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Steven CONDAMINE





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Cursus:
Bachelor degree in Cell. & Mol. Biology, Univ. Paris XI/ Bordeaux Univ (2010)
Master in Neurosciences and Neurophsyco- pharmacology, Bordeaux Univ. (2012)
Ph.D. in Neuroscience, University of Montreal (2019)


Expertise: Electrophysiology, Patch clamp, Calcium imaging, Optogenetic, Intracerebral viral injection, Confocal imaging





2 publication(s) depuis Février 2018:


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04/10/2018 | J Vis Exp   IF 1.2
Analyzing the Size, Shape, and Directionality of Networks of Coupled Astrocytes.
Condamine S, Verdier D, Kolta A

Abstract:
It has become increasingly clear that astrocytes modulate neuronal function not only at the synaptic and single-cell levels, but also at the network level. Astrocytes are strongly connected to each other through gap junctions and coupling through these junctions is dynamic and highly regulated. An emerging concept is that astrocytic functions are specialized and adapted to the functions of the neuronal circuit with which they are associated. Therefore, methods to measure various parameters of astrocytic networks are needed to better describe the rules governing their communication and coupling and to further understand their functions. Here, using the image analysis software (e.g., ImageJFIJI), we describe a method to analyze confocal images of astrocytic networks revealed by dye-coupling. These methods allow for 1) an automated and unbiased detection of labeled cells, 2) calculation of the size of the network, 3) computation of the preferential orientation of dye spread within the network, and 4) repositioning of the network within the area of interest. This analysis can be used to characterize astrocytic networks of a particular area, compare networks of different areas associated to different functions, or compare networks obtained under different conditions that have different effects on coupling. These observations may lead to important functional considerations. For instance, we analyze the astrocytic networks of a trigeminal nucleus, where we have previously shown that astrocytic coupling is essential for the ability of neurons to switch their firing patterns from tonic to rhythmic bursting(1). By measuring the size, confinement, and preferential orientation of astrocytic networks in this nucleus, we can build hypotheses about functional domains that they circumscribe. Several studies suggest that several other brain areas, including the barrel cortex, lateral superior olive, olfactory glomeruli, and sensory nuclei in the thalamus and visual cortex, to name a few, may benefit from a similar analysis.




Abstract:
Stimuli that induce rhythmic firing in trigeminal neurons also increase astrocytic coupling and reveal networks that define the boundaries of this particular population. Rhythmic firing depends on astrocytic coupling which in turn depends on S100beta. In many nervous functions that rely on the ability of neuronal networks to generate a rhythmic pattern of activity, coordination of firing is an essential feature. Astrocytes play an important role in some of these networks, but the contribution of astrocytic coupling remains poorly defined. Here we investigate the modulation and organization of astrocytic networks in the dorsal part of the trigeminal main sensory nucleus (NVsnpr), which forms part of the network generating chewing movements. Using whole-cell recordings and the dye coupling approach by filling a single astrocyte with biocytin to reveal astrocytic networks, we showed that coupling is limited under resting conditions, but increases importantly under conditions that induce rhythmic firing in NVsnpr neurons. These are: repetitive electrical stimulation of the sensory inputs to the nucleus, local application of NMDA and decrease of extracellular Ca(2+) . We have previously shown that rhythmic firing induced in NVsnpr neurons by these stimuli depends on astrocytes and their Ca(2+) -binding protein S100beta. Here we show that extracellular blockade of S100beta also prevents the increase in astrocytic coupling induced by local application of NMDA. Most of the networks were small and remained confined to the functionally distinct area of dorsal NVsnpr. Disrupting coupling by perfusion with the nonspecific gap junction blocker, carbenoxolone or with GAP26, a selective inhibitor of connexin 43, mostly expressed in astrocytes, abolished NMDA-induced rhythmic firing in NVsnpr neurons. These results suggest that astrocytic coupling is regulated by sensory inputs, necessary for neuronal bursting, and organized in a region specific manner.