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SummaryThe prefrontal cortex (PFC) is a hub for cognitive control, and dopamine profoundly influences its functions. In other brain regions, astrocytes sense diverse neurotransmitters and neuromodulators and, in turn, orchestrate regulation of neuroactive substances. However, basic physiology of PFC astrocytes, including which neuromodulatory signals they respond to and how they contribute to PFC function, is lacking. Here, we characterize divergent signaling signatures in astrocytes of PFC and primary sensory cortex in mice, which are linked to differential responsivity to locomotion. We find that PFC astrocytes express receptors for dopamine, but are unresponsive through the Gs/Gi-cAMP pathway. Instead, fast calcium signals in PFC astrocytes are time-locked to dopamine release, and are mediated by α1-adrenergic receptors both ex vivo and in vivo. Further, we describe dopamine-triggered regulation of extracellular ATP at PFC astrocyte territories. Thus, we identify astrocytes as active players in dopaminergic signaling in PFC, contributing to PFC function though neuromodulator receptor crosstalk.Graphical Abstract

Recent work examining astrocytic physiology centers on fluorescence imaging, due to development of sensitive fluorescent indicators and observation of spatiotemporally complex calcium activity. However, the field remains hindered in characterizing these dynamics, both within single cells and at the population level, because of the insufficiency of current region-of-interest-based approaches to describe activity that is often spatially unfixed, size-varying and propagative. Here we present an analytical framework that releases astrocyte biologists from region-of-interest-based tools. The Astrocyte Quantitative Analysis (AQuA) software takes an event-based perspective to model and accurately quantify complex calcium and neurotransmitter activity in fluorescence imaging datasets. We apply AQuA to a range of ex vivo and in vivo imaging data and use physiologically relevant parameters to comprehensively describe the data. Since AQuA is data-driven and based on machine learning principles, it can be applied across model organisms, fluorescent indicators, experimental modes, and imaging resolutions and speeds, enabling researchers to elucidate fundamental neural physiology.

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).

Recent work examining astrocytic physiology centers on fluorescence imaging, due to development of sensitive fluorescent indicators and observation of spatiotemporally complex calcium activity. However, the field remains hindered in characterizing these dynamics, both within single cells and at the population level, because of the insufficiency of current region-of-interest-based approaches to describe activity that is often spatially unfixed, size-varying and propagative. Here we present an analytical framework that releases astrocyte biologists from region-of-interest-based tools. The Astrocyte Quantitative Analysis (AQuA) software takes an event-based perspective to model and accurately quantify complex calcium and neurotransmitter activity in fluorescence imaging datasets. We apply AQuA to a range of ex vivo and in vivo imaging data and use physiologically relevant parameters to comprehensively describe the data. Since AQuA is data-driven and based on machine learning principles, it can be applied across model organisms, fluorescent indicators, experimental modes, and imaging resolutions and speeds, enabling researchers to elucidate fundamental neural physiology.

OptoGluNAM4.1, a negative allosteric modulator (NAM) of metabotropic glutamate receptor 4 (mGlu4) contains a reactive group that covalently binds to the receptor and a blue-light-activated, fast-relaxing azobenzene group that allows reversible receptor activity photocontrol in vitro and in vivo. OptoGluNAM4.1 induces light-dependent behavior in zebrafish and reverses the activity of the mGlu4 agonist LSP4-2022 in a mice model of chronic pain, defining a photopharmacological tool to better elucidate the physiological roles of the mGlu4 receptor in the nervous system. © 2016 Elsevier Ltd, We are grateful to C. Serra, L. Muñoz, J. Hernando, F. Malhaire, Y. Pérez, M. Izquierdo-Serra, F. Aguado, S. Laffray, E. Bourinet, F.Codony (GenIUL), and Y. Chomis (Viewpoint) for helpful discussions and technical support. A.F. is supported by a Fondation Lefoulon Delalande postdoctoral fellowship , C.J. by a grant from INSERM ATIP-AVENIR and Marie Curie CIG ( PCIG12-GA-2012-332772 ). A.F. and C.J. are members of the Laboratory of Excellence Ion Channel Science and Therapeutics supported by a grant from the ANR . J.-P.P. is a member of the Laboratory of Excellence Epingenmed. We acknowledge financial support from the European Union's Seventh Framework Program for research, technological development, and demonstration under grant agreements 270483 (Focus), 210355 (Opticalbullet), and 335011 (Theralight) to P.G.; the Federation of European Biochemical Societies ; the Catalan government ( 2012FI_B 01122 to S.P., 2014SGR-1251 to P.G., and 2014SGR-0109 to A. Llebaria); the Spanish Government ( SAF2014-58396-R to J.G., CTQ2014-57020-R to A.L., and CTQ2013-43892R to P.G.); the ERANET Neuron LIGHTPAIN project (to A.L., J.G., and J.-P.P.); the Ramón Areces Foundation , the ERANET SynBio Modulightor project (to P.G.); the HBP Wavescales project (to P.G.); the Fondation Recherche Médicale (FRM team DEQ20130326522 to J.P.P.); the Agence Nationale de la Recherche ( ANR-13-BSV1-006 to C.G.) and the Beatriu de Pinós program of Agència de Gestió d'Ajuts Universitaris i de Recerca (AGAUR) for the support of X.R.

Phenylazopyridines are photoisomerizable compounds with high potential to control biological functions with light. We have obtained a series of phenylazopyridines with light dependent activity as negative allosteric modulators (NAM) of metabotropic glutamate receptor subtype 5 (mGlu5). Here we describe the factors needed to achieve an operational molecular photoisomerization and its effective translation into in vitro and in vivo receptor photoswitching, which includes zebrafish larva motility and the regulation of the antinociceptive effects in mice. The combination of light and some specific phenylazopyridine ligands displays atypical pharmacological profiles, including light-dependent receptor overactivation, which can be observed both in vitro and in vivo. Remarkably, the localized administration of light and a photoswitchable compound in the peripheral tissues of rodents or in the brain amygdalae results in an illumination-dependent analgesic effect. The results reveal a robust translation of the phenylazopyridine photoisomerization to a precise photoregulation of biological activity. © 2016 American Chemical Society., We are grateful to C. Serra and L. Muñoz for synthetic and analytical support, F. Malhaire for technical support in cell-based pharmacological assays, and Y. Pérez for NMR support. This research has been supported by RecerCaixa foundation (2010ACUP00378 to P.G., J.G., and A.L.), the Marató de TV3 Foundation (110230 to J.G., 110231 to A.L., 110232 to C.G., and 111531 to P.G.), the Catalan government (2010 BP-A 00194 to X.R., 2012FI_B 01122 to S.P., 2012 CTP 00033 and 2012 BE1 00597 to X.G.-S., 2014SGR-1251 to P.G., and 2014SGR-00109 to A.L.), the Spanish Government (CTQ2014-57020-R and PCIN-2013-017-C03-01 to A.L., PIE14/00034, SAF2014-55700-P, and PCIN-2013-019-C03-03 to F.C., and SAF2014-58396-R to J.G.), AWT (SBO-140028) to F.C., and the ERANET Neuron LIGHTPAIN project (to A.L., F.C., J.G., and J.-P.P.); SynBio MODULIGHTOR, Human Brain Project WAVESCALES and Ramon Areces foundation grants (to P.G.); the Agence Nationale de la Recherche (ANR-16-CE16-0010 to A.L. and C.G.).

Light-regulated drugs allow remotely photoswitching biological activity and enable plausible therapies based on small molecules. However, only freely diffusible photochromic ligands have been shown to work directly in endogenous receptors and methods for covalent attachment depend on genetic manipulation. Here we introduce a chemical strategy to covalently conjugate and photoswitch the activity of endogenous proteins and demonstrate its application to the kainate receptor channel GluK1. The approach is based on photoswitchable ligands containing a short-lived, highly reactive anchoring group that is targeted at the protein of interest by ligand affinity. These targeted covalent photoswitches (TCPs) constitute a new class of light-regulated drugs and act as prosthetic molecules that photocontrol the activity of GluK1-expressing neurons, and restore photoresponses in degenerated retina. The modularity of TCPs enables the application to different ligands and opens the way to new therapeutic opportunities., We are grateful to G. Swanson (Northwestern University Feinberg School of Medicine) for the GluK1-2b receptor clone and advice for DRG neuronal culture, and to M. Mayer (National Institutes of Health) for GluK1 S1S2 plasmid and purification protocol. We also thank E. Vázquez (Institut de Biotecnologia i Biomedicina, Universitat Autònoma de Barcelona) for providing the Origami-B (DE3) strain, and O. Seria, J.A. del Rio, G. Callejo and X. Gasull for help with DRG neuron cultures. We are grateful to D. Soto and A. Llobet for helpful discussions. MS was performed at the IRB Barcelona Mass Spectrometry Core Facility, which actively participates in the BMBS European COST Action BM 1403 and is a member of Proteored, PRB2-ISCIII, supported by grant PRB2 (IPT13/0001-ISCIII-SGEFI / FEDER). We want to thank M. Vilaseca and M. Vilanova for technical support with MS. We acknowledge financial support from the RecerCaixa foundation (2010ACUP00378); the Marató de TV3 Foundation (grants 110231 and 111531); the Human Brain Project (HBP SGA 1), the Catalan government (2012FI_B 01122, 2014SGR-1251, 2014SGR-00109 and 2009SGR-1072); the Spanish Government (SAF2012-36375, CTQ2013-43892R and CTQ2014-57020-R); the Ramón Areces foundation and the ERANET Neuron LIGHTPAIN and SynBio MODULIGHTOR projects.

Chronic orofacial pain encompasses a range of debilitating conditions, however in contrast to other body regions, few animal models are available to investigate mechanisms and treatments in the trigeminal area. Particularly, there is a lack of reliable models and testing methods in mice. We have behaviourally tested C57BL/6 mice subjected to unilateral chronic constriction injury (CCI) of the infraorbital nerve (IoN) or unilateral injections of Complete Freunds Adjuvant (CFA) into the vibrissal pad region with the aid of von Frey filaments and air-puffs and the use of a newly designed restraining device. These models were validated by suppressing the pain responses with appropriate drugs. The IoN-CCI group showed significant hyperalgesia on the ipsilateral side in comparison to baseline values for up to 20 days post-CCI following von Frey and air-puff stimulation. Gabapentin (60mg/kg), but not saline, temporarily reversed the hyperalgesia. Animals that received a CFA injection showed hyperresponsivity to both von Frey and air-puff stimulation for up to 4 days post injection. These effects were transiently reversed with 3mg/kg i.p. morphine but not saline. Our study proposes a new restraining device for mice, and validates a behavioural testing procedure of several facial pain models in mice, allowing for reproducible and robust assessment of the effects of pain-related agents and treatments, or phenotyping of genetically modified animals.

A new azobenzene-based photoswitch, 2, has been designed to enable optical control of ionotropic glutamate receptors in neurons via sensitized two-photon excitation with NIR light. In order to develop an efficient and versatile synthetic route for this molecule, a modular strategy is described which relies on the use of a new linear fully protected glutamate derivative stable in basic media. The resulting compound undergoes one-photon trans-cis photoisomerization via two different mechanisms: direct excitation of its azoaromatic unit and irradiation of the pyrene sensitizer, a well-known two-photon sensitive chromophore. Moreover, 2 presents large thermal stability of its cis isomer, in contrast to other two-photon responsive switches relying on the intrinsic nonlinear optical properties of push-pull substituted azobenzenes. As a result, the molecular system developed herein is a very promising candidate for evoking large photoinduced biological responses during the multiphoton operation of neuronal glutamate receptors with NIR light, which require accumulation of the protein-bound cis state of the switch upon repeated illumination.

Controlling drug activity with light offers the possibility of enhancing pharmacological selectivity with spatial and temporal regulation, thus enabling highly localized therapeutic effects and precise dosing patterns. Here we report on the development and characterization of what is to our knowledge the first photoswitchable allosteric modulator of a G protein-coupled receptor. Alloswitch-1 is selective for the metabotropic glutamate receptor mGlu5 and enables the optical control of endogenous mGlu5 receptors.

This is an open access article published under an ACS AuthorChoice License. See Standard ACS AuthorChoice/Editors' Choice Usage Agreement - https://pubs.acs.org/page/policy/authorchoice_termsofuse.html Synthetic photochromic compounds can be designed to control a variety of proteins and their biochemical functions in living cells, but the high spatiotemporal precision and tissue penetration of two-photon stimulation have never been investigated in these molecules. Here we demonstrate two-photon excitation of azobenzene-based protein switches and versatile strategies to enhance their photochemical responses. This enables new applications to control the activation of neurons and astrocytes with cellular and subcellular resolution.