de ratas con ansiedad asociada a diabetes mellitus. Esta corteza es fundamental en la memoria del miedo condicionado, habiéndose demostrado que los aumentos de excitabilidad neuronal y eficacia sináptica en neuronas piramidales de capa 5 facilitan la memoria de extinción. En esta tesis denostamos que IGF‐I tiene la capacidad de disminuir las corrientes de potasio dependientes de calcio que median la posthiperpolarización de cinética lenta (sIAHP), lo que produce un aumento de la excitabilidad. Además, IGF‐I deprime a largo plazo tanto las corrientes sinápticas excitadoras como la inhibidoras, traduciéndose en una potenciación a largo plazo (LTP) de los potenciales postsinápticos. A nivel comportamental, estos efectos moduladores de IGF‐I en la actividad de la mPFC resulta en una facilitación de la extinción del miedo condicionadoEste estudio ha sido financiado con los siguientes proyectos: Ministerio de Economía y Competitividad, España (MINECO; BFU2013‐43668‐P y BFU2016‐80802‐P AEI/FEDER, UE)

Endocannabinoid and nitric oxide-dependent IGF-I-mediated synaptic plasticity at mice barrel cortex

Insulin-like growth factor-I (IGF-I) signaling plays a key role in learning and memory. IGF-I increases the spiking and induces synaptic plasticity in the mice barrel cortex (Noriega-Prieto et al., 2021), favoring the induction of the long-term potentiation (LTP) by Spike Timing-Dependent Proto-cols (STDP) (Noriega-Prieto et al., 2021). Here, we studied whether these IGF-I effects depend on endocannabinoids (eCBs) and nitric oxide (NO). We recorded both excitatory postsynaptic currents (EPSCs) and inhibitory postsynaptic currents (IPSCs) evoked by stimulation of the basal dendrites of layer II/III pyramidal neurons of the Barrel Cortex and analyzed the effect of IGF-I in the presence of a CB1 R antagonist, AM251, and inhibitor of the NO synthesis, L-NAME, to prevent the eCBs and the NO-mediated signaling. Interestingly, L-NAME abolished any modulatory effect of the IGF-I-induced excitatory and inhibitory transmission changes, suggesting the essential role of NO. Surprisingly, the inhibition of CB1Rs did not only block the potentiation of EPSCs but reversed to a depression, highlighting the remarkable functions of the eCB system. In conclusion, eCBs and NO play a vital role in deciding the sign of the effects induced by IGF-I in the neocortex, suggesting a neuromodulatory interplay among IGF-I, NO, and eCBsThis research was funded by MINECO and MICINN grants number BFU2016-80802-P AEI/FEDER, UE (MINECO) and PID2020-119358GB-I00/AEI/10.13039/501100011033 (MICINN).The APC was funded by PID2020-119358GB-I00/AEI/10.13039/501100011033 (MICINN

Nitric Oxide-Dependent LTD at Infralimbic Cortex

Dendritic calcium (Ca2+) spikes play a key role in the genesis of long-term synaptic plasticity. Although synaptic plasticity in the infralimbic cortex is critical for the extinction of fear-conditioned memory, the role of Ca2+-spikes in the induction of synaptic plasticity at this cortex has not been explored in depth. Here we show that Ca2+-spikes in layer 5 pyramidal neurons (L5 PNs) of the rat infralimbic cortex are crucial in the induction of long-term depression of the excitatory postsynaptic currents (EPSCs). The lack of effect on the postsynaptic currents evoked by puffing glutamate and the changes in the variance of the EPSC amplitude that paralleled its inhibition suggest that this LTD of the EPSCs is mediated presynaptically. However, its induction requires cytosolic calcium elevations because it is prevented when the recorded L5 PN is loaded with BAPTA. Moreover, it depends on the synthesis of nitric oxide (NO) because it is absent on slices incubated with nitric oxidase synthase inhibitor L-NAME. Therefore, Ca2+-spikes can trigger LTD of the ESPCs through the NO dependent presynaptic form of synaptic plasticity, thus providing a novel form of inducing synaptic plasticity at L5 PNs of the rat infralimbic cortexThis work was supported by grants from Ministerio de Ciencia e Innovación, Spain (MICINN; BFU2011-23522) and Ministerio de Economía y Competitividad, Spain (MINECO; BFU2013-43668-P and BFU2016-80802-P AEI/FEDER, UE) to Dr. D. Fernández de Sevilla, professor at the Departamento de Anatomía, Histología y Neurociencia, Facultad de Medicina, UniversidadAutónoma de Madri

Endocannabinoid-Dependent Long-Term Potentiation of Synaptic Transmission at Rat Barrel Cortex

Brain-derived neurotrophic factor (BDNF) plays a critical role in modulating plasticity in sensory cortices. Indeed, a BDNF-dependent long-term potentiation (LTP) at distal basal excitatory synapses of Layer 5 pyramidal neurons (L5PNs) has been demonstrated in disinhibited rat barrel cortex slices. Although it is well established that this LTP requires the pairing of excitatory postsynaptic potentials (PSPs) with Ca2+ spikes, its induction when synaptic inhibition is working remains unexplored. Here we show that low-frequency stimulation at basal dendrites of L5PNs is able to trigger a PSP followed by an action potential (AP) and a slow depolarization (termed PSP-Ca2+ response) in thalamocortical slices without blocking synaptic inhibition. We demonstrate that AP barrage-mediated release of endocannabinoids (eCBs) from the recorded L5PNs induces PSP-Ca2+ response facilitation and BDNF-dependent LTP. Indeed, this LTP requires the type 1 cannabinoid receptors activation, is prevented by postsynaptic intracellular 1,2-bis(2-aminophenoxy) ethane-N,N,N,N′-tetraacetic acid (BAPTA) or the anandamide membrane transporter inhibitor AM404, and only occurs in L5PNs neurons showing depolarization-induced suppression of inhibition. Additionally, electrical stimulation at the posteromedial thalamic nucleus induced similar response and LTP. These results reveal a novel form of eCB-dependent LTP at L5PNs that could be relevant in the processing of sensory information in the barrel cortexThis work was supported by grants from Ministerio de Ciencia e innovación, Spain (MICINN; BFU2011-23522) and Ministerio de Economía y Competitividad, Spain (MINECO; BFU2013-43668-P and BFU2016-80802-P AEI/FEDER, UE) to Dr. D. Fernández de Sevilla, profesor at the Departamento de Anatomía, Histología y Neurociencia, Facultad de Medicina, Universidad Autónoma de Madrid

Bidirectional modulation of synaptic transmission by insulin-like growth factor-I

Insulin-like growth factor-I (IGF-I) plays a key role in the modulation of synaptic plasticity and is an essential factor in learning and memory processes. However, during aging, IGF-I levels are decreased, and the effect of this decrease in the induction of synaptic plasticity remains unknown. Here we show that the induction of N-methyl-D-aspartate receptor (NMDAR)-dependent long-term potentiation (LTP) at layer 2/3 pyramidal neurons (PNs) of the mouse barrel cortex is favored or prevented by IGF-I (10 nM) or IGF-I (7 nM), respectively, when IGF-I is applied 1 h before the induction of Hebbian LTP. Analyzing the cellular basis of this bidirectional control of synaptic plasticity, we observed that while 10 nM IGF-I generates LTP (LTPIGF-I) of the post-synaptic potentials (PSPs) by inducing long-term depression (LTD) of the inhibitory post-synaptic currents (IPSCs), 7 nM IGF-I generates LTD of the PSPs (LTDIGF-I) by inducing LTD of the excitatory post-synaptic currents (EPSCs). This bidirectional effect of IGF-I is supported by the observation of IGF-IR immunoreactivity at both excitatory and inhibitory synapses. Therefore, IGF-I controls the induction of Hebbian NMDARdependent plasticity depending on its concentration, revealing novel cellular mechanisms of IGF-I on synaptic plasticity and in the learning and memory machinery of the brainThe author(s) declare financial support was received for the research, authorship, and/or publication of this article. This work was supported by the following Grants: BFU2016-80802-P and PID2020-119358GB-I00 (AEI/FEDER, UE) to DS, PID2019-104376RB-I00 (AEI/FEDER, UE) to IA and PI21/00915 (Instituto Salud Carlos III/ FEDER, UE) to A

Igf-1 facilitates extinction of conditioned fear

Insulin-like growth factor-1 (IGF-1) plays a key role in synaptic plasticity, spatial learning, and anxiety-like behavioral processes. While IGF-1 regulates neuronal firing and synaptic transmission in many areas of the central nervous system, its signaling and consequences on excitability, synaptic plasticity, and animal behavior dependent on the prefrontal cortex remain unexplored. Here, we show that IGF-1 induces a long-lasting depression of the medium and slow post-spike afterhyperpolarization (mAHP and sAHP), increasing the excitability of layer 5 pyramidal neurons of the rat infralimbic cortex. Besides, IGF-1 mediates a presynaptic long-term depression of both inhibitory and excitatory synaptic transmission in these neurons. The net effect of this IGF-1-mediated synaptic plasticity is a long-term potentiation of the postsynaptic potentials. Moreover, we demonstrate that IGF-1 favors the fear extinction memory. These results show novel functional consequences of IGF-1 signaling, revealing IGF-1 as a key element in the control of the fear extinction memor

Astrocytic IGF-IRs induce adenosine-mediated inhibitory downregulation and improve sensory discrimination

Insulin-like growth factor-I (IGF-I) signaling plays a key role in learning and memory processes. While the effects of IGF-I on neurons have been studied extensively, the involvement of astrocytes in IGF-I signaling and the consequences on synaptic plasticity and animal behavior remain unknown. We have found that IGF-I induces long-term potentiation (LTPIGFI) of the postsynaptic potentials that is caused by a long-term depression of inhibitory synaptic transmission in mice. We have demonstrated that this long-lasting decrease in the inhibitory synaptic transmission is evoked by astrocytic activation through its IGF-I receptors (IGF-IRs). We show that LTPIGFI not only increases the output of pyramidal neurons, but also favors the NMDAR-dependent LTP, resulting in the crucial information processing at the barrel cortex since specific deletion of IGF-IR in cortical astrocytes impairs the whisker discrimination task. Our work reveals a novel mechanism and functional consequences of IGF-I signaling on cortical inhibitory synaptic plasticity and animal behavior, revealing that astrocytes are key elements in these processesThis work was supported by Grants BFU2016-80802-P from Agencia Estatal de Investigación Spain/Fondo Europeo de Desarrollo Regional, and from the European Union [Ministerio de Economía y Competitividad (MINECO)] to D.F.d.S.; Grants R01-NS-097312 and R01-DA-048822 from National Institutes of Health/National Institute of Neurological Disorders and Stroke to A.A.; and grants from Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED) and Grant SAF2016-76462-C2-1-P from MINECO to I.T.-A. J.A.Z.-V. was supported by the National Council of Science, Technology and Technological Innovation (CONCYTEC, Perú) through the National Fund for Scientific and Technological Development (FONDECYT, Perú). J.F. received a postdoctoral fellowship from Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP; Grants #2017/ 14742-0 and #2019/03368-5). We thank the University of Minnesota Viral Vector and Cloning Core for production of some of the viral vectors used in this study; and Dr. G. Perea and Dr. Washington Buño for helpful comment