NEUGLIANET · ROLE OF ASTROCYTES IN NEURONAL NETWORK FUNCTION IN VISUAL CORTEX
FP7 — People (Marie Curie Actions)
- Duration
- 2010-08-01 → 2014-01-31
- EU contribution
- €234,338
- Participants
- 1
- Scheme
- MC-IOF
Lines connect the coordinator with its partners.
Results in brief
Periodic Report Summary - NEUGLIANET (Role of astrocytes in neuronal network function in visual cortex)
The project entitled NEUGLIANET (Grant Agreement No. 253635) was started on 1 August 2010 at Massachusetts Institute of Technology (MIT) (United States). During the outgoing phase at Dr Mriganka Sur lab (Picower Institute for Learning and Memory, MIT), Dr Gertruids Perea has got access to use the state-of-the-art techniques for real-time physiological recordings of neuronal and astrocyte activities in visual cortical regions (V1). She has successfully implemented in the Sur lab the use of channelrhodopsin-2 (ChR2) in astrocytes using viral vectors that was an essential issue to accomplish the current objectives of the project. The use of optogenetic tools to manipulate selectively the activity of astrocytes was critical to evaluate its consequences on neuronal network activity. The results obtained during the outgoing phase of NEUGLIANET project have been sent to publication; the paper 'Astrocyte activation modulates excitatory / inhibitory balance and response selectivity of visual cortex neurons in vivo' is currently under review in the journal 'Science'. Using two-photon microscopy for calcium imaging and electrophysiological recordings to monitor neuronal electrical activity of single cells or population cells in vitro and in vivo, this project utilises cutting-edge tools and represents an important conceptual advance. In particular, the main findings of the project are: 1. Astrocytes were selectively targeted with adeno-associated viral vector with light-sensitive ChR2 under glial fibrillary acidic protein (GFAP) promoter and neuronal activity was recorded from layer 2 / 3 neurons of V1. The selective expression of ChR2 in cortical astrocytes was confirmed by GFAP staining, and the ability of this construct to evoke Ca2+ responses was measured in V1 cortical astrocytes where transduced cells showed robust increases in intracellular Ca2+ in response to 473 nm light stimulation. 2. The analysis of neuronal activity showed that optogenetic activation of astrocytes evoked a transient potentiation of both spontaneous excitatory and inhibitory synaptic transmission, increasing the frequency of postsynaptic currents without modifying their amplitudes. 3. The increase of synaptic activity was prevented in the presence of MCPG, an antagonist of metabotropic glutamate receptor (mGluR)s, suggesting that AAV-GFAP-ChR2-expressed astrocytes can release glutamate that activates mGluRs at presynaptic terminals. 4. The effect of astrocyte activity was cell specific showing that excitatory pyramidal cells and inhibitory gamma-aminobutyric acid (GABA)-ergic cells (parvoalbumin-positive neurons (PV+)) displayed an increase in the excitatory drive through mGluRs activation. 5. To confirm the ability of ChR2-expressed astrocytes to release glutamate, I recorded slow inward currents (SICs), i.e. N-methyl-D-aspartate (NMDA)-mediated currents induced by glutamate released from astrocytes. To optimise SIC recordings magnesium was removed from the artificial cerebrospinal fluid (ACSF), and tetrodotoxin (TTX) was added to block action potential-mediated neuronal activity. In those conditions, optogenetic astrocyte stimulation evoked both increase of SIC frequency and potentiation of miniature excitatory synaptic currents. SICs were abolished by antagonists of NMDA glutamate receptors. 6. Combining two-photon microscopy and single cell-attached electrophysiological recordings in vivo, I showed that selective photostimulation of astrocytes in vivo enhances spontaneous firing rate of inhibitory PV+ neurons and excitatory neurons in visual cortex. 7. Astrocytes impact key visual response features of visual cortex neurons. Astrocyte activation selectively increases the baseline visual response level of PV+ neurons and reduces their orientation selectivity, whereas excitatory neurons show either increased or decreased baseline visual responses together with complementary changes in visual response features. 8. Astrocytes influence inhibitory transmission in cortical networks through the stimulation of particular subsets of inhibitory neurons, such as PV+ neurons rather than somatostatin-positive (SOM+) neurons. 9. In summary, these results show that astrocytes in vivo modulate excitation / inhibition balance in cortical circuits, through the dual control of excitatory drive and of PV+ inhibitory drive, and thus influence integrative response features of neurons critical for sensory information processing.
Data: CORDIS, © European Union
Project objective
The biology of astrocyte–neuron interaction has emerged as a rapidly expanding field and has become one of the most exciting topics in current neuroscience that is changing our understanding of the physiology of the nervous system. In the last few years, evidence obtained by many laboratories has established the existence of neuron-astrocyte communication in culture preparations and brain slices. However, the properties of astrocytes and their physiological role in vivo is largely unknown Numerous in vitro studies have focused on investigating the basic molecular mechanisms as well as the subcellular and cellular processes involved in astrocyte-neuron communication. Yet, to begin to understand the actual active role of astrocytes in the brain function, we need to analyze this communication and its effects at a higher level of complexity, such as during neural network function and information processing in vivo. The main objective of present project is to elucidate the impact of astrocytes in neural network function and sensory information processing in vivo. The achievement of the proposed objectives will increase our current knowledge of the role of astrocytes at a higher level of complexity, filling the gap currently existing on this area of neuroscience, and therefore, will significant extend our knowledge of the physiology and function of the nervous system. Using a conceptual interdisciplinary approach that will cover different levels of analysis (from molecules to cells and networks) to gain a comprehensive vision of the nervous system function, I propose to combine multidisciplinary techniques that include electrophysiology, Ca2+ imaging, two-photon microscopy in vitro and in vivo and genetic manipulation of animal models, to characterize the functional consequences of astrocyte activity in the sensory information processing by neural networks of the visual cortex.
Original text from CORDIS.
Participants
- AGENCIA ESTATAL CONSEJO SUPERIOR DE INVESTIGACIONES CIENTIFICAS · MadridCoordinatorSpain
Links
Data: CORDIS, © European Union