Suchergebnisse

Interneurons play a critical role in precise control of network operation. Indeed, higher brain capabilities such as working memory, cognitive flexibility, attention, or social interaction rely on the action of GABAergic interneurons. Evidence from excitatory neurons and synapses has revealed astrocytes as integral elements of synaptic transmission. However, GABAergic interneurons can also engage astrocyte signaling; therefore, it is tempting to speculate about different scenarios where, based on particular interneuron cell type, GABAergic-astrocyte interplay would be involved in diverse outcomes of brain function. In this review, we will highlight current data supporting the existence of dynamic GABAergic-astrocyte communication and its impact on the inhibitory-regulated brain responses, bringing new perspectives on the ways astrocytes might contribute to efficient neuronal coding. ; The authors are grateful to Dr. C. Sánchez-Puelles and C. GonzálezArias for helpful comments. NB Revisions was used for manuscript editing. This work was supported by the PhD fellowship program (MINECO, BES-2014-067594) to SM; and MINECO grant (BFU2016- 75107-P), and and Cajal Blue Brain Project (Spanish partner of the Blue Brain Project initiative from EPFL) and the European Union Horizon 2020 research and innovation program under grant agreement No. 720270 (Human Brain Project, https://www.humanbrainproject.eu/) to GP.

Endocannabinoids (eCBs) play key roles in brain function, acting as modulatory signals in synaptic transmission and plasticity. They are recognized as retrograde messengers that mediate long-term synaptic depression (LTD), but their ability to induce long-term potentiation (LTP) is poorly known. We show that eCBs induce the long-term enhancement of transmitter release at single hippocampal synapses through stimulation of astrocytes when coincident with postsynaptic activity. This LTP requires the coordinated activity of the 3 elements of the tripartite synapse: 1) eCB-evoked astrocyte calcium signal that stimulates glutamate release; 2) postsynaptic nitric oxide production; and 3) activation of protein kinase C and presynaptic group I metabotropic glutamate receptors, whose location at presynaptic sites was confirmed by immunoelectron microscopy. Hence, while eCBs act as retrograde signals to depress homoneuronal synapses, they serve as lateral messengers to induce LTP in distant heteroneuronal synapses through stimulation of astrocytes. Therefore, eCBs can trigger LTP through stimulation of astrocyte-neuron signaling, revealing novel cellular mechanisms of eCB effects on synaptic plasticity. ; Ministerio de Economia y Competitividad, Spain (MINECO; BFU2010-15832), European Union (HEALTH-F2-2007-202167), and Cajal Blue Brain to A.A. Grants from Spain (MINECO; BFU-2009-08404 and CSD2008-00005) to R.L. Grants from Spain (MINECO; Consolider, CSD2010-00045; Ramón y Cajal Program, RYC-2012-12014; and BFU2013-47265) to G.P. ; Peer Reviewed

Long-term potentiation (LTP) of synaptic transmission represents the cellular basis of learning and memory. Astrocytes have been shown to regulate synaptic transmission and plasticity. However, their involvement in specific physiological processes that induce LTP in vivo remains unknown. Here we show that in vivo cholinergic activity evoked by sensory stimulation or electrical stimulation of the septal nucleus increases Ca2+ in hippocampal astrocytes and induces LTP of CA3-CA1 synapses, which requires cholinergic muscarinic (mAChR) and metabotropic glutamate receptor (mGluR) activation. Stimulation of cholinergic pathways in hippocampal slices evokes astrocyte Ca2+ elevations, postsynaptic depolarizations of CA1 pyramidal neurons, and LTP of transmitter release at single CA3-CA1 synapses. Like in vivo, these effects are mediated by mAChRs, and this cholinergic-induced LTP (c-LTP) also involves mGluR activation. Astrocyte Ca2+ elevations and LTP are absent in IP3R2 knock-out mice. Downregulating astrocyte Ca2+ signal by loading astrocytes with BAPTA or GDPbS also prevents LTP, which is restored by simultaneous astrocyte Ca2+ uncaging and postsynaptic depolarization. Therefore, cholinergic-induced LTP requires astrocyte Ca2+ elevations, which stimulate astrocyte glutamate release that activates mGluRs. The cholinergicinduced LTP results from the temporal coincidence of the postsynaptic activity and the astrocyte Ca2+ signal simultaneously evoked by cholinergic activity. Therefore, the astrocyte Ca2+ signal is necessary for cholinergic-induced synaptic plasticity, indicating that astrocytes are directly involved in brain storage information ; Supported by grants from Ministerio de Ciencia e Innovacio´n (BFU2010-15832, BFU2008-03488, BFU2008-04196, CSD2010-00045), Spain, European Union (HEALTH-F2-2007-202167) and Cajal Blue Brain. G.P. is supported by a Marie Curie Fellowship (FP7-253635). E.D.M. is supported by INCRECyT project from European Social Fund and JCCM.

The physiological activity of proteins is often studied with loss-of-function genetic approaches, but the corresponding phenotypes develop slowly and can be confounding. Photopharmacology allows direct, fast, and reversible control of endogenous protein activity, with spatiotemporal resolution set by the illumination method. Here, we combine a photoswitchable allosteric modulator (alloswitch) and 2-photon excitation using pulsed near-infrared lasers to reversibly silence metabotropic glutamate 5 (mGlu5) receptor activity in intact brain tissue. Endogenous receptors can be photoactivated in neurons and astrocytes with pharmacological selectivity and with an axial resolution between 5 and 10 μm. Thus, 2-photon pharmacology using alloswitch allows investigating mGlu5-dependent processes in wild-type animals, including synaptic formation and plasticity, and signaling pathways from intracellular organelles. © 2019 National Academy of Sciences. All rights reserved. ; ACKNOWLEDGMENTS. We thank Jordi Hernando (Autonomous University of Barcelona) for useful discussions on 2-photon excitation; Pere Català (Utrecht University) for help with GCaMP; Francisco Ciruela (University of Barcelona) for mGlu5-eYFP plasmid; Erin Schuman and Stephan Junek (Max Planck Institute for Brain Research, Frankfurt) for preliminary 2-photon excitation experiments; and Ashraf Muhaisen (University of Barcelona) for help with slicing. This research received funding from European Union Research and Innovation Programme Horizon 2020 [Human Brain Project SGA2 Grant Agreement 785907 (WaveScalES)], European Research ERA-Net SynBio programme (Modulightor project), and financial support from Agency for Management of University and Research Grants/Generalitat de Catalunya (CERCA Programme; 2017-SGR-1442 project), Fonds Européen de Développement Économique et Régional (FEDER) funds, Ministry of Economy and Competitiveness (MINECO)/FEDER (Grant CTQ2016-80066-R), and the Fundaluce foundation. S.P. was supported by an FI fellowship from the Agency for Management of University and Research Grants/Generalitat de Catalunya (2014FI_B2 00160). H.L. was supported by an Institute for Bioengineering of Catalonia Severo Ochoa International PhD Programme fellowship from MINECO. M.B. was supported by a H2020-MSCA-IF Reintegration Grant. K.E.P. receives support from NIH/National Institute of Neurological Disorders and Stroke Grant R01NS099254 and NSF Biophotonics Grant 1604544. E.S. receives support from MINECO (Grant SAF2016-7426). ; Peer reviewed

Altres ajuts: This research was mainly funded by grants TV3-20141430, TV3-20141432 and TV3-20141431 from La Marató de Televisió de Catalunya (TV3) to EG, AG and JV respectively, co-financed by FEDER funds from European Union to AG. Co-financed by European Regional Development Fund to MDG. ; The apolipoprotein E (APOE) gene exists in three isoforms in humans: APOE2, APOE3 and APOE4. APOE4 causes structural and functional alterations in normal brains, and is the strongest genetic risk factor of the sporadic form of Alzheimer's disease (LOAD). Research on APOE4 has mainly focused on the neuronal damage caused by defective cholesterol transport and exacerbated amyloid-β and Tau pathology. The impact of APOE4 on non-neuronal cell functions has been overlooked. Astrocytes, the main producers of ApoE in the healthy brain, are building blocks of neural circuits, and Ca 2+ signaling is the basis of their excitability. Because APOE4 modifies membrane-lipid composition, and lipids regulate Ca 2+ channels, we determined whether APOE4 dysregulates Ca 2+ signaling in astrocytes. Ca 2+ signals were recorded in astrocytes in hippocampal slices from APOE3 and APOE4 gene targeted replacement male and female mice using Ca 2+ imaging. Mechanistic analyses were performed in immortalized astrocytes. Ca 2+ fluxes were examined with pharmacological tools and Ca 2+ probes. APOE3 and APOE4 expression was manipulated with GFP- APOE vectors and APOE siRNA. Lipidomics of lysosomal and whole-membranes were also performed. We found potentiation of ATP-elicited Ca 2+ responses in APOE4 versus APOE3 astrocytes in male, but not female, mice. The immortalized astrocytes modeled the male response, and showed that Ca 2+ hyperactivity associated with APOE4 is caused by dysregulation of Ca 2+ handling in lysosomal-enriched acidic stores, and is reversed by the expression of APOE3, but not of APOE4, pointing to loss of function due to APOE4 malfunction. Moreover, immortalized APOE4 astrocytes are refractory to control of Ca 2+ fluxes by extracellular ...